Exhaust gas aftertreatment system for an internal combustion engine and method for exhaust gas aftertreatment of an internal combustion engine

Abstract

Method for exhaust gas aftertreatment of an internal combustion engine (10) with an air supply system (20); an exhaust system (40); a low-pressure exhaust gas recirculation (60) which connects the exhaust system (40) downstream of a turbine (42) of an exhaust gas turbocharger (36) to the air supply system (20) upstream of a compressor (24) of the exhaust gas turbocharger (36); an exhaust flap (48) with which an exhaust duct (44) of the exhaust system (40) can be at least partially blocked; wherein a main duct (66) of the low-pressure exhaust gas recirculation (60) branches off from the exhaust duct (44) at a branching point (78) downstream of the turbine (42) and upstream of the exhaust flap (48) and opens into a low-pressure exhaust gas recirculation line (70); and wherein an exhaust gas recirculation cooler (64) is arranged in the main channel (66), wherein a bypass (68) is formed parallel to the main channel (66), which bypasses the exhaust gas recirculation cooler (64);wherein a control valve (62) is arranged at a junction (82) or a branch (94) of the main channel (66) and the bypass (68), with which control valve an exhaust gas flow between the bypass (68) and the main channel (66) can be controlled; wherein a filter (72, 74) is arranged in each of the main channel (66) and the bypass (68), characterized in that; - in a first operating state, no exhaust gas recirculation takes place via the low-pressure exhaust gas recirculation (60), - in a second operating state, an uncooled exhaust gas recirculation takes place via the bypass (68), and - in a third operating state, a cooled exhaust gas recirculation takes place via the main channel (66) of the low-pressure exhaust gas recirculation (60), and - in a further operating state, the exhaust flap (48) is substantially closed, so that a large part of the exhaust gas flow of the internal combustion engine (10) is introduced into the main channel (66) of the low-pressure exhaust gas recirculation (60), wherein this exhaust gas flow is divided by the control valve (62) into a first partial flow and a second partial flow, wherein the first partial flow is fed to the air supply system (20) via the low-pressure exhaust gas recirculation line (70) and the second partial flow is passed back into the exhaust channel (44) via the bypass (68), wherein - in the first operating state, the exhaust gas flap (48) is at least partially closed, wherein an exhaust gas flow is passed through the main channel (66) of the low-pressure exhaust gas recirculation (60) and the control valve (62) is set such that the exhaust gas flow is passed via the bypass (68) back into the exhaust gas channel (44) of the internal combustion engine (10).

Description

[0001] 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 patent claims.

[0002] Current and increasingly stringent emissions legislation places high demands on raw engine emissions and exhaust aftertreatment in internal combustion engines. The demands for further reduced fuel consumption and the further tightening of emissions standards regarding permissible nitrogen oxide emissions pose a challenge for engine developers. In gasoline engines, exhaust gas purification is achieved in the usual way via a three-way catalyst, as well as additional catalysts upstream and downstream of the three-way catalyst. Diesel engines currently use exhaust aftertreatment systems that include an oxidation catalyst or NOx storage catalyst, a catalyst for the selective catalytic reduction of nitrogen oxides (SCR catalyst), a particulate filter for the separation of soot particles, and possibly additional catalysts. Ammonia is the preferred reducing agent.Because handling pure ammonia is complex, vehicles typically use a synthetic, aqueous urea solution, which is mixed with the hot exhaust stream in a mixing device upstream of the SCR catalyst. This mixing heats the aqueous urea solution, releasing ammonia into the exhaust 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 components, there is still a demand for further reductions in combustion engine fuel consumption and increased thermal efficiency.

[0003] 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 duct downstream of an exhaust aftertreatment component, in particular a particulate filter, and fed to the air supply system upstream of a compressor.

[0004] Low-pressure exhaust gas recirculation systems typically incorporate an exhaust gas recirculation cooler to reduce the exhaust gas temperature of the recirculated exhaust gas. However, the disadvantage of this solution is that, in cold exhaust gases, especially in conjunction with a cold cooling medium in the exhaust gas recirculation cooler, the water vapor present in the recirculated exhaust gas can condense, potentially causing compressor damage.

[0005] DE 10 2008 020 408 A1 discloses an internal combustion engine with low-pressure exhaust gas recirculation, in which the exhaust gas can be returned to the exhaust duct after flowing through the exhaust gas recirculation cooler to reduce the exhaust gas temperature. However, the solution proposed in DE 10 2008 020 408 A1 does not allow the temperature in the exhaust gas recirculation to be reduced or increased to a lesser extent.

[0006] From EP 2 956 657 B1, an internal combustion engine with a mechanically driven compressor and a bypass channel is known, with which the mechanical compressor can be bypassed, wherein a control valve is provided with which an inlet or an outlet of the mechanically driven compressor can be selectively opened or closed.

[0007] WO 2009 / 071 754 A2 discloses an exhaust gas aftertreatment system for an internal combustion engine with a low-pressure exhaust gas recirculation system in which an exhaust gas recirculation cooler is arranged, and wherein a second exhaust gas recirculation channel is provided, via which the exhaust gas can be recirculated uncooled.

[0008] DE 10 2008 036 896 A1 discloses an exhaust gas recirculation system for an internal combustion engine with an emissions control system. The exhaust gas recirculation system comprises an emissions control system bypass and an exhaust gas recirculation line with a first extraction line branching off from the emissions control system bypass and a recirculation line leading into the intake tract of the internal combustion engine upstream of a turbocharging system.

[0009] DE 10 2015 216 751 A1 describes a motor vehicle with an internal combustion engine connected to an intake tract and an exhaust system. A low-pressure exhaust gas recirculation system is provided, in which an exhaust gas recirculation cooler is arranged. A bypass is formed on the exhaust gas recirculation cooler, allowing the exhaust gas to be recirculated uncooled.

[0010] WO 2004 / 042 222 A1 discloses an exhaust system for an internal combustion engine having at least one exhaust line, wherein the exhaust line has at least one catalytically active reaction chamber in which long-chain hydrocarbons contained in the exhaust gas are decomposed.

[0011] From DE 10 2014 002 940 A1 an engine cooling system for an internal combustion engine is known, which has a coolant channel through which a coolant circulates from a water pump via a water jacket of a cylinder head and an exhaust gas recirculation cooler.

[0012] In addition, US 2016 / 0 040 629 A1 shows an exhaust gas aftertreatment system for an internal combustion engine, in which exhaust gas is discharged from the exhaust duct downstream of an outlet of the internal combustion engine and upstream of a turbine of an exhaust gas turbocharger and is fed back into the intake tract directly upstream of an inlet of the internal combustion engine via an exhaust gas recirculation cooler.

[0013] DE 10 2012 022 154 A1 describes an exhaust gas aftertreatment system for an internal combustion engine and a method for operating an internal combustion engine. A turbine of an exhaust gas turbocharger is arranged in the exhaust system, which drives a compressor in an air supply system of the internal combustion engine. The internal combustion engine has a high-pressure exhaust gas recirculation system and a low-pressure exhaust gas recirculation system, with a total exhaust gas recirculation rate being determined depending on an operating state of the internal combustion engine. The proportions of the high-pressure exhaust gas recirculation and the low-pressure exhaust gas recirculation are determined depending on at least one operating parameter of the internal combustion engine.

[0014] From US 5 592 925 A an exhaust gas recirculation system for an internal combustion engine is known, wherein a particle filter is arranged in the exhaust gas recirculation and wherein a compressed air source is provided in order to be able to remove the particles trapped in the particle filter from the particle filter against the main flow direction of the exhaust gas recirculation.

[0015] 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 to prevent condensation of liquid in the low-pressure exhaust gas recirculation.

[0016] According to the invention, this 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 system that 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 system comprises a main duct and a bypass, wherein the main duct of the low-pressure exhaust gas recirculation system branches off from the exhaust duct at a branching point downstream of the turbine and upstream of the exhaust flap and opens 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 bridges the exhaust gas recirculation cooler. At a junction or branching point of the main channel and the bypass, a control valve is arranged, with which an exhaust gas flow between the bypass and the main channel can be controlled, in particular switched or split between the main channel and the bypass. An internal combustion engine according to the invention offers the advantage that it is possible to switch between a shutdown of the low-pressure exhaust gas recirculation, an uncooled exhaust gas recirculation, and a cooled exhaust gas recirculation with just one control valve. Thus, the low-pressure exhaust gas recirculation can be adapted to the respective operating temperature of the internal combustion engine in a simple and cost-effective manner, and condensation of liquid in the low-pressure exhaust gas recirculation can be reliably prevented.

[0017] According to the invention, a filter is arranged in each of the main channel and 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 combustion engine's air supply system downstream of the inlet of the low-pressure exhaust gas recirculation line. Furthermore, malfunctions caused by soot particles, which would otherwise be deposited on the control valve, can be prevented.

[0018] The features listed in the dependent claims enable advantageous improvements and further developments of the internal combustion engine specified in the independent claim.

[0019] In a preferred embodiment of the invention, the control valve is designed as a 3 / 3-way valve. A 3 / 3-way valve allows for particularly simple switching between the individual operating states of the combustion engine. Alternatively, two simple valves can be used, connected in series to create a 3 / 3-way function.

[0020] It is particularly preferred if a first connection opening of the control valve is connected to the main channel, a second connection opening to the bypass, and a third connection opening to the low-pressure exhaust gas recirculation line. If the main channel of the low-pressure exhaust gas recirculation is connected to a first connection opening, the bypass to a second connection opening, and the low-pressure exhaust gas recirculation line to a third connection opening of the control valve, simple control and distribution of the exhaust gas flow is possible, so that the exhaust gas flow can be recirculated or fed to the exhaust gas channel depending on the exhaust gas temperature and / or the cooling water temperature of the internal combustion engine.

[0021] In a further preferred embodiment of the invention, the bypass is connected to the exhaust duct of the internal combustion engine downstream of the exhaust flap. This allows the internal combustion engine to heat up to its operating temperature via the exhaust flap, as the exhaust gas flow from the internal combustion engine is directed through the exhaust gas recirculation cooler located in the main duct of the low-pressure exhaust gas recirculation system, 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.

[0022] An advantageous improvement of the invention provides for the main channel to branch off from the exhaust passage of the internal combustion engine downstream of a particulate filter with a coating for the selective, catalytic reduction of nitrogen oxides. By branching off the low-pressure exhaust gas recirculation downstream of the particulate filter, a large proportion of the particles can be removed from the exhaust stream of the internal combustion engine by the particulate filter and retained in the particulate filter. A particulate filter with a coating for the selective, catalytic reduction of nitrogen oxides is particularly preferred, as this also significantly reduces nitrogen oxide emissions.

[0023] According to the invention, a method for exhaust gas aftertreatment of an internal combustion engine according to the invention is proposed, wherein in a first operating state of the internal combustion engine, no exhaust gas recirculation takes place via the low-pressure exhaust gas recirculation, in a second operating state, uncooled exhaust gas recirculation takes place via the bypass, and in a third operating state of the internal combustion engine, cooled exhaust gas recirculation takes place via the main duct and the exhaust gas recirculation cooler of the low-pressure exhaust gas recirculation, and in a further operating state, the exhaust flap is substantially closed, so that a large part of the exhaust gas flow of the internal combustion engine is introduced into the main duct of the low-pressure exhaust gas recirculation, wherein this exhaust gas flow is divided by the control valve into a first partial flow and a second partial flow,The first partial flow is fed to the air supply system via the low-pressure exhaust gas recirculation line, and the second partial flow is redirected back into the exhaust duct via the bypass. A method according to the invention allows exhaust gas recirculation via the low-pressure exhaust gas recirculation system to be controlled depending on the temperature of the exhaust gas, the cooling water, and / or the engine oil of the internal combustion engine in such a way that condensation of liquid is avoided. Due to the possibility of uncooled exhaust gas recirculation, the low-pressure exhaust gas recirculation system can be activated earlier after a cold start of an internal combustion engine, thereby reducing the internal combustion engine's emissions.

[0024] According to the invention, the exhaust flap is at least partially closed in the first operating state, with an exhaust gas flow being directed through the main channel of the low-pressure exhaust gas recirculation system, and the control valve being positioned such that the exhaust gas flow is directed back into the exhaust channel of the internal combustion engine via the bypass. This allows the residual heat of the exhaust gas to be used to heat the cooling water of the internal combustion engine via the exhaust gas recirculation cooler, thus helping the internal combustion engine reach its operating temperature more quickly after a cold start. This allows the low-pressure exhaust gas recirculation system to be activated more quickly, and the internal combustion engine's emissions can be reduced.

[0025] In a preferred embodiment of the method, below a first threshold temperature of the exhaust gas or the cooling water of the internal combustion engine, no exhaust gas recirculation takes place via the low-pressure exhaust gas recirculation system; above the first threshold temperature and below a second threshold temperature of the exhaust gas or the cooling water of the internal combustion engine, uncooled exhaust gas recirculation takes place via the bypass; and above the second threshold temperature, cooled exhaust gas recirculation takes place via the main channel of the low-pressure exhaust gas recirculation system. Below the first threshold temperature, 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 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 exhaust gas turbocharger compressor and to parts of the combustion engine. Therefore, below this first threshold temperature, exhaust gas recirculation via the low-pressure exhaust gas recirculation is prevented. 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. Therefore, in a temperature range above the first threshold temperature and below a second threshold temperature of approximately 80°C cooling water temperature and 180°C exhaust gas temperature, the exhaust gas is bypassed past the exhaust gas recirculation cooler to prevent additional cooling of the exhaust gas and the associated risk of water droplets condensing.Above the second threshold temperature, the exhaust gas flow is advantageously recirculated into 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 reduce the raw nitrogen oxide emissions.

[0026] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case.

[0027] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Identical components or components with the same function are identified by the same reference numerals in the drawings. They show: Fig. 1 shows 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; Fig. 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 guided through the main duct and the bypass back into the exhaust duct; Fig. 3 a third operating state of the internal combustion engine in which the exhaust gas is recirculated into the intake tract of the internal combustion engine via the main duct and the exhaust gas recirculation cooler; Fig. 4 an operating situation of the internal combustion engine in which an exhaust gas flow is recirculated via the main duct and then divided so that a first partial flow is recirculated into the intake tract via the low-pressure exhaust gas recirculation and a second partial flow is recirculated into the exhaust duct via the bypass; Fig. 5 a second operating state of the internal combustion engine, wherein an exhaust gas flow is recirculated via the bypass past the exhaust gas recirculation cooler into the intake tract; Fig. 6 shows an alternative embodiment of an internal combustion engine according to the invention, wherein the bypass is connected upstream and downstream of the exhaust gas recirculation cooler to the main channel of the low-pressure exhaust gas recirculation; and Fig. 7 shows a further alternative embodiment of an internal combustion engine according to the invention, wherein the bypass is connected upstream and downstream of the exhaust gas recirculation cooler to the main channel of the low-pressure exhaust gas recirculation and the control valve is arranged downstream of the exhaust gas recirculation cooler.

[0028] Fig. 1 shows an internal combustion engine 10 for a motor vehicle, which is designed as a compression-ignition internal combustion engine 10 based on the diesel principle. The internal combustion engine 10 is connected by its outlet 16 to an exhaust system 40. The outlet 16 comprises an exhaust manifold, which feeds the exhaust gases from the various combustion chambers 12 of the internal combustion engine 10 to an exhaust duct 44 of the exhaust system 30. The internal combustion engine 10 is connected by an inlet 14 to an air supply system 20. The air supply system 20 has an air filter 22 in the flow direction of the fresh air through the air supply system 20 and, downstream of this air filter 22, a compressor 24 of an exhaust gas turbocharger 36, with which the intake air is compressed and fed to the combustion chambers 12 of the internal combustion engine 10. The air supply system 20 further comprises a fresh gas line 26 which connects the air filter 22 to the inlet 14 of the internal combustion engine 10.Downstream of the air filter 22, an air mass meter 30 is provided on the fresh gas line 26. A coolant circuit 18 is provided on the internal combustion engine 10, which supplies the engine block and other coolers, in particular a charge air cooler 28, with coolant. Downstream of the charge air cooler 28 and upstream of the intake 14, a control flap 32 is provided for controlling the air flow of the internal combustion engine 10. Furthermore, a high-pressure exhaust gas recirculation valve 34 is provided on the internal combustion engine, with which exhaust gas can be recirculated within the engine.

[0029] The exhaust system 40 has an exhaust duct 44 in which a turbine 42 of the exhaust gas turbocharger 36 and downstream of the turbine 42 at least one first exhaust gas aftertreatment component 46 for exhaust gas aftertreatment of the internal combustion engine 10, preferably a particulate filter 54, particularly preferably an oxidation catalyst 58 with a downstream particulate filter 54 with a coating for the selective, catalytic reduction of nitrogen oxides, are arranged in the flow direction of an exhaust gas of the internal combustion engine 10 through the exhaust system 40. In the illustrated embodiment of the internal combustion engine 10, a NOx storage catalyst 50 is arranged downstream of the turbine 42 of the exhaust gas turbocharger 36, a dosing system 52 for a reducing agent is arranged downstream of the NOx storage catalyst 50, and a particulate filter 54 with a coating for the selective, catalytic reduction of nitrogen oxides is arranged downstream of the dosing system 52.Downstream of the particulate filter 54 with the SCR coating, a main duct 66 of a low-pressure exhaust gas recirculation 60 branches off from the exhaust duct 44 at a branching point 78. The main duct 66 connects the exhaust duct 44 to a low-pressure exhaust gas recirculation line 70. An exhaust gas recirculation cooler 64 is arranged in the main duct 66, with which the temperature of the recirculated exhaust gas can be reduced. For this purpose, the exhaust gas recirculation cooler 64 is connected to the coolant circuit 18 of the internal combustion engine 10 and is flowed through by the coolant. The low-pressure exhaust gas recirculation line 70 opens into the fresh gas duct 26 downstream of the air filter 22 and upstream of the compressor 24. Downstream of the branching point 78, an exhaust flap 48 is arranged in the exhaust duct 44. The exhaust duct 44 can be at least partially closed downstream of the branching point 78 by the exhaust flap 48.Downstream of the exhaust flap 48, a further SCR catalyst 56 and an oxidation catalyst 58 are arranged in the exhaust duct 44.

[0030] Downstream of the exhaust flap 48 and upstream of the further SCR catalyst 56, a bypass 68 branches off from the exhaust duct 44 at a further branching point 80 and runs essentially parallel to the main duct 66 of the low-pressure exhaust gas recirculation 60. A control valve 62 is arranged at a junction 82 of the main duct 66 and the bypass 68. The control valve 62 is preferably designed as a 3 / 3-way valve. A first connection opening 84 of the control valve 62 is connected to the main duct 66, a second connection opening 86 of the control valve 62 is connected to the bypass 68, and a third connection opening 88 is connected to the low-pressure exhaust gas recirculation line 70 of the low-pressure exhaust gas recirculation 60. The low-pressure exhaust gas recirculation line 70 opens into the fresh gas line 26 of the air supply system 20 at an inlet 76 downstream of the air mass meter 30 and upstream of the compressor 24.A filter 72, 74 is arranged on the main channel 66 and the bypass 68, which prevents or at least reduces the penetration of soot particles into the low-pressure exhaust gas recirculation 70.

[0031] The internal combustion engine 10 also includes a control unit 90 with a machine-readable program code, which is connected to the exhaust flap 48 and the control valve 62 via signal lines 92. The position of the exhaust flap 48 and the control valve 62 can be adjusted via the control unit 90, so that the exhaust gas flow through the low-pressure exhaust gas recirculation 60 can be controlled.

[0032] In Fig. 2 shows a first operating state of the internal combustion engine 10, in which the low-pressure exhaust gas recirculation channel 70 is closed by the control valve 62. In this first operating state, in particular when the internal combustion engine, cooling water, exhaust gas, and / or engine oil are cold, the exhaust flap 48 in the exhaust channel 44 is opened, so that the exhaust channel 44 is essentially closed. As a result, the exhaust gas flow of the internal combustion engine 10 is guided upstream of the exhaust flap 48 through the main channel 66 and then diverted into the bypass 68 by the control valve 62, so that the diverted exhaust gas flow is fed back into the exhaust channel 44 downstream of the exhaust flap 48 and upstream of the further SCR catalyst 56. The exhaust gas flow is passed through the exhaust gas recirculation cooler 64, whereby the residual heat of the exhaust gas flow is transferred to the coolant of the exhaust gas recirculation cooler 64 and thus to the coolant circuit 18.Thus, the residual heat of the exhaust gas, particularly after a cold start of the internal combustion engine 10, can be used to bring the internal combustion engine 10 to its operating temperature as quickly as possible after a cold start. By closing the low-pressure exhaust gas recirculation line 70, the risk of water vapor condensing in the low-pressure exhaust gas recirculation line 70 or in the fresh gas line 26, and the water droplets causing damage to the components, is eliminated.

[0033] In Fig. 5 shows a second operating state of the internal combustion engine 10, in which the internal combustion engine 10, the coolant circuit 18 and / or the engine oil have a higher temperature than in the Fig. 2. In this case, the exhaust flap 48 is essentially fully opened, so that the exhaust gas flow flows through the exhaust duct 44 in the direction of the further SCR catalyst 56. A partial flow of the exhaust gas passes through the bypass 68 into the low-pressure exhaust gas recirculation line 70, but without passing through the exhaust gas recirculation cooler 64. This reduces the risk of water droplets condensing. As a result, the low-pressure exhaust gas recirculation 60 can be activated even when the exhaust gas, coolant, or engine oil is less hot, and exhaust gas can be mixed with the intake air in the fresh gas line 26. As a result, the formation of nitrogen oxides during fuel combustion in the combustion chambers 12 of the internal combustion engine 10 can be reduced in a known manner, so that fewer raw nitrogen oxide emissions are fed to the exhaust system 40.

[0034] In Fig. Figure 3 shows a third operating state of the internal combustion engine 10, in which the internal combustion engine 10 has reached its operating temperature and a partial flow of the exhaust gas is recirculated via the main duct 66 of the low-pressure exhaust gas recirculation and cooled by the exhaust gas recirculation cooler 64 arranged in the main duct 66. For this purpose, the exhaust flap 48 is opened, so that the exhaust backpressure in the exhaust duct 44 is increased. Furthermore, the control valve 62 is positioned such that a connection from the main line 66 to the low-pressure exhaust gas recirculation line 70 is opened. This allows the combustion temperature in the combustion chambers 12 of the internal combustion engine 10 to be reduced, which has a positive effect on the raw nitrogen oxide emissions of the internal combustion engine 10.

[0035] In Fig. 4 shows a further operating state of the internal combustion engine 10. In this case, the exhaust flap 48 is essentially closed, so that a large portion of the exhaust gas flow of the internal combustion engine 10 is introduced into the main duct 66 of the low-pressure exhaust gas recirculation system 60. This exhaust gas flow is divided by the control valve 62 into a first partial flow and a second partial flow. The first partial flow is fed to the air supply system 20 via the low-pressure exhaust gas recirculation line, so that the combustion temperature and, associated with it, the raw emissions of the internal combustion engine 10 can be reduced. The second partial flow is guided back into the exhaust duct 44 via the bypass 68. This enables maximum heat recovery of the waste heat from the exhaust gas via the exhaust gas recirculation cooler 64 and simultaneous, cooled low-pressure exhaust gas recirculation.

[0036] If the exhaust gas temperature T EG and / or the coolant temperature T CFbelow a first threshold temperature T S1 or the coolant temperature T CF or the exhaust gas temperature T EF after a cold start of the combustion engine 10 below this first threshold temperature T S1 , there is a risk that the water vapor contained in the exhaust gas will condense in the low-pressure exhaust gas recirculation system 60 and, if exhaust gas recirculation occurs, damage the compressor 24 of the exhaust gas turbocharger 36. To avoid this, exhaust gas recirculation via the low-pressure exhaust gas recirculation system is avoided in a first operating state. If the exhaust gas temperature T EG during operation below a second threshold temperature T S2 or the exhaust gas temperature T EG and / or the coolant temperature T CF after a cold start of the combustion engine 10 below this second threshold temperature T S1, there is a risk that the water vapor contained in the exhaust gas will condense in the low-pressure exhaust gas recirculation 60 if the exhaust gas flow is additionally cooled by the exhaust gas recirculation cooler 64. This is particularly critical with cold coolant and a correspondingly strong cooling effect of the exhaust gas recirculation cooler 64. In this second operating state, the recirculated exhaust gas flow is guided through the bypass 68 and thus past the exhaust gas recirculation cooler 64, so that the exhaust gas temperature of the exhaust gas recirculated via the low-pressure exhaust gas recirculation 60 remains essentially constant. Such an operating state is in Fig. 5. For this purpose, the exhaust flap 48 is essentially fully opened to prevent exhaust gas from being introduced into the main channel 66 of the low-pressure exhaust gas recirculation system 60. Due to the flow resistance of the additional SCR catalyst 56 and the oxidation catalyst 58, a partial flow of the exhaust gas is directed into the bypass 68 and from there, uncooled, via the low-pressure exhaust gas recirculation line into the air supply system 20 upstream of the compressor 24.

[0037] It is preferred if, in a bypass mode in which the exhaust gas recirculated via the low-pressure exhaust gas recirculation 60 is introduced past the exhaust gas recirculation cooler 64 into the fresh gas line 26, a bypass is also provided at the charge air cooler 28 of the internal combustion engine 10, with which this charge air cooler 28 can also be bypassed. This can promote the heating of the internal combustion engine 10 at a high exhaust gas recirculation rate, and the recirculated energy is not dissipated by the charge air cooler 28 to the coolant circuit 18.

[0038] In Fig. 6 shows an alternative embodiment of an internal combustion engine 10 according to the invention. With essentially the same structure as Fig. 1 to 5, only the differences from the first exemplary embodiment will be discussed below. In this embodiment, the bypass 68 branches off from the main channel 66 upstream of the exhaust gas recirculation cooler 64 at a branch 94 and flows back into the main channel 66 downstream of the exhaust gas recirculation cooler 64 at the junction 82. The exhaust flap 48 can be arranged downstream of the branching point 78 and upstream of the further SCR catalyst 56, as in the first exemplary embodiment; alternatively, the exhaust flap can be arranged downstream of the further SCR catalyst 56, in particular downstream of the oxidation catalyst 58, at any desired point in the exhaust channel 44 downstream of the branching point 78. In this exemplary embodiment, there is no direct connection between the bypass 68 and the exhaust channel 44.The control valve 62 is arranged at the branch 94 so that exhaust gas recirculation can be selectively blocked, and the recirculated exhaust gas flow can be cooled via the exhaust gas recirculation cooler 64 or recirculated uncooled via the bypass 68.

[0039] In Fig. 7 shows a further alternative embodiment of an internal combustion engine 10 according to the invention. With essentially the same structure as Fig. 6, in this exemplary embodiment, the control valve 62 is arranged at the junction 82 of the bypass 68 and the main channel 66 of the low-pressure exhaust gas recirculation 60. Alternatively, simple switching valves, in particular exhaust gas flaps, can also be arranged at the branch 94 and the junction 82, with which the exhaust gas flow is directed through the bypass 68 and / or through the main channel 66 of the low-pressure exhaust gas recirculation.

[0040] In summary, it can be stated that an internal combustion engine 10 according to the invention can utilize the residual heat of the exhaust gas and prevent the condensation of water vapor contained in the exhaust gas recirculated via the low-pressure exhaust gas recirculation system 40. The low-pressure exhaust gas recirculation system can be activated more quickly after a cold start if uncooled exhaust gas is recirculated, thereby reducing the nitrogen oxide emissions of the internal combustion engine. List of reference symbols 10 Combustion engine 12 combustion chamber 14 Entrance 16 Outlet 18 Coolant circuit 20 Air supply system 22 air filters 24 compressors 26 Fresh gas line 28 intercooler 30 air mass meters 32 Control valve 34 High-pressure exhaust gas recirculation valve 36 exhaust gas turbochargers 40 Exhaust system 42 turbines 44 exhaust duct 46 first exhaust aftertreatment component 48 Exhaust flap 50 NOx storage catalyst 52 Dosing system 54 particulate filters with SCR coating 56 SCR catalyst 58 Oxidation 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 filters 74 filters 76 Junction 78 branch point 80 branching point 82 Merger 84 first connection opening 86 second connection opening 88 third connection opening 90 Control unit 92 Signal line 94 Branching T Temperature T CFCoolant temperature of the combustion engine T CFL Threshold for coolant temperature T EG Exhaust gas temperature T S1 first threshold temperature T S2 second threshold temperature

Claims

[1] Method for exhaust gas aftertreatment of an internal combustion engine (10) with an air supply system (20); an exhaust system (40); a low-pressure exhaust gas recirculation system (60) which connects the exhaust system (40) downstream of a turbine (42) of an exhaust gas turbocharger (36) to the air supply system (20) upstream of a compressor (24) of the exhaust gas turbocharger (36); an exhaust flap (48) with which an exhaust duct (44) of the exhaust system (40) can be at least partially blocked; wherein a main duct (66) of the low-pressure exhaust gas recirculation system (60) branches off from the exhaust duct (44) at a branching point (78) downstream of the turbine (42) and upstream of the exhaust flap (48) and opens into a low-pressure exhaust gas recirculation line (70); and wherein an exhaust gas recirculation cooler (64) is arranged in the main channel (66), wherein a bypass (68) is formed parallel to the main channel (66), which bypasses the exhaust gas recirculation cooler (64);wherein a control valve (62) is arranged at a junction (82) or a branch (94) of the main channel (66) and the bypass (68), with which control valve an exhaust gas flow between the bypass (68) and the main channel (66) can be controlled; wherein a filter (72, 74) is arranged in each of the main channel (66) and the bypass (68); characterized by , that - in a first operating state, no exhaust gas recirculation takes place via the low-pressure exhaust gas recirculation (60), - in a second operating state, an uncooled exhaust gas recirculation takes place via the bypass (68), and - in a third operating state, a cooled exhaust gas recirculation takes place via the main channel (66) of the low-pressure exhaust gas recirculation (60), and - in a further operating state, the exhaust flap (48) is substantially closed, so that a large part of the exhaust gas flow of the internal combustion engine (10) is introduced into the main channel (66) of the low-pressure exhaust gas recirculation (60), wherein this exhaust gas flow is divided by the control valve (62) into a first partial flow and a second partial flow, wherein the first partial flow is fed to the air supply system (20) via the low-pressure exhaust gas recirculation line (70) and the second partial flow is passed back into the exhaust channel (44) via the bypass (68), wherein - in the first operating state, the exhaust gas flap (48) is at least partially closed, wherein an exhaust gas flow is passed through the main channel (66) of the low-pressure exhaust gas recirculation (60) and the control valve (62) is set such that the exhaust gas flow is passed via the bypass (68) back into the exhaust gas channel (44) of the internal combustion engine (10). [2] Method according to claim 1, characterized bythat below a first threshold temperature (T S1 ) of the exhaust gas or the cooling water of the internal combustion engine (10), no exhaust gas recirculation takes place via the low-pressure exhaust gas recirculation, above the first threshold temperature (T S1 ) and below a second threshold temperature (T S2 ) of the exhaust gas or the cooling water of the internal combustion engine (10), an uncooled exhaust gas recirculation takes place via the bypass (68) and above the second threshold temperature (T S2 ) cooled exhaust gas recirculation takes place via the main channel (66) of the low-pressure exhaust gas recirculation (60). [3] Internal combustion engine (10) with an air supply system (20); an exhaust system (40); a low-pressure exhaust gas recirculation (60) which connects the exhaust system (40) downstream of a turbine (42) of an exhaust gas turbocharger (36) to the air supply system (20) upstream of a compressor (24) of the exhaust gas turbocharger (36); an exhaust flap (48) with which an exhaust duct (44) of the exhaust system (40) can be at least partially blocked; wherein a main duct (66) of the low-pressure exhaust gas recirculation (60) branches off from the exhaust duct (44) at a branching point (78) downstream of the turbine (42) and upstream of the exhaust flap (48) and opens into a low-pressure exhaust gas recirculation line (70); and wherein an exhaust gas recirculation cooler (64) is arranged in the main channel (66), wherein a bypass (68) is formed parallel to the main channel (66), which bypasses the exhaust gas recirculation cooler (64);wherein a control valve (62) is arranged at a junction (82) or a branch (94) of the main duct (66) and the bypass (68), with which control valve an exhaust gas flow between the bypass (68) and the main duct (66) can be controlled; wherein a filter is arranged in each of the main duct (66) and the bypass (68); and with a control unit (90) with a machine-readable program code, which is connected to the exhaust flap (48) and the control valve (62) via signal lines (92), wherein the control unit (90) is configured to carry out a method according to claim 1 or claim 2 when the machine-readable program code is executed by the control unit (90). [4] Internal combustion engine (10) according to claim 3, characterized by 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. [5] Internal combustion engine (10) according to claim 3 or 4, characterized bythat a first connection opening (84) of the control valve (62) is connected to the main channel (66), a second connection opening (86) is connected to the bypass (68) and a third connection opening (88) is connected to the low-pressure exhaust gas recirculation line (70). [6] Internal combustion engine (10) according to one of claims 3 to 5, characterized by that the bypass (68) downstream of the exhaust flap (48) is connected to the exhaust duct (44) of the internal combustion engine (10). [7] Internal combustion engine (10) according to one of claims 3 to 6, characterized by that the main channel (66) of the low-pressure exhaust gas recirculation (60) branches off from the exhaust channel (44) of the internal combustion engine (10) downstream of a particle filter (54) with a coating for the selective, catalytic reduction of nitrogen oxides.

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