DE102014203015A1 - Method and device for guiding an exhaust gas flow of an internal combustion engine with a load-dependent heat transfer coefficient - Google Patents

Abstract

The invention relates to an exhaust system (1) for guiding an exhaust gas stream (3) of an internal combustion engine (5), having a first fluid path (7) for guiding a first partial flow (9) of the exhaust gas flow (3), a second fluid path (11) for guiding a second partial flow (13) of the exhaust gas flow (3), a first outlet valve (15) of the internal combustion engine (5) upstream of the first fluid path (7), a second outlet valve (17) upstream of the second fluid path (11) and at least one of the fluid paths (7, 11) upstream control device (19), by means of which at least one of the partial flows (9, 13) of the exhaust gas stream (3) is controllable. In order to achieve a heat transfer coefficient dependent on an operating state (63) of the internal combustion engine (5), it is provided that the first fluid path (7) and the second fluid path (11) have a common partition (21).

Description

The invention relates to an exhaust system for guiding an exhaust gas flow of an internal combustion engine, in particular with a first fluid path for guiding a first partial flow of the exhaust gas flow, a second fluid path for guiding a second partial flow of the exhaust gas flow, a first outlet valve of the internal combustion engine upstream of the first fluid path, a second fluid path upstream second outlet valve and a at least one of the fluid paths upstream control device by means of which at least one of the partial flows of the exhaust gas flow is controllable, a method for controlling the exhaust system and a method and / or device according to motor vehicle.

Exhaust manifolds and / or exhaust conduits may be used to guide exhaust gas streams from internal combustion engines. These are usually connected downstream of at least one exhaust valve of the internal combustion engine, wherein the exhaust gas flow flows through the exhaust valve in the exhaust system. In order to avoid heat losses, it is known to thermally isolate exhaust ducts, for example by providing an air gap. In addition, exhaust ducts are known which serve in addition to the guiding of the exhaust gas stream of a detoxification thereof, for example, have relatively hot reaction surfaces for afterburning. It is also known to variably control the exhaust valves of the internal combustion engine upstream of the exhaust system.

The DE 10 2010 014 250 A1 relates to a device and associated method for controlling the exhaust gas flow of an internal combustion engine. For this purpose, each cylinder of the internal combustion engine has two exhaust valves, in which the first exhaust valve operated via a first controllably operated valve train is connected to a first exhaust passage and the second exhaust valve operated via a second controllably operated valve train is connected to a second exhaust passage into which a heat exchanger for exhaust heat recovery is arranged. After the heat exchanger, the two exhaust channels are connected to each other, wherein the common line is connected to a turbine of an exhaust gas turbocharger.

The DE 24 52 556 A1 relates to a device for detoxifying the exhaust gases of internal combustion engines in motor vehicles by afterburning, optionally with the supply of fresh air into the effluent from the cylinder exhaust gases - wherein the exhaust gas streams are passed from two cylinders through an exhaust manifold in each case a pre-pipe, each two Vorrohre a have common wall, in particular, a common, heat-insulating sheath for each pair of Vorrohren is arranged.

The DE 39 30 243 A1 shows an internal combustion engine with a heat-insulated executed and made of a corrosion-resistant material exhaust manifold.

The DE 39 15 988 A1 and the DE 27 44 734 A1 each show a heat-insulated exhaust pipe or a heat-insulated outlet duct of an internal combustion engine.

The object of the invention is to provide a structurally small exhaust system for guiding an exhaust gas flow of an internal combustion engine, which allows a controllable, dependent on an operating condition of the engine heat transfer coefficient, in particular thereby depending on the operating condition of the internal combustion engine a desired low or desirably high heat transfer from the exhaust gas flow in an environment of the exhaust system allows.

The object is solved with the features of the independent claims. It is in an exhaust system for guiding an exhaust gas stream of an internal combustion engine, having a first fluid path for guiding a first partial flow of the exhaust gas flow, a second fluid path for guiding a second partial flow of the exhaust gas flow, a first outlet valve of the internal combustion engine upstream of the first fluid path, upstream of the second fluid path second outlet valve and a at least one of the fluid paths upstream control device, by means of which at least one of the partial flows of the exhaust gas flow is controllable, achieved in that the first and the second fluid path having a common partition wall. Advantageously, it is possible by means of the control device to control the partial flows of the exhaust gas flow, in particular to shut off at least one of the partial flows. As a result, it is advantageously possible to use one of the fluid paths predominantly for guiding the respective partial flow and the respective other, in particular switched-off, of the fluid paths as additional thermal insulation. Advantageously, a load-dependent heat transfer coefficient between the exhaust gas guide and an environment surrounding it can thereby be achieved, depending on the control device or the resulting control of the partial flows. In addition, it is possible through the partition wall, since these together delimits the first fluid path and the second fluid path to achieve a comparatively small exhaust system. In particular, it is advantageously possible, depending on an operating state of the internal combustion engine, to set as high or as small a heat transfer as possible from the exhaust gas flow into the environment. For this purpose, the control device can control the partial flows of the exhaust gas flow as a function of the operating state of the exhaust gas flow Control internal combustion engine. In particular, it is possible to at least reduce or shut off one of the partial flows in a low load state of the internal combustion engine. As a result, a minimal heat transfer into the environment takes place advantageously in the respective other partial flow, with the exhaust gas system considered as a whole having a particularly small heat transfer coefficient. Under heat transfer coefficient can be understood in this application, a measure with the unit watts per m ² per Kelvin (W / (m ² + K)). In particular, an indication of this heat transfer coefficient may be understood as an average value over a surface, in particular overall surface, of the exhaust gas routing and / or at least one of the two fluid paths to the surroundings. The exhaust system is followed in particular by an aggregate. The unit is preferably a turbine wheel of an exhaust gas turbocharger. Alternatively or additionally, the exhaust gas guide can also be followed by an exhaust gas purification device, in particular a catalytic converter. Advantageously, in the low load operation, a higher energy content of the exhaust gas flow can be achieved, so that the exhaust gas turbocharger can deliver a higher mechanical power and / or especially in a warm-up phase of the internal combustion engine, the exhaust gas purification device reaches a light-off temperature faster, so a better emission control is possible. Advantageously, the control of the heat transfer coefficient and thus the heat transfer can be achieved only by controlling the exhaust gas flow, ie without any mechanically movable insulation parts, heat exchangers and / or fans / air ducts.

In one exemplary embodiment of the exhaust system, it is provided that at least one of the exhaust valves can be controlled by means of the control device. Advantageously, the at least one exhaust valve or alternatively both exhaust valves can be controlled as a function of the operating state of the internal combustion engine. In particular, the at least one exhaust valve can be closed depending on the operating state of the internal combustion engine. In particular, the at least one exhaust valve can be closed in the light load operation. Advantageously, at least one or alternatively both exhaust gas streams can thus be controlled by means of the control device via the at least one outlet valve. In particular, a ratio of the partial flows to one another can be set, that is to say how much of the total exhaust gas flow flows through the respective fluid path. Alternatively or additionally, the control of the partial flows of the exhaust gas flow can also be effected by a throttle provided in at least one of the fluid paths.

In a further exemplary embodiment of the exhaust system, it is provided that at least one of the fluid paths has thermal insulation towards an environment. By means of the thermal insulation, it can be ensured that the exhaust gas stream has a particularly high energy content or loses as little energy as possible in the form of thermal energy when it flows through the exhaust gas system. The thermal insulation can be achieved in particular by an air gap and / or high-temperature-resistant fiber materials. In particular, the heat insulation extends only or even on a portion of the exhaust system, which leads directly from the respective exhaust valve to a cylinder head flange, ie already within a cylinder head of the internal combustion engine.

In a further exemplary embodiment of the exhaust system, it is provided that the first fluid path has a first heat transfer coefficient and the second fluid path has a second heat transfer coefficient to the surroundings, the heat transfer coefficients differing from one another, in particular by 10% to 500%, 50% to 400%, 100% to 300%, 150% to 250% or about 300%. Advantageously, the fluid paths themselves may have different heat transfer coefficients, so that advantageously an average load-dependent heat transfer coefficient of the entire exhaust system can be controlled within still further limits. An average heat transfer coefficient can be understood to be a heat transfer coefficient averaged over an outer surface of the exhaust system in contact with the environment. Advantageously, this can be exploited to the effect that particularly in a high-load operation, a particularly high heat flow can be dissipated to the environment, in particular as component protection for the unit / s and / or the exhaust unit downstream. The exhaust system and this downstream units can be characterized advantageous in terms of temperature stability weaker and / or characterized cheaper.

In a further exemplary embodiment of the exhaust gas guide, it is provided that the first fluid path has a first flow cross section and the second fluid path has a second flow cross section, wherein the flow cross sections differ from one another. In particular, the provided for the low load operation fluid path can be made relatively smaller, resulting in an even better thermal insulation. In particular, an advantageous compromise between a throttling by the comparatively small cross-section and the advantageous low heat transfer coefficient and thereby heat transfer can be selected.

In a further embodiment of the exhaust system is provided that the first Flow cross section is about 50% of the second flow cross section, in particular between 10% and 80%, 20% and 70%, 30% and 65%, 40% and 60% or 10% and 50%. Advantageously, an optimum between a comparatively good thermal insulation in the low load operation, a not too large throttling and a particularly good heat dissipation in the heavy load and / or full load operation of the internal combustion engine can be achieved.

In a further exemplary embodiment of the exhaust system, provision is made for the first fluid path to run completely within the second fluid path. Advantageously, the first fluid path thus has no delimitation or outer wall which is in direct contact with the environment. Advantageously, the entire second fluid path can thereby serve as additional heat insulation. This makes it possible, by switching off the second fluid path to achieve a smaller heat transfer coefficient, ie a better thermal insulation. In this case, the entire boundary of the first fluid path represents the partition wall.

In a further exemplary embodiment of the exhaust system, it is provided that the first fluid path is delimited by a first outer wall and the dividing wall and the second fluid path is delimited by a second outer wall and the dividing wall. Advantageously, the dividing wall is not in contact with the environment, so that there is advantageously no direct heat transfer to the environment. Advantageously, a more favorable, ie a smaller heat transfer coefficient can be achieved during operation of only one of the fluid paths, since the respective non-operated fluid path serves as additional insulation. Advantageously, the load-dependent heat transfer coefficient can thus be achieved by means of the control device, that is, by controlling the exhaust gas flows. The partition is thus acted upon on a first side with the first partial flow of the exhaust gas flow and on a second side opposite thereto with the second partial flow of the exhaust gas flow. As a result, in the event that both partial flows are equally strong, in particular have an identical flow velocity and temperature, no heat transfer takes place via the dividing wall.

The object is also achieved in a method for controlling a previously described exhaust system. This results in the advantages described above. The method comprises predominantly guiding the exhaust gas flow through the first fluid path in a first operating state of the internal combustion engine. By predominantly guiding the exhaust gas flow, it can be understood that it has a higher flow velocity, a higher mass flow and / or a higher temperature than a remaining part of the exhaust gas flow, which is conducted through the second fluid path. In particular, predominant guiding may mean that the entire exhaust gas flow is guided through the first fluid path. Advantageously, as described above, a lower heat loss of the exhaust gas flow and / or the load-dependent heat transfer coefficient can be achieved.

In one embodiment of the method, the first operating state has a partial load operation of the internal combustion engine. Advantageously, despite the comparatively low-energy partial load operation of the internal combustion engine, a comparatively high energy of the exhaust gas flow, in particular in the form of pneumatic, kinetic and / or thermal energy that can drive the turbine wheel, can be achieved.

In a further embodiment of the method, an at least partial blocking of the second fluid path for predominantly guiding the exhaust gas flow through the first fluid path is provided. Advantageously, the predominant guiding of the exhaust gas flow through the first fluid path can thereby be achieved.

In a further embodiment of the method, opening of the first exhaust valve and of the second exhaust valve is provided in a second operating state of the internal combustion engine. By opening one of the exhaust valves can also be understood in this application that this is opened and closed alternately according to working cycles of the internal combustion engine, so exhaust gas can be ejected at a Ausschiebetakt from the combustion chamber. By closing one of the exhaust valves, it can be understood that this is not opened and closed alternately, ie in particular remains closed during the exhaust stroke, so that no exhaust gas can be expelled from the combustion chamber. Advantageously, by the simultaneous opening or operation of the exhaust valves, a maximum flow cross-section of the exhaust system can be provided. This is in the high-load and / or full load operation in addition to the good heat dissipation also to the effect that the lowest possible throttling, so a maximum power delivery of the engine is possible.

In a further embodiment of the method, the second operating state has a heavy load and / or full load operation of the internal combustion engine. Advantageously, in the heavy load and / or full load operation, a minimum flow resistance or a maximum flow cross section of the exhaust gas guide can be achieved.

The object is also achieved in a motor vehicle with a previously described exhaust system. In addition, the object is achieved in a motor vehicle equipped, constructed, designed and / or equipped with software suitable for carrying out a previously described method. This results in the advantages described above.

Further advantages, features and details will become apparent from the following description in which - where appropriate, with reference to the drawings - at least one embodiment is described in detail. Described and / or illustrated features may form the subject of the invention itself or in any meaningful combination, optionally also independent of the claims, and in particular may also be the subject of one or more separate application / s. The same, similar and / or functionally identical parts are provided with the same reference numerals.

Show it:

1 a partially illustrated internal combustion engine with an exhaust passage shown in a sectional view;

2A and 2 B each different embodiments of a cross section of in 1 illustrated exhaust system along the line II-II; and

3 a schematic flow diagram of a method for controlling the in the 1 and 2 shown exhaust system.

1 shows an exhaust system 1 for guiding an exhaust gas flow 3 a partially illustrated internal combustion engine 5 , The internal combustion engine 5 is part of a motor vehicle 39 and is used in particular for driving the same. The internal combustion engine 5 has a combustion chamber, not shown, in a cylinder head 45 of the internal combustion engine 5 is introduced. In the combustion chamber, not shown, open two inlet channels, which via a first inlet valve 41 and a second inlet valve 43 are controllable. In particular, the intake valves 41 and 43 variably controllable. About the intake valves 41 and 43 can air and / or an ignitable mixture the combustion chamber of the internal combustion engine 5 be supplied. In addition, the combustion chamber has outlets, which via a first exhaust valve 15 and a second exhaust valve 17 are controllable. At least one of the exhaust valves, in particular the second exhaust valve 17 , is variably controllable, in particular switched off. Alternatively or additionally, both exhaust valves 15 . 17 variably controllable. For this purpose, the exhaust system 1 a control device 19 on, the control device 19 Control commands for controlling the exhaust valves 15 . 17 generated. Depending on the control device 19 and the exhaust valves 15 . 17 gets out of the combustion chamber of the internal combustion engine 5 the exhaust gas flow 3 in a first fluid path 7 and / or a second fluid path 11 dismiss. The first fluid path 7 is the first exhaust valve 15 and the second fluid path 11 the second exhaust valve 17 downstream. Depending on the control of the exhaust valves 15 . 17 results in the first fluid path 7 a first partial flow 9 and in the second fluid path 11 a second partial flow 13 the exhaust stream 3 , In particular, by means of the control device 19 a ratio between the first partial flow 9 and the second partial flow 13 be set. in particular, this can be dependent on an operating condition 63 of the internal combustion engine 5 respectively.

The exhaust system 1 runs from the exhaust valves 15 . 17 downstream through the cylinder head 45 up to a cylinder head flange 47 , Starting from there, the exhaust system runs 1 further to a downstream of the exhaust valves 15 . 17 arranged turbine wheel 49 a not fully shown exhaust gas turbocharger. Between the exhaust valves 15 . 17 and the turbine wheel 49 are the fluid paths 7 . 11 guided in parallel and to do so by means of a partition 21 separated from each other. The partition 21 is therefore possibly on both sides of the exhaust stream 3 applied. Immediately upstream of the turbine wheel 49 become the first fluid path 7 and the second fluid path 11 reunited, leaving no path through the first fluid path 7 or second fluid path 11 the turbine wheel 49 by means of the entire exhaust gas flow 3 is drivable.

Optionally, the exhaust system 1 a thermal insulation 23 on ', which is a heat transfer from the exhaust stream 3 in a the exhaust system 1 surrounding environment 25 reduced. The exhaust system 1 , especially the thermal insulation 23 , points to the first fluid path 7 a first heat transfer coefficient 27 and at the second fluid path 11 a second heat transfer coefficient 29 on. Averaged over an entire surface, the first fluid path 7 and the second fluid path 11 to the environment 25 demarcate, this has an average heat transfer coefficient 30 on.

Advantageously, this average heat transfer coefficient 30 depending on the operating condition 63 be set. For this purpose, the control device 19 the ratio of the partial flows 9 and 13 control, wherein advantageously the fluid path acted upon by a lower volume flow serves as additional heat insulation, whereby the average heat transfer coefficient 30 lowered, so a better overall Thermal insulation of the exhaust system 1 is possible. Advantageously, this can be exploited in a low-load operation, advantageously thereby the exhaust gas flow 3 upstream of the turbine wheel 49 has a higher energy content, so that the turbine wheel 49 can give off a higher mechanical energy. In particular, this can be achieved in that in a low-load operation, the second exhaust valve 17 remains closed. For a heavy load operation additionally the second exhaust valve 17 be opened so that the first fluid path 7 and the second fluid path 11 completely for guiding the exhaust gas flow 3 be available.

In a particularly preferred alternative it is provided that the first heat transfer coefficient 27 smaller than the second heat transfer coefficient 39 , As a result, on the one hand in a low load operation, a particularly good thermal insulation and a heavy load and / or full load operation, in which both fluid paths 7 and 11 be operated, a particularly high heat dissipation of the exhaust stream 3 to the environment 25 possible. Advantageously, characterized in the high-load operation and / or full load operation, a temperature of the exhaust stream 3 be lowered, which in particular as component protection for the exhaust valves 15 . 17 Downstream components, in particular the exhaust system 1 itself, the cylinder head 45 , the fluid paths 7 and 11 and / or the turbine wheel 49 can serve. Alternatively or additionally, the turbine wheel 49 downstream of an exhaust gas purification device, which can also advantageously be protected either from overheating or by the higher energy content of the exhaust stream 3 in the low load operation has a better response, especially during a start phase earlier achieved a light-off temperature.

The 2A and 2 B each show a cross section through the in 1 shown exhaust system 1 along the line II-II in various embodiments.

2A shows the first fluid path 7 and the second fluid path 11 in a respective approximately semicircular cross-section, whereby these through the partition wall 21 are separated from each other and, moreover, semicircular to the environment 25 are delimited. For this purpose, the first fluid path 7 a first outer wall 35 and the second fluid path 11 a second outer wall 37 on. The first fluid path 7 So it's from the first outer wall 35 and the partition 21 opposite the environment 25 demarcated. The second fluid path 11 is by means of the second outer wall 37 and also by means of the partition 21 from the surroundings 25 demarcated.

It can be seen that the dividing wall 21 on both sides of the exhaust stream 3 is acted upon, so that this with a uniform guidance of the exhaust stream 3 through the first fluid path 7 and the second fluid path 11 no heat transfer takes place. However, if through the fluid paths 7 . 11 different strong partial flows 9 . 13 are guided, the respectively weaker acted upon fluid path 7 . 11 as an additional heat insulation effective or used, wherein a heat transfer first of the more pressurized fluid path over the partition 21 towards the weaker acted fluid path and then only over the outer wall to the environment 25 ,

2 B shows a further embodiment of the cross section of the fluid paths 7 . 11 , Again 2 B can be seen, run the fluid paths 7 . 11 annularly concentric with each other, wherein the first fluid path 7 completely within the second fluid path 11 is guided. In this case, the first fluid path has 7 a circular and the second fluid path 11 an annular cross-section. In this embodiment, the first outer wall forms 35 of the first fluid path 7 at the same time the partition 21 not in direct heat exchange with the environment 25 stands.

It is conceivable that the first fluid path 7 a first flow cross-section 31 and the second fluid path 11 a different second flow cross-section 33 having. Particularly advantageous is the first flow cross-section 31 about 50% of the second flow area 33 , This can advantageously the heat transfer of the first fluid path 7 to the environment 25 additionally minimized. In addition, the heat transfer in a full load case of the second fluid path 11 to the environment 25 be maximized.

3 shows a flowchart of a method for controlling the in the 1 and 2 shown exhaust system 1 , By means of a query 51 becomes a load point 53 of the operating state 63 of the internal combustion engine 5 checked. In the event that an actual load point of the internal combustion engine 5 the load point 53 falls short, is in a first step 55 the second exhaust valve 17 closed and in a second step 57 the first exhaust valve 15 open. The exhaust gas flow 3 Thus, it becomes predominantly 100% through the first fluid path 7 guided. Alternatively, it is conceivable, the second exhaust valve 17 only partially close, so the second partial flow 13 just to reduce.

If the query 51 shows that the actual load point of the internal combustion engine 5 the load point 53 exceeds, is in a third step 59 branches, which is the second exhaust valve 17 opens and in a fourth step 61 , which is also the first exhaust valve 15 opens. The exhaust gas flow 3 So it is through the first fluid path 7 and the second fluid path 11 as described above. The load point 53 is in particular between 10% and 90% of a full load of the internal combustion engine 5 , in particular between 20% and 80%, between 30% and 70%, between 35% and 55% or about 40%. The load point 53 may be due to a design of the exhaust system 1 , the internal combustion engine 5 and / or the motor vehicle 39 , in particular a load collective, depend.

Advantageously, the exhaust system 1 optional the thermal insulation 23 between the exhaust valves 15 . 17 and the turbine wheel 49 on.

The exhaust gas flow becomes advantageous 3 through the completely separate fluid paths 7 and 11 to the turbine wheel 49 guided.

A percentage cross-sectional portion of the fluid paths 7 and 11 may be advantageous as a compromise of low throttling and a minimum heat transfer surface to the environment 25 be designed towards, in particular depending on a size of the internal combustion engine 5 and / or a combination with the motor vehicle 39 , in particular the load collective.

In particular, the first fluid path 7 and the second fluid path 11 different materials, in particular different thermal insulation 23 , in particular for achieving the different heat transfer coefficients 27 and 29 , in particular, the first fluid path is thereby 7 for a partial load operation of the internal combustion engine 5 designed so that the minimum average heat transfer coefficient 30 results. In addition, the second fluid path 11 Preferably designed in such a way, in particular has a corresponding material and a corresponding outer contour, that in the high-load operation and / or the full-load operation, a larger average heat transfer coefficient 30 , So a maximum heat dissipation can be achieved, so that an over-temperature protection for subsequent components, in particular the turbine wheel 49 and / or the exhaust gas purification device can be achieved.

Advantageously, a temperature increase before the exhaust gas purification device, which in particular has an oxidation catalyst, an increased flow velocity in the low load operation on the turbine wheel 49 and a comparatively small surface with direct heat transfer to the environment 25 be achieved.

LIST OF REFERENCE NUMBERS

1

exhaust system

3

exhaust gas flow

5

internal combustion engine

7

first fluid path

9

first partial flow

11

second fluid path

13

second partial flow

15

first exhaust valve

17

second exhaust valve

19

control device

21

partition wall

23

thermal insulation

25

Surroundings

27

first heat transfer coefficient

29

second heat transfer coefficient

30

average heat transfer coefficient

31

first flow cross section

33

second flow cross section

35

first outer wall

37

second outer wall

39

motor vehicle

41

first inlet valve

43

second inlet valve

45

cylinder head

47

cylinder head flange

49

turbine

51

query

53

load point

55

first step

57

second step

59

Third step

61

fourth step

63

operating condition

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 102010014250 A1 [0003]
• DE 2452556 A1 [0004]
• DE 3930243 A1 [0005]
• DE 3915988 A1 [0006]
• DE 2744734 A1 [0006]

Claims (14)

Exhaust system ( 1 ) for guiding an exhaust gas flow ( 3 ) of an internal combustion engine ( 5 ), comprising: - a first fluid path ( 7 ) for guiding a first partial flow ( 9 ) of the exhaust gas stream ( 3 ), - a second fluid path ( 11 ) for guiding a second partial flow ( 13 ) of the exhaust gas stream ( 3 ), - a first fluid path ( 7 ) upstream first exhaust valve ( 15 ) of the internal combustion engine ( 5 ), - one the second fluid path ( 11 ) upstream second outlet valve ( 17 ) of the internal combustion engine ( 5 ), - at least one of the fluid paths ( 7 . 11 ) upstream control device ( 19 ), by means of at least one of the partial flows ( 9 . 13 ) of the exhaust gas stream ( 3 ), characterized in that the first fluid path ( 7 ) and the second fluid path ( 11 ) a common partition ( 21 ) exhibit. Exhaust duct according to the preceding claim, characterized in that by means of the control device ( 19 ) at least one of the exhaust valves ( 15 . 17 ) is controllable. Exhaust duct according to one of the preceding claims, characterized in that at least one of the fluid paths ( 7 . 11 ) a thermal insulation ( 23 ) to an environment ( 25 ). Exhaust duct according to the preceding claim 3, characterized in that the first fluid path ( 7 ) a first heat transfer coefficient ( 27 ) and the second fluid path ( 11 ) a second heat transfer coefficient ( 29 ) to the environment ( 25 ), whereby the heat transfer coefficients ( 27 ) and ( 29 ), in particular by 10% -500%, 50% -400%, 100% -300%, 150% -250% or about 300%. Exhaust duct according to one of the preceding claims, characterized in that the first fluid path ( 7 ) a first flow cross-section ( 31 ) and the second fluid path ( 11 ) has a second flow cross-section ( 33 ), wherein the flow cross sections ( 31 . 33 ) differ from each other. Exhaust duct according to the preceding claim, characterized in that the first flow cross-section ( 31 ) about 50% of the second flow cross section ( 33 ), in particular between 10% and 80%, 20% and 70%, 30% and 65%, 40% and 60% or 10% and 50%. Exhaust duct according to one of the preceding claims, characterized in that the first fluid path ( 7 ) completely within the second fluid path ( 11 ) runs. Exhaust duct according to one of the preceding claims, characterized in that the first fluid path ( 7 ) from a first outer wall ( 35 ) and the partition ( 21 ) and the second fluid path ( 11 ) from a second outer wall ( 37 ) and the partition ( 21 ) are limited. Method for controlling an exhaust system ( 1 ) according to one of the preceding claims, comprising: - predominantly guiding the exhaust gas flow ( 3 ) through the first fluid path ( 7 ) in a first operating state of the internal combustion engine ( 5 ). Method according to the preceding claim, wherein the first operating state is a partial load operation of the internal combustion engine ( 5 ) having. Method according to one of the preceding claims 9 or 10, comprising: - at least partially shutting off the second fluid path ( 11 ) for predominantly guiding the exhaust gas flow ( 3 ) through the first fluid path ( 7 ). Method according to one of the preceding claims 9 to 11, comprising: - opening the first exhaust valve ( 15 ) and the second exhaust valve ( 17 ) in a second operating state of the internal combustion engine ( 5 ). Method according to the preceding claim 12, wherein the second operating state of a heavy load or full load operation of the internal combustion engine ( 5 ) having. Motor vehicle ( 39 ) with an exhaust system ( 1 ) according to one of the preceding claims 1 to 8 and / or set up, designed, constructed and / or with software for carrying out a method according to one of the preceding claims 9 to 13.

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