Methods for exhaust aftertreatment of an internal combustion engine and exhaust aftertreatment system

Abstract

Method for exhaust aftertreatment of an internal combustion engine (10) with an exhaust aftertreatment system, wherein an exhaust system (20) is connected to an outlet (18) of the internal combustion engine (10), and wherein at least one catalyst (28, 30, 32, 34, 36, 38) is arranged in the exhaust system (20), which can be heated by means of an external heating medium (42, 44, 46, 48), comprising the following steps: - Starting the internal combustion engine (10), - Activation of the external heating medium (42, 44, 46, 48), whereby the catalyst (28, 30, 32, 34, 36, 38) is heated, wherein - in a first section of the cold start phase of the internal combustion engine (10) with a stoichiometric combustion air ratio (λ E = 1) is operated and internal engine heating measures of the combustion engine (10) are reduced or completely avoided in order to reduce raw emissions of the combustion engine (10), and - after the first part of the cold start phase, the in-engine heating measures are activated to accelerate further heating of the catalyst (28, 30, 32, 34, 36, 38) up to its light-off temperature (TL / O_K1, TL / o_K2), whereby - the in-engine heating measures after the first part of the cold start phase enable the operation of the internal combustion engine (10) with a substoichiometric combustion air ratio (λ E < 1) or include a lambda split operation between combustion chambers (12) of the internal combustion engine (10).

Description

[0001] The invention relates to a method for the exhaust aftertreatment of an internal combustion engine and to an exhaust aftertreatment system for carrying out such a method according to the preamble of the independent claims.

[0002] Current and increasingly stringent emissions legislation places high demands on the tailpipe emissions of combustion engine vehicles. The period immediately following a cold start is particularly important with regard to emissions, as the exhaust aftertreatment components must be heated to their operating temperature as quickly as possible during this phase to enable efficient exhaust aftertreatment. In gasoline engines, the heating of a (close-coupled) three-way catalytic converter is especially crucial for vehicle emissions. Prior art describes combustion engines with a secondary air system in which secondary air is introduced into the exhaust system downstream of an exhaust outlet of the combustion engine and upstream of the three-way catalytic converter to heat it.Furthermore, exhaust aftertreatment systems with an exhaust gas burner are known, in which hot exhaust gas from the burner is introduced into the exhaust system to heat the three-way catalytic converter to its operating temperature. An exhaust gas burner can also heat a three-way catalytic converter located under the floor to its operating temperature immediately after a cold start of the combustion engine, since the hot burner gases can be introduced into the exhaust system at the appropriate point, thus enabling the heating of the three-way catalytic converter essentially independently of the exhaust gas flow from the combustion engine.

[0003] From DE 10 2008 032 600 A1, a method for operating an exhaust system is known, wherein an exhaust gas burner is arranged on the exhaust system, which is operated with different combustion air ratios in order to heat a particulate filter to its regeneration temperature, wherein an oxidation catalyst is arranged downstream of an inlet point of the exhaust gas burner. The combustion engine is operated with a superstoichiometric combustion air ratio and the exhaust gas burner with a substoichiometric combustion air ratio, wherein the unburned exhaust gas components of the exhaust gas burner are exothermically reacted with the residual oxygen from the exhaust gas stream of the combustion engine by the oxidation catalyst, thus additionally heating the exhaust gas before it enters the particulate filter.

[0004] German patent DE 10 2009 003 738 A1 discloses an exhaust gas purification system for an internal combustion engine, wherein an exhaust gas purification unit is arranged in the exhaust system, which, in addition to the exhaust gas flow, can be heated via a second inlet by means of an exhaust gas burner. The exhaust gas burner is supplied with fuel from the internal combustion engine by means of a fuel pump and with fresh air by means of a secondary air system, the exhaust gas burner providing the thermal energy required to trigger or assist the operation of the exhaust gas purification system.

[0005] Furthermore, DE 10 2012 011 603 A1 discloses a spark-ignition combustion engine with an exhaust system, wherein an HC adsorber and a three-way catalyst downstream of the HC adsorber are arranged in the exhaust system. It is provided that hot burner exhaust gas from an exhaust gas burner is introduced into the exhaust duct downstream of the HC adsorber and upstream of the three-way catalyst in order to accelerate the heating of the three-way catalyst to its light-off temperature.

[0006] German patent application DE 10 2008 023 394 A1 discloses a method for heating a catalyst in the exhaust system of an internal combustion engine, in which external and internal engine heating measures are combined to heat the catalyst to its light-off temperature as quickly as possible and to maintain it above this temperature continuously during operation. The aim is to keep the duration of the electrically heated catalyst's energization as short as possible in order to limit the heating phases and enable the conversion of pollutants as soon as possible after a cold start of the internal combustion engine.

[0007] DE 41 27 596 A1 discloses a method for heating an exhaust aftertreatment system after a cold start of the internal combustion engine. In this method, a first catalyst is arranged close to the engine and a second catalyst is arranged further away from the engine in the exhaust system, with the catalyst close to the engine and the catalyst further away being supplied with air via separate exhaust manifolds.

[0008] DE 41 06 249 A1 describes a method for operating a catalyst assembly in the exhaust system of an internal combustion engine. To prevent overheating of a catalyst located close to the engine, exhaust gases from the combustion chambers associated with the catalyst assembly are only supplied to it. An exhaust gas cooling line is installed upstream of the catalyst located close to the engine.

[0009] From DE 10 2009 047 841 A1, an emission reduction system is known which includes an emission control module. Based on a first temperature of a catalyst, the emission control module selectively controls the fuel injection at a lean fuel-air mixture. Based on this first temperature, an electrically heated catalyst is activated. During a power stroke, a fuel injection module selectively injects fuel into an engine cylinder based on a second temperature of the electrically heated catalyst.

[0010] However, a disadvantage of the known solutions is that either large, powerful exhaust gas burners with high heating outputs or in-engine heating measures during the cold start phase lead to an increase in the raw emissions of the combustion engine, which can only be insufficiently converted into unlimited exhaust gas components until the light-off temperature of the catalyst is reached.

[0011] The invention is based on the objective of minimizing emissions during a cold start phase while simultaneously ensuring that the light-off temperatures of the exhaust aftertreatment components are reached quickly in order to enable efficient conversion of pollutants in the exhaust stream of the combustion engine.

[0012] According to the invention, this problem is solved by a method for the exhaust aftertreatment of an internal combustion engine, in particular a spark-ignition gasoline engine, with an exhaust aftertreatment system, wherein an exhaust system is connected to an outlet of the internal combustion engine. At least one catalyst is arranged in the exhaust system, which can be heated by means of an external heating medium, in particular an electrically heated heating medium. The method comprises the following steps: - Starting the combustion engine, - Activating the external heating medium, whereby the externally heated catalyst is heated, wherein - in the first part of the cold start phase of the internal combustion engine with a stoichiometric air-fuel ratio (λ) E = 1) is operated and internal engine heating measures of the combustion engine are reduced or completely prevented in order to reduce the raw emissions of the combustion engine, and wherein - after the first part of the cold start phase, the in-engine heating measures are activated to accelerate the further heating of the catalyst up to its light-off temperature, whereby - the in-engine heating measures after the first part of the cold start phase enable the combustion engine to operate with a substoichiometric air-fuel ratio (λ) E < 1) or include a lambda split operation between the combustion chambers of the internal combustion engine.

[0013] In this context, external heating measures are understood to be those that, unlike in-engine heating measures, allow direct heat input into the exhaust system upstream of the catalyst being heated. These include, in particular, electric heating elements and external exhaust gas burners that can be operated independently of the combustion engine. The first phase of the cold start, in this context, refers to the period immediately following engine start, during which the exhaust system temperature corresponds to the ambient temperature and the exhaust aftertreatment components need to be heated. This first phase of the cold start can end before the light-off temperature of at least one catalyst is reached. The procedure involves activating the external heating measures to heat at least one catalyst to its light-off temperature more quickly. An inventive method for exhaust aftertreatment of an internal combustion engine reduces cold-start emissions compared to a prior art cold-start method. Due to the higher efficiency of the internal combustion engine in the first part of the cold-start phase, pollutants can be reduced during this phase as well as during the subsequent heating of the catalyst, without sacrificing rapid catalyst heating and the associated potential for converting pollutants in the exhaust gas.

[0014] The features listed in the dependent claims enable advantageous improvements and non-trivial further developments of the exhaust aftertreatment method for an internal combustion engine specified in the independent claim.

[0015] In a preferred embodiment of the invention, the external heating elements are activated immediately upon starting the combustion engine, particularly simultaneously with the engine start. This optimizes the heating of the externally heated catalyst. Especially immediately after a cold start of the combustion engine, the exhaust gas flow is relatively low due to the low power demand, meaning the exhaust gas flow exerts only a minimal cooling effect on the external heating element. The exhaust gas flow can be used to promote convective heat transfer between the external heating element and the catalyst, thereby accelerating the heating process.

[0016] According to the invention, the internal combustion engine is operated with a stoichiometric air-fuel ratio during the first part of the cold start phase. A stoichiometric air-fuel ratio, and in particular the elimination of cold start enrichment, minimizes the raw emissions of the internal combustion engine. A stoichiometric air-fuel ratio, especially when combined with avoiding retarding the ignition timing, leads to higher thermal efficiency, minimizing not only limited gaseous exhaust gas components such as unburned hydrocarbons, carbon monoxide, and nitrogen oxides, but also raw particulate emissions and carbon dioxide emissions.

[0017] A further improvement to the process involves selecting the ignition timing for igniting the fuel-air mixture in the combustion chambers of the internal combustion engine during the initial phase of the cold start to optimize thermal efficiency. Foregoing adjustment of the ignition timing results in higher thermal efficiency but lower heat input into the exhaust system. This lower heat input is compensated for by external heating elements, ensuring that at least one catalytic converter still reaches its light-off temperature promptly after a cold start of the internal combustion engine, and no adverse effects on its conversion performance are expected.

[0018] It is advantageously provided that the first part of the cold start phase lasts between 2 and 25 seconds, preferably between 3 and 15 seconds, and particularly preferably between 5 and 10 seconds. With prior art methods involving in-engine heating measures such as cold start enrichment and / or retarded ignition timing, the first part of the cold start phase leads to particularly high raw emissions. These emissions cannot yet be converted by the exhaust aftertreatment components during this phase and are therefore emitted into the environment as tailpipe emissions. It is therefore advantageous to suppress or completely eliminate in-engine heating measures during the first few seconds of the cold start phase in order to improve the combustion engine's emission performance.

[0019] In an advantageous embodiment of the method, the in-engine heating measures remain activated after the externally heated catalyst reaches its light-off temperature until the exhaust system upstream of the catalyst is thoroughly heated. This prevents the catalyst from cooling down and dropping below its light-off temperature. This prevents the catalyst, heated to its light-off temperature by external heating elements, from cooling below this temperature again due to the subsequent flow of colder exhaust gas, thus reducing the conversion of pollutants in the combustion engine's exhaust gas.

[0020] In an advantageous embodiment of the method, the in-engine heating measures include retarding the ignition timing. By retarding the ignition timing at a stoichiometric air-fuel ratio, the combustion center of gravity is shifted, thereby reducing the thermal efficiency of the combustion engine. This results in hotter exhaust gas entering the exhaust system, where it can be used to heat the exhaust aftertreatment components. However, this leads to an increase in raw emissions from the combustion engine and higher fuel consumption. Therefore, this measure should be time-limited and only activated after the initial phase of the cold start to minimize the increase in emissions.

[0021] According to the invention, the in-engine heating measures include operating the internal combustion engine with a substoichiometric air-fuel ratio and, optionally, injecting secondary air or operating in lambda-split mode between the different combustion chambers of the internal combustion engine. Lambda-split mode is defined as operating the internal combustion engine in which at least one combustion chamber, preferably a first group of combustion chambers, is operated with a substoichiometric air-fuel ratio and at least one further combustion chamber, preferably a second group of combustion chambers, is / are operated with a superstoichiometric air-fuel ratio.In this process, the unburned exhaust gas components from the combustion chambers operated with a substoichiometric combustion air ratio can react exothermically with the residual oxygen from the combustion chambers operated with a superstoichiometric combustion air ratio at the catalytically effective surface of the catalyst, resulting in a further heat input into the catalyst, which promotes the further heating of the catalyst.

[0022] In an advantageous embodiment of the method, the external heating means comprise an electric heating element with which the externally heated catalyst is heated essentially independently of the exhaust gas flow from the combustion engine. The heat input into the heated catalyst can be precisely controlled by the electric heating element. Heating can thus occur independently of the operating state of the combustion engine. However, the exhaust gas flow causes convective heat transfer from the electric heating element to the exhaust gas flow, which can promote the heating of the catalytically active structure of the catalyst.

[0023] According to the invention, an exhaust aftertreatment system for an internal combustion engine is proposed, comprising an exhaust system in which at least one catalyst is arranged and which can be heated by external heating elements. The exhaust aftertreatment system further comprises an engine control unit configured to carry out an inventive method for the exhaust aftertreatment of an internal combustion engine. Such an exhaust aftertreatment system can reduce cold-start emissions and accelerate the heating of at least one catalytically active exhaust aftertreatment component. This can reduce both the raw emissions of the internal combustion engine and improve the conversion behavior of the exhaust aftertreatment components. Consequently, tailpipe emissions during the cold-start phase can be significantly reduced.

[0024] In a preferred embodiment of the invention, the external heating means comprise an electric heating element, in particular an electric heating disc, which is integrated into the externally heated catalyst or is connected upstream of the externally heated catalyst. An electric heating element allows an external heating means to be integrated into the exhaust system simply and cost-effectively, requiring minimal installation space.

[0025] Alternatively, it is advantageous for the external heating element to include an exhaust gas burner, which introduces hot exhaust gas from the burner into the exhaust system upstream of the externally heated catalyst. Compared to an electric heating element, an exhaust gas burner can introduce significantly larger amounts of heat into the exhaust system, thus promoting the heating of the catalyst. However, exhaust gas burners require more installation space than electric heating elements and result in higher costs for the exhaust system.

[0026] In a preferred embodiment of the exhaust aftertreatment system, the exhaust system comprises a first catalyst located close to the engine and a second catalyst arranged downstream of the first catalyst, the second catalyst preferably being located in the underbody of the vehicle. The use of two catalysts increases the available catalyst volume. Since the installation space for a catalyst located close to the engine is particularly limited, an additional catalyst can advantageously be provided in the underbody of the vehicle to increase the conversion efficiency.

[0027] It is particularly advantageous if the second catalyst can be heated by means of an external heating element. Catalytic converters are subject to thermal aging due to the high exhaust gas temperatures that occur under high engine loads. This aging particularly affects catalysts located close to the engine. A catalyst located under the floor exhibits less aging under the same operating conditions of the combustion engine, but reaches its light-off temperature comparatively late when heated solely by the exhaust gas flow and in-engine heating measures. Therefore, it is particularly advantageous to heat an underfloor-mounted catalyst using an external heating element, as the additional heat input from heating promotes this without leading to excessively rapid aging of the catalyst.

[0028] In a preferred embodiment of the invention, the exhaust system comprises at least one catalyst with three-way functionality and at least one particulate filter or a four-way catalyst. A catalyst with three-way functionality converts the limited gaseous exhaust gas components into unlimited exhaust gas components. An additional particulate filter, in particular a catalytically coated particulate filter designed as a four-way catalyst, can also retain the soot particles produced during combustion in the combustion chambers. Since the catalytically active coating of a particulate filter is generally subject to greater aging than the catalytic coating of a three-way catalyst, it is advantageous to combine a three-way catalyst located close to the engine with a four-way catalyst located under the vehicle floor and heated by external heating elements.

[0029] In an advantageous embodiment of the exhaust aftertreatment system, a turbine of an exhaust gas turbocharger is arranged in the exhaust system downstream of an exhaust outlet of the internal combustion engine and upstream of the at least one catalyst. To achieve high engine outputs with comparatively compact internal combustion engines, the use of an exhaust gas turbocharger to increase specific power has become established practice. This exhaust gas turbocharger is generally located directly downstream of an exhaust outlet of the internal combustion engine and upstream of all exhaust aftertreatment components. Therefore, during a cold start of an internal combustion engine, if heating is provided solely by the exhaust gas flow and internal engine heating measures, the turbine of the exhaust gas turbocharger must be heated in addition to the at least one catalyst.This leads to an increase in the time interval from the start of the combustion engine until it reaches its light-off temperature. Therefore, especially in combustion engines turbocharged with an exhaust gas turbocharger, it is necessary to provide external heating elements to accelerate the heating of at least one catalytic converter. This allows tailpipe emissions to be reduced, as the external heating elements enable the catalytic converter to reach its light-off temperature more quickly.

[0030] In a further preferred embodiment of the invention, a further catalyst or a gasoline particulate filter is arranged downstream of the second catalyst. An additional catalyst, in particular a further three-way catalyst, can further increase the catalytically effective volume. Moreover, breakthroughs through the second catalyst can be compensated for, so that a rich or lean breakthrough through the second catalyst does not lead to an increase in tailpipe emissions. A particulate filter makes it possible to additionally remove soot particles from the exhaust stream of the combustion engine. This may be necessary to meet the emission requirements of increasingly stringent emissions legislation for high-performance gasoline engines and / or heavy vehicles.

[0031] Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0032] 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. The drawings show: Fig. 1 a preferred embodiment of an internal combustion engine with an exhaust aftertreatment system according to the invention; Fig. 2 another embodiment of an exhaust aftertreatment system for an internal combustion engine, wherein the exhaust aftertreatment system comprises a first catalyst located near the engine and a second catalyst located under the floor; Fig. 3 an alternative embodiment of an exhaust aftertreatment system for an internal combustion engine, wherein the exhaust aftertreatment system comprises a four-way catalyst located close to the engine and an electrically heated three-way catalyst located under the floor; Fig. 4 another alternative embodiment of an exhaust aftertreatment system for an internal combustion engine, wherein the exhaust aftertreatment system comprises a three-way catalyst located close to the engine and an electrically heated four-way catalyst located under the floor; Fig. 5 a flowchart for carrying out a method according to the invention for the exhaust aftertreatment of an internal combustion engine; and Fig. 6 diagrams for comparing the raw emissions, the amount of heat input, the catalyst temperature and the tailpipe emissions when carrying out an exhaust aftertreatment method according to the invention in comparison to a cold start phase of an internal combustion engine known from the prior art.

[0033] Fig. Figure 1 shows a schematic representation of an internal combustion engine 10 with multiple combustion chambers 12, which is connected to an exhaust system 20 via its exhaust port 18. The internal combustion engine 10 is designed as a direct-injection gasoline engine and has a fuel injector 14 and a spark plug 16 in each combustion chamber 12 for igniting a combustible fuel-air mixture in the combustion chambers 12. The combustion chamber 12 is bounded by a piston, which is arranged to be linearly displaceable within a cylinder bore of the internal combustion engine 10. The piston is connected via a connecting rod to a crankshaft of the internal combustion engine 10, which transmits the power of the internal combustion engine 10 to a transmission. Alternatively, the internal combustion engine 10 can also be designed as a direct-injection diesel engine or as a gasoline engine with port fuel injection.

[0034] The exhaust system 20 comprises an exhaust duct 22 in which, in the direction of flow of exhaust gas from the internal combustion engine 10 through the exhaust duct 22, a turbine 26 of an exhaust gas turbocharger 24 is arranged. This turbine drives a compressor (not shown) in the intake manifold of the internal combustion engine 10 via a shaft. The exhaust gas turbocharger 24 can be designed as an exhaust gas turbocharger 24 with variable turbine geometry. For this purpose, adjustable guide vanes are arranged upstream of a turbine wheel of the turbine 26, by means of which the flow of exhaust gas onto the blades of the turbine 26 can be varied. Alternatively, the speed of the exhaust gas turbocharger 24 is controlled by a wastegate circuit around the turbine 26. Downstream of the turbine 26, at least one catalyst 28 is arranged, which can be heated by external heating elements 42, 44, 46, 48 essentially independently of the exhaust gas flow of the internal combustion engine 10.The at least one catalyst 28 is preferably configured as a three-way catalyst 30 or as a four-way catalyst 32. The external heating elements 42, 44, 46, 48 preferably comprise an electric heating element 44, in particular an electric heating disc 46, which is integrated into the catalyst 28, 30, 32. Thus, the at least one catalyst 28, 30, 32 is configured as an electrically heated catalyst 42. The electric heating elements 42, 44, 46 are connected to a battery 56, from which the electric heating elements 42, 44, 46 are supplied with electric current. The battery 56 is powered by a generator, preferably a belt-driven starter generator.

[0035] Alternatively, the external heating elements 42, 44, 46, 48 can also include an exhaust gas burner 48, with which hot burner exhaust gas can be introduced upstream of the catalyst 28 into the exhaust gas channel 22, thus enabling external heating of the catalyst 28. Downstream of the turbine 26 of the exhaust gas turbocharger 24, a first lambda sensor 50, in particular a wideband sensor, is arranged to control the air-fuel ratio of the internal combustion engine 10. Downstream of the catalyst 28, a further lambda sensor 52 can be provided to monitor the function of the three-way catalyst and, in particular, to detect rich or lean breakthroughs through the catalyst 28. The internal combustion engine 10 is connected to an engine control unit 60, which controls the amount of fuel metered into the combustion chambers 12 and the ignition timing.

[0036] In Fig. Figure 2 shows an alternative embodiment of an internal combustion engine 10 with an exhaust aftertreatment system according to the invention. The exhaust aftertreatment system comprises an exhaust system 20, which is connected to an outlet 18 of the internal combustion engine 10. The exhaust system 20 comprises an exhaust channel 22 in which a turbine 26 of an exhaust gas turbocharger 24 is arranged. Downstream of the turbine 26 of the exhaust gas turbocharger 24, a three-way catalyst 30 is arranged in the exhaust channel 22 as a first catalyst 28 located close to the engine. Downstream of the three-way catalyst 30 located close to the engine, a second catalyst 34, in particular a further three-way catalyst 36, is arranged in an underbody position of a motor vehicle. Alternatively, instead of a second catalyst 34, a gasoline particulate filter 40 can also be arranged downstream of the first catalyst 28.

[0037] Downstream of the turbine 26 of the exhaust gas turbocharger and upstream of the first catalyst 28 located near the engine, an electric heating element 42 is arranged, with which the first three-way catalyst 28 can be heated externally. Downstream of the turbine 26 of the exhaust gas turbocharger 24 and upstream of the first catalyst 28, a first lambda sensor 50 is arranged. Downstream of the first catalyst 28 and upstream of the second catalyst 34, a second lambda sensor 52 is provided. Furthermore, additional sensors 54, 58, in particular a temperature sensor 54 and / or an exhaust gas sensor 58, can be arranged in the exhaust system.

[0038] In Fig. Figure 3 shows a further embodiment of an internal combustion engine 10 with an exhaust aftertreatment system according to the invention. With essentially the same construction as shown in Figure 3, the embodiment of this engine is further illustrated. Fig. As described in Figure 2, the first catalyst 28 in this embodiment is designed as a four-way catalyst 32, i.e., as a particulate filter with a catalytically active coating. An electric heating element 44, in particular an electric heating disc 46, is provided, which is preferably arranged in the housing of the four-way catalyst upstream of the catalytically coated filter substrate. The four-way catalyst 32 can be heated externally by means of the electric heating element 44. Alternatively, the substrate of the four-way catalyst 32 can also be electrically conductive and directly heatable, so that the four-way catalyst 32 is designed as an electrically heated catalyst 42. In this case, the electric heating element 44 can also be used to assist in heating the four-way catalyst 32 to its regeneration temperature.

[0039] In Fig. Figure 4 shows a preferred embodiment of an exhaust aftertreatment system for an internal combustion engine 10. With essentially the same design as shown in Figure 4, the following embodiments are also shown: Fig. 2 and Fig. As described in Figure 3, the exhaust aftertreatment system comprises a three-way catalyst 30 located close to the engine as the first catalyst 28 and a four-way catalyst 38 located under the floor as the second catalyst 34. The four-way catalyst 38 can be heated externally by external heating means 44, 46, 48, preferably by an electric heating element 44, in particular an electric heating disc 46. Alternatively, the four-way catalyst 38 can also be heated by means of an external exhaust gas burner 48.

[0040] Due to its placement in the underbody position, the four-way catalyst 38 is exposed to lower temperatures during normal operation of the combustion engine 10 than the three-way catalyst 30 located near the engine. This slows down the thermal aging of the catalytically active coating of the four-way catalyst 38. For the cold start phase, however, the four-way catalyst 38 can be quickly heated to its light-off temperature by the external heating elements 44, 46, 48, thus enabling effective conversion of harmful exhaust gas components shortly after a cold start of the combustion engine 10.Furthermore, the external heating media 44, 46, 48 can be used to initiate a regeneration of the four-way catalyst 38 if the heat introduced into the four-way catalyst 38 by the exhaust gas flow is insufficient to heat the four-way catalyst 38 to a regeneration temperature of approximately 600°C, at which the soot particles retained in the four-way catalyst 38 can be oxidized.

[0041] In Fig. Figure 5 shows a flowchart for carrying out a process according to the invention for the exhaust aftertreatment of an internal combustion engine 10. In a first process step <100> The combustion engine 10 is started. In a second process step <110> The external heating elements 42, 44, 46, 48 are activated to heat the externally heated catalyst 28, 30, 32, 34, 36, 38. Simultaneously, in a process step... <120> The internal engine heating measures are suspended or only activated to a limited extent in order to reduce the raw emissions of the combustion engine 10. After a delay phase of approximately 2–25 seconds, preferably 3–15 seconds, particularly preferably 5–10 seconds, the internal engine heating measures are switched off in a process step. <130> activated or intensified to promote the heating of the exhaust aftertreatment components 28, 30, 32, 34, 36, 38 to their respective light-off temperature.Has the catalyst 28, 30, 32, 34, 36, 38, which can be heated with external heating media 44, 46, 48, in a process step <140> its light-off temperature T. L / O_K1 , T L / O_K2 Once this temperature is reached, the unburned exhaust gas components can react exothermically on the catalyst 28, 30, 32, 34, 36, 38, which promotes further heating of the catalyst 28, 30, 32, 34, 36, 38. If the exhaust system 20 is completely heated, so that the risk of the catalysts 28, 30, 32, 34, 36, 38 cooling below their respective light-off temperatures no longer exists, the external and internal engine heating measures can be carried out in a single process step. <150> to be completed.

[0042] By avoiding internal engine heating measures in the first part of the cold start phase, an improved thermal efficiency of the combustion engine 10 is achieved. This allows the pollutants emitted by the combustion engine 10 during this first part of the cold start phase to be reduced without foregoing rapid heating of the at least one catalyst 28, 30, 32, 34, 36, 38.

[0043] In Fig. 6 are the raw emissions of the combustion engine 10 ( Fig. 6a), the heat input into the externally heated catalyst ( Fig. 6b), the temperature profile of the externally heated catalyst during the cold start phase ( Fig. 6c) and the emissions downstream of the externally heated catalyst during the cold start phase ( Fig.Figure 6d) illustrates this. The dotted curve shows the curve for a cold start and a prior art method of heating the catalyst exclusively using in-engine heating. The dashed curve shows the curve for a cold start in which in-engine heating is initially omitted and only activated later. The solid curve shows the curve for a method according to the invention in which external heating is activated during the cold start phase, in-engine heating is omitted in the first section I of the cold start phase, and the in-engine heating is activated in a second section II of the cold start phase. It can be seen that in a method according to the invention, the catalyst 28, 30, 32, 34, 36, 38 reaches its light-off temperature T more quickly. L / O_K1 , T L / O_K2The emissions downstream of the externally heated catalyst 28, 30, 32, 34, 36, 38 can be significantly reduced by dispensing with the internal engine heating measures in the first section I of the cold start phase. Reference symbol list 10 Internal combustion engine 12 Combustion chamber 14 Fuel injector 16 Spark plug 18 Outlet 20 Exhaust system 22 Exhaust duct 24 exhaust gas turbochargers 26 Turbine 28 first catalyst 30 Three-way catalytic converter 32 Four-way catalytic converter 34 second catalyst 36 Three-way catalytic converter 38 Four-way catalytic converter 40 gasoline particulate filters 42 electrically heated catalyst 44 electric heating element 46 electric heating disc 48 exhaust gas burners 50 first lambda sensor 52 second lambda sensor 54 Temperature sensor 56 Battery 58 Exhaust gas sensor 60 Engine control unit EE tailpipe emissions FWC four-way catalytic converter Q Heat input into the catalyst RE Raw emissions S Starting the combustion engine Temperature T K1 Temperature of the first catalyst T K2 Temperature of the second catalyst T L / O_K1 Light-off temperature of the first catalyst T L / O_K2 Light-off temperature of the second catalyst TWC three-way catalytic converter t time t VERZ Delay time

Claims

[1] Method for exhaust gas aftertreatment of an internal combustion engine (10) with an exhaust gas aftertreatment system, wherein an exhaust system (20) is connected to an outlet (18) of the internal combustion engine (10), and wherein at least one catalyst (28, 30, 32, 34, 36, 38) is arranged in the exhaust system (20), which catalyst can be heated by means of an external heating means (42, 44, 46, 48), comprising the following steps: - Start of the combustion engine (10), - activating the external heating means (42, 44, 46, 48), whereby the catalyst (28, 30, 32, 34, 36, 38) is heated, whereby - in a first section of the cold start phase, the internal combustion engine (10) is operated with a stoichiometric combustion air ratio (λ E = 1) and internal heating measures of the combustion engine (10) are reduced or completely avoided in order to reduce raw emissions of the combustion engine (10), and - after the first section of the cold start phase, the internal engine heating measures are activated in order to accelerate further heating of the catalyst (28, 30, 32, 34, 36, 38) up to its light-off temperature (TL / O_K1, TL / o_K2), whereby - the internal engine heating measures after the first section of the cold start phase result in the internal combustion engine (10) operating with a substoichiometric combustion air ratio (λ E < 1) or a lambda split operation between combustion chambers (12) of the internal combustion engine (10). [2] Method for exhaust gas aftertreatment of an internal combustion engine (10) according to claim 1, characterized by that the external heating means (42, 44, 46, 48) are activated from the start (S) of the combustion engine (10). [3] Method for exhaust gas aftertreatment of an internal combustion engine (10) according to one of claims 1 or 2, characterized bythat an ignition angle for igniting a fuel-air mixture in the combustion chambers (12) of the internal combustion engine (10) in the first section of the cold start phase is selected with a view to optimum thermal efficiency. [4] Method for exhaust gas aftertreatment of an internal combustion engine (10) according to one of claims 1 to 3, characterized by that the first part of the cold start phase lasts between 2 seconds and 25 seconds. [5] Method for exhaust gas aftertreatment of an internal combustion engine (10) according to one of claims 1 to 4, characterized by that the internal engine heating measures include adjusting the ignition angle towards late. [6] Method for exhaust gas aftertreatment of an internal combustion engine (10) according to one of claims 1 to 5, characterized bythat the external heating means (42, 44, 46) comprise an electric heating element (44) with which the externally heatable catalyst (28, 30, 32, 34, 36, 38) is heated substantially independently of the exhaust gas flow of the internal combustion engine (10). [7] Exhaust gas aftertreatment system for an internal combustion engine (10), comprising an exhaust system (20) which can be connected to an outlet (18) of the internal combustion engine (10), wherein at least one catalyst (28, 30, 32, 34, 36, 38) is arranged in the exhaust system (20), which catalyst can be heated by means of an external heating means (42, 44, 46, 48), and with an engine control unit (60) which is designed to carry out a method according to one of claims 1 to 6 [8] Exhaust aftertreatment system according to claim 7, characterized by that the external heating means (42, 44, 46) comprise an electric heating element (44), in particular an electric heating disc (46). [9] Exhaust aftertreatment system according to claim 7, characterized by that the external heating means (48) comprise an exhaust gas burner (48). [10] Exhaust gas aftertreatment system according to one of claims 7 to 9, characterized by that the exhaust system (20) has a first catalyst (28) close to the engine and a second catalyst (34) arranged downstream of the first catalyst (28) close to the engine, preferably in the underbody position of a motor vehicle. [11] Exhaust aftertreatment system according to claim 10, characterized by that the second catalyst (34) can be heated by means of external heating means (42, 44, 46, 48). [12] Exhaust aftertreatment system according to one of claims 7 to 11, characterized by that the exhaust system (20) has at least one catalyst (28, 30, 34, 36) with a three-way functionality and at least one particle filter (40) or a four-way catalyst (32, 38). [13] Exhaust gas aftertreatment system according to one of claims 7 to 12, characterized by that a turbine (26) of an exhaust gas turbocharger (24) is arranged in the exhaust system (20) downstream of the outlet (18) of the internal combustion engine (10) and upstream of the at least one catalyst (28, 30, 32, 34, 36, 38).

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