DE102016210188A1 - Method and device for exhaust aftertreatment - Google Patents

Abstract

A method for the aftertreatment of exhaust gas of an internal combustion engine (1) is described, wherein a lean NOx trap (4) and a bypass trap flow channel (5) bypassing the lean NOx trap (4) are provided with a by-pass. Pass valve (6) and in the flow direction (13) of the exhaust gas downstream of the lean NOx trap (4) arranged SCR catalyst (7) is used. The method comprises the following steps: determining a temperature range (31) of the SCR catalyst (7); Setting a threshold value for the exhaust gas mass flow (32) through the SCR catalytic converter (7); Detecting the temperature (33) of the SCR catalyst (7); Detecting the exhaust mass flow (34) through the SCR catalyst (7); if the detected temperature of the SCR catalyst is within the predetermined temperature range (35) and the detected exhaust mass flow exceeds the threshold (36), directing an exhaust mass flow through the lean NOx trap (4) and increasing an exhaust gas recirculation rate to a value that is one automatic NOx desorption in the lean NOx trap is effected (37); and passing the exhaust gas (38) leaving the lean NOx trap (4) to the SCR catalyst (7).

Description

The present invention relates to a method and a device for the aftertreatment of exhaust gas of an internal combustion engine with an improved regeneration of a lean NO _x trap.

A lean _NOx trap (LNT English -. Lean _NOx Trap), hereinafter abbreviated as LNT stores nitrogen oxides during lean operation of the engine and converts the stored nitrogen oxide by during short periods of rich operation of the engine. During these rich purges, the internal combustion engine operates with a sub-stoichiometric air-fuel mixture (lambda <1), with large amounts of hydrocarbon (HC) and carbon monoxide (CO) being added to the lean NO _x trap to facilitate the conversion of NO _x to enable. To regenerate a lean NO _x trap, fuel is required and CO _{2 is} released.

Since selective catalytic reduction systems only provide very limited NO _x conversion during a cold start, it is necessary to keep the storage level of the lean NO _x trap below a certain threshold so that the lean NO _x trap for a next cold start remains prepared.

The maintenance of the performance of the lean NO _x trap during its lifetime is fundamentally of considerable importance. In this context, challenges typically arise. Thus, in particular in the context of a regeneration in rich operation additional fuel consumption is undesirable.

In the document US 2007/0271908 A1 An exhaust aftertreatment system is described which comprises a combination of a lean NO _x trap (LNT) and a passive SCR catalyst (SCR selective catalytic reduction). In this case, the ammonia (NH ₃ ) required for the SCR catalyst is generated by the lean NO _x trap. A similar system is in US 2006/0273187 A1 disclosed. Again, a combination of a NO _x absorber and a passive SCR catalyst will be described.

Against the background described, it is an object of the present invention to provide an advantageous method for exhaust aftertreatment for an internal combustion engine and a corresponding device, which minimizes the fuel consumption for the regeneration of the lean NO _x trap.

This object is achieved by a method for exhaust aftertreatment according to claim 1, an apparatus according to claim 12 and a motor vehicle according to claim 16. The dependent claims contain further, advantageous embodiments of the invention.

In the context of the inventive method for the aftertreatment of exhaust gas of an internal combustion engine is a lean NO _x trap and the lean NO _x trap fluidly bridging by-pass flow channel with a by-pass valve and downstream in the flow direction of the exhaust gas Lean NO _x trap arranged SCR catalyst used.

Without the by-pass flow duct all the exhaust gas would flow through the lean _NOx trap, with a portion of the nitrogen oxides automatically in the lean NO _x trap would be stored before they reach the SCR catalyst. The storage capacity of the lean NO _x trap would thus be unnecessarily burdened without bypass pass channel.

The method according to the invention comprises the following steps: A temperature range of the SCR catalyst is determined, preferably a temperature range for an efficient NO _x conversion. A threshold value for the exhaust gas mass flow or exhaust gas mass flow through the SCR catalytic converter is determined, preferably an exhaust gas mass flow for an efficient NO _x conversion. The temperature of the SCR catalyst is detected, for example, measured or otherwise determined. The exhaust gas mass flow or exhaust gas mass flow through the SCR catalytic converter is detected, for example measured or otherwise determined. If the detected temperature of the SCR catalyst within the predetermined temperature range and the detected exhaust gas mass flow exceeds the threshold value, an exhaust gas mass flow is passed through the lean NO _x trap and an exhaust gas recirculation rate increases to a value of an automatic or natural NO _x - desorption in the lean NO _x trap causes. The exhaust gas leaving the lean NO _x trap is forwarded to the SCR catalyst. Preferably, an active SCR catalyst is used. In principle, another catalyst for NO _x conversion can be used.

In the context of the method, the by-pass valve can be set or switched so that the exhaust gas of the internal combustion engine is first passed through the by-pass flow channel past the lean NO _x trap in the presence of the above conditions the lean NO _x trap is passed through.

The increased in the context of the method exhaust gas recirculation rate causes a large amount of the exhaust gas recirculated and thus the flow or Power is limited or restricted by the exhaust pipe. This allows a longer residence time of the nitrogen oxides in the SCR catalyst, which in turn allows an improved conversion of nitrogen oxides. The longer residence time is particularly advantageous because, in the case of NO _x desorption of the lean NO _x trap, an increased amount of nitrogen oxide upstream of the SCR catalyst occurs compared to normal operation.

The invention is based on the idea, in an exhaust aftertreatment configuration with a further NO _x -converting device downstream of the lean NO _x trap, of providing a bypass pass channel around the lean NO _x trap, and in the presence of certain conditions during the normal operation to direct the exhaust stream through the lean NO _x trap to desorb the stored nitrogen oxides NO _x . The desorbed nitrogen oxides are then converted in an active selective catalytic reduction apparatus, hereinafter referred to as the SCR active catalyst, while minimizing the volumetric flow rate and thus maximizing the residence time through the SCR catalyst.

The operation of the lean NO _x trap is therefore not limited to cold start situations, but is temporarily operated during a normal, warm SCR operation during phases in which a limited conversion efficiency of the SCR catalyst is detected and this to the total NO _x Conversion can contribute.

In a variant embodiment, a lower threshold temperature of the lean NO _x trap and / or a lower threshold temperature of the SCR catalyst is determined. As long as the lower threshold temperature of the lean NO _x trap and / or the lower threshold temperature of the SCR catalyst are exceeded, the bypass valve is adjusted so that no exhaust gas mass flow flows through the by-pass flow channel. The by-pass valve is closed in other words. In another variant, the by-pass valve is adjusted so that an exhaust gas mass flow flows through the by-pass flow channel when the lower threshold temperature of the SCR catalyst is reached or exceeded. In other words, the by-pass valve is partially or fully opened.

In another embodiment variant, a lower threshold NO _x storage level of the lean NO _x trap is determined. The by-pass valve is adjusted until the lower threshold NO _x storage level of the lean NO _x trap is exceeded, so that no exhaust gas mass flow flows through the by-pass flow channel. The by-pass valve thus remains closed until the nitrogen oxides stored in the lean NO _x trap are partially or completely desorbed. This ensures that the lean NO _x trap is available for a coming cold start to store nitrogen oxides.

In an advantageous variant, the efficiency of the SCR catalyst for the NO _x conversion is set. In addition, the temperature range of the SCR catalyst _x conversion can be set for the specified efficiency of NO _x conversion and / or the exhaust gas mass flow or exhaust-gas mass flow through the SCR catalyst for the specified efficiency of NO.

The efficiency of the SCR catalyst for NO _x conversion is preferably determined by means of a kinetic model describing the conversion by the SCR catalyst. This can be done online, for example.

In principle, a by-pass valve can be used, which can be opened and closed discontinuously or continuously from 0% to 100%. Thus, in the context of the method according to the invention, the exhaust gas can be conducted completely or partially through the lean NO _x trap.

In addition, after leaving the lean NO _x trap or leaving the by-pass flow channel, the exhaust gas of the internal combustion engine may be introduced into the SCR catalyst, for example into the SCR catalyst, by a diesel oxidation catalyst disposed upstream of the SCR catalyst such as the SCR active catalyst active SCR catalyst.

In a further variant, the exhaust gas of the engine after exiting the lean NO _x trap or after leaving the by-pass flow passage through an upstream of the SCR catalyst, in particular of the active SCR catalyst arranged DPF is, in particular a catalytically coated Diesel particulate filter CDPF, directed into the SCR catalyst, in particular into the active SCR catalyst.

In addition, may be located downstream of the lean NO _x trap and upstream of the (active) urea SCR catalyst are injected into the exhaust gas.

The lean NO _x trap used may advantageously be arranged in a low pressure exhaust gas recirculation system. The system used may include a compressor and / or a turbocharger.

The described method allows to switch from a low-pressure EGR operation with a lean NO _x trap and an SCR catalyst to an operating with a diesel oxidation catalyst and the SCR catalyst.

The method according to the invention has the advantage that it enables a flexible and fuel-saving regeneration of the lean NO _x trap. This is achieved by not regenerating the lean NO _x trap in a fuel-consuming rich operation, but releasing the stored nitrogen oxides from the lean NO _x trap under suitable conditions and converting them through the SCR catalyst. As a result, the method contributes to an increase in the efficiency of the exhaust aftertreatment system.

The exhaust gas aftertreatment device according to the invention for an internal combustion engine with an exhaust gas outlet is designed to carry out a method as described above. The device comprises an exhaust gas inlet that can be fluidly connected or connected to the exhaust gas outlet, a lean NO _x trap arranged downstream of the exhaust gas inlet in the flow direction of the exhaust gas, and a by-pass flow channel bridging the lean NO _x trap with a by-pass flow channel. Valve. At this time, downstream of the lean NO _x trap and the by-pass flow channel, there are disposed a urea injector and an active selective catalytic reduction (SCR active catalyst) apparatus with the SCR active catalyst disposed downstream of the urea injector , The urea injector may be configured, for example, as an AdBlue (NH ₃ ) injector.

The device basically has the same advantages as the method according to the invention described above.

The by-pass flow channel may include a by-pass valve that either directs exhaust gas flow completely through the lean NO _x trap or bypasses the lean NO _x trap. In this case, the valve can either 0% or 100% allow a flow of current in one direction or the other or it can be designed so that there is a continuous variation between 0% and 100% current flow through the respective flow channel, ie the by-pass Flow channel or the flow channel to the lean NO _x trap, allowed. This makes it possible to allow a small flow of exhaust gas through the lean NO _x trap to maintain its operating temperature.

The exhaust aftertreatment device includes a lean NO _x trap followed by a second NO _x aftertreatment device, namely a downstream SCR active catalyst. This combination of exhaust aftertreatment components enables higher conversion efficiency, which is required in the context of real world driving emissions (RDE) requirements and their fulfillment, as well as in the context of the proposed very low EU xenvironment NO _x emission limits compared to the EU6 standard or be.

The apparatus of the invention may also include a diesel oxidation catalyst (DOC). The diesel oxidation catalyst is preferably downstream of the lean _NOx trap and downstream of the by-pass flow passage and upstream of the Harnstoffinjektors and active SCR catalyst disposed. With the aid of the DOC, a HC and a CO conversion are ensured, while the exhaust gas flow is bypassed around the lean NO _x trap, that is to say the bypass gas flow channel predominantly passes. While the DOC is located downstream of the lean NO _x trap, this is not a problem unless the flow of exhaust gas past the LNT occurs only after the DOC has reached its light-off temperature.

The device according to the invention preferably comprises a catalytically coated diesel particulate filter CDPF (catalyzed diesel particulate filter). The CDPF is located downstream of the lean NO _x trap and by-pass flow channel and upstream of the urea injector and SCR active catalyst. The CDPF causes a further improvement of the exhaust aftertreatment.

In a preferred variant, the device comprises a low-pressure exhaust gas recirculation passage, the exhaust gas from a position of the lean _NOx trap downstream to a compressor passes.

Due to the separate urea injection, the active SCR catalyst can in principle also be operated without the lean NO _x trap, but with a correspondingly increased NO _x emission during the cold start. The NO _x trap causes a corresponding NO _x storage and conversion here.

Without the by-pass flow channel, all of the exhaust and sulfur from the fuel would flow through the lean NO _x trap. Having disposed at said location by-pass flow channel of the exhaust gas flow can be controlled based on the operating status of the active SCR catalyst and the ammonia load of the lean NO _x trap.

The motor vehicle according to the invention comprises a device according to the invention described above. It basically has the same properties and advantages as the exhaust gas aftertreatment device according to the invention already described.

In principle, in the context of the invention for further improvement and optimization of the exhaust aftertreatment additional Information to be used. Such information may be available, for example, via GPS, known future routes, route prediction or navigation systems, V2V (vehicle-to-vehicle connection), ie information exchanged wirelessly between vehicles, traffic light information, an adaptive cruise control system, or otherwise.

Further features, properties and advantages of the present invention will be described in more detail below with reference to exemplary embodiments with reference to the accompanying figures. All features described above and below are advantageous both individually and in any combination with each other. The exemplary embodiments described below are merely examples which, however, do not limit the subject matter of the invention.

1 schematically shows a flowchart of a method according to the invention.

2 schematically shows an inventive device for exhaust aftertreatment.

3 schematically shows a motor vehicle according to the invention.

The 1 schematically shows a flowchart of a method according to the invention. An example of a method according to the invention for after-treatment of exhaust gas of an internal combustion engine comprises the following steps:
At step 31 For example, a temperature range of the SCR catalyst is determined, preferably a temperature range for efficient NO _x conversion. At step 32 a threshold value for the exhaust gas mass flow or exhaust gas mass flow is determined or determined by the SCR catalytic converter, preferably an exhaust gas mass flow for an efficient NO _x conversion. The order of execution of the steps 31 and 32 is arbitrary, so it can be reversed.

At step 33 For example, the temperature of the SCR catalyst is detected, for example, measured or otherwise determined. At step 34 the exhaust gas mass flow or exhaust gas mass flow is detected by the SCR catalyst, for example, measured or otherwise determined. The order of execution of the steps 33 and 34 is arbitrary, so it can be reversed.

If at step 35 the detected temperature of the SCR catalyst is within the specified temperature range and at step 36 the detected exhaust gas mass flow exceeds the threshold, an exhaust mass flow becomes at step 37 passed through the lean NO _x trap and increases an exhaust gas recirculation rate to a value that causes an automatic or natural NO _x desorption in the lean NO _x trap. If any of the in step 35 and 36 If the tested conditions are not met, the procedure in step 33 continued. The order of execution of the steps 35 and 36 is arbitrary, so it can be reversed.

The exhaust gas leaving the lean NO _x trap is in step 38 to the SCR catalyst 7 forwarded. Preferably, an active SCR catalyst is used. In principle, another catalyst for NO _x conversion can be used.

As part of the process, the by-pass valve used 6 be set or switched so that the exhaust gas of the internal combustion engine 1 first through the by-pass flow channel 5 at the lean NO _x trap 4 is passed through in the event of the above conditions by the lean NO _x trap 4 is passed through.

The increased exhaust gas recirculation rate in the context of the method causes a large amount of the exhaust gas to recirculate and thus limit or restrict the flow or flow through the exhaust gas end pipe. This allows a longer residence time of the nitrogen oxides in the SCR catalyst 7 , which in turn allows for improved conversion of nitrogen oxides. The longer residence time is particularly advantageous because in the case of NOx desorption of the lean NO _x trap increased compared to normal operation amount of nitrogen oxide upstream of the SCR catalyst 7 occurs.

For setting, in particular for increasing the exhaust gas recirculation rate, a low-pressure exhaust gas recirculation system 25 with a valve 26 , such as in 2 shown to be used.

The 2 schematically shows an embodiment of a device according to the invention. The device according to the invention 21 includes an exhaust inlet 3 , The exhaust inlet 3 is with an exhaust outlet 2 an internal combustion engine 1 connected or connectable. In the variant shown, the device comprises one in the flow direction 23 in front of the combustion engine 1 arranged compressor or compressor 22 and a fluidically between the exhaust outlet 2 and the exhaust inlet 3 arranged turbocharger 24 , An embodiment without turbocharger is also possible.

In the flow direction 13 of the exhaust gas are downstream of the exhaust gas inlet 3 a lean NO _x trap 4 and downstream of it, an active SCR catalyst 7 arranged and via a flow channel 10 fluidly connected to each other. A by-pass flow channel 5 bridged fluidically the lean NO _x trap 4 , This is done by the flow channel 10 via a by-pass valve 6 a branch provided the inlet 15 into the by-pass flow channel 5 forms. Also, downstream is the lean NO _x trap 4 and the by-pass flow channel 5 , as well as upstream of the SCR catalyst 7 a urea injector 8th arranged. The urea injector 8th enables autonomous operation of the active SCR catalyst 7 ,

In addition, between the lean NO _x trap 4 and the by-pass flow channel 5 on the one hand and the urea injector 8th and the active SCR catalyst 7 on the other side a diesel oxidation catalyst (DOC) 9 and / or diesel particulate filter DPF 19 , For example, a catalytically coated diesel particulate filter CDPF be arranged. The diesel oxidation catalyst and / or the (catalytically coated) particulate filter prevent too high HC and CO emissions.

The in the 2 shown variant also includes a low pressure exhaust gas recirculation passage 25 , This branches downstream of the lean NO _x trap 4 and upstream of the SCR catalyst 7 , preferably between the diesel particulate filter 19 and the diesel oxidation catalyst 9 , from the flow channel 10 and directs exhaust gas back to a position upstream of the compressor 22 , This is a valve 26 upstream of the compressor 22 intended. This is relevant for increasing the exhaust gas recirculation rate in the context of the method according to the invention, wherein the valve 26 can be designed to adjust the exhaust gas recirculation rate.

The by-pass flow channel 5 also has the advantage that by bridging the lean NO _x trap after a cold start, the sulfur deposition is cumulated and significantly reduced over a long distance. The desulphurisation intervals can thereby be increased considerably, the fuel consumption can be reduced and thermal aging is likewise reduced. Overall, so the life of the entire catalyst is extended. Furthermore, the NO _x storage capacity is increased with respect to the life of the NO _x trap.

The exhaust gas of the internal combustion engine 1 becomes after leaving the lean NO _x trap 4 or after leaving the by-pass flow channel 5 if it is not over the flow channel 25 to the compressor 22 is returned by an upstream of the SCR catalyst 7 arranged diesel oxidation catalyst (DOC) 9 in the SCR catalyst 7 directed. As a result, an HC conversion and a CO conversion are ensured, in particular with regard to the exhaust gas flowing past the lean NO _x trap from the by-pass flow channel.

The exhaust gas of the internal combustion engine after leaving the lean NO _x trap or after leaving the by-pass flow channel arranged in a further variant, by a upstream of the SCR catalyst active diesel particulate filter 19 , for example, a catalytically coated diesel particulate filter CDPF, in the SCR catalyst 7 directed.

Optionally, downstream of the lean NO _x trap 4 and upstream of the active SCR catalyst 7 Urea, for example in the form of AdBlue, injected into the exhaust gas. If a DOC 9 is provided, the urea is preferably injected downstream of the DOC 8th ,

In principle, additional information can be used within the scope of the invention for the further improvement and optimization of the exhaust gas aftertreatment. Such information may be available, for example, via GPS, known future routes, route prediction or navigation systems, V2V (vehicle-to-vehicle connection), ie information exchanged wirelessly between vehicles, traffic light information, an adaptive cruise control system, or otherwise.

The 3 schematically shows a motor vehicle 20 which is a device described above 21 for regulating the exhaust gas temperature. The motor vehicle has the same advantages as the device according to the invention described above 21 , The motor vehicle may be, for example, a passenger car or a lorry.

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• US 2007/0271908 A1 [0005]
• US 2006/0273187 A1 [0005]

Claims (16)

Process for the aftertreatment of exhaust gas of an internal combustion engine ( 1 ), where a lean NO _x trap ( 4 ) and the lean NO _x trap ( 4 ) Fluidically bridging by-pass flow channel ( 5 ) with a by-pass valve ( 6 ) and one in the flow direction ( 13 ) of the exhaust gas downstream of the lean NO _x trap ( 4 ) arranged SCR catalyst ( 7 ), characterized in that the method comprises the following steps: - defining a temperature range ( 31 ) of the SCR catalyst ( 7 ), - setting a threshold value for the exhaust gas mass flow ( 32 ) through the SCR catalyst ( 7 ), - detecting the temperature ( 33 ) of the SCR catalyst ( 7 ), - detecting the exhaust gas mass flow ( 34 ) through the SCR catalyst ( 7 ), If the detected temperature of the SCR catalyst is within the specified temperature range ( 35 ) and the detected exhaust gas mass flow exceeds the threshold value ( 36 ), Passing an exhaust gas mass flow through the lean NO _x trap ( 4 and increasing an exhaust gas recirculation rate to a value that causes an automatic NO _x desorption in the lean NO _x trap ( 37 ), and - forwarding the lean NO _x trap ( 4 ) leaving exhaust gas ( 38 ) to the SCR catalyst ( 7 ). A method according to claim 1, characterized in that a lower threshold temperature of the lean NO _x trap ( 4 ) and / or a lower threshold temperature of the SCR catalyst ( 7 ) and as long as the lower threshold temperature of the lean NO _x trap ( 4 ) and / or the lower threshold temperature of the SCR catalyst ( 7 ) are the by-pass valve ( 6 ) is adjusted so that no exhaust gas mass flow through the by-pass flow channel ( 5 ) flows. A method according to claim 2, characterized in that the by-pass valve ( 6 ) is adjusted so that an exhaust gas mass flow through the by-pass flow channel ( 5 ) flows when the lower threshold temperature of the SCR catalyst ( 7 ) is reached or exceeded. Method according to one of claims 1 to 3, characterized in that a lower threshold NO _x storage level of the lean NO _x trap ( 4 ) and the by-pass valve ( 6 ) to the lower threshold NO _x storage level of the lean NO _x trap ( 4 ) is set so that no exhaust gas mass flow through the by-pass flow channel ( 5 ) flows. Method according to one of claims 1 to 4, characterized in that an active SCR catalyst ( 7 ) is used. Method according to one of claims 1 to 5, characterized in that the efficiency of the SCR catalyst ( 7 ) is set for the NO _x conversion and the temperature range of the SCR catalyst for the specified efficiency of the NO _x conversion is set and / or the exhaust gas mass flow is determined by the SCR catalyst for the specified efficiency of NO _x conversion. A method according to claim 6, characterized in that the efficiency of the SCR catalyst ( 7 ) for NO _x conversion using a kinetic model describing the conversion by the SCR catalyst. Method according to one of claims 1 to 7, characterized in that a by-pass valve ( 6 ) which can be opened and closed discontinuously or continuously from 0% to 100%. Method according to one of claims 1 to 8, characterized in that the exhaust gas of the internal combustion engine ( 1 ) after leaving the lean NO _x trap ( 4 ) or after leaving the by-pass flow channel ( 5 ) through an upstream of the SCR catalyst ( 7 ) arranged diesel oxidation catalyst ( 9 ) into the SCR catalyst ( 7 ). Method according to one of claims 1 to 9, characterized in that the exhaust gas of the internal combustion engine ( 1 ) after leaving the lean NO _x trap ( 4 ) or after leaving the by-pass flow channel ( 5 ) through an upstream of the SCR catalyst ( 7 ) arranged diesel particulate filter ( 19 ) into the SCR catalyst ( 7 ). Method according to one of claims 1 to 10, characterized in that downstream of the lean NO _x trap ( 4 ) and upstream of the SCR catalyst ( 7 ) Urea is injected into the exhaust gas. Device for exhaust aftertreatment ( 21 ) for an internal combustion engine ( 1 ) with an exhaust gas outlet ( 2 ) designed for carrying out a method according to one of the preceding claims, wherein the device ( 21 ) one with the exhaust outlet ( 2 ) fluidically connectable or connected exhaust gas inlet ( 3 ), one in the flow direction ( 13 ) of the exhaust gas downstream of the exhaust gas inlet ( 3 ) arranged lean NO _x trap ( 4 ) and the lean NO _x trap ( 4 ) flow-bridging by-pass flow channel ( 5 ) with a by-pass valve ( 6 ) downstream of the lean NO _x trap ( 4 ) and by-pass flow channel ( 5 ) a urea injector ( 8th ) and an apparatus for active selective catalytic reduction (active SCR catalyst) ( 7 ), wherein the active SCR catalyst ( 7 ) downstream of the urea injector ( 8th ) is arranged. Contraption ( 21 ) according to claim 12, wherein the device ( 21 ) a diesel oxidation catalyst ( 9 ) located downstream of the lean NO _x trap ( 4 ) and by-pass flow channel ( 5 ) and upstream of the urea injector ( 8th ) and the active SCR catalyst ( 7 ) is arranged. Contraption ( 21 ) according to claim 12 or 13, wherein the device ( 21 ) a diesel particulate filter DPF ( 19 ) located downstream of the lean NO _x trap ( 4 ) and by-pass flow channel ( 5 ) and upstream of the urea injector ( 8th ) and the active SCR catalyst ( 7 ) is arranged. Contraption ( 21 ) according to one of claims 12 to 14, wherein the device has a low-pressure exhaust gas recirculation channel ( 25 ), the exhaust gas from a position downstream of the lean NO _x trap ( 4 ) to a compressor ( 23 ). Motor vehicle ( 20 ), characterized in that it comprises a device ( 21 ) according to any one of claims 12 to 15.

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