DE102019209792A1 - System and procedure for exhaust gas aftertreatment - Google Patents

Abstract

A system for exhaust gas aftertreatment comprises a close-coupled catalytic converter, which is designed to carry out a catalytic treatment of exhaust gas that originates from an internal combustion engine; an underfloor catalyst which is configured to receive the exhaust gas from the close-coupled catalyst and to perform a catalytic treatment of the obtained exhaust gas; and a heat exchange system configured to exchange heat between the close-coupled catalyst and the underfloor catalyst by means of a heat exchange fluid.

Description

Technical area

The present invention relates to a system for exhaust gas aftertreatment, particularly during the operation of an internal combustion engine of an automobile, for example a diesel engine. The present invention also relates to a method for exhaust gas aftertreatment.

background

A catalytic converter is an exhaust gas purification device that converts toxic gases and pollutants in the exhaust gas of an internal combustion engine into less toxic or non-toxic substances and / or filters such substances from the exhaust gas flow. Catalysts are used in particular in internal combustion engines that run on either gasoline or diesel.

Selective catalytic reduction (SCR) is a well-known technique that is used in catalytic converters, in which nitrogen oxides, so-called NOx, are converted into diatomic nitrogen and water with the aid of a catalytic converter. A gaseous and / or liquid reducing agent, e.g. anhydrous ammonia, aqueous ammonia or urea, is added to an exhaust gas stream and adsorbed on the catalyst.

SCR converters need a certain temperature in order to function properly, so that the catalytic reaction is typically only initiated above a so-called start temperature (“light-off temperature”). Normally the SCR is heated by the exhaust gases flowing through it. It therefore takes a relatively long time for the SCR converter to be heated up, in particular during a cold start, and thus for NOx emissions to be effectively reduced.

Manufacturers have addressed this shortcoming by introducing so-called close-coupled catalytic converters, which move the catalytic converter bracket in the vehicle's exhaust system from an underfloor location to an under-hood location to be closer to the engine's exhaust manifold, thereby reducing the time it takes to run the catalyst needs to reach the starting temperature. The pamphlet US 2008/0078165 A1 describes such a close-coupled catalyst.

In order to meet the strict requirements for NOx emissions due to the latest emissions legislation, work is being carried out on improving the general thermal management of catalytic converters in order to ensure effective emission reduction over a wide temperature range. In addition to the low temperature range, very high engine temperatures can also cause difficulties, as temperatures above 500 ° C, e.g. due to high engine loads, can lead to a deterioration in the SCR efficiency.

Summary of the invention

Thus there is a need to find solutions to operate catalysts more efficiently.

To this end, the present invention provides a system according to claim 1 and a method according to claim 8.

According to one aspect of the invention, a system for exhaust gas aftertreatment comprises a close-coupled catalytic converter which is designed to carry out a catalytic treatment of exhaust gas originating from an internal combustion engine; an underfloor catalyst which is configured to receive the exhaust gas from the close-coupled catalyst and to carry out a catalytic treatment of the exhaust gas obtained; and a heat exchange system configured to exchange heat between the close-coupled catalyst and the underfloor catalyst by means of a heat exchange fluid.

According to a further aspect of the invention, a method for exhaust gas aftertreatment comprises carrying out a catalytic treatment of exhaust gas with a catalytic converter close to the engine, the exhaust gas originating from an internal combustion engine; Obtaining the exhaust gas with an underfloor catalyst from the close-coupled catalyst and carrying out a catalytic treatment of the obtained exhaust gas with the underfloor catalyst; and exchanging heat between the close-coupled catalyst and the underfloor catalyst using a heat exchange fluid of a heat exchange system.

According to a further aspect of the invention, a motor vehicle with an internal combustion engine and a system for exhaust gas aftertreatment according to the invention is provided.

One idea of the present invention is to couple two separate catalytic converters via a sophisticated and demand-driven heat management system based on a heat exchange fluid, which transfers heat from one catalytic converter to the other in order to improve the efficiency and / or the effectiveness of the overall system. Any suitable liquid and / or gas can be used as the heat exchange fluid so long as the necessary properties are provided for efficient and effective heat transfer between the catalysts will. In order to transport heat via the fluid, a flow control device, such as a pump or the like, can be provided between the catalytic converters, which can be controlled as required in order to adjust the rate of heat transfer.

The above-mentioned thermal management and the fact that one of the catalytic converters is located near the engine enables sufficient exhaust gas temperatures in front of the catalytic converter system for good catalytic converter efficiency under low exhaust gas temperature conditions (e.g. engine start, low load city driving). In addition, the system is able to avoid hot spots, e.g. above 500 ° C, which can lead to a deterioration in the converter efficiency at high engine loads by transferring excess heat from the catalytic converter close to the engine to the underbody catalytic converter. Heat transfer from the catalytic converter close to the engine to the underfloor catalytic converter can also be generally advantageous at higher engine loads if the underfloor catalytic converter is still too cold for efficient NOx conversion. Likewise, in certain cases, the heat from the underbody catalytic converter can be transferred back to the catalytic converter close to the engine.

As a result, the operating efficiency of the catalyst system at low temperatures and at high temperatures is improved. However, even at medium temperatures, the heat energy can be shared by the two catalysts in order to improve efficiency and effectiveness.

It should be understood that the term "vehicle" or other similar term used herein includes motor vehicles in general, such as passenger cars including sport utility vehicles (SUV), buses, trucks, various commercial vehicles and the like, and hybrid vehicles, electric vehicles, plug-in vehicles -Hybrid electric vehicles, hydrogen-powered vehicles and vehicles that run on alternative fuels (e.g. fuels obtained from resources other than petroleum). In the present case, a hybrid vehicle is understood to mean a vehicle which has two or more energy sources, for example both gasoline-powered and electrically powered vehicles.

Advantageous refinements and developments emerge from the subclaims.

According to a further development of the invention, the system can furthermore comprise a control unit which is designed to control a flow of the heat exchange fluid between the close-coupled catalytic converter and the underbody catalytic converter in such a way that both catalytic converters are operated with an optimized combined operating efficiency for a predetermined engine operating state. The method can accordingly include regulating a flow of the heat exchange fluid between the close-coupled catalytic converter and the underfloor catalytic converter with a control unit such that both catalytic converters are operated with an optimized combined operating efficiency for a predetermined engine operating state.

Thus, heat can be transferred from one catalyst to the other in order to achieve the highest emission reduction efficiency for the combined system of both catalysts. For example, there can be enough energy on the close-coupled catalytic converter to give off heat to the underbody catalytic converter. By transferring this excess heat, the efficiency of the latter can be increased in certain driving situations and / or engine operating states.

According to a development of the invention, the system can furthermore comprise a first temperature sensor which is arranged upstream of the catalytic converter close to the engine in order to measure an engine outlet temperature of the exhaust gas. The system may further include a second temperature sensor, which is arranged downstream of the close-coupled catalyst and upstream of the underfloor catalyst to measure an exhaust pipe temperature of the exhaust gas. The control unit can be designed to control the flow of the heat exchange fluid on the basis of the measured temperatures. The method may accordingly include measuring an engine outlet temperature of the exhaust gas with a first temperature sensor upstream of the close-coupled catalyst and measuring an exhaust pipe temperature of the exhaust gas with a second temperature sensor downstream of the close-coupled catalyst and upstream of the underfloor catalyst.

For this purpose, the system can use temperature sensors that are already provided by the catalytic converters. Additionally or alternatively, the system can use sensors that are specially designed for this task. The control unit can be communicatively coupled to the temperature sensors as well as to a flow control device, for example a pump, in order to control the fluid flow between the catalytic converters. The control unit can comprise a computing unit, for example a microprocessor or the like, and / or be coupled to such a device, so that advanced and complex control strategies for the optimal operation of the catalytic converter system can also be designed and executed. For this purpose, the control unit can be coupled to and / or part of an engine controller and / or an engine control device, which the Control unit supplied with information about the current engine operating state and / or the current driving situation. In addition, the system can be coupled to a supported and / or autonomous driving unit of the vehicle, which can also supply the system with driving history and / or further driving data that can be taken into account when determining the control strategy for the heat exchange system.

According to a development of the invention, the control unit can be designed to control the flow of the heat exchange fluid in such a way that heat is transferred from the catalytic converter close to the engine to the underbody catalytic converter in the event that the engine operating state includes high-load driving.

Thus, in one possible control mode of the heat exchange system, heat can be transferred from the catalytic converter close to the engine to the underbody catalytic converter. In one example, the close-coupled catalyst may already be warmed up and fully functional within an efficient operating range so that excess thermal energy can be transferred to the underbody catalyst to improve its efficiency, e.g. if it has not yet reached its starting temperature and / or its optimal temperature. In a further example, the temperature of the exhaust gas in front of the close-coupled catalytic converter can be too high, e.g. when driving in town, driving on the motorway, driving uphill etc. In this case, the temperature of the exhaust gas and the close-coupled catalytic converter can be reduced quickly by transferring part of the available heat to the underbody catalytic converter will. A deterioration in efficiency due to overheating of the catalytic converter close to the engine can thereby be avoided. At the same time, the underbody catalytic converter can be operated at a more efficient operating point.

According to a development of the invention, the control unit can be designed to regulate the flow of the heat exchange fluid in such a way that heat is transferred from the underbody catalytic converter to the close-coupled catalytic converter in the event that the engine operating state changes from high-load driving to at least one of low-load driving, idling and one Motor-off phase includes.

Thus, in a further possible control mode of the heat exchange system, heat can be transferred from the underbody catalytic converter to the catalytic converter close to the engine. In one example, the close-coupled catalytic converter can be prevented from cooling down rapidly by using energy that is already stored in the underbody catalytic converter. This can be used, for example, every time the vehicle changes operation, in which it switches from high-load driving to idling and / or low-load driving. Even when the internal combustion engine is switched off, e.g. in an electric driving mode of a hybrid vehicle, energy could be transferred from the underbody catalytic converter. The heat can thus be used to keep the close-coupled catalytic converter at a suitable temperature, e.g. above its start temperature.

According to a development of the invention, the control unit can be designed to control the flow of the heat exchange fluid in such a way that no heat is transferred from the close-coupled catalytic converter to the underbody catalytic converter in the event that the engine operating state includes at least one of an engine warm-up phase and low-load driving.

If, for example, the engine is operated at low exhaust gas temperatures in an engine warm-up mode (e.g. a cold start) or during a city trip or similar, the entire available exhaust gas energy can be held by the catalytic converter close to the engine in order to bring it into the efficient operating range as quickly as possible and / or stop there.

The present invention is explained in more detail below with reference to the exemplary embodiments specified in the schematic figures.

Figure list

• 1 zeigt schematisch ein Kraftfahrzeug mit einem System zur Abgasnachbehandlung gemäß einer Ausführungsform der Erfindung.
• 2 zeigt ein Flussdiagramm eines Verfahrens zur Abgasnachbehandlung mit dem System aus 1.
• 3 bis 5 zeigen beispielhafte Betriebsmodi des Systems aus 1.

The accompanying figures are intended to provide a further understanding of the invention and form part of the present disclosure. They illustrate embodiments of the invention and, together with the description, serve to explain principles and concepts of the invention. Other embodiments of the invention and many of the recited advantages of the invention will become apparent in view of the following detailed description. The elements of the drawings are not necessarily shown to scale with one another. In the figures, the same reference symbols denote the same or functionally identical elements, unless otherwise stated.

• 1 shows schematically a motor vehicle with a system for exhaust gas aftertreatment according to an embodiment of the invention.
• 2 FIG. 4 shows a flow diagram of a method for exhaust gas aftertreatment with the system from FIG 1 .
• 3 to 5 show exemplary operating modes of the system 1 .

While specific embodiments are illustrated and described herein, it will be apparent to those skilled in the art that a variety of alternative and / or equivalent implementations may replace the specific exemplary embodiments illustrated and described without departing from the scope of the present invention. In general, the application covers any adaptations or variations of the specific exemplary embodiments described herein.

Detailed description of the exemplary embodiments

1 shows schematically a motor vehicle 100 with one system 10 for exhaust gas aftertreatment according to one embodiment of the invention. 2 shows a flow diagram of a method M. for exhaust aftertreatment with the system 10 out 1 . 3 to 5 show exemplary operating modes of the system 10 out 1 .

The system 10 is designed to exhaust gas 8th to clean which of the internal combustion engine 101 , for example a diesel engine, of the motor vehicle 100 is expelled. For this purpose the system includes 10 a range of exhaust aftertreatment systems including a close-coupled catalytic converter 1 and an underbody catalytic converter 2 . It is understood, however, that the system 10 could have additional catalytic converters, eg diesel particulate filters and so on. The catalysts 1 , 2 are designed in this specific embodiment as devices for selective catalytic reduction (SCR), which the exhaust gas 8th Can treat in the usual way by adding gaseous and / or liquid reducing agent to the exhaust gas 8th is injected, which acts as a reducing agent in the catalytic process inside the catalytic converters 1 , 2 serves. For example, the catalysts 1 , 2 comprise a catalytically active substrate which is arranged between an input surface and an output surface (not shown). The substrate can, for example, comprise a ceramic monolith in the usual way, for example with a honeycomb structure which provides a multiplicity of catalytically active sub-channels through which the exhaust gas 8th is passed to the catalytic treatment.

The close-coupled catalyst 1 is right behind the engine 101 arranged to undergo a catalytic treatment of the engine 101 originating exhaust gas 8th perform. This treated exhaust gas 8th is then through an exhaust pipe 11 to the underbody catalytic converter 2 directed further downstream of the engine 101 on an underbody of the vehicle 100 is arranged. After treatment in the underfloor catalyst 2 becomes the exhaust 8th at an exhaust outlet 14th blown off.

The system 10 further comprises a heat exchange system 3 , which is designed to heat between the close-coupled catalyst 1 and the underbody catalytic converter 2 via a heat exchange fluid 4th to be exchanged (cf. 3 to 5 ). The heat exchange system 3 is controlled by a control unit 5 regulated, which is designed to control a flow of the heat exchange fluid 4th between the close-coupled catalytic converter 1 and the underbody catalytic converter 2 to regulate so that both catalysts 1 , 2 be operated with an optimized combined operating efficiency for a given engine operating condition.

The system 10 further comprises a first temperature sensor 6th , which is upstream of the close-coupled catalyst 1 is arranged to be an engine outlet temperature of the exhaust gas 8th to measure, and a second temperature sensor 7th , which is downstream of the close-coupled catalyst 1 and upstream of the underfloor catalyst 2 is arranged to an exhaust pipe temperature of the exhaust gas 8th to eat. The temperature sensors 6th , 7th are communicative with the control unit 5 coupled, which in turn can be coupled to and / or part of a motor controller (not shown). The measured temperatures can therefore be used by the control unit 5 used to find a suitable control strategy for the heat exchange system 3 as a function of a current engine operating state and / or a current driving situation of the vehicle 100 to set up.

The heat exchange system 3 includes several heat exchange tubes 12th showing the catalysts 1 , 2 connect together and the heat exchange fluid 4th between the catalysts 1 , 2 guide back and forth. For this purpose are the catalysts 1 , 2 with heat storage shells 13th laterally to the flow direction of the exhaust gas 8th through the catalysts 1 , 2 educated. The heat storage shells 13th contain the heat exchange fluid 4th and are in fluid communication with the heat exchange tubes 12th .

The system also includes 10 at least one fluid pump 9 , which is designed to be the heat exchange fluid 4th through the heat exchange pipes 12th to pump. The fluid pump 9 can thus be continuously adjustable to the flow of the heat exchange fluid 4th to regulate. The fluid pump 9 is controlled by the control unit 5 controlled to a heat transfer between the catalysts 1 , 2 adjust to the working temperatures of both catalysts 1 , 2 to bring it to an optimal operating point with optimal emission reduction efficiency.

3 to 5 show exemplary operating modes of the system 1 .

3 can cold start the vehicle 100 show when the engine was just started and is now warming up. In this case, the close-coupled catalytic converter may have top priority 1 to the start temperature, e.g. 180 ° C, to the system 10 to a point where it begins to effectively reduce NOx emissions.

In this case, the flow of the heat exchange fluid 4th from the control unit 5 regulated so that no heat from the close-coupled catalytic converter 1 to the underbody catalytic converter 2 is transmitted to the close-coupled catalyst 1 heat up as quickly as possible. The close-coupled catalyst 1 is placed close to the engine so that heat is lost through the exhaust pipe 11 between the engine and the close-coupled catalytic converter 1 be minimized.

The operating mode can be selected accordingly 1 can be used for other scenarios with low exhaust gas temperatures, e.g. city driving or similar.

As soon as the close-coupled catalyst 1 has reached an acceptable working temperature, any excess energy can be transferred to the underfloor catalyst 2 be transmitted.

4th shows an example of an operating mode where heat energy from the close-coupled catalyst 1 to the underbody catalytic converter 2 is transferred by the heat exchange fluid 4th via the heat exchange pipes 12th from the close-coupled catalytic converter 1 to the underbody catalytic converter 2 and is circulated back. The heat exchange fluid 4th is attached to the heat storage shell 13th of the close-coupled catalytic converter 1 heated up (see arrows at the top left in 4th ). The heat energy is then transferred to the respective heat storage shell 13th to the underbody catalytic converter 2 transferred (top right in 4th ). In this process, the heat exchange fluid 4th cooled and then to the close-coupled catalyst 1 returned. This creates a closed heat cycle between the catalytic converters 1 , 2 provided.

The operating mode in 4th can also be used for driving conditions where the temperature of the exhaust gas 8th at the inlet of the close-coupled catalytic converter 1 is so high that there would be a reduction in efficiency, for example above 500 ° C. Examples of such scenarios include driving around town, driving on the motorway, driving uphill, cleaning a diesel particulate filter, etc. The central (efficient) operating area of the close-coupled catalytic converter 1 can for example be between 180 ° C and 450 ° C (engine outlet temperature). The underbody catalytic converter 2 on the other hand, it can basically work at higher engine outlet temperatures between, for example, 350 ° C. and 750 ° C. due to the heat losses along the exhaust pipe 11 . The control unit 5 of the system 10 can now a heat flow and thus the temperature range between the two catalysts 1 , 2 regulate in such a way that an optimal operating point is reached in every engine operating state.

5 shows another example in which heat from the underfloor catalyst 2 back to the close-coupled catalytic converter 1 is convicted. An example of such an engine operating state could be, for example, a change from a high-load phase to an idle and / or engine-off phase. The control unit 5 regulates the heat flow in this case in such a way that the close-coupled catalytic converter 1 maintains its temperature and can therefore continue to run in an efficient operating mode.

The procedure M. out 2 includes accordingly under M1 Carrying out a catalytic treatment of the exhaust gas 8th with the close-coupled catalytic converter 1 , the exhaust gas 8th from the internal combustion engine 101 originates, and under M2 Obtaining the exhaust 8th with the underbody catalytic converter 2 from the close-coupled catalytic converter 1 and carrying out a catalytic treatment of the exhaust gas obtained ( 8th ) with the underbody catalytic converter 2 . The procedure M. includes under M3 further exchanging heat between the close-coupled catalyst 1 and the underbody catalytic converter 2 by means of the heat exchange fluid 4th the heat exchange system 3 . The procedure M. includes under M4 further measuring the engine outlet temperature of the exhaust gas 8th with the first temperature sensor 6th upstream of the close-coupled catalyst 1 . The procedure M. includes under M5 furthermore measuring the exhaust pipe temperature of the exhaust gas 8th with the second temperature sensor 7th downstream of the close-coupled catalyst 1 and upstream of the underfloor catalyst 2 . The procedure M. includes under M6 further regulating the flow of the heat exchange fluid 4th between the close-coupled catalytic converter 1 and the underbody catalytic converter 2 with the control unit 5 such that both catalysts 1 , 2 be operated with an optimized combined operating efficiency for a given engine operating condition.

In the preceding detailed description, various features have been summarized in one or more examples in order to improve the stringency of the presentation. It should be clear, however, that the above description is merely illustrative, but not restrictive. It serves to cover all alternatives, modifications and equivalents. Many other examples will be immediately apparent to those skilled in the art based on their technical knowledge in view of the above description. The Exemplary embodiments have been selected and described in order to be able to illustrate the principles on which the invention is based and its possible applications in practice, so that it is possible for those skilled in the art to optimally modify and use the invention and its various exemplary embodiments with regard to the intended application.

List of reference symbols

1

close-coupled catalytic converter

2

Underbody catalytic converter

3

Heat exchange system

4th

Heat exchange fluid

5

Control unit

6

first temperature sensor

7th

second temperature sensor

8th

Exhaust gas

9

Fluid pump

10

Exhaust aftertreatment system

11

Exhaust pipe

12

Heat exchange tube

13

Heat storage shell

14th

Exhaust outlet

100

Motor vehicle

101

Internal combustion engine

M.

Procedure

M1-M6

Process step

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 2008/0078165 A1 [0005]

Claims (13)

System (10) for exhaust aftertreatment comprising: a close-coupled catalytic converter (1) which is designed to carry out a catalytic treatment of exhaust gas (8) originating from an internal combustion engine (101); an underbody catalytic converter (2) which is designed to receive the exhaust gas (8) from the close-coupled catalytic converter and to carry out a catalytic treatment of the obtained exhaust gas (8); and a heat exchange system (3) which is designed to exchange heat between the catalytic converter (1) close to the engine and the underbody catalytic converter (2) by means of a heat exchange fluid (4). System (10) Claim 1 , further comprising: a control unit (5) which is designed to regulate a flow of the heat exchange fluid (4) between the close-coupled catalytic converter (1) and the underbody catalytic converter (2) in such a way that both catalytic converters (1, 2) with an optimized combined operating efficiency can be operated for a given engine operating condition. System (10) Claim 2 , further comprising: a first temperature sensor (6) which is arranged upstream of the close-coupled catalyst (1) to measure an engine outlet temperature of the exhaust gas (8); and a second temperature sensor (7) which is arranged downstream of the close-coupled catalyst (1) and upstream of the underbody catalyst (2) to measure an exhaust pipe temperature of the exhaust gas (8); wherein the control unit (5) is designed to control the flow of the heat exchange fluid (4) on the basis of the measured temperatures. System (10) Claim 2 or 3 , wherein the control unit (5) is designed to regulate the flow of the heat exchange fluid (4) in such a way that heat is transferred from the catalytic converter (1) close to the engine to the underbody catalytic converter (2) in the event that the engine operating state includes high-load driving. System (10) according to one of the Claims 2 to 4th , the control unit (5) being designed to regulate the flow of the heat exchange fluid (4) in such a way that heat is transferred from the underbody catalytic converter (2) to the catalytic converter (1) close to the engine in the event that the engine operating state changes from high-load driving to includes at least one of low load driving, idling and an engine off phase. System (10) according to one of the Claims 2 to 5 , the control unit (5) being designed to regulate the flow of the heat exchange fluid (4) in such a way that no heat is transferred from the catalytic converter (1) close to the engine to the underbody catalytic converter (2) in the event that the engine operating state is at least one of a Includes engine warm-up and low-load driving. Motor vehicle (100) with an internal combustion engine (101) and a system (10) for exhaust gas aftertreatment according to one of the Claims 1 to 6th . Method (M) for exhaust gas aftertreatment, comprising: Carrying out (M1) a catalytic treatment of exhaust gas (8) with a catalytic converter (1) close to the engine, the exhaust gas (8) originating from an internal combustion engine (101); Receiving (M2) the exhaust gas (8) with an underbody catalytic converter (2) from the close-coupled catalytic converter (1) and carrying out a catalytic treatment of the obtained exhaust gas (8) with the underbody catalytic converter (2); and Exchange (M3) of heat between the close-coupled catalytic converter (1) and the underbody catalytic converter (2) by means of a heat exchange fluid (4) of a heat exchange system (3). Procedure (M) according to Claim 8 , further comprising: regulating (M6) a flow of heat exchange fluid (4) between the close-coupled catalytic converter (1) and the underbody catalytic converter (2) with a control unit (5) such that both catalytic converters (1, 2) with an optimized combined operating efficiency for be operated in a predetermined engine operating state. Procedure (M) according to Claim 9 , further comprising: measuring (M4) an engine outlet temperature of the exhaust gas (8) with a first temperature sensor (6) upstream of the close-coupled catalyst (1); and measuring (M5) an exhaust pipe temperature of the exhaust gas (8) with a second temperature sensor (7) downstream of the close-coupled catalyst (1) and upstream of the underfloor catalyst (2); wherein the flow of the heat exchange fluid (4) is controlled by the control unit (5) on the basis of the measured temperatures. Procedure (M) according to Claim 9 or 10 , the flow of the heat exchange fluid (4) being controlled by the control unit (5) in such a way that heat is transferred from the catalytic converter (1) close to the engine to the underbody catalytic converter (2) in the event that the engine operating state includes high-load driving Method (M) according to one of the Claims 9 to 11 , wherein the flow of the heat exchange fluid (4) is regulated by the control unit (5) such that heat is transferred from the underbody catalytic converter (2) to the close-coupled catalytic converter (1) in the event that the engine operating state changes from high-load driving to at least one of Includes low-load driving, idling and an engine-off phase. Method (M) according to one of the Claims 9 to 12th , the flow of the heat exchange fluid (4) being controlled by the control unit (5) in such a way that no heat is transferred from the catalytic converter (1) close to the engine to the underbody catalytic converter (2) in the event that the engine operating state is at least one of an engine warm-up phase and low-load driving includes.

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