DE102020106911A1 - Process for exhaust aftertreatment of an internal combustion engine and exhaust aftertreatment system - Google Patents

Abstract

The invention relates to a method for exhaust gas aftertreatment of an internal combustion engine (10), in whose exhaust system (40) an electrically heatable catalyst (66), downstream of the electrically heatable catalyst (66) a particle filter (52) with an SCR coating (54) and downstream of the particle filter (52, 54) an SCR catalyst (58) is arranged, with a first metering element (38) upstream of the particle filter (52, 54) and a second downstream of the particle filter (52) and upstream of the SCR catalyst (58) Dosing element (56) is arranged, comprising the following steps: - determining a temperature of the SCR catalytic converter (58), - determining an NH3 fill level of the SCR catalytic converter (58), - heating the exhaust gas aftertreatment components (52, 54, 58) by the electrically heatable catalytic converter (66), - switching off the metering of reducing agent by the first metering element (38), - shifting a load point of the internal combustion engine (10) in order to reduce the heat input in to increase the exhaust system (40), the load point being shifted in the direction of higher raw NOx emissions in order to reduce the ammonia loading of the SCR catalytic converter (58). The invention also relates to an exhaust gas aftertreatment system for carrying out such a method.

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, and one that will become increasingly strict in the future, place high demands on the engine-related raw emissions and the 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. Upstream and downstream catalytic converters. 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 separating out soot particles and possibly other catalytic converters. Ammonia is preferably used as the reducing agent. Because dealing with pure ammonia is complex, a synthetic, aqueous urea solution is usually used in vehicles, which is mixed with the hot exhaust gas flow in a mixing device upstream of the SCR catalytic converter. As a result of this mixing, the aqueous urea solution is heated, 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.

Furthermore, exhaust gas aftertreatment systems with at least two exhaust gas aftertreatment components for the selective, catalytic reduction of nitrogen oxides are known, through which an exhaust gas stream of the internal combustion engine flows sequentially, the first exhaust gas aftertreatment component being arranged close to the engine and the second exhaust gas aftertreatment component being arranged in the underbody position of a motor vehicle, each exhaust gas aftertreatment component having a metering element for metering in aqueous urea solution is assigned in order to be able to operate at least one exhaust gas aftertreatment component in a temperature range, depending on the operating situation of the internal combustion engine, in order to enable an efficient conversion of the nitrogen oxide emissions.

Every device for catalytic exhaust gas cleaning requires that a minimum temperature, the so-called light-off temperature, be exceeded in order to be effective. During a cold start of a motor vehicle, the internal combustion engine and the components for exhaust gas aftertreatment have a temperature level approximately at ambient temperature. Even with a high energy input into the exhaust system, the thermally inert mass of the exhaust system must first be overcome and the radiation or convection losses compensated in order to achieve at least a partial effectiveness of the exhaust gas aftertreatment components. During this time, the raw emissions of the internal combustion engine are emitted largely uncleaned. Depending on the energy input into the exhaust system, this period can be shortened, but never reduced to zero.

In diesel engines, it is known to connect a NOx storage catalytic converter upstream of an SCR exhaust gas purification system, which already provides good conversion performance in the 120-200 ° C range, while the SCR catalytic converter only enables nitrogen oxide emissions to be converted from around 180 ° C. The exhaust gas aftertreatment components can be supported individually or as a whole during their heating phase, in particular up to the respective light-off temperature, by electrical heating elements or thermal exhaust gas burners.

From the DE 10 2017 214 572 A1 An internal combustion engine with an exhaust gas aftertreatment system is known in which an oxidation catalyst is arranged in the flow direction of an exhaust gas through an exhaust system of the internal combustion engine, a low-temperature nitrogen oxide storage catalyst downstream of the oxidation catalyst and a particle filter with an SCR coating further downstream.

From the US 10 113 464 B2 a method for introducing a reducing agent into the exhaust system of an internal combustion engine is known in which two SCR catalytic converters are arranged in series. The ammonia loading of the second SCR catalytic converter is calculated from the amount of reducing agent metered in upstream of the first SCR catalytic converter and the slip through the first SCR catalytic converter.

the US 9 206 722 B2 discloses a method for metering reducing agent into the exhaust system of an internal combustion engine. The ammonia concentration is determined downstream of a first SCR catalytic converter and the nitrogen oxide concentration in the exhaust gas flow of the internal combustion engine is determined downstream of a second SCR catalytic converter.

The invention is now based on the object of reducing the ammonia emissions of the exhaust gas aftertreatment system, and in particular to prevent undesired ammonia discharge from an SCR catalytic converter in the underbody position.

• - Ermitteln einer Temperatur der zweiten Abgasnachbehandlungskomponente zur selektiven, katalytischen Reduktion von Stickoxiden,
• - Ermitteln eines Ammoniak-Füllstands der zweiten Abgasnachbehandlungskomponente zur selektiven, katalytischen Reduktion von Stickoxiden,
• - Aufheizen der Abgasnachbehandlungskomponenten durch den elektrisch beheizbaren Katalysator,
• - Abschalten der Eindosierung von Reduktionsmittel durch das erste Dosierelement,
• - Verschieben eines Lastpunktes des Verbrennungsmotors, um den Wärmeeintrag in die Abgasanlage zu erhöhen, wobei der Lastpunkt in Richtung höherer NOx-Rohemissionen verschoben wird, um die Ammoniak-Füllstand der zweiten Abgasnachbehandlungskomponente zu verringern.

According to the invention, this object is achieved by a method for exhaust gas aftertreatment of an internal combustion engine, in whose exhaust system an electrically heatable catalytic converter, downstream of the electrically heatable catalytic converter a first exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides and downstream of the first exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides, a further exhaust gas aftertreatment component is arranged for the selective, catalytic reduction of nitrogen oxides, a first metering element being arranged upstream of the first exhaust gas aftertreatment component and a second metering element being arranged downstream of the first exhaust gas aftertreatment component and upstream of the second exhaust gas aftertreatment component, which comprises the following steps:

• - Determining a temperature of the second exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides,
• - Determination of an ammonia level of the second exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides,
• - The exhaust gas aftertreatment components are heated by the electrically heated catalytic converter,
• - Switching off the metering of reducing agent by the first metering element,
• - Shifting a load point of the internal combustion engine in order to increase the heat input into the exhaust system, the load point being shifted in the direction of higher raw NOx emissions in order to reduce the ammonia level of the second exhaust gas aftertreatment component.

The method according to the invention helps to avoid uncontrolled discharge of ammonia from the second exhaust gas aftertreatment component by specifically reducing the fill level of the second exhaust gas aftertreatment component. The ammonia stored in the second exhaust gas aftertreatment component is converted with the additional nitrogen oxides from the exhaust gas flow of the internal combustion engine. By switching off the metering in of reducing agent upstream of the first exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides, reloading of the second exhaust gas aftertreatment component with ammonia is temporarily avoided. In this way, an ammonia breakthrough when the exhaust gas aftertreatment system is heated up can be reliably prevented.

The features mentioned in the dependent claims allow advantageous further developments and improvements of the method for exhaust gas aftertreatment mentioned in the independent claim.

In a preferred embodiment of the method it is provided that the method is initiated when the level of the second exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides is above a threshold value for the level and the temperature of the second exhaust gas aftertreatment component is below a threshold temperature. In order to enable an efficient conversion of nitrogen oxides, the presence of a reducing agent and a minimum temperature for selective, catalytic reduction are necessary. If this minimum temperature is not reached, the ammonia stored in the second exhaust gas aftertreatment component cannot be broken down, so that there is a risk of an increase in ammonia emissions. In order to avoid this in an operationally reliable manner, when a defined threshold value for the ammonia loading of the second exhaust gas aftertreatment component is reached and the temperature falls below a threshold value, the method described is initiated in order to avoid an ammonia breakthrough.

In an advantageous improvement of the method, it is provided that the operating point shift of the internal combustion engine is implemented by operating a belt starter generator that can be coupled to the internal combustion engine. By coupling the starter belt generator with the internal combustion engine, a direct power supply of the electrically heated catalytic converter is possible, whereby the battery of a motor vehicle is relieved. In addition, by coupling the starter belt generator, a load point can be shifted in a simple manner with constant drive power without greatly reducing the internal engine efficiency of the internal combustion engine. This enables the exhaust gas aftertreatment components to be heated up efficiently.

It is particularly preferred if the threshold temperature is between 160.degree. C. and 250.degree. C., preferably between 170.degree. C. and 200.degree. Below about 180 ° C, the conversion of nitrogen oxides is severely restricted or impossible by a selective, catalytic reduction. As a result, the ammonia stored in the second exhaust gas aftertreatment component cannot be broken down. A selective, catalytic reduction in the temperature range from 250 ° C to 350 ° C is particularly efficient.

In a preferred embodiment of the method, it is provided that the threshold value for the fill level with a load is 50% to 90%, preferably between 60% and 85%, particularly preferably between 70% and 80% of the maximum possible fill level. In order to avoid uncontrolled discharge of ammonia, a certain distance from the maximum storage capacity of the second exhaust gas aftertreatment component is necessary, since the storage capacity is also dependent on the temperature of the exhaust gas aftertreatment component. At the same time, the aim is to keep the ammonia level as high as possible in order to enable the most efficient possible conversion of the nitrogen oxides.

Another aspect of the invention relates to an exhaust gas aftertreatment system for an internal combustion engine, in whose exhaust system an electrically heatable catalytic converter, downstream of the electrically heated catalytic converter a first exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides and downstream of the first exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides, a further exhaust gas aftertreatment component is arranged for the selective, catalytic reduction of nitrogen oxides. A first metering element is arranged upstream of the first exhaust gas aftertreatment component and a second metering element is arranged upstream of the second exhaust gas aftertreatment component. A control device is set up to carry out a method according to the invention when a machine-readable program code is executed by the control device. With an exhaust gas aftertreatment system of this type, ammonia can be reliably prevented from being discharged from the second exhaust gas aftertreatment component, in particular from an SCR catalytic converter in the underbody position of a motor vehicle, and an associated increase in ammonia emissions.

In an advantageous embodiment of the exhaust gas aftertreatment system, it is provided that an exhaust gas flap is arranged downstream of the first exhaust gas aftertreatment component. The exhaust gas aftertreatment system has a low-pressure exhaust gas recirculation which branches off from the first exhaust duct at a first junction downstream of the first exhaust aftertreatment component and upstream of an exhaust flap and connects the first exhaust duct to an intake duct of an air supply system of the internal combustion engine. An exhaust gas recirculation cooler is arranged in the low-pressure exhaust gas recirculation. Downstream of the exhaust gas recirculation cooler, an exhaust gas recirculation duct of the low-pressure exhaust gas recirculation is provided with a second branch at which a second exhaust duct branches off, which connects the exhaust gas recirculation duct of the low-pressure exhaust gas recirculation with the first exhaust duct downstream of the exhaust flap. As a result, the exhaust gas recirculation cooler can also be used for temperature management of the temperature of the second exhaust gas aftertreatment component. In addition, the exhaust gas flow can be used to heat the cooling water of the internal combustion engine immediately after a cold start and thus to reduce cold start emissions.

In a preferred embodiment of the invention it is provided that the electrically heatable catalyst is embedded in an oxidation catalyst, the electrically heatable catalyst being arranged downstream of a first oxidation catalyst and upstream of a second oxidation catalyst. By means of the electrically heatable catalytic converter, the oxidation catalytic converter and the further exhaust gas aftertreatment components arranged downstream of the oxidation catalytic converter can be heated to their light-off temperature essentially independently of the exhaust gas flow from the internal combustion engine. In this context, “essentially independent of the exhaust gas flow” means that the exhaust gas is used as a carrier flow for convective heat transfer from the heating element to the corresponding exhaust gas aftertreatment component, but the energy used for heating primarily from the electrically heatable catalytic converter and not or only too little comes from the exhaust gas of the internal combustion engine. A carrier current may be necessary in order to prevent overheating at certain points in an electrical heating element of the electrically heatable catalytic converter and thus a shutdown or thermal damage to the electrical heating element.

In a preferred embodiment of the invention it is provided that an ammonia barrier catalytic converter is arranged downstream of the second exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides. This allows ammonia broken through by the second exhaust gas aftertreatment component to be eliminated. Such an elimination of the ammonia leads, however, to an increase in nitrogen oxide emissions, which is why the aim is to convert the ammonia essentially completely to the two exhaust gas aftertreatment components and to avoid such ammonia breakthroughs.

In an advantageous embodiment of the exhaust gas aftertreatment system, it is provided that the first exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides is a particle filter with a coating for the selective, catalytic reduction of nitrogen oxides and the second exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides is an SCR catalyst. A particulate filter with an SCR Coating combines the functionality of a particle filter with the functionality of an SCR catalytic converter. As a result, it may be possible to dispense with an additional SCR catalytic converter, which reduces the costs for the exhaust gas aftertreatment system and simplifies assembly. The coating of the particle filter increases the exhaust gas back pressure, which means that shorter regeneration intervals are necessary under the same operating conditions. In addition to the particulate filter with the SCR coating, a further SCR catalytic converter can be provided in order to increase the functional area in which at least one of the SCR catalytic converters is operated in the required temperature range through different positions in the exhaust system. The particle filter with the SCR coating is preferably arranged in a position close to the engine and the SCR catalytic converter is arranged in an underbody position of the motor vehicle remote from the engine. In this context, a position close to the engine is to be understood as a position in the exhaust system with an exhaust gas run length of less than 80 cm from an outlet of the internal combustion engine.

Another improvement of the exhaust gas aftertreatment system provides that a device for exhaust gas heat recovery is arranged in an exhaust gas recirculation line of the low-pressure exhaust gas recirculation downstream of the first branch and upstream of the second branch. An exhaust gas heat recovery device can extract heat from the exhaust gas flow, whereby the temperature management for the second exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides can be further improved. In particular, during high-load or full-load operation of the internal combustion engine, the exhaust gas temperature can be lowered in such a way that the nitrogen oxides can be efficiently converted by the second exhaust gas aftertreatment component.

In an advantageous embodiment of the exhaust gas aftertreatment system, it is provided that a filter is arranged in the exhaust gas recirculation duct, downstream of the branch and upstream of an exhaust gas recirculation cooler. The primary purpose of the filter is to filter particles from the recirculated exhaust gas, which may arise when parts of the monolith of the filter body of the particle filter break out. Otherwise, these particles could damage the compressor of the exhaust gas turbocharger if they were to enter the intake tract of the internal combustion engine via the low-pressure exhaust gas recirculation system. By connecting the filter upstream of the exhaust gas recirculation cooler, it can also be prevented that a layer of soot is deposited on the exhaust gas recirculation cooler and thus restricts the function of this exhaust gas recirculation cooler. This increases the durability of the exhaust gas recirculation cooler.

In an advantageous embodiment of the exhaust gas aftertreatment system it is provided that a control element, in particular an exhaust gas recirculation valve, is arranged in the exhaust gas recirculation channel downstream of the second branch, with which a gas flow through the exhaust gas recirculation channel and / or the second exhaust gas channel can be controlled. Such a control element makes it easy to switch between a heating mode, in which the exhaust gas is fed back to the first exhaust gas channel via the second exhaust gas channel, and an exhaust gas recirculation mode, in which the exhaust gas is mixed with the fresh air in the intake channel. This means that the exhaust gas aftertreatment can be optimized through the corresponding operating mode depending on the exhaust gas temperature.

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

• 1 einen Verbrennungsmotor mit einem Luftversorgungssystem und einer Abgasanlage mit einem erfindungsgemäßen Abgasnachbehandlungssystem;
• 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;
• 2 a flow chart for carrying out a method according to the invention 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 20th and an exhaust system 40 . The internal combustion engine 10 is designed as a direct injection diesel engine and has several combustion chambers 12th on. At the combustion chambers 12th is a fuel injector each 14th for injecting a fuel into the respective combustion chamber 12th arranged. The internal combustion engine 10 is with his inlet 16 with an air supply system 20th and with its outlet 18th and with an exhaust system 40 tied together. The internal combustion engine 10 further comprises a high pressure exhaust gas recirculation 100 with an exhaust gas recirculation duct 102 , in which a high pressure exhaust gas recirculation valve 104 is arranged. Via the high pressure exhaust gas recirculation 100 can be a partial exhaust gas flow from the internal combustion engine 10 from the outlet 18th to the inlet 16 to be led back. At the combustion chambers 12th inlet valves and outlet valves are arranged, with which a fluidic connection from the air supply system 20th to the combustion chambers 12th or from the combustion chambers 12th to the Exhaust system 40 can be opened or closed.

The air supply system 20th includes an intake duct 28 , in which in the direction of flow of fresh air through the intake duct 28 an air filter 22nd , downstream of the air filter 22nd an air mass meter 24 , in particular a hot film air mass meter, downstream of the air mass meter 24 a compressor 26th of an exhaust gas turbocharger 36 , downstream of the compressor 26th a throttle 30th and further downstream an intercooler 32 are arranged. The air mass meter can do this 24 also in a filter housing of the air filter 22nd be arranged so that the air filter 22nd and the air mass meter 24 forms an assembly. Downstream of the air filter 22nd and upstream of the compressor 26th is a confluence 34 provided on which an exhaust gas recirculation line 86 a low pressure exhaust gas recirculation 80 in the intake duct 28 flows out.

The exhaust system 40 comprises a first 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 is arranged, which the compressor 26th in the air supply system 20th drives over a shaft. The exhaust gas turbocharger 36 is preferably used as an exhaust gas turbocharger 36 designed with variable turbine geometry. To do this are a turbine wheel of the turbine 44 adjustable guide vanes are connected upstream, via 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 48 , 50 , 52 , 54 , 58 , 64 intended. This is immediately downstream of the turbine 44 as the first component of the exhaust gas aftertreatment, a first oxidation catalytic converter 64 arranged. The first oxidation catalyst 64 is an electrically heated catalytic converter 66 with an electrical heating element, preferably in the form of an electrical heating disk, connected downstream. Downstream of the first oxidation catalyst 64 is a second oxidation catalyst 50 provided, which is preferably located directly on the electrically heatable catalyst 66 connects. Downstream of the second oxidation catalyst 50 is a particulate filter 52 with a coating 54 arranged for the selective catalytic reduction of nitrogen oxides. Downstream of the particulate filter 52 is another SCR catalytic converter 58 arranged. Downstream of the particulate filter 52 and upstream of the further SCR catalytic converter 58 is in the first exhaust duct 42 an exhaust flap 78 provided with which the cross section of the first exhaust duct 42 can be at least partially blocked to reduce the exhaust gas back pressure in the first exhaust duct 42 to increase. Downstream of the particulate filter 52 and upstream of the exhaust flap 78 is on the first exhaust duct 42 a branch 76 provided on which an exhaust gas recirculation line 86 a low pressure exhaust gas recirculation 80 from the first exhaust duct 42 branches off. Downstream of the SCR catalyst 58 is an ammonia barrier catalyst 94 arranged to avoid ammonia emissions.

At least one of the oxidation catalysts 50 , 64 can additionally have a storage component for the temporary storage of nitrogen oxide emissions and be designed as a NOx storage catalytic converter 48. Furthermore, instead of the particle filter 52 with the SCR coating 54 an SCR catalytic converter 56 and an uncoated particulate filter 52 or a particle filter 52 be provided with a catalytically active coating.

The low-pressure exhaust gas recirculation 80 includes in addition to the exhaust gas recirculation line 86 an exhaust gas recirculation cooler 82 and an exhaust gas recirculation valve 84 , via which the exhaust gas recirculation through the exhaust gas recirculation line 86 is controllable. On the exhaust gas recirculation line 86 the exhaust gas recirculation 80 is a temperature sensor 70 provided, over which an exhaust gas temperature in the low-pressure exhaust gas recirculation 80 can be determined to the exhaust gas recirculation 80 to activate as soon as the exhaust gas temperature in the low-pressure exhaust gas recirculation 80 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 low-pressure exhaust gas recirculation 80 or in the air supply system 20th leads to damage or deposits. Downstream of the branch 76 and upstream of the EGR cooler 82 is a filter 92 provided to prevent the entry of particles into the low-pressure exhaust gas recirculation 80 to minimize. Downstream of the EGR cooler 82 is a second branch 88 formed on which a second exhaust duct 62 from the exhaust gas recirculation duct 86 branches off and the exhaust gas recirculation duct 86 with the first exhaust duct 42 downstream of the exhaust flap 76 connects. At an intersection 60 the second exhaust duct opens 62 back into the first exhaust duct 42 . In the second exhaust duct 62 is a second control 96 provided in the form of an exhaust flap with which the second exhaust duct 62 can be opened and closed. Alternatively, the second control 96 also be designed as a throttle valve to the cross section of the second exhaust duct 62 variable to enlarge or reduce. In the low-pressure exhaust gas recirculation 80 is also a third exhaust gas recirculation valve 98 provided with which the exhaust gas recirculation line 86 downstream of the second branch 88 can be closed to an exhaust gas recirculation in the intake duct 28 to prevent.

In the exhaust system 40 is a temperature sensor 70 provided with which an exhaust gas temperature in the exhaust system 40 can be monitored to ensure effective and efficient exhaust gas aftertreatment of the exhaust gas of the internal combustion engine 10 to enable. There are also differential pressure sensors 72 provided to create a pressure difference across the particulate filter 52 to determine. In this way, the loading status of the particle filter 52 and a regeneration of the particle filter when a defined load level is exceeded 52 be initiated. Furthermore, is in the first exhaust duct 42 downstream of the oxidation catalysts 50 , 64 and upstream of the particulate filter 52 with the SCR coating 54 a first metering element 38 provided to a reducing agent, in particular aqueous urea solution, upstream of the particle filter 52 into the first exhaust duct 42 to be dosed. The first metering element 38 is a first exhaust mixer 46 downstream to the distribution of the reducing agent in the first exhaust duct 42 before entering the particle filter 52 to improve.

Downstream of the first branch 76 , especially downstream of the confluence 60 and upstream of the SCR catalyst 58 is a second metering element 56 provided to a reducing agent, in particular aqueous urea solution, upstream of the SCR catalytic converter 58 into the first exhaust duct 42 to be dosed. The second dosing element 56 is a second exhaust mixer 68 downstream to the distribution of the reducing agent in the first exhaust duct 42 before entering the SCR catalytic converter 58 to improve.

The internal combustion engine 10 is with an engine control unit 90 connected, which via signal lines, not shown, with the pressure, exhaust gas and temperature sensors 70 , 72 , 74 as well as with the fuel injectors 14th of the internal combustion engine 10 and the control devices 24 , 30th , 38 , 78 , 84 , 96 , 98 of the air supply system 20th as well as the exhaust system 40 connected is. In the first exhaust duct 42 are a plurality of temperature sensors 70 arranged. Further are downstream of the particulate filter 52 and downstream of the SCR catalyst 58 in each case a NOx sensor 74, preferably a NOx-NH3 combination sensor, is arranged.

In 2 a flowchart for carrying out a method according to the invention for exhaust gas aftertreatment is shown. In a method step <100>, a temperature of the second exhaust gas aftertreatment component is set 58 for the selective, catalytic reduction of nitrogen oxides, in particular an SCR catalytic converter in the underbody position of a motor vehicle. Furthermore, the ammonia fill level of this second exhaust gas aftertreatment component is determined in a method step <110> 58 determined. In a method step <120>, the temperature and the fill level are set with a threshold temperature T _S and a threshold value F _S for the permissible fill level of the second exhaust gas aftertreatment component 58 compared. If the temperature is below the threshold temperature T _S and the fill level is above the threshold value F _S for the permissible fill level, the exhaust gas aftertreatment components are set in a method step <130> 48 , 52 , 54 , 58 , 64 by activating the electrically heatable catalytic converter 66 heated up. At the same time or with a second offset, the metering in of reducing agent by the first metering element is carried out in a method step <140> 38 upstream of the first exhaust aftertreatment component 52 , 54 set for the selective, catalytic reduction of nitrogen oxides. In a method step <150>, a load point of the internal combustion engine becomes 10 shifted in the direction of higher raw nitrogen oxide emissions and preferably in the direction of higher load to the ammonia level of the second exhaust gas aftertreatment component 58 to reduce. This can be done in particular by coupling a starter belt generator 104 take place, which the electrically heated catalyst 66 powered and / or a battery 106 of the vehicle is charging. In a method step <160>, the metering in of reducing agent is carried out by the first metering element 38 and / or the second metering element 56 reactivated when the level of the second exhaust gas aftertreatment component 58 lies below a second threshold value and a temperature level is reached at which an efficient conversion of nitrogen oxides is possible through a selective, catalytic reduction.

List of reference symbols

10

Internal combustion engine

12th

Combustion chamber

14th

Fuel injector

16

inlet

18th

Outlet

20th

Air supply system

22nd

Air filter

24

Air mass meter

26th

compressor

28

Intake duct

30th

throttle

32

Intercooler

34

Confluence

36

Exhaust gas turbocharger

38

first metering element

40

Exhaust system

42

Exhaust duct

44

turbine

46

first exhaust mixer

48

NOx storage catalytic converter

50

Oxidation catalyst

52

Particle filter

54

SCR coating

56

second metering element

58

SCR catalytic converter

60

Confluence

62

Exhaust duct

64

Oxidation catalyst

66

electrically heated catalytic converter

68

second exhaust mixer

70

Temperature sensor

72

Differential pressure sensors

74

NOx sensor

76

branch

78

Exhaust flap

80

Exhaust gas recirculation

82

Exhaust gas recirculation cooler

84

Exhaust gas recirculation valve

86

Exhaust gas recirculation line

88

second branch

90

Control unit

92

filter

94

Ammonia barrier catalyst

96

second control

98

third control

100

High pressure exhaust gas recirculation

102

Exhaust gas recirculation duct

104

Exhaust gas recirculation valve

106

Belt starter generator

108

battery

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• DE 102017214572 A1 [0006]
• US 10113464 B2 [0007]
• US 9206722 B2 [0008]

Claims (10)

A method for exhaust gas aftertreatment of an internal combustion engine (10), in whose exhaust system (40) an electrically heatable catalytic converter (66), downstream of the electrically heatable catalytic converter (66) a first exhaust gas aftertreatment component (52, 54) for the selective, catalytic reduction of nitrogen oxides and downstream of the first Exhaust aftertreatment component (52, 54) for the selective, catalytic reduction of nitrogen oxides, a further exhaust aftertreatment component (58) for the selective, catalytic reduction of nitrogen oxides is arranged, upstream of the first exhaust aftertreatment component (52, 54) a first metering element (38) and downstream of the first exhaust aftertreatment component (52, 54) and a second metering element (56) is arranged upstream of the second exhaust gas aftertreatment component (58), comprising the following steps: - Determining a temperature of the second exhaust gas aftertreatment component (58) for the selective, catalytic reduction of nitrogen oxides, - Determining an ammonia level of the second exhaust gas aftertreatment component (58) for the selective, catalytic reduction of nitrogen oxides, - Heating of the exhaust gas aftertreatment components (52, 54, 58) by the electrically heatable catalytic converter (66), - Switching off the metering of reducing agent by the first metering element (38), - Shifting a load point of the internal combustion engine (10) in order to increase the heat input into the exhaust system (40), the load point being shifted in the direction of higher raw NOx emissions in order to reduce the ammonia level of the second exhaust gas aftertreatment component (58). Process for exhaust aftertreatment according to Claim 1 , characterized in that the method is initiated when the level of the second exhaust gas aftertreatment component (58) for the selective, catalytic reduction of nitrogen oxides above a threshold value (F _S ) for the level and the temperature of the second exhaust gas aftertreatment component (58) below a threshold temperature (T _S ) lies. Process for exhaust gas aftertreatment according to one of the Claims 1 until 2 , characterized in that the operating point shift of the internal combustion engine (10) is implemented by operating a belt starter generator (106) which can be coupled to the internal combustion engine (10). Process for exhaust aftertreatment according to Claim 2 or 3 , characterized in that the threshold _{temperature (T S} ) is between 160 ° C and 250 ° C. Process for exhaust gas aftertreatment according to one of the Claims 2 until 4th , characterized in that the threshold value (F _S ) for the fill level when the second exhaust gas aftertreatment component (58) is loaded is 50% to 90% of the maximum possible fill level. Exhaust gas aftertreatment system for an internal combustion engine (10), in the exhaust system (40) of which an electrically heatable catalytic converter (66), downstream of the electrically heatable catalytic converter (66) a first exhaust gas aftertreatment component (52, 54) for the selective, catalytic reduction of nitrogen oxides and downstream of the first exhaust gas aftertreatment component (52, 54) for the selective, catalytic reduction of nitrogen oxides, a further exhaust gas aftertreatment component (58) for the selective, catalytic reduction of nitrogen oxides is arranged, with a first metering element (38) upstream of the first exhaust gas aftertreatment component (52, 54) and downstream of the first exhaust gas aftertreatment component ( 52, 54) and a second metering element (56) is arranged upstream of the second exhaust gas aftertreatment component (58), as well as with a control unit (90) which is set up to implement a method according to one of the Claims 1 until 5 perform when a machine-readable program code is executed by the control device (90). Exhaust aftertreatment system for an internal combustion engine (10) after Claim 6 , characterized in that an exhaust flap (78) is arranged in the exhaust system (40) downstream of the first exhaust gas aftertreatment component (52, 54), the exhaust system (40) comprising a low-pressure exhaust gas recirculation (80) which is connected to a first branch (76 ) branches off downstream of the first exhaust gas aftertreatment component (52, 54) and upstream of the exhaust flap (78) from a first exhaust duct (42) of the exhaust system (40) and the first exhaust duct (42) with an intake duct (28) of an air supply system (20) of the internal combustion engine (10) connects, an exhaust gas recirculation cooler (82) being arranged in an exhaust gas recirculation duct (86) of the low-pressure exhaust gas recirculation (80), a second branch (88) being provided downstream of the exhaust gas recirculation cooler (82) on the exhaust gas recirculation duct (86), at which a second exhaust gas duct (62) branches off, which connects the exhaust gas recirculation duct (86) with the first exhaust gas duct (42) downstream of the exhaust gas flap (78). Exhaust aftertreatment system according to one of the Claims 6 or 7th , characterized in that an ammonia barrier catalytic converter (94) is arranged downstream of the second exhaust gas aftertreatment component (58) for the selective, catalytic reduction of nitrogen oxides. Exhaust aftertreatment system according to one of the Claims 6 until 8th , characterized in that the first exhaust gas aftertreatment component (52, 54) for the selective catalytic reduction of nitrogen oxides is a particle filter (52) with a coating (54) for the selective, catalytic reduction of nitrogen oxides and the second exhaust gas aftertreatment component (58) for the selective, catalytic reduction of Nitrogen oxides is an SCR catalytic converter (58). Exhaust aftertreatment system according to one of the Claims 7 until 9 , characterized in that a device for exhaust gas heat recovery is arranged in an exhaust gas recirculation line (86) of a low-pressure exhaust gas recirculation (80) downstream of the first branch (76) and upstream of the second branch (88).

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