DE102018104151A1 - Exhaust gas aftertreatment system and method for exhaust aftertreatment of an internal combustion engine - Google Patents

Abstract

The invention relates to an exhaust aftertreatment system (30) for an internal combustion engine (10). The exhaust aftertreatment system (30) comprises an exhaust system (32), in which in the flow direction of an exhaust gas of the internal combustion engine (10) through the exhaust system (32) a close-coupled first catalyst (40), in particular a diesel oxidation catalyst (44) or a NO _x - Storage catalyst (42) is arranged. Downstream of the first catalyst (40) close to the engine, a first SCR catalytic converter (46), preferably a particle filter (58) with a coating (60) for the selective catalytic reduction of nitrogen oxides, is arranged. Downstream of the first SCR catalytic converter (46), at least one further SCR catalytic converter (50) is arranged in the exhaust system (32), wherein each of the SCR catalytic converters (46, 50) has a metering element (48, 52) for metering in an aqueous urea solution assigned.
Downstream of an outlet (14) of the internal combustion engine (10) and upstream of the near-engine first catalyst (40) on the exhaust system (32), a switchable bypass (72) is provided, in which a bypass catalyst (70) is arranged. In a first operating state of the internal combustion engine (10), in particular in a cold start phase, the bypass catalytic converter (70) flows through the exhaust gas flow of the internal combustion engine (10) and is decoupled from the exhaust gas flow of the internal combustion engine (10) in a second operating state.

Description

The invention relates to an exhaust aftertreatment system for the exhaust aftertreatment of an internal combustion engine and to a method for exhaust aftertreatment of an internal combustion engine according to the preamble of the independent claims.

The current and increasingly stringent future exhaust gas legislation places high demands on the engine raw emissions and the exhaust aftertreatment of internal combustion engines. The demands for a further reduction in consumption and the further tightening of emission standards with regard to permissible nitrogen oxide emissions pose a challenge for the engine developers. Diesel engines currently use exhaust aftertreatment systems which contain an oxidation catalyst, a catalyst for the selective catalytic reduction of nitrogen oxides (SCR). Catalyst) and a particulate filter for the separation of soot particles and optionally further catalysts, in particular a NO _x storage catalytic converter have. The reducing agent used for the SCR catalyst is preferably ammonia. Because the handling of pure ammonia is complicated, in vehicles usually a synthetic, aqueous urea solution is used, which is mixed in a SCR catalyst upstream mixing device with the hot exhaust gas stream. By this mixing, the aqueous urea solution is heated, wherein the aqueous urea solution releases ammonia in the exhaust gas passage. A commercial aqueous urea solution generally consists of 32.5% urea and 67.5% water.

Increasingly efficient combustion engines lead to lower exhaust gas temperatures. At the same time, legislators demand compliance with exhaust emission standards under real driving conditions (Real Drive Emissions = RDE) for future emission standards. In diesel engines exhaust aftertreatment systems are known, which have a near-engine NOx storage catalyst and a downstream of the NO _x storage catalytic converter arranged SCR catalyst. This has the advantage that the nitrogen oxides can be stored in the NO _x storage catalytic converter at low exhaust gas temperatures, in particular after a cold start of the internal combustion engine. The disadvantage, however, is that in the subsequent normal operation of the internal combustion engine by the NO _x storage catalyst for the downstream selective, catalytic reduction of nitrogen oxides unfavorable ratio of nitrogen monoxide and nitrogen dioxide is formed, whereby the effectiveness of the SCR catalyst is reduced. Furthermore, the NO _x storage catalytic converter must be regenerated periodically, the internal combustion engine for regeneration with a rich combustion air mixture and a resulting lower efficiency must be operated. The exhaust aftertreatment systems known from the prior art have the disadvantage that they do not allow optimal conversion or retention of the pollutants under all operating conditions of an internal combustion engine. The NO _x storage catalytic converter requires a temperature of at least 100 ° C in order to effectively store and buffer nitrogen oxide emissions.

From the DE 10 2016 223 558 A1 an exhaust aftertreatment system for an internal combustion engine is known, in which in the exhaust system downstream of a turbine of an exhaust gas turbocharger, an oxidation catalyst or a NO _x storage catalytic converter is arranged. Further downstream, a first metering element for metering in a reducing agent for the selective, catalytic reduction of nitrogen oxides is arranged, which is followed by a first SCR catalyst or a particle filter with a coating for the selective, catalytic reduction of nitrogen oxides. Further downstream, a second metering element for metering in a reducing agent is arranged in the exhaust system, which is followed by a second SCR catalyst downstream.

From the DE 10 2014 214 588 A1 an exhaust aftertreatment system with a switchable pre-turbo catalyst is known, wherein the catalyst can be coupled via a valve unit in the exhaust stream of the engine or decoupled from this. The pre-turbo-catalyst has an input and an output, which are arranged parallel to each other and form a side arm of the exhaust passage of the internal combustion engine.

The invention is based on the object to further reduce the pollutant emissions in real driving in an internal combustion engine and in particular to further reduce in the cold start phase or in high load operation.

According to the invention, this object is achieved by an exhaust aftertreatment system for an internal combustion engine, which is connected to its exhaust with an exhaust system, wherein in the exhaust system a close-coupled first catalyst, downstream of the near-engine first catalyst, a first SCR catalyst and downstream of the first SCR catalyst second SCR catalyst are arranged. In this case, each of the SCR catalysts is in each case assigned a metering element for metering in a reducing agent, in particular aqueous urea solution, into the exhaust system. In the exhaust system is downstream of a Outlet of the internal combustion engine and upstream of the first close-coupled catalyst formed a bypass in which a bypass catalyst is arranged. This bypass catalytic converter is flowed through in a first operating state of the internal combustion engine by an exhaust gas stream of the internal combustion engine and is decoupled in a second operating state of the exhaust gas stream of the internal combustion engine. In this case, a position close to the engine is understood to mean a position in the exhaust system with a mean exhaust gas flow path of at most 80 cm, in particular of at most 50 cm, after the outlet of the internal combustion engine. An engine-remote position is found in particular in an underfloor position of a motor vehicle and has a mean exhaust flow path of at least 80 cm, preferably at least 100 cm after the outlet of the internal combustion engine. By two different SCR catalysts, which are arranged at different distances to the outlet of the internal combustion engine, prevail at both SCR catalysts different temperatures. Thus, it is possible to operate at least one of the SCR catalysts in a temperature window to allow an efficient reduction of nitrogen oxides. By the two SCR catalysts, the operating range of the internal combustion engine can be extended, in which at least one of the catalysts operates in a temperature range in which an efficient conversion of nitrogen oxides by one of the SCR catalysts is possible. Above a limit temperature of about 450 ° C, there is an oxidation of ammonia, so that in this temperature range, the effectiveness of the SCR catalysts decreases sharply, since the reducing agent is thermally decomposed. Therefore, at high exhaust gas temperatures, the metering of reducing agent is switched over from the metering element on the first SCR catalytic converter close to the engine to the metering element on the second SCR catalytic converter. Since SCR catalysts enable efficient conversion of nitrogen oxides only at a temperature of about 170 ° C., these nitrogen oxides are temporarily stored at low loads and in the cold start phase in the first catalyst close to the engine. In order to extend the functional range to even lower loads and further reduce the cold start emissions, the close-coupled bypass catalytic converter is switched on, because due to its position it reaches an operating temperature even earlier than the first catalytic converter close to the engine.

The features listed in the dependent claims advantageous improvements and developments of the exhaust gas aftertreatment system specified in the independent claim are possible.

In a preferred embodiment of the invention it is provided that the bypass catalyst is designed as a diesel oxidation catalyst, NO _x storage catalytic converter or passive NO _x adsorber. The bypass catalyst is preferably provided as a starting catalyst when the downstream catalysts have not yet their operating temperature and thus no or only a limited effectiveness. In this case, the catalyst can take over the function of storing pollutants, in particular nitrogen oxides, between them, until they can be converted by the downstream catalysts, in particular by the SCR catalysts, into innocuous exhaust gas constituents. Further, the bypass catalyst may allow exothermic, oxidative conversion of pollutants, thereby promoting heating of the downstream catalysts.

In a preferred embodiment of the exhaust aftertreatment system it is provided that a switching element is provided on the exhaust passage, with which the exhaust aftertreatment system is switchable between the first operating state and the second operating state. By a switching element, a simple switching between the first operating state and the second operating state is possible, wherein a preferably electromechanical actuator is provided, with which the switching element of a first switching position, in which the exhaust gas stream of the engine is passed through the bypass, in the second operating state , in which the bypass is decoupled from the exhaust stream, can be brought.

It is particularly preferred if the switching element comprises a flap valve or a slide valve. By a flap valve or a slide valve, the exhaust gas flow of the internal combustion engine can be particularly easily redirected so that it is passed through the bypass in a valve position, and the bypass is closed in a second valve position, so that the exhaust gas stream is bypassed by the bypass and the bypass Catalyst is decoupled from the exhaust stream.

In an advantageous embodiment of the invention it is provided that in the exhaust system, a turbine of an exhaust gas turbocharger is arranged, wherein the bypass catalyst is arranged in the exhaust gas flow direction upstream of the turbine. Since the exhaust gas temperature of the internal combustion engine upstream of the turbine is usually much higher than downstream of the turbine, an arrangement of the bypass upstream of the turbine is particularly advantageous in order to achieve a rapid heating of the bypass catalyst.

Alternatively, it is advantageously provided that the bypass catalytic converter is arranged in the bypass downstream of the turbine and upstream of the first catalytic converter close to the engine. By an arrangement downstream of the turbine, the thermal load of the bypass catalyst can be further reduced. In this case, the additional catalyst volume of the bypass catalyst can be used to reduce the volume of the engine near first catalyst and thus contribute to the fact that this close-coupled first catalyst heats up faster to its operating temperature after a cold start or engine stop.

In a further, preferred embodiment of the invention it is provided that a turbine of an exhaust gas turbocharger is arranged in the exhaust system, wherein the bypass catalyst is arranged in a wastegate channel of the exhaust gas turbocharger or a bypass connected to the waste gate channel. This allows a turbocharger assembly in which a switchable catalyst is integrated, and thus reduces the number of components that must be assembled in the assembly of the exhaust aftertreatment system.

In a further improvement of the invention it is provided that at least one electrical heating element for electrically heating at least one of the catalysts is arranged in the exhaust system. An electric heating element can shorten the time to an operating temperature, at which an efficient conversion of pollutants by the respective catalyst can take place. In this case, an electrical heating element, preferably in the form of a heating disk, is provided in particular on the near-engine NO _x storage catalyst in order to enable a storage of nitrogen oxides as soon as possible after a cold start and thus to significantly reduce the nitrogen oxide emissions in the cold start phase.

According to an advantageous embodiment of the exhaust aftertreatment system, it is provided that the bypass catalyst has a washcoat or a coating which has a high low-temperature activity. Because the bypass catalyst is primarily used as a start-up catalyst or in low-load operating phases, the wash-coat or coating can be optimized specifically for a low-temperature range. Since the bypass catalytic converter can be decoupled from the exhaust gas flow at a higher exhaust gas temperature and / or higher engine load and exhaust gas is not passed through in these phases, there is no risk that these operating situations will result in thermal damage to the bypass catalytic converter.

According to the invention, a method for exhaust aftertreatment of an internal combustion engine with an exhaust aftertreatment system according to the invention is proposed, wherein an exhaust gas stream of the internal combustion engine is passed through the bypass in a first operating situation of the internal combustion engine and the bypass is decoupled from the exhaust gas flow of the internal combustion engine in a second operating situation of the internal combustion engine. This makes it possible to selectively switch on the bypass catalyst, if, for example, the other catalysts can not or can not sufficiently ensure exhaust gas purification on their own.

In a preferred embodiment of the method, it is provided that the exhaust gas flow is conducted through the bypass below a first threshold temperature and the bypass above this threshold temperature is decoupled from the exhaust gas flow of the internal combustion engine. Preference is given to the use of the bypass catalyst as starting catalyst, since it reaches its operating temperature particularly quickly after a cold start of the internal combustion engine by the position close to the engine, in particular by a position upstream of the turbine of the exhaust gas turbocharger. Furthermore, the decoupling can prevent thermal damage or premature aging of the bypass catalytic converter occurring above a threshold temperature.

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

• 1 einen Verbrennungsmotor mit einem Ansaugtrakt und einem erfindungsgemäßen Abgasnachbehandlungssystem;
• 2 ein Ausführungsbeispiel für ein erfindungsgemäßes Abgasnachbehandlungssystem; und
• 3 ein weiteres Ausführungsbeispiel für ein erfindungsgemäßes Abgasnachbehandlungssystem.

The invention will be explained below in embodiments with reference to the accompanying drawings. Identical components or components with the same function are identified in the drawings with the same reference numerals. Show it:

• 1 an internal combustion engine with an intake tract and an exhaust aftertreatment system according to the invention;
• 2 an embodiment of an inventive exhaust aftertreatment system; and
• 3 a further embodiment of an inventive exhaust aftertreatment system.

1 shows an internal combustion engine 10 with an air supply system 20 and an exhaust system 32 , The internal combustion engine 10 has a plurality of combustion chambers 16 on, in which a fuel-air mixture is burned. The internal combustion engine 10 has an inlet 12 on which with the air supply system 20 connected is. The air supply system 20 includes a suction channel 26 in which an air filter 22 is arranged. Downstream of the air filter 22 is a compressor 24 an exhaust gas turbocharger 36 provided to compress the intake fresh air and compresses the combustion chambers 16 of the internal combustion engine 10 supply. Downstream of the compressor 24 is a charge air cooler 28 provided to cool the compressed fresh air and thus the filling of the combustion chambers 16 continue to improve.

The internal combustion engine 10 also has an outlet 14 on, which with the exhaust system 32 connected is. At the internal combustion engine 10 is a high pressure exhaust gas recirculation 18 provided, which the outlet 14 with the inlet 12 combines. In the high-pressure exhaust gas recirculation 18 an exhaust gas recirculation valve is arranged, with which the amount of recirculated exhaust gas is controllable. In the exhaust system 32 is a turbine 38 an exhaust gas turbocharger 36 arranged. In the flow direction of the exhaust gas through the exhaust system 32 is downstream of the turbine 38 a close-coupled first catalyst 40 arranged, which is designed in this embodiment as a NO _x storage 42. In this case, the engine-near first catalyst 40 a heating element 64 , in particular a heating disk 66 be assigned, with which the close-coupled first catalyst 40 is heated. Downstream of the first catalyst near the engine 40 is in the exhaust duct 34 the exhaust system 32 a first SCR catalyst 46 arranged, which preferably as a particle filter 58 is designed with a coating for the selective, catalytic reduction of nitrogen oxides. Downstream of the first catalyst near the engine 40 and upstream of the first SCR catalyst 48 is on the exhaust duct 34 a first metering element 48 for dosing a reducing agent, in particular aqueous urea solution provided. In addition, in the exhaust passage downstream of the first metering element 48 and upstream of the first SCR catalyst 46 a first mixing element 54 be provided to the reducing agent with the exhaust gas stream of the internal combustion engine 10 to mix and thus the reducing agent before entering the first SCR catalyst 46 evenly over the flow cross-section of the exhaust passage 34 to distribute. Downstream of the first SCR catalyst 46 is a branch 82 formed, at which a low-pressure exhaust gas recirculation 80 from the exhaust duct 34 branches. Downstream of the branch is a second metering element 52 provided, with which alternatively or in addition to the first metering element 48 Reducing agent in the exhaust duct 34 can be metered. Downstream of the second metering element 52 is a second SCR catalyst 50 arranged, which has a second mixing element 56 can be upstream. The second SCR catalyst 50 preferably comprises an ammonia blocking catalyst 62 to keep emissions of unreacted reducing agent low. Downstream of the second SCR catalyst 50 is an exhaust flap 68 provided, with which the low-pressure exhaust gas recirculation 80 supplied amount of exhaust gas can be controlled.

The low pressure exhaust gas recirculation 80 includes an exhaust gas recirculation passage in which an exhaust gas recirculation cooler 86 and a low pressure exhaust gas recirculation valve 84 are arranged. The exhaust gas recirculation channel of the low-pressure exhaust gas recirculation opens downstream of the air filter 22 and upstream of the compressor 24 in the intake channel 26 ,

Downstream of the outlet 14 of the internal combustion engine 10 and upstream of the turbine 38 the exhaust gas turbocharger 36 is a so-called pre-turbo catalyst 96 as a switchable bypass catalyst 70 in a bypass 72 the exhaust duct 34 arranged. At the bypass 72 is a switching element 74 , in particular a slide valve 79 , provided with which the exhaust gas flow of the internal combustion engine 10 optionally through the bypass 72 can be routed or the bypass 72 from the exhaust duct 34 can be separated. According to the switching position of the switching element 74 becomes the bypass catalyst 70 in a first switching position of the exhaust gas stream of the internal combustion engine 10 flows through, while the bypass catalyst 70 in a second switching position of the switching element 74 from the exhaust duct 34 is decoupled and is not flowed through with exhaust gas. The bypass catalyst is preferably as a NO _x storage catalyst 92 or as a passive NO _x adsorber 94 designed, in particular in a cold start phase, the NO _x emissions of the internal combustion engine 10 to reduce.

The position of a catalyst upstream of the turbine 38 the exhaust gas turbocharger 36 can in certain operating points of the internal combustion engine 10 lead to a higher thermal load of the catalyst and thus to damage or premature aging of the catalyst, in particular a catalytically active coating. By the switching element 74 may be the bypass catalyst 70 in such operating situations from the exhaust gas flow of the internal combustion engine 10 be decoupled to the risk of thermal damage or premature aging of the bypass catalyst 70 to minimize. Another advantage of a switchable bypass catalyst 70 is due to the fact that a sulfurization of the bypass catalyst 70 is reduced by the decoupling from the exhaust stream, and thus a lower frequency for desulfurization of this catalyst 70 consists. Since such a desulfurization is associated with an increased thermal load, the decoupling the aging behavior of the bypass catalyst 70 further improved. Another advantage of the invention is the use of coatings with high low temperature activity for the bypass catalyst 70 , Preferably, a coating with NO _x adsorbing effect, which at higher thermal load, the adsorbed exhaust gas component again desorb. This process can be achieved by the switching element 74 be controlled specifically.

The interaction of the pre-turbo catalyst 96 for an increase in the low-temperature activity, in particular after a cold start of the internal combustion engine 10 , with the exhaust aftertreatment components 40 . 46 . 50 downstream of the turbine 38 the exhaust gas turbocharger 36 leads to a widening of the temperature window, in which an efficient conversion of exhaust gas components is possible. Thus, the emissions in real driving operation by an inventive exhaust aftertreatment system 30 be reduced.

In 2 is a further illustration of the exhaust aftertreatment system according to the invention 30 shown. With essentially the same structure as 1 In the following, only the differences will be discussed. In the exhaust system 32 is an electric heating element 64 provided to at least one catalyst 40 . 46 . 50 independent of the exhaust gas flow of the combustion engine 10 to be able to heat. Here is the heating element 64 in this embodiment as a heating disk 66 formed, which input side to the first close-coupled catalyst 40 is arranged. Alternatively or additionally, there is also a heating element 64 on one of the SCR catalysts 46 . 50 possible. The close-coupled first catalyst 40 is preferably as a NO _x storage catalyst 42 or as an oxidation catalyst 44 executed. Downstream of the first metering valve 48 and upstream of the first SCR catalyst near the engine 46 is in the exhaust system 32 a first exhaust gas mixer 54 arranged. Downstream of the second metering valve 52 and upstream of the second SCR catalyst 50 is in the exhaust system 32 a second exhaust mixer 56 arranged. The second SCR catalyst 50 is an ammonia blocking catalyst 62 downstream to prevent in the second SCR catalyst 50 unreacted ammonia enters the environment as a pollutant emission.

In 3 is another embodiment of an exhaust aftertreatment system according to the invention 30 for an internal combustion engine 10 shown. In essence, how to 2 executed structure is the bypass in this embodiment 72 downstream of the turbine 38 the exhaust gas turbocharger 36 and upstream of the first catalyst near the engine 40 educated. The bypass 72 is in turn by a switching element 74 switchable, so that in a first operating state of the internal combustion engine 10 Exhaust through the bypass 72 arranged by-pass catalyst 70 is passed and this bypass catalyst 70 in a second operating state from the exhaust gas stream of the internal combustion engine 10 is decoupled.

LIST OF REFERENCE NUMBERS

10

internal combustion engine

12

inlet

14

outlet

16

combustion chamber

18

High-pressure exhaust gas recirculation

20

Air supply system

22

air filter

24

compressor

26

suction

28

Intercooler

30

aftertreatment system

32

exhaust system

34

exhaust duct

36

turbocharger

38

turbine

40

close to the engine first catalyst

42

NO _x storage catalyst

44

oxidation catalyst

46

first SCR catalyst

48

first metering element

50

second SCR catalyst

52

second metering element

54

first exhaust mixer

56

second exhaust mixer

58

particulate Filter

60

Coating for the selective catalytic reduction of nitrogen oxides

62

Ammonia slip catalyst

64

heating element

66

heated window

68

exhaust flap

70

switchable catalyst

72

bypass

74

switching element

76

probe

78

flap valve

79

spool valve

80

Low-pressure exhaust gas recirculation

82

branch

84

Low pressure exhaust gas recirculation valve

86

Exhaust gas recirculation cooler

88

junction

90

control unit

91

oxidation catalyst

92

NO _x storage catalyst

94

passive NO _x adsorber

96

Pre-Turbo Catalyst

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 102016223558 A1 [0004]
• DE 102014214588 A1 [0005]

Claims (10)

Exhaust gas aftertreatment system (30) for an internal combustion engine (10), which is connected to an exhaust system (32) with its exhaust, wherein in the exhaust system (32) a first close-coupled catalyst (40), downstream of the first catalyst close to the engine (40), a first SCR Catalyst (46) and downstream of the first SCR catalyst (46) a second SCR catalyst (50) are arranged, and wherein each of the SCR catalysts (46, 50) each have a metering element (48, 52) for metering a reducing agent in the exhaust system (34) is associated, characterized in that in the exhaust system (32) downstream of the outlet (14) of the internal combustion engine (10) and upstream of the near-engine first catalyst (40), a bypass (72) is formed, in which a Bypass catalyst (70) is arranged, wherein the bypass catalyst (70) in a first operating state of the internal combustion engine (10) is flowed through by an exhaust gas stream of the internal combustion engine (10) and in a second Operating state of the exhaust stream of the internal combustion engine (10) is decoupled. Exhaust after-treatment system (30) according to Claim 1 , characterized in that the bypass catalyst (70) as an oxidation catalyst (91), NO _x storage catalyst (92) or as a passive NO _x adsorber (94) is formed. Exhaust after-treatment system (30) according to Claim 1 or 2 , characterized in that on the exhaust passage (24), a switching element (74) is provided, with which the exhaust aftertreatment system (30) is switchable between the first operating state and the second operating state. Exhaust after-treatment system (30) according to Claim 3 , characterized in that the switching element (74) comprises a flap valve (78) or a slide valve (79). Exhaust after-treatment system (30) according to one of Claims 1 to 4 , characterized in that in the exhaust system (32) a turbine (38) of an exhaust gas turbocharger (36) is arranged, wherein the bypass catalyst (70) in the exhaust gas flow direction upstream of the turbine (38) is arranged. Exhaust after-treatment system (30) according to one of Claims 1 to 4 , characterized in that in the exhaust system (32) a turbine (38) of an exhaust gas turbocharger (36) is arranged, wherein the bypass catalyst (70) in a waste-gate channel of the exhaust gas turbocharger (36) or one with the Waste- Gate channel connected bypass (72) is arranged. Exhaust after-treatment system (30) according to one of Claims 1 to 6 , characterized in that in the exhaust system (32) at least one electric heating element for electrically heating at least one of the catalysts (40, 46, 50, 70) is arranged. Exhaust after-treatment system (30) according to one of Claims 1 to 7 characterized in that the bypass catalyst (70) comprises a washcoat or coating having high low temperature activity. A method for exhaust aftertreatment of an internal combustion engine (10) with an exhaust aftertreatment system (30) according to one of Claims 1 to 8th , characterized in that an exhaust gas flow of the internal combustion engine (10) in a first operating situation of the internal combustion engine (10) through the bypass (72) and thus through the bypass catalyst (70) is passed and the bypass (72) in a second operating situation the exhaust stream of the internal combustion engine (10) is decoupled. Process for exhaust aftertreatment after Claim 9 , characterized in that the exhaust gas flow below a first threshold temperature (T _s ) through the bypass (72) is passed and the bypass (72) above this threshold temperature (T _s ) from the exhaust stream of the internal combustion engine (10) is decoupled.

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