DE102021005098A1 - Method for operating an exhaust gas aftertreatment device for an internal combustion engine, in particular a motor vehicle - Google Patents

Abstract

The invention relates to a method for operating an exhaust gas aftertreatment device (14) for an internal combustion engine (12), in which the exhaust gas aftertreatment device (14) has at least one SCR system (18), which has at least one SCR catalytic converter (20), at least one dosing element ( 22), by means of which a reducing agent can be introduced into the exhaust gas at an introduction point (E) arranged upstream of the SCR catalytic converter (20), and a first heating element (24) arranged upstream of the introduction point (E), comprising at least one downstream of the Introduction point (E) arranged second heating element (26), which is designed as an upstream of the SCR catalyst (20) or as a provided with the catalytic coating heating element, wherein the second heating element (26) is activated when a in the SCR The amount of reducing agent stored in the catalytic converter (20) exceeds a threshold value and a temperature of the SCR system (18) falls below a temperature threshold value, and the first heating element (24) is activated when the amount of reducing agent stored in the SCR catalytic converter (20) exceeds the Level falls below the threshold value and the temperature of the SCR system (18) falls below the temperature threshold value.

Description

The invention relates to a method for operating an exhaust gas aftertreatment device for an internal combustion engine, in particular a motor vehicle, according to the preamble of patent claim 1.

Such a method for operating an exhaust gas aftertreatment device for an internal combustion engine, in particular a motor vehicle, is already known, for example DE 10 2010 049 070 A1 to be taken as known. The exhaust gas aftertreatment device through which exhaust gas from the internal combustion engine can flow has at least one SCR system, which includes at least one SCR catalytic converter. The SCR catalytic converter has a catalytic coating, which is also referred to as an SCR coating. The SCR system also includes at least one dosing element, by means of which a reducing agent can be introduced into the exhaust gas at an introduction point arranged upstream of the SCR catalytic converter and thus upstream of the SCR coating. Furthermore, the SCR system comprises a first heating element for active heating, which is arranged upstream of the insertion point.

In addition, the DE 10 2017 106 766 A1 an exhaust system with a nitrogen oxide storage catalytic converter, an electric heating element and a nitrogen oxide reduction catalytic converter, the heating element being located downstream of the nitrogen oxide storage catalytic converter.

The object of the present invention is to further develop a method of the type mentioned at the outset in such a way that a particularly advantageous exhaust gas aftertreatment can be implemented.

This object is achieved by a method having the features of patent claim 1. Advantageous configurations with expedient developments of the invention are specified in the remaining claims.

In order to further develop a method of the type specified in the preamble of claim 1 in such a way that a particularly advantageous exhaust gas aftertreatment can be implemented, at least one second heating element arranged downstream of the introduction point and designed for active heating is provided. The second heating element is designed, for example, as a heating element arranged upstream of the SCR catalytic converter and thus upstream of the catalytic coating, which is therefore free of the coating of the SCR catalytic converter and preferably generally free of a catalytically active coating. In this case, the heating element is preferably arranged directly upstream of the SCR catalytic converter, that is to say arranged directly in front of the SCR catalytic converter. Alternatively, the heating element is designed as a heating element provided with the catalytic coating of the SCR catalytic converter, which is thus coated with the catalytically active coating of the SCR catalytic converter. The SCR catalytic converter or its coating, also referred to as an SCR coating, is catalytically active for the so-called selective catalytic reduction (SCR), so that the SCR is brought about and/or supported by the catalytic coating. Selective catalytic reduction is a chemical reaction in which the nitrogen oxides contained in the exhaust gas react with ammonia to form water and nitrogen. The ammonia is the reducing agent or is provided by the reducing agent or originates from the reducing agent. The reducing agent is preferably an aqueous urea solution. The reducing agent is heated, for example, in particular after it has been introduced into the exhaust gas at the point of introduction, with the reducing agent providing the ammonia as a result of this heating of the reducing agent.

The heating elements are active heating elements, ie active heating measures, by means of which the exhaust gas and/or at least a respective partial area of the SCR system can be actively heated and thus heated. The first heating element and/or the second heating element can be designed, for example, as an electrical heating element, by means of which the exhaust gas and/or at least the respective subregion of the SCR system can be actively heated using electrical energy. It is also conceivable that the first heating element and/or the second heating element is a chemical heating measure, by means of which the exhaust gas and/or the respective partial area of the SCR system is heated using chemical energy, ie chemical heat or chemically bound energy can be. The chemical heating measure can be understood in particular to mean that a substance can be introduced into the exhaust gas, for example by means of the first heating element at at least one first heating point arranged upstream of the introduction point and/or by means of the second heating element at at least one second heating point arranged downstream of the introduction point, through which energy or heat is chemically bound. The substance is, for example, a liquid substance, in particular a liquid fuel such as fuel, by means of which the internal combustion engine can be operated or is operated in its fired mode. By or after the introduction of the substance into the exhaust gas, the substance is heated, for example, as a result of which chemical energy is converted into heat. Here this heats the exhaust gas and/or at least the respective sub-area of the SCR system.

In the method, it is also provided according to the invention that the second heating element is activated, in particular while the first heating element is and remains deactivated, if a quantity of the reducing agent stored in the SCR catalytic converter and also referred to as fill level or NH3 fill level exceeds a fill level threshold value and a temperature of the SCR system, in particular of the SCR catalytic converter, falls below a temperature threshold value. Furthermore, it is provided in the method according to the invention that the first heating element is activated, in particular while the second heating element is deactivated and remains deactivated when the quantity of reducing agent stored in the SCR catalytic converter falls below the level threshold and the temperature of the SCR system, in particular of the SCR catalytic converter falls below the temperature threshold.

In an advantageous embodiment of the invention, it is provided that 0.5 grams of the reducing agent per liter volume of the SCR catalytic converter is used as the level threshold value.

In an advantageous embodiment of the invention, it is provided that a maximum of 250 degrees Celsius, in particular a maximum of 225 degrees Celsius, is used as the temperature threshold value.

In an advantageous embodiment of the invention, it is provided that the temperature is calculated on the basis of a calculation model using an electronic calculation device.

In an advantageous embodiment of the invention, it is provided that the quantity stored in the SCR catalytic converter is calculated on the basis of a calculation model using an electronic calculation device.

The invention is based in particular on the following findings and considerations: The aim of the invention is to use the active heating measures depending on the NH3 fill level of the SCR catalytic converter and thus of the SCR system, i.e. to activate or deactivate them, that the exhaust gas is post-treated in a particularly advantageous manner, in particular so that a particularly advantageous reduction of nitrogen oxides (NOx) contained in the exhaust gas is realized by the SCR system. The exhaust gas aftertreatment device is, for example, a component of an exhaust system through which the exhaust gas of the internal combustion engine can flow. The internal combustion engine is preferably designed as a diesel engine, with the internal combustion engine preferably being a component of a motor vehicle that can be driven by the internal combustion engine. The exhaust aftertreatment device is used, for example, to reduce engine pollutants that are provided by the internal combustion engine. The SCR system can in particular include a so-called mixing section, which is arranged or runs upstream of the SCR catalytic converter, in particular in such a way that at least a length of the mixing section is arranged downstream of the introduction point. In particular, the mixing section serves to mix the reducing agent introduced into the exhaust gas at the introduction point by means of the dosing element with the exhaust gas in order to particularly advantageously cause the reducing agent to provide the ammonia. In particular, the positions of the active heating measures, i.e. the heating points at which the exhaust gas and/or at least the respective partial areas of the SCR system can be actively heated by means of the heating elements, are defined or designed in such a way that the first heating element is arranged upstream of the introduction point, and that the second heating element is either arranged directly in front of the SCR catalytic converter or is provided with the SCR coating and is thus designed as part of the SCR catalytic converter. In addition, the exhaust gas aftertreatment device can also include other exhaust gas aftertreatment elements for exhaust gas aftertreatment, such as an oxidation catalytic converter, in particular a diesel oxidation catalytic converter (DOC), a nitrogen oxide storage catalytic converter (NSK), a particulate filter, in particular a diesel particulate filter (DPF) and/or an ammonia slip catalytic converter (ASC). .

Nitrogen oxides contained in the exhaust gas can be effectively converted at least essentially continuously by means of the SCR catalytic converter, in particular by its coating, in particular if the following conditions are met: On the one hand, a temperature that is advantageous for the SCR should prevail in the SCR catalytic converter. On the other hand, the reducing agent or the ammonia should be available. Ammonia can be stored in or on the SCR catalytic converter. If no ammonia or only a small amount of ammonia is stored in the SCR catalytic converter, it is advantageous for an advantageous nitrogen oxide reduction to introduce, in particular to inject, reducing agent into the exhaust gas by means of the dosing element. The introduction, in particular injection, of the reducing agent by means of the dosing element is also referred to as dosing. For dosing, it is advantageous if the dosing element, also known as the dosing unit, and the at least between the dosing element or the point of introduction and the SCR catalyst arranged mixing section each have a minimum temperature, otherwise the reducing agent will not evaporate sufficiently and decomposes into ammonia, but settles on a wall of the mixing section. For this reason, for example, metering is only enabled above a certain minimum temperature of the metering unit, so that the SCR catalytic converter may not be able to convert nitrogen oxides due to a lack of ammonia, even if it itself has a temperature sufficient for nitrogen oxide reduction.

As long as there is still a sufficient amount of ammonia stored in or on the SCR catalytic converter, basically only the temperature of the SCR catalytic converter is relevant for the effective conversion of nitrogen oxides; the temperature of the mixing section and the dosing unit is less important in this case.

In order to bring the exhaust system, in particular the exhaust gas aftertreatment device, to the temperatures that are advantageous for effective exhaust gas aftertreatment as quickly as possible, active heating measures are used in addition to the heat from the engine combustion process. However, depending on the outside conditions and, for example in the case of electrical heating, the available electrical power, not all active heating measures can be operated simultaneously with maximum power. For this reason, an operating strategy is proposed in which the power is distributed to the active heating measures depending on the NH3 fill level in or on the SCR catalytic converter. In the case of a sufficient NH3 filling level in or on the SCR catalytic converter, in the event that the SCR system does not have the temperature required for effective nitrogen oxide conversion, the active heating measure should be used in particular, which should be directly upstream of the SCR if possible -catalyst sits or is part of the SCR catalytic converter as a heatable substrate in order to achieve the fastest possible and delay-free heating of the SCR catalytic converter. Especially in the case of low mass flows, the heat transport through the exhaust system is slow and the wall heat losses are high, resulting in significantly faster heating.

In the case of an empty SCR system with no NH3 filling level or with only a low NH3 filling level, the active heating measure, i.e. the first heating element, should be used, which also heats the dosing unit and the mixing section, in order to obtain a dosing release as quickly as possible . After the NH3 treatment temperature has been exceeded and a dosing release has been received, the heating measure should be given priority again, i.e. with the second heating element after the mixing section or after the point of introduction, if the desired or advantageous temperature of the SCR system has not yet been reached and either the dosing release is retained or a sufficient NH3 level has built up on the SCR catalytic converter.

Overall, it can be seen that it is determined which of the two heating elements is activated, for example, at the beginning of a driving cycle, depending on the temperature of the SCR system, in particular the SCR catalytic converter, and depending on the NH3 fill level. For example, the temperature of the SCR system is a model temperature that is calculated using the aforementioned calculation model using the electronic calculation device. If the NH3 level in the SCR catalytic converter exceeds the threshold level, preferably 0.5 grams per liter of catalytic converter volume of the SCR catalytic converter, and the model temperature is below the temperature threshold value of, for example, 250 degrees Celsius, in particular 225 degrees Celsius, the rear, second heating element is activated , in particular while the front, first heating element is and remains deactivated. If this is not the case, at a model temperature of less than 250 degrees Celsius, in particular less than 225 degrees Celsius, the front, first heating element is activated, in particular while the rear, second heating element is deactivated and remains so. If, after activation of the front, first heating element, the NH3 preparation temperature is subsequently exceeded, the front, first heating element is deactivated, and if the temperature on the SCR catalytic converter is less than 250 degrees Celsius, in particular 225 degrees Celsius, the rear, second heating element activated. Especially at low exhaust gas mass flows of preferably less than 100 kilograms per hour, the heat transport along the exhaust system is very slow, and the wall heat losses are high. The direct activation of the rear, second heating element after the preparation of metering readiness can thus make the functional readiness of the SCR catalytic converter by activating the rear, second heating element much earlier than in conventional solutions. The release of the dosing is linked to the temperature in the vicinity of the mixing section, and this is influenced by the operation of the front, first heating element, i.e. it is increased much faster.

Further advantages, features and details of the invention result from the following description of a preferred exemplary embodiment and from the drawing. The features and feature combinations mentioned above in the description and the features and characteristics mentioned below in the description of the figures and/or shown alone in the single figure Mal combinations can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the invention.

In the single figure, the drawing shows an exhaust gas aftertreatment device for an internal combustion engine of a motor vehicle.

The only figure shows a schematic representation of an exhaust system 10 for an internal combustion engine 12 of a motor vehicle, in particular a motor vehicle preferably designed as a passenger car. The motor vehicle can be driven by means of the internal combustion engine 12 . For example, internal combustion engine 12 is designed as a diesel engine. During its fired operation, internal combustion engine 12 provides exhaust gas that can flow through exhaust system 10 . The exhaust system 10 includes an exhaust gas aftertreatment device 14 through which the exhaust gas of the internal combustion engine 12 can flow and by means of which the exhaust gas is aftertreated. An arrow 16 illustrates that the exhaust gas flows out of the exhaust gas aftertreatment device 14 , in particular out of the exhaust system 10 .

The exhaust gas aftertreatment device 14 includes an SCR system 18, by means of which the exhaust gas can be denitrified. This is to be understood as meaning that nitrogen oxides (NOx) contained in the exhaust gas can be at least partially removed from the exhaust gas, and therefore reduced, in that the so-called selective catalytic reaction (SCR) is catalytically effected and/or supported by means of the SCR system 18 . SCR is a chemical reaction in which the nitrogen oxides contained in the exhaust gas react at least partially with ammonia to form water and nitrogen, i.e. are converted. The ammonia is provided by a reducing agent, which means that it originates from the reducing agent that is introduced into the exhaust gas flowing through the exhaust gas aftertreatment device 14 and is subsequently thermally decomposed.

The SCR system 18 has at least one SCR catalytic converter 20 which has a catalytic coating, ie a catalytically active coating, which is also referred to as an SCR coating. The SCR coating is catalytically active for the SCR, so that the SCR is catalytically supported and/or effected by the SCR coating. Furthermore, the SCR system 18 comprises at least one dosing element 22, by means of which the reducing agent can be introduced into the exhaust gas or is introduced at an introduction point E arranged upstream of the SCR catalytic converter 20. For example, the reducing agent is an aqueous urea solution. The SCR system 18 also includes a first heating element 24 arranged upstream of the insertion point E for active heating. The feature that the heating element 24 is arranged upstream of the injection point E is to be understood in particular as meaning that the heating element 24 at a first heating point H1 arranged upstream of the injection point E is used to actively heat the exhaust gas and/or at least a first partial area of the SCR -System 18 causes, that is, can be carried out. For this purpose, for example, the heating element 24 is designed as an electrical heating element, by means of which the exhaust gas and/or the first partial region, in particular at or starting from the heating point H1, can be actively heated using electrical energy. It is also conceivable that a liquid substance, for example a liquid fuel, can be introduced, in particular injected, into the exhaust gas at the heating point H1 by means of the heating element 24, as a result of which the exhaust gas is heated starting at the heating point H1 or starting from the heating point H1 and/or the SCR system 18 or at least the first sub-area can be or is actively brought about.

In order to be able to post-treat the exhaust gas particularly advantageously, the SCR system has a second heating element 26 for active heating, with the heating element 26 being arranged downstream of the introduction point E. Analogous to the explanations regarding the heating element 24, this means that the exhaust gas and/or at least a second partial area of the SCR system 18 can be actively heated by means of the heating element 26 at a second heating point H2 arranged downstream of the introduction point E. In other words, the heating element 26 can actively bring about a heating of the exhaust gas and/or at least the second partial region of the SCR system 18 which takes place at the heating point H2 and/or starts from the heating point H2. For this purpose, the heating element 26 is designed, for example, as an electrical heating element, by means of which the exhaust gas and/or the second partial area can be actively heated at or starting from the heating point H2 using electrical energy. It is also conceivable that the heating element 26 is designed to introduce, in particular to inject, a liquid substance, for example, such as the aforementioned fuel, into the exhaust gas at the heating point H2. The fuel injected into the exhaust gas at heating point H1 or H2 is converted, for example, in particular as part of an exothermic reaction and thus initially releases chemically bound heat or energy, whereby the exhaust gas and/or at least the respective partial area at or starting from the respective heating point H1 or H2 is actively heated.

The second heating element 26 is now, for example, a heating element arranged upstream of the SCR catalytic converter 20 and thus upstream of the SCR coating, which heating element can be free of the SCR coating and, in principle, free of a catalytically active coating. In this case, the heating element 26 is arranged, for example, directly in front of the SCR catalytic converter 20, in particular directly in front of the SCR coating, so that, for example, no longitudinal area is arranged between the heating element 26 and the SCR catalytic converter 20, in particular the SCR coating, which is free from the SCR coating. Furthermore, it is conceivable that the heating element 26 is provided with the SCR coating and is therefore part of the SCR catalytic converter 20 .

A method for operating the exhaust gas aftertreatment device 14 is described with reference to the figure. The method is carried out, for example, using an electronic computing device 28, which is also referred to as a control unit. Electronic computing device 28 activates second heating element 26, in particular while heating element 24 is and remains deactivated, when a quantity of the reducing agent, in particular ammonia, stored in SCR catalytic converter 20 and also referred to as the NH3 level exceeds a level threshold value and a temperature of the SCR system 18, in particular of the SCR catalytic converter 20, falls below a temperature threshold value. Electronic computing device 28 activates first heating element 24, in particular while heating element 26 is and remains deactivated, when the quantity of reducing agent stored in SCR catalytic converter 20 falls below the filling level threshold and the temperature of SCR system 18, in particular of the SCR -Catalyst 20, the temperature falls below threshold.

reference list

10

exhaust system

12

internal combustion engine

14

exhaust aftertreatment device

16

Arrow

18

SCR system

20

SCR catalytic converter

22

dosing element

24

first heating element

26

second heating element

28

electronic computing device

E

entry point

H1

first heating point

H2

second heating point

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited 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 102010049070 A1 [0002]
• DE 102017106766 A1 [0003]

Claims (5)

Method for operating an exhaust gas aftertreatment device (14) for an internal combustion engine (12), in which the exhaust gas aftertreatment device (14) through which exhaust gas from the internal combustion engine (12) can flow has at least one SCR system (18), which has at least one SCR catalytic converter having a catalytic coating (20), at least one dosing element (22), by means of which a reducing agent can be introduced into the exhaust gas at an introduction point (E) arranged upstream of the SCR catalytic converter (20), and a first heating element (24 ) for active heating, characterized by at least one second heating element (26) arranged downstream of the introduction point (E) and designed for active heating, which is arranged as a heating element upstream of the SCR catalytic converter (20) or as one provided with the catalytic coating heating element is formed, wherein: - the second heating element (26) is activated when a quantity of the reducing agent stored in the SCR catalytic converter (20) exceeds a filling level threshold value and a temperature of the SCR system (18) falls below a temperature threshold value, and - that the first heating element (24) is activated when the quantity of reducing agent stored in the SCR catalytic converter (20) falls below the level threshold and the temperature of the SCR system (18) falls below the temperature threshold. procedure after claim 1 , characterized in that 0.5 grams of the reducing agent per liter volume of the SCR catalytic converter is used as the filling level threshold value. procedure after claim 1 or 2 , characterized in that at most 250 degrees Celsius, in particular at most 225 degrees Celsius, is used as the temperature threshold value. Method according to one of the preceding claims, characterized in that the temperature is calculated on the basis of a calculation model using an electronic calculation device (28). Method according to one of the preceding claims, characterized in that the quantity stored in the SCR catalytic converter (20) is calculated on the basis of a calculation model using an electronic calculation device (28).

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