Determination of a NOx concentration downstream of at least one catalyst of an internal combustion engine

Abstract

Method for determining a NOx concentration (r NOx,ds,Stg ) downstream of at least one catalyst (22) of an internal combustion engine (10), wherein the at least one catalyst (22) is arranged in an exhaust gas line (11) and is flowed through by exhaust gas, wherein a catalyst temperature (T Kat ) of the at least one catalyst (22) is determined, wherein a first NOx concentration (r Nox,us ) upstream of the at least one catalyst (22), wherein a first NOx sensor (32) is arranged downstream of the at least one catalyst (22) and a sensor NOx concentration (r NOx,ds,sens ), whereby a model (M) is used to determine a modeled NOx concentration (r Nox,ds,mod ) downstream of the at least one catalyst (22), wherein in a first phase for the at least one catalyst (22) the NOx concentration (r NOx,ds,Stg ) using the modeled NOx concentration (r Nox,ds,mod), wherein after a transition from the first phase to a second phase for the at least one catalyst (22) and depending on the first NOx concentration (NOx us ) and the sensor NOx concentration (r NOx,ds,sens ) the NOx concentration (r NOx,ds,Stg ) from the modeled NOx concentration (r NOx,us,mod ) on the sensor NOx concentration (r NOx,ds,sens ) is switched.

Description

State of the art

[0001] DE 10 2014 201 304 A1 relates to a method for operating a catalyst system intended for reducing nitrogen oxides in exhaust gases of an internal combustion engine, which catalyst system comprises at least one SCR catalyst (150) which is operated with a reactant which can be stored in the SCR catalyst (150) so that a specific reactant fill level is present in the SCR catalyst (150), wherein the metered addition of reactant is carried out on the basis of models (604, 606) with the aid of an NH3 fill level controller (602), modeling errors are compensated with the aid of an NH3 fill level observer (605). Disclosure of the invention

[0002] In a first aspect, the invention relates to a method for determining a NOx concentration downstream of at least one catalyst of an internal combustion engine, wherein the at least one catalyst is arranged in an exhaust system and is flowed through by exhaust gas, wherein a catalyst temperature of the at least one catalyst is continuously determined, wherein a first NOx concentration upstream of the at least one catalyst is determined, wherein a first NOx sensor is arranged downstream of the at least one catalyst and determines a sensor NOx concentration, wherein a modeled NOx concentration downstream of the at least one catalyst is determined by means of a model, wherein in a first phase for the at least one catalyst the NOx concentration is determined by means of the modeled NOx concentration, wherein after a transition from the first phase to a second phase for the at least one catalyst and depending on the first NOx concentration and the sensor NOx concentration, the NOx concentration is switched from the modeled NOx concentration to the sensor NOx concentration.

[0003] Another advantage of this method is its ease of use. It requires no complex steps or manual adjustments, but rather enables automatic and reliable switching from the modeled NOx concentration to the sensor NOx concentration. This simplifies handling and enables efficient monitoring and optimization of NOx emissions in internal combustion engines.

[0004] The method has the particular advantage of enabling a safe and robust switchover from a modeled NOx concentration downstream of a catalyst to a sensor-based NOx concentration. The present invention can prevent the possibility of the total emissions determined during the NOx concentration calculation during the driving cycle being too high if the switchover time from the modeled NOx concentration signal to the measured NOx concentration signal coincides with or precedes the desorption phase of the catalyst. This would otherwise result in the NOx emissions absorbed during the catalyst start-up phase being determined twice.

[0005] This allows for more precise exhaust gas aftertreatment, thus optimizing emissions. The process thus contributes to improving air quality and compliance with emissions regulations. Overall, the process offers a precise and reliable method for determining the NOx concentration downstream of at least one catalyst in an internal combustion engine.

[0006] In an advantageous development, in the first phase, no approval is given for the first NOx sensor downstream of the at least one catalyst, in particular because a valid sensor NOx concentration is not yet available. Approval for the NOx sensor cannot or must not be given if moisture is present on the measuring element or if there is a high probability of moisture. This applies especially during cold start phases for the internal combustion engine.

[0007] In a further embodiment, the first NOx sensor downstream of the at least one catalyst is enabled for measurement operation when a temperature for the first NOx sensor exceeds a release temperature, in particular when a valid sensor NOx concentration is present. The NOx sensor is advantageously enabled for measurement readiness when a minimum temperature for the NOx sensor or its measuring element has been reached.

[0008] In a particular embodiment, the first phase corresponds to an absorption phase for the at least one catalyst, wherein the at least one catalyst stores NOx emissions in this first phase, in particular up to a loading limit.

[0009] The term absorption phase can be understood as a phase in which at least one catalyst absorbs NOx emissions from the exhaust stream. During this phase, the catalyst binds the NOx molecules to its surface and stores them there up to a certain loading limit.

[0010] The term "loading limit" can be understood as the point at which at least one catalyst in the first phase of the NOx emissions absorption phase is saturated and is no longer able to absorb any further NOx emissions. This point is reached when the active surface of the catalyst is completely covered with NOx molecules and cannot absorb any more. The loading limit can vary depending on the type of catalyst and the NOx emissions and is usually determined through experimental testing. Once the loading limit is reached, the catalyst must be regenerated to restore its effectiveness.

[0011] In a further embodiment, the second phase corresponds to a desorption phase for the at least one catalyst, wherein the at least one catalyst releases NOx emissions in this second phase.

[0012] During this desorption phase, the catalyst releases NOx emissions that were stored in the first phase, especially the absorption phase.

[0013] In a particular embodiment, the at least one catalyst absorbs NOx emissions when the catalyst temperature falls below a predeterminable first temperature threshold of the at least one catalyst.

[0014] The first temperature threshold corresponds to a temperature specific to the at least one catalyst up to which the at least one catalyst is capable of absorbing NOx emissions.

[0015] In a further embodiment, the at least one catalyst desorbs stored NOx emissions when the catalyst temperature exceeds a predeterminable first temperature threshold and falls below a second predeterminable temperature threshold of the at least one catalyst.

[0016] The second temperature threshold corresponds to a temperature specific to the at least one catalyst, above which the at least one catalyst desorbs stored NOx emissions or NOx molecules.

[0017] In a particular embodiment, the at least one catalyst converts NOx emissions when the catalyst temperature exceeds a third predeterminable third temperature threshold, in particular a light-off temperature for the at least one catalyst.

[0018] The third temperature threshold corresponds to a light-off temperature specific for at least one catalyst.

[0019] The term light-off temperature can be understood as the temperature at which the catalyst begins to work effectively and convert pollutants such as NOx. This temperature is also known as the activation temperature and is an important indicator of a catalyst's performance. The light-off temperature depends on various factors, such as the composition of the catalyst material, the size and shape of the catalyst, and the type of exhaust gas composition. Typically, the light-off temperature for a catalyst is in the range of 200 to 400 °C. Once the light-off temperature is reached, the catalyst begins to reduce the pollutants in the exhaust gas and minimize emissions.

[0020] In a further embodiment, the switching of the NOx concentration from the modeled NOx concentration to the sensor NOx concentration is carried out when the catalyst temperature has exceeded the second predeterminable temperature threshold and falls below the third predeterminable threshold.

[0021] This is particularly advantageous because in this temperature range, desorption of NOx emissions stored in the first phase has already taken place.

[0022] Therefore, switching to the sensor NOx concentration is already possible in this temperature range.

[0023] Switching is particularly possible if there is an enable for the NOx sensor in the control unit.

[0024] In an advantageous embodiment, the switching of the NOx concentration from the modeled NOx concentration to the sensor NOx concentration is carried out when the sensor NOx concentration falls below the first NOx concentration for a predeterminable time.

[0025] Switching to the sensor NOx concentration is particularly advantageous if the sensor NOx concentration falls below the NOx concentration determined upstream of the at least one catalyst for a predeterminable period of time.

[0026] This is particularly advantageous because a sensor value allows for more precise determination than a model value and / or because mandatory legislation favors the use of sensors.

[0027] In a further embodiment, heat is introduced into the exhaust system in order to exceed at least the second predeterminable temperature threshold and / or the third predeterminable temperature threshold for the catalyst temperature.

[0028] In a special embodiment, when the catalyst temperature reaches the third predeterminable temperature, the NOx concentration is switched from the modeled NOx concentration to the sensor NOx concentration.

[0029] In a further embodiment, the first NOx concentration is determined by means of a NOx concentration model or by means of a second NOx sensor arranged downstream of the internal combustion engine and upstream of the at least one catalyst.

[0030] In a particular embodiment, the at least one catalyst is designed as a zeolitic catalyst.

[0031] In further aspects, the invention relates to a device, in particular a control unit and a computer program, which are configured, in particular programmed, to execute one of the methods. In yet another aspect, the invention relates to a machine-readable storage medium on which the computer program is stored. Short description of the drawings

[0032] The invention is explained in more detail below using an exemplary embodiment illustrated in the figures. They show: Fig. 1 shows a schematic representation of an SCR system with an SCR catalyst of an internal combustion engine, Fig. 2 a) an exemplary measurement of a catalyst temperature T Cat over time t, b) an exemplary measurement of a NOx concentration r NOx,us ; r NOx,ds upstream and downstream of the at least one catalyst with the temperature profile from diagram a). Fig. 3 a schematic flow diagram of an exemplary embodiment of the method according to the invention for estimating the NOx and NH3 concentration downstream of at least one SCR catalyst of an internal combustion engine. Embodiments of the invention

[0033] An internal combustion engine 10 has an SCR system 20 in its exhaust system 11, which Fig. 1. This has a reducing agent dosing unit 21, with which a urea-water solution (AdBlue) can be injected into the exhaust system 11. Ammonia is released from this at the high temperatures of the exhaust gas. Downstream of the reducing agent dosing unit 21 is a first SCR catalyst 22. Additional SCR catalysts can be arranged downstream of the first SCR catalyst 22. A second NOx sensor 31 and a temperature sensor 12 are arranged upstream of the reducing agent dosing unit 21 and downstream of an internal combustion engine 10 in the exhaust system 11. The second NOx sensor 31 measures a NOx concentration value NOx us upstream of the at least one catalyst 22, preferably as a NOx concentration or as a NOx mass flow. A first NOx sensor 32 is arranged downstream of the at least one SCR catalyst 22 and measures a sensor NOx concentration sensor value r NOx,ds,sens, preferably as a NOx concentration or as a NOx mass flow.

[0034] All NOx sensors 31, 32 transmit their signals to an electronic control unit 100. Since the NOx sensors 31, 32 are cross-sensitive to ammonia in addition to nitrogen oxides, their signals are combined signals of nitrogen oxides and ammonia. Reducing agent metering unit 21 also reports the amount of ammonia metered into the exhaust system 11 to the control unit 100.

[0035] Furthermore, model M is stored on the control unit 100, which, depending on the first NOx concentration sensor value NOx1 and the second NOx concentration sensor value NOx2, generates a modeled NOx concentration r NOx,ds,mod downstream of the catalyst 22. Optionally, an exhaust gas temperature of the temperature sensor 12, an exhaust gas mass flow dm exh be used as an input variable for modeling.

[0036] It should be noted that the present Model M cannot represent absorption and desorption of emissions in the catalyst 22, in particular of NOx molecules, or can represent them too inaccurately, so that the Model M cannot be used permanently to determine the NOx concentration downstream of the catalyst 22.

[0037] In the Fig. Figure 2 shows an example measurement for the presented method. The time axis t as the abscissa applies to both diagrams a) and b).

[0038] The upper diagram a) shows an example measurement for the catalyst temperature T Kat of at least one catalyst 22 over time t. Furthermore, a first, a second, and a third temperature threshold TS1; TS2; TS3 are shown.

[0039] As the temperature T increases, it is shown that at a first time t1, the first predeterminable temperature threshold TS1 is reached or exceeded. Furthermore, the catalyst temperature T Kat at a second time t2 the second predeterminable temperature threshold value TS2.

[0040] At a third time t3, the catalyst temperature T Kat the third preset temperature threshold TS3.

[0041] In diagram b) a measurement of the NOx concentration r NOx,us ; r NOx,ds upstream and downstream of the NOx catalyst 22 over time t with increasing catalyst temperature T Kat shown.

[0042] In the following, the first NOx concentration refers to the NOx concentration upstream of the at least one catalyst 22 and the second NOx concentration refers to the NOx concentration downstream of the at least one catalyst 22.

[0043] At the start time t0, the first NOx concentration r NOx,us upstream of the catalyst 22 already a visible NOx concentration r NOx . In contrast, the second NOx concentration r NOx,ds only a visible NOx concentration r NOx , if the catalyst temperature T Kat the first preset temperature threshold TS1 is reached or exceeded.

[0044] This region is referred to as the first phase or absorption phase for the catalyst 22, whereby the catalyst 22 initially stores nitrogen oxide molecules up to a loading limit during this phase. Thus, nitrogen oxides are already measurable upstream of the catalyst 22 at the start of the internal combustion engine 10 at time t0, whereas no nitrogen oxides are measurable downstream of the catalyst 22.

[0045] When the first temperature threshold TS1 is reached, the second NOx concentration NOx us,sensincreases sharply, exceeds the first NOx concentration, reaches a maximum and decreases, then settles at a similar NOx concentration level to that of the first NOx concentration r NOX,us to commute.

[0046] When the first predeterminable temperature threshold TS1 is reached or exceeded, a second phase begins, in particular a desorption phase for the catalyst, whereby the catalyst desorbs the NOx molecules stored in the first phase, in particular abruptly. The first NOx concentration r NOX,us remains almost unchanged in this time range between the first time t1 and the second time t2.

[0047] In the time range between the second time t2 and the third time t3, the first and second NOx concentrations r NOx,us ; r NOx,ds,sens at a similar NOx concentration level. The catalyst temperature T Kat continues to rise during this period.

[0048] When the third temperature threshold TS3 is reached by the catalyst temperature T Kat the second NOx concentration r NOx,ds,sens slowly until no NOx concentration r Nox are no longer available.

[0049] The first NOx concentration r NOx,us remains unchanged and then increases slightly.

[0050] When the third predeterminable temperature threshold TS3 is reached, the light-off temperature for the at least one catalyst 22 is reached, so that it has reached its convertible temperature range and can convert nitrogen oxides. With increasing catalyst temperature T Kat the conversion capacity of at least one catalyst 22 increases visibly. Thus, the second NOx concentration r NOx,ds,sens with increasing catalyst temperature T Kat from the third time t3.

[0051] In the Fig. 3 is the exemplary sequence of the method for determining a NOx concentration r NOx,ds,Stg downstream of at least one catalyst 22 of an internal combustion engine 10, is shown using a flow chart.

[0052] The present example is described starting from a cold start for the internal combustion engine 10, wherein there is still no release for the first NOx sensor 32.

[0053] In a first step 200, a catalyst temperature T Kat of at least one catalyst 22 is determined and stored by a control unit 100.

[0054] If the catalyst temperature T Kat a predeterminable temperature, which in particular corresponds to a predeterminable temperature for the at least one catalyst 22 and the control unit 100 has already released the operation of the first NOx sensor NOx Ds ; 32, the procedure will be terminated or restarted.

[0055] If the catalyst temperature falls below T Kat the predeterminable temperature, the process continues in a step 210.

[0056] In a step 210, the catalyst temperature T Kat continuously determined and stored in the control unit 100.

[0057] Due to the heat input via the exhaust gas, at least one catalyst 22 heats up and is controlled overall toward a light-off temperature to ensure the conversion capability of the catalyst 22. The sensors installed in the exhaust system are also heated by the heat input via the exhaust gas.

[0058] In this case, the at least one catalyst 22 is provided with an exhaust gas mass flow dm exh flows through.

[0059] The first NOx sensor 32 is not directly ready for measurement during a cold start or below a component-specific minimum temperature and must first exceed a minimum temperature. In advantageous embodiments, the first NOx sensor 32 can be designed with an additional heater for the measuring element, wherein the heating element cannot be directly activated due to possible moisture on the measuring element, as this would otherwise result in the destruction or a shortened operating period of the first NOx sensor 32. Therefore, a function is calculated in the control unit 100 which determines the temperature for the first NOx sensor 32, in particular from the ambient temperature and the exhaust gas temperature, and carries out additional heating and the release for the measurement readiness of the first NOx sensor 32.

[0060] The first NOx sensor 32 downstream of the at least one catalyst 22 heats up later than the components arranged upstream of the at least one catalyst 22 and downstream of the internal combustion engine 10.

[0061] In a first phase for the at least one catalyst 22, in particular a first absorption phase for the catalyst 22, the catalyst 22 increasingly stores nitrogen oxides up to a loading limit. This results in temporary storage effects of NOx molecules until they are released with increasing catalyst temperature T Kat be released again.

[0062] In this first phase, for the internal calculation of the NOx concentration r NOx,ds,Stg a modeled NOx concentration r NOx,ds,mod used because the first NOx sensor 32 does not yet have a measurement release due to the component temperature being too low.

[0063] The determination of the modeled NOx concentration r NOx,ds,modis dependent on the first NOx concentration r NOx,us upstream of the catalyst 22, an exhaust gas mass flow dm exh , an exhaust gas temperature T exh , a speed n eng , an optional injection quantity of ammonia and optionally an exhaust gas recirculation rate.

[0064] The method then continues in a step 220.

[0065] In a step 220, the catalyst temperature T Kat determined and monitored by control unit 100. Upon reaching a first temperature threshold TS1, the at least one catalyst 22 transitions from an absorption phase to a desorption phase. In the desorption phase, the stored NOx molecules are released again, resulting in an overshoot in the NOx concentration downstream of the at least one catalyst 22.

[0066] When the predeterminable first temperature threshold TS1 is exceeded, the catalyst 22 enters a second phase, in particular a desorption phase, and releases stored NOx molecules again, see Fig. 2.

[0067] If at this point in time or upon reaching this desorption phase the sensor NOx concentration r NOx,ds,sens for the internal determination of the NOx concentration r NOx,ds,Stg would result in a calculation error when determining the internally used NOx concentration r NOx,ds,Stg Thus, even if the control unit 100 has already given the go-ahead for the first NOx sensor 32 to be ready for measurement, the modeled NOx concentration r NOx,ds,mod for the NOx concentration r NOx,ds,Stg used.

[0068] A granted measurement readiness for the NOx sensor 32 should be understood in particular to mean that a valid sensor NOx concentration r nox,ds,sens for the first NOX sensor 32 for the control unit 100. If the catalyst temperature T Kat a second predeterminable temperature threshold TS2, the control unit 100 can switch from the modeled NOx concentration r NOx,ds,mod downstream of the catalyst 22 to the sensor NOx concentration T Nox,ds,sens for the NOx concentration r NOx,ds,Stg When the catalyst temperature T exceeds the second preset temperature threshold TS2 Kat the desorption phase for the catalyst 22 is completed, or a complete desorption of NOx molecules stored in the absorption phase has taken place.

[0069] In a preferred embodiment, a temporal debouncing for exceeding the second predeterminable temperature threshold TS2 by the catalyst temperature T Kat by the control unit 100. A switch from the modeled NOx concentration r NOx,ds,mod on the sensor NOx concentration r NOx,ds,sens for the NOx concentration r NOx,ds,Stg then further depends on whether there is already an approval for the measurement readiness of the first NOx sensor 32 downstream of the at least one catalytic converter 22 in the control unit 100.

[0070] To this end, control unit 100 checks, in particular, whether the temperature for the first NOx sensor 32 downstream of the at least one catalytic converter 22 has already reached or exceeded the predeterminable minimum temperature. If the temperature for the first NOx sensor 32 exceeds the predeterminable minimum temperature, the release is given.

[0071] Thus, a switch from the modeled NOx concentration r NOx,ds,mod on the sensor NOx concentration r Nox,ds,sens for the NOx concentration r NOx,ds,Stg be performed.

[0072] In an alternative embodiment, the switchover is carried out from the modeled NOx concentration r NOx,ds,mod on the sensor NOx concentration r NOx,ds,mod for the determined NOx concentration r NOx,ds,Stg , if the sensor NOx concentration r NOx,ds,sens the first NOx concentration r NOx,us for a specified period of time.

[0073] In a preferred embodiment, the switching takes place from the modeled NOx concentration r NOx,ds,mod on the sensor NOx concentration r NOx,ds,mod at the latest when the catalyst temperature T Kat exceeds the predeterminable third temperature threshold TS3, in particular the light-off temperature of the at least one catalyst 22.

[0074] The method can then be started again from the beginning in step 200 or continued in a step 230.

[0075] In a step 230, the determined NOx concentration r NOx,ds,Stg fed to an emissions control system for the internal combustion engine 100. For example, to determine the injection quantity for a selective catalytic exhaust aftertreatment system.

[0076] The process can then be terminated or started again in step 200. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2014 201 304 A1

[0001]

Claims

[1] Method for determining a NOx concentration (r NOx,ds,Stg ) downstream of at least one catalyst (22) of an internal combustion engine (10), wherein the at least one catalyst (22) is arranged in an exhaust gas line (11) and is flowed through by exhaust gas, where a catalyst temperature (T Kat ) of the at least one catalyst (22) is determined, where a first NOx concentration (r NOx,us ) upstream of the at least one catalyst (22), wherein a first NOx sensor (32) is arranged downstream of the at least one catalyst (22) and a sensor NOx concentration (r NOx,ds,sens ) determined, where a model (M) is used to determine a modeled NOx concentration (r Nox,ds,mod ) downstream of the at least one catalyst (22), characterized bythat in a first phase for the at least one catalyst (22) the NOx concentration (r NOx,ds,Stg ) using the modeled NOx concentration (r Nox,ds,mod ) is determined, wherein after a transition from the first phase to a second phase for the at least one catalyst (22) and depending on the first NOx concentration (NOx us ) and the sensor NOx concentration (r NOx,ds,sens ) the NOx concentration (r Nox,ds,Stg ) from the modeled NOx concentration (r NOx,us,mod ) on the sensor NOx concentration (r NOx,ds,sens ) is switched. [2] Method according to claim 1, characterized by that in the first phase for the at least one catalyst (22) there is no release for a measuring operation of the first NOx sensor (32) downstream of the at least one catalyst (22), in particular that no valid sensor NOx concentration (r NOx,ds,sens ) is present. [3] Method according to claim 2, characterized bythat a release for the measuring operation of the first NOx sensor (32) downstream of the at least one catalyst (22) is granted when a temperature (T Nox,ds ) for the first NOx sensor (32) a release temperature (T S,NOx,ds ), in particular that a valid sensor NOx concentration (r NOx,ds,sens ) is present. [4] Method according to claim 1, characterized by that the first phase corresponds to an absorption phase for the at least one catalyst (22), wherein the at least one catalyst (22) stores NOx emissions in this first phase, in particular up to a loading limit. [5] Method according to claim 1, characterized by that the second phase corresponds to a desorption phase for the at least one catalyst (22), wherein the at least one catalyst (22) releases NOx emissions in this second phase. [6] Method according to claim 4, characterized bythat the at least one catalyst (22) absorbs NOx emissions when the catalyst temperature (T Kat ) a predeterminable first temperature threshold (TS1) of the at least one catalyst (22) falls below [7] Method according to claim 4, characterized by that the at least one catalyst (22) desorbs stored NOx emissions, in particular stored NOx emissions in the first phase, when the catalyst temperature (T Kat ) exceeds a predeterminable first temperature threshold (TS1) and falls below a second predeterminable temperature threshold (TS2) of the at least one catalyst (22). [8] Method according to one of the preceding claims, characterized by that the at least one catalyst (22) converts NOx emissions when the catalyst temperature (T Kat ) exceeds a third predeterminable third temperature threshold (TS3), in particular a light-off temperature for the at least one catalyst (22). [9] Method according to one of the preceding claims, characterized by that the switching of the NOx concentration (r NOx,ds,Stg ) from the modeled NOx concentration (r NOx,us,mod ) on the sensor NOx concentration (r NOx,ds,sens ) is carried out when the catalyst temperature (T Kat ) has exceeded the second preset temperature threshold (TS2) and falls below the third preset threshold (TS3). [10] Method according to claim 9, characterized by that the switching of the NOx concentration (r NOx,ds,Stg ) from the modeled NOx concentration (r NOx,us,mod ) on the sensor NOx concentration (r NOx,ds,sens ) is performed when the sensor NOx concentration (r NOx,ds,sens ) the first NOx concentration (r NOx,us ) for a specified time (t s ) falls below. [11] Method according to one of the preceding claims, characterized bythat a heat input is introduced into the exhaust system in order to at least reach the second predeterminable temperature threshold (TS2) and / or the third predeterminable temperature threshold (TS3) for the catalyst temperature (T Kat ) to be exceeded. [12] Method according to claim 1, characterized by that when the third preset temperature (TS3) is reached by the catalyst temperature (T Kat ) the NOx concentration (r NOx,ds,Stg ) from the modeled NOx concentration (r NOx,us,mod ) on the sensor NOx concentration (r NOx,sens ) is switched. [13] Method according to claim 1, characterized by that the first NOx concentration (r NOx,us ) is determined by means of a NOx concentration model or by means of a second NOx sensor (31) arranged downstream of the internal combustion engine (10) and upstream of the at least one catalyst (22). [14] Method according to claim 1, characterized bythat the at least one catalyst (22) is designed as a zeolitic catalyst (22). [15] Computer program which is designed to carry out a method according to one of claims 1 to 14. [16] An electronic storage medium comprising a computer program according to claim 15. [17] Device, in particular control device (100), which is designed to carry out a method according to one of claims 1 to 14.

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