DE202010008788U1 - Exhaust system of an internal combustion engine - Google Patents

Abstract

Exhaust system of an internal combustion engine (2) with an exhaust line (10) and at least one in the exhaust line (10) arranged exhaust aftertreatment device (17) comprising at least one SCR catalyst and / or NOx storage catalyst, wherein the exhaust line (10) upstream of the exhaust aftertreatment device ( 17) is at least partially divided into at least two separate exhaust branches (12, 13), at least one exhaust branch (13) has a heat source and at least one other exhaust branch (12) has a heat sink and the exhaust flow through the respective separate exhaust branches (12, 13) at least one flow control means (15) is controllable.

Description

The The present invention relates to an exhaust system of an internal combustion engine.

It is well known, the exhaust gases of an internal combustion engine, for example an Otto or diesel engine, arranged by means of a in the exhaust tract Exhaust after-treatment device to treat the pollutant emissions to reduce. Here, the efficiency or the efficiency the exhaust aftertreatment device very decisively from the in the exhaust aftertreatment prevailing temperature level and the fuel-air ratio used in the combustion of Internal combustion engine affected.

at Gasoline engines come, for example catalytic according to the prior art Reactors using catalytic materials, which increase the speed of certain reactions, one Oxidation of hydrocarbon (HC) and carbon monoxide (CO) also at low temperatures. Should also nitrogen oxides (NOx) can be reduced by using a three-way catalyst be achieved, but this to a running within narrow limits stoichiometric Operation (λ ≈ 1) of the gasoline engine requires. The nitrogen oxides are not using the existing oxidized exhaust gas components, namely carbon monoxide and unburned hydrocarbons, wherein at the same time these exhaust gas components are oxidized.

at Internal combustion engines, which are operated with an excess of air, so for example in Lean operating gasoline engines, but especially direct injection Diesel engines but also directly injecting gasoline engines, can in the Exhaust gas nitrogen oxides inherently, that is due to the missing reducing agent, can not be reduced.

to Oxidation of unburned hydrocarbons and carbon monoxide In particular, an oxidation catalyst is provided in the exhaust stream. To realize a sufficient conversion is a certain Operating temperature required. The so-called light-off temperature can be 120 ° C up to 250 ° C be.

The Reduction of the nitrogen oxide emission of an excess of air Internal combustion engine, in particular a diesel engine, can with a ammonia-containing reducing agent on a selectively working Catalyst, a so-called SCR catalyst, to nitrogen dioxide (N2) and water (H2O) take place (SCR: Selective Catalytic Reduction). As a reducing agent either gaseous ammonia (NH3), ammonia in aqueous solution or Urea used in aqueous solution. When using urea as a reducing agent of urea injected upstream of a hydrolysis catalyst directly into the exhaust tract and converted there by hydrolysis to ammonia. The at the Incineration in the internal combustion engine generated nitrogen oxides then by means of the cached in the SCR catalyst ammonia selectively reduced to water and nitrogen. In particular, the SCR catalyst ammonia at low temperatures until reaching a certain storage capacity store, which is desorbed again at high temperatures.

When Reducing agents are also unburned in addition to ammonia and urea Hydrocarbons used. The latter is also called HC enrichment designated, wherein the unburned hydrocarbons directly in the exhaust tract be introduced or by internal engine Activities, namely by a post-injection of additional fuel in the Combustion chamber after the actual combustion, to be supplied. The nacheingespritzte fuel should not in the combustion chamber through the still running main combustion or by the - even after Termination of the main combustion - high combustion gas temperatures ignited be, but during the charge change into the exhaust tract be initiated.

Basically, the Nitrogen oxide emissions with so-called nitrogen oxide or NOx storage catalysts (LNT: lean NOx trap). This will be the nitrogen oxides first while a lean operation of the internal combustion engine adsorbed in the catalyst, that means collected and then saved to while a regeneration phase, for example by means of a substoichiometric Operating (for example, λ <0.95) of the internal combustion engine be reduced in oxygen deficiency.

Further inner engine possibilities to realize a fat, that is a substoichiometric Operation of the internal combustion engine provides the exhaust gas recirculation (EGR) and diesel engine throttling in the intake system. On the inside engine activities can be omitted if the reducing agent directly into the Exhaust tract is introduced, for example by injecting additional Fuel. While the regeneration phase, the nitrogen oxides are released and in the Substantially in nitrogen dioxide (N2), carbon dioxide (CO2) and Water (H2O) converted. The frequency The regeneration phase is determined by the total emission of nitrogen oxides and the storage capacity of the NOx storage catalyst (LNT) determined.

The temperature of the storage catalyst (LNT) should preferably be in a Temperaturfens ter between 200 ° C and 450 ° C, so that on the one hand a rapid reduction of nitrogen oxides is ensured and on the other hand, no desorption takes place without converting the re-released nitrogen oxides, which can be triggered by excessive temperatures.

A Difficulty in use and in particular in the arrangement of the NOx storage catalyst in the exhaust system results from the exhaust gas contained sulfur, which also adsorbs in the NOx storage catalyst and in the context of a so-called desulfurization, ie. H. one Desulphurisation regularly removed must become. Therefor must the NOx storage catalyst to high temperatures, usually between 600 ° C and 700 ° C, heated and be supplied with a reducing agent, which in turn is due to the transition to a rich operation of the internal combustion engine can be achieved. The higher the temperature of the NOx storage catalyst is, the more effective it is Desulphurization from, with a maximum permissible temperature not exceeded should be, because then wears the desulfurization of the NOx storage catalyst due to excessive Temperatures significantly to thermal aging of the catalyst at. This will be the wanted Conversion of nitrogen oxides toward the end of the life of the NOx storage catalyst adversely affected, in particular, the storage capacity decreases due to thermal aging.

to Minimizing the emission of soot particles According to the state of the art, so-called regenerative particle filters are used used the soot particles Filter out and store the exhaust, these soot particles as part of the regeneration of the filter usually at high temperatures about 550 ° C be intermittently burned. The intervals of regeneration Among other things, this is due to the exhaust back pressure, which is due to the increasing flow resistance of the filter due to the increasing particle mass in the filter, certainly.

There both the exhaust gases of gasoline engines and the exhaust gases of diesel engines - albeit in different quantities and qualities - unburned hydrocarbons, Carbon monoxide, nitrogen oxides and soot particles contained come according to the prior art usually combined exhaust aftertreatment devices used, the one or more of the catalysts described above and / or filters.

at the above-described method for reducing nitrogen oxide emissions by means of SCR catalyst and / or NOx storage catalyst (LNT) In general, the problem of an uncontrolled (thermal) Desorption of ammonia from the SCR catalyst (so-called ammonia slip) or nitrogen oxides from the NOx storage catalytic converter (so-called nitrogen oxide slip). This thermal desorption occurs in particular during a ringing, sudden temperature rise in the exhaust system, as he, for example after a load jump of the internal combustion engine due to a sudden Performance request by a user (kick-down) the episode can be. This increases the NOx raw emissions of the internal combustion engine on the one hand, and the exhaust gas temperature on the other hand jump. At the same time, the adsorption capacity of the SCR catalyst or NOx storage catalyst with the rising temperature of the exhaust gas and in the exhaust system or the respective catalysts reproducing temperature rise lower.

There the time constants of the SCR catalyst or NOx storage catalyst units generally not enough are big, more is desorbed by the ammonia stored in the SCR catalyst, as in the course of the conversion of nitrogen oxide emissions in a natural way is consumed. Likewise, those in a NOx storage catalytic converter stored nitrogen oxides by a too rapid rise in temperature desorbed, although no regeneration phase, for example by means of a substoichiometric Operation of the internal combustion engine in oxygen deficiency or by additional Injecting reducing agent, for example fuel, into the Exhaust tract as already described takes place.

One sudden increase in the exhaust gas temperature in the exhaust system can For example, at the beginning of a regeneration phase of a Particulate filter or desulfurization of a NOx storage catalyst, which, as already described above, are carried out at high temperatures. In particular, from such a temperature jump in a Exhaust gas treatment device downstream of the particle filter to be regenerated or the NOx storage catalyst arranged catalysts and / or Filter affected.

Against this background, the present invention has the object to provide an exhaust system of an internal combustion engine, which substantially no or compared to exhaust systems according to the prior art significantly reduced ammonia and / or nitrogen oxide slip of an SCR catalyst or NOx storage catalytic converter during an Instationärbetriebs of the internal combustion engine, for example in a sudden change in exhaust gas temperature due to a load jump of the internal combustion engine, and thus an optimal and effective operation of the exhaust system and the exhaust aftertreatment device with respect to the Abgasreinigungs- or Konvertie enabling performance.

These Task is by an exhaust system of an internal combustion engine with the features of claim 1 solved. Further, particularly advantageous embodiments The invention discloses the respective subclaims.

It It should be noted that the features listed individually in the claims combined in any technically meaningful way can be and show further embodiments of the invention. The description characterizes and specifies the invention particularly in context in addition to the figures.

A Exhaust system according to the invention an internal combustion engine has an exhaust line and at least a arranged in the exhaust line exhaust aftertreatment device on. The exhaust aftertreatment device has at least one SCR catalyst and / or NOx storage catalyst, in particular an LNT on. Upstream the exhaust gas aftertreatment device according to the invention, the exhaust line according to the invention at least partially divided into at least two separate exhaust branches, wherein at least one exhaust branch a heat source and at least one another exhaust branch a heat sink has, so that the one exhaust branch as a heat source and the other heat sink is operable. Further, the exhaust gas flow amount through the respective separate exhaust branches by means of at least one flow control means controllable.

When heat sink in the context of the present invention is a thermodynamic environment or a heat transfer body understand, which has a high heat capacity and thereby is able, with high heat absorption, a quasi-stationary temperature state to keep. In contrast, a heat source in the sense of this description in a quasi-stationary Temperature state heat continuously deliver.

The Division of the exhaust system into at least two separate exhaust lines, wherein at least one exhaust branch as a heat source and at least one other exhaust branch can be operated as a heat sink, allows the targeted influencing of the exhaust gas temperature of the respective exhaust branches flowing through Exhaust gases. In particular, it is provided by the invention Flow control means possible, the exhaust flow amount to dose precisely through the respective exhaust branches and thus the Control exhaust gas temperature downstream of the separate exhaust branches, the is called after the exhaust branches again open into the exhaust system. hereby is an optimal operation of a downstream exhaust aftertreatment device, in particular an SCR catalytic converter and / or a NOx storage catalytic converter has reached, since even in a Instationärbetrieb the internal combustion engine, the is called For example, with a sudden change in the exhaust gas temperature due to a load jump of the internal combustion engine, the exhaust gas temperature kept almost constant at the entrance of the exhaust aftertreatment device can be or the temperature change at the entrance of the exhaust aftertreatment device at least clearly delayed, with a much smaller amount, and also in a substantial amount larger period occurs. A sudden temperature change at the entrance of the exhaust aftertreatment device is through the exhaust system according to the invention prevented in any case.

One As a result of an abrupt increase in the exhaust gas temperature, as already described, in an SCR catalyst or a NOx storage catalyst to a uncontrolled thermal desorption of in the SCR catalyst stored ammonia (ammonia slip) or in the NOx storage catalytic converter adsorbed nitrogen oxides (nitric oxide slip). This ammonia or Nitrogen oxide slip is with the exhaust system according to the invention effectively prevents both the reproductive rate the temperature change within the exhaust system as well as the amount of temperature change by means of as a heat source or heat sink operable exhaust branches are substantially attenuated or reduced.

If the exhaust gas temperature of the internal combustion engine rises suddenly, for example, due to a sudden Power requirement to the internal combustion engine, for example by a sudden Acceleration process of a user (kick-down), is in this Case by means of the flow control device the exhaust gas at least partially, advantageously also completely by as a heat sink passed operable exhaust branch. The flow control means is for this purpose preferably designed such, the operable as a heat source exhaust branch and / or as a heat sink operable exhaust branch partially to completely close or to open.

The exhaust gas conducted through the exhaust branch which can be operated as a heat sink is cooled in accordance with the function of a heat sink, so that the exhaust gas temperature can be selectively controlled at the inlet of the exhaust gas after-treatment device arranged downstream of the exhaust branch, which has in particular an SCR catalytic converter and / or a NOx storage catalytic converter. An uncontrolled desorption of the ammonia stored in the SCR catalytic converter or of the nitrogen oxides stored in the NOx storage catalytic converter as a result of a sudden increase in temperature is avoided. The ammonia stored in the SCR catalyst is released used in the normal implementation of nitrogen oxide emissions. Likewise, the nitrogen oxides stored in the NOx storage catalytic converter are not released in an uncontrolled manner, in particular outside a regeneration phase. The exhaust system according to the invention thus enables the optimal operation of the SCR catalytic converter or the NOx storage catalytic converter independently of the instantaneous operating state of the internal combustion engine.

If the power requirement of the internal combustion engine withdrawn is and therefore the exhaust gas temperature of the internal combustion engine decreases, the exhaust gas by means of the flow control means at least partially, advantageously also completely by as a heat source passed operable exhaust branch. This will cause the temperature level the flowing through this exhaust branch Exhaust gases kept constant or raised, so that always an optimal Temperature window for the Operation of the exhaust branch downstream SCR catalytic converter or NOx storage catalytic converter ensured is also independent from the instantaneous power requirement of the internal combustion engine.

to Achieve as much as possible accurate and finely graduated control of the exhaust gas temperature within he exhaust system, in particular downstream of the separate exhaust branches, is the exhaust gas flow amount through the respective exhaust branches by means of the flow control means advantageously dependent on at least from the exhaust gas temperature of the internal combustion engine and / or the exhaust gas mass flow and / or the ratio of the in the SCR catalyst stored ammonia based on the ammonia storage capacity of the SCR catalyst and / or the relationship the stored in the NOx storage catalyst nitrogen oxides based on the nitrogen oxide storage capacity the NOx storage catalyst controllable. This can be the flow control means optimally in accordance with the current operating state of the exhaust system according to the invention Taxes. In particular, in this way an optimal position the flow control means can be determined, the as the heat source operable exhaust branch and / or operated as a heat sink exhaust branch partly to completely closes or opens and thus an accurate and finely graduated control of the exhaust gas temperature downstream of the separate exhaust branches allowed.

In an advantageous embodiment of the exhaust system according to the invention is between as a heat source operable exhaust branch and operable as a heat sink exhaust branch a heat exchanger intended. This allows a heat transfer between the respective exhaust branches, so that of the as a heat sink operable exhaust branch absorbed heat as a heat source operable exhaust branch available can be made. On an additional, heat-generating source for as Heat source operable Exhaust branch can thus be dispensed with, which according to the invention a particularly energy efficient operable exhaust system allows.

Of the heat exchangers may also be designed such that it can be operated on the as a heat source Emission branch not deliverable heat energy only as a heat sink relates to operable exhaust branch, but also from other, additional Heat sources, which are available in the operation of the internal combustion engine.

In a further advantageous embodiment of the exhaust system according to the invention has the as a heat sink operable exhaust branch an exhaust gas dynamics to delay the Heat transmission on. In particular, by appropriate size or volume design a separate exhaust branch with respect to a desired exhaust gas dynamics the pressure and suction waves are achieved in this exhaust branch such that the exhaust gases introduced into the exhaust branch with a certain temporal delay flow through the exhaust branch, this means the space velocity of the exhaust gases is determined by the thus designed Exhaust branch significantly reduced in an advantageous manner. In a particularly simple embodiment, the as a heat sink operable exhaust branch for this purpose, for example, a much larger volume on as the heat source operable exhaust branch.

One Exhaust gas temperature jump at the beginning of such a trained exhaust branch is thus delayed passed through it. The longer residence time or lower Space velocity of the exhaust gases can be used, for example, more heat to the environment or a heat exchanger leave. Further leads the induced by the exhaust branch lower space velocity Consequently, the exhaust gases also to a higher residence time of the exhaust gases in a downstream exhaust aftertreatment device, in particular an SCR catalyst or NOx storage catalyst, resulting in a more efficient conversion and overall an improved cleaning performance can be achieved.

In a further particularly simple embodiment of the exhaust system according to the invention, the exhaust branch which can be operated as a heat source is essentially an exhaust branch formed from a conventional exhaust pipe, which, however, is substantially shorter than the exhaust branch which can be operated as a heat sink. Also, the operable as a heat sink exhaust branch is in this case in a particularly simple manner formed from a conventional exhaust pipe exhaust branch, but this one we has considerably greater length than the exhaust branch which can be operated as a heat source.

Of the as a heat source operable exhaust branch can also advantageously a heat insulation for storing the heat have in the exhaust branch. The operable as a heat sink exhaust branch in contrast for example, cooling fins have as much as possible fast heat transfer to enable the environment. Furthermore, as a heat sink operable exhaust branch advantageously made of a material that a particularly good heat transfer for example to the environment or a heat exchanger allows for example, by a high thermal conductivity. In this way, the as a heat sink operable exhaust branch capable of an exhaust gas temperature jump at the entrance of the exhaust branch to a considerable extent for a downstream exhaust aftertreatment device, especially for an SCR catalyst and / or a NOx storage catalyst, too dampen. In terms of which propagates due to the temperature jump in the exhaust system heat wave put that as a heat sink operable exhaust branch thus represents a low-pass filter.

The Passing the exhaust gases through the operable as a heat sink exhaust branch leads generally to a lowering of the exhaust gas temperature downstream of the exhaust branch, since heat is extracted from the exhaust gas in the exhaust branch as described above. The exhaust system according to the invention thus allows also an increase the storage capacity of a the exhaust branch downstream NOx storage catalytic converter. This hangs in known Way from the operating temperature of the NOx storage catalyst from and increases with increasing temperature above a certain value steadily off. A large storage capacity of the NOx storage catalytic converter is particularly advantageous because, for example, at a Load jump of the internal combustion engine due to a sudden Power requirement in addition to the exhaust gas temperature and the NOx raw emissions of the internal combustion engine increase suddenly, which then from the NOx storage catalytic converter recorded, that is can be stored. In addition, with a larger storage capacity of the NOx storage catalyst an enlargement of the Time interval between the regeneration phases of the NOx storage catalyst possible. The regeneration can thus, for example, only after the withdrawal the power requirement by means of a substoichiometric operation of Internal combustion engine in the absence of oxygen or by additional Injecting reducing agent, for example fuel, into the Exhaust tract be initiated to convert the adsorbed nitrogen oxides and the NOx storage catalyst for a new storage cycle prepare.

In a further advantageous embodiment of the exhaust system according to the invention is another upstream of the at least two separate exhaust branches Exhaust gas aftertreatment device arranged in the exhaust line. These Exhaust after-treatment device may, for example, at least one Oxidation catalyst, particulate filter, SCR catalyst and / or NOx storage catalytic converter and various combinations thereof. Thus it is for example also possible, Catalysts or filters, on the one hand in a higher temperature range To operate optimally and on the other hand less sensitive to temperature fluctuations are, closer at the outlet of Arrange internal combustion engine and this with such catalysts or Filtering in a common exhaust system to combine in a lower temperature window an optimal cleaning or Achieve conversion performance and efficient operation in particular, sudden temperature changes by means of herein described invention can be avoided.

through the exhaust system according to the invention can also sudden temperature changes, for example, due to a regeneration carried out at high temperatures a particulate filter or a NOx storage catalyst occur for the in the Exhaust line downstream of arranged catalysts or filters mitigated or avoided. This creates a greater degree of freedom for the arrangement or sequence of catalysts or filters within an exhaust system.

Further Advantageous details and effects of the invention are as follows explained in more detail with reference to an embodiment shown in the drawing. It shows schematically:

1 An embodiment of an exhaust system according to the invention of an internal combustion engine.

In 1 is an embodiment of an exhaust system according to the invention 1 an internal combustion engine 2 shown schematically. Generally, the internal combustion engine sucks 2 Air over an air filter 3 for the combustion of a fuel-air mixture in a combustion chamber, not shown, of the internal combustion engine 2 at. At the in 1 illustrated internal combustion engine 2 gets the air with the help of a turbocharger 4 , in particular a compressor 5 , in the intake tract 6 the internal combustion engine 2 compacted. The turbocharger 4 This is done in a known manner via a turbine 7 that over a wave 8th with the compressor 5 is connected, of which the internal combustion engine 2 after the combustion leaving exhaust gas flow 9 driven.

Downstream of the turbine 7 of the turbocharger 4 is in the embodiment shown in the exhaust system 10 a first (optional) exhaust aftertreatment device 11 arranged. The first exhaust aftertreatment device 11 For example, it may comprise at least one oxidation catalyst, particulate filter, SCR catalyst and / or NOx storage catalyst, in particular an LNT, and any combinations thereof. The first exhaust aftertreatment device 11 serves a first emission control.

Downstream of the first exhaust aftertreatment device 11 shares the exhaust system 10 of in 1 illustrated embodiment in two separate exhaust branches 12 and 13 , wherein the exhaust branch 12 as a heat sink is operable and the exhaust branch 13 is operable as a heat source. As 1 it can be seen further in the region of the upstream branching point 14 a flow control means 15 , For example, a flow flap or a changeover valve in the exhaust system 10 arranged. The flow control means 15 is designed in the embodiment described here such that it optionally the exhaust branch 12 or the exhaust branch 13 partially to completely close or can open. Thus, only one flow control means is 15 required, with the complete control of the exhaust gas flow through both exhaust branches 12 . 13 is possible. Of course, the arrangement of several flow control means 15 , For example, each a separate exhaust branch each 12 . 13 associated flow control means 15 , possible.

Depending on the position of the flow control means 15 is thus in the exhaust system 10 guided exhaust gas flow both completely over the heat sink operable exhaust branch 12 conductive, that is the flow control means 15 closes the exhaust branch which can be operated as a heat source 13 completely, or the exhaust gas flow is completely over the operable as a heat source exhaust branch 13 conductive, that is the flow control means 15 closes the exhaust branch which can be operated as a heat sink 12 Completely. Furthermore, in the in 1 illustrated embodiment, the exhaust gas flow also by means of any intermediate positions of the flow control means 15 between the aforementioned end positions simultaneously both via the one exhaust branch 12 as well as over the other exhaust branch 13 be conducted. Thus, a particularly accurate and finely graduated control of the exhaust gas temperature to the downstream branch point 16 That is, after the confluence of the two exhaust branches 12 and 13 in the exhaust system 10 , possible. In a simpler embodiment of an exhaust system according to the invention, however, also a flow control means is used, which only the one exhaust branch 12 or the other exhaust branch 13 completely close or can open and thus does not allow intermediate positions.

Downstream of the separate exhaust branches 12 and 13 that is, after both exhaust branches 12 and 13 at the downstream branching point 16 back into the exhaust system 10 join, is a second exhaust aftertreatment device 17 in the exhaust system 10 arranged. This exhaust aftertreatment device 17 has at least one SCR catalytic converter and / or one NOx storage catalytic converter. To the SCR catalyst in the second exhaust aftertreatment device 17 Reducing agent, for example, ammonia or urea in aqueous solution to supply, is upstream of the second exhaust aftertreatment device 17 a reducing agent injection device 18 for injecting the reducing agent into the exhaust gas line 10 intended.

The flow control means 15 , in particular the position of the flow control means 15 , is preferably of a in the 1 Control device not shown controlled. As an input parameter for determining the optimal position of the flow control means 15 In particular, the exhaust gas temperature of the internal combustion engine 2 and / or the exhaust gas mass flow and / or the ratio of in one of the exhaust branches 12 and 13 downstream SCR catalyst stored ammonia based on the ammonia storage capacity of the SCR catalyst and / or the ratio of in one of the exhaust branches 12 and 13 downstream NOx storage catalyst stored nitrogen oxides based on the nitrogen oxide storage capacity of the NOx storage catalyst and any combination thereof used.

The abovementioned parameters can be measured by means of suitable sensors in a known manner or optionally also from already existing measured values of other operating parameters of the exhaust system 1 or the internal combustion engine 2 be calculated. Thus, there is always one to the current operating state of the exhaust system 1 optimally adapted control or position of the flow control means 15 guaranteed. The flow control means 15 this can be controlled both electrically and mechanically.

For example, when a load jump of the internal combustion engine 2 as occurs, for example, in a sudden power demand of a user, the exhaust gas temperature of the internal combustion engine 2 increases abruptly, the exhaust gas flow after passing the first exhaust aftertreatment device 11 in which the exhaust gases undergo a first purification or conversion, for example by means of an oxidation catalyst and / or a particulate filter, at least partially or completely by means of the flow control means 15 by the as Heat sink operable exhaust branch 12 directed. In the exhaust branch 12 Heat is removed from the exhaust gas, for example, over at the exhaust branch 12 arranged, in 1 not shown cooling fins is discharged to the environment. Instead of or in addition to the cooling fins may be on the exhaust branch 12 an Indian 1 merely indicated heat exchanger 19 be arranged, with which the exhaust branch 12 extracted heat at the operable as a heat source exhaust branch 13 is transferable and then to heat the through the exhaust branch 13 flowing exhaust gases is available.

The passage of the exhaust gases through the exhaust branch 12 causes the sudden increase in exhaust gas temperature at the upstream branch point 14 not or at least with considerable delay and with a significantly weakened amount and, in addition, within a much longer period to the downstream branching point 16 propagates, whereby the exhaust gas temperature at the beginning of the second exhaust aftertreatment device 17 , in particular the beginning of the covered by this SCR catalyst and / or NOx storage catalyst, is specifically controlled. As a result, an uncontrolled thermal desorption of the ammonia stored in the SCR catalytic converter or an ammonia slip is avoided and only the ammonia required for the normal conversion of the nitrogen oxide emissions is consumed. Likewise, the nitrogen oxide slip by an uncontrolled thermal desorption of the in a NOx storage catalytic converter of the exhaust aftertreatment device 17 prevents stored nitrogen oxides. Furthermore, increases due to the lower inlet temperature at the exhaust gas aftertreatment device 17 or the NOx storage catalyst whose nitrogen oxide storage capacity significantly, so that the regeneration phases can be performed for the NOx storage catalyst at a greater time interval.

Decreases the exhaust gas temperature of the internal combustion engine 2 , For example, after a withdrawal of the power requirement of the internal combustion engine 2 , the exhaust gas flow is after passing the first exhaust aftertreatment device 11 at least partially or completely by means of the flow control means 15 by the exhaust branch which can be operated as a heat source 13 directed. In the exhaust branch 13 For example, heat is supplied to the exhaust gas, for example via the heat exchanger 19 , The heat exchanger 19 can this between the operable as a heat sink exhaust branch 12 and the exhaust branch 13 be arranged so that it from the exhaust branch 12 dissipates emitted heat and to the exhaust branch 13 transfers. Instead of or in addition to the heat exchanger 19 can the exhaust branch 13 with an in 1 be provided heat insulation not shown.

The passage of the exhaust gases through the operable as a heat source exhaust branch 13 causes, despite the decreasing exhaust gas temperature of the internal combustion engine 2 the exhaust gas temperature level between the upstream branch point 14 and the downstream branch point 16 can be substantially held or raised, whereby the exhaust gas temperature at the beginning of the second exhaust aftertreatment device 17 , in particular the beginning of the covered by this SCR catalyst and / or NOx storage catalyst, is specifically controlled. Thus, with the exhaust system according to the invention always the optimal for the operation of the SCR catalytic converter or NOx storage catalytic converter temperature window can be ensured, in particular independent of the current operating state of the internal combustion engine 2 and thus also during an instationary operation of the internal combustion engine 2 ,

The Exhaust system according to the invention is self-evident not to that described herein and shown in the drawing Embodiment limited. So In particular, the invention is not limited to use of SCR catalysts or NOx storage catalysts downstream of the separate exhaust branches Exhaust after-treatment device limited. There may also be further catalysts and / or filters used in this exhaust aftertreatment device be, especially those for the one temperature control in the context of the present invention is of particular advantage.

Furthermore, the exhaust system according to the invention is not limited to those in the 1 limited shown two separate exhaust branches. For example, a third, thermally neutral exhaust branch could also be arranged in the exhaust system according to the invention, which allows an even more accurate and finer temperature control downstream of the separate exhaust branches by means of a correspondingly designed flow control means.

Likewise, the arrangement of in the 1 shown branches of the separate exhaust branches to understand only by way of example. These can be arranged arbitrarily along the exhaust line of the exhaust system. In particular, it is also not necessary for the invention that the separate exhaust branches each branch off at a common branch point of the exhaust line or re-enter into this.

In a preferred embodiment, the exhaust system according to the invention for an internal combustion engine, in particular for a gasoline or diesel engine of a motor vehicle, is used and includes a downstream of the internal combustion engine arranged in the exhaust line first exhaust aftertreatment device having an oxidation catalyst and / or a particulate filter, further at least two separate exhaust branches, in which the exhaust line is divided downstream of the first exhaust aftertreatment device, of which one exhaust branch is operated as a heat source and the other exhaust branch as a heat sink is operable and the exhaust gas flow of the internal combustion engine by means of a flow control means partially to completely through the one exhaust branch and / or through the other exhaust branch can be conducted, and a downstream of the separate exhaust branches arranged in the exhaust line second exhaust aftertreatment device, the at least one SCR catalyst and / or a NOx Storage Catalyst has.

LIST OF REFERENCE NUMBERS

1

exhaust system

2

Internal combustion engine

3

air filter

4

turbocharger

5

compressor

6

intake system

7

turbine

8th

wave

9

exhaust gas flow

10

exhaust gas line

11

First exhaust treatment device

12

When heat sink operable separate exhaust branch

13

When heat source operable separate exhaust branch

14

Upstream branch point

15

Flow control means

16

Downstream branch point

17

Second exhaust treatment device

18

Reductant injection device

19

heat exchangers

Claims (10)

Exhaust system of an internal combustion engine ( 2 ) with an exhaust gas line ( 10 ) and at least one in the exhaust line ( 10 ) arranged exhaust gas aftertreatment device ( 17 ), which has at least one SCR catalytic converter and / or NOx storage catalytic converter, wherein the exhaust gas line ( 10 ) upstream of the exhaust aftertreatment device ( 17 ) at least partially into at least two separate exhaust branches ( 12 . 13 ), at least one exhaust branch ( 13 ) a heat source and at least one other exhaust branch ( 12 ) has a heat sink and the exhaust gas flow rate through the respective separate exhaust branches ( 12 . 13 ) by means of at least one flow control means ( 15 ) is controllable. Exhaust system according to claim 1, wherein the exhaust gas flow rate through the respective exhaust branches ( 12 . 13 ) by means of the flow control means ( 15 ) as a function of the exhaust gas temperature of the internal combustion engine ( 2 ) and / or the exhaust gas mass flow and / or the ratio of the ammonia stored in the SCR catalyst based on the ammonia storage capacity of the SCR catalyst and / or the ratio of stored in the NOx storage catalyst nitrogen oxides based on the nitrogen oxide storage capacity of the NOx storage catalyst is controllable. Exhaust system according to claim 1 or 2, wherein by means of the flow control means ( 15 ) which can be operated as a heat source exhaust branch ( 13 ) and / or operated as a heat sink exhaust branch ( 12 ) is partially to completely openable and closable. Exhaust system according to one of the preceding claims, wherein between the operable as a heat source exhaust branch ( 13 ) and operable as a heat sink exhaust branch ( 12 ) A heat exchanger is provided. Exhaust system according to one of the preceding claims, wherein the heat sink operable exhaust branch ( 12 ) has an exhaust gas dynamics for delayed heat transmission. Exhaust system according to one of the preceding claims, wherein the exhaust gas branch operable as a heat source ( 13 ) is shorter than the heat sink operable exhaust branch ( 12 ). Exhaust system according to one of the preceding claims, wherein the heat sink operable exhaust branch ( 12 ) has a larger volume than the heat source operable exhaust branch ( 13 ). Exhaust system according to one of the preceding claims, wherein the exhaust gas branch operable as a heat source ( 13 ) has a thermal insulation. Exhaust system according to one of the preceding claims, wherein the heat sink operable exhaust branch ( 12 ) Has cooling fins. Exhaust system according to one of the preceding claims, wherein upstream of the at least two separate exhaust branches ( 12 . 13 ) a further exhaust aftertreatment device ( 11 ) in the exhaust line ( 10 ) is arranged, which has at least one oxidation catalyst and / or a particulate filter and / or a NOx storage catalyst and / or an SCR catalyst.