DE102016118309A1 - Method for operating an internal combustion engine and device for exhaust aftertreatment of such an internal combustion engine - Google Patents

Abstract

The invention relates to an internal combustion engine operating method with the purpose of increasing the exhaust gas temperature to increase the efficiency of an exhaust aftertreatment system. It is provided that in the exhaust passage of the internal combustion engine is provided at least one catalyst for the selective catalytic reduction of nitrogen oxides (SCR catalyst) or a particulate filter with a coating for the selective catalytic reduction of nitrogen oxides. In order to avoid or at least reduce cooling of the SCR catalytic converter or of the particulate filter with the SCR-active coating, it is provided that the filling of the combustion chambers of the internal combustion engine is reduced at low partial load or in overrun operation of the internal combustion engine in order to achieve convective cooling of the SCR Catalyst by a high volume flow of fresh air through the exhaust passage to avoid and thus to increase the efficiency of the SCR catalyst. Furthermore, a device for exhaust aftertreatment is provided with which such a method can be carried out.

Description

The invention relates to a method for operating an internal combustion engine, in particular for exhaust aftertreatment of an internal combustion engine, particularly preferably an internal combustion engine operating method with the purpose of increasing an exhaust gas temperature of the internal combustion engine to increase the efficiency of an exhaust aftertreatment system, and an apparatus for performing such a method.

The current and increasingly stringent emissions legislation in the future places high demands on engine raw emissions and the exhaust aftertreatment of internal combustion engines. The vehicle and engine manufacturers are required to further reduce the consumption of internal combustion engines and the associated CO2 emissions. Among other things, this leads to the development of consumption-optimized combustion processes for internal combustion engines. In diesel engines, direct fuel injection and improved combustion processes have made it possible to achieve a significant increase in the efficiency of the internal combustion engine. Since NOx emissions can no longer be adequately reacted with a conventional three-way catalytic converter from the exhaust gas in a diesel engine or a lean-burn gasoline engine, additional catalysts such as catalysts for the selective, catalytic reduction of nitrogen oxides (SCR catalysts) are available. necessary with which the nitrogen oxide emissions in the exhaust gas can be reduced.

To reduce the raw emissions of internal combustion engines and compliance with exhaust gas recirculation are provided in modern internal combustion engines. These exhaust gas recirculations can be designed both as so-called high-pressure exhaust gas recirculations and as low-pressure exhaust gas recirculations. In this case, an exhaust gas stream is removed upstream of a turbine of the exhaust gas turbocharger and fed to the fresh air line downstream of a compressor of the exhaust gas turbocharger in a high-pressure exhaust gas recirculation. In a low-pressure exhaust gas recirculation, the recirculated exhaust gas stream downstream of the turbine is removed from the exhaust passage and introduced into the fresh air line of the internal combustion engine upstream of the compressor. The metering of a recirculated exhaust gas flow into the fresh air line is generally effected by means of an exhaust gas recirculation valve.

From the DE 10 2008 015 600 A1 An exhaust system for an internal combustion engine is known in which exhaust gas is passed through a particulate filter, and is introduced downstream of the particulate filter in a low-pressure exhaust gas recirculation. For this purpose, an exhaust flap is provided in the exhaust passage downstream of the branch of the low-pressure exhaust gas recirculation, with the exhaust gas back pressure and thus the introduced into the low-pressure exhaust gas recirculation exhaust gas can be increased. During the regeneration of the particulate filter, the high-pressure exhaust gas recirculation valve is completely closed and the low-pressure exhaust gas recirculation valve is opened in order to improve the heating of the particulate filter and to ensure a component protection of a fresh air duct of the internal combustion engine.

From the DE 10 2013 212 733 A1 an exhaust system of an internal combustion engine is known in which a particulate filter is arranged in a main path of the exhaust system, and downstream of the particulate filter branches off a low-pressure exhaust gas recirculation from the main path. In the low-pressure exhaust gas recirculation, a filter element is arranged at a small distance from the particle filter, which is traversed during the regeneration of the particulate filter with exhaust gas, wherein the heating of the particulate filter causes sufficient heating to regenerate the filter element. A disadvantage of such a solution, however, is that it can not be ensured at a greater distance between the filter element and the outlet of the particulate filter, that the exhaust gas flow guided by the exhaust gas recirculation causes sufficient for regeneration heating of the filter element.

In addition, the reveals DE 101 39 848 A1 an internal combustion engine for a motor vehicle with a control and control unit, via which an air inlet member of the internal combustion engine is controlled such that the amount of air supplied to the engine depending on the temperature in the exhaust gas purification system of the engine is adjustable and further in the overrun mode, the amount of air supplied in dependence the temperature of the emission control system is adjustable. For this purpose, the temperature is determined in the exhaust gas purification system and determines the operating parameters of the internal combustion engine and operated at low load or coasting when falling below a predetermined target range of the temperature of the exhaust gas purification system, the air inlet member.

The invention is based on the object, in an internal combustion engine, to avoid or at least reduce the cooling of a catalyst for the selective, catalytic reduction in order to achieve the highest possible efficiency of the SCR system.

The object is achieved by an inventive method for operating an internal combustion engine, preferably a diesel engine, with an exhaust gas passage, in which at least one catalyst for the selective, catalytic reduction of Nitrogen oxides is arranged dissolved, wherein in the exhaust duct, preferably upstream of the catalyst for the selective catalytic reduction of nitrogen oxides, an exhaust gas temperature is determined, and the filling of the combustion chambers of the internal combustion engine is reduced when the exhaust gas temperature is below a threshold temperature. In this context, the filling of the internal combustion engine is to be understood as meaning the quantity of gas flowing into the combustion chambers of the internal combustion engine, which is composed of the fresh air mass and the recirculated exhaust gas mass, in particular the exhaust gas mass recirculated via a high-pressure exhaust gas recirculation. A high-pressure exhaust gas recirculation means an exhaust gas recirculation, which takes exhaust gas from the combustion chambers of the internal combustion engine or the exhaust gas duct upstream of a turbine of the exhaust gas turbocharger and feeds this to the inlet side fresh air stream, preferably downstream of a throttle valve of the internal combustion engine. For the selective, catalytic reduction of nitrogen oxides, in addition to a reducing agent, in particular in addition to an aqueous urea solution, a sufficient temperature on the catalyst for selective, catalytic reduction necessary to reduce the nitrogen oxides in the exhaust gas of the internal combustion engine in molecular nitrogen can. By means of the method according to the invention, it can be prevented that the exhaust duct cools down in an operating point with low load or in overrun mode such that an efficient conversion of the nitrogen oxides is not possible immediately but only after a motorized heating phase in a following operating phase and in such a heating phase there is a slip in nitrogen oxide emissions. In this case, reducing the mass flow through the exhaust gas channel is reduced by the reduction of the filling, whereby cooling of the components for the exhaust gas aftertreatment and in particular of the catalyst for the selective, catalytic reduction of nitrogen oxides, is slowed down. As a result of the method according to the invention, the catalyst for the selective, catalytic reduction of nitrogen oxides thus remains in its efficient operating range for a longer time, so that the nitrogen oxide emissions can be reduced.

The measures listed in the dependent claims advantageous developments and improvements of the method specified in the independent claim for exhaust aftertreatment are possible.

In a preferred embodiment of the invention, it is provided that the filling is reduced by employing a throttle valve arranged in an intake line of the internal combustion engine. By shutting off the throttle flap, the filling of the combustion chambers of the internal combustion engine can be reduced in an efficient manner and the mass flow through the exhaust gas channel can be reduced.

In a further preferred embodiment of the invention, it is provided that the exhaust gas recirculation rate is kept at least substantially constant as a percentage of the amount of fresh air supplied to the internal combustion engine. A substantially constant exhaust gas recirculation rate is to be understood as a deviation of not more than 5 percent, preferably not more than 3 percent, particularly preferably less than 2 percent. As a result, a ratio over the entire operating map of the internal combustion engine can be set in a simple manner, whereby only a few mode transitions must be taken into account and thus the general operating behavior of the internal combustion engine and in particular a driving behavior of a motor vehicle in which the internal combustion engine is installed as a drive unit can be improved can. As a result, no further engine measures are necessary, which lead to changed raw NOx emissions and / or increased particulate emissions of the internal combustion engine.

In a preferred development of the invention, it is provided that the throttle valve is turned on in a coasting operation of the internal combustion engine and thus the flow cross section of the intake line is strongly blocked. Under a strong obstruction is an obstruction operating point dependent on at least 60%, preferably at least 80 percent, more preferably at least 85% of the flow cross section of the intake to understand. In a coasting operation, there is no combustion of an ignitable combustion mixture in the combustion chambers of the internal combustion engine, so that the temperature of the exhaust gas pushed out into the exhaust gas duct is particularly low during overrun operation. As a result, with an unthrottled inflow of fresh air into the combustion chambers, a particularly strong cooling of the components for exhaust gas aftertreatment would be to be feared, which is reduced by a strong throttling and a correspondingly low gas throughput through the combustion chambers and the exhaust gas duct.

According to an advantageous embodiment of the method, it is provided that in addition an exhaust gas flap arranged downstream of the catalytic converter for the selective, catalytic reduction of nitrogen oxides is made and thus the flow cross-section of the exhaust gas duct is strongly blocked. By employing an exhaust flap in the exhaust duct, a back pressure can be generated which counteracts cooling of the exhaust gas by increasing the pressure in the exhaust duct. In addition, by adjusting the exhaust flap, a larger volume flow of exhaust gas via a low-pressure exhaust gas recirculation to the intake passage be fed so that the heat remains essentially in the system and is not discharged through an exhaust duct to the environment.

In a preferred embodiment of the method, it is provided that a second exhaust gas temperature is determined in the exhaust gas channel, wherein a temperature at the inlet into the catalyst for the selective, catalytic reduction of nitrogen oxides is determined from the difference of the first exhaust gas temperature and the second exhaust gas temperature. By two temperatures in the exhaust passage, the inlet temperature of the exhaust gas when entering the catalyst for selective, catalytic reduction can be determined more accurately, since in addition to the absolute temperature at a temperature sensor, a heat loss along the exhaust duct on the temperature difference between the two temperature sensors can be determined.

In a preferred embodiment of the invention it is provided that the threshold temperature is in a range of 180 ° C to 220 ° C, preferably at about 200 ° C. On the one hand, the goal is to minimize the losses during a heating phase of the components for exhaust aftertreatment. On the other hand, a particularly efficient catalytic reduction of nitrogen oxides by the ammonia obtained from the aqueous urea solution in a temperature range of about 200 ° C to 300 ° C instead. Therefore, the threshold temperature is advantageously chosen so that the inventive method is initiated to heat the components of the exhaust aftertreatment as quickly as possible to an operating temperature and in operation a (further) drop in exhaust gas temperature when entering the catalyst for selective catalytic reduction of nitrogen oxides under to avoid this threshold temperature and thus to increase the efficiency of the catalytic reduction of nitrogen oxides.

According to the invention, a device for exhaust aftertreatment of an internal combustion engine is proposed, which has at least one exhaust gas channel and a catalyst arranged in the exhaust duct for the selective catalytic reduction of nitrogen oxides, a temperature sensor for determining an exhaust gas temperature in the exhaust duct and a control device with a machine-readable program code for performing a method according to the invention , By an inventive device for exhaust aftertreatment, the implementation of the method according to the invention is possible.

In a preferred embodiment of the device it is provided that two catalysts for the selective, catalytic reduction of nitrogen oxides are arranged in the exhaust gas channel. By a first and a second catalyst for the selective, catalytic reduction of nitrogen oxides, which are preferably arranged in series, it is possible that at least one of the two catalysts in the temperature window for particularly efficient reduction of nitrogen oxides can be operated and thus the best possible exhaust aftertreatment Exhaust gases of the internal combustion engine is achieved. Alternatively, in addition to a catalyst for the selective, catalytic reduction of nitrogen oxides, a NOx storage catalyst may also be installed in the exhaust gas duct. Even with such a combination of NOx storage catalyst and SCR catalyst, the inventive method has advantages, since the exhaust gas temperature

It is particularly preferred if an exhaust gas recirculation line branches off from the exhaust gas channel downstream of the first catalytic converter for the selective catalytic reduction of nitrogen oxides and upstream of the second catalytic converter for the selective catalytic reduction of nitrogen oxides. This allows heat to be dissipated via the exhaust gas recirculation line, so that the second catalyst in the flow direction can be operated at a significantly lower temperature than the first catalyst. As a result, with regard to further operating situations, in particular to operating situations in which an upper threshold value for efficient, selective catalytic reduction of the nitrogen oxides is exceeded, there are further possible applications in order to achieve a particularly effective reduction of the nitrogen oxide emissions in the exhaust gas.

According to an advantageous improvement of the device, it is provided that the first catalyst for the selective, catalytic reduction of nitrogen oxides is designed as a particle filter with a coating for the selective, catalytic reduction of nitrogen oxides and the second catalyst as an SCR catalyst. For many applications, it is advantageous if the exhaust aftertreatment device has both a particulate filter for reducing soot emissions and a catalyst for the selective, catalytic reduction of nitrogen oxides. Since for the regeneration of the particulate filter higher temperatures, in particular temperatures above 600 ° C are necessary, it is advantageous to arrange this particulate filter close to the engine in order to achieve a necessary for the regeneration of the particulate filter temperature with low motor heating measures. It is advantageous if the particulate filter has a coating for the selective, catalytic reduction of nitrogen oxides, since in this near-engine position after a cold start, in a low-power operation or in a coasting operation the temperature window for the efficient reduction of nitrogen oxides is achieved faster.

According to an advantageous further development of the invention, it is provided that a first temperature sensor and a second temperature sensor are arranged in the exhaust gas channel upstream of the first catalytic converter for the selective, catalytic reduction of nitrogen oxides. On the one hand, redundancy can be achieved by the two temperature sensors so that a determination of the exhaust gas temperature is still possible even if one of the temperature sensors fails. Furthermore, a temperature at the inlet to one of the catalysts for selective, catalytic reduction can be determined more accurately, since heat losses along the exhaust gas channel can be determined from the temperature difference between the two temperature sensors.

It is particularly preferred if the first temperature sensor is arranged downstream of an outlet of the internal combustion engine and upstream of a turbine of an exhaust gas turbocharger, and the second temperature sensor downstream of the turbine of the exhaust gas turbocharger and upstream of the first catalytic converter in the flow direction for the selective catalytic reduction of nitrogen oxides. As a result, a first temperature of the exhaust gas can be detected as close to the engine as possible

According to a preferred embodiment of the invention it is provided that in the exhaust passage downstream of an outlet of the internal combustion engine, a turbine of an exhaust gas turbocharger and downstream of an oxidation catalyst are arranged, downstream of the oxidation catalyst and upstream of the catalyst for selective catalytic reduction of nitrogen oxides, a metering module for metering a Reductant is disposed in the exhaust passage. By an oxidation catalyst upstream of the catalyst for selective, catalytic reduction, unburned hydrocarbon, carbon monoxide and hydrogen can be exothermically reacted, whereby the exhaust gas is heated. In this way, on the one hand, these emissions can be converted into innocuous exhaust gas components, in particular into steam and carbon dioxide, on the other hand, the temperature at the inlet to the catalyst for selective, catalytic reduction can be raised, whereby it is possible, even in low load phases, a temperature range for efficient To achieve reduction of nitrogen oxides.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

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

1 an internal combustion engine with a device according to the invention for the exhaust aftertreatment of the internal combustion engine and for carrying out the method according to the invention for the exhaust aftertreatment; and

2 a flow diagram of a method according to the invention for the exhaust aftertreatment of the internal combustion engine.

1 shows an internal combustion engine 10 , preferably a diesel engine, which at its inlet 50 with a fresh air line 44 and at its outlet 52 with an exhaust duct 12 connected is. The internal combustion engine 10 has an exhaust gas turbocharger 22 on, its turbine 24 in a main exhaust path of the exhaust passage 12 is arranged. The turbine 24 the exhaust gas turbocharger 22 drives a compressor 26 in the fresh air line 44 on, with which the combustion chambers of the internal combustion engine 10 be supplied with fresh air, with the fresh air through the compressor 26 is precompressed to a pressure higher than the ambient pressure. In the main exhaust path 14 is in the flow direction of the exhaust gas of the internal combustion engine 10 downstream of the turbine a catalyst 14 , in particular an oxidation catalyst 58 arranged. Further downstream is in the exhaust duct 12 a particle filter 16 with a coating 18 arranged for selective catalytic reduction, which filters out soot particles from the exhaust gas of the internal combustion engine and on the surface of the particulate filter 16 attaches. The coating 18 for selective, catalytic reduction 18 serves as a first catalyst 18 for the selective, catalytic reduction of nitrogen oxides. Downstream of the catalyst 14 and upstream of the particulate filter 16 are a dosing module 28 for introducing a reducing agent, in particular aqueous urea solution, into the exhaust gas duct 12 as well as a mixer 30 arranged for uniform distribution of the reducing agent. Downstream of the outlet 52 and upstream of the turbine 24 the exhaust gas turbocharger 22 is a first temperature sensor 54 for detecting a first exhaust gas temperature T _A1 at the exhaust duct 12 arranged. Downstream of the turbine 24 and upstream of the dosing module 28 , in particular to the oxidation catalyst 58 is a second temperature sensor 56 arranged to detect a second exhaust gas temperature T _A2 . A load of the particulate filter 16 can through two pressure sensors 70 . 72 be monitored, of which a first pressure sensor 70 upstream of the particulate filter 16 and a second pressure sensor 72 downstream of the particulate filter 16 are arranged and thus a pressure difference across the particulate filter 16 be measured can. With increasing soot loading of the particulate filter 16 increases this pressure difference so that the differential pressure across the particulate filter 16 as a measure of the loading of the particulate filter 16 can be used. Downstream of the particulate filter 16 is a branch in the exhaust duct 34 provided at the a low-pressure exhaust gas recirculation line 36 from the exhaust duct 12 branches. Downstream of this junction 34 is in the exhaust duct 12 a second catalyst 20 arranged for the selective, catalytic reduction of nitrogen oxides, which is preferably designed as a conventional SCR catalyst. Further downstream is in the exhaust passage 12 an exhaust flap 32 arranged, with which an exhaust gas flow through the exhaust duct 12 can be throttled. Downstream of the particulate filter 16 with the coating 18 for the selective, catalytic reduction of nitrogen oxides and upstream of the SCR catalyst 20 branches the low-pressure exhaust gas recirculation line 36 from the exhaust duct 12 from which the exhaust duct 12 at a junction 66 with the suction line 44 downstream of an air filter 46 and upstream of the compressor 26 combines. In the low-pressure exhaust gas recirculation line 36 is a filter element 38 arranged. Further, in the low pressure exhaust gas recirculation line 36 an exhaust gas recirculation valve 42 arranged, with which a volume flow of recirculated exhaust gas through the low-pressure exhaust gas recirculation line 36 can be regulated. Downstream of the filter element 38 and upstream of the exhaust gas recirculation valve 42 is an exhaust gas recirculation cooler (EGR cooler) 40 provided with the temperature of the intake pipe 44 supplied exhaust gas can be reduced. Alternatively, the exhaust gas recirculation cooler 40 also downstream of the exhaust gas recirculation valve 42 in the low pressure exhaust gas recirculation line 36 be arranged.

The internal combustion engine 10 has a high pressure exhaust gas recirculation valve 62 on, with which exhaust gas from the combustion chambers or from the exhaust duct 12 upstream of the turbine 24 the exhaust gas turbocharger 22 removed and the suction line 44 downstream of the throttle 48 is supplied.

The suction line 44 has an air filter 46 on which suction side at one end of the suction line 44 is arranged. Downstream of the air filter 46 or in the air filter 46 integrated is an air mass meter 64 , in particular a hot-film air mass meter, provided to a volume flow of fresh air sucked in the intake pipe 44 of the internal combustion engine 10 to determine. Downstream of the compressor 26 is a throttle 48 provided with the fresh air flow can be throttled in the combustion chambers of the internal combustion engine. Downstream of the throttle 48 and upstream of the inlet 50 is a charge air cooler 60 provided to cool the compressed air and thus the filling of the combustion chambers of the internal combustion engine 10 continue to improve. The pressure sensors 70 . 72 as well as the temperature sensors 54 . 56 are via signal lines 74 with a control unit 68 of the internal combustion engine 10 connected to the need for regeneration of the particulate filter 16 and exhaust gas temperatures T _A1 , T _{A2 and} to determine from these exhaust gas temperatures T _A1 , T _A2 an inlet temperature T _E when the exhaust gas enters the particle filter 16 as the first catalyst 18 to determine the selective, catalytic reduction of nitrogen oxides.

In 2 is a flow diagram of a method according to the invention for the exhaust aftertreatment of an internal combustion engine 10 shown. The aim of the process is to increase the exhaust gas temperature upstream of the system for the selective, catalytic reduction of nitrogen oxides (SCR system) and to increase its efficiency. Thus, the temperature of at least one catalyst for the selective, catalytic reduction of nitrogen oxides 18 . 20 be kept above a critical threshold temperature, below which the efficiency of the nitric oxide reduction is significantly limited. In a first step < 100 > is a first exhaust gas temperature T _{A1 of} the exhaust gas of the internal combustion engine 10 in the exhaust duct 12 determined. In addition, in a further method step < 110 > a second exhaust gas temperature T _A2 at another point in the exhaust duct 12 be determined. If the first exhaust gas temperature T _{A1 is} below a threshold temperature T _s , then in a further method step < 120 > the throttle 48 employed and thus the filling of the combustion chambers of the internal combustion engine 10 reduced. Preferably takes place by the high-pressure exhaust gas recirculation valve 62 a percentage with respect to the fresh air mass flow percentage at least substantially constant admixture of exhaust gas, so that the filling of the combustion chambers is reduced to the same extent, as the fresh air mass flow by hiring the throttle 48 is reduced. In a further process step < 130 > gets the throttle 48 even in a coasting operation of the internal combustion engine 10 employed and the high-pressure exhaust gas recirculation valve 62 open. This reduces the "cold" exhaust gas mass flow through one of the catalysts 18 . 20 for the selective, catalytic reduction of nitrogen oxides in non-fired operation of the internal combustion engine. Will the high-pressure exhaust gas recirculation valve 62 opened in overrun, so can by a vacuum in the intake 44 a lot of exhaust gas are circulated and thus a heat loss can be kept low. In addition, in a further method step < 140 > the exhaust flap 32 adjusted to the back pressure in the exhaust duct 12 increase and thus use the heat accumulation, to cool the catalysts 18 . 20 to prevent or at least to selective, catalytic reduction of nitrogen oxides slow it down. The inventive method can be an exhaust gas temperature T _E in a typical city cycle when entering the particulate filter 16 with the coating for selective, catalytic reduction of nitrogen oxides in the catalyst by about 20-40 ° C raise, creating a much more efficient implementation of nitrogen oxides by the catalysts for selective, catalytic reduction 18 . 20 is possible.

LIST OF REFERENCE NUMBERS

10

internal combustion engine

12

exhaust duct

14

catalyst

16

particulate Filter

18

Coating for the selective, catalytic reduction of nitrogen oxides

20

SCR catalyst

22

turbocharger

24

turbine

26

compressor

28

dosing

30

mixer

32

exhaust flap

34

branch

36

Exhaust gas recirculation line

38

filter element

40

exhaust gas cooler

42

Exhaust gas recirculation valve

44

suction

46

air filter

48

throttle

50

inlet

52

outlet

54

first temperature sensor

56

second temperature sensor

58

oxidation catalyst

60

Intercooler

62

High-pressure exhaust gas recirculation valve

64

Air flow sensor

66

junction

68

control unit

70

first pressure sensor

72

second pressure sensor

74

signal line

T _A1

Exhaust gas temperature at the first temperature sensor

T _A2

Exhaust gas temperature at the second temperature sensor

T _E

 Exhaust gas temperature entering the catalyst for selective, catalytic reduction

T _S

 threshold temperature

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• DE 102008015600 A1 [0004]
• DE 102013212733 A1 [0005]
• DE 10139848 A1 [0006]

Claims (15)

Method for operating an internal combustion engine ( 10 ), in particular a diesel engine, and for exhaust aftertreatment of this internal combustion engine ( 10 ), with an exhaust duct ( 12 ) in which at least one catalyst ( 18 . 20 ) is arranged for the selective, catalytic reduction of nitrogen oxides, characterized in that in the exhaust gas channel ( 12 ), preferably upstream of the catalyst ( 18 . 20 ) for selective, catalytic reduction, an exhaust gas temperature (T _A1 ) is determined, and the filling of the combustion chambers of the internal combustion engine ( 10 ) is reduced when the exhaust gas temperature (T _A1 ) is below a threshold temperature (T _S ). Method for operating an internal combustion engine ( 10 ) according to claim 1, characterized in that the filling by a hiring one in a suction ( 44 ) of the internal combustion engine ( 10 ) arranged throttle valve ( 48 ) is reduced. Method for operating an internal combustion engine ( 10 ) according to claim 1 or 2, characterized in that the exhaust gas recirculation rate as a percentage of the internal combustion engine ( 10 ) supplied amount of fresh air is kept at least substantially constant. Method for operating an internal combustion engine ( 10 ) according to claim 2, characterized in that the throttle valve ( 48 ) in a coasting operation of the internal combustion engine ( 10 ) and thus the flow cross-section of the suction line ( 44 ) is strongly blocked. Method for operating an internal combustion engine ( 10 ) according to one of claims 1 to 4, characterized in that in addition one in the exhaust duct ( 12 ) downstream of the catalyst ( 18 . 20 ) for the selective, catalytic reduction of nitrogen oxides arranged exhaust flap ( 32 ) is hired. Method for operating an internal combustion engine ( 10 ) according to one of claims 1 to 5, characterized in that in the exhaust duct ( 12 ) a second exhaust gas temperature (T _A2 ) is determined, wherein from the difference of the first exhaust gas temperature (T _A1 ) and the second exhaust gas temperature (T _A2 ) a temperature at the inlet into the catalyst ( 18 . 20 ) is determined for the selective, catalytic reduction of nitrogen oxides. Method for operating an internal combustion engine ( 10 ) according to one of claims 1 to 6, characterized in that the threshold temperature (T _S ) is in a range of 180 ° C to 220 ° C. Control unit ( 68 ) with a machine-readable program code, which is set up to perform a method according to one of claims 1 to 7 when executing the program code. Device for exhaust aftertreatment of an internal combustion engine ( 10 ) with an exhaust duct ( 12 ) in which at least one catalyst ( 18 . 20 ) is arranged for the selective, catalytic reduction of nitrogen oxides, with a temperature sensor ( 54 . 56 ) for determining an exhaust gas temperature in the exhaust gas duct ( 12 ) as well as with a control unit ( 68 ) with a machine-readable program code, which is arranged to perform a method according to one of claims 1 to 7. Aftertreatment device according to claim 9, characterized in that in the exhaust gas duct ( 12 ) two catalysts ( 18 . 20 ) are arranged for the selective, catalytic reduction of nitrogen oxides. Device for exhaust gas aftertreatment according to claim 10, characterized in that an exhaust gas recirculation line ( 36 ) downstream of the first catalyst ( 18 ) for the selective, catalytic reduction of nitrogen oxides and upstream of the second catalyst ( 20 ) for the selective, catalytic reduction of nitrogen oxides from the exhaust gas channel ( 12 ) branches off. Aftertreatment device according to claim 10 or 11, characterized in that the first catalyst ( 18 ) for the selective, catalytic reduction of nitrogen oxides as a particulate filter ( 16 ) with a coating for the selective, catalytic reduction of nitrogen oxides and the second catalyst ( 20 ) are formed as an SCR catalyst. Aftertreatment device according to one of claims 9 to 12, characterized in that in the exhaust gas duct ( 12 ) upstream of the first catalyst ( 18 ) for the selective, catalytic reduction of nitrogen oxides, a first temperature sensor ( 54 ) and a second temperature sensor ( 56 ) are arranged. Apparatus according to claim 13, characterized in that the first temperature sensor ( 54 ) downstream of an outlet ( 52 ) of the internal combustion engine ( 10 ) and upstream of a turbine ( 24 ) of an exhaust gas turbocharger ( 22 ) and the second temperature sensor ( 54 ) downstream of the turbine ( 24 ) and upstream of an inlet of the catalyst ( 18 . 20 ) are arranged for the selective, catalytic reduction of nitrogen oxides. Device according to one of claims 9 to 14, characterized in that in the exhaust duct ( 12 ) downstream of an outlet ( 52 ) of Internal combustion engine ( 10 ) a turbine ( 24 ) of an exhaust gas turbocharger ( 22 ) and further downstream an oxidation catalyst ( 14 ), wherein downstream of the oxidation catalyst ( 14 ) and upstream of the catalyst ( 18 . 20 ) for the selective, catalytic reduction of nitrogen oxides, a dosing module ( 28 ) for metering a reducing agent into the exhaust gas channel ( 12 ) is arranged.

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