DE102019110992A1 - Process for exhaust aftertreatment of an internal combustion engine and exhaust aftertreatment system - Google Patents

Abstract

The invention relates to a method for exhaust gas aftertreatment of an internal combustion engine (10). For this purpose, the internal combustion engine (10) is connected with its outlet (18) to an exhaust system (20) in which at least one catalytic converter (28, 30, 32, 34, 36, 38) is arranged, which is equipped with external heating means (42, 44 , 46, 48) is heatable. The at least one catalytic converter (28, 30, 32, 34, 36, 38) is heated with the external heating means (42, 44, 46, 48) from the start of the internal combustion engine (10), with the combustion in the combustion chambers (12 ) of the internal combustion engine (10) is optimized with regard to the raw emissions arising during combustion. For this purpose, heating measures inside the engine are avoided or at least reduced in order to lower the raw emissions. This operating state of the internal combustion engine (10) is maintained at least until the catalytic converter (28, 30, 32, 34, 36, 38) which can be heated by the external heating means (42, 44, 46, 48) reaches its light-off temperature (TL / O_K1, TL / O_K2). The invention also relates to an exhaust gas aftertreatment system for carrying out such a method.

Description

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

The current exhaust gas legislation and one that will become increasingly strict in the future place high demands on the tailpipe emissions of motor vehicles with internal combustion engines. The period immediately after a cold start of the internal combustion engine is of particular importance with regard to emissions, since in this phase the exhaust gas aftertreatment components should be heated up to their operating temperature as quickly as possible in order to enable efficient exhaust aftertreatment. In the case of gasoline engines, the heating of a three-way catalytic converter (close to the engine) is particularly important for the emissions of a motor vehicle. Internal combustion engines with a secondary air system are known from the prior art in which secondary air is introduced into the exhaust system downstream of an outlet of the internal combustion engine and upstream of the three-way catalytic converter to heat the three-way catalytic converter. Furthermore, exhaust gas aftertreatment systems with an exhaust gas burner are known, in which a hot exhaust gas from the exhaust gas burner is introduced into the exhaust system in order to heat the three-way catalytic converter to its operating temperature. An exhaust gas burner can also be used to heat a three-way catalytic converter in the underbody position to its operating temperature immediately after a cold start of the internal combustion engine, since the hot burner gases can be introduced into the exhaust system at the appropriate point, thus essentially heating the three-way catalytic converter allow independently of the exhaust gas flow of the combustion engine.

From the DE 10 2008 032 600 A1 A method for operating an exhaust system is known, an exhaust gas burner being arranged on the exhaust system, which is operated with different combustion air ratios in order to heat a particle filter to its regeneration temperature, an oxidation catalyst being arranged downstream of an inlet point of the exhaust gas burner. The internal combustion engine is operated with an over-stoichiometric combustion air ratio and the exhaust gas burner with an under-stoichiometric combustion air ratio, the unburned exhaust gas components of the exhaust gas burner being converted exothermically by the oxidation catalytic converter with the residual oxygen from the exhaust gas flow of the internal combustion engine and thus additionally heating the exhaust gas before it enters the particle filter.

The DE 10 2009 003 738 A1 discloses an exhaust gas purification system for an internal combustion engine, an exhaust gas purification unit being arranged in the exhaust system, which, in addition to the exhaust gas flow, can be heated by means of an exhaust gas burner via a second inlet. The exhaust gas burner is supplied with the fuel of 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 support operation of the exhaust gas cleaning system.

In addition, the DE 10 2012 011 603 A1 an externally ignited internal combustion engine with an exhaust system, with an HC adsorber and a three-way catalytic converter downstream of the HC adsorber being arranged in the exhaust system. It is provided that a hot burner exhaust gas from an exhaust gas burner is introduced into the exhaust gas duct downstream of the HC absorber and upstream of the three-way catalytic converter in order to accelerate the heating of the three-way catalytic converter to its light-off temperature.

From the DE 10 2008 023 394 A1 a method for heating a catalytic converter in an exhaust system of an internal combustion engine is known, with external heating measures and internal engine heating measures being combined in order to heat the catalyst as quickly as possible to its light-off temperature and to keep it permanently above this temperature during operation. The duration of the energization of the electrically heatable catalyst should be kept as short as possible in order to limit the time of the heating phases and to enable the conversion of pollutants as soon as possible after a cold start of the internal combustion engine.

The disadvantage of the known solutions, however, is that either large, powerful exhaust gas burners with high heating outputs or internal engine heating measures in the cold start phase lead to an increase in the raw emissions of the internal combustion engine, which only insufficiently converts into unlimited exhaust gas components until the light-off temperature of the catalytic converter is reached can be.

The invention is based on the task of minimizing the emissions in a cold start phase and at the same time ensuring that the light-off temperatures of the exhaust gas aftertreatment components are reached quickly in order to enable the pollutants in the exhaust gas flow of the internal combustion engine to be efficiently converted.

• - Start des Verbrennungsmotors,
• - Aktivieren des externen Heizmittels, wobei der extern beheizbare Katalysator aufgeheizt wird, wobei
• - innermotorische Heizmaßnahmen des Verbrennungsmotors in einem ersten Abschnitt der Kaltstartphase reduziert oder komplett unterbunden werden, um die Rohemissionen des Verbrennungsmotors zu reduzieren, und wobei
• - die innermotorischen Heizmaßnahmen nach dem ersten Abschnitt der Kaltstartphase aktiviert werden, um das weitere Aufheizen des Katalysators bis zu seiner Light-Off-Temperatur zu beschleunigen.

According to the invention this object is achieved by a method for exhaust gas aftertreatment of an internal combustion engine, in particular one externally ignited gasoline engine, solved with an exhaust gas treatment system, wherein an exhaust system is connected to an outlet of the internal combustion engine. In this case, at least one catalytic converter is arranged in the exhaust system, which can be heated by means of an external heating means, in particular by means of an electrically heatable heating means. The procedure consists of the following steps:

• - start of the combustion engine,
• - Activation of the external heating means, the externally heatable catalyst being heated, wherein
• - Internal engine heating measures of the internal combustion engine are reduced or completely prevented in a first section of the cold start phase in order to reduce the raw emissions of the internal combustion engine, and wherein
• - the internal engine heating measures are activated after the first section of the cold start phase in order to accelerate the further heating of the catalytic converter up to its light-off temperature.

In this context, external heating measures are to be understood as heating measures which, in contrast to heating measures inside the engine, enable a direct heat input into the exhaust system upstream of the catalytic converter to be heated. This includes in particular electrical heating elements and external exhaust gas burners, which can be operated independently of the internal combustion engine. In this context, the first section of the cold start phase is to be understood as a section immediately after the start of the internal combustion engine, in which the temperature of the exhaust system corresponds to the ambient temperature and the exhaust gas aftertreatment components need to be heated up. This first section of the cold start phase can end before the light-off temperature of the at least one catalytic converter is reached. The method provides for the putting into operation of the external heating measures for faster heating of at least one catalytic converter to its light-off temperature.

A method according to the invention for exhaust gas aftertreatment of an internal combustion engine can reduce the cold start emissions compared to a cold start method known from the prior art. Due to the higher efficiency of the internal combustion engine in the first section of the cold start phase, the pollutants can be reduced during this section as well as during the further heating of the catalytic converter, without having to forego rapid heating of the catalytic converter and the associated potential for converting pollutants in the exhaust gas.

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

In a preferred embodiment of the invention it is provided that the external heating means are activated immediately from the start of the internal combustion engine, in particular at the same time as the internal combustion engine is started. This allows the heating of the externally heated catalytic converter to be optimized. Especially immediately after the internal combustion engine has been cold-started, the exhaust gas flow is relatively low due to a low power requirement, so that the exhaust gas flow only has a low cooling effect for the external heating means. The exhaust gas flow can be used to promote convective heat transfer between the external heating means and the catalytic converter in order to accelerate the heating process.

In an advantageous embodiment of the method it is provided that the internal combustion engine is operated with a stoichiometric combustion air ratio in the first section of the cold start phase. The raw emissions of the internal combustion engine can be minimized by a stoichiometric combustion ratio and in particular by dispensing with cold start enrichment. A stoichiometric combustion air ratio, especially together with the fact that the ignition angle is not adjusted in the "retarded" direction, leads to a higher thermal efficiency, whereby in addition to the limited gaseous exhaust gas components such as unburned hydrocarbons, carbon monoxide and nitrogen oxides, the raw particle emissions and the carbon dioxide emissions are also minimized.

In a further improvement of the method, it is provided that the ignition angle for igniting the fuel-air mixture in the combustion chambers of the internal combustion engine in the first section of the cold start phase is selected with a view to optimum thermal efficiency. Dispensing with an adjustment of the ignition angle leads to a higher thermal efficiency, but a lower heat input into the exhaust system. This lower heat input is compensated for by the external heating means, so that the at least one catalytic converter nevertheless reaches its light-off temperature promptly after a cold start of the internal combustion engine and no disadvantages with regard to the conversion behavior are to be expected.

It is advantageously provided that the first section of the cold start phase takes between 2 seconds and 25 seconds, preferably between 3 seconds Seconds and 15 seconds, particularly preferably between 5 seconds and 10 seconds. Especially the first section of the cold start phase leads to particularly high raw emissions in processes known from the prior art with internal engine heating measures such as cold start enrichment and / or an ignition angle adjustment in the "late" direction, which in addition cannot yet be converted by the exhaust gas aftertreatment components in this phase are thus emitted as tailpipe emissions to the environment. It is therefore advantageous to suppress the internal engine heating measures in the first few seconds of the cold start phase or to completely dispense with internal engine heating measures in order to improve the emissions behavior of the internal combustion engine.

In an advantageous embodiment of the method, it is provided that the internal engine heating measures remain activated after the light-off temperature of the catalytic converter which can be heated with external heating means has been reached, until the exhaust system upstream of the catalytic converter is warmed through, in order to cool down and the catalytic converter temperature to drop below the light -Avoid off-temperature. This prevents the catalytic converter, which is heated to its light-off temperature by means of external heating means, from cooling down again below this temperature due to the inflowing colder exhaust gas and a conversion of pollutants in the exhaust gas of the internal combustion engine is reduced.

In an advantageous embodiment of the method it is provided that the internal engine heating measures include an adjustment of the ignition angle in the “retarded” direction. By adjusting the ignition angle at a stoichiometric combustion air ratio, the center of combustion is shifted, thereby reducing the thermal efficiency of the internal combustion engine, with hotter exhaust gas entering the exhaust system and being used there to heat the exhaust gas aftertreatment components. However, this leads to an increase in the raw emissions of the internal combustion engine and increased fuel consumption, so this measure should be limited in time and only be activated after the first section of the cold start phase in order to keep the increase in emissions as low as possible.

Alternatively or additionally, it is advantageously provided that the internal engine heating measures include operation of the internal combustion engine with a substoichiometric combustion air ratio and, if necessary, injection of secondary air or lambda split operation between the different combustion chambers of the internal combustion engine. Lambda split operation is to be understood as an operation of the internal combustion engine in which at least one combustion chamber, preferably a first group of combustion chambers, is operated with a sub-stoichiometric combustion air ratio and at least one further combustion chamber, preferably a second group of combustion chambers, is operated with an over-stoichiometric combustion air ratio /will. The unburned exhaust gas components from the combustion chambers operated with a sub-stoichiometric combustion air ratio can react exothermically with the residual oxygen from the combustion chambers operated with an over-stoichiometric combustion air ratio on the catalytically active surface of the catalytic converter, whereby further heat is introduced into the catalytic converter, which favors the further heating of the catalytic converter.

In an advantageous embodiment of the method it is provided that the external heating means comprise an electrical heating element with which the externally heatable catalyst is heated essentially independently of the exhaust gas flow of the internal combustion engine. The heat input into the heatable catalytic converter can be precisely controlled by means of an electrical heating element. The heating can take place independently of the operating state of the internal combustion engine. However, the exhaust gas flow results in a convective heat transfer from the electrical heating element to the exhaust gas flow, which can promote the heating of the catalytically active structure of the catalytic converter.

According to the invention, an exhaust gas aftertreatment system for an internal combustion engine is proposed which comprises an exhaust system, at least one catalytic converter being arranged in the exhaust system, which can be heated with external heating means. The exhaust gas aftertreatment system further comprises an engine control device which is set up to carry out a method according to the invention for exhaust gas aftertreatment of an internal combustion engine when a machine-readable program code is executed by the engine control device. Such an exhaust gas aftertreatment system can reduce cold start emissions and accelerate the heating of at least one catalytically active exhaust gas aftertreatment component. As a result, both the raw emissions of the internal combustion engine can be reduced and the conversion behavior of the exhaust gas aftertreatment components can be improved. This means that the tailpipe emissions can be significantly reduced in the cold start phase.

In a preferred embodiment of the invention it is provided that the external heating means comprise an electrical heating element, in particular an electrical heating disk, which is or is integrated into the externally heatable catalyst is connected upstream of the externally heatable catalyst. By means of an electrical heating element, an external heating means can be integrated into the exhaust system simply and inexpensively and with little space requirement.

Alternatively, it is advantageously provided that the external heating means comprise an exhaust gas burner, with which a hot exhaust gas from the exhaust gas burner can be introduced into the exhaust system upstream of the externally heatable catalytic converter. Compared to an electrical heating element, an exhaust gas burner can bring particularly large amounts of heat into the exhaust system, which favors the heating of the catalytic converter. However, compared to electrical heating elements, exhaust gas burners require more space and lead to higher costs for the exhaust system.

In a preferred embodiment of the exhaust gas aftertreatment system, it is provided that the exhaust system has a first catalytic converter close to the engine and a second catalytic converter arranged downstream of the first catalytic converter close to the engine, the second catalytic converter preferably being arranged in an underbody position of a motor vehicle. The available catalyst volume can be increased by using two catalysts. Since, in particular, the installation space for an arrangement of the catalytic converter close to the engine is limited, an additional catalytic converter can advantageously be provided in the underbody position of a motor vehicle in order to increase the conversion performance.

It is particularly preferred if the second catalyst can be heated by means of external heating means. Catalysts are exposed to thermal aging due to the high exhaust gas temperatures that occur with high engine loads. This aging affects in particular catalytic converters arranged close to the engine. A catalytic converter in the underbody position shows less aging under the same operating conditions of the internal combustion engine, but reaches its light-off temperature comparatively late if it is heated exclusively by the exhaust gas flow and heating measures inside the engine. It is therefore particularly advantageous to heat up a catalytic converter in the underbody position by means of external heating means, since the additional heat input from heating favors without leading to impermissibly severe aging of the catalytic converter.

In a preferred embodiment of the invention it is provided that the exhaust system has at least one catalytic converter with a three-way functionality and at least one particle filter or a four-way catalytic converter. The limited gaseous exhaust gas components can be converted into unlimited exhaust gas components by means of a catalytic converter with a three-way functionality. An additional particle filter, in particular a catalytically coated particle filter, which is designed as a four-way catalytic converter, can also hold back the soot particles that occur in the combustion chambers during combustion. Since the catalytically active coating of a particle filter is generally more subject to aging than the catalytic coating of a three-way catalytic converter, it is advantageous to add a three-way catalytic converter close to the engine with a four-way catalytic converter in the underbody position that can be heated with external heating means combine.

In an advantageous embodiment of the exhaust gas aftertreatment system it is provided that a turbine of an exhaust gas turbocharger is arranged in the exhaust system downstream of an outlet of the internal combustion engine and upstream of the at least one catalytic converter. In order to be able to represent high engine outputs with comparatively compact combustion engines, the use of an exhaust gas turbocharger to increase the specific output has become established. This exhaust gas turbocharger is usually arranged immediately downstream of an outlet of the internal combustion engine and upstream of all exhaust gas aftertreatment components. In the case of a cold start of an internal combustion engine, the turbine of the exhaust gas turbocharger must therefore be warmed up in addition to the at least one catalytic converter in the case of exclusive heating via the exhaust gas flow and internal heating measures. This leads to an extension of the time interval from the start of the internal combustion engine until the internal combustion engine reaches the light-off temperature. It is therefore necessary, in particular in the case of internal combustion engines that are charged by means of an exhaust gas turbocharger, to provide external heating means in order to accelerate the heating of the at least one catalytic converter. The tailpipe emissions can thus be reduced, since the catalytic converter reaches its light-off temperature more quickly thanks to the external heating means.

In a further preferred embodiment of the invention it is provided that a further catalytic converter or a gasoline particle filter is arranged downstream of the second catalytic converter. The catalytically effective volume can be increased further by means of a further catalytic converter, in particular a further three-way catalytic converter. In addition, breakthroughs through the second catalytic converter can be compensated so that a rich or lean breakthrough through the second catalytic converter does not lead to an increase in tailpipe emissions. A particle filter can also be used to remove soot particles from the exhaust gas flow of the internal combustion engine. This may be necessary in order to meet the emission requirements of the increasingly stringent exhaust gas legislation in the case of high-performance gasoline engines and / or high-weight motor vehicles.

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

• 1 ein bevorzugtes Ausführungsbeispiel eines Verbrennungsmotors mit einem erfindungsgemäßen Abgasnachbehandlungssystem;
• 2 ein weiteres Ausführungsbeispiel eines Abgasnachbehandlungssystems für einen Verbrennungsmotor, wobei das Abgasnachbehandlungssystem einen ersten motornahen Katalysator und einen zweiten Katalysator in Unterbodenlage aufweist;
• 3 ein alternatives Ausführungsbeispiel eines Abgasnachbehandlungssystems für einen Verbrennungsmotor, wobei das Abgasnachbehandlungssystem einen motornahen Vier-Wege-Katalysator und einen elektrisch beheizbaren Drei-Wege-Katalysator in Unterbodenlage aufweist;
• 4 ein weiteres alternatives Ausführungsbeispiel eines Abgasnachbehandlungssystems für einen Verbrennungsmotor, wobei das Abgasnachbehandlungssystem einen motornahen Drei-Wege-Katalysator und einen elektrisch beheizbaren Vier-Wege-Katalysator in Unterbodenlage aufweist;
• 5 ein Ablaufschema zur Durchführung eines erfindungsgemäßen Verfahrens zur Abgasnachbehandlung eines Verbrennungsmotors; und
• 6 Diagramme zum Vergleich der Rohemissionen, der eingetragenen Wärmemenge, der Katalysatortemperatur und der Endrohremissionen bei der Durchführung eines erfindungsgemäßen Verfahrens zur Abgasnachbehandlung im Vergleich zu einer aus dem Stand der Technik bekannten Kaltstartphase eines Verbrennungsmotors.

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

• 1 a preferred embodiment of an internal combustion engine with an exhaust gas aftertreatment system according to the invention;
• 2 a further exemplary embodiment of an exhaust gas aftertreatment system for an internal combustion engine, the exhaust gas aftertreatment system having a first catalytic converter close to the engine and a second catalytic converter in the underbody position;
• 3 an alternative embodiment of an exhaust gas aftertreatment system for an internal combustion engine, the exhaust gas aftertreatment system having a close-coupled four-way catalytic converter and an electrically heatable three-way catalytic converter in the underbody position;
• 4th a further alternative exemplary embodiment of an exhaust gas aftertreatment system for an internal combustion engine, the exhaust gas aftertreatment system having a three-way catalytic converter close to the engine and an electrically heatable four-way catalytic converter in the underbody position;
• 5 a flow chart for performing a method according to the invention for exhaust gas aftertreatment of an internal combustion engine; and
• 6 Diagrams to compare the raw emissions, the amount of heat entered, the catalyst temperature and the tailpipe emissions when carrying out a method according to the invention for exhaust gas aftertreatment in comparison to a cold start phase of an internal combustion engine known from the prior art.

1 shows the schematic representation of an internal combustion engine 10 with several combustion chambers 12 , which with its outlet 18th with an exhaust system 20th connected is. The internal combustion engine 10 is designed as a direct-injection gasoline engine and has each combustion chamber 12 a fuel injector 14th and a spark plug 16 for igniting a combustible fuel-air mixture in the combustion chambers 12 on. The combustion chamber 12 is limited by a piston which is in a cylinder bore of the internal combustion engine 10 is arranged to be linearly displaceable. The piston is connected to a crankshaft of the internal combustion engine via a connecting rod 10 connected, which is the power of the internal combustion engine 10 transferred to a gear. Alternatively, the internal combustion engine 10 can also be designed as a direct-injection diesel engine or as a gasoline engine with intake manifold injection.

The exhaust system 20th includes an exhaust duct 22nd , in which in the flow direction of an exhaust gas of the internal combustion engine 10 through the exhaust duct 22nd a turbine 26th of an exhaust gas turbocharger 24 is arranged, which has a compressor, not shown, in the intake tract of the internal combustion engine 10 drives over a shaft. The exhaust gas turbocharger 24 can be used as an exhaust gas turbocharger 24 be designed with variable turbine geometry. To do this are a turbine wheel of the turbine 26th adjustable guide vanes are connected upstream, via which the flow of the exhaust gas onto the blades of the turbine 26th can be varied. Alternatively, the speed of the exhaust gas turbocharger 24 through a waste gate circuit around the turbine 26th controlled. Downstream of the turbine 26th is at least one catalyst 28 arranged, which by means of external heating means 42 , 44 , 46 , 48 essentially independent of the exhaust gas flow of the internal combustion engine 10 is heatable. The at least one catalyst 28 is preferably used as a three-way catalyst 30th or as a four-way catalyst 32 executed. The external heating means 42 , 44 , 46 , 48 preferably comprise an electrical heating element 44 , in particular an electric heating disk 46 which in the catalyst 28 , 30th , 32 is integrated. Thus, the at least one is a catalyst 28 , 30th , 32 as an electrically heated catalyst 42 executed. The electric heating means 42 , 44 , 46 are with a battery 56 connected from which the electric heating means 42 , 44 , 46 be supplied with electricity. The battery 56 is fed by a generator, preferably a belt starter generator.

Alternatively, the external heating means 42 , 44 , 46 , 48 also an exhaust burner 48 include, with which a hot burner exhaust gas upstream of the catalyst 28 in the exhaust duct 22nd can be initiated and thus an external heating of the catalyst 28 enables. Downstream of the turbine 26th of the exhaust gas turbocharger 24 is a first lambda probe 50 , in particular a broadband probe, arranged to the combustion air ratio of the internal combustion engine 10 to regulate. Downstream of the catalyst 28 can use another lambda probe 52 be provided to monitor the function of the three-way catalytic converter and in particular rich or lean breakthroughs through the catalytic converter 28 to detect. The internal combustion engine 10 is with an engine control unit 60 connected via which the into the combustion chambers 12 metered amount of fuel and the ignition timing can be controlled.

In 2 Figure 3 is an alternative embodiment for an internal combustion engine 10 shown with an exhaust aftertreatment system according to the invention. The exhaust aftertreatment system includes an exhaust system 20th , which with an outlet 18th of the internal combustion engine 10 connected is. The exhaust system 20th includes an exhaust duct 22nd in which a turbine 26th of an exhaust gas turbocharger 24 is arranged. Downstream of the turbine 26th of the exhaust gas turbocharger 24 is the first catalytic converter close to the engine 28 a three way catalyst 30th in the exhaust duct 22nd arranged. Downstream of the close-coupled three-way catalytic converter 30th is a second catalytic converter in an underbody layer of a motor vehicle 34 , especially another three-way catalyst 36 , arranged. Alternative to a second catalyst 34 can be downstream of the first catalyst 28 also a gasoline particle filter 40 be arranged.

Downstream of the turbine 26th of the exhaust gas turbocharger and upstream of the first catalytic converter close to the engine 28 is an electrical heating element 42 arranged with which the first three-way catalyst 28 can be heated externally. Downstream of the turbine 26th of the exhaust gas turbocharger 24 and upstream of the first catalyst 28 is a first lambda probe 50 arranged. Downstream of the first catalyst 28 and upstream of the second catalyst 34 is a second lambda probe 52 intended. Further sensors can also be installed in the exhaust system 54 , 58 , especially a temperature sensor 54 and / or an exhaust gas sensor 58 be arranged.

In 3 is another embodiment for an internal combustion engine 10 shown with an exhaust aftertreatment system according to the invention. With essentially the same structure as to 2 executed is the first catalyst 28 in this embodiment as a four-way catalytic converter 32 , so designed as a particle filter with a catalytically active coating. There is an electrical heating element 44 , in particular an electric heating disk 46 provided, which is preferably arranged in the housing of the four-way catalytic converter upstream of the catalytically coated filter substrate. By the electric heating element 44 can be the four-way catalyst 32 be externally heated. Alternatively, the substrate of the four-way catalyst can also be used 32 run electrically conductive and be directly heated, so that the four-way catalytic converter 32 as an electrically heated catalyst 42 is executed. The electrical heating element 44 can also be used to heat up the four-way catalytic converter 32 to support its regeneration temperature.

In 4th Figure 3 is a preferred embodiment of an exhaust gas aftertreatment system for an internal combustion engine 10 shown. With essentially the same structure as to 2 and 3 executed, the exhaust aftertreatment system has a close-coupled three-way catalytic converter 30th as the first catalyst 28 and a four-way catalyst 38 in the underbody position as a second catalytic converter 34 on. Here is the four-way catalyst 38 by external heating means 44 , 46 , 48 , preferably by an electrical heating element 44 , in particular an electric heating disk 46 , externally heatable. Alternatively, the four-way catalytic converter 38 also by means of an external exhaust gas burner 48 be heated.

The four-way catalytic converter is located in the underbody position 38 in normal operation of the internal combustion engine 10 exposed to lower temperatures than the close-coupled three-way catalytic converter 30th . This can cause thermal aging of the catalytically active coating of the four-way catalytic converter 38 be slowed down. The four-way catalytic converter can be used for the cold start phase 38 however by the external heating means 44 , 46 , 48 quickly heated to its light-off temperature, so that an effective conversion of harmful exhaust gas components promptly after a cold start of the internal combustion engine 10 is possible. Furthermore, the external heating means 44 , 46 , 48 can be used to regenerate the four-way catalytic converter 38 initiate when the through the exhaust gas flow in the four-way catalytic converter 38 heat introduced is insufficient to the four-way catalytic converter 38 heat up to a regeneration temperature of about 600 ° C, at which the in the four-way catalytic converter 38 retained soot particles can be oxidized.

In 5 Fig. 3 is a flow chart for performing a method according to the invention for exhaust gas aftertreatment of an internal combustion engine 10 shown. In a first method step <100> the internal combustion engine 10 started. In a second method step <110> the external heating means 42 , 44 , 46 , 48 activated to the externally heated catalyst 28 , 30th , 32 , 34 , 36 , 38 to heat. At the same time, in a method step <120>, the internal engine heating measures are suspended or only activated to a small extent in order to reduce the raw emissions of the internal combustion engine 10 to reduce. After a delay phase of approx. 2-25 seconds, preferably 3-15 seconds, particularly preferably 5-10 seconds, the heating measures inside the engine are activated or intensified in a method step <130> in order to heat up the exhaust gas aftertreatment components 28 , 30th , 32 , 34 , 36 , 38 to favor their respective light-off temperature. Has the one with external heating means 44 , 46 , 48 heatable catalyst 28 , 30th , 32 , 34 , 36 , 38 its light-off temperature in a method step <140> T _{L / O_K1} , T _{L / O_K2} reached, so the unburned exhaust gas components on the catalytic converter 28 , 30th , 32 , 34 , 36 , 38 implemented exothermically will be causing further catalyst heating 28 , 30th , 32 , 34 , 36 , 38 favored. Is the exhaust system 20th completely warmed through, so there is a risk of the catalysts cooling down 28 , 30th , 32 , 34 , 36 , 38 is no longer below its respective light-off temperature, the external and internal engine heating measures can be ended in a method step <150>.

Due to the avoidance of internal engine heating measures in the first section of the cold start phase, an improved thermal efficiency of the internal combustion engine is achieved 10 reached. This allows the internal combustion engine 10 emitted pollutants are reduced during this first section of the cold start phase without a rapid heating of the at least one catalyst 28 , 30th , 32 , 34 , 36 , 38 to renounce.

In 6 are the raw emissions of the internal combustion engine 10 ( 6a) , the heat input into the externally heatable catalytic converter ( 6b) , the temperature curve of the externally heated catalytic converter in the cold start phase ( 6c ) and the emissions downstream of the externally heated catalytic converter in the cold start phase ( 6d ) shown. The dotted curve shows the course in the case of a cold start and heating of the catalytic converter known from the prior art exclusively with internal engine heating. The dashed curve shows the course during a cold start, in which internal engine heating measures are initially dispensed with and these are only activated later. The solid curve shows the course in a method according to the invention in which external heating measures are activated in the cold start phase and internal engine heating measures are dispensed with in the first section I of the cold start phase and the internal engine heating measures are activated in a second section II of the cold start phase. It can be seen that in a process according to the invention, the catalyst 28 , 30th , 32 , 34 , 36 , 38 its light-off temperature faster T _{L / O_K1} , T _{L / O_K2} achieves the emissions downstream of the externally heatable catalytic converter by dispensing with the internal engine heating measures in the first section I of the cold start phase 28 , 30th , 32 , 34 , 36 , 38 can be significantly reduced.

List of reference symbols

10

Internal combustion engine

12

Combustion chamber

14th

Fuel injector

16

spark plug

18th

Outlet

20th

Exhaust system

22nd

Exhaust duct

24

Exhaust gas turbocharger

26th

turbine

28

first catalyst

30th

Three way catalytic converter

32

Four way catalytic converter

34

second catalyst

36

Three way catalytic converter

38

Four way catalytic converter

40

Otto particle filter

42

electrically heated catalyst

44

electric heating element

46

electric heating disc

48

Exhaust burner

50

first lambda probe

52

second lambda probe

54

Temperature sensor

56

battery

58

Exhaust gas sensor

60

Engine control unit

EE

Tailpipe emissions

FWC

Four way catalytic converter

Q

Entry of heat into the catalytic converter

RE

Raw emissions

S.

Start of the internal combustion engine

T

temperature

T _K1

First catalyst temperature

T _K2

Second catalyst temperature

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 _DELAY

Delay Time

QUOTES INCLUDED IN THE DESCRIPTION

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

Patent literature cited

• DE 102008032600 A1 [0003]
• DE 102009003738 A1 [0004]
• DE 102012011603 A1 [0005]
• DE 102008023394 A1 [0006]

Claims (15)

A 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 in the exhaust system (20) at least one catalytic converter (28, 30, 32, 34, 36, 38), which can be heated by means of an external heating means (42, 44, 46, 48), comprising the following steps: - starting the internal combustion engine (10), - activating the external heating means (42, 44, 46, 48), whereby the catalytic converter (28, 30, 32, 34, 36, 38) is heated, whereby - internal heating measures of the internal combustion engine (10) are reduced or completely avoided in a first section of the cold start phase in order to reduce the raw emissions of the internal combustion engine (10 ), whereby - the internal engine heating measures are activated after the first section of the cold start phase in order to continue heating the catalytic converter (28, 30, 32, 34, 36, 38) up to its light-off temperature (T _{L / O_K1} , T _{L / o_K2} ) to accelerate. Method for exhaust gas aftertreatment of an internal combustion engine (10) according to Claim 1 , characterized in that the external heating means (42, 44, 46, 48) are activated from the start (S) of the internal combustion engine (10). Method for exhaust gas aftertreatment of an internal combustion engine (10) according to Claim 1 or 2 , characterized in that the internal combustion engine (10) is operated in the first section of the cold start phase with a stoichiometric combustion air ratio (λ _E = 1). Method for exhaust gas aftertreatment of an internal combustion engine (10) according to one of the Claims 1 to 3 , characterized in that the ignition angle for igniting the fuel-air mixture in the combustion chambers (12) of the internal combustion engine (10) is selected in the first section of the cold start phase with a view to optimum thermal efficiency. Method for exhaust gas aftertreatment of an internal combustion engine (10) according to one of the Claims 1 to 4th , characterized in that the first section of the cold start phase lasts between 2 seconds and 25 seconds. Method for exhaust gas aftertreatment of an internal combustion engine (10) according to one of the Claims 1 to 5 , characterized in that the internal engine heating measures include an adjustment of the ignition angle in the late direction. Method for exhaust gas aftertreatment of an internal combustion engine (10) according to one of the Claims 1 to 6 , characterized in that the internal engine heating measures include operation of the internal combustion engine (10) with a substoichiometric combustion air ratio (λ _E <1) or a lambda split operation between the combustion chambers (12) of the internal combustion engine (10). Method for exhaust gas aftertreatment of an internal combustion engine (10) according to one of the Claims 1 to 7th , characterized in that the external heating means (42, 44, 46) comprise an electrical heating element (44) with which the externally heatable catalytic converter (28, 30, 32, 34, 36, 48) is essentially independent of the exhaust gas flow of the internal combustion engine ( 10) is heated. An 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), with at least one catalytic converter (28, 30, 32, 34, 36) in the exhaust system (20) , 38), which can be heated by means of an external heating means (42, 44, 46, 48), and with an engine control device (60) which is set up to implement a method according to one of the Claims 1 to 8th to be carried out when a machine-readable program code is executed by the engine control unit (60). Exhaust aftertreatment system Claim 9 , characterized in that the external heating means (42, 44, 46, 48) comprise an electrical heating element (44), in particular an electrical heating disk (46). Exhaust aftertreatment system Claim 9 , characterized in that the external heating means (42, 44, 46, 48) comprise an exhaust gas burner (48). Exhaust aftertreatment system according to one of the Claims 9 to 11 , characterized in that the exhaust system (20) has a first catalytic converter (28) close to the engine and a second catalytic converter (34) arranged downstream of the first catalytic converter (28) close to the engine, preferably in the underbody position of a motor vehicle. Exhaust aftertreatment system Claim 12 , characterized in that the second catalyst (34) can be heated by means of external heating means (42, 44, 46, 48). Exhaust aftertreatment system according to one of the Claims 9 to 13 , characterized in that the exhaust system (20) has at least one catalyst (30, 32, 36, 38) with a three-way Has functionality and at least one particle filter (40) or a four-way catalyst (32, 38). Exhaust aftertreatment system according to one of the Claims 9 to 14th , characterized in that in the exhaust system (20) downstream of an outlet (18) of the internal combustion engine (10) and upstream of the at least one catalytic converter (28, 30, 32, 34, 36, 38) a turbine (26) of an exhaust gas turbocharger (24 ) is arranged.

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