DE102020116160B3 - Process for exhaust aftertreatment of an internal combustion engine and exhaust aftertreatment system - Google Patents

Abstract

The invention relates to a method and a system for exhaust gas aftertreatment of an internal combustion engine (10) with an exhaust system (40), in which an exhaust gas aftertreatment component (52, 54) through an exhaust duct (42) of the exhaust system (40) in the flow direction of an exhaust gas stream of the internal combustion engine (10) , 56) for the selective catalytic reduction of nitrogen oxides and downstream of this exhaust gas aftertreatment component (52, 54, 56) a blocking catalytic converter (58) is arranged. A bypass (62) branches off from the exhaust gas duct (42) upstream of the exhaust gas aftertreatment component (52, 54, 56) at a junction (76) which, downstream of the junction (76) and upstream of the exhaust gas aftertreatment component (52, 54, 56) at a The confluence (92) opens again into the exhaust gas duct (42). A passive NOx adsorber (88) is arranged in the bypass (62). An adjusting element (78) is provided on the exhaust gas duct (42), with which the exhaust gas flow from the internal combustion engine (10) can be routed either through a main duct (94) of the exhaust gas duct (42) or through the bypass (62). The passive NOx adsorber is loaded with nitrogen oxides in a cold start phase of the internal combustion engine (10) and regenerated again when the exhaust gas aftertreatment component (52, 54, 56) is ready for use.

Description

The invention relates to a method for exhaust gas aftertreatment of an internal combustion engine, in particular a diesel engine, as well as an exhaust gas aftertreatment system for carrying out such a method according to the preamble of the independent claims.

The current exhaust gas legislation, and one that will become increasingly strict in the future, place high demands on the engine-related raw emissions and the exhaust gas aftertreatment of internal combustion engines. The demands for a further decrease in consumption and the further tightening of the exhaust gas standards with regard to the permissible nitrogen oxide emissions represent a challenge for the engine developers. Upstream and downstream catalytic converters. Exhaust gas aftertreatment systems are currently used in diesel engines which have an oxidation catalytic converter, a catalytic converter for the selective catalytic reduction of nitrogen oxides (SCR catalytic converter) and a particle filter for separating out soot particles and possibly other catalytic converters. Ammonia is preferably used as the reducing agent. Because dealing with pure ammonia is complex, a synthetic, aqueous urea solution is usually used in vehicles, which is mixed with the hot exhaust gas flow in a mixing device upstream of the SCR catalytic converter. As a result of this mixing, the aqueous urea solution is heated, the aqueous urea solution releasing ammonia in the exhaust gas duct. A commercially available, aqueous urea solution generally consists of 32.5% urea and 67.5% water.

Every device for catalytic exhaust gas cleaning requires that a minimum temperature, the so-called light-off temperature, be exceeded in order to be effective. During a cold start of a motor vehicle, the internal combustion engine and the components for exhaust gas aftertreatment have a temperature level approximately at ambient temperature. Even with a high energy input into the exhaust system, the thermally inert mass of the exhaust system must first be overcome and the radiation or convection losses compensated in order to achieve at least a partial effectiveness of the exhaust gas aftertreatment components. During this time, the raw emissions of the internal combustion engine are emitted largely uncleaned. Depending on the energy input into the exhaust system, this period can be shortened, but never reduced to zero.

In diesel engines, it is known to connect a NOx storage catalytic converter upstream of an SCR exhaust gas purification system, which already provides good conversion performance in the 120-200 ° C range, while the SCR catalytic converter only enables nitrogen oxide emissions to be converted from around 180 ° C. The exhaust gas aftertreatment components can be supported individually or as a whole during their heating phase, in particular up to the respective light-off temperature, by electrical heating elements or thermal exhaust gas burners.

the DE 698 17 090 T2 discloses an exhaust gas aftertreatment system with an exhaust system which has a main duct and a bypass, the bypass opening back into the main duct of the exhaust system upstream of a De-NOx catalyst, a NOx adsorber being arranged in the bypass. In this case, a control valve is arranged at the branching from the main channel and the bypass, with which the gas flow can be directed through the main channel or the bypass. An electrical heating element with which the NOx adsorber can be heated is provided on the NOx adsorber.

From the DE 197 40 702 C1 an exhaust gas aftertreatment system for an internal combustion engine is known. The exhaust gas aftertreatment system comprises an exhaust system with a main exhaust line and a bypass, with an exhaust flap being arranged in the main exhaust line, with which an exhaust gas flow from the internal combustion engine can optionally be directed through the main exhaust line or the bypass. The bypass opens into the main exhaust line upstream of an SCR catalytic converter. A NOx storage catalytic converter is arranged in the bypass, upstream of which a hydrolysis catalytic converter, via which the NOx storage catalytic converter can be regenerated.

the US 2013/0 118 150 A1 discloses an exhaust gas aftertreatment system for an internal combustion engine and a method for exhaust gas aftertreatment of the internal combustion engine. The exhaust gases from the internal combustion engine are stored in a passive NOx adsorber and are released again at a later point in time, when an SCR catalytic converter has reached its operating temperature, and converted by this SCR catalytic converter.

From the DE 10 2018 122 875 A1 an exhaust gas aftertreatment system for a compression ignition internal combustion engine based on the diesel principle is known. In the exhaust system of the internal combustion engine, there is a first catalytic converter in the flow direction of the exhaust gas, and a first catalytic converter downstream of the first catalytic converter Exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides and further downstream a second exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides. A low-temperature NOx storage catalytic converter is arranged downstream of the first exhaust gas aftertreatment component and upstream of the second exhaust gas aftertreatment component. It is provided that in a cold start phase of the internal combustion engine, the nitrogen oxides are stored in the low-temperature NOx storage catalytic converter and, before the nitrogen oxides desorb from this low-temperature NOx storage catalytic converter, at least one further nitrogen oxide-reducing exhaust gas aftertreatment component is heated to its light-off temperature in order to to convert nitrogen oxides released from the low-temperature NOx storage catalytic converter.

EP 3 428 415 A1 describes an exhaust gas aftertreatment system for exhaust gas aftertreatment of an internal combustion engine with an SCR catalytic converter and a blocking catalytic converter arranged downstream of the SCR catalytic converter, a passive NOx adsorber being arranged upstream of the SCR catalytic converter, which can be bypassed with a bypass.

From the DE 101 52 187 A1 an exhaust gas purification system for purifying the exhaust gas of a predominantly lean-burn internal combustion engine, in particular a motor vehicle, with an exhaust line in which a three-way catalytic converter, a nitrogen oxide storage catalytic converter and an SCR catalytic converter are arranged one behind the other in the direction of flow is known. The exhaust gas cleaning device has a bypass line with which exhaust gas flowing out of the three-way catalytic converter can be fed to the SCR catalytic converter while bypassing the nitrogen oxide storage catalytic converter.

the DE 10 2007 030 235 B4 describes a method for treating exhaust gases from an internal combustion engine, in which the exhaust gas supplied by the internal combustion engine is fed to a NOx storage catalytic converter for storing nitrogen oxides and an SCR catalytic converter arranged downstream of the NOx storage catalytic converter for the selective catalytic reduction of nitrogen oxides. The NO storage catalytic converter is arranged in a secondary exhaust gas line of the exhaust system that runs parallel to a primary exhaust gas line, with an exhaust gas flow over the NO storage catalytic converter being selectively interrupted or enabled depending on the operating state of the SCR catalytic converter and / or the NO storage catalytic converter.

It is also known from the prior art to arrange one or more exhaust gas aftertreatment components upstream of a turbine of an exhaust gas turbocharger in order to use the higher exhaust gas temperature upstream of the turbine for faster heating to the light-off temperature of this exhaust gas aftertreatment component. Insulations for reducing heat losses on the walls of the exhaust system are also known. All of these devices take some time to activate. During this period, a particularly high-pollutant driving style can already lead to the permissible emission limit values for an RDE trip (Real Driving Emissions) being exceeded, so that even with a subsequent 100% conversion rate, the entire driving cycle would have to be rated as "failed". The NOx emissions, which increase disproportionately with increasing driving dynamics, are particularly critical here.

The invention is now based on the object of further developing the exhaust system of the internal combustion engine in such a way that improved exhaust gas aftertreatment is possible and, in particular, the nitrogen oxide emissions can be reduced after a cold start of the internal combustion engine.

• - Starten des Verbrennungsmotors, wobei der gesamte Abgasstrom des Verbrennungsmotors durch den Bypass geleitet wird und die Stickoxide im passiven NOx-Adsorber eingespeichert werden,
• - Ermitteln einer Abgastemperatur oder eines Füllstands des passiven NOx-Adsorbers, wobei bei Überschreiten eines ersten Schwellenwertes für die Abgastemperatur oder eines Schwellenwertes des Füllstands der Abgasstrom des Verbrennungsmotors durch den Hauptkanal geleitet wird, und
• - Regenerieren des passiven NOx-Adsorbers, indem der Abgasstrom des Verbrennungsmotors zumindest anteilig durch den Bypass geleitet wird, wenn die Abgasnachbehandlungskomponente zur selektiven katalytischen Reduktion ihre Betriebstemperatur erreicht hat und die Abgastemperatur einen zweiten Schwellenwert erreicht hat.

According to the invention, this object is achieved by a method for exhaust gas aftertreatment of an internal combustion engine with an exhaust system in which an exhaust gas aftertreatment component for the selective catalytic reduction of nitrogen oxides is arranged in the flow direction of an exhaust gas flow of the internal combustion engine through an exhaust gas duct of the exhaust system and a blocking catalyst is arranged downstream of this exhaust gas aftertreatment component. A bypass branches off from the exhaust gas duct at a branch upstream of the exhaust gas aftertreatment component, which bypass opens again into the exhaust gas duct at a junction downstream of the branch and upstream of the exhaust gas aftertreatment component. A passive NOx adsorber is arranged in the bypass. An adjusting element is provided on the exhaust gas duct, with which the exhaust gas flow from the internal combustion engine can optionally be directed through a main duct of the exhaust gas duct or through the bypass. The process consists of the following steps:

• - Starting the internal combustion engine, whereby the entire exhaust gas flow of the internal combustion engine is passed through the bypass and the nitrogen oxides are stored in the passive NOx adsorber,
• - Determining an exhaust gas temperature or a fill level of the passive NOx adsorber, the exhaust gas flow of the internal combustion engine being passed through the main duct when a first threshold value for the exhaust gas temperature or a threshold value for the fill level is exceeded, and
• - Regeneration of the passive NOx adsorber by the exhaust gas flow of the internal combustion engine at least partially through the bypass is routed when the exhaust gas aftertreatment component for selective catalytic reduction has reached its operating temperature and the exhaust gas temperature has reached a second threshold value.

The distribution of the exhaust gas flow between the bypass and the main channel can also be done proportionally by the adjusting element. The proportion of the exhaust gas flow through the NOx adsorber depends on the difference between the possible NOx conversion of the downstream SCR system and the current raw NOx level.

Such a method can reduce the nitrogen oxide emissions in the cold start phase compared to the solutions known from the prior art. The nitrogen oxide emissions are stored in the passive NOx adsorber in a first phase after the cold start of the internal combustion engine. The passive NOx adsorber stores nitrogen oxides in a temperature range of 80 ° C to around 200 ° C and releases them again above this temperature. In this way, the nitrogen oxides produced in the cold start phase can be temporarily stored until the SCR catalytic converter has reached its operating temperature and enables nitrogen oxides to be converted by means of a selective, catalytic reduction. An operating temperature of the SCR catalytic converter is to be understood in this context as the temperature range in which an efficient conversion of the nitrogen oxides is possible by means of selective catalytic reduction. With known SCR catalytic converters, this temperature range is between 200 ° C and 380 ° C. After the cold start phase, the exhaust gas aftertreatment takes place in a known manner, preferably via a particle filter with an SCR coating and a downstream SCR catalytic converter.

The passive NOx adsorber can enable a good, but only temporary, NOx reduction very soon after a cold start of the internal combustion engine. By combining it with a particle filter with an SCR coating or an SCR catalytic converter, which is heated to its light-off temperature during the cold start phase and reaches this before the nitrogen oxides are desorbed from the passive NOx adsorber, the Nitrogen oxide emissions in the cold start phase of the internal combustion engine are significantly reduced. The position of the passive NOx adsorber in a bypass to the exhaust gas duct ensures that the passive NOx adsorber can be decoupled from the exhaust gas flow after the cold start phase or can be regenerated through a targeted control so that the passive NOx adsorber when a new one occurs Starting process is essentially completely emptied and can store a sufficient amount of nitrogen oxides.

Furthermore, the passive NOx adsorber can be decoupled from the exhaust gas flow at higher temperatures, in particular at temperatures above the desorption temperature of the nitrogen oxides stored in the passive NOx adsorber, in order to reduce thermal aging of the passive NOx adsorber and / or the flow resistance in the Reduce exhaust system.

The features mentioned in the dependent claims enable advantageous further developments and non-trivial improvements of the method for exhaust gas aftertreatment specified in the independent claim.

In a preferred embodiment of the invention it is provided that the first threshold value is below the second threshold value of the exhaust gas temperature. This can prevent the nitrogen oxides from thermally desorbing to a greater extent before the exhaust gas aftertreatment component for the selective catalytic reduction of nitrogen oxides has reached its operating temperature.

It is preferred here if the first threshold value for the exhaust gas temperature is in the range from 150 ° C. to 250 ° C., preferably in the range from 150 ° C. to 200 ° C. The second threshold value for the exhaust gas temperature is preferably in the range from 200 ° C. to 350 ° C., particularly preferably in the range from 220 ° C. to 300 ° C.

In an advantageous embodiment of the method it is provided that the threshold value for the fill level of the passive NOx adsorber is in the range of 50% -100%, preferably at least 80%, particularly preferably 90%.

Another aspect of the invention relates to an exhaust gas aftertreatment system for exhaust gas aftertreatment of an internal combustion engine with an exhaust system, in which an exhaust gas aftertreatment component for the selective catalytic reduction of nitrogen oxides is arranged in the flow direction of an exhaust gas flow of the internal combustion engine through an exhaust duct of the exhaust system and a blocking catalyst is arranged downstream of this exhaust gas aftertreatment component. Upstream of the exhaust gas aftertreatment component, a bypass branches off from the exhaust gas duct at a junction which, downstream of the branch and upstream of the exhaust gas aftertreatment component, opens again into the exhaust duct at a confluence, a passive NOx adsorber being arranged in the bypass. An adjusting element is provided on the exhaust gas duct, with which the exhaust gas flow from the internal combustion engine can optionally be directed through a main duct of the exhaust gas duct or through the bypass.

In this context, a passive NOx adsorber is to be understood as a storage catalytic converter which has a high NOx storage capacity in a temperature range of 80 ° C - 200 ° C, but which emits the stored nitrogen oxides again unconverted at higher temperatures. Such a passive NOx adsorber can therefore enable a good, but only temporary, NOx reduction very soon after a cold start of the internal combustion engine. By combining it with a particle filter with an SCR coating or an SCR catalytic converter, which is heated to its light-off temperature during the cold start phase and reaches this before the nitrogen oxides are desorbed from the passive NOx adsorber, the Nitrogen oxide emissions in the cold start phase of the internal combustion engine are significantly reduced. Furthermore, the passive NOx adsorber can be decoupled from the exhaust gas flow at higher temperatures, in particular at temperatures above the desorption temperature of the nitrogen oxides stored in the passive NOx adsorber, in order to reduce thermal aging of the passive NOx adsorber and / or the flow resistance in the Reduce exhaust system.

According to the invention it is provided that an exhaust gas recirculation line of a low-pressure exhaust gas recirculation branches off from the exhaust gas duct at the branch, the passive NOx adsorber being arranged in the exhaust gas recirculation line. The exhaust gas recirculation line has a further branch at which a bypass branches off from the exhaust gas recirculation line, which connects the exhaust gas recirculation line to the exhaust gas duct downstream of the control element and upstream of the exhaust gas aftertreatment component for the selective catalytic reduction of nitrogen oxides. The installation space can be optimally used by arranging the passive NOx adsorber in the low-pressure exhaust gas recirculation system. In addition, the number of additional components can be reduced, whereby the additional costs can be reduced. By reducing the NOx emissions in the recirculated exhaust gas flow of the internal combustion engine, the raw emissions of the internal combustion engine can also be reduced, whereby the tailpipe emissions can be minimized, especially in the cold start phase of the internal combustion engine.

According to the invention it is provided that a device for exhaust gas heat recovery, in particular an exhaust gas recirculation cooler for the low pressure exhaust gas recirculation, is arranged in the exhaust gas recirculation line downstream of the passive NOx adsorber and upstream of the further branch. The coolant of the internal combustion engine can be heated more quickly by the recirculated exhaust gas, whereby the friction of the internal combustion engine can be reduced. This leads to a consumption advantage and lower raw emissions in the cold start phase.

In an advantageous embodiment of the exhaust aftertreatment system it is provided that the exhaust aftertreatment system has a first exhaust aftertreatment component close to the engine for the selective catalytic reduction of nitrogen oxides and a two exhaust aftertreatment component arranged downstream of the first exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides, the bypass branching off the first exhaust gas duct downstream of the first exhaust gas duct and opens up into the exhaust duct again upstream of the two exhaust gas aftertreatment components. Since the exhaust aftertreatment component close to the engine heats up faster than the second exhaust aftertreatment component remote from the engine, the first exhaust aftertreatment component can reach its operating temperature for selective catalytic reduction before there is significant desorption of nitrogen oxides from the passive NOx adsorber. Thus, at least one exhaust gas aftertreatment component is always active to reduce nitrogen oxide emissions, which means that cold start emissions can be further reduced.

In a further improvement of the invention it is provided that an outlet of the internal combustion engine is arranged downstream and a first metering element is arranged upstream of the first exhaust gas aftertreatment component for the selective catalytic reduction of nitrogen oxides and a second metering element is arranged downstream of the confluence and upstream of the two exhaust gas aftertreatment components for the selective catalytic reduction of nitrogen oxides. As a result, the operating range of the exhaust gas aftertreatment system can be expanded so that at least one exhaust gas aftertreatment component for the selective catalytic reduction of nitrogen oxides is operated in a temperature range ideal for converting the nitrogen oxides even in a high load or full load range.

In an advantageous embodiment of the exhaust gas aftertreatment system, it is provided that the last exhaust gas aftertreatment component in the flow direction is followed by a barrier catalytic converter for the selective catalytic reduction of nitrogen oxides. This can prevent unused ammonia from being emitted into the environment.

The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless stated otherwise in the individual case.

• 1 einen Verbrennungsmotor mit einem Luftversorgungssystem und einer Abgasanlage mit einem erfindungsgemäßen Abgasnachbehandlungssystem;
• 2 ein weiteres Ausführungsbeispiel für ein erfindungsgemäßes Abgasnach behand lungssystem;
• 3 bis 5 das Abgasnachbehandlungssystem aus 2 in drei verschiedenen Betriebszuständen; und
• 6 bis 8 das Abgasnachbehandlungssystem aus 1 in drei verschiedenen Betriebszuständen.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. The same components or components with the same function are identified with the same reference symbols. Show it:

• 1 an internal combustion engine with an air supply system and an exhaust system with an exhaust gas aftertreatment system according to the invention;
• 2 a further embodiment for an inventive exhaust gas treatment system;
• 3 until 5 the exhaust aftertreatment system 2 in three different operating states; and
• 6th until 8th the exhaust aftertreatment system 1 in three different operating states.

1 shows the schematic representation of an internal combustion engine 10 . The internal combustion engine 10 is designed as a direct injection diesel engine. The internal combustion engine 10 has several combustion chambers 12th on. At the combustion chambers 12th is a fuel injector each 14th for injecting a fuel into the respective combustion chamber 12th arranged. The internal combustion engine 10 is with his inlet 16 with an air supply system 20th and with its outlet 18th with an exhaust system 40 tied together. The internal combustion engine 10 further comprises a high pressure exhaust gas recirculation 30th with an exhaust gas recirculation line 36 and a high pressure EGR valve 38 , via which an exhaust gas from the internal combustion engine 10 from the outlet 18th to the inlet 16 can be traced back. At the combustion chambers 12th inlet valves and outlet valves are arranged, with which a fluidic connection from the air supply system 20th to the combustion chambers 12th or from the combustion chambers 12th to the exhaust system 40 can be opened or closed.

The air supply system 20th includes an intake duct 28 , in which in the direction of flow of fresh air through the intake duct 28 an air filter 22nd , downstream of the air filter 22nd an air mass meter 24 , in particular a hot film air mass meter, downstream of the air mass meter 24 a compressor 26th of an exhaust gas turbocharger 60 , downstream of the compressor 26th an intercooler 32 are arranged. The air mass meter can do this 24 also in a filter housing of the air filter 22nd be arranged so that the air filter 22nd and the air mass meter 24 form an assembly. Downstream of the air filter 22nd and upstream of the compressor 26th is a confluence 34 provided on which an exhaust gas recirculation line 86 a low pressure exhaust gas recirculation 80 in the intake duct 28 flows out.

The exhaust system 40 includes an exhaust duct 42 , in which in the flow direction of an exhaust gas of the internal combustion engine 10 through the exhaust duct 42 a turbine 44 of the exhaust gas turbocharger 60 is arranged, which the compressor 26th in the air supply system 20th drives over a shaft. The exhaust gas turbocharger 60 is preferably used as an exhaust gas turbocharger 60 designed with variable turbine geometry. To do this are a turbine wheel of the turbine 44 adjustable guide vanes are connected upstream, via which the flow of the exhaust gas onto the blades of the turbine 44 can be varied. Downstream of the turbine 44 are several exhaust aftertreatment components 46 , 48 , 50 , 52 , 54 , 56 , 58 intended. This is immediately downstream of the turbine 44 as the first component of the exhaust gas aftertreatment, a first catalytic converter 46 , in particular a NOx storage catalytic converter 48 or an oxidation catalytic converter 40 arranged. Downstream of the first catalyst 46 is a particulate filter 52 with a coating 54 arranged for the selective catalytic reduction of nitrogen oxides. Downstream of the particulate filter 52 is another SCR catalytic converter 56 arranged, which a blocking catalyst 58 is downstream. Downstream of the particulate filter 52 is in the exhaust duct 42 an exhaust flap 78 provided with which the cross section of the exhaust duct 42 can be at least partially blocked to reduce the exhaust gas back pressure in the exhaust gas duct 42 to increase. Downstream of the particulate filter 52 and upstream of the exhaust flap 78 is on the exhaust duct 42 a branch 76 provided on which an exhaust gas recirculation line 86 a low pressure exhaust gas recirculation 80 from the exhaust duct 42 branches off.

The low-pressure exhaust gas recirculation 80 includes in addition to the exhaust gas recirculation line 86 a low pressure exhaust gas recirculation cooler 82 and an exhaust gas recirculation valve 84 , via which the exhaust gas recirculation through the exhaust gas recirculation line 86 is controllable. It is also in the low-pressure exhaust gas recirculation 80 downstream of the branch 76 and upstream of the EGR cooler 82 a passive NOx adsorber 88 arranged. Downstream of the EGR cooler 82 is on the exhaust gas recirculation line 86 another branch 74 formed on which a bypass from the exhaust gas recirculation line 86 branches off which the exhaust gas recirculation duct 86 with the exhaust duct 42 downstream of the exhaust flap 78 and upstream of the SCR catalyst 56 connects.

In the bypass 62 is a control 64 arranged with which the bypass 62 can be opened and closed. On the exhaust gas recirculation line 86 the low-pressure exhaust gas recirculation 80 is a temperature sensor 70 provided, over which an exhaust gas temperature in the low-pressure exhaust gas recirculation 80 can be determined to the low pressure exhaust gas recirculation 80 to Activate as soon as the exhaust gas temperature is in the low-pressure exhaust gas recirculation 80 has exceeded a defined threshold. It can thus be prevented that water vapor or reducing agent contained in the exhaust gas for the selective catalytic reduction of nitrogen oxides, in particular liquid urea solution, condenses out and in the low-pressure exhaust gas recirculation 80 or in the air supply system 20th leads to damage or deposits.

In the exhaust duct 42 is, preferably on one of the exhaust aftertreatment components 46 , 48 , 50 , 52 , 54 , 56 , 58 , especially on the particle filter 52 or on the SCR catalytic converter 56 , a temperature sensor 70 provided with which an exhaust gas temperature in the exhaust system 40 can be monitored to ensure effective and efficient exhaust gas aftertreatment of the exhaust gas of the internal combustion engine 10 to enable. There are also differential pressure sensors 72 provided to create a pressure difference across the particulate filter 52 to determine. In this way, the loading status of the particle filter 52 and a regeneration of the particle filter when a defined load level is exceeded 52 be initiated. It is also on the exhaust duct 42 at least one dosing module 66 , 68 provided to a reducing agent, in particular aqueous urea solution, upstream of the SCR catalytic converter 56 and / or upstream of the particulate filter 52 in the exhaust duct 42 to dose. There are preferably two metering elements 66 , 68 provided, the first metering element 66 downstream of the first catalyst 46 and upstream of the particulate filter 52 and the second metering element 68 downstream of the exhaust flap 78 and upstream of the SCR catalyst 56 is arranged. Every dosing element 66 , 68 can be an exhaust mixer 94 be connected downstream in order to achieve an improved mixing of the exhaust gas flow with the reducing agent.

The internal combustion engine 10 is with an engine control unit 90 connected, which via signal lines, not shown, with the pressure and temperature sensors 70 , 72 as well as with the fuel injectors 14th of the internal combustion engine 10 and the control devices 24 , 38 , 64 , 66 , 68 , 78 , 84 of the air supply system 20th as well as the exhaust system 40 connected is.

In 2 an alternative embodiment of an exhaust gas aftertreatment system according to the invention is shown. With essentially the same structure, in this exemplary embodiment only the one in the flow direction of an exhaust gas flow through the exhaust system 40 rear section of the exhaust system 40 shown. The exhaust system 40 includes an exhaust duct 42 , which is at a branch 76 in a main channel 94 and a bypass 62 branched. In the main channel 94 is an exhaust flap 78 arranged with which the main channel 94 can be locked. In the bypass 62 is a passive NOx adsorber 88 arranged. The bypass 62 opens at a confluence 92 back into the exhaust duct 42 a. Downstream of the confluence 92 is a dosing element 66 , 68 , in particular a second metering element 68 arranged, which an exhaust mixer 98 is downstream. Downstream of the exhaust mixer 98 is an exhaust aftertreatment component 52 , 54 , 56 on selective catalytic reduction of nitrogen oxides, in particular an SCR catalytic converter 56 arranged. The SCR catalytic converter 56 is a blocking catalyst in the flow direction of the exhaust gas flow 58 , in particular an oxidation catalytic converter or an ammonia barrier catalytic converter, arranged in order to prevent an escape of reducing agent and an associated environmental emission.

In 3 is that in 2 Exhaust aftertreatment system described shown in a first operating state, which allows operation with a cold exhaust system 40 , for example immediately after a cold start of the internal combustion engine 10 represents. The exhaust flap is in the first operating state 78 closed, so that the entire exhaust gas flow of the internal combustion engine 10 through the bypass 62 is conducted, the nitrogen oxide emissions in the passive NOx adsorber 88 can be saved.

In 4th a second operating state of the exhaust gas aftertreatment system is shown. This operating state is selected when the exhaust gas temperature _{has exceeded a first threshold value T EGS1} and / or the passive NOx adsorber 88 a threshold value F _pNAS for the level F _{pNA of} the passive NOx adsorber 88 has achieved, especially when the passive NOx adsorber is almost completely filled and has no further storage capacity to absorb nitrogen oxides. The exhaust flap is in this second operating state 78 opened and the exhaust gas flow of the internal combustion engine 10 through the main channel 94 out, so the passive NOx adsorber 88 essentially from the exhaust gas flow of the internal combustion engine 10 is decoupled.

In this operating state, the nitrogen oxides are absorbed by the (in the 2 - 5 ) Not shown close to the engine exhaust aftertreatment component 52 , 54 for the selective catalytic reduction of nitrogen oxides or through the SCR catalytic converter 56 converted, provided that it has already reached its operating temperature.

In 5 a third operating state of the exhaust gas aftertreatment system is shown. The exhaust flap is in this third operating state 78 closed to a hot exhaust gas stream of the internal combustion engine 10 through the bypass 62 respectively. The exhaust gas temperature T _{EG is} above the desorption temperature of the passive NOx adsorber 88 so the nitrogen oxides, preferably completely, from the passive NOx adsorber 88 desorb and through the SCR catalytic converter 56 downstream of the passive NOx adsorber 88 can be converted. This becomes the passive NOx adsorber 88 emptied and regenerated when the internal combustion engine is restarted 10 to be able to store nitrogen oxides again.

In the 6th - 8th are three operating states of the in 1 illustrated exhaust aftertreatment system. The in 6th The operating state shown represents an operation immediately after a cold start of the internal combustion engine 10 in which the exhaust aftertreatment components 46 , 48 , 50 , 52 , 54 , 56 , 58 have not yet reached their operating temperature and cannot contribute to an efficient conversion of the pollutants. The exhaust flap is in the first operating state 78 closed, so that the entire exhaust gas flow of the internal combustion engine 10 through the bypass 62 is conducted, the nitrogen oxide emissions in the passive NOx adsorber 88 can be saved. The bypass 62 In this embodiment, the exhaust gas aftertreatment system includes the first section of the exhaust gas recirculation line from the first branch 76 until further branching 74 as well as the section of the bypass 62 , which is the further branch 74 with the confluence 92 in the exhaust duct 92 connects. The control flaps are in the first operating state 78 as well as the exhaust gas recirculation valve 84 the low-pressure exhaust gas recirculation 80 closed and the control 64 in bypass 62 opened.

In 7th a second operating state of the exhaust gas aftertreatment system is shown, which follows the first operating state when the exhaust gas temperature _{has exceeded a first threshold value T EGS1} and / or the passive NOx adsorber 88 a threshold value F _pNAS for the level F _{pNA of} the passive NOx adsorber 88 has achieved, especially when the passive NOx adsorber is almost completely filled and has no further storage capacity to absorb nitrogen oxides. The exhaust flap is in this second operating state 78 opened and the exhaust gas flow of the internal combustion engine 10 through the main channel 94 out, so the passive NOx adsorber 88 essentially from the exhaust gas flow of the internal combustion engine 10 is decoupled. To do this, the control 64 closed. If the exhaust gas temperature T _{EG has} a threshold value for enabling the low-pressure exhaust gas recirculation 80 exceeded, the exhaust gas recirculation valve 84 opened so that the low-pressure exhaust gas recirculation 80 Returned partial exhaust gas flow through the passive NOx adsorber 88 to be led.

In 8th a third operating state of the exhaust gas aftertreatment system is shown, which is used to regenerate the passive NOx adsorber 88 serves. The exhaust flap is in this third operating state 78 closed to a hot exhaust gas stream of the internal combustion engine 10 through the bypass 62 respectively. The exhaust gas temperature T _{EG is} above the desorption temperature of the passive NOx adsorber 88 so that the nitrogen oxides, preferably completely, from the passive NOx adsorber 88 desorb and through the SCR catalytic converter 56 downstream of the passive NOx adsorber 88 can be converted. This becomes the passive NOx adsorber 88 emptied and regenerated when the internal combustion engine is restarted 10 to be able to store nitrogen oxides again.

List of reference symbols

10

Internal combustion engine

12th

Combustion chamber

14th

Fuel injector

16

inlet

18th

Outlet

20th

Air supply system

22nd

Air filter

24

Air mass meter

26th

compressor

28

Intake duct

30th

High pressure exhaust gas recirculation

32

Intercooler

34

Confluence

36

Exhaust gas recirculation duct

38

High pressure exhaust gas recirculation valve

40

Exhaust system

42

Exhaust duct

44

turbine

46

first catalyst

48

NOx storage catalytic converter

50

Oxidation catalyst

52

Particle filter

54

SCR coating

56

SCR catalytic converter

58

Barrier catalytic converter

60

Exhaust gas turbocharger

62

bypass

64

Control

66

first metering element

68

second metering element

70

Temperature sensor

72

Differential pressure sensors

74

further branching

76

branch

78

Exhaust flap

80

Low pressure exhaust gas recirculation

82

Low pressure exhaust gas recirculation cooler

84

Exhaust gas recirculation valve

86

Exhaust gas recirculation line

88

passive NOx adsorber

90

Control unit

92

Confluence

94

Main channel

96

Device for exhaust gas heat recovery

98

Exhaust mixer

Claims (8)

Method for exhaust gas aftertreatment of an internal combustion engine (10) with an exhaust system (40), in which an exhaust gas aftertreatment component (52, 54, 56) for selective catalytic reduction in the flow direction of an exhaust gas flow of the internal combustion engine (10) through an exhaust duct (42) of the exhaust system (40) of nitrogen oxides and downstream of this exhaust gas aftertreatment component (52, 54, 56) a blocking catalytic converter (58) is arranged, a bypass (62) branching off from the exhaust gas duct (42) upstream of the exhaust gas aftertreatment component (52, 54, 56) at a junction (76) downstream of the junction (76) and upstream of the exhaust gas aftertreatment component (52, 54, 56) at a junction (92) back into the exhaust gas duct (42), a passive NOx adsorber (88) being arranged in the bypass (62) is, and wherein an adjusting element (78) is provided on the exhaust gas duct (42), with which the exhaust gas flow of the internal combustion engine (10) optionally through a main duct (94) of the exhaust gas duct (42) or through the bypass (62), an exhaust gas recirculation line (86) of a low-pressure exhaust gas recirculation (80) branching off from the exhaust gas channel (42) at the junction (76), the passive NOx adsorber (88) in the exhaust gas recirculation line (86 ) is arranged, and wherein the exhaust gas recirculation line has a further branch (74) at which a bypass (62) branches off (50) from the exhaust gas recirculation line (86) which connects the exhaust gas recirculation line (86) with the exhaust gas duct (42) downstream of the actuating element ( 78) and upstream of the exhaust gas aftertreatment components (52, 54, 56) for the selective catalytic reduction of nitrogen oxides, wherein in the exhaust gas recirculation line (86) downstream of the passive NOx adsorber (88) and upstream of the further branch (74) a device for exhaust gas heat recovery ( 82, 96), comprising the following steps: starting the internal combustion engine (10), wherein the entire exhaust gas flow of the internal combustion engine (1st 0) is passed through the bypass (62) and nitrogen oxides are stored in the passive NOx adsorber (88), - determining an exhaust gas temperature (T _EC) or a filling level (F _pNA) of the passive NOx adsorber, wherein a first is exceeded Threshold value (T _EGS1 ) for the exhaust gas temperature (T _EG ) or a threshold value (F _pNAS ) of the filling level (F _pNA ) the exhaust gas flow of the internal combustion engine (10) is passed through the main duct (94), and - regeneration of the passive NOx adsorber ( 88), in that the exhaust gas flow of the internal combustion engine (10) is at least partially passed through the bypass (62) when the exhaust gas aftertreatment component (54, 56, 58) for selective catalytic reduction has reached its operating temperature (T _B ) and the exhaust gas temperature (T _EG ) has reached a second threshold value (T _EGS2 ). Process for exhaust aftertreatment according to Claim 1 , characterized in that the first threshold value (T _EGS1 ) is below the second threshold value (T _EGS2 ) of the exhaust gas temperature (T _EG ). Process for exhaust aftertreatment according to Claim 1 or 2 , characterized in that the first threshold value (T _EGS1 ) of the exhaust gas temperature (T _EG ) lies in the range from 150 ° C to 250 ° C and the second threshold value (T _EGS2 ) lies in the range from 200 ° C to 350 ° C. Process for exhaust gas aftertreatment according to one of the Claims 1 until 3 , characterized in that the threshold value (F _pNAS ) of the fill level (F _pNA ) of the passive NOx adsorber (88) is in the range from 50% to 100%. Exhaust aftertreatment system for exhaust aftertreatment of an internal combustion engine (10) with an exhaust system (40) in which an exhaust gas aftertreatment component (52, 54, 56) for selective catalytic reduction in the flow direction of an exhaust gas flow of the internal combustion engine (10) through an exhaust duct (42) of the exhaust system (40) of nitrogen oxides and downstream of this exhaust gas aftertreatment component (52, 54, 56) a blocking catalytic converter (58) is arranged, a bypass (62) branching off from the exhaust gas duct (42) upstream of the exhaust gas aftertreatment component (52, 54, 56) at a junction (76) , which is downstream of the Branch (76) and upstream of the exhaust gas aftertreatment component (52, 54, 56) at a junction (92) opens again into the exhaust gas duct (42), a passive NOx adsorber (88) being arranged in the bypass (62), and wherein an adjusting element (78) is provided on the exhaust gas duct (42), with which the exhaust gas flow of the internal combustion engine (10) can optionally be passed through a main duct (94) of the exhaust gas duct (42) or through the bypass (62), characterized in that an the branch (76) an exhaust gas recirculation line (86) of a low-pressure exhaust gas recirculation (80) branches off from the exhaust gas duct (42), the passive NOx adsorber (88) being arranged in the exhaust gas recirculation line (86), and the exhaust gas recirculation line having a further branch (74 ), at which a bypass (62) branches off (50) from the exhaust gas recirculation line (86), which branches the exhaust gas recirculation line (86) with the exhaust gas duct (42) downstream of the actuating element (78) and upstream of the exhaust gas aftertreatment gskomponenten (52, 54, 56) for the selective catalytic reduction of nitrogen oxides connects, wherein in the exhaust gas recirculation line (86) downstream of the passive NOx adsorber (88) and upstream of the further branch (74) a device for exhaust gas heat recovery (82, 96) is arranged is. Exhaust aftertreatment system after Claim 5 , characterized in that the exhaust gas aftertreatment system has a first exhaust aftertreatment component (52, 54, 56) close to the engine for the selective catalytic reduction of nitrogen oxides and a second exhaust aftertreatment component (52, 54, 56) arranged downstream of the first exhaust aftertreatment component (52, 54, 56) close to the engine for selective having catalytic reduction of nitrogen oxides, the bypass (62) branches off downstream of the first exhaust gas aftertreatment component (52, 54, 56) from the exhaust gas duct (42) and upstream of the second exhaust gas aftertreatment component (52, 54, 56) opens back into the exhaust gas duct (42) . Exhaust aftertreatment system after Claim 6 , characterized in that downstream of an outlet (18) of the internal combustion engine (10) and upstream of the first exhaust gas aftertreatment component (52, 54, 56) for the selective catalytic reduction of nitrogen oxides, a first metering element (66) and downstream of the confluence (92) and upstream of the second exhaust gas aftertreatment component (52, 54, 56) for the selective catalytic reduction of nitrogen oxides, a second metering element (52, 54, 56) is arranged. Exhaust aftertreatment system according to one of the Claims 5 until 7th , characterized in that the last exhaust gas aftertreatment component (52, 54, 56) for the selective catalytic reduction of nitrogen oxides is connected downstream of a blocking catalyst (58).

Images