DE102019107236A1 - Exhaust aftertreatment system for an internal combustion engine and method for exhaust aftertreatment of an internal combustion engine - Google Patents

Abstract

The invention relates to an internal combustion engine (10) with a low-pressure exhaust gas recirculation (60). An exhaust gas recirculation cooler (64) is arranged in a main channel (66) of the low-pressure exhaust gas recirculation (60). In order to be able to bypass this exhaust gas recirculation cooler (64) in certain operating situations and not to cool the recirculated exhaust gas in these operating situations so much that water vapor contained in the exhaust gas condenses out, a bypass (68) is provided which enables exhaust gas recirculation without additional cooling of the exhaust gas. A control valve (62) is arranged at a junction (82) of the bypass (68) and the main channel (66) of the low-pressure exhaust gas recirculation (60), with which an exhaust gas flow from the internal combustion engine (10) between the bypass (68) and the Main channel (66) is controllable. Furthermore, when the exhaust flap (48) is closed, the exhaust gas flow can be deflected through the main duct (66) and returned to the exhaust duct (48) through the bypass (68) so that the residual heat of the exhaust gas can be used to cool the internal combustion engine ( 10) to be heated and not allowed to escape unused through the exhaust gas channel (48). It is provided that in the exhaust gas channel (44) downstream of the branch for the low-pressure exhaust gas recirculation (60) a metering element (96) for metering in a reducing agent and downstream of the Dosing element (96) an SCR catalyst (56) are arranged.

Description

The invention relates to an exhaust gas aftertreatment system for an internal combustion engine and a method for exhaust gas aftertreatment 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 norms 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 or NOx storage catalytic converter, a catalytic converter for the selective catalytic reduction of nitrogen oxides (SCR catalytic converter) and a particle filter for separating soot particles and, if necessary, further catalytic converters. Particularly with regard to nitrogen oxide emissions, further efforts must be made in order to achieve the future EU7 emissions standards and the following standards in order to comply with the limit values under all operating conditions. In particular, the conversion rate for nitrogen oxides in the exhaust gas aftertreatment must be increased without at the same time leading to a significant deterioration in the emissions of unburned hydrocarbons, carbon monoxide or the raw particulate emissions. Furthermore, the emission of carbon dioxide is to be further reduced. 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, with 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. In addition to the emissions of the limited exhaust gas components, there is still a demand for a further reduction in the consumption of internal combustion engines and an increase in thermal efficiency.

Internal combustion engines with low-pressure exhaust gas recirculation are known from the prior art, in which the exhaust gas of the internal combustion engine is diverted from the exhaust gas duct downstream of an exhaust gas aftertreatment component, in particular a particle filter, and fed to the air supply system upstream of a compressor. In this case, an exhaust gas recirculation cooler is generally provided in low-pressure exhaust gas recirculations, with which the exhaust gas temperature of the recirculated exhaust gas is reduced. The disadvantage of such a solution, however, is that when the exhaust gas is cold, especially in connection with cold cooling medium in the exhaust gas recirculation cooler, the water vapor present in the recirculated exhaust gas can condense out and damage the compressor.

From the DE 10 2008 020 408 A1 an internal combustion engine with low-pressure exhaust gas recirculation is known, in which the exhaust gas can be fed back to the exhaust gas duct after flowing through the exhaust gas recirculation cooler in order to lower the exhaust gas temperature. The ones in the DE 10 2008 020 408 A1 However, the proposed solution does not make it possible to reduce or increase the temperature in the exhaust gas recirculation less strongly.

From the EP 2 956 657 B1 an internal combustion engine with a mechanically driven compressor and a bypass duct is known with which the mechanical compressor can be bridged, a control valve being provided with which an inlet or an outlet of the mechanically driven compressor can be opened or closed as desired.

The object of the invention is to enable low-pressure exhaust gas recirculation as early as possible after a cold start and to use the residual heat of the exhaust gas in order to avoid condensation of liquid in the low-pressure exhaust gas recirculation and thus to lower the raw nitrogen oxide emissions and / or the conversion rates of nitrogen oxides to improve exhaust aftertreatment.

According to the invention, the object is achieved by an internal combustion engine with an air supply system and an exhaust system, as well as with a low-pressure exhaust gas recirculation, which connects the exhaust system downstream of a turbine of an exhaust gas turbocharger with the air supply system upstream of a compressor of the exhaust gas turbocharger. An exhaust flap is provided in the exhaust system, with which an exhaust duct of the exhaust system can be at least partially blocked. The low-pressure exhaust gas recirculation comprises a main channel and a bypass, the main channel of the low-pressure exhaust gas recirculation branching off from the exhaust gas channel at a branching point downstream of the turbine and upstream of the exhaust gas flap and opening into a low-pressure exhaust gas recirculation line. An exhaust gas recirculation cooler is arranged in the main duct. A bypass is formed parallel to the main channel, which the Exhaust gas recirculation cooler bridged, with a control valve being arranged at a junction or a junction of the main channel and the bypass, with which an exhaust gas flow between the bypass and the main channel can be controlled, in particular switchable or split between the main channel and the bypass. It is provided that a metering element is arranged in the exhaust gas duct downstream of the branching point, an SCR catalytic converter being arranged downstream of the metering element.

An internal combustion engine according to the invention offers the advantage that the combination of exhaust gas heat recovery by the low-pressure exhaust gas recirculation cooler and loading of at least one SCR catalytic converter enables the nitrogen oxides in the exhaust gas of the internal combustion engine to be efficiently converted shortly after a cold start of the internal combustion engine. In particular, the coolant of the internal combustion engine is heated by the exhaust gas flow, which means that the charge air cooler can also be used to heat the fresh air that is drawn in. This increases the combustion temperature in the combustion chambers of the internal combustion engine, as a result of which the raw emissions, in particular the emissions of unburned hydrocarbons, carbon monoxide and the raw particulate emissions, are reduced. Furthermore, the low-pressure exhaust gas recirculation can be switched between switching off the low-pressure exhaust gas recirculation, an uncooled exhaust gas recirculation and a cooled exhaust gas recirculation with only one control valve. In this way, the low-pressure exhaust gas recirculation can be easily and inexpensively adapted to the respective operating temperature of the internal combustion engine and a condensation of liquid in the low-pressure exhaust gas recirculation can be reliably avoided, whereby the period from cold start of the internal combustion engine to activation of the low-pressure exhaust gas recirculation can be shortened .

The features listed in the dependent claims enable advantageous improvements and developments of the internal combustion engine specified in the independent claim.

In a preferred embodiment of the invention it is provided that a first metering element is arranged in the exhaust gas duct downstream of the turbine and a first SCR catalytic converter is arranged downstream of the first metering element and upstream of the branching point and a second metering element is arranged downstream of the branching point and a second SCR catalytic converter is arranged downstream of the second metering element are. The SCR catalytic converter can be loaded with ammonia sooner after a cold start of the internal combustion engine, since exhaust gas heat recovery shortens the heating phase until the SCR catalytic converters reach the light-off temperature.

In a preferred embodiment of the invention it is provided that the first SCR catalytic converter is designed as a particle filter with an SCR coating, the main channel of the low-pressure exhaust gas recirculation downstream of the particle filter with the coating for the selective, catalytic reduction of nitrogen oxides from the exhaust gas channel of the internal combustion engine branches off. By branching off the low-pressure exhaust gas recirculation downstream of the particle filter, the majority of the particles can already be removed from the exhaust gas flow of the internal combustion engine by the particle filter and retained in the particle filter. This reduces the risk of particles getting into the air supply system via the low-pressure exhaust gas recirculation and causing damage there to the compressor of the exhaust gas turbocharger. A particle filter with a coating for the selective, catalytic reduction of nitrogen oxides is particularly preferred, since this also brings about a significant reduction in nitrogen oxide emissions.

In an advantageous embodiment of the internal combustion engine it is provided that the bypass is connected to the exhaust gas duct of the internal combustion engine at a branching point downstream of the exhaust flap, the second metering element being arranged downstream of this branching point. This can ensure that reducing agent metered in by the second metering element does not get back into the air supply system either via the main duct of the low-pressure exhaust gas recirculation or via the bypass. As a result, deposits from crystallizing reducing agent in the low-pressure exhaust gas recirculation can be avoided, as a result of which a cross-section reduction and / or an increase in the flow resistance in the low-pressure exhaust gas recirculation can be avoided.

In a preferred embodiment of the invention it is provided that the control valve is designed as a 3/3-way valve. A 3/3-way valve enables particularly simple switching between the individual operating states of the internal combustion engine. Alternatively, two simple valves can also be used, which are connected in series in such a way that a 3/3-way function results.

It is particularly preferred if a first connection opening of the control valve is connected to the main channel, a second connection opening is connected to the bypass and a third connection opening is connected to the low-pressure exhaust gas return line. Are the main duct of the low pressure Exhaust gas recirculation with a first connection opening, the bypass with a second connection opening and the low-pressure exhaust gas recirculation line connected with a third connection opening of the control valve, a simple control and division of the exhaust gas flow is possible so that the exhaust gas flow can be fed back depending on the exhaust gas temperature and / or the cooling water temperature of the internal combustion engine can or is fed to the exhaust duct. In particular, exhaust gas heat recovery is possible in this way, in which the coolant of the internal combustion engine is heated by the exhaust gas flow.

In a further preferred embodiment of the invention it is provided that the bypass is connected to the exhaust gas duct of the internal combustion engine downstream of the exhaust gas flap. This allows the combustion engine to heat up to its operating temperature via the exhaust flap, in that the exhaust gas flow of the combustion engine is passed through the exhaust gas recirculation cooler located in the main duct of the low-pressure exhaust gas recirculation and can thus also be used to heat the cooling water. The waste heat from the exhaust gas can thus be used to heat the internal combustion engine.

According to a preferred embodiment of the invention it is provided that a filter is arranged in each case in the main channel and in the bypass. A filter can prevent or reduce the penetration of soot particles into the low-pressure exhaust gas recirculation system. This can reduce wear on the control valve and on the components of the air supply system of the internal combustion engine downstream of the confluence of the low-pressure exhaust gas recirculation line. Furthermore, malfunctions caused by soot particles can be prevented, which would be deposited on the control valve without a filter.

• - ein Abgasstrom des Verbrennungsmotors über einen Abgasrückführungskühler geleitet wird, welcher mit einem Kühlmittelkreislauf des Verbrennungsmotors verbunden ist, wobei
• - bei einem Kaltstart des Verbrennungsmotors das Kühlmittel durch den Abgasrückführungskühler erwärmt wird, wobei
• - durch die Erwärmung des Kühlmittels die Abgastemperatur des Verbrennungsmotors angehoben wird, und wobei
• - ein Reduktionsmittel stromabwärts der Verzweigungsstelle in den Abgaskanal eindosiert wird.

According to the invention, a method for exhaust gas aftertreatment of an internal combustion engine according to the invention is proposed, wherein

• - An exhaust gas flow of the internal combustion engine is passed through an exhaust gas recirculation cooler which is connected to a coolant circuit of the internal combustion engine, wherein
• - During a cold start of the internal combustion engine, the coolant is heated by the exhaust gas recirculation cooler, wherein
• - The exhaust gas temperature of the internal combustion engine is raised by the heating of the coolant, and wherein
• - A reducing agent is metered into the exhaust gas duct downstream of the branching point.

A method according to the invention can activate at least one SCR catalyst as quickly as possible, depending on the temperature of the exhaust gas, the cooling water and / or the engine oil of the internal combustion engine. The exhaust gas heat recovery via the low-pressure exhaust gas recirculation cooler can shorten the heating of the internal combustion engine and the exhaust gas aftertreatment components. This makes it possible to heat the SCR catalytic converters to their light-off temperature much earlier, which can improve the exhaust gas aftertreatment. In this way, the emissions of the internal combustion engine can be reduced. In addition, the exhaust gas heat recovery in a warm-up phase of the internal combustion engine leads to better combustion quality, whereby the raw exhaust emissions, in particular the emissions of unburned hydrocarbons, carbon monoxide and the raw particulate emissions can be reduced. The exhaust gas recirculation can be controlled via the low pressure exhaust gas recirculation in such a way that the waste heat from the internal combustion engine is used to accelerate the heating of the coolant of the internal combustion engine and at least one of the SCR catalytic converters with reducing agent, in particular with ammonia, shortly after a cold start of the internal combustion engine, to load. As a result, the conversion of nitrogen oxides can be improved in a cold start phase and thus the tailpipe emissions can be reduced. Due to the possibility of uncooled exhaust gas recirculation, the low-pressure exhaust gas recirculation can be activated earlier after a cold start of an internal combustion engine, whereby the raw emissions of the internal combustion engine can be reduced.

In an advantageous improvement of the method it is provided that in a first operating state of the internal combustion engine, the exhaust flap is at least partially closed, an exhaust gas flow being passed through the main duct of the low-pressure exhaust gas recirculation and the control valve being set in such a way that the exhaust gas flow is returned via the bypass the exhaust duct of the internal combustion engine is conducted. As a result, the residual heat of the exhaust gas can be used to heat the cooling water of the internal combustion engine via the exhaust gas recirculation cooler and thus contribute to the internal combustion engine reaching its operating temperature more quickly after a cold start of the internal combustion engine. As a result, the low-pressure exhaust gas recirculation can be activated more quickly and the emissions from the combustion engine can be reduced.

In a preferred embodiment of the method it is provided that below a first threshold temperature of the exhaust gas or a second threshold temperature of the coolant of the Internal combustion engine, there is no exhaust gas recirculation via the low-pressure exhaust gas recirculation, above the first threshold temperature and below a third threshold temperature of the exhaust gas or a fourth threshold temperature of the coolant of the internal combustion engine, an uncooled exhaust gas recirculation takes place via the bypass and above the third threshold temperature and / or the fourth threshold temperature a cooled exhaust gas recirculation takes place takes place via the main duct of the low-pressure exhaust gas recirculation. Below the first and second threshold temperatures, in particular below a cooling water temperature of 50 ° C and an exhaust gas temperature of less than 120 ° C, there is a risk that the water vapor contained in the exhaust gas will condense out in the low-pressure exhaust gas recirculation system and enter the air supply system of the internal combustion engine as a water plug. This can lead to damage to the compressor of the exhaust gas turbocharger and to parts of the internal combustion engine. Exhaust gas recirculation via the low-pressure exhaust gas recirculation is therefore suppressed below this first threshold temperature. Above the first threshold temperature and below a second threshold temperature, additional cooling of the exhaust gas flow recirculated via the low-pressure exhaust gas recirculation can lead to the water vapor condensing out. Therefore, in a temperature range above the first and second threshold temperature and below the third and fourth threshold temperature of about 80 ° cooling water temperature and 180 ° C exhaust gas temperature, the exhaust gas is bypassed past the exhaust gas recirculation cooler in order to additionally cool the exhaust gas and the associated risk of a Avoid condensation of water droplets. Above the third and fourth threshold temperature, the exhaust gas flow is advantageously returned to the air supply system via the main duct of the low-pressure exhaust gas recirculation and the exhaust gas recirculation cooler, in order to lower the combustion temperature in the combustion chambers of the internal combustion engine and thus to reduce the raw nitrogen oxide emissions.

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 ein Ausführungsbeispiel eines erfindungsgemäßen Verbrennungsmotors, wobei in einer Niederdruck-Abgasrückführung eine Abgasrückführung mit einem Abgasrückführungskühler und eine parallele Abgasrückführung ohne einen Kühler vorgesehen sind, welche über ein Steuerventil schaltbar sind und stromabwärts einer Verzweigung der Niederdruck-Abgasrückführung ein Dosierelement und ein SCR-Katalysator angeordnet sind;
• 2 einen ersten Betriebszustand des Verbrennungsmotors, wobei eine Abgasrückführung in den Ansaugtrakt unterbunden ist, und ein Abgasstrom des Verbrennungsmotors durch den Hauptkanal und den Bypass zurück in den Abgaskanal geleitet wird;
• 3 einen dritten Betriebszustand des Verbrennungsmotors, bei dem das Abgas über den Hauptkanal und den Abgasrückführungskühler in den Ansaugtrakt des Verbrennungsmotors zurückgeführt wird;
• 4 eine Betriebssituation des Verbrennungsmotors, bei dem ein Abgasstrom über den Hauptkanal zurückgeführt und dann geteilt wird, sodass ein erster Teilstrom über die Niederdruck-Abgasrückführung in den Ansaugtrakt zurückgeführt wird und ein zweiter Teilstrom über den Bypass zurück in den Abgaskanal geleitet wird; und
• 5 einen zweiten Betriebszustand des Verbrennungsmotors, wobei ein Abgasstrom über den Bypass an dem Abgasrückführungskühler vorbei in den Ansaugtrakt zurückgeführt wird.

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 in the drawings with the same reference numbers. Show it:

• 1 an embodiment of an internal combustion engine according to the invention, wherein an exhaust gas recirculation with an exhaust gas recirculation cooler and a parallel exhaust gas recirculation without a cooler are provided in a low pressure exhaust gas recirculation, which can be switched via a control valve and a metering element and an SCR catalyst are arranged downstream of a branch of the low pressure exhaust gas recirculation ;
• 2 a first operating state of the internal combustion engine, wherein exhaust gas recirculation into the intake tract is prevented, and an exhaust gas flow of the internal combustion engine is passed through the main duct and the bypass back into the exhaust gas duct;
• 3 a third operating state of the internal combustion engine, in which the exhaust gas is returned via the main duct and the exhaust gas recirculation cooler into the intake tract of the internal combustion engine;
• 4th an operating situation of the internal combustion engine in which an exhaust gas flow is returned via the main duct and then divided, so that a first partial flow is returned to the intake tract via the low-pressure exhaust gas recirculation and a second partial flow is passed back into the exhaust gas duct via the bypass; and
• 5 a second operating state of the internal combustion engine, an exhaust gas flow being returned to the intake tract via the bypass past the exhaust gas recirculation cooler.

1 shows an internal combustion engine 10 for a motor vehicle acting as a compression ignition internal combustion engine 10 is designed according to the diesel principle. The internal combustion engine 10 is with its outlet 16 with an exhaust system 40 connected. The outlet 16 includes an exhaust manifold, which the exhaust gases from the different combustion chambers 12th of the internal combustion engine 10 an exhaust duct 44 the exhaust system 30th feeds. The internal combustion engine 10 is with an inlet 14th with an air supply system 20th connected. The air supply system 20th points in the direction of flow of the fresh air through the air supply system 20th an air filter 22nd and downstream of this air filter 22nd a compressor 24 of an exhaust gas turbocharger 36 with which the sucked-in air is compressed and the combustion chambers 12th of the internal combustion engine 10 is fed. The air supply system 20th also has a fresh gas line 26th on which the air filter 22nd with the inlet 14th of the internal combustion engine 10 connects. Downstream of the air filter 22nd is an air mass meter 30th on the fresh gas line 26th intended. On the internal combustion engine 10 is a coolant circuit 18th provided with which the engine block and further coolers, in particular a charge air cooler 28 , be supplied with coolant. Downstream of the intercooler 28 and upstream of the inlet 14th is a control flap 32 to control the amount of air in the internal combustion engine 10 intended. It is also on the internal combustion engine 10 a high pressure exhaust gas recirculation with an exhaust gas recirculation line 38 and a high pressure EGR valve 34 provided, with which exhaust gas can be returned inside the engine.

The exhaust system 40 has an exhaust duct 44 in which in the flow direction of an exhaust gas of the internal combustion engine 10 through the exhaust system 40 a turbine 42 of the exhaust gas turbocharger 36 and downstream of the turbine 42 several exhaust aftertreatment components 46 , 50 , 54 , 56 , 58 are arranged. In the illustrated embodiment of the internal combustion engine 10 are downstream of the turbine 42 of the exhaust gas turbocharger 36 initially an oxidation catalytic converter or a NOx storage catalytic converter 50, downstream of the oxidation catalytic converter or the NOx storage catalytic converter 50 a first metering element 52 for a reducing agent, in particular aqueous urea solution and downstream of the first metering element 52 a first SCR catalytic converter 54 , especially a particulate filter 54 arranged with a coating for the selective, catalytic reduction of nitrogen oxides. Downstream of the first metering element 52 and upstream of the first SCR catalyst 54 can be an exhaust mixer 98 be arranged to evaporate the reducing agent and / or the uniform distribution of the reducing agent in the exhaust gas flow before entering the first SCR catalytic converter 54 to improve. Downstream of the particulate filter 54 with the SCR coating branches out of the exhaust duct 44 at a branch point 78 a main channel 66 a low-pressure exhaust gas recirculation 60 from. The main channel 66 connects the exhaust duct 44 with a low pressure exhaust gas recirculation line 70 . In the main channel 66 is an exhaust gas recirculation cooler 64 arranged, with which the temperature of the recirculated exhaust gas can be reduced. The exhaust gas recirculation cooler is for this purpose 64 to the coolant circuit 18th of the internal combustion engine 10 connected and the coolant flows through it. The low pressure exhaust gas recirculation line 70 opens downstream of the air filter 22nd and upstream of the compressor 24 into the fresh gas duct 26th . Downstream of the branch office 78 is in the exhaust duct 44 an exhaust flap 48 arranged. The exhaust duct 44 is downstream of the branch point 78 through the exhaust flap 48 at least partially closable. Downstream of the exhaust flap 48 are in the exhaust duct 44 a second metering element 96 and downstream of the second metering element 96 another SCR catalytic converter 56 and an ammonia barrier catalyst 58 or an oxidation catalyst is arranged. Downstream of the second metering element 96 and upstream of the second SCR catalyst 56 can be an exhaust mixer 98 be arranged to evaporate and / or uniformly distribute the reducing agent in the exhaust gas stream before entering the second SCR catalytic converter 56 to improve.

Downstream of the exhaust flap 48 and upstream of the further SCR catalyst 56 branches at another branch point 80 a bypass 68 from the exhaust duct 44 and runs essentially parallel to the main channel 66 the low pressure exhaust gas recirculation 60 . At a merger 82 of the main channel 66 and bypass 68 is a control valve 62 arranged. The control valve 62 is preferably designed as a 3/3-way valve. There is a first connection opening 84 of the control valve 62 with the main channel 66 , a second connection opening 86 of the control valve 62 with the bypass 68 and a third connection opening 88 with the low pressure exhaust gas return line 70 the low pressure exhaust gas recirculation 60 connected. The low pressure exhaust gas recirculation line 70 opens at a confluence 76 downstream of the air mass meter 30th and upstream of the compressor 24 into the fresh gas line 26th of the air supply system 20th . On the main channel 66 and the bypass 68 is one filter each 72 , 74 arranged, which prevents the penetration of soot particles into the low-pressure exhaust gas recirculation 70 prevented or at least reduced.

The internal combustion engine 10 is also with a control unit 90 connected, which comprises a memory and a computer, wherein a machine-readable program code is stored in the memory. The control unit 90 is via signal lines 92 with the exhaust flap 48 and the control valve 62 connected. Via the control unit 90 is the position of the exhaust flap 48 and the control valve 62 adjustable so that the exhaust gas flow through the low pressure exhaust gas recirculation 60 can be controlled.

In 2 is a first operating state of the internal combustion engine 10 shown in which the low-pressure exhaust gas recirculation channel 70 through the control valve 62 is locked. In this first operating state, in particular with a cold internal combustion engine, cold cooling water, cold exhaust gas and / or cold engine oil, the exhaust gas flap is 48 in the exhaust duct 44 employed so that the exhaust duct 44 is essentially closed. This causes the exhaust gas flow of the internal combustion engine 10 upstream of the exhaust flap 48 through the main channel 66 and passed through the control valve 62 then into the bypass 68 deflected so that the deflected exhaust gas flow downstream of the exhaust flap 48 and upstream of the further SCR catalyst 56 back to the exhaust duct 44 is fed. The exhaust gas flow is through the exhaust gas recirculation cooler 64 passed, the residual heat of the exhaust gas flow on the coolant of the exhaust gas recirculation cooler 64 and thus on the coolant circuit 18th of the internal combustion engine 10 is transmitted. Thus, the residual heat of the exhaust gas, in particular after a cold start of the internal combustion engine 10 , used to power the internal combustion engine 10 as soon as possible after a Bring cold start to its operating temperature. By closing the low-pressure exhaust gas return line 70 the risk of water vapor in the low-pressure exhaust gas recirculation line is eliminated 70 or in the fresh gas line 26th condenses out and the water droplets damage the components. Furthermore, the faster heating of the coolant also raises the exhaust gas temperature T _EG , which causes the SCR catalytic converters 54 , 56 reach their operating temperature faster. Thus, a metering of reducing agent into the exhaust duct 44 downstream of the branches 78 , 80 take place without the risk of this reducing agent in the low-pressure exhaust gas recirculation 60 got. This means that the second SCR catalytic converter is loaded 56 possible with ammonia, with the second SCR catalyst reaching a light-off temperature 56 an efficient conversion of nitrogen oxides in the exhaust gas flow of the internal combustion engine 10 becomes possible. The shortened warm-up time can thus reduce cold start emissions.

In 5 is a second operating state of the internal combustion engine 10 shown in which the internal combustion engine 10 , the coolant circuit 18th and / or the engine oil has a higher temperature than in 2 have outlined first operating condition. This is the exhaust flap 48 essentially fully open so that the exhaust gas flow through the exhaust duct 44 in the direction of the further SCR catalytic converter 56 flows. Due to the shortened heating phase of the SCR catalytic converters 56 In this operating state, there is already a significant reduction in nitrogen oxide emissions through the SCR catalytic converters 54 , 56 possible. A partial flow of the exhaust gas passes through the bypass 68 into the low pressure exhaust gas recirculation line 70 but without the exhaust gas recirculation cooler 64 to happen. This reduces the risk of water droplets condensing out. As a result, the low-pressure exhaust gas recirculation can be used even with less hot exhaust gas, less warm coolant or engine oil 60 are activated and exhaust gas of the intake air in the fresh gas line 26th are mixed in. As a result, the formation of nitrogen oxides during the combustion of the fuel in the combustion chambers can be prevented in a known manner 12th of the internal combustion engine 10 be decreased so that the exhaust system 40 fewer raw nitrogen oxide emissions are supplied.

In 3 is a third operating state of the internal combustion engine 10 shown in which the internal combustion engine 10 has reached its operating temperature and a partial flow of the exhaust gas via the main duct 66 the low pressure exhaust gas recirculation 60 and through the in the main channel 66 arranged exhaust gas recirculation cooler 64 is cooled. This is the exhaust flap 48 employed so that the exhaust back pressure in the exhaust duct 44 is increased. The control valve is also 62 so placed that a connection from the main line 66 to the low pressure exhaust gas return line 70 is open. This can reduce the combustion temperature in the combustion chambers 12th of the internal combustion engine 10 reduced, which has a positive effect on the raw nitrogen oxide emissions of the internal combustion engine 10 affects.

In 4th is another operating state of the internal combustion engine 10 shown. Here is the exhaust flap 48 essentially closed, so that a large part of the exhaust gas flow of the internal combustion engine 10 in the main channel 66 the low pressure exhaust gas recirculation 60 is initiated. This exhaust gas flow is through the control valve 62 divided into a first substream and a second substream. The first partial flow is fed to the air supply system via the low-pressure exhaust gas return line 20th supplied so that the combustion temperature and the associated raw emissions of the internal combustion engine 10 can be lowered. The second partial flow is via the bypass 68 back into the exhaust duct 44 directed. This enables maximum heat recovery of the waste heat from the exhaust gas via the exhaust gas recirculation cooler 64 as well as a simultaneous, cooled low-pressure exhaust gas recirculation 60 possible. As a result of the heat recovery, the exhaust gas temperature T _{EG can be} increased by the internal combustion engine 10 in the in 3 to be able to transfer the operating state shown.

If the exhaust gas temperature T _EG falls below a first threshold temperature T _S1 and / or the coolant temperature T _CF falls below a second threshold temperature T _S2 or is the coolant temperature T _CF or the exhaust gas temperature T _EF after a cold start of the internal combustion engine 10 Below these threshold temperatures T _S1 , T _S2 , there is a risk that the water vapor contained in the exhaust gas in the low-pressure exhaust gas recirculation 60 condenses out and the compressor in the case of exhaust gas recirculation 24 of the exhaust gas turbocharger 36 damaged. In order to avoid this, exhaust gas recirculation via the low-pressure exhaust gas recirculation is implemented in a first operating state 60 avoided. If the exhaust gas temperature T _EG falls below a third threshold temperature T _S3 or the cooling water temperature T _CF below a fourth threshold temperature T _S4 or are the exhaust gas temperature T _EG and / or the coolant temperature T _CF after a cold start of the internal combustion engine 10 Below this third or fourth threshold temperature T _S3 , T _S4 , there is a risk that the water vapor contained in the exhaust gas in the low-pressure exhaust gas recirculation 60 condenses out when the exhaust gas flow also through the exhaust gas recirculation cooler 64 is cooled. This is particularly the case when the coolant is cold and the exhaust gas recirculation cooler has a correspondingly strong cooling effect 64 critical. In this second operating state, the recirculated exhaust gas flow through the bypass 68 and thus past the exhaust gas recirculation cooler 64 guided so that the exhaust gas temperature T _EG of the low-pressure exhaust gas recirculation 60 recirculated exhaust gas remains essentially constant. Such an operating state is in 5 shown. The exhaust flap is used for this 48 essentially fully open to allow exhaust gas to be introduced into the main duct 66 the low pressure exhaust gas recirculation 60 to avoid. Due to the flow resistance of the further SCR catalytic converter 56 and the ammonia barrier catalyst 58 or the oxidation catalytic converter is a partial flow of the exhaust gas into the bypass 68 from there, uncooled, via the low-pressure exhaust gas return line 70 into the air supply system 20th upstream of the compressor 24 .

It is preferred if in a bypass operation, in which this is done via the low-pressure exhaust gas recirculation 60 recirculated exhaust gas to the exhaust gas recirculation cooler 64 over into the fresh gas line 26th is introduced on the intercooler 28 of the internal combustion engine 10 a bypass is also provided with which this charge air cooler 28 can also be bridged. This can cause the internal combustion engine to heat up when the exhaust gas recirculation rate is high 10 are favored, and the returned energy is not used by the intercooler 28 to the coolant circuit 18th discharged.

In summary, it can be stated that an internal combustion engine according to the invention 10 the residual heat of the exhaust gas is used and, at the same time, the ammonia storage of the SCR catalytic converters is filled 54 , 56 can be improved. This enables the SCR catalytic converters 54 , 56 reach their light-off temperature faster, reducing emissions in a cold start phase of the internal combustion engine 10 can be significantly reduced. The low-pressure exhaust gas recirculation 60 faster after a cold start of the internal combustion engine 10 activated when uncooled exhaust gas is recirculated, thereby reducing the raw nitrogen oxide emissions of the internal combustion engine 10 can be lowered.

List of reference symbols

10

Internal combustion engine

12

Combustion chamber

14th

inlet

16

Outlet

18th

Coolant circuit

20th

Air supply system

22nd

Air filter

24

compressor

26th

Fresh gas line

28

Intercooler

30th

Air mass meter

32

Control flap

34

High pressure exhaust gas recirculation valve

36

Exhaust gas turbocharger

38

Exhaust gas recirculation line

40

Exhaust system

42

turbine

44

Exhaust duct

46

first exhaust aftertreatment component

48

Exhaust flap

50

NOx storage catalytic converter

52

first metering element

54

Particle filter with SCR coating

56

SCR catalytic converter

58

Oxidation catalyst / ammonia barrier catalyst

60

Low pressure exhaust gas recirculation

62

Control valve

64

Exhaust gas recirculation cooler

66

Main channel of the low-pressure exhaust gas recirculation

68

Low pressure exhaust gas recirculation bypass

70

Low pressure exhaust gas recirculation line

72

filter

74

filter

76

Confluence

78

Branching point

80

Branching point

82

Merging

84

first connection opening

86

second connection opening

88

third connection opening

90

Control unit

92

Signal line

96

second metering element

98

Exhaust mixer

T

temperature

T _CF

Coolant temperature of the internal combustion engine

T _CFL

Threshold for the coolant temperature

T _EG

Exhaust gas temperature

T _S1

first threshold temperature

T _S2

second threshold temperature

T _S3

third threshold temperature

T _S4

fourth threshold temperature

QUOTES INCLUDED IN THE DESCRIPTION

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

Patent literature cited

• DE 102008020408 A1 [0004]
• EP 2956657 B1 [0005]

Claims (10)

Internal combustion engine (10) with an air supply system (20) and an exhaust system (40), as well as with a low-pressure exhaust gas recirculation (60), which connects the exhaust system (40) with the air supply system (20) downstream of a turbine (42) of an exhaust gas turbocharger (36) upstream of a compressor (24) connects the exhaust gas turbocharger (36), as well as with an exhaust gas flap (48) with which an exhaust gas duct (44) of the exhaust system (40) can be at least partially blocked, a main duct (66) of the low-pressure exhaust gas recirculation ( 60) downstream of the turbine (42) and upstream of the exhaust flap (48) branches off from the exhaust gas duct (44) at a branch point (78) and opens into a low-pressure exhaust gas recirculation line (70), and in this main channel (66) an exhaust gas recirculation cooler (64) is arranged, wherein a bypass (68) is formed parallel to the main channel (66), which bypasses the exhaust gas recirculation cooler (64), wherein at a junction (82) or a branch of the main k anals (66) and the bypass (68) a control valve (62) is arranged with which an exhaust gas flow between the bypass (68) and the main channel (66) can be controlled, characterized in that in the exhaust channel (44) downstream of the branching point (78) a metering element (96) is arranged, an SCR catalytic converter (56) being arranged downstream of the metering element (96). Internal combustion engine (10) after Claim 1 , characterized in that in the exhaust gas duct (44) downstream of the turbine (42) a first metering element (52) and downstream of the first metering element (52) and upstream of the branching point (78) a first SCR catalyst (54) and downstream of the branching point (78) a second metering element (96) and a second SCR catalytic converter (56) are arranged downstream of the second metering element (96). Internal combustion engine (10) after Claim 2 , characterized in that the first SCR catalytic converter (54) is designed as a particle filter with an SCR coating, the main channel (66) of the low-pressure exhaust gas recirculation (60) downstream of the particle filter with the coating for selective, catalytic reduction of nitrogen oxides branches off from the exhaust duct (44) of the internal combustion engine (10). Internal combustion engine (10) according to one of the Claims 1 to 3 , characterized in that the bypass (68) is connected downstream of the exhaust flap (48) to the exhaust duct (44) of the internal combustion engine (10) at a branch point (80), the second metering element (96) being arranged downstream of this branch point (80) is. Internal combustion engine (10) according to one of the Claims 1 to 4th , characterized in that the control valve (62) is designed as a 3/3-way valve or a combination of two valves to form a 3/3-way function. Internal combustion engine (10) after Claim 5 , characterized in that a first connection opening (84) of the control valve (62) is connected to the main channel (66), a second connection opening (86) to the bypass (68) and a third connection opening (88) to the low-pressure exhaust gas return line (70) . Internal combustion engine (10) according to one of the Claims 1 to 6th , characterized in that a filter (72, 74) is arranged in each case in the main channel (66) and in the bypass (68). Method for exhaust gas aftertreatment of an internal combustion engine (10) according to one of the Claims 1 to 7th , characterized in that - an exhaust gas flow of the internal combustion engine (10) is passed through an exhaust gas recirculation cooler (64) which is connected to a coolant circuit (18) of the internal combustion engine (10), wherein - when the internal combustion engine (10) starts cold, the coolant flows through the exhaust gas recirculation cooler (64) is heated, with the exhaust gas temperature (T _EG ) of the internal combustion engine (10) being increased by the heating of the coolant, and with a reducing agent being metered into the exhaust gas duct (44) downstream of the branch point (78). Procedure according to Claim 8 , characterized in that the exhaust flap (48) is at least partially closed, with an exhaust gas flow through the Main channel (66) of the low-pressure exhaust gas recirculation (60) and the control valve (62) is set in such a way that the exhaust gas flow is directed via the bypass (68) back into the exhaust gas channel (44) of the internal combustion engine (10). Procedure according to Claim 8 or 9 , characterized in that below a first threshold temperature (T _S1 ) of the exhaust gas or a threshold temperature (T _S2 ) of the coolant of the internal combustion engine (10) there is no exhaust gas recirculation via the low-pressure exhaust gas recirculation, above the first threshold temperature (T _S1 ) and below a third Threshold temperature (T _S3 ) of the exhaust gas or a fourth threshold temperature (T _S4 ) of the coolant of the internal combustion engine (10) an uncooled exhaust gas recirculation takes place via the bypass (68) and above the third threshold temperature (T _S3 ) and / or the fourth threshold temperature (T _S4 ) a cooled exhaust gas recirculation takes place via the main channel (66) of the low-pressure exhaust gas recirculation (60).

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