DE102019208501A1 - Method for operating an exhaust gas aftertreatment device with at least one NOx storage catalytic converter - Google Patents

Abstract

The invention relates to a method for operating an exhaust gas aftertreatment device (8) with at least one NOx storage catalytic converter (12) for cleaning an exhaust gas flow of a motor vehicle (2) with an internal combustion engine (6), with the steps: (S100) detecting a simulated NOx Load value (RB) indicative of accumulated NOx in the NOx storage catalytic converter (12), (S200) for the presence of at least one predetermined condition (RgnAb) detection of a progress value (FW) indicative of a portion of a simulated complete regeneration of the NOx storage catalytic converter (12), (S400) Stopping the detection of the simulated NOx loading value (BW) indicative of accumulated NOx in the NOx storage catalytic converter (12) if the progress value (FW) indicative of a portion of a simulated complete regeneration has a maximum value (MW) indicative of complete regeneration and providing a fictitious NOx load value (BW), (S500) generating or similar the updating of a histogram data set (HD) using the fictitious NOx loading value (BW) indicative of accumulated NOx in the NOx storage catalytic converter (12), and (S600) evaluating the histogram data set (HD) by a value for a NOx -Threshold value (SW) indicative of a probability less than 100% for a complete regeneration to be determined.

Description

The invention relates to a method for operating an exhaust gas aftertreatment device with at least one NOx storage catalytic converter for cleaning an exhaust gas flow of a motor vehicle with an internal combustion engine.

With exhaust gas aftertreatment devices, combustion gases are cleaned mechanically, catalytically or chemically after they have left the combustion chamber or the combustion chamber of the internal combustion engine, in order to be able to comply with statutory pollutant limits.

To achieve strict emission conditions, exhaust gas aftertreatment devices have several different catalytic converters which can be arranged close to the engine and / or in the vehicle underbody, rather remote from the engine. To remove e.g. Nitrogen oxides (NOx) from the exhaust gas flow have such exhaust gas aftertreatment devices SCR catalytic converters and NOx storage catalytic converters, the NOx storage catalytic converter being arranged upstream of the SCR catalytic converter.

Diesel engines and modern lean-burn gasoline engines operate in a lean-burn mode, i.e. with an excess of oxygen (λ> 1). Conventional three-way catalytic converters can therefore not be used. Although the oxidation of carbon monoxide (CO) and incompletely burned hydrocarbons (CmHn) is still possible in the case of excess oxygen, analogous to the conventional three-way catalytic converter, nitrogen oxides (NOx) must be converted after they have been temporarily stored. Their catalytic reduction takes place cyclically with a stoichiometric to rich exhaust gas mixture. Therefore, catalytic converters with additional chemical elements that enable nitrogen oxides to be stored, so-called NOx storage catalytic converters, are required.

To achieve this intermediate storage of nitrogen oxides in the NOx storage catalytic converter, a noble metal catalytic converter such as platinum and a NOx storage component, which is usually an alkaline earth metal such as barium, are applied to suitable supports. In the lean, i.e. oxygen-rich, atmosphere, the nitrogen oxides are oxidized under the action of the noble metal catalyst, absorbed in the catalyst with the formation of nitrates such as barium nitrate and thus removed from the exhaust gas flow. Regular, brief “enrichment” of the exhaust gas causes these reactions to run in the opposite direction, whereby the NOx molecules are released back into the exhaust gas stream and converted to nitrogen by the reducing components such as hydrocarbons and / or carbon monoxide present in the rich atmosphere.

If the absorption capacity of the NOx storage catalytic converter is exhausted, a rich substoichiometric, reducing exhaust gas mixture is set by a control unit for a few seconds. In this brief regeneration mode, the NOx temporarily stored in the NOx storage catalytic converter is reduced to nitrogen and the NOx storage catalytic converter is thus prepared for the next storage cycle. This procedure makes it possible to minimize the pollutant emissions from internal combustion engines operated with excess air and to comply with pollutant limit values.

Enriching to carry out such a regeneration of the NOx storage catalytic converters can be carried out by fuel injection, late fuel injection, by changing the ratio of the fuel quantity in the main injection to the fuel quantity in the post injection, by means of air throttling, can be achieved through increased exhaust gas recirculation rates or other measures. The duration and frequency of the regenerations are determined by the control unit as a function of the stored amount of nitrogen oxide, exhaust gas temperature, exhaust gas mass flow and other parameters.

However, incomplete regenerations can lead to storage loading, which is critical. Incomplete regenerations can occur if e.g. a driver takes his foot off the accelerator pedal. In this case, the fuel supply is interrupted and the mixture becomes lean again.

As a result, desorption of stored NOx becomes likely or the storage efficiency becomes too low. In both cases there is a risk that the NOx emissions will exceed permissible limits.

Such incomplete regenerations occur above all in urban environments, in which the driving style is typically more dynamic than in rural environments.

From the US 9,551,258 B2 an exhaust gas aftertreatment system is known which uses a GPS system to regenerate an exhaust gas aftertreatment system from a driver profile, an application profile assigned to the motor vehicle and a probability value. The probability value indicates the probability that the regeneration will be started and ended in this mission profile. With the aid of the GPS data, a period of time is determined in order to start a regeneration of the exhaust gas aftertreatment system and a complete regeneration in this End time span. The deployment profile is determined using a route that is calculated using a navigation system.

From the US 7,017,337 B2 it is known to select a threshold value that triggers regenerations as a function of a driving style.

From the US 9,303,579 B2 It is known to determine rates of change of such a threshold value as a function of the driving behavior of a driver.

There is therefore a need to show ways in which the operation of such an exhaust gas aftertreatment device can be further improved.

• Erfassen eines simulierten NOx-Beladungswertes indikativ für akkumuliertes NOx in dem NOx-Speicherkatalysator,
• auf ein Vorliegen zumindest einer vorbestimmten Bedingung hin Erfassen von einem Fortschrittswert indikativ für einen Anteil einer simulierten vollständigen Regeneration des NOx-Speicherkatalysators,
• Stoppen des Erfassens des NOx-Beladungswertes indikativ für akkumuliertes NOx in dem NOx-Speicherkatalysator, wenn der Fortschrittswert indikativ für einen Anteil einer simulierten vollständigen Regeneration einen Maximalwert indikativ für eine vollständige Regenration erreicht hat, und Bereitstellen eines fiktiven NOx-Beladungswertes,
• Erzeugen oder Aktualisieren eines Histogramm-Datensatzes unter Verwendung des fiktiven NOx-Beladungswertes indikativ für akkumuliertes NOx in dem NOx-Speicherkatalysator, und
• Auswerten des Histogramm-Datensatzes um einen Wert für einen NOx-Schwellwert indikativ für eine Wahrscheinlichkeit kleiner als 100% für eine vollständige Regeneration zu bestimmen.

The object of the invention is achieved by a method for operating an exhaust gas aftertreatment device with at least one NOx storage catalytic converter for cleaning an exhaust gas flow of a motor vehicle with an internal combustion engine, with the steps:

• Detection of a simulated NOx loading value indicative of accumulated NOx in the NOx storage catalytic converter,
• if at least one predetermined condition is present, a progress value is recorded indicative of a portion of a simulated complete regeneration of the NOx storage catalytic converter,
• Stopping the detection of the NOx loading value indicative of accumulated NOx in the NOx storage catalytic converter if the progress value indicative of a part of a simulated complete regeneration has reached a maximum value indicative of a complete regeneration, and providing a fictitious NOx loading value,
• Generating or updating a histogram data set using the fictitious NOx loading value indicative of accumulated NOx in the NOx storage catalytic converter, and
• Evaluation of the histogram data set in order to determine a value for a NOx threshold value indicative of a probability less than 100% for complete regeneration.

The amount of NOx accumulating in the NOx storage catalytic converter is thus continuously recorded by simulation. For this purpose, the NOx content of the exhaust gas flow can be recorded and taken into account with a NOx sensor upstream of the NOx storage catalytic converter. In order to take into account the storage behavior of the NOx storage catalytic converter, provision can also be made to take into account a variable for the storage efficiency by which the amount of non-accumulated NOx is multiplied.

The progress value relates to a simulated full regeneration. A regeneration is actually not carried out. In other words, both the NOx loading value of the NOx storage catalytic converter and the progress value are simulation values and not measured values.

If regeneration would have been possible on the basis of the simulation, the latest status of the simulated NOx loading value becomes the fictitious NOx loading value. In other words, the fictitious NOx loading value can also be viewed as a simulated current NOx loading value.

The predetermined condition is indicative of a regeneration probability. The regeneration probability can e.g. can be determined as a function of the NOx storage catalytic converter temperature and / or the vehicle speed and / or operating parameters of the internal combustion engine. If the predetermined condition is met, that is to say the conditions for a regeneration are present, the progress value is recorded indicatively for a portion of a simulated complete regeneration. This can be a duration or the percentage of the duration for a complete regeneration. It should be noted that no regeneration is carried out here, but only the length of the period of time during which a regeneration would be possible is recorded. Instead of the duration, other variables can also be recorded if they are indicative of the progress of a regeneration.

As soon as the progress value is indicative of a part of a complete regeneration, the recording of the NOx loading value is stopped and the value determined up to that point is used as the current NOx loading value.

In other words, the simulated NOx loading value indicative of accumulated NOx in the NOx storage catalytic converter is continuously integrated until the progress value, which is also integrated, corresponds to the maximum value indicative of complete regeneration.

A histogram data set is then created or updated. The histogram data set assigns respective NOx loading values indicative of NOx accumulated in the NOx storage catalytic converter to respective probabilities during which regeneration was possible, this regeneration not actually being carried out.

The histogram data record is then evaluated by a value for a NOx threshold value to be determined indicatively for a probability of less than 100% for a complete regeneration, e.g. for a probability of 95%. For this purpose, the individual probabilities of the respective phases can be added up or integrated until the value for the NOx threshold value SW is reached.

It is therefore proposed not to reduce the number of interrupted regenerations, but rather the value for a NOx threshold value is lowered so that the probability of a regeneration is increased. This means that a regeneration is carried out before a maximum NOx load is reached.

According to one embodiment, the acquisition of the progress value indicative of a portion of a simulated complete regeneration is stopped if at least one predetermined termination condition is present, the simulated NOx loading value indicative of accumulated NOx in the NOx storage catalytic converter is updated according to the regeneration, and the acquisition of a progress value is indicative for a portion of a simulated complete regeneration, at least one predetermined condition is continued. The acquisition of the progress value indicative of a portion of a simulated complete regeneration is therefore stopped when at least one predetermined termination condition is present. The termination condition can e.g. be a release of an accelerator pedal of the motor vehicle by the driver, which leads to a lean and therefore unsuitable mixture for regeneration. If there is no termination condition in the meantime, the duration for a simulated complete regeneration will be reached. In other words, the progress value indicative of a portion of a simulated complete regeneration will reach or correspond to the value indicative of a complete regeneration. A complete regeneration would have been possible under these conditions. The progress value indicative of a portion of a simulated complete regeneration is not set to zero, but is updated as soon as the predetermined conditions are met again. This increases the probability of a regeneration even if this leads to aborted or interrupted regenerations.

According to a further embodiment, the updating of the histogram data set comprises that the values representative of the probabilities for the fictitious NOx load value and for the respective simulated archived NOx load values, whose assigned NOx load is greater than or equal to the fictitious NOx load, are decreased. Load value is. The respective probabilities can be increased by a predetermined value. The histogram data record is updated by taking into account the most recently obtained data.

According to a further embodiment, the updating of the histogram data set comprises that the values are increased representative of the probabilities of the respective simulated archived NOx load values whose assigned NOx load is less than the fictitious NOx load value. The respective probabilities can be increased by a predetermined value. In this way, by choosing the respective values accordingly, it can be ensured that the total probability or overall probability remains at one or 100%. In other words, the histogram data set is a normalized histogram data set

The invention also includes a computer program product, a control device, an exhaust gas aftertreatment device with such a control device and a motor vehicle with such an exhaust gas aftertreatment device.

• 1 in schematischer Darstellung Komponenten einer Abgasnachbehandlungsvorrichtung eines Kraftfahrzeugs mit einer Brennkraftmaschine.
• 2 in schematischer Darstellung einen Histogramm-Datensatz
• 3 in schematischer Darstellung einen Verfahrensablauf zum Betrieb des in 1 dargestellten Komponenten.

The invention will now be explained with reference to a drawing. Show it:

• 1 a schematic representation of components of an exhaust gas aftertreatment device of a motor vehicle with an internal combustion engine.
• 2 a schematic representation of a histogram data set
• 3 a schematic representation of a process sequence for operating the in 1 illustrated components.

It gets on first 1 Referenced.

Components of a drive train are shown 4th of a motor vehicle 2 , such as a car. This will be under the drive train 4th of the motor vehicle 2 understood all components that are in the motor vehicle 2 Generate a torque for the drive and transmit it to the road.

1 shows of the components an internal combustion engine serving as a traction motor 6th , an exhaust aftertreatment device 8th for cleaning an exhaust gas flow of the internal combustion engine 6th and a control unit 10 . In a departure from the present exemplary embodiment, the motor vehicle 2 also have more than one traction motor, e.g. if the motor vehicle 2 is provided with a hybrid drive train.

The internal combustion engine 6th is a lean operated in the present embodiment Diesel engine, ie the diesel engine is operated with excess oxygen (λ> 1) in normal operation. The internal combustion engine can deviate from this 6th can also be designed as a gasoline engine in lean operation to increase the engine efficiency.

The internal combustion engine 6th can be turbo-charged, so that in the exhaust gas flow of the internal combustion engine 6th a turbine of an exhaust gas turbocharger is connected downstream.

The one in the exhaust gas flow direction of the internal combustion engine 6th downstream exhaust gas aftertreatment device 8th has in the present exemplary embodiment a NOx storage catalytic converter 12 and a diesel particulate filter 14th on.

The NOx storage catalytic converter 12 is designed to store NOx (nitrogen oxides). It has a structure with a suitable carrier with a noble metal catalyst such as platinum and a NOx storage component such as an alkaline earth metal such as barium.

The diesel particulate filter 14th is designed to be used in the internal combustion engine 6th to filter resulting soot particles from the exhaust gas.

The internal combustion engine 6th is the control unit 10 assigned, which causes a change from an operation with excess oxygen to a substoichiometric operation and vice versa, to a regeneration of the NOx storage catalytic converter 12 to effect.

For this purpose and for the tasks and functions described below, the control unit 10 Hardware and / or software components.

In addition to the catalysts mentioned, the exhaust gas aftertreatment device 8th also have further catalytic converters which, for example, the diesel particulate filter in the exhaust gas flow direction 14th are downstream.

Furthermore, the control unit 10 designed to provide a simulated NOx loading value BW indicative of accumulated NOx in the NOx storage catalytic converter 12 read in.

For this purpose, the NOx content of the exhaust gas flow can be detected upstream of the NOx storage catalytic converter with a NOx sensor (not shown). About the storage behavior of the NOx storage catalytic converter 12 To be taken into account, provision can also be made to take into account a variable for the storage efficiency by which the amount of the accumulated NOx is multiplied. In the present exemplary embodiment, the in the NOx storage catalytic converter is used to determine 12 For accumulated NOx, a model can also be used that takes into account temperature values and values for space velocities as input parameters. In other words, the simulated NOx loading value BW indicative of accumulated NOx in the NOx storage catalytic converter 12 is provided by a model.

When the control unit 10 captures that predetermined conditions RgnAb are fulfilled, the control unit records 10 a progress value FW indicative of a part of a simulated complete regeneration. The predetermined condition RgnAb is indicative of the likelihood of regeneration. The regeneration probability can, for example, depend on the temperature of the NOx storage catalytic converter 12 and / or the vehicle speed and / or operating variables of the internal combustion engine 6th to be determined. Also the progress value FW indicative of a proportion of a simulated complete regeneration is provided by a model.

If the predetermined condition RgnAb is fulfilled, i.e. the conditions for a regeneration are present, the progress value becomes FW recorded indicative of a part of a simulated complete regeneration. This can be a duration or the percentage of the duration for a complete regeneration. Instead of the duration, other variables can also be recorded if they are indicative of the progress of a regeneration.

When the control unit 10 detects that the predetermined termination condition FROM is present, the control unit stops 10 the recording of the progress value FW indicative of a part of a simulated complete regeneration. With the termination condition FROM In the present exemplary embodiment, it is a release of an accelerator pedal of the motor vehicle 2 by the driver. The control unit 10 sets the recording of the progress value FW indicative of a part of a simulated complete regeneration for a renewed presence of the predetermined condition RgnAb away.

In other words, the control unit 10 continuously integrates the simulated NOx loading value BW indicative of accumulated NOx in the NOx storage catalytic converter 12 until the also from the control unit 10 on built-in progress value FW the maximum value MW indicative of a complete regeneration and takes into account interruptions in the regeneration.

If the progress value FW The maximum value is indicative of a part of a simulated complete regeneration MW indicative of a complete regeneration, ie the progress value FW indicative of a part of a complete regeneration the maximum value MW indicative of corresponds to a complete regeneration, the control unit generates 12 the histogram data set HD or update it.

It will now be made with additional reference to FIG 2 the histogram data set HD explained.

The histogram data set HD assigns the respective simulated NOx loading values BW indicative of accumulated NOx in the NOx storage catalytic converter 12 respective probabilities W. during which regeneration was possible, which regeneration was not actually carried out. In other words, the histogram data set HD is representative of an accumulated amount of NOx that is stored until the next favorable opportunity for regeneration. There can also be multiple histogram data sets HD are formed for different benefit levels.

In other words, the histogram data set HD assigns, for example, a simulated NOx loading value BW for 0.1 g of accumulated NOx a probability W _0.1g , for a simulated NOx loading _value BW for 0.2g of accumulated NOx, a probability of W _0.2g , etc. becomes. Where is the histogram data set HD normalized in the present _exemplary embodiment, ie the sum of all probabilities from W _0.1g to W _2.5g is equal to one or 100%.

In the present exemplary embodiment, the histogram data record HD a simulated NOx loading value BW assigned for 1.3g of accumulated NOx. This is a fictitious NOx loading value BW indicative of accumulated NOx in the NOx storage catalytic converter 12 with a corresponding probability W _1.3g .

In addition to the fictitious NOx loading value BW are still the simulated archived NOx load values aBW + , aBW - shown. These data are assigned to the histogram data set HD on before the fictitious load value BW is taken into account. In other words, this is an existing histogram data set HD updated.

The simulated archived NOx load values aBW + are assigned to the probabilities for at least 1.4g of accumulated NOx, ie for the probabilities from W _1.4g , while the archived NOx load _values aBW- the probabilities of 0.1g to 1.2g accumulated NOx are assigned, ie for the probabilities of W _0.1g to W _1.2g .

The control unit 10 updates the histogram data set HD , in which the values are representative of the probability W _1.3g for the fictitious NOx loading _value BW and the probabilities W _0.1g to W _1.2g for the respective simulated archived NOx load _values aBW- humiliated.

The control unit also updates 10 the histogram data set HD , in which the values for the probabilities W _1.4g to W _2.5g for the respective simulated archived NOx load values aBW + elevated.

The control unit also evaluates 12 the histogram data set HD off by a value for a NOx threshold value SW to be determined indicative of a probability less than 100% for a complete regeneration.

In the present exemplary embodiment, the value for the probability is less than 100% 95%. The individual probabilities W. added up or integrated to the sum value ΣW to determine. In the present _exemplary embodiment, these are the probabilities from W _0.1g to W _1.3g .

Based on the total value determined in this way ΣW can then the NOx threshold SW to be determined.

It will now be made with additional reference to FIG 3 a procedure for the operation of the in 1 illustrated components explained.

The control unit 10 starts in a first step S100 with the continuous recording of the simulated NOx loading value BW indicative of accumulated NOx in the NOx storage catalytic converter 12 and updates it.

When the control unit 10 detects that the predetermined conditions RgnAb are fulfilled, the control unit begins 12 in a further step S200 a progress value FW to continuously record indicative of a portion of a simulated complete regeneration and to update this.

When the control unit 10 detects that the predetermined termination condition FROM is present, stops in a further step S300 the control unit 12 the recording of the progress value FW indicative of a part of a simulated complete regeneration.

When the control unit 10 that detected the predetermined conditions RgnAb is fulfilled again, the control unit resets 10 the recording of the progress value FW indicative of a part of a simulated complete regeneration.

The control unit also updates 10 the simulated NOx loading value BW indicative of Accumulated NOx in the NOx storage catalytic converter 12 according to the regenerations, ie according to the progress of the regenerations. In other words, there will be the interrupted regenerations and their influence on the simulated NOx loading value BW considered.

If the progress value FW indicative of a portion of a simulated complete regeneration has reached a value indicative of a complete regeneration, ie the progress value FW indicative of a portion of a simulated complete regeneration corresponds to the value indicative of a complete regeneration, the control unit stops 12 in a further step S400 the detection of the simulated NOx loading value BW indicative of accumulated NOx in the NOx storage catalytic converter 12 . This value is then the fictitious NOx loading value BW .

In a further step S500 creates or updates the control unit 10 the histogram data set HD using the fictitious NOx loading value BW indicative of accumulated NOx in the NOx storage catalytic converter 12 . Thus the histogram data set HD only updated if a complete regeneration with or without interruption would be possible.

If already the histogram record HD generated updates the control unit 12 the histogram data set HD by making the values representative of the probabilities as already described W. increased or decreased.

In a further step S600 evaluates the control unit 12 as already described the histogram data set HD off by a value for a NOx threshold value SW to be determined indicative of a probability less than 100% for a complete regeneration.

In a departure from the present exemplary embodiment, the sequence of the steps can also be different. Furthermore, several steps can also be carried out at the same time or simultaneously.

It is therefore proposed that the value for a NOx threshold value SW lower in order to increase the likelihood of regeneration. This means that a regeneration is carried out before a maximum NOx load is reached.

List of reference symbols

2

Motor vehicle

4th

Powertrain

6th

Internal combustion engine

8th

Exhaust aftertreatment device

10

Control unit

12

Diesel particulate filter

14th

NOx storage catalytic converter

aBW +

simulated archived NOx loading value

aBW-

simulated archived NOx loading value

FROM

Termination condition

BW

simulated NOx loading value

FW

Progress value

HD

Histogram data set

MW

Maximum value

RgnAb

predetermined condition

SW

NOx threshold

W.

probability

ΣW

Total value

S100

step

S200

step

S300

step

S400

step

S500

step

S600

step

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

• US 9551258 B2 [0011]
• US 7017337 B2 [0012]
• US 9303579 B2 [0013]

Claims (11)

Method for operating an exhaust gas aftertreatment device (8) with at least one NOx storage catalytic converter (12) for cleaning an exhaust gas flow of a motor vehicle (2) with an internal combustion engine (6), comprising the steps: (S100) Detection of a simulated NOx loading value (BW) indicative of accumulated NOx in the NOx storage catalytic converter (12), (S200), upon the presence of at least one predetermined condition (RgnAb), detecting a progress value (FW) indicative of a portion of a simulated complete regeneration of the NOx storage catalytic converter (12), (S400) stopping the detection of the simulated NOx loading value (BW) indicative of accumulated NOx in the NOx storage catalytic converter (12) when the progress value (FW) indicative of a portion of a simulated complete regeneration a maximum value (MW) indicative of a complete Has reached regeneration and provides a fictitious NOx load value (BW), (S500) generating or updating a histogram data set (HD) using the fictitious NOx loading value (BW) indicative of accumulated NOx in the NOx storage catalytic converter (12), and (S600) Evaluation of the histogram data set (HD) in order to determine a value for a NOx threshold value (SW) indicative of a probability of less than 100% for complete regeneration. Procedure according to Claim 1 , wherein the detection of the progress value (FW) indicative of a portion of a simulated complete regeneration is stopped on the presence of at least one predetermined termination condition (AB), the simulated NOx loading value (BW) indicative of accumulated NOx in the NOx storage catalytic converter (12) according to the regeneration is updated, and the detection of the progress value (FW) indicative of a portion of a simulated complete regeneration is continued on the presence of at least one predetermined condition (RgnAb). Procedure according to Claim 1 or 2 , wherein the updating of the histogram data set (HD) comprises that the values representative of the probabilities for the fictitious NOx load value (BW) and for the respective simulated archived NOx load values (aBW-) are decreased, their associated NOx load are less than or equal to the fictitious NOx loading value (BW). Procedure according to Claim 1 , 2 or 3 , wherein the updating of the histogram data set (HD) comprises that the values representative of the probabilities of the respective simulated archived NOx load values (aBW +) are increased, the associated NOx load of which are greater than the fictitious NOx load value (BW). Computer program product designed to carry out a method according to one of the Claims 1 to 4th . Control unit (10) for operating an exhaust gas aftertreatment device (8) with at least one NOx storage catalytic converter (12) for cleaning an exhaust gas flow of a motor vehicle (2) with an internal combustion engine (6), the control unit (10) being designed to generate a simulated NOx Read in load value (BW) indicative of accumulated NOx in the NOx storage catalytic converter (12), to detect a progress value (FW) indicative of a portion of a simulated complete regeneration of the NOx storage catalytic converter (12) if at least one predetermined condition (RgnAb) is present to stop the detection of the simulated NOx loading value (BW) indicative of accumulated NOx in the NOx storage catalytic converter (12) when the progress value (FW) indicative of a portion of a simulated complete regeneration a maximum value (MW) indicative of a complete regeneration and to provide a fictitious NOx load value (BW), a histogram data set (HD ) using the fictitious NOx loading value (BW) indicative of accumulated NOx in the NOx storage catalytic converter (12) or to update it, and to evaluate the histogram data set (HD) in order to obtain a value for a NOx threshold value (SW) to be determined indicative of a probability less than 100% for a complete regeneration. Control unit (10) Claim 6 , the control unit (10) being designed to stop the detection of the progress value (FW) indicative of a portion of a simulated complete regeneration if at least one predetermined termination condition (AB) is present, the NOx loading value (BW) indicative of accumulated NOx in to update the NOx storage catalytic converter (12) according to the regeneration and to continue reading in the progress value (FW) indicative of a portion of a simulated complete regeneration on the presence of at least one predetermined condition (RgnAb). Control unit (10) Claim 6 or 7th , wherein the control device (10) is designed to update the histogram data set (HD) to decrease the values representative of the probabilities for the fictitious NOx load value (BW) and for the respective simulated archived NOx load values (aBW-) whose assigned NOx load is less than or equal to the fictitious NOx load value (BW). Control unit (10) according to one of the Claims 6 to 8th , wherein the control device (10) is designed to update the histogram data set (HD) to increase the values representative of the probabilities of the respective simulated archived NOx load values (aBW +) whose assigned NOx load is greater than the fictitious NOx- Load value (BW) are. Exhaust aftertreatment device (8) with a control unit (10) according to one of the Claims 6 to 9 . Motor vehicle (2) with an exhaust gas aftertreatment device (8) after Claim 10 .

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