WO2012095132A1

WO2012095132A1 - Exhaust system of an internal combustion engine, and method for operating an exhaust system

Info

Publication number: WO2012095132A1
Application number: PCT/EP2011/006161
Authority: WO
Inventors: Michael Wagenplast
Original assignee: Daimler Ag
Priority date: 2011-01-14
Filing date: 2011-12-08
Publication date: 2012-07-19
Also published as: DE102011008568A1

Abstract

The invention relates to an exhaust system of an internal combustion engine, comprising a first exhaust-gas turbocharger (12) with a first turbine (16) which can be driven by exhaust gas of the internal combustion engine, and comprising a second exhaust-gas turbocharger (24) with a second turbine (26) which can be driven by exhaust gas of the internal combustion engine, and comprising an exhaust-gas catalytic converter (50), and also comprising a valve-controlled line arrangement by means of which exhaust gas of the internal combustion engine can be conducted via the first and/or the second turbine (16; 26). According to the invention, the exhaust-gas catalytic converter (50) has a first catalytic converter part (50a) and a second catalytic converter part (50b) which is positioned downstream with respect to the exhaust-gas flow direction, and a fraction of exhaust gas conducted via the first turbine (16) can be conducted directly to the second catalytic converter part (50b), said fraction being determined as a function of the temperature of the exhaust gas provided by the internal combustion engine and/or as a function of a power output of the internal combustion engine.

Description

Exhaust system of an internal combustion engine and method for operating a

exhaust system

The invention relates to an exhaust system of an internal combustion engine in the

The preamble of claim 1 specified type and a method for operating a catalytic converter, which is connected to a first and a second exhaust gas turbocharger having charging device of an internal combustion engine.

US 2009/0178406 discloses an exhaust system of an internal combustion engine having a first exhaust gas turbocharger and a second exhaust gas turbocharger. For the first exhaust gas turbocharger, a bypass line controlled by a valve is provided. Depending on the degree of opening of the valve, the exhaust gas emitted by the internal combustion engine can only be conducted via the turbine of the first turbocharger or both via the turbine of the first turbocharger and via the turbine of the second exhaust gas turbocharger or only via the turbine of the second exhaust gas turbocharger. Between the turbine of the first and the second exhaust gas turbocharger, an exhaust gas catalyst is arranged, which is flowed through by the entire, guided via the turbine of the first exhaust gas turbocharger exhaust gas.

The object of the invention is to provide an exhaust system and a method for operating an exhaust system, which allows for the best possible performance of the associated internal combustion engine improved exhaust gas purification, especially at low exhaust gas temperatures.

This object is achieved by an exhaust system having the features of claim 1 and by a method having the features of claim 8.

The exhaust system according to the invention comprises a first exhaust gas turbocharger with a first turbine which can be driven by exhaust gas of the internal combustion engine and a second exhaust gas turbocharger with a second exhaust gas of the internal combustion engine drivable turbine, an exhaust gas catalyst and a valve-controlled line arrangement, with which exhaust gas of the internal combustion engine via the first and / or the second turbine can be conducted. In this case, the exhaust gas catalytic converter has a first catalyst part and a second catalytic converter part connected downstream with respect to the exhaust gas flow direction and an exhaust gas supplied by the internal combustion engine depending on the temperature of the engine and / or a fraction of the first turbine directed according to a power output of the internal combustion engine Exhaust gas can be conducted directly to the second catalyst part. As a result of this embodiment, a rapid onset of the catalytic converter or a high cleaning effect of the catalytic converter is made possible especially at low temperatures. A direct supply of exhaust gas to the second catalyst part is understood to mean that exhaust gas flowing out of the turbine housing of the second exhaust gas turbocharger is supplied to the second catalyst part via a corresponding line of the line arrangement while avoiding a flow through the first catalyst part or the second turbine. It is preferably provided that in the corresponding line section no further exhaust gas treatment component is arranged.

In an embodiment of the invention, exhaust gas of the internal combustion engine can only be conducted via the first turbine or via the first and the second turbine or only via the second turbine. The first and the second exhaust gas turbochargers form a two-stage

Charging device, wherein a respective turbine associated compressor is arranged in an intake system of the internal combustion engine such that compressed air from the compressors of the internal combustion engine can be supplied. Here, combustion air is to be understood here as in the following also an exhaust gas recirculation optionally formed by exhaust gas recirculation. Via lines of the line arrangement, exhaust gas conducted via the first turbine can be conducted directly to the second catalyst part and the second turbine in respectively variable and mutually complementary proportions. The shares can vary between 0% and 100%. It is provided that at low temperature of the exhaust gas emitted by the internal combustion engine or at low load or power of the internal combustion engine, a high proportion of exhaust gas passed through the first turbine is passed directly to the second catalyst part. With increasing exhaust gas temperature or load, this proportion decreases in particular continuously and it is complementarily directed in particular continuously increasing proportions to the second turbine. On the one hand, this enables a rapid heating of the second catalyst part during a cold start or warm-up and thus a rapid achievement of its catalytic activity (light-off). Likewise, cooling at low load is avoided. At the same time a continuous run-up, in particular the second turbine and thus the associated compressor allows. A so-called turbo lag, as typically occurs in a two-stage supercharger with an abrupt connection of the second exhaust gas turbocharger, is thereby also effectively avoided. The line arrangement comprises switchable lines arranged on the intake side for the combustion air to be sucked or compressed. In connection with a different flow through the lines of the exhaust-gas line arrangement, different operating states can be represented, which enable effective and comfortable release of power of the internal combustion engine and effective exhaust gas purification. In one of these operating conditions, which is active at low load or low part load, the internal combustion engine supplied combustion air is compressed either alone or almost alone from the compressor of the first exhaust gas turbocharger. In another operating state with contrast increased load (partial load) takes place in a serial operation in a sequential flow to the compressor of the first and second exhaust gas turbocharger, a two-stage compression of the combustion air. In a further operating state with a further increased load, parallel compaction takes place in parallel operation with an at least predominantly parallel flow of the two compressors. Finally, in a further operating state at elevated partial load to full load, compression of the combustion air takes place mainly or almost completely through the compressor of the second exhaust gas turbocharger. The transitions between these operating states can also be fluent. This results in terms of power development of the internal combustion engine, a particularly good response, especially in unsteady driving.

In a further embodiment of the invention, exhaust gas conducted via the second turbine can be fed to the first catalyst part. From the first catalyst part, the exhaust gas passes directly and immediately further to the second catalyst part. Has the first part of the catalyst its

Light-off temperature or its full effectiveness has not yet been reached, a pollutant conversion in the subsequent second catalyst part is made possible because it has typically already reached a conversion capability at an earlier time due to the exhaust system according to the invention. The above-mentioned operating conditions are associated with corresponding, different flows of the first and the second catalyst part. As the load or power output of the internal combustion engine increases, substantially decreasing portions of the exhaust gas guided via the first turbine and thus of the total exhaust gas emitted by the internal combustion engine are guided by the first turbine directly to the second catalytic converter part. On the other hand, more exhaust gas over the second turbine and then to the first Led catalyst part and after the flow through the second

Catalyst part passed. As a result of this flow control a particularly rapid onset of pollutant conversion is possible. In particular, there is a very rapid start of the second catalyst part, which is sufficient for a pollutant conversion of this catalyst part directly supplied, comparatively low exhaust gas flow. Thus, especially in conjunction with a cold start or warm-up but also generally at low load and correspondingly low exhaust gas temperatures a particularly good pollutant conversion allows.

In a further embodiment of the invention, the line arrangement has a bypass line controlled by a first valve for the first turbine and a connection line controlled by a second valve, with which exhaust gas from the first turbine can be conducted directly to the second catalyst part. This embodiment allows a targeted flow control of the exhaust gas. It is particularly advantageous if the valves are self-controlling, i. can be actuated as a result of the applied across the valve pressure difference. Preferred is an embodiment in the nature of a spring-loaded check valve. This eliminates expensive control means.

In a further embodiment of the invention, the exhaust gas catalytic converter is designed as a starting catalyst arranged close to the engine. The starting catalyst is thus preferably the first catalytically effective exhaust aftertreatment component of the exhaust system, as seen in the exhaust gas flow direction. Preferred is an embodiment as an oxidation catalyst. This can also be designed with a low or no oxygen storage capacity. As a result of the arrangement close to the engine, a particularly rapid starting is possible.

In a further embodiment of the invention, the first catalyst part and the second catalyst part are arranged at a small distance in a common housing. Due to this arrangement, a particularly good heat transfer between the two catalyst parts is possible. In particular, heating of the first catalyst part is made possible by heat radiation emitted from the downstream, second catalyst part and acting on the first catalyst part.

In a further embodiment of the invention, the first exhaust gas turbocharger is dimensioned smaller than the second exhaust gas turbocharger. This allows a particularly fast

Response and run-up of the first exhaust gas turbocharger. It is preferred if the first exhaust gas turbocharger is a so-called VTG supercharger with a variable turbine geometry. is formed. The second exhaust gas turbocharger preferably has a fixed, fixed turbine and compressor geometry.

Another aspect of the invention relates to a method for operating an exhaust system of an internal combustion engine having a first and a second exhaust gas turbocharger charging device and an exhaust gas catalyst having a first catalyst part and a downstream with respect to the exhaust gas flow direction second catalyst part. This is a function of the

Temperature of the exhaust gas supplied by the internal combustion engine and / or a determined depending on a power output of the internal combustion engine portion of passed over the turbine of the first exhaust gas turbocharger exhaust passed directly to the second catalyst part.

The proportion of exhaust gas led directly to the second catalytic converter part via the turbine of the first exhaust gas turbocharger typically decreases with increasing exhaust gas temperature and / or with increasing output of the internal combustion engine. In this way, starting from low catalyst temperatures, a very rapid heating, in particular of the second catalyst part, is made possible. Accordingly quickly a pollutant conversion on the catalytic converter, in particular on its second part allows. Even at low part load of the internal combustion engine with correspondingly less hot exhaust gas, effective pollutant conversion is possible.

In an embodiment of the method, the proportion of the turbine of the first

Exhaust gas turbocharger discharged exhaust gas, which is not passed directly to the second catalyst part, passed over the turbine of the second exhaust gas turbocharger. Exhaust gas routed via the turbine of the second exhaust gas turbocharger is preferably conducted directly further to the first catalyst part. It is provided in a further embodiment of the method that passed over the first catalyst part exhaust gas is passed completely over the second catalyst part. Preferably, a supply of exhaust gas which has flowed over the first catalyst part to the second catalyst part likewise takes place directly, ie without a further intermediate treatment. The second catalyst part thus always receives the entire output from the internal combustion engine exhaust gas flow, in particular at low to medium exhaust gas temperature and power output a relatively high proportion of the second catalyst part is fed directly, without flow through the first catalyst part. In contrast, the first catalyst part receives at low to medium exhaust gas temperature or power output, a comparatively small proportion of the exhaust gas or only negligible amounts of exhaust gas. With rising Exhaust gas temperature and / or power output, this proportion increases substantially. This approach allows a particularly effective temperature of the catalytic converter, which is thus active even at low power output.

Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively indicated combination but also in other combinations or alone, without the scope of the To leave invention.

The figures show in:

Fig. 1 is a schematic diagram of a preferred embodiment of air supply system and

Exhaust system of an internal combustion engine,

2 is a further schematic diagram of the system according to FIG. 1 supplemented by flow arrows corresponding to a first operating state, FIG.

3 is a further schematic diagram of the system according to FIG. 1 supplemented by flow arrows corresponding to a second operating state, FIG.

4 is a further schematic diagram of the system according to FIG. 1 supplemented by flow arrows corresponding to a third operating state, FIG.

Fig. 5 is a further schematic diagram of the system of FIG. 1 supplemented by flow arrows corresponding to a fourth operating state and

Fig. 6 is a further schematic diagram of the system according to FIG. 1 supplemented by flow arrows corresponding to a fifth operating state. Fig. 1 shows a schematic representation of an inventive, preferred embodiment of air supply system and exhaust system of an internal combustion engine such as a diesel engine or a gasoline engine of a motor vehicle, especially a passenger car. The exhaust system comprises a first exhaust gas turbocharger 12 with a first turbine 16 arranged in an exhaust tract 14 of the internal combustion engine and a first compressor 20 arranged in an intake tract 18 of the internal combustion engine. The first turbine 16 comprises a turbine housing, in which one with a shaft 22 of the first exhaust gas turbocharger 12 rotatably connected turbine wheel is rotatably received. The first compressor 20 comprises a compressor housing, in which a likewise rotatably connected to the shaft 22 compressor wheel is rotatably received. The first compressor 20 serves to compress air to be supplied to the internal combustion engine.

In addition, the exhaust system comprises a second exhaust gas turbocharger 24, which also has a second turbine 26 arranged in the exhaust gas tract 14. Also, the second turbine 26 includes a turbine housing in which a rotatably connected to a further shaft 28 of the second exhaust gas turbocharger 24 turbine wheel is rotatably received. The second exhaust gas turbocharger 24 includes a second compressor 30 with a compressor housing, in which a with the other shaft 28 rotatably connected compressor wheel is rotatably received. Also by means of the second compressor 30 of the internal combustion engine to be supplied air is compressible. The first compressor 20 and the second compressor 30 can be driven by the respectively corresponding first turbine 16 and the second turbine 26. The first turbine 16 and the second turbine 26 are drivable as a result of exhaust gas passed over them. With the exhaust gas, the turbine wheels are acted upon and thereby driven, so that via the shaft 22 and the further shaft 28, the compressor wheels of the first and second compressor 20 and 30 are driven.

The exhaust system further comprises an exhaust gas catalytic converter 50, which according to the invention has a first catalytic converter part 50a and a downstream second catalytic converter part 50b. The exhaust gas catalyst 50 is preferably followed by one or more of the exhaust gas purification exhaust aftertreatment components, which is not shown in detail. This may be, for example, a particulate filter and / or an SCR catalytic converter and / or a nitrogen oxide storage catalytic converter. The catalytic converter 50 is preferably designed as a starting catalyst arranged close to the engine in the manner of an oxidation catalytic converter or a three-way catalytic converter, the two catalytic converter parts 50a, 50b being present in a common housing are arranged. It is preferred if the second catalyst part 50b is arranged at a small distance from the first catalyst part. As a result of such a close

In the adjacent arrangement, thermal radiation emanating from the inlet side of the second catalyst part 50b can reach the upstream first catalyst part 50a with little loss and, if necessary, warm it up. It is also preferred if the catalyst parts 50a and 50b are dimensioned approximately the same. The second

However, catalyst portion 50b may be made slightly smaller than the first catalyst portion 50a to be about 30% of the volume of the entire catalytic converter 50. As a result, an improved starting behavior is optionally possible.

In order to be able to supply the exhaust gas of the internal combustion engine to the first turbine 16, the second turbine 26 and / or the exhaust gas catalytic converter 50, a line arrangement with one of a plurality of exhaust gas lines 32, 34, 36, 38, 40 and 42 is provided, through which exhaust gas can flow are.

An exhaust manifold 44 of the internal combustion engine collects the exhaust gas flowing from combustion chambers, in particular cylinders, of the internal combustion engine, which is further supplied to the exhaust pipe 32 which is fluidically connected to the exhaust manifold 44.

The first turbine 16 is fluidly connected on the input side to the exhaust pipe 34, which in turn is fluidically connected to the exhaust pipe 32 at a junction 48. On the output side, the first turbine 16 is fluidically connected to the exhaust pipe 40, so that the exhaust gas flowing through the first turbine 16 can be discharged from the first turbine 16 and directly to the second catalyst part 50b.

The second turbine 26 is fluidly connected on the input side with the exhaust pipe 36 so that exhaust gas of the internal combustion engine can also be routed directly to the second turbine 26. On the output side, the second turbine 26 is connected to the exhaust pipe 42, discharged by means of which exhaust gas from the second turbine 26 and the first

Catalyst part 50a can be passed.

In order to be able to realize various operating states, the line arrangement comprises a control valve 52, which is arranged in the exhaust line 36, and a valve 54, which is arranged in the exhaust line 40. The control valve 52 and the valve 54 are adjustable between a closed position fluidically blocking the exhaust pipe 36 and 40 and a release position fluidically releasing the exhaust pipe 36 or 40, so that exhaust gas in the release position, the exhaust pipe 36 and 40 can flow through or in the closed position, the exhaust pipe 36 and 40 can not flow through.

In addition, it is possible, in particular the valve 54 and / or optionally the control valve 52 to switch at least one intermediate division, in which a

Flow cross section of the exhaust pipe 36 and 40 by means of the control valve 52 and the valve 54 is shown, which is greater than in the closed position, however, lower than in the release position. In other words, this means that the exhaust gas in the intermediate position can flow through the exhaust pipe 36 or 40, but over a smaller cross-section than in the release position, so that it can flow through the exhaust pipe 36 and 40 against the release position throttled.

As can be seen from FIG. 1, the exhaust gas line 38 is fluidly connected at one connection point 53 to the exhaust gas line 40, wherein the connection point 53 is arranged downstream of the first turbine 16 and upstream of the valve 54. On the other hand, the exhaust pipe 38 is fluidly connected to the exhaust pipe 36 at a joint 56, the joint 56 being located downstream of the control valve 52 and upstream of the second turbine 26. Depending on the degree of opening of the valve 54, exhaust gas conducted via the first turbine 16 thus passes directly to the second catalyst part 50b or directly to the second turbine 26.

Air ducts 58, 60, 62, 64 and 66 disposed in the intake duct 18 serve to supply air to be compressed to the first compressor 20 and the second compressor 30 and to discharge compressed air therefrom.

On the one hand, the air line 58 is connected to an air filter 68 arranged in the intake tract 18, by means of which air sucked in by the internal combustion engine is to be filtered. On the other hand, the air line 58 is fluidly connected to the second compressor 30, so that the second compressor 30 via the air line 58 to be compressed air filtered can be supplied. On the output side, the second compressor 30 is connected to the air line 60 in order to remove the compressed air from this. The air line 60 is further fluidly connected to a charge air cooler 72. By means of the charge air cooler 72, the air heated as a result of the compression is cooled in order to increase the degree of charging.

The first compressor 20 is connected on the input side to the air line 64 in order to be able to feed filtered air to the compressor 20. On the output side is the first compressor 20 connected to the air line 66 in order to discharge the compressed air from the first compressor 20 of this can.

The air line 62 is fluidly connected on the one hand at a connection point 74 fluidly with the air line 58 and on the other hand at a connection point 76 with the air line 60. At the junction 76 and the air line 64 is fluidly connected to the air line 60. To illustrate different operating conditions, the intake manifold 18 further includes a presently designed as a self-regulating check valve valve 78, which is arranged in the air line 62 between the connection point 74 and the connection point 76. In addition, a presently also designed as a self-regulating non-return valve further valve 80 is provided, which is arranged in the air line 60. The check valve 80 is arranged downstream of the connection point 76 and upstream of a further connection point 82 to which the air line 66 is fluidically connected to the air line 60. The check valves 78 and 80 are thereby self-regulating between an air line 62 and 60 fluidly obstructing closed position and a fluid line 62 and 60 fluidly releasing release position actuated by the applied differential pressure or adjustable.

In the present case, the first turbine 16 has a so-called variable turbine geometry and is thereby adaptable to different operating points of the internal combustion engine, that is, to different mass flows of the exhaust gas flowing through the exhaust gas tract 14. By means of the variable turbine geometry can be an effective

Flow cross section of the first turbine 16 is set, d. H. be enlarged and reduced in contrast.

In the present case, the second turbine 26 has a fixed turbine geometry. The second turbine 26 is, as shown schematically in FIG. 1, designed to be larger in terms of their effective flow cross-section and designed for particularly large mass flows of the exhaust gas tract 14 flowing through the exhaust gas. Accordingly, the turbine wheel has a higher inertia compared to the inertia of the turbine wheel of the first turbine 16, but due to its compared to the first turbine 16 larger flow cross section, a lower flow resistance for the exhaust gas than the first turbine 16. In contrast, the first turbine 16 has the advantage on that their turbine wheel has a lower inertia than the turbine wheel of the second turbine 26 and, accordingly, is faster to accelerate, which is particularly advantageous at lower mass flows of the exhaust gas. The operation of the exhaust gas system according to the invention is explained in more detail below with reference to FIGS. 2 to 6 for different operating states. This is without

From the general point of view, it is assumed that starting from a cold state of the internal combustion engine and of the exhaust system, the internal combustion engine is raised in terms of its output from low values to nominal power, so that the entire load range is covered. For this purpose, reference is initially made to FIG. 2, in which the system shown in FIG. 1 is supplemented by flow arrows corresponding to an operating state with a low load or exhaust gas temperature.

In this operation, referred to below as the first operating state, which ranges from idling to a low load of approximately 30% to 40% of the rated load and comparatively low rotational speeds, exclusively or almost exclusively the first exhaust gas turbocharger 12 is in operation. Thus, a compression of the internal combustion engine supplied combustion air only by means of the first compressor 20. In this first operating state, the control valve 52 is in its closed position, while the valve 54 is in its release position. In this operating state, the exhaust gas from the exhaust manifold 44 flows into the exhaust pipe 32 according to the directional arrow 46 and flows through the closed control valve 52 on the junction 48 in the exhaust pipe 34 according to a directional arrow 84 and the first turbine 16, whereby the turbine of the first turbine 16 and thus the compressor wheel of the first compressor 20 is driven. After flowing through the first turbine 16, the exhaust gas flows further into the exhaust pipe 40 according to a directional arrow 86. The exhaust pipe 40 passes the exhaust gas via the open valve 54 according to a direction arrow 88 to the second catalyst part 50b.

Due to the given pressure gradient, the exhaust gas does not flow or only a very small part of the exhaust gas from the exhaust pipe 40 via the connection point 53 into the exhaust pipe 38, so that the second turbine 26 is not driven by the exhaust gas. This means that only the first exhaust gas turbocharger 12 with the first turbine 16 is active while the second exhaust gas turbocharger 24 with the second turbine 26 is inactive.

Thus, the entire exhaust gas supplied by the internal combustion engine, or at least its predominant over the first turbine 16 passes directly to the second catalyst part 50b, which is heated from a cold state. Since only the second catalyst part 50b, typically comprising about half or a smaller part of the total volume of the catalytic converter 50, has the Exhaust gas of the internal combustion engine is applied, despite an according to the low load of the internal combustion engine low exhaust gas temperature is still effective and rapid warming of the second catalyst portion 50b. Another advantage that is particularly important for the low loads in the first operating state is the reduced pressure loss compared to a flow through the entire exhaust gas catalytic converter 50.

On the side of the intake tract 18, the check valve 80 is in its closed position, while the check valve 78 is in its open position. Thereby, the air flows from the air filter 68 according to a direction arrow 70 in the air line 58 and due to the closed check valve 80 and the inactive second

Exhaust gas turbocharger 24 via the junction 74 in the air line 62 and on the open check valve 78 according to a direction arrow 90 to the first compressor 20, which is driven by the first turbine 16 and by means of which the air is compressed. After the first compressor 20 has compressed the air, it continues to flow according to a directional arrow 92 to the connection point 82, flows into the air line 60 downstream of the check valve 80 and according to a directional arrow 94 to the charge air cooler 72nd

In this first operating state, therefore, the air can be compressed particularly efficiently even at low loads and / or rotational speeds and at low mass flows of the exhaust gas, since the first turbine 16, as described, can be driven particularly well under these conditions. Preferably, at such low speed and / or load ranges of the internal combustion engine by means of the variable turbine geometry of the first turbine 16, an effective flow cross section of the first turbine 16 is set, which is lower compared to a variable by means of the variable turbine geometry maximum flow cross-section. So there is a throttled operation of the first turbine 6, in which they also with very low mass flows of

Exhaust gas is particularly good drivable.

The conditions when increasing the power output and thus increasing temperature of the exhaust gas emitted by the internal combustion engine of a second operating state are outlined in FIG. 3. In the second operating state, which may also be referred to as a transitional state or intermediate region with an exhaust gas temperature or load of approximately 40% to 50% of the nominal load and typically increased average rotational speed, the first exhaust gas turbocharger 12 is in operation and the second exhaust gas turbocharger 24 is located in a start-up state with about 0% to 20% of its rated speed. In the second operating state, the control valve 52 remains in its exhaust line 36 fluidly obstructing the closed position. Also, the check valve 78 remains in its release position, and the check valve 80 remains in its closed position.

In contrast to the first operating state described with reference to FIG. 2, the valve 54 is transferred into its intermediate position so that exhaust gas can only flow through the exhaust gas line 40 in a throttled manner. This causes a higher resistance to the exhaust gas compared to the first operating state, which causes a portion of exhaust gas led via the first turbine 16 to flow via the connection point 53 from the exhaust gas line 40 into the exhaust gas line 38 in accordance with a directional arrow 96. The complementary, typically larger proportion of the exhaust gas delivered by the internal combustion engine as a whole and guided via the first turbine 16 continues to pass directly from the first turbine 16 to the second catalytic converter part 50b.

Exhaust flowing into the exhaust conduit 38 continues to flow via the connection point 56 into the exhaust conduit 36 and into the second turbine 26, whereby the second turbine 26 or its turbine wheel can be driven and started up. After flowing through the second turbine 26, the exhaust gas flows according to a directional arrow 98 into the exhaust pipe 42, by means of which the exhaust gas to the first catalyst part 50 a and after its

Flow through the second catalyst portion 50b is passed. Typically, at least the second catalytic converter part 50b is already so active that the entire exhaust gas supplied by the internal combustion engine and conducted via the second catalytic converter part 50b is catalytically cleaned in accordance with the cleaning function of the catalytic converter 50. The second catalyst part 50b is further heated, in particular by the exhaust gas, which is supplied to it directly from the first turbine 16 and now significantly hotter. The first catalyst part 50 a is warmed up by the exhaust gas supplied to it by the second turbine 26. In addition, the first catalyst part 50a is heated up by thermal radiation emanating from the second catalyst part 50b arranged close to it. As a result, an effective heating of the entire catalytic converter 50 is made possible.

In the second operating state, the variable turbine geometry of the first turbine 16 is preferably set such that it has a larger flow cross section than the first operating state. This has the advantage that the enlarged flow cross section is not an undesirably large flow resistance for the larger mass flow of the exhaust gas, as for example in a In contrast, smaller and preferably present in the first operating state flow cross section would be the case.

By this transitional operating state, it is possible to gradually start the second turbine 26 and thus the second exhaust gas turbocharger 24 and bring it to speed without an undesirably abrupt transition before a first to another operating state is given. However, it should be noted that even in the transition state of the internal combustion engine supplied combustion air is completely or at least for the most part only by means of the first compressor 20 is compressed. The second compressor 30 contributes in this transition state not or only slightly to the compression of the combustion air.

The conditions with a further increase in the power output and thus further increasing temperature of the exhaust gas emitted by the internal combustion engine of a third operating state are outlined in FIG. 4. In this operating state with compared to the second operating state further increased exhaust gas temperature or load of about 50% to 60% of the rated load and typically further increased speed, a two-stage serial compression of the combustion air through the first compressor 20 and the second compressor 30 is given. The control valve 52 is still in its closed position while the valve 54 is in its intermediate position. Thus, analogous to the first and the second operating state, the entire exhaust gas supplied by the internal combustion engine flows via the first turbine 16. The variable turbine geometry of the first turbine 16 has a larger flow cross-section than in the first operating state. Likewise, it can be provided that the variable turbine geometry is maximally open to display a maximally adjustable effective flow cross section of the first turbine 16.

Typically, the degree of opening of the valve 54 is reduced relative to the second operating state and a correspondingly reduced proportion of the exhaust gas conducted via the first turbine 16 is led via the exhaust gas line 40 according to the directional arrows 86, 88 directly to the second catalyst part 50b. As a result, an undesirably high, in particular thermal loading of the second catalyst part 50b is avoided. The complementary, typically larger share of the

Internal combustion engine discharged altogether and guided over the first turbine 16 exhaust gas passes through the exhaust pipe 38 to the second turbine 26. Thus, a run-up of the second exhaust gas turbocharger 24 and the second turbine 26 and the turbine wheel has a significant speed, so that thereby driven second compressor 30 can contribute to the compression of combustion air to a considerable extent. A catalytic exhaust gas purification by the catalytic converter 50 can be done easily, since it is fully active and for the greater part of the total exhaust gas flow, the full catalyst volume is available.

In contrast to the previous operating states, however, now the check valves 78 and 80 are set in their closed positions. This causes the air now does not flow into the air line 62 via the connection point 74, but according to a directional arrow 100 flows via the air line 58 to the second compressor 30 and flows into it. After the second compressor 30 has compressed the air, it continues to flow according to a directional arrow 102 through the air line 60 and flows due to the closed check valve 80 via the junction 76 in the air line 64 according to a direction arrow 90 and the first compressor 20 of the first exhaust gas turbocharger 12 supplied.

In the third operating state shown in FIG. 4, the combustion air is thus first through the second compressor 30 as a first stage and then through the serially connected to the second compressor 30 and in the flow direction of

Combustion air through the intake duct 18 downstream of this arranged first

Compressor 20 as a second stage two stages successively compressed.

In this operating state, not only the first compressor 20 and the second one

Compressor 30 but, as in the transitional operating state shown in FIG. 3, and the first turbine 16 and the second turbine 20 connected in series with each other. This means that exhaust gas first flows through first turbine 16 and then subsequently through second turbine 26. Thus, this exhaust gas is first expanded by the first turbine 16 and then again by the second turbine 26. Since the exhaust gas upstream of the first turbine 16 has a higher pressure than upstream of the second turbine 26 and downstream of the first turbine 16, the first turbine 16 in such operating conditions as a high-pressure turbine and thus the first exhaust gas turbocharger 12 as a high-pressure exhaust gas turbocharger and the second Turbine 26 as a low-pressure turbine and thus the second exhaust gas turbocharger 24 referred to as a low-pressure exhaust gas turbocharger. It should be noted that the second turbine 26 and its turbine wheel as in the second operating state of FIG. 3 still in a so-called start-up or

Start-up phase is in which the second turbine 26 and the corresponding turbine wheel is still accelerated in terms of its speed. In the case of further increasing the loads and / or the rotational speeds of the internal combustion engine proceeding from the operating state described with reference to FIG. 4, a further, fourth operating state becomes active, which is explained below with reference to FIG.

In this operating state, which may also be considered as a transient condition with an associated typically relatively narrow power band of about 65% of the rated load, the control valve 52 is in its closed position. The entire exhaust gas supplied by the internal combustion engine is conducted via the first turbine 16. In this case, the variable turbine geometry of the turbine 16 is preferably at its maximum adjustable, d. H. set the maximum effective flow area, so that it is not undesirable high flow resistance for the increased mass flow of the exhaust gas associated with the increased speeds and / or loads.

In contrast to the operating states explained above, the valve 54 is now in its closed position, so that exhaust gas can not flow through the exhaust gas line 40. The entire exhaust gas supplied by the internal combustion engine thus passes from the first turbine 16 on via the exhaust pipe 38 in accordance with the

Directional arrow 96 to the second turbine 26. In this case, the speed of the second turbine 26 and the rotational speed of the corresponding turbine wheel increases further in the direction of rated speed. The first exhaust gas turbocharger 12 and the second exhaust gas turbocharger 24 are therefore operated or switched on the exhaust side or on the turbine side in series, resulting in a particularly good power development of the internal combustion engine. As a result of the closed valve 54, the now further increased in terms of quantity and temperature exhaust gas flow passes completely through the exhaust pipe 42 according to the directional arrow 98 to the input side of the first catalyst part 50a. Thus, the entire volume of the catalytic converter 50 is used for exhaust gas purification. This allows a particularly good cleaning effect, since an overload of the second catalyst part 50b is avoided.

The check valve 78 is, however, due to differential pressure in its closed position, while the check valve 80 is in its open position. The entire combustion air supplied to the internal combustion engine is first fed via the air line 58 to the second compressor 30, through which the

Combustion air is compressed. Subsequently, a typically larger part of the already compressed combustion air flows via the air line 60 to the charge air cooler 72 according to a directional arrow 106. A typically smaller proportion of the combustion air compressed by the second compressor 30 passes through junction 76 and the air duct 64 to the first compressor 20, through which it is further compressed and according to the directional arrow 92 through the air duct 66 and via the junction 82nd flows into the air line 60 and according to the directional arrow 94 as well to the intercooler 72nd

Thereby, a parallel operation of the first compressor 20 and the second compressor 30 is shown, which compress combustion air at the same time. The turbines 16 and 26, however, are still connected in series with one another and exhaust gas flows through them in succession. Both exhaust gas turbochargers, the first exhaust gas turbocharger 12 and the second exhaust gas turbocharger 24 are active. As a result of this compressor circuit a particularly good power delivery of the internal combustion engine is possible.

Upon further increase of the load or the power and / or the speed of the

Internal combustion engine enters this in or near the full load range with typically at least 70% of the rated power and there is another, fifth operating state active, which is explained with reference to FIG. 6 below.

In this fifth operating state, the valve 54 remains in its closed position, whereas the control valve 52 is adjusted in its release position. Of the

Internal combustion engine discharged exhaust gas therefore largely bypasses the first turbine 16 and flows in particular due to given pressure gradients on the exhaust pipe 36 and the open control valve 52 at least substantially directly to the second turbine 26 and drives them. In this fifth operating state, a particularly high power and a particularly high torque can be represented, since the second turbine 26, which is larger, in particular in terms of its dimensions, and in particular its flow cross section, in relation to the first turbine 16 is solely active and is driven by the exhaust gas. The exhaust gas does not have to flow in a comparatively small flow cross-section of the first turbine 16 in relation to the second turbine 26 in such full-load areas or full-load-related operating areas, which would represent an undesirably high flow resistance.

Analogous to the fourth operating state, the entire exhaust gas of the internal combustion engine reaches via the exhaust pipe 42 according to the directional arrow 98 to the input side of the first catalyst part 50a. Thus stands for the high exhaust gas mass flow of fifth operating state, the entire volume of the exhaust catalyst 50 for exhaust gas purification available.

On the side of the intake tract 18, the check valve 78 remains in its closed position, while the check valve 80 remains in its open position. Thus, the first compressor 20 is at least substantially bypassed and there is now a compression of the entire internal combustion engine combustion air supplied at least substantially only by means of the second compressor 30 and no longer and / or additionally by the compressor 20, as in the operating conditions according to Figures 4 and 5 is the case. In the fifth operating state thus takes place

Compression of the combustion air as well as in the first operating state only by a single exhaust gas turbocharger. In contrast to the first operating state according to FIG. 2, however, the compression of the air is now effected not by the first compressor 20 of the first, smaller exhaust gas turbocharger 12, but by the second compressor 30 of the larger, more powerful second one assigned to the second turbine 26

Exhaust gas turbocharger 24.

As can be seen from Figures 1 to 6, the exhaust system is particularly flexible adaptable to different operating conditions of the engine and the catalytic converter and has a particularly good and low response, so at operating point transitions, the so-called turbo lag is at least substantially avoided and the internal combustion engine at least can advantageously be supplied with compressed air almost in their entire map. This is beneficial to the driving behavior of the internal combustion engine, since at least virtually all of the characteristic map desired performances and / or torques are to be realized. This means in particular a very good adaptability of the driving behavior of the internal combustion engine to different driving situations such as driving in city traffic or over land. In terms of exhaust gas cleaning results in a particularly rapid onset, which is a particularly low-emission cold start and warm-up is possible.

Of course, additional and / or other valve devices than those shown in FIGS. 1 to 6 may be provided to realize the described operating conditions. Another arrangement is possible. For example, upstream of the first turbine 16, a valve device, in particular a self-regulating

Provided check valve. Furthermore, it is possible to use a valve acting as a wastegate downstream of the first turbine 16 and upstream of the second turbine 26, to regulate the boost pressure. Alternatively or additionally, it is possible for the first turbine 16 and / or the second turbine 26 to be assigned a valve acting as a wastegate. It goes without saying that the valves, control valve and check valve, are adjustable or can be configured self-regulating.

It is further understood that the illustrated system can also be constructed analogously in a double embodiment, in order to process exhaust gases from two cylinder groups separately from one another or to supply them combustion air separately from one another.

Claims

claims

1. exhaust system of an internal combustion engine, comprising

- A first exhaust gas turbocharger (12) with a first exhaust gas of the

Internal combustion engine drivable turbine (16), and

- A second exhaust gas turbocharger (24) with a second, of exhaust gas of the

Internal combustion engine drivable turbine (26), and

- An exhaust gas catalyst (50), as well

- A valve-controlled line arrangement, with which exhaust gas of the

Internal combustion engine via the first and / or the second turbine (16; 26) is conductive,

characterized in that

- The exhaust catalyst (50) comprises a first catalyst part (50 a) and a downstream with respect to the exhaust gas flow direction second catalyst part (50 b), and

- A depending on the temperature of the exhaust gas supplied by the internal combustion engine and / or a determined in dependence on a power output of the internal combustion engine portion of passed through the first turbine (16) exhaust gas directly to the second catalyst part (50b) is conductive.

2. Exhaust system according to claim 1,

characterized in that

Exhaust gas of the internal combustion engine can only be conducted via the first turbine (16) or via the first and the second turbine (16; 26) or only via the second turbine (26).

3. Exhaust system according to claim 1 or 2,

characterized in that Exhaust gas conducted via the second turbine can be fed to the first catalyst part (50a).

4. Exhaust system according to one of claims 1 to 3

characterized in that

the conduit arrangement controls a bypass line for the first turbine (16) controlled by a first valve (52) and a valve controlled by a second valve (54)

Connecting line (40), with which exhaust gas from the first turbine (16) directly to the second catalyst part (50b) is conductive.

5. Exhaust system according to one of claims 1 to 4

characterized in that

the exhaust gas catalytic converter (50) is designed as a starting catalytic converter arranged close to the engine.

6. Exhaust system according to one of claims 1 to 5

characterized in that

the first catalyst part (50a) and the second catalyst part (50b) are arranged at a short distance in a common housing.

7. Exhaust system according to one of claims 1 to 6

characterized in that

the first exhaust gas turbocharger (12) is dimensioned smaller than the second

Exhaust gas turbocharger (24).

8. A method of operating an exhaust system of an internal combustion engine having a first and a second exhaust gas turbocharger (12, 24)

A supercharger and an exhaust gas catalytic converter (50) having a first catalyst part (50a) and a second catalytic converter part (50b) connected downstream of the exhaust gas flow direction, one depending on the temperature of the exhaust gas supplied by the internal combustion engine and / or one depending on a power output the combustion engine, certain proportion of exhaust gas led via the turbine (16) of the first exhaust gas turbocharger (12) is conducted directly to the second catalyst part (50b).

9. The method according to claim 8,

characterized in that the proportion of exhaust gas conducted via the turbine (16) of the first exhaust-gas turbocharger (12), which is not conducted directly to the second catalytic-converter part (50b), is conducted via the turbine (26) of the second exhaust-gas turbocharger (24).

10. The method according to claim 9,

characterized in that

Exhaust gas conducted via the first catalyst part (50a) is conducted completely via the second catalyst part (50b).