DE102018119599A1 - Exhaust aftertreatment system and method for exhaust aftertreatment of an internal combustion engine - Google Patents

Abstract

The invention relates to an exhaust gas aftertreatment system for an internal combustion engine (10) with an exhaust gas system (40). The exhaust system (40) has an exhaust duct (42), in which a first catalytic converter (38, 46) in the flow direction of an exhaust gas of the internal combustion engine (10) through the exhaust duct (42), and a particle filter downstream of the first catalytic converter (38, 46) (48), further downstream a first SCR catalytic converter (56), and still further downstream a second SCR catalytic converter (58) are arranged. A metering valve (54) for metering a reducing agent into the exhaust gas duct (42) is provided downstream of the particle filter (48) and upstream of the first SCR catalytic converter (56). A combination sensor (62) is arranged downstream of the first SCR catalytic converter (56) and upstream of the second SCR catalytic converter (58) for detecting the NO concentration and for detecting the ammonia concentration in the exhaust gas downstream of the first SCR catalytic converter (56) The invention further relates to a method for exhaust gas aftertreatment of an internal combustion engine (10) with such an exhaust gas aftertreatment system.

Description

The invention relates to an exhaust gas aftertreatment system for exhaust gas aftertreatment of an internal combustion engine, in particular a diesel engine, and a method for operating such an exhaust gas aftertreatment system.

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, the exhaust gas cleaning takes place in a known manner using a three-way catalytic converter and the three-way catalytic converter - 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 of the internal combustion engine. This mixing heats the aqueous urea solution, the aqueous urea solution releasing ammonia in the exhaust gas duct. A commercially available, aqueous urea solution generally consists of 32.5% urea and 67.5% water.

In addition to a constant reduction in raw emissions, ever higher conversion rates of the exhaust gas aftertreatment system are required to comply with the strictest exhaust gas standards. With regard to the nitrogen oxide emissions in lean-running internal combustion engines, in particular in lean-running diesel engines or Otto lean-burn engines, additional catalysts are therefore necessary in order to convert the nitrogen oxides that occur during combustion. So-called twin-dosing systems are known from the prior art, with which, depending on the temperature and / or the power of the internal combustion engine, urea solution can be metered into the exhaust gas duct at two different points. The SCR catalytic converter is preferably designed as an SCR-coated particle filter. A disadvantage of such a solution, however, is that the particle filter with the SCR coating requires a temperature for regeneration which is above the temperature for the selective catalytic reduction of nitrogen oxides. The SCR function of the particle filter is therefore restricted during regeneration. High exhaust gas temperatures also lead to aging of the SCR catalytic converters, which results in a decrease in the conversion performance over the life of the SCR catalytic converter.

From the DE 10 2012 015 046 A1 An exhaust gas aftertreatment system for the selective catalytic reduction of nitrogen oxides is provided, in which a reducing agent is mixed with compressed air in a mixing chamber and then metered into the exhaust system of an internal combustion engine. The mixing chamber is divided into two areas by an adjustable element, the processing and metering of the reducing agent each taking place in one of these areas.

The DE 11 2009 000 968 T5 discloses an exhaust gas aftertreatment system for an internal combustion engine, in which an SCR catalytic converter is provided downstream of a particle filter and an ammonia blocking catalytic converter is provided further downstream. A reducing agent is metered in downstream of the particle filter and upstream of the SCR catalytic converter. If the reducing agent is overdosed, the ammonia obtained from the reducing agent is retained by the ammonia blocking catalyst or converted into molecular nitrogen and water vapor in order to avoid ammonia emissions.

From the DE 11 2011 102 569 T5 Furthermore, an exhaust gas aftertreatment system for an internal combustion engine is known, in which a catalytic converter has two catalytic converter substrates, which are arranged in a common housing but are spaced apart from one another by a gap. The first catalyst substrate can be designed, for example, as an oxidation catalyst and the second catalyst substrate can be designed, for example, as an SCR catalyst. The catalyst substrates are each covered by an insulating mat in order to reduce heat radiation from the respective catalyst substrate and thus to accelerate the heating of the catalyst substrates after a cold start of the internal combustion engine.

The invention is based on the object of improving the exhaust gas aftertreatment of an internal combustion engine and, in particular, of further improving the conversion performance with regard to nitrogen oxide emissions.

According to the invention, this object is achieved by an exhaust gas aftertreatment system for an internal combustion engine, comprising an exhaust system with a first exhaust gas duct, in which a first catalytic converter in the flow direction of an exhaust gas of the internal combustion engine through the exhaust gas duct A particle filter is arranged downstream of the first catalytic converter, a first SCR catalytic converter is arranged downstream of the particle filter, and a second SCR catalytic converter is arranged further downstream. It is provided that a metering valve for metering a reducing agent into the exhaust gas channel, in particular for metering aqueous urea solution, is provided downstream of the particle filter and upstream of the first SCR catalytic converter. A combination sensor for detecting the ammonia concentration and for detecting the nitrogen oxide concentration in the exhaust gas is arranged downstream of the first SCR catalytic converter downstream of the first SCR catalytic converter and upstream of the second SCR catalytic converter. Such an exhaust gas aftertreatment system makes it possible to supply both SCR catalytic converters with a single metering valve. An amount of reducing agent is metered in, which is higher than the reducing agent required by the first SCR catalytic converter for selective catalytic reduction. An aqueous urea solution from which ammonia is obtained is in particular provided as the reducing agent. The excess ammonia can be detected by the combination sensor downstream of the first SCR catalytic converter, so that the remaining reducing agent can be converted on the second SCR catalytic converter. The amount of ammonia supplied to the second SCR catalytic converter can be regulated by the combination sensor in order to enable the most efficient conversion of nitrogen oxides. This means that a larger catalyst volume is available for converting the nitrogen oxide emissions, which means that, especially with large exhaust gas volumes and high exhaust gas speeds due to high speeds, high output and high exhaust gas temperatures of the internal combustion engine, a better conversion of these nitrogen oxide emissions can take place.

Advantageous further developments and non-trivial improvements of the exhaust gas aftertreatment system specified in the independent claim are possible due to the features mentioned in the dependent claims.

In a preferred embodiment of the exhaust gas aftertreatment system it is provided that the second SCR catalytic converter is followed by an ammonia blocking catalytic converter. An ammonia blocking catalyst can be used to retain reducing agent which has passed through the second SCR catalyst, so that a breakthrough of ammonia through this second SCR catalyst does not necessarily lead to an increase in the tailpipe emissions of the internal combustion engine.

In an advantageous embodiment of the invention it is provided that the particle filter has a coating for the selective catalytic reduction of nitrogen oxides (SCR coating) and thus forms a third SCR catalyst, with a further metering valve in the exhaust gas duct downstream of the first catalyst and upstream of the particle filter is arranged for metering a reducing agent. No further SCR catalytic converter can be formed by an SCR coating of the particle filter, as a result of which the conversion performance can be further increased. Three SCR catalytic converters can be supplied with reducing agent using only two metering valves, which means that an additional metering valve can be dispensed with. As a result, the costs and the assembly effort for the exhaust gas aftertreatment system can be reduced. Furthermore, in the event of a failure of an SCR catalytic converter, two functioning SCR catalytic converters are still available, as a result of which a high conversion performance is still achieved by the exhaust gas aftertreatment system even in the event of a total failure of one of the SCR catalysts.

In a preferred embodiment variant of the exhaust gas aftertreatment system, it is provided that a branch is provided on the exhaust gas duct downstream of the particle filter and upstream of the metering valve, at which a low-pressure exhaust gas recirculation line branches off from the exhaust gas duct. As a result, the first SCR catalytic converter and the second SCR catalytic converter can be supplied with reducing agent without the risk that unused reducing agent can get into the low-pressure exhaust gas recirculation system in the event of an overdose. Deposits and condensate formation in the low-pressure exhaust gas recirculation can thus be avoided, as a result of which undesirable recirculation of ammonia into the air supply system is excluded.

It is preferred if the first SCR catalytic converter and the second SCR catalytic converter are arranged downstream of the branch.

In a further preferred embodiment of the exhaust gas aftertreatment system, it is provided that the particle filter is arranged in a position close to the engine and the two SCR catalysts are arranged in a position remote from the engine. In this context, a position near the engine means a position of the particle filter with an exhaust gas run length of less than 80 cm, preferably less than 50 cm, from the outlet of the internal combustion engine. In this context, a position remote from the engine means a position in the exhaust system with an exhaust gas run length of more than 100 cm, preferably of more than 120 cm, from the outlet of the internal combustion engine. The position close to the engine enables the particulate filter to heat up particularly quickly after a cold start of the internal combustion engine. Furthermore, the particle filter can be in this position easier and faster on its to oxidize retained soot, the necessary regeneration temperature can be heated. The position of the two further SCR catalytic converters away from the engine cools the exhaust gas on the way from the internal combustion engine through the exhaust system. The two further SCR catalytic converters can thus be operated in a temperature window in which an efficient conversion of nitrogen oxides is possible, in particular during high-load operation and / or during regeneration of the particle filter. The temperature at the particle filter exceeds this temperature window, so that the particle filter with the SCR coating can only make a limited contribution to converting the nitrogen oxide emissions.

It is particularly preferred if the two SCR catalysts are arranged in an underbody position of a motor vehicle. In an underbody position, the SCR catalytic converters are cooled by an air flow carried under the vehicle, so that additional convective heat dissipation takes place. This means that the SCR catalysts can also be operated at maximum load in the temperature range required for the selective catalytic reduction of nitrogen oxides.

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, wherein a reducing agent is metered in through the metering valve, and wherein the nitrogen oxide concentration and the ammonia concentration are determined downstream of the first SCR catalytic converter and upstream of the second SCR catalytic converter. This means that two SCR catalytic converters can be supplied with a reducing agent using just one metering valve. In this way, a metering valve can be saved, as a result of which the manufacturing costs and the assembly outlay for the exhaust gas aftertreatment system can be reduced.

In an advantageous embodiment of the method it is provided that the reducing agent is overdosed when both the first SCR catalytic converter and the second SCR catalytic converter have reached their operating temperature. The second SCR catalytic converter can be supplied with a reducing agent, in particular ammonia, by overdosing, so that the second SCR catalytic converter provides additional catalyst volumes. As a result, the efficiency of the nitrogen oxide conversion can be improved, in particular at high load points and / or high speeds of the internal combustion engine.

According to a further improvement of the method, it is provided that the particle filter has a coating for the selective catalytic reduction of nitrogen oxides and a further metering valve is arranged upstream of the particle filter, the metering of reducing agent depending on the exhaust gas temperature and / or the temperature of the SCR catalysts through the metering valve or through the further metering valve. As a result, the selective catalytic reduction can be adapted to the temperatures prevailing in the exhaust system, so that one or more SCR catalysts are always supplied with reducing agents which give the best possible conversion of nitrogen oxides. This reduces the consumption of reducing agents and increases the efficiency of exhaust gas aftertreatment.

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

• 1 einen Verbrennungsmotor mit einem Luftversorgungssystem und einer Abgasanlage mit einem erfindungsgemäßen Abgasnachbehandlungssystem; und
• 2 ein Ablaufdiagramm zur Durchführung eines erfindungsgemäßen Verfahrens zur Abgasnachbehandlung eines Verbrennungsmotors.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Show it:

• 1 an internal combustion engine with an air supply system and an exhaust system with an exhaust gas aftertreatment system according to the invention; and
• 2 a flowchart for performing an inventive method for exhaust gas aftertreatment of an internal combustion engine.

1 shows the schematic representation of an internal combustion engine 10 with an air supply system 20 and an exhaust system 40 , The internal combustion engine 10 is a direct injection diesel engine in this embodiment and has several combustion chambers 12 on. At the combustion chambers 12 is a fuel injector 14 for injecting a fuel into the respective combustion chamber 12 arranged. The internal combustion engine 10 is with his entrance 16 with an air supply system 20 and with its outlet 18 with an exhaust system 40 connected. The internal combustion engine 10 further comprises a high-pressure exhaust gas recirculation with a high-pressure exhaust gas recirculation valve, via which an exhaust gas of the internal combustion engine 10 from the outlet 18 to the entrance 16 can be traced back. At the combustion chambers 12 Inlet valves and outlet valves are arranged, with which a fluid connection from the air supply system 20 to the combustion chambers 12 or from the combustion chambers 12 to the exhaust system 40 can be opened or closed.

The air supply system 20 includes an intake duct 28 , in which in the direction of flow of fresh air through the intake duct 28 an air filter 22 , downstream of the air filter 22 an air mass meter 24 , in particular a hot film air mass meter, downstream of the air mass meter 24 a compressor 26 of an exhaust gas turbocharger 36 . downstream of the compressor 26 a throttle valve 30 and further downstream an intercooler 32 are arranged. The air mass meter 24 also in a filter housing of the air filter 22 be arranged so that the air filter 22 and the air mass meter 24 forms an assembly. Downstream of the air filter 22 and upstream of the compressor 26 is a confluence 34 provided on which an exhaust gas recirculation line 76 a low pressure exhaust gas recirculation 70 into the intake duct 28 empties.

The exhaust system 40 includes an exhaust duct 42 , in which in the flow direction of an exhaust gas of the internal combustion engine 10 through the first exhaust duct 42 a turbine 44 of the exhaust gas turbocharger 36 arranged which is the compressor 26 in the air supply system 20 drives over a shaft. The exhaust gas turbocharger 36 is preferably used as an exhaust gas turbocharger 36 designed with variable turbine geometry. For this are a turbine wheel of the turbine 44 adjustable guide vanes upstream, through which the flow of the exhaust gas onto the blades of the turbine 44 can be varied. Downstream of the turbine 44 are several exhaust aftertreatment components 38 . 46 . 48 . 52 . 56 . 58 . 60 intended. It is immediately downstream of the turbine 44 an oxidation catalytic converter as the first component of exhaust gas aftertreatment 46 or a NO _x storage catalytic converter 38 is arranged. The oxidation catalyst 46 or the NO _x storage catalytic converter 38 follows in the flow direction of the exhaust gas of the internal combustion engine 10 a particle filter 48 , which preferably with a coating 52 is provided for the selective catalytic reduction of nitrogen oxides (SCR coating). Downstream of the particle filter 48 are a first SCR catalyst 56 and further downstream a second SCR catalytic converter 58 arranged. Downstream of the second SCR catalytic converter 58 is an ammonia barrier catalyst 60 provided, which prevents leakage of unused ammonia and converts it into nitrogen, water vapor. Downstream of the particle filter 48 and upstream of the first SCR catalyst 56 is in the exhaust duct 42 an exhaust flap 78 provided with which the cross section of the exhaust duct 42 can be at least partially blocked to the exhaust back pressure in the exhaust duct 42 to increase. Downstream of the particle filter 48 and upstream of the exhaust flap 78 is on the exhaust duct 42 a branch 68 provided on which an exhaust gas recirculation line 76 exhaust gas recirculation 70 from the exhaust duct 42 branches.

The exhaust gas recirculation 70 includes in addition to the exhaust gas recirculation line 76 an exhaust gas recirculation cooler 72 and an exhaust gas recirculation valve 74 , via which the exhaust gas recirculation through the exhaust gas recirculation line 76 is controllable. On the exhaust gas recirculation line 76 exhaust gas recirculation 70 can be provided a further temperature sensor, via which an exhaust gas temperature in the exhaust gas recirculation 70 can be determined to the exhaust gas recirculation 70 to activate as soon as the exhaust gas temperature in the exhaust gas recirculation 70 has exceeded a defined threshold. It can thus be prevented that water vapor or reducing agent contained in the exhaust gas for the selective catalytic reduction of nitrogen oxides, in particular liquid urea solution, condenses out and in the exhaust gas recirculation 70 or in the air supply system 20 leads to damage or deposits.

In the exhaust system 40 is downstream of the first SCR catalytic converter 56 and upstream of the second SCR catalyst 58 a combination sensor 62 provided with which the nitrogen oxide concentration and the ammonia concentration downstream of the first SCR catalyst 56 can be determined. A temperature sensor can also be located in the exhaust system 70 be provided with which an exhaust gas temperature in the exhaust system 40 can be monitored to ensure an effective and efficient exhaust aftertreatment of the exhaust gas of the internal combustion engine 10 to enable. There are also differential pressure sensors 66 provided a pressure difference across the particulate filter 48 to determine. In this way, the loading status of the particle filter 48 determined and, if a defined loading level is exceeded, regeneration of the particle filter 48 be initiated. Also on the exhaust duct 42 at least one metering module 50, 54 is provided to contain a reducing agent, in particular aqueous urea solution, upstream of the two SCR catalysts 56 . 58 in the exhaust duct 42 to meter. There is a first metering valve 54 provided with which reducing agent downstream of the branch 68 in the exhaust duct 42 is dosed. There is also another metering valve 50 provided with which the reducing agent downstream of the oxidation catalyst 46 or the NO _x storage catalyst 38 and upstream of the particulate filter 48 in the exhaust duct 42 is introduced. In the exhaust duct 42 can each downstream of the respective metering valve 50 . 54 Mixing elements can be arranged to mix the reducing agent with the exhaust gas of the internal combustion engine 10 to favor.

The internal combustion engine 10 is with an engine control unit 80 connected, which via signal lines, not shown, to the combination sensor 62 , the pressure and temperature sensors 64 . 66 , with the fuel injectors 14 of the internal combustion engine 10 as well as with the control devices 24 . 30 of the air supply system 20 connected is.

An exhaust gas aftertreatment with an exhaust gas aftertreatment system according to the invention is shown in 2 shown. In a first step < 100 > becomes the internal combustion engine 10 through the fuel injectors 14 supplied with fuel, which in the combustion chambers 12 of the internal combustion engine 10 burns. The gaseous exhaust components through the oxidation catalyst 46 or NO _x storage catalyst 38 oxidized. In this normal operation, the nitrogen oxide emissions are caused by metering in reducing agent through at least one of the metering valves 50 . 54 and a subsequent SCR catalytic converter 56 . 58 . 82 converted. When burning the fuel in the combustion chambers 12 soot particles are created in the particle filter 48 retained. Reaches the particle filter 48 in the operation of the internal combustion engine 10 a defined loading limit, then in one process step < 110 > regeneration of the particle filter 48 necessary. For this purpose, the exhaust gas temperature of the internal combustion engine 10 increased in a known manner, for example by shifting the injection timing in the “late” direction. Because of the regeneration of the particle filter 48 necessary temperature is in a temperature range in which there is a thermal decomposition of the ammonia, in a process step < 120 > the metering of reducing agent onto the metering valve at the rear in the direction of flow 54 postponed. In one process step < 130 > through the combination sensor 62 the concentrations of ammonia and nitrogen oxides downstream of the first SCR catalyst 56 measured. The conversion performance of the first SCR catalytic converter is sufficient 56 not enough to completely convert the nitrogen oxide emissions into harmless exhaust gas components, the metered amount of reducing agent is increased and it takes place in one process step < 140 > an overdose of reducing agent. More reducing agent is metered in than the first SCR catalytic converter 56 needed to convert nitrogen oxide emissions. Thus lies downstream of the first SCR catalytic converter 56 and upstream of the second SCR catalyst 58 unused ammonia, which is used for selective catalytic reduction by the second SCR catalyst 58 can be used. Is the regeneration of the particle filter 48 completed, in a process step < 150 > Switched back to normal operation and the reducing agent is metered in through the metering valve 50 . 54 , which depends on the exhaust gas temperature in the exhaust system 40 the most efficient conversion of nitrogen oxide emissions can be expected.

With the combination sensor 62 can also function as the first SCR catalyst 56 checked, so that an easy way to on-board diagnosis of the first SCR catalyst 56 given is. If one of the SCR catalysts fails 56 . 58 . 82 two functional SCR catalysts are still available, so that even in the event of a total failure of one of the SCR catalysts 56 . 58 . 82 sufficient conversion performance of the exhaust gas aftertreatment system is achieved.

LIST OF REFERENCE NUMBERS

10

internal combustion engine

12

combustion chamber

14

fuel injector

16

inlet

18

outlet

20

Air supply system

22

air filter

24

Air flow sensor

26

compressor

28

intake port

30

throttle

32

Intercooler

34

junction

36

turbocharger

38

NO _x storage catalytic converter

40

exhaust system

42

exhaust duct

44

turbine

46

oxidation catalyst

48

particulate Filter

50

first metering valve

52

SCR coating

54

second metering valve

56

first SCR catalytic converter

58

second SCR catalytic converter

60

Ammonia slip catalyst

62

Kombisensor

64

temperature sensor

66

Differential Pressure Sensor

68

branch

70

Exhaust gas recirculation

72

Exhaust gas recirculation cooler

74

Exhaust gas recirculation valve

76

Exhaust gas recirculation line

78

exhaust flap

80

control unit

82

SCR catalyst

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 102012015046 A1 [0004]
• DE 112009000968 T5 [0005]
• DE 112011102569 T5 [0006]

Claims (10)

Exhaust gas aftertreatment system for an internal combustion engine (10), comprising an exhaust system (40) with a first exhaust gas duct (42), in which a first catalytic converter (38, 46) downstream of the exhaust gas of the internal combustion engine (10) through the exhaust gas duct (42) a first filter (38, 46) a particle filter (48) and downstream of the particle filter (48) a first SCR catalyst (56) and further downstream a second SCR catalyst (58), characterized in that downstream of the particle filter (48 ) and upstream of the first SCR catalytic converter (56) a metering valve (54) is provided for metering a reducing agent into the exhaust gas duct (42), with a downstream of the first SCR catalytic converter (56) and upstream of the second SCR catalytic converter (58) Combination sensor (62) for detecting the NO _x concentration and for detecting the ammonia concentration in the exhaust gas is arranged downstream of the first SCR catalytic converter (56). Exhaust aftertreatment system after Claim 1 , characterized in that the second SCR catalytic converter (58) is followed by an ammonia blocking catalytic converter (60). Exhaust aftertreatment system after Claim 1 or 2 , characterized in that the particle filter (48) has a coating (52) for the selective catalytic reduction of nitrogen oxides and thus forms a third SCR catalytic converter (82), the exhaust gas duct (42) downstream of the first catalytic converter (38, 46) and a further metering valve (50) for metering in a reducing agent is arranged upstream of the particle filter (48). Exhaust aftertreatment system according to one of the Claims 1 to 3 , characterized in that a branch (68) is provided on the exhaust duct (42) downstream of the particle filter (48) and upstream of the metering valve (54), at which a low-pressure exhaust gas recirculation line (46) branches off from the exhaust duct (42). Exhaust aftertreatment system after Claim 4 , characterized in that the first SCR catalytic converter (56) and the second SCR catalytic converter (58) are arranged downstream of the branch (68). Exhaust aftertreatment system according to one of the Claims 1 to 5 , characterized in that the particle filter (48) in a position close to the engine and the two SCR catalysts (56, 58) are arranged in a position remote from the engine. Exhaust aftertreatment system after Claim 6 , characterized in that the two SCR catalysts (56, 58) are arranged in an underbody position of a motor vehicle. 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 7 , characterized in that a reducing agent is metered in through the metering valve (54), the nitrogen oxide concentration and the ammonia concentration being determined downstream of the first SCR catalytic converter (56) and upstream of the second SCR catalytic converter (58). Method for exhaust gas aftertreatment of an internal combustion engine (10) Claim 8 , characterized in that the reducing agent is overdosed when both the first SCR catalytic converter (56) and the second SCR catalytic converter (58) have reached their operating temperature, in such a way that this occurs when the first SCR catalytic converter (56) flows through Unused reducing agent (58) is used for selective catalytic reduction on the second SCR catalyst (58). Method for exhaust gas aftertreatment of an internal combustion engine (10) Claim 8 or 9 characterized in that the particle filter (48) has a coating (52) for the selective catalytic reduction of nitrogen oxides and a further metering valve (50) is arranged upstream of the particle filter (48), the metering of reducing agent depending on the exhaust gas temperature and / or the temperature of the SCR catalytic converter (56, 58, 82) by the metering valve (54) or by the further metering valve (50).

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