DE102022004159A1 - Exhaust system for an internal combustion engine of a motor vehicle and motor vehicles with such an exhaust system - Google Patents

Abstract

The invention relates to an exhaust system (10) for an internal combustion engine (12) of a motor vehicle, with a first SCR catalyst (20) through which exhaust gas from the internal combustion engine (12) can flow for denitrifying the exhaust gas, with a second exhaust aftertreatment element (22) arranged downstream of the first SCR catalyst (20) in the flow direction of the exhaust gas flowing through the exhaust system (10), spaced from the first SCR catalyst (20) and through which the exhaust gas can flow, which has a second SCR catalyst (24) for denitrifying the exhaust gas, and with a metering device (26) by means of which a reducing agent designed to provide ammonia for denitrifying the exhaust gas can be introduced into the exhaust gas at a point (S1) arranged upstream of the first SCR catalyst (20), wherein the second exhaust aftertreatment element (22) has a nitrogen oxide storage catalyst (28) having.

Description

The invention relates to an exhaust system for an internal combustion engine of a motor vehicle according to the preamble of patent claim 1. Furthermore, the invention relates to a motor vehicle with such an exhaust system.

The EN 10 2016 202 235 A1 discloses a method for metering a reducing agent into an exhaust system of an internal combustion engine. Furthermore, the EN 10 2017 009 612 A1 a method for operating an internal combustion engine of a motor vehicle is known.

The object of the present invention is to provide an exhaust system for an internal combustion engine of a motor vehicle and a motor vehicle with such an exhaust system, so that a particularly advantageous exhaust gas aftertreatment can be realized.

This object is achieved by an exhaust system having the features of patent claim 1 and by a motor vehicle having the features of patent claim 10. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

A first aspect of the invention relates to an exhaust system, also referred to as an exhaust tract, for an internal combustion engine of a motor vehicle, preferably designed as a reciprocating piston machine or reciprocating piston engine and also referred to as an internal combustion engine. This means that the motor vehicle, preferably designed as a motor vehicle, in particular as a passenger car, in its fully manufactured state has the internal combustion engine and can be driven by means of the internal combustion engine. In its fired operation, the internal combustion engine provides exhaust gas, which in the fired operation results from combustion processes taking place in the internal combustion engine, in particular in at least one combustion chamber of the internal combustion engine. During the respective combustion process, a fuel-air mixture, also simply referred to as a mixture, is burned, which comprises air and a particularly liquid fuel.

The exhaust system through which the exhaust gas can flow has a first SCR catalyst through which the exhaust gas from the internal combustion engine can flow for denitrifying the exhaust gas. The first SCR catalyst is a first exhaust aftertreatment element or is also referred to as the first exhaust aftertreatment element of the exhaust system. Denitrifying the exhaust gas means that nitrogen oxides contained in the exhaust gas are at least partially removed from the exhaust gas, in particular by selective catalytic reduction (SCR), in the course of which nitrogen oxides (NOx) contained in the exhaust gas react with ammonia to form nitrogen and water. The first SCR catalyst is catalytically active or effective for the selective catalytic reduction. This means that the first SCR catalyst catalytically causes and/or supports the selective catalytic reduction, which takes place, for example, in the first SCR catalyst and by means of which the exhaust gas is denitrified.

The exhaust system also has a second exhaust aftertreatment element for aftertreating the exhaust gas, which is arranged downstream of the first SCR catalyst in the flow direction of the exhaust gas flowing through the exhaust system, is spaced from the first SCR catalyst and through which the exhaust gas can flow. The feature that the second exhaust aftertreatment element is spaced from the first SCR catalyst is to be understood in particular that at least one length of the exhaust system through which the exhaust gas can flow is arranged between the first SCR catalyst and the second exhaust aftertreatment element in the flow direction of the exhaust gas flowing through the exhaust system, wherein the length is completely free of an exhaust aftertreatment element for aftertreating the exhaust gas. Furthermore, it is preferably provided that the exhaust system is free of an SCR catalyst that is spaced apart from the first SCR catalyst and from the second exhaust gas aftertreatment element and arranged downstream of the first SCR catalyst and upstream of the second exhaust gas aftertreatment element, so that preferably no SCR catalyst that is spaced apart from the first SCR catalyst and from the second exhaust gas aftertreatment element is arranged between the first SCR catalyst and the second exhaust gas aftertreatment element, that is to say downstream of the first SCR catalyst and upstream of the second exhaust gas aftertreatment element.

The second exhaust aftertreatment element has a second SCR catalyst for denitrifying the exhaust gas. As already described above with regard to the first SCR catalyst, the second SCR catalyst is also catalytically active or effective for selective catalytic reduction (SCR), in the context of which nitrogen oxides contained in the exhaust gas react with ammonia to form nitrogen and water.

The exhaust system further comprises, in particular, a metering device by means of which a reducing agent, in particular a liquid one, designed to provide ammonia in the exhaust gas for denitrification of the exhaust gas can be introduced, in particular injected, into the exhaust gas at a point arranged upstream of the first SCR catalyst. In particular, the metering device can meter the reducing agent into the exhaust gas. This is to be understood in particular that an amount of the reducing agent to be introduced into the exhaust gas can be adjusted by means of the metering device. The reducing agent is preferably an aqueous urea solution, which is also referred to as AdBlue. The reducing agent is designed to provide the ammonia in the exhaust gas, which reacts with nitrogen oxides contained in the exhaust gas in the SCR catalyst to form nitrogen and water during the selective catalytic reduction. As is known, ammonia (NH ₃ ) is formed from the aqueous urea solution injected into the exhaust gas by means of thermolysis and hydrolysis.

In order to be able to realize a particularly advantageous exhaust gas aftertreatment and thus a particularly low-emission operation, it is provided according to the invention that the second exhaust gas aftertreatment element has a nitrogen oxide storage catalyst (NSK - NOx storage catalyst).

When the motor vehicle is fully manufactured, it has a structure preferably designed as a self-supporting body, through which an interior of the motor vehicle, also referred to as the passenger compartment or passenger cell, is formed or delimited. During a respective journey of the motor vehicle, people such as the driver of the motor vehicle can be in the interior. The interior is delimited in the vertical direction of the vehicle at least partially, in particular at least predominantly or completely, by a floor of the structure, in particular the self-supporting body, wherein the floor is also referred to as the underbody. Furthermore, in its fully manufactured state, the motor vehicle has an engine compartment in which the internal combustion engine is at least partially, in particular at least predominantly or completely, arranged. For example, the engine compartment is separated to the rear in the longitudinal direction of the vehicle by a partition arranged between the engine compartment and the interior, wherein the partition, also referred to as the front wall or bulkhead, can be a component of the structure, in particular the self-supporting body. For example, the partition wall extends in the transverse direction of the vehicle between two vehicle pillars of the motor vehicle, in particular of the superstructure and especially of the self-supporting body, which adjoin the partition wall on both sides in the transverse direction of the vehicle and are designed, for example, as A-pillars.

Since the first SCR catalyst is arranged upstream of the second exhaust gas aftertreatment element in the flow direction of the exhaust gas flowing through the exhaust system and thus upstream of the second SCR catalyst and upstream of the nitrogen oxide storage catalyst, the first SCR catalyst is preferably an SCR catalyst close to the engine, and thus an exhaust gas aftertreatment element close to the engine. It is preferably provided that the first SCR catalyst is arranged at least partially, in particular or at least predominantly completely, in the engine compartment. It can be provided that the second exhaust gas aftertreatment element and thus the second SCR catalyst and the nitrogen oxide storage catalyst, which is also referred to below simply as the storage catalyst, are preferably arranged completely outside the engine compartment and in the vertical direction of the vehicle below the floor (underbody), in particular in such a way that the second exhaust gas aftertreatment element is at least partially, in particular at least predominantly and thus at least more than half and very preferably completely, covered by the floor in the vertical direction of the vehicle. The second exhaust aftertreatment element is thus, for example, an underbody exhaust aftertreatment element (UB exhaust aftertreatment element), and for example the underbody exhaust aftertreatment element is or forms an underbody exhaust aftertreatment system (UB exhaust aftertreatment system), or the second exhaust aftertreatment element is part of such an underbody exhaust aftertreatment system. It is also conceivable that the first SCR catalyst and the metering device form an exhaust aftertreatment system close to the engine, in particular an SCR system close to the engine, or are parts of such an SCR system close to the engine. Since the second exhaust aftertreatment element has the second SCR catalyst, the underbody exhaust aftertreatment system can be, form or have an underbody SCR system.

The invention is based in particular on the following findings and considerations: Known SCR systems for denitrification of exhaust gases, i.e. for removing nitrogen oxides from the exhaust gases of an internal combustion engine, can have an SCR system close to the engine and an underbody SCR system remote from the engine, which is arranged downstream of the SCR system close to the engine and spaced apart from the SCR system close to the engine. While the SCR system close to the engine is usually arranged in the engine compartment, the underbody SCR system remote from the engine is arranged outside the engine compartment and under the underbody. The engine-mounted SCR system can - as described above - have the first SCR catalyst and the metering device. It is conceivable that a particle filter, in particular a diesel particle filter (DPF), is arranged upstream of the first SCR catalyst in the flow direction of the exhaust gas flowing through the exhaust system, by means of which particles, in particular soot particles, can be filtered out of the exhaust gas. The particle filter can be part of the engine-mounted SCR system. It is conceivable that the particle filter has a catalytically effective or active coating for the selective catalytic reduction, so that the particle filter designed as a diesel particle filter, for example, is then also referred to as an SDPF. It is therefore particularly conceivable that the internal combustion engine is designed as a diesel engine.

The underbody SCR system usually comprises a second metering device, i.e. a second metering device, by means of which the or a reducing agent for providing ammonia for denitrification of the exhaust gas can be introduced, in particular injected, into the exhaust gas at a second introduction point. The second introduction point is usually arranged in the flow direction of the exhaust gas flowing through the exhaust system downstream of the first SCR catalyst and upstream of the second SCR catalyst. A sufficiently high temperature of the exhaust gas, also referred to as the exhaust gas temperature, is advantageous in order to form ammonia with the exhaust gas by means of thermolysis and hydrolysis, for example from the reducing agent introduced into the exhaust gas at the exhaust gas temperature, whereby the reducing agent provides the ammonia in the exhaust gas for the selective catalytic reduction in the SCR catalyst. However, since the normal exhaust gas temperatures in the area of the underbody are at least largely too low for the introduction of the reducing agent, as they are usually less than 170 degrees Celsius (°C), the main nitrogen oxide conversion takes place on or in the SCR system close to the engine. The nitrogen oxide conversion or the main nitrogen oxide conversion means that the exhaust gas is denitrified, whereby with regard to the SCR system close to the engine and the underbody SCR system remote from the engine, the SCR system close to the engine removes a larger amount of nitrogen oxides from the exhaust gas much more effectively and/or within a period of time than the underbody SCR system. In special conditions such as during regeneration of the particle filter, during strong acceleration and during continuous high-load operation of the internal combustion engine and especially when the exhaust gas temperature at or in the SCR system close to the engine and/or a temperature of the SCR system close to the engine itself rises to more than 500 degrees Celsius and spatial velocities increase sharply, the underbody SCR system located away from the engine can be activated. Activation of the underbody SCR system located away from the engine means in particular that the reducing agent is introduced into the exhaust gas at the second penetration point using the second metering device, provided that a sufficient temperature of the exhaust gas is reached. If the reducing agent is not introduced at the second introduction point, the underbody SCR system is deactivated, i.e. inactive, particularly with regard to denitrification of the exhaust gas.

An exhaust system with two consecutive SCR catalysts, i.e. for example with the previously described close-coupled SCR system and with the previously described underbody SCR system as well as with the two metering devices, the first introduction point and the second introduction point, and without a nitrogen oxide storage catalyst arranged downstream of the first SCR catalyst, may enable a sufficiently high nitrogen oxide conversion in all operating states of the internal combustion engine, but can also have some disadvantages. A first of the disadvantages is that the second metering device, which is arranged for example under the underbody and also referred to as an underbody injection injector, has a high risk of sticking or clogging with urea or urea byproducts due to very rare activation of the underbody SCR system and thus of the second metering device. A second of the disadvantages is that regular, necessary filling and emptying, in particular of the underbody SCR system, cannot always be reliably guaranteed. A third disadvantage is that in the case of large nitrogen oxide raw emission peaks, for example in the course of strong acceleration gradients, the temperature of the exhaust gas in the area of the underbody or the temperature of the underbody SCR system can be less than 170 degrees Celsius, so that it is then not possible to introduce the reducing agent at the second introduction point. A fourth disadvantage is that a control and/or regulation effort is required for the second dosing device provided in addition to the first dosing device, including an on-board diagnostic monitoring system that is then advantageous and may be required, and at least one heated media line through which reducing agent can flow for guiding the reducing agent can be necessary and highly complex, which causes additional costs. A fifth disadvantage is that due to the previously described sticking and clogging problems of the second dosing device and in the case of locally occurring high temperatures temperatures of, for example, more than 250° Celsius, a minimum amount of the reducing agent is introduced regularly or when required at the second dosing device on or in the underbody even without nitrogen oxide-related requirements, i.e. even at the second introduction point in the exhaust gas when this is not actually necessary to denitrify the exhaust gas. This introduction of the reducing agent is also referred to as component protection dosing, since although it can protect components of the exhaust system from excessive wear and/or damage and/or failure, this could lead to unwanted ammonia or, after its oxidation in or on a normally provided ammonia slip catalyst (ASC), to unwanted nitrogen oxide slip into the ambient air. A sixth disadvantage is that sufficient preparation of the reducing agent, which is formed, for example, as an aqueous urea solution, in the area of the underbody, i.e. beneath the underbody, can require a complex mixing and evaporation system in the exhaust system. This increases the pressure loss of the exhaust system or increases the pressure loss of the exhaust gases already caused by the exhaust system, which can lead to a reduction in peak power and increased fuel consumption of the internal combustion engine.

The problems and disadvantages mentioned above can now be avoided by the invention. For this purpose, in particular instead of an ammonia slip catalyst of the second exhaust gas aftertreatment element in known exhaust systems, the nitrogen oxide storage catalyst is used, which is preferably arranged under the underbody and outside the engine compartment. It has proven to be advantageous if the second exhaust gas aftertreatment element, in particular the exhaust system as a whole and especially the motor vehicle as a whole, is free of an ammonia slip catalyst (ASC).

Preferably, a nitrogen oxide storage window of the storage catalyst is in a temperature range of 150° Celsius up to and including 600° Celsius. This is to be understood in particular that in the temperature range mentioned, nitrogen oxides from the exhaust gas can be stored in or by the storage catalyst. The nitrogen oxide storage catalyst has, in particular catalytically active components, in particular precious metal components, by means of which nitrogen oxides from the exhaust gas can be stored. It is conceivable that due to the components of the storage catalyst that are particularly catalytically active for the storage of nitrogen oxides from the exhaust gas, the storage catalyst, in particular by means of the components, can also oxidize ammonia and thus oxidatively remove any ammonia slip from the exhaust gas. The term ammonia slip is to be understood in particular as meaning that the reducing agent introduced into the exhaust gas or the ammonia provided by the reducing agent introduced into the exhaust gas flows through the second SCR catalyst and leaves it unused, i.e. is not converted in the second SCR catalyst, i.e. does not react with nitrogen oxides to form nitrogen and water, and is thus still present in elemental form, for example, downstream of the second SCR catalyst.

It is conceivable that a second nitrogen oxide storage catalyst is arranged upstream of the first SCR catalyst, in particular upstream of the particle filter. In particular, a nitrogen oxide storage catalyst (NSK) is provided which can store nitrogen oxides (NOx) from the exhaust gas even at relatively low temperatures. Such nitrogen oxide storage catalysts are also known as NSKlight. Advantageously, harmful nitrogen oxides can be at least partially removed from the exhaust gas even at low temperatures, for example during a cold start, before the SCR system has reached its operating temperature. The second nitrogen oxide storage catalyst is preferably spaced apart from the first SCR catalyst, in particular from the particle filter. Thus, a further length region of the exhaust system is preferably arranged between the second nitrogen oxide storage catalyst and the SCR catalyst, in particular between the second nitrogen oxide storage catalyst and the particle filter, the further length region of which is completely free of an exhaust gas aftertreatment element for aftertreating the exhaust gas. The advantage here is that combustion processes for regenerating or desulfurizing the second nitrogen oxide storage catalyst can be used, for example to also regenerate or desulfurize the first nitrogen oxide storage catalyst accordingly. This so-called desulfurization (sulfur regeneration) of the catalyst must take place at certain intervals, since sulfur limits the ability of the nitrogen oxide storage catalyst to absorb nitrogen oxides (NOx). For desulfurization, the exhaust gas is briefly heated to more than 650° Celsius and the internal combustion engine is operated with a rich mixture (lambda < 1) in order to provide as little oxygen (O ₂ ) as possible in the exhaust gas. The second nitrogen oxide storage catalyst is preferably arranged close to the engine or at least partially, in particular at least predominantly or completely, arranged in the engine compartment.

The invention can be used to achieve the following advantages in particular: If, for example, a nitrogen oxide slip (NOx slip) occurs in the SCR system close to the engine, in particular in the first SCR catalyst, for example due to excessively high local temperatures during regeneration of the particle filter or during strong acceleration, this nitrogen oxide slip, i.e. nitrogen oxides forming the nitrogen oxide slip, which were not removed from the exhaust gas by means of the first SCR catalyst and, for example, also not by means of the second SCR catalyst, can be stored in the first nitrogen oxide storage catalyst, and thus stored in the first nitrogen oxide storage catalyst. When the nitrogen oxide storage catalyst is mentioned above and below, this is to be understood - unless otherwise stated - as the first nitrogen oxide storage catalyst of the second exhaust gas aftertreatment element. Since the second exhaust aftertreatment element has the nitrogen oxide storage catalyst, and since, for example, the second exhaust aftertreatment element is an underfloor exhaust aftertreatment element, and is therefore arranged under the underfloor, the nitrogen oxide storage catalyst is, for example, an underfloor storage catalyst (UB-NSK), which is arranged under the underfloor. A further advantage is that sulfurization of the nitrogen oxide storage catalyst hardly ever occurs, for example when the second, close-to-the-engine nitrogen oxide storage catalyst is used, which stores the entire sulfur load and should therefore be regularly regenerated. Regular desulfurization (desulfatization) of the first nitrogen oxide storage catalyst of the second exhaust aftertreatment element can therefore be avoided. In addition, the use of the previously described second introduction point and thus the use of the second metering device downstream of the first SCR catalyst and upstream of the second SCR catalyst can be dispensed with if necessary. If the appropriate conditions are met, in particular a sufficiently high exhaust gas temperature upstream of the second SCR catalyst, an appropriate amount of aqueous urea solution can be injected using the first metering device provided, so that a sufficient amount of ammonia is present in the second SCR catalyst to denitrify the nitrogen oxides upstream of the second SCR catalyst. This also means that all the necessary measures in connection with the second metering device and the second introduction point, such as mixing and preparation components, can be avoided. This also eliminates the restrictions described above in terms of peak performance and fuel consumption.

In an advantageous embodiment of the invention, the nitrogen oxide storage catalyst is arranged downstream of the second SCR catalyst. As a result, excessive nitrogen oxide slip and excessive ammonia slip can be effectively and efficiently avoided.

In order to be able to achieve particularly low-emission operation, it is provided in a further embodiment of the invention that the second SCR catalyst is formed by an SCR catalyst region, in particular of the second exhaust gas aftertreatment element, wherein it is preferably provided that the second SCR catalyst or the SCR catalyst region is free of a nitrogen oxide storage catalyst, i.e. free of catalytically active substances that act as a nitrogen oxide storage catalyst. As a result, the exhaust gas can be aftertreated particularly advantageously and excessive nitrogen oxide slip can be effectively and efficiently avoided.

It has proven to be particularly advantageous if a storage area forming the nitrogen oxide storage catalyst is arranged downstream of the SCR catalyst area in the flow direction of the exhaust gas, which storage area preferably immediately or directly adjoins the SCR catalyst area. This is to be understood in particular that no other, further, catalytically active or effective area is arranged between the SCR catalyst area and the storage area in the flow direction of the exhaust gas. This allows the exhaust gas to be advantageously aftertreated in a particularly space-saving manner.

The storage area can be free of an SCR catalyst, i.e. free of substances that are catalytically active for the SCR, so that a large amount of nitrogen oxides from the exhaust gas can be stored effectively and efficiently by means of the storage area in a space-saving manner.

However, it has been shown to be particularly advantageous if the storage area of the first nitrogen oxide storage catalyst has at least one first coating acting as the nitrogen oxide storage catalyst and at least one second coating, which is also arranged in the SCR catalyst area and thus acts as the second SCR catalyst and is separate from the first coating. The feature that the second coating is separate from the first coating or vice versa is to be understood as meaning that the coatings are not mixed with one another, but are spatially or locally separated from one another and are therefore arranged next to one another and/or on top of one another. Preferably, a zoning of the coatings is provided, so that, for example, the first coating is a zoned NSK coating, which is arranged, for example, in an outlet region of the SCR catalyst and adjoins the SCR catalyst region in the flow direction of the exhaust gas, in which the second coating, also referred to as SCR coating, is arranged, but the SCR catalyst region is free of the first coating and free of a nitrogen oxide storage catalyst. The zoned NSK coating can be arranged or applied, for example, as a zoning or as a layer, either on or under the SCR coating. This makes it possible to achieve particularly advantageous aftertreatment of the exhaust gas in a space-saving manner.

It has also been shown to be particularly advantageous if the storage area has at least one coating, which is also referred to as a mixed coating or mixed washcoat and is designed as a mixture of first catalytically active substances that act as the nitrogen oxide storage catalyst and second catalytically active substances that are also provided in the SCR catalyst area and act as the second SCR catalyst in the SCR catalyst area. The respective coating is arranged on a carrier, for example, and carried by the carrier. By using the mixed washcoat, a particularly advantageous exhaust gas aftertreatment can be achieved in a space-saving manner.

In a further, particularly advantageous embodiment of the invention, the exhaust system, in particular with the exception of the nitrogen oxide storage catalyst of the second exhaust gas aftertreatment element, is free of an ammonia slip catalyst (SCR) arranged downstream of the first SCR catalyst. Preferably, the entire exhaust system, in particular the entire motor vehicle, in particular with the exception of the nitrogen oxide storage catalyst of the second exhaust gas aftertreatment element, is free of an ammonia slip catalyst (SCR).

This allows the exhaust gas to be treated particularly advantageously in a way that is weight- and installation space-efficient.

In a further, particularly advantageous embodiment of the invention, the exhaust system is free of an introduction point arranged downstream of the first SCR catalyst and upstream of the second exhaust gas aftertreatment element, at which a reducing agent designed to provide ammonia can be introduced into the exhaust gas. This makes it possible to avoid the previously described problems of sticking and clogging as well as additional regulation and/or control expenditure, so that the exhaust gas can be aftertreated in a particularly advantageous and cost-effective manner.

Alternatively, it is provided that, in order to implement a particularly advantageous exhaust gas aftertreatment, a or the second metering device is provided, by means of which a reducing agent designed to provide ammonia for denitrification of the exhaust gas, in particular the aforementioned reducing agent, can be introduced into the exhaust gas at a second location arranged downstream of the first exhaust gas aftertreatment element (first SCR catalyst) and upstream of the second exhaust gas aftertreatment element. The second location is preferably the aforementioned second introduction location.

It is also conceivable to arrange the nitrogen oxide storage catalyst particularly far away from the engine, in particular such that at least a third length region of the exhaust system is arranged between the second SCR catalyst and the nitrogen oxide storage catalyst arranged downstream of the second SCR catalyst in the flow direction of the exhaust gas flowing through the exhaust system, the third length region being completely free of an exhaust aftertreatment element for aftertreating the exhaust gas. In this case, it is particularly conceivable that the nitrogen oxide storage catalyst of the second exhaust aftertreatment element is integrated into a muffler or rear silencer of the exhaust system. This shifts a temperature window towards lower temperatures on the nitrogen oxide storage catalyst.

A second aspect of the invention relates to a motor vehicle, preferably designed as a passenger car, which has an internal combustion engine or the aforementioned internal combustion engine for driving the motor vehicle. In addition, the motor vehicle comprises an exhaust system through which exhaust gas from the internal combustion engine can flow, according to the first aspect of the invention. Advantages and advantageous embodiments of the first aspect of the invention are to be regarded as advantages and advantageous embodiments of the second aspect of the invention, and vice versa.

Further advantages, features and details of the invention emerge from the following description of a preferred embodiment and from the drawing. 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 in the single figure alone Combinations can be used not only in the combination specified, but also in other combinations or alone, without departing from the scope of the invention.

The drawing shows in the only figure a schematic representation of an exhaust system according to the invention for an internal combustion engine of a motor vehicle preferably designed as a passenger car.

The only figure shows a schematic representation of an exhaust system 10, also referred to as an exhaust tract, for an internal combustion engine 12 of a motor vehicle, preferably designed as a passenger car. This means that the motor vehicle, in its fully manufactured state, has the exhaust system 10 and the internal combustion engine 12 and can be driven by means of the internal combustion engine 12, also referred to as an internal combustion engine. The internal combustion engine 12 is designed as a reciprocating piston machine and has cylinders 14, which partially delimit respective combustion chambers 16 of the internal combustion engine 12. During fired operation of the internal combustion engine 12, combustion processes take place in the combustion chambers 16, resulting in exhaust gas from the internal combustion engine 12. The internal combustion engine 12 can provide the exhaust gas. In other words, the exhaust gas can be discharged from the combustion chambers 16 and - as illustrated in the figure by an arrow 18 - introduced into the exhaust system 10. The exhaust system 10 can thus be flowed through by the exhaust gas of the internal combustion engine 12. The exhaust system 10 has a first exhaust gas aftertreatment element in the form of a first SCR catalyst 20 through which the exhaust gas can flow for denitrification and thus for aftertreating the exhaust gas. The exhaust system 10 also comprises a second exhaust gas aftertreatment element 22 which is arranged downstream of the first SCR catalyst 20 in the flow direction of the exhaust gas flowing through the exhaust system 10 and through which the exhaust gas can flow, which second exhaust gas aftertreatment element 22 can be an independently assembled module, i.e. considered on its own, and thus a unit or structural unit. The second exhaust gas aftertreatment element 22 has a second SCR catalyst 24 for denitrification of the exhaust gas. The second exhaust gas aftertreatment element 22 and thus the second SCR catalyst 24 are spaced apart from the first SCR catalyst 20. This means that the exhaust system 10 has at least one length region L1 in the flow direction of the flowing exhaust gas between the SCR catalyst 20 and the exhaust aftertreatment element 22 and thus the SCR catalyst 24, which is completely free of an exhaust aftertreatment element for, in particular, active, aftertreatment of the exhaust gas. In particular, it is conceivable that only one exhaust pipe through which the exhaust gas can flow is arranged in the length region L1, through which the exhaust gas flows without being aftertreated.

The exhaust system 10 further comprises a metering device 26, by means of which a reducing agent, in particular a liquid one, can penetrate, in particular be injected, into the exhaust gas at a point S1 arranged upstream of the SCR catalyst 20 and also referred to as the introduction point. The reducing agent is, for example, an aqueous urea solution and is designed to provide ammonia in the exhaust gas, which reacts with nitrogen oxides contained in the exhaust gas to form nitrogen and water during selective catalytic reduction (SCR). The selective catalytic reduction can take place in the respective SCR catalyst 20 or 24 and is catalytically supported and/or brought about in particular by the respective SCR catalyst 20 or 24. As a result of the selective catalytic reduction (SCR) process, the ammonia from the reducing agent reacts with the nitrogen oxides contained in the exhaust gas to form nitrogen and water, and the nitrogen oxides that react with the ammonia from the reducing agent to form nitrogen and water are removed from the exhaust gas. This means that the exhaust gas is denitrified.

In order to be able to aftertreat the exhaust gas particularly advantageously and subsequently achieve particularly low-emission operation, the second exhaust gas aftertreatment element 22 has a nitrogen oxide storage catalyst 28. The nitrogen oxide storage catalyst 28 is also referred to as an NSK (NOx storage catalyst).

In the embodiment shown in the figure, the nitrogen oxide storage catalyst 28 is arranged downstream of the second SCR catalyst 24, wherein it is conceivable that the SCR catalyst 24 and the nitrogen oxide storage catalyst 28 form the aforementioned structural unit or are part of the structural unit. In particular, it is conceivable that the SCR catalyst 24 and the nitrogen oxide storage catalyst 28 are arranged in a common housing of the second exhaust gas aftertreatment element 22. In particular, it is conceivable that the nitrogen oxide storage catalyst 28 is immediately or directly connected to the second SCR catalyst 24, so that no other, further exhaust gas aftertreatment element for aftertreating the exhaust gas is arranged between the nitrogen oxide storage catalyst 28 and the SCR catalyst 24, and preferably no length region is arranged between the SCR catalyst 24 and the nitrogen oxide storage catalyst 28, which is free of an exhaust gas aftertreatment element for aftertreating the exhaust gas.

Furthermore, it is preferably provided that the exhaust system 10 is free of an ammonia slip catalyst arranged downstream of the second SCR catalyst 24, in particular downstream of the nitrogen oxide storage catalyst 28. Furthermore, it is provided here that the exhaust system 10, in particular with the exception of the nitrogen oxide storage catalyst 28, is free of an ammonia slip catalyst arranged downstream of the first SCR catalyst 20. In addition, the exhaust system 10 is free of an introduction point arranged downstream of the first SCR catalyst 20 and upstream of the second exhaust gas aftertreatment element 22, at which a reducing agent designed to provide ammonia can penetrate into the exhaust gas.

According to the embodiment shown in the figure, the exhaust system 10 has a particle filter 30, which is arranged upstream of the first SCR catalyst in the exhaust system 10. The internal combustion engine 12 can be designed as a diesel engine, so that the particle filter 30 is designed, for example, as a diesel particle filter (DPF). By means of the particle filter 30, particles, in particular soot particles, can be filtered out of the exhaust gas. The particle filter 30 preferably has a coating that is catalytically effective or active for the selective catalytic reduction, so that the particle filter 30 can preferably be designed as an SDPF. For example, the SCR catalyst 20 and the particle filter 30 form an independent, assembled, further structural unit. It is conceivable that the particle filter 30 and the SCR catalyst 20 are arranged in a common housing, in particular the further structural unit.

The exhaust system 10 also includes a second nitrogen oxide storage catalyst 32, which is arranged upstream of the SCR catalyst 20 and thus upstream of the particle filter 30 and in particular upstream of the point S1. The second nitrogen oxide storage catalyst 32 is spaced from the particle filter 30 in such a way that a second length range L2 of the exhaust system 10 is arranged between the particle filter 30 and the second nitrogen oxide storage catalyst 32. The second length range L2 can be free of an exhaust gas aftertreatment element for aftertreating the exhaust gas, in particular except for the point S1 or the metering device 26. In particular, at least part of the second length range L2 can be completely free of an exhaust gas aftertreatment element for aftertreating the exhaust gas. The SCR catalyst 20, the particle filter 30 and the second nitrogen oxide storage catalyst 32 are preferably components close to the engine that are arranged in an engine compartment of the motor vehicle. The internal combustion engine 12 is also arranged in the engine compartment. For example, the metering device 26 is also arranged in the engine compartment, so that the point S1 is also arranged in the engine compartment. The exhaust gas aftertreatment element 22 and thus the second SCR catalyst 24 and the first nitrogen oxide catalyst 28 are components remote from the engine that are arranged, for example, beneath an underbody of a self-supporting body of the motor vehicle. The components remote from the engine are arranged completely outside the engine compartment.

As an alternative to the embodiment shown in the figure, it is possible to arrange the nitrogen oxide storage catalyst 28 so far away from the engine and thus so far away from the internal combustion engine 12 and in particular from the SCR catalyst 24 that, for example, in the flow direction of the exhaust gas flowing through the exhaust system 10, a third length region of the exhaust system 10 is arranged between the second SCR catalyst 24 and the nitrogen oxide storage catalyst 28 arranged downstream of the second SCR catalyst 24, wherein the third length region is completely free of an exhaust gas aftertreatment element for aftertreating the exhaust gas. It is also conceivable that only an exhaust pipe of the exhaust system 10 through which the exhaust gas can flow is arranged in the third length region. The nitrogen oxide storage catalyst 28 is thus spaced apart from the SCR catalyst 24. In particular, it is provided that the exhaust system 10 is free of an exhaust gas aftertreatment element for aftertreating the exhaust gas, which is arranged in the flow direction of the exhaust gas flowing through the exhaust system 10 between the SCR catalyst 24 and the nitrogen oxide storage catalyst 28.

Furthermore, an exhaust gas recirculation device 34 is provided, which can be partially seen in the figure, by means of which an exhaust gas recirculation, in particular a low-pressure exhaust gas recirculation (LP-ADR), can be carried out. The low-pressure exhaust gas recirculation (LP-ADR), which is known per se, is provided on a low-pressure side of an exhaust gas turbocharger (not shown in detail in the figure) of the internal combustion engine 12 and thus downstream of a compressor of the exhaust gas turbocharger and upstream of a turbine of the exhaust gas turbocharger. In addition to the low-pressure exhaust gas recirculation (LP-ADR), a high-pressure exhaust gas recirculation (HD-ADR), which is known per se, can also be provided. The low-pressure exhaust gas recirculation device 34 comprises a return line 36, which is fluidically connected to the exhaust system 10 at a branch point A. Furthermore, the return line 36 fluidically connected to an intake tract of the internal combustion engine 12. Air can flow through the intake tract, which is guided to and into the respective combustion chamber 16 by means of the intake tract. At the branch point A, at least part of the exhaust gas flowing through the exhaust system 10 can be branched off from the exhaust system 10 by means of the return line 36 and introduced into the return line 36. The exhaust gas introduced into the return line 36 can flow through the return line 36 and is returned to the intake tract by means of the return line 36 and introduced into the intake tract. The exhaust gas recirculation device 34 comprises a valve element 38, which is arranged, for example, in the return line 36 and is also referred to as an EGR valve and which is designed, for example, as a pivotable flap. The amount of exhaust gas to be recirculated can be adjusted by means of the valve element 38. From the figure it can be seen that the branch point A is arranged in the flow direction of the exhaust gas flowing through the exhaust system 10 downstream of the SCR catalyst 20 and upstream of the exhaust gas aftertreatment element 22 and thus upstream of the second SCR catalyst 24.

List of reference symbols

10

Exhaust system

12

Internal combustion engine

14

cylinder

16

Combustion chamber

18

Arrow

20

SCR catalyst

22

second post-treatment element

24

second SCR catalyst

26

Dosing device

28

Nitrogen oxide storage catalyst

30

Particle filter

32

second nitrogen oxide storage catalyst

34

Exhaust gas recirculation system

36

Return initiation

38

Valve element

A

Junction point

L1

Length range

L2

Length range

QUOTES INCLUDED IN THE DESCRIPTION

This list of 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 accepts no liability for any errors or omissions.

Cited patent literature

• DE 102016202235 A1 [0002]
• DE 102017009612 A1 [0002]

Claims (10)

Exhaust system (10) for an internal combustion engine (12) of a motor vehicle, with a first SCR catalyst (20) through which exhaust gas from the internal combustion engine (12) can flow for denitrifying the exhaust gas, with a second exhaust aftertreatment element (22) arranged downstream of the first SCR catalyst (20) in the flow direction of the exhaust gas flowing through the exhaust system (10), spaced from the first SCR catalyst (20) and through which the exhaust gas can flow, which has a second SCR catalyst (24) for denitrifying the exhaust gas, and with a metering device (26) by means of which a reducing agent designed to provide ammonia for denitrifying the exhaust gas can be introduced into the exhaust gas at a point (S1) arranged upstream of the first SCR catalyst (20), characterized in that the second exhaust aftertreatment element (22) has a nitrogen oxide storage catalyst (28) having. Exhaust system (10) according to Claim 1 , characterized in that the nitrogen oxide storage catalyst (28) is arranged downstream of the second SCR catalyst (24). Exhaust system (10) according to Claim 1 or 2 , characterized in that the second SCR catalyst (24) is formed by an SCR catalyst region which is free of a nitrogen oxide storage catalyst. Exhaust system (10) according to Claim 3 , characterized in that a storage region forming the nitrogen oxide storage catalyst (28) is arranged downstream of the SCR catalyst region in the flow direction of the exhaust gas. Exhaust system (10) according to Claim 4 , characterized in that the storage area is free of an SCR catalyst. Exhaust system (10) according to Claim 4 , characterized in that the storage region has at least one first coating acting as the nitrogen oxide storage catalyst (28) and at least one second coating which is also arranged in the SCR catalyst region and thereby acts as the second SCR catalyst (24) and is separate from the first coating. Exhaust system (10) according to Claim 4 , characterized in that the storage region has at least one coating which is formed as a mixture of first catalytically active substances acting as the nitrogen oxide storage catalyst (28) and second catalytically active substances acting as the second SCR catalyst (24) in the SCR catalyst region. Exhaust system (10) according to one of the preceding claims, characterized in that the exhaust system (10) is free of an ammonia slip catalyst arranged downstream of the first SCR catalyst (20). Exhaust system (10) according to one of the preceding claims, characterized in that: - the exhaust system (10) is free of an introduction point arranged downstream of the first SCR catalyst (20) and upstream of the second exhaust gas aftertreatment element (22), at which a reducing agent designed to provide ammonia can be introduced into the exhaust gas, or - a second metering device is provided, by means of which a reducing agent designed to provide ammonia for denitrification of the exhaust gas can be introduced into the exhaust gas at a second point arranged downstream of the first SCR catalyst (20) and upstream of the second exhaust gas aftertreatment element (22). Motor vehicle, with an internal combustion engine (12), by means of which the motor vehicle can be driven, and with an exhaust system (10) according to one of the preceding claims through which exhaust gas from the internal combustion engine (12) can flow.

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