Method for controlling an internal combustion engine and internal combustion engine

Abstract

Method for controlling an internal combustion engine (10) with at least one combustion chamber (12), wherein the internal combustion engine (10) is connected on the intake side to an air supply system (20) and on the exhaust side to an exhaust system (40), wherein the exhaust system (40) is connected to the air supply system (20) via a high-pressure exhaust gas recirculation (90) and a low-pressure exhaust gas recirculation (80), comprising the following steps: - determining an ambient temperature, - determining a temperature of an exhaust aftertreatment component (50, 52) for the selective catalytic reduction of nitrogen oxides, - determining a power demand and / or a torque demand on the internal combustion engine, - determining a NOx concentration in the exhaust system (40), - temporarily enabling the low-pressure exhaust gas recirculation (80) when • the ambient temperature is below a first threshold temperature (TUS),• the power requirement and / or the torque requirement to the internal combustion engine (10) exceeds a threshold value (hp, mp), and • the conversion capability of the exhaust aftertreatment component (50, 52) for selective catalytic reduction of nitrogen oxides is below a second threshold (KNAS) or the temperature of the exhaust aftertreatment components (50, 52) for selective catalytic reduction of nitrogen oxides is below a second threshold temperature (TNAS).

Description

The invention relates to a method for controlling an internal combustion engine, in particular a diesel engine, and to an internal combustion engine for carrying out such a method according to the preamble of the independent claims. Current and increasingly stringent emissions legislation places high demands on raw engine emissions and exhaust aftertreatment in combustion engines. In gasoline engines, exhaust gas purification is achieved in the familiar manner via a three-way catalytic converter, as well as additional catalysts upstream and downstream of the three-way catalytic converter and a particulate filter. In diesel engines, exhaust gas purification is generally achieved by an exhaust aftertreatment system that includes at least an oxidation catalyst, a particulate filter, and a catalyst for the selective catalytic reduction of nitrogen oxides and / or a NOx storage catalyst. Every catalytic exhaust gas purification system requires exceeding a minimum temperature, the so-called light-off temperature, to become effective. During a cold start of a vehicle, the combustion engine and the exhaust aftertreatment components are at approximately ambient temperature. Even with a high energy input into the exhaust system, the thermal inertia of the exhaust system must first be overcome and radiation and convection losses compensated for in order to achieve at least partial effectiveness of the exhaust aftertreatment components. During this time, the raw emissions from the combustion engine are emitted largely untreated. Depending on the energy input into the exhaust system, this period can be shortened. The faster the light-off temperatures of the catalysts are reached, the lower the emissions can be when the combustion engine is operated in combination with the exhaust aftertreatment system.Furthermore, the actively heated catalyst volume has a significant influence on the conversion performance. To meet future emission regulations, it may therefore be necessary to support the achievement of the component temperatures of the exhaust aftertreatment components through an additional external heating measure. Since the introduction of the Euro 6 emissions standard, limits for nitrogen oxides (NOx) must not only be met during the type approval cycle, but also under Real Driving Emissions (RDE) conditions. These stringent limits must also be met during the urban driving portion of an RDE cycle, for which a minimum distance is defined for determining specific NOx emissions. For compliance with future nitrogen oxide limits, the cold start component of nitrogen oxide emissions is of particular importance. Cold start emissions and the subsequent warm-up of the combustion engine, with the associated heating of the catalytic converters until they reach the "light-off" stage, account for the majority of total emissions in the urban portion of the test cycle. To effectively convert the unavoidable raw emissions into emissions after the engine is switched on, catalytic converters are installed in the exhaust system of the combustion engine. For these catalytic converters to convert the pollutants, a minimum temperature level of the exhaust gas and the catalytic converter must be exceeded in the exhaust system. To bring these catalytic converters up to a light-off temperature as quickly as possible after a cold start of the combustion engine, engine heating measures are used, such as retarding the ignition timing or operating the combustion engine at substoichiometric speeds with the simultaneous introduction of secondary air. In diesel engines, late post-injection is also commonly used to increase the exhaust gas temperature and improve the heating of the exhaust aftertreatment components. Furthermore, to heat the catalytic converter quickly and precisely, it is possible to heat it using an electric heating element. In-engine heating measures have the disadvantage that they can worsen the raw emissions of the combustion engine. Furthermore, the heat is generated significantly upstream of the catalyst, resulting in heat losses in the combustion chambers of the engine and in the exhaust system upstream of the catalyst being heated. To ensure minimal tailpipe emissions, it is therefore necessary to minimize the raw emissions of the combustion engine and continuously adjust them to the efficiency of the exhaust aftertreatment components. This can be achieved, in particular, by controlling the activation of the exhaust gas recirculation (EGR) systems and the recirculated exhaust gas flow rate. It is known that EGR increases the specific heat capacity of the cylinder charge and reduces the oxygen concentration in the combustion chamber. Both effects reduce the resulting raw NOx emissions. Furthermore, high-pressure EGR systems with and without cooling, as well as with switchable cooling, and permanently cooled low-pressure EGR systems are known. In high-pressure EGR systems, the recirculated exhaust gas is routed to the respective high-pressure sides of the turbine and compressor of the exhaust gas turbocharger.More precisely, exhaust gas is extracted from the exhaust system upstream of the turbocharger turbine and routed into the intake manifold downstream of the turbocharger compressor. Due to this enthalpy extraction upstream of the turbocharger turbine, a conflict arises between the exhaust gas recirculation rate and the associated nitrogen oxide reduction, and the maximum achievable fresh air mass and the resulting maximum engine torque. Low-pressure exhaust gas recirculation systems extract the recirculated exhaust gas downstream of the turbocharger turbine (i.e., on its low-pressure side) and reintroduce it into the intake system upstream of the compressor (also on its low-pressure side).The advantage of low-pressure exhaust gas recirculation (EGR) is that the enthalpy flow across the exhaust turbine is not reduced by the recirculated exhaust gas mass flow, thus resolving the conflict between nitrogen oxide reduction and torque achievement. However, a disadvantage of low-pressure EGR is that at low temperatures, it can lead to condensation or icing within the recirculation system, which prevents its immediate activation after every cold start of the combustion engine. The release strategies of the exhaust gas recirculation (EGR) system and the requirements of EU7 emissions legislation result in a significant limitation of engine power during cold starts if low-pressure EGR is not available from the moment the combustion engine starts. Such power limitation is typically achieved by limiting a combination of engine speed and torque. Different combinations of speed and torque can lead to the same power limitation. Based on the preferred ranges for both the desired speed and torque, an optimal combination of speed and torque limits can be selected for a given power limitation. The operating range of the exhaust aftertreatment system, from the moment the engine starts until the aftertreatment components reach their respective light-off temperatures, is considered particularly critical in this context. From US patent 2020 / 0141366A1, an internal combustion engine with an exhaust aftertreatment system and a method for controlling the internal combustion engine are known, in which a low-pressure exhaust gas recirculation of the internal combustion engine is enabled depending on a coolant temperature of the internal combustion engine in order to reduce the raw emissions of the internal combustion engine and to avoid condensation in the low-pressure exhaust gas recirculation. German patent DE 10 2004 064 173 B4 describes a diesel engine with a turbocharger and a double-loop exhaust gas recirculation system, comprising: a combustion chamber connected to an intake manifold and an exhaust port, a compressor located upstream of the intake manifold, a turbine located in the exhaust port for driving the compressor, and a particulate filter located downstream of the turbine in the exhaust port. The exhaust gas recirculation system includes a high-pressure loop for exhaust gas recirculation, through which exhaust gas can be extracted from the exhaust port upstream of the turbine and returned downstream of the compressor to the intake manifold, and a low-pressure loop for exhaust gas recirculation, through which exhaust gas can be extracted from the exhaust port downstream of the particulate filter and returned upstream of the compressor to the intake manifold.The system includes a control unit which, in a first operating mode, uses both the high-pressure loop and the low-pressure loop for exhaust gas recirculation. From DE 10 2008 008 492 A1, a method for controlling a cold-start phase of a motor vehicle internal combustion engine arrangement is known. The arrangement comprises an internal combustion engine with a charge air inlet and an exhaust gas outlet, a charge air supercharger with a drive turbine and a compressor, a coolant circuit with a control element for coolant flow control for on-demand cooling of the internal combustion engine, an exhaust gas catalyst connected to the outlet with an exhaust gas temperature sensor, a low-pressure exhaust gas recirculation line from the outlet side downstream of the exhaust gas catalyst to the charge air side downstream of the compressor, and an exhaust gas recirculation control valve for controlling the exhaust gas flow through the exhaust gas recirculation line. Furthermore, DE 10 2011 013 183 A1 discloses a nitrous oxide-optimized exhaust aftertreatment system for a motor vehicle combustion engine, which has at least one exhaust aftertreatment component at which or through which nitrous oxide is formed and nitrous oxide is released into the exhaust gas. Furthermore, DE 10 2011 013 183 A1 discloses a method for operating such an exhaust aftertreatment system. A disadvantage of solutions known from the prior art is that the emission-optimized cooled exhaust gas recirculation systems, especially low-pressure exhaust gas recirculation, are not immediately available from the moment the combustion engine starts. Instead, due to significant condensation, these exhaust gas recirculation systems are only activated with a delay under ambient temperature-dependent activation conditions, which leads to higher raw emissions during the cold start phase. The invention is based on the objective of reducing the performance limitations during a cold start of the internal combustion engine while still enabling emission-minimal cold start operation of the internal combustion engine in order to comply with the strict exhaust emission regulations. The problem is solved by a method for controlling an internal combustion engine with at least one combustion chamber, wherein the internal combustion engine is connected to an air supply system on the intake side and to an exhaust system on the exhaust side. The exhaust system is connected to the air supply system via high-pressure and low-pressure exhaust gas recirculation. The method comprises the following steps: - Determining an ambient temperature, - Determining the temperature of an exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides, - Determining a power demand and / or a torque demand on the internal combustion engine, and - Determining a NOx concentration in the exhaust system.- This involves a temporary release of the low-pressure exhaust gas recirculation if: • the ambient temperature is below a first threshold temperature, • the power demand and / or the torque demand on the combustion engine exceeds a threshold value, and the temperature of the exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides is below a second threshold temperature. The method according to the invention makes it possible to significantly reduce emissions during the cold start phase of the combustion engine and, in particular, to reduce emission peaks by means of a short-term, higher torque or power demand during the cold start phase, especially during acceleration. Furthermore, such a method can eliminate or reduce power or torque limitations during the cold start phase, since the elimination of emission peaks ensures that emission targets are met. By temporarily enabling low-pressure exhaust gas recirculation during increased power and / or torque demands in the cold start phase, the raw emissions of the combustion engine are reduced, whereby the duration of the low-pressure exhaust gas recirculation activation is chosen in such a way that condensation in the low-pressure exhaust gas recirculation system and / or in the intake tract of the combustion engine is significantly reduced compared to an unlimited activation of low-pressure exhaust gas recirculation from the start of the combustion engine. The features listed in the dependent claims enable advantageous further developments and improvements of the method for controlling an internal combustion engine mentioned in the independent claim. In an advantageous embodiment of the method, low-pressure exhaust gas recirculation is activated when the measured NOx concentration in the exhaust system exceeds a threshold value during operation of high-pressure exhaust gas recirculation. If it is not possible to keep the raw emissions below the threshold value solely through exhaust gas recirculation via high-pressure recirculation, low-pressure exhaust gas recirculation is additionally activated. This reduces the raw emissions of the combustion engine by means of the exhaust gas recirculated via low-pressure recirculation, thus eliminating the need for a power limitation of the combustion engine or allowing for a less severe power limitation than with known methods in order to comply with emission limits during the cold start phase. In a preferred embodiment of the method, the first threshold temperature is in the range of 15°C to 25°C. At higher ambient temperatures, the low-pressure exhaust gas recirculation can generally be enabled from the start of the combustion engine, since less condensate formation in the low-pressure exhaust gas recirculation system is expected in this temperature range. Therefore, at higher ambient temperatures, the method according to the invention is not necessary to reduce raw emissions, particularly nitrogen oxide emissions, during the start-up phase of the combustion engine. In a further preferred embodiment of the method, the second threshold temperature for the exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides is at least 150°C, preferably at least 220°C, and particularly preferably at least 280°C. This second threshold temperature is in the range of the light-off temperature of an exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides in the exhaust system of the combustion engine. Once such an exhaust aftertreatment component has reached its light-off temperature, the NOx emissions can be converted by the exhaust aftertreatment component, and additional exhaust gas recirculation via the low-pressure exhaust gas recirculation system can be omitted to minimize the risk of condensation in the low-pressure exhaust gas recirculation system. In an advantageous embodiment of the method, the threshold for the torque requirement is set at a maximum of 60%, preferably at a maximum of 40%, and more preferably at a maximum of 30%, of the maximum torque of the internal combustion engine. Since dynamic load requirements, particularly during the cold start phase, lead to increased raw emissions, especially nitrogen oxide emissions, the method is implemented particularly when a torque requirement and / or a speed requirement during the cold start phase exceeds the threshold. Alternatively or additionally, it is advantageously provided that the threshold for the power requirement is set at a maximum of 60% of the maximum power of the combustion engine. Since dynamic load requirements, particularly during the cold start phase, lead to increased raw emissions, especially nitrogen oxide emissions, the procedure is executed especially when a power requirement during the cold start phase exceeds the threshold. In a preferred embodiment of the method, it is provided that the release of the low-pressure exhaust gas recirculation is additionally dependent on the rotational speed of the internal combustion engine. It is particularly preferred if the release of the low-pressure exhaust gas recirculation takes place at a speed of at least 750 rpm, preferably at least 1400 rpm, in particular at least 1600 rpm and at a maximum of 3500 rpm, preferably at a maximum of 3000 rpm, in particular at a maximum of 2500 rpm. In an advantageous embodiment of the method, the temporary release of the low-pressure exhaust gas recirculation is provided for a period of a maximum of 5 seconds, preferably a maximum of 3 seconds, and particularly preferably a maximum of 2 seconds. The time interval for the temporary release of the low-pressure exhaust gas recirculation is selected such that no or only a tolerably low amount of condensate forms in the low-pressure exhaust gas recirculation system, thus reliably preventing damage to components in the low-pressure exhaust gas recirculation system, particularly to an exhaust gas recirculation valve. A further improvement to the process involves temporarily disabling the low-pressure exhaust gas recirculation (EGR) system when at least one exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides (NOx) reaches its light-off temperature. This prevents the introduction of cold exhaust gas into the low-pressure EGR system, which could potentially lead to condensation. Since the exhaust aftertreatment component is capable of converting harmful NOx at this point, low-pressure EGR can be temporarily omitted until the exhaust system is fully heated and the risk of condensation and / or component damage to the air and exhaust system is eliminated. Another aspect of the invention relates to an engine control unit with a processing unit and a storage unit, wherein a computer program code is stored in the storage unit, which is configured to carry out the method according to the invention when the computer program code is executed by the processing unit of the engine control unit. Such an engine control unit enables the simple control of all components in the exhaust system and the intake tract of the internal combustion engine in order to carry out a method according to the invention. Another aspect of the invention relates to a computer program product comprising computer program code configured to execute all steps of a method described in the preceding sections. Another aspect of the invention relates to an internal combustion engine with an engine control unit configured to execute a method described in the preceding sections when a computer program code is executed by a processing unit of the engine control unit. The internal combustion engine according to the invention makes it possible to significantly reduce emissions during a cold start phase and, in particular, to reduce emission peaks by means of a short-term, higher torque or power demand during the cold start phase, especially during acceleration. Furthermore, such a method can eliminate or reduce power or torque limitations during the cold start phase, since the elimination of emission peaks ensures that emission targets are met. Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another. The invention is explained below in exemplary embodiments with reference to the accompanying drawings. The drawings show: Fig. 1 an internal combustion engine with an exhaust aftertreatment system for carrying out a method according to the invention for controlling the internal combustion engine; Fig. 2 a flow diagram for carrying out a method according to the invention for controlling an internal combustion engine with an exhaust aftertreatment system; Fig. 3 a speed profile and a profile of the raw and tailpipe emissions during the carrying out of a method according to the invention in comparison to a method known from the prior art. Fig. 1 shows a schematic representation of a diesel engine 10 with an intake manifold 20 and an exhaust system 40. The diesel engine 10 is designed as a direct-injection diesel engine and has several combustion chambers 12. A fuel injector 14 is arranged on each combustion chamber 12 for injecting fuel into the respective combustion chamber 12. The diesel engine 10 is connected to an intake manifold 20 via its inlet 16 and to an exhaust system 40 via its outlet 18. The diesel engine 10 also includes a high-pressure exhaust gas recirculation system 90 with an exhaust gas recirculation line 96, in which a high-pressure exhaust gas recirculation valve 98 is arranged, through which exhaust gas from the diesel engine 10 can be recirculated from the outlet 18 to the inlet 16. Furthermore, an exhaust gas recirculation cooler 110 can be arranged in the high-pressure exhaust gas recirculation 90, which is designed as a switchable exhaust gas recirculation cooler 110 and can be bypassed by a bypass 112.Inlet valves and outlet valves are arranged on the combustion chambers 12, with which a fluidic connection from the intake tract 20 to the combustion chambers 12 or from the combustion chambers 12 to the exhaust system 40 can be opened or closed. The intake tract 20 comprises an intake channel 28 in which, in the direction of fresh air flow through the intake channel 28, an air filter 22, an air mass meter 24 (in particular a hot-film air mass meter), a compressor 26 of an exhaust gas turbocharger 36 (downstream of the air mass meter 24), a throttle valve 30 (downstream of the compressor 26), and a charge air cooler 32 (further downstream) are arranged. The air mass meter 24 can also be arranged in a filter housing of the air filter 22, so that the air filter 22 and the air mass meter 24 form a single assembly. An inlet 34 is provided downstream of the air filter 22 and upstream of the compressor 26, at which an exhaust gas recirculation line 86 of a low-pressure exhaust gas recirculation system 80 opens into the intake channel 28. The exhaust system 40 comprises an exhaust duct 42 in which, in the direction of flow of exhaust gas from the diesel engine 10 through the first exhaust duct 42, a turbine 44 of the exhaust gas turbocharger 36 is arranged, which drives the compressor 26 in the intake manifold 20 via a shaft. The exhaust gas turbocharger 36 is preferably designed as an exhaust gas turbocharger 36 with variable turbine geometry. For this purpose, adjustable guide vanes are arranged upstream of a turbine wheel of the turbine 44, by means of which the flow of exhaust gas onto the blades of the turbine 44 can be varied. Several exhaust aftertreatment components 46, 48, 50, 52, 54, 94 are provided downstream of the turbine 44. An oxidation catalyst 46 or a NOx storage catalyst 94 is arranged immediately downstream of the turbine 44 as the first component of the exhaust aftertreatment.Downstream of the oxidation catalyst 46 or the NOx storage catalyst 94, a first SCR catalyst 48 located close to the engine, preferably a particulate filter 50 with a coating for the selective catalytic reduction of nitrogen oxides (SCR coating), is arranged. Downstream of the first SCR catalyst 48 located close to the engine, a second SCR catalyst 52 is preferably arranged in the exhaust duct 42 in the underbody of a motor vehicle. The second SCR catalyst 52 has an ammonia blocking catalyst 54. Downstream of the oxidation catalyst 46 or the NOx storage catalyst 94 and upstream of the first SCR catalyst 48, a first metering element 56 is provided for metering a reducing agent 78 into the exhaust duct 42.Downstream of the first SCR catalyst 48, in particular downstream of the particulate filter 50 with the SCR coating, an exhaust gas recirculation line 86 of a low-pressure exhaust gas recirculation system 80 branches off from the exhaust channel 42 at a junction 70. Downstream of the junction 70 and upstream of the second SCR catalyst 52, a second metering element 58 is arranged to meter the reducing agent 78 into the exhaust channel 42. The first metering element 56 and the second metering element 58 are each connected via a reducing agent line 72, 74 to a common reducing agent reservoir 76 in which the reducing agent 78 is stored. Furthermore, the exhaust system 40 includes an exhaust flap 60 with which the exhaust gas recirculation via the low-pressure exhaust gas recirculation system 80 can be controlled. The low-pressure exhaust gas recirculation system 80 comprises, in addition to the exhaust gas recirculation line 86, an exhaust gas recirculation cooler 82 and an exhaust gas recirculation valve 84, which controls the exhaust gas recirculation through the exhaust gas recirculation line 86. In the exhaust gas channel 42, an exhaust gas temperature TEG can be detected by a temperature sensor 38 or calculated by the engine control unit 100 to activate the low-pressure exhaust gas recirculation system 80 as soon as the exhaust gas temperature TEG exceeds a defined threshold. A further temperature sensor can be provided on the exhaust gas recirculation line 86 of the low-pressure exhaust gas recirculation system 80 to determine the temperature of the recirculated exhaust gas downstream of the exhaust gas recirculation cooler 82. This prevents the recirculated exhaust gas from being cooled so much that the dew point is reached and water droplets condense in the exhaust gas recirculation line 86.This prevents water vapor or gas components contained in the exhaust gas from condensing and causing damage or deposits in the low-pressure exhaust gas recirculation system 80 or in the intake tract 20. A filter can also be provided downstream of the branch 70 and upstream of the exhaust gas recirculation cooler 82 to minimize the introduction of particles into the low-pressure exhaust gas recirculation system 80. The exhaust gas recirculation line 86 opens into the intake duct 28 of the intake tract 20 at an inlet 34. In the exhaust system 40, an exhaust gas sensor 62 for detecting the ammonia concentration in the exhaust duct 42 is arranged downstream of the branch 70 for the low-pressure exhaust gas recirculation and upstream of the second metering element 58. The exhaust gas sensor 62 is preferably designed as an NH3 sensor 88 or as an NH3-NOx combination sensor 92. Furthermore, the particulate filter 50 has a differential pressure sensor 64 with which a pressure difference Δp across the particulate filter 50 is determined. In this way, the loading state of the particulate filter 50 can be determined and regeneration of the particulate filter 50 can be initiated if a defined loading level is exceeded. A temperature sensor 38 is also provided in the exhaust system 40 to determine the exhaust gas temperature. Downstream of the first metering element 56 and upstream of the first SCR catalyst 48, a first exhaust gas mixer 66 can be provided to improve the mixing of the exhaust gas stream from the diesel engine 10 and the reducing agent 78 before they enter the first SCR catalyst 48 and to shorten the length of the mixing path. Downstream of the second metering element 58 and upstream of the second SCR catalyst 52, a second exhaust gas mixer 68 can be arranged to improve the mixing of the exhaust gas stream and the reducing agent 78 and to promote the evaporation of the reducing agent 78 in the exhaust gas channel 42. The diesel engine 10 is connected to an engine control unit 100, which is connected via signal lines (not shown) to the exhaust gas sensor 62, 88, 92, the differential pressure sensor 64, the temperature sensor 38, as well as to the fuel injectors 14 of the diesel engine 10 and the metering elements 56, 58. The engine control unit 100 has a processing unit 102 and a storage unit 104, in which a machine-readable program code 106 for carrying out a method according to the invention for exhaust aftertreatment of the diesel engine 10 is stored. Figure 2 shows a flowchart for carrying out a method according to the invention for controlling an internal combustion engine 10, in particular a diesel engine, wherein the internal combustion engine 10 is connected with its inlet 16 to an air supply system 20 and with its outlet 18 to an exhaust system 40. In one process step <200> An ambient temperature is determined. Furthermore, the temperature of an exhaust aftertreatment component 50, 52 for the selective catalytic reduction of nitrogen oxides is determined. In addition, a power requirement for the combustion engine 10 and a NOx concentration in the exhaust system 40 of the combustion engine 10 are determined. Alternatively or additionally, a torque requirement for the combustion engine 10 and a NOx concentration in the exhaust system 40 of the combustion engine 10 can be determined. In one process step <210> The measured ambient temperature is compared with a first threshold temperature TUS. If the temperature is above the threshold temperature TUS, no restrictions are necessary for enabling the low-pressure exhaust gas recirculation 80. If the ambient temperature is below the first threshold temperature TUS, then in one process step <220> It was tested whether the exhaust aftertreatment components 50, 52 are capable of selectively catalytically reducing nitrogen oxides by converting at least 80%, preferably at least 90%, and most preferably at least 95% of the raw NOx emissions. To determine the conversion efficiency of the exhaust aftertreatment components 50, 52 for the selective catalytic reduction of nitrogen oxides, a first NOx sensor 93 and a second NOx sensor 95 are arranged upstream of the exhaust aftertreatment components 50, 52. If such a conversion efficiency is ensured, activation of the low-pressure exhaust gas recirculation can be omitted.Alternatively or additionally, the conversion performance of the exhaust aftertreatment components 50, 52 for the selective catalytic reduction of nitrogen oxides can be determined via the temperature(s) of the at least one exhaust aftertreatment component 50, 52. If the determined temperature is below a second threshold temperature (TNAS), at which sufficient conversion of the nitrogen oxide emissions by the exhaust aftertreatment components 50, 52 cannot be expected, the process is discontinued with process step <230> continued. If the temperature is above the second threshold temperature TNAS, exhaust aftertreatment of the exhaust gas of the combustion engine 10 can be carried out by the corresponding exhaust aftertreatment component 50, 52 for the selective catalytic reduction of nitrogen oxides and it is not necessary to enable the low-pressure exhaust gas recirculation 80 in order to comply with the emission limits. If the temperature is below the second threshold temperature TNAS, so that efficient exhaust aftertreatment by the exhaust aftertreatment component 50, 52 is not possible, then in a process step <230> It was checked whether the determined NOx concentration in the exhaust system 40 exceeds a threshold value when the high-pressure exhaust gas recirculation 90 is in operation, at which compliance with the emission limits is no longer possible solely by reducing the raw emissions via the high-pressure exhaust gas recirculation 90. Furthermore, in one procedural step <240> Checked whether a power requirement and / or a torque requirement to the internal combustion engine 10 exceeds a threshold value PS and / or MS. If the ambient temperature is below the first threshold temperature TUS, the temperature of the exhaust aftertreatment component 50, 52 is below the second threshold temperature TNAS for the exhaust aftertreatment component 50, 52, the power requirement and / or the torque requirement is above the respective threshold value PS, MS, and the determined NOX concentration in the exhaust system exceeds the threshold value NOxS, at which the raw emissions can no longer be sufficiently reduced solely by the high-pressure exhaust gas recirculation 90, then in one process step <250> a temporary release of the low-pressure exhaust gas recirculation 80 to avoid emission peaks during the cold start phase under dynamic load requirements. Figure 3 shows the speed profile of a motor vehicle with such an internal combustion engine 10, the raw NOx emissions of the internal combustion engine 10, and the tailpipe emissions of the exhaust system 40 downstream of the internal combustion engine 10. As can be seen in Figure 3, in known methods where the low-pressure exhaust gas recirculation 80 is blocked during the cold start phase, a dynamic load demand leads to a peak in nitrogen oxide emissions, which jeopardizes compliance with nitrogen oxide limits. Therefore, in known solutions in this area, the power or torque is limited during the cold start phase to avoid such emission peaks. By temporarily enabling the low-pressure exhaust gas recirculation (EGR) 80 during this cold start phase, a similarly good result can be achieved as with a power limitation of the combustion engine 10, without requiring a corresponding restriction for the driver. At time point I, the combustion engine 10 is cold-started. In phase II, a dynamic load demand is placed on the combustion engine, during which it becomes apparent that emissions can be effectively reduced by enabling the low-pressure EGR 80 of the combustion engine 10. In phase III, the combustion engine 10 operates without any special load demands, during which emissions can be effectively minimized via the high-pressure EGR 90. In phase IV, another dynamic load demand follows, during which the low-pressure EGR 80 is once again enabled to minimize emissions.In Phase V, the exhaust aftertreatment components 48, 50, and 52 reach temperatures above the light-off temperature, enabling efficient conversion of the limited exhaust gas component by these components. As an example, at time VI, a reduction in nitrogen oxide emissions through the selective catalytic reduction of nitrogen oxides by one exhaust aftertreatment component 50 or 52 is shown. In Phase VI, without the use of low-pressure exhaust gas recirculation 80, a high raw emission peak is converted by at least one exhaust aftertreatment component 50 or 52 to the selective catalytic reduction of nitrogen oxides. Reference symbol list 10 Internal combustion engine / diesel engine 12 Combustion chamber 14 Fuel injector 16 Inlet 18 Outlet 20 Intake tract 22 Air filter 24 Mass air flow sensor 26 Compressor 28 Intake manifold 30 Throttle valve 32 Intercooler 34 Inlet 36 Exhaust turbocharger 38 Temperature sensor 40 Exhaust system 42 Exhaust duct 44 Turbine 46 Oxidation catalyst 48 First SCR catalyst 50 Particulate filter with SCR coating 52 Second SCR catalyst 54 Ammonia blocking catalyst 56 First metering element 58 Second metering element 60 Exhaust flap 62 Exhaust gas sensor 64 Differential pressure sensor 66 First exhaust mixer 68 Second exhaust mixer 70 Branch 72 First reducing agent line 74 Second reducing agent line 76 Reducing agent reservoir 78 Reducing agent 80 Low-pressure exhaust gas recirculation 82 Exhaust gas recirculation cooler 84 Exhaust gas recirculation valve 86 Exhaust gas recirculation line 88 NH3 sensor 90 High-pressure exhaust gas recirculation 92 NH3-NOx combination sensor 93 NOx sensor before SCR catalyst 94 NOx storage catalyst 95 NOx sensor after SCR catalyst96 Exhaust gas recirculation line 98 High-pressure exhaust gas recirculation valve 100 Engine control unit 102 Processing unit 104 Storage unit 106 Computer program code 110 Exhaust gas recirculation cooler 112 Bypass

Claims

Method for controlling an internal combustion engine (10) with at least one combustion chamber (12), wherein the internal combustion engine (10) is connected on the intake side to an air supply system (20) and on the exhaust side to an exhaust system (40), wherein the exhaust system (40) is connected to the air supply system (20) via a high-pressure exhaust gas recirculation (90) and a low-pressure exhaust gas recirculation (80), comprising the following steps: - determining an ambient temperature, - determining a temperature of an exhaust aftertreatment component (50, 52) for the selective catalytic reduction of nitrogen oxides, - determining a power demand and / or a torque demand on the internal combustion engine, - determining a NOx concentration in the exhaust system (40), - temporarily enabling the low-pressure exhaust gas recirculation (80) when • the ambient temperature is below a first threshold temperature (TUS),• the power requirement and / or the torque requirement to the internal combustion engine (10) exceeds a threshold value (hp, mp), and • the conversion capability of the exhaust aftertreatment component (50, 52) for selective catalytic reduction of nitrogen oxides is below a second threshold (KNAS) or the temperature of the exhaust aftertreatment components (50, 52) for selective catalytic reduction of nitrogen oxides is below a second threshold temperature (TNAS). Method according to claim 1, wherein the low-pressure exhaust gas recirculation (80) is activated when the determined NOx concentration in the exhaust system (40) exceeds a threshold value (NOxS) during operation of the high-pressure exhaust gas recirculation (90). Method according to claim 1 or 2, wherein the first threshold temperature (TUS) is in the range of 15 to 25°C. Method according to any one of claims 1 to 3, wherein the second threshold temperature (TNAS) is at least 150°C. Method according to one of claims 1 to 4, wherein the threshold value (MS) for the torque request is at a maximum of 60% of the maximum torque (Mmax) of the internal combustion engine (10) or the threshold value (PS) for the power request is at a maximum of 60% of the maximum power of the internal combustion engine (10). Method according to one of claims 1 to 5, wherein the release of the low-pressure exhaust gas recirculation (80) additionally takes place depending on a speed of the internal combustion engine (10). Method according to claim 6, wherein the low-pressure exhaust gas recirculation is enabled in a speed range of 750 rpm to 3500 rpm. Method according to any one of claims 1 to 7, wherein the low-pressure exhaust gas recirculation is blocked when at least one exhaust aftertreatment component (50, 52) for selective catalytic reduction of nitrogen oxides has reached its light-off temperature and has a NOx conversion rate of at least 80% of the raw nitrogen oxide emissions of the combustion engine (10). Internal combustion engine (10) with an engine control unit (100) which is configured to execute a method according to one of claims 1 to 8 when a computer program code (106) is executed by a computing unit (102) of the engine control unit (100).

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