CN111927607B

CN111927607B - Monitoring the status of catalytic converters for reducing nitrogen oxides

Info

Publication number: CN111927607B
Application number: CN202010396394.2A
Authority: CN
Inventors: A.巴斯托雷亚勒; T.菲斯特
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-05-13
Filing date: 2020-05-12
Publication date: 2025-02-25
Anticipated expiration: 2040-05-12
Also published as: CN111927607A; DE102019206873A1

Abstract

The invention relates to a method for monitoring the state of a catalytic converter (12, 13) for reducing nitrogen oxides, the method comprising: calculating (31) at least one modeled exhaust gas measurement value for a predetermined state of a model catalytic converter; detecting (30) at least one corresponding measured exhaust gas measurement value downstream of a first catalytic converter (12, 13); and determining whether the catalytic converter (12, 13) is intact or damaged based on the at least one modeled exhaust gas measurement value and the at least one measured exhaust gas measurement value.

Description

Monitoring the status of a catalytic converter for reducing nitrogen oxides

Technical Field

The invention relates to a method for monitoring the state of a catalytic converter for reducing nitrogen oxides, a computing unit for carrying out the method and a computer program for carrying out the method.

Background

In the field of vehicles, in order to reduce nitrogen oxides (NO _x) in the exhaust gas, in particular, SCR catalytic purifiers (SELECTIVE CATALYTIC Reduction) can be used. Here, the nitrogen monoxide NO and the nitrogen dioxide NO ₂ are collectively referred to as nitrogen oxides. The basic principle of an SCR catalytic cleaner is that nitrogen oxide molecules are reduced to elemental nitrogen on the surface of the catalytic cleaner in the presence of ammonia (NH ₃) as a reducing agent. The reductant is typically provided in the form of an aqueous urea solution (HWL) that releases NH ₃, which is provided by a controlled dosing device upstream of the SCR catalytic cleaner.

Currently, the precondition for using SCR catalytic purifiers is also the use of at least one nitrogen oxide sensor. However, two nitrogen oxide sensors are often used, one before and one after the SCR catalytic cleaner. In many markets, regulations for vehicle Diagnostics (OBD, on board-Diagnostics) require very accurate monitoring of the system and in particular the SCR catalytic cleaner. If the catalytic converter ages and is thereby no longer able to convert nitrogen oxides sufficiently, the corresponding warning light must be activated and the catalytic converter replaced reliably before the required limit value is exceeded.

Aging and/or damage of the SCR catalytic converter can be monitored by means of suitable sensors in front of and behind the catalytic converter by means of an evaluation of nitrogen oxides. For this purpose, in passive diagnostic methods, the nitrogen oxide concentration, the nitrogen oxide mass flow or the nitrogen oxide conversion is generally measured in a phase in which it is possible to sufficiently distinguish an undamaged SCR catalytic converter from a damaged SCR catalytic converter. The diagnostic conditions are generally selected such that the nitrogen oxide conversion of the undamaged SCR catalytic converter is high and the nitrogen oxide conversion of the damaged catalytic converter (boundary part) to be detected is as low as possible. With this identification, the SCR catalytic converter or its status that is not yet damaged is also referred to as WPA (worstperformingacceptable (acceptable worst performance)) catalytic converter, while the damaged status is referred to as BPU (best performing unacceptable (unacceptable best performance)). The greater the distinction between these states under the current conditions, the more robust the diagnostic method based on.

Since conventional nitrogen oxide sensors are cross-sensitive to ammonia, i.e. show a summation signal of NO _x and NH ₃, so-called ammonia slip after the SCR catalytic cleaner can lead to a significant decrease in efficiency, since ammonia also leads to an increased sensor signal, which can be misinterpreted as an increase in nitrogen oxides. Thus, on the one hand, the BPU catalytic converter can be more easily recognized, since it appears to be worse than in practice, and on the other hand, the WPA component also appears to be worse erroneously, making it difficult to distinguish between the states. Thus, these methods generally have the objective of selecting the conditions such that no ammonia leakage occurs.

If the accuracy of such a passive method is not sufficient, an active method can be applied which determines the ammonia storage capacity of the SCR catalytic converter by means of an intervention on the dosage of urea solution. This ammonia storage capacity is very well correlated with thermal or chemical damage to the SCR catalytic converter.

Disclosure of Invention

According to the invention, a method for monitoring the state of a catalytic converter is proposed, as well as a computing unit for carrying out the method and a computer program for carrying out the method. Advantageous embodiments are the subject matter of the following description.

The invention makes use of the measure that the measured value detected downstream of the catalytic converter is compared with the exhaust gas measured value modeled for a predefined state of the model catalytic converter or a value derived or filtered therefrom, respectively, for example an integral or a sum, and that it is determined on the basis of the comparison whether the catalytic converter is undamaged or damaged.

By using the model as a comparison, all operating conditions can be physically mapped and thereby considered in the diagnosis. Instead of the previous determination of the efficiency and emissions (Ableitung) of the catalytic converter, this direct determination of the aging of the catalytic converter can thus be achieved with a better differentiation between catalytic converter damage and damage or malfunctions of other components.

The at least one measured exhaust gas measurement and the at least one modeled exhaust gas measurement can each be in particular an nox measurement, an ammonia measurement or a combined nox-ammonia measurement, and can each be used to indicate the concentration or the mass flow of an exhaust gas component (such as the nitrogen oxides or ammonia mentioned). For this purpose, no structural changes are required with respect to conventional exhaust gas lines, and common sensors can be used. In particular, the measured exhaust gas value can be detected by means of a nitrogen oxide sensor having a cross sensitivity to ammonia. Here, the cross sensitivity is advantageously incorporated into the diagnostic method by taking into account two aging mechanisms of the catalytic converter—lower storage capacity for ammonia and poorer conversion of nitrogen oxides in terms of quantity.

Thereby, active intervention on dosing, which affects efficiency and emissions, can be avoided. In addition, the undamaged catalytic converter can be more accurately distinguished from the damaged catalytic converter, so that the robustness and resolution accuracy of diagnosis are improved.

Preferably, the determination of whether the catalytic converter is undamaged or damaged based on the at least one modeled exhaust gas measurement and the at least one measured exhaust gas measurement includes differencing the at least one measured exhaust gas measurement and the at least one modeled exhaust gas measurement, integrating the plurality of differences over a predetermined period of time, comparing the integrated value to a threshold value, and determining whether the catalytic converter is undamaged or damaged based on the comparison. It is readily understood that integrating values will be implemented in practice as a summation. In this embodiment, it can be inferred very easily from the sign of the integral value whether the catalytic converter is working better or worse than the model. It is also possible to first integrate the model values and the measured values separately and then to make the difference.

According to one embodiment, each difference value can also be multiplied by a weighting factor before integrating, wherein the weighting factor is determined on the basis of predefined operating conditions of the catalytic converter. In this way, phases of high accuracy of modeling and/or measurement may affect diagnosis more, while effects of values that may not be precisely determined or modeled may be limited.

Such operating conditions for determining the weighting factor may include, for example, one or more of the following operating conditions, tolerance characteristics of the ammonia level of the catalytic converter, temperature gradient of the catalytic converter, permitted conditions of the sensors used, exhaust gas mass flow, nitrogen oxide mass flow.

Furthermore, according to one embodiment, the grant condition may be further checked before integrating using the difference value, and the integration using the difference value to which the grant condition belongs may be performed only if the grant condition is satisfied. Thereby, the whole diagnosis is not forced to be discarded, and it is still ensured that the value of the evidence deficiency has no influence on the evaluation. In this way, the evaluation frequency and the resolution accuracy are further improved. The permitting conditions may for example comprise a maximum ammonia leakage after modeling behind the catalytic converter and/or a maximum temperature gradient in the catalytic converter, since for example the emission of ammonia at high temperatures may lead to a distortion of the evaluation or a high temperature gradient due to a change in the course of the reaction may lead to modeling difficulties.

The calculation of the at least one modeled exhaust gas measurement value can be carried out, for example, on the basis of a reaction dynamics model or a data-based model (that is to say a complex characteristic model). Well-known models are also known from the literature, for example, "Unsteady analysis of NO Reduction over Selective Catalyst Reduction–De-NOxMonolith Catalysts",E Tronconi,A.Cavanna,P.Forzatti,Ind.Eng.Chem.Res 1998, 37, pages 2341-2349. These models can be implemented in modern motor vehicle (Kfz) control devices and depict not only NO _x conversion but also NH ₃ slip of the SCR catalytic cleaner.

The computing unit according to the invention, for example a control device of a motor vehicle, is designed in particular in a program-technology manner for carrying out the method according to the invention.

In particular, when the control device to be implemented is also used for other tasks and is thus always present, an implementation of the method according to the invention in the form of a computer program or a computer program product having a program code for executing all method steps is also advantageous, since this results in particularly low costs. In particular, data carriers suitable for providing the computer program are magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs and the like. It is also possible to download the program via a computer network (internet, intranet, etc.).

Further advantages and embodiments of the invention emerge from the description and the attached drawings.

The invention is schematically illustrated in the drawings and is described below with reference to the drawings according to embodiments.

Drawings

FIG. 1 schematically illustrates an exemplary catalytic purification system suitable for embodiments of the present invention;

FIG. 2 depicts the principle of catalytic cleaner diagnostics according to an embodiment of the invention;

FIG. 3 shows an exemplary graph of integrated differences for an undamaged (WPA) catalytic converter and a damaged (BPU) catalytic converter in accordance with one embodiment of the invention

Fig. 4 shows exemplary method steps according to an embodiment of the invention.

Detailed Description

Fig. 1 shows an exemplary system in which embodiments of the present invention may be applied. In this case, one or more catalytic converter elements are arranged in the exhaust gas line, into which an exhaust gas stream 10 is introduced from the internal combustion engine for exhaust gas treatment. In this figure, a diesel oxidation catalytic cleaner (DOC) 11 is first shown, to which two SCR catalytic cleaner elements 12 and 13 are connected downstream, which may for example also comprise a particulate filter with SCR Coating (SCRF) 12. In front of each SCR catalytic converter element 12, 13, a dosing module 14 and 15 is arranged for dosing an aqueous urea solution (HWL) into the system. Each dosing module 14, 15 is controlled by a control unit 19, wherein preferably all modules of the same unit, e.g. an engine control device, are controlled. A plurality of sensors 16, 17 and 18 are also installed, which can measure exhaust gas values at different locations of the system.

In particular, a nitrogen oxide sensor and/or an ammonia gas sensor can be installed upstream and/or downstream of each catalytic converter element 11, 12/13, which nitrogen oxide sensor and/or ammonia gas sensor measures the concentration and/or the conversion and/or the mass flow of the respective component in the exhaust gas flow. Here, a NO _x sensor may be involved, which NO _x sensor is also cross-sensitive to ammonia (NH ₃), or a multi-gas sensor may be involved, which may output the values of NO _x and NH ₃ separately. Likewise, individual sensors for NO _x and NH ₃ can also be arranged at the respective locations 16, 17, 18 in the exhaust gas flow. The measured values of all sensors are forwarded to the control unit 19 for processing. Of course, other sensors not shown here, such as temperature sensors, oxygen sensors, air mass flow meters, and other sensors at different locations of the system, may also be used.

In order to now identify the state of the SCR catalytic converter 12, 13 in such a system or the like, i.e. to be able to carry out a diagnosis concerning damage or aging of the catalytic converter, according to one embodiment of the invention the measured exhaust gas value is compared with the modeled exhaust gas value and integrated over a defined period of time.

In this case, a theoretical catalytic converter model can be used which models the expected values of nitrogen oxides and ammonia in the catalytic converter or in the exhaust gas stream downstream of the catalytic converter in the specified predefined state, for example in the as yet undamaged WPA state (worst performing acceptable) of the catalytic converter. The model may be, for example, a reaction kinetics model or a data-based model, which are substantially known in the art. As variables relevant for modeling and measurement, the concentration of the exhaust gas components, i.e. in particular the concentration of NH ₃ and NO _x, can be used, as well as alternatively the mass flow of these variables. It is also possible to model the exhaust gas values using a model based on the integrated characteristic curve.

FIG. 2 depicts the principle of catalytic converter diagnostics for a catalytic converter according to an embodiment of the invention. The modeled NO _x concentration behind the relevant catalytic cleaner is calculated according to the appropriate model 31 of the SCR catalytic cleanerModeled NH ₃ concentrationFor this purpose, the ammonia concentration upstream of the catalytic converter, i.e.As an input quantity influence model 31, the ammonia concentration can be determined on the basis of actuation of the respective dosing module, and the nitrogen oxide concentration upstream of the catalytic converterAs an input quantity influence model 31, the nitrogen oxide concentration can either be measured by a corresponding sensor upstream of the catalytic converter or can be determined on the basis of the model as a function of the operating state of the engine.

The calculated sum signal 32 of the two modeled parameters

Can be compared with the signal measured at the NO _x sensor after the catalytic converter 30.

In this embodiment, the measured sensor signal is the value of the NO _x sensor, which NO _x sensor is cross-sensitive to NH ₃ and is arranged downstream after the catalytic converter 30, wherein both components give rise to a signal. I.e. in practice, the measured signal indicates a combined value of the respective concentrations of NO _x and NH ₃ at this point, which combined value essentially corresponds to the sum of the concentrations present after the catalytic converter 30,

Then, to compare the measured value with the modeled value, the difference 34 between the two summed values may be found,

That is, the summation value 32 modeled for the catalytic converter output is subtracted from the summation values measured for NO _x and NH ₃ after the catalytic converter.

The difference obtained hereThe integration is performed for a predetermined evaluation period, for example by means of an integrator 36, and the obtained integration is compared with a threshold value. The comparison is then evaluated by a diagnostic system 38, such as OBD diagnostic software.

If a WPA catalytic converter is used as model 31, it is applicable in the case of a measured catalytic converter which is still undamaged, i.e. a WPA catalytic converter

That is, the difference between the model value and the measured value fluctuates around a zero value, and the resulting integral is thereby also close to 0. And in the case of aged or damaged catalytic purifiers (BPU)

That is to say that the measured signal is higher than the modeled value, i.e. the integral rises above the threshold value. It may thereby be provided that the catalytic converter 30 is classified as damaged in respect of the OBD diagnosis 38 once this threshold value is exceeded in the comparison of the integrated value with the threshold value, whereas the catalytic converter 30 is classified as still undamaged as long as the obtained signal is below this threshold value.

The difference between the measured value and the modeled value, which is increased when the catalytic converter is damaged (and thus also includes an integral above the threshold value), can be explained essentially on the basis of the two effects that approximately half relates to ammonia (NH ₃) which can NO longer be stored sufficiently in the damaged catalytic converter compared to WPA catalytic converter, and the other half comes from nitrogen oxides NO _x which can NO longer be converted sufficiently by the damaged catalytic converter and thus also appear increasingly after the catalytic converter. Thus, both major aging effects, i.e. reduced NH ₃ storage capacity and lower NO _x conversion, are taken into account in a single monitored parameter for diagnosing the catalytic converter.

Instead of WPA catalytic converter, for exhaust gas values after catalytic converterAndAlso a so-called middle layer catalytic converter between WPA and BPU state can be considered for the modeling 31 of (c). In this case, the integrator 36 will operate positively in the case of a measured BPU catalytic cleaner and negatively in the case of WPA.

Fig. 3 shows an exemplary statistical evaluation of integrated values, that is to say integrated differences for diagnostic measurements on BPU and WPA components, and modeling of such an intermediate-layer catalytic converter, wherein the integrated values are plotted with respect to time ts. Here, the point above the graph (greater than 0) is the integrated value in the case of the catalytic converter being damaged (BPU), and the value below (less than 0) indicates the integrated value in the case of the catalytic converter being undamaged (WPA).

For example, based on the NO _x integral, a standardized time period can be used as an evaluation time point or length of the individual monitoring phases for diagnosis, so that the diagnosis is evaluated after the NO _x quantity reaches, for example, 2g, respectively.

The accuracy of such diagnostics strongly depends on the accuracy of the modeling used for the catalytic converter. In order to make this influence the diagnosis, weighting factors can be applied to the differences between the measured and modeled values, which differences may vary depending on the operating parameters. These weighting factors are determined separately for each round or for each difference and multiplied by the difference. Thus, phases with expected high model accuracy can be considered to a greater extent, while phases with expected lower accuracy only conditionally or do not affect the diagnosis at all.

For example, general operating conditions, such as the grant to the NO _x sensor and dosing module of the aqueous urea solution, may be used as these weighted conditions. Furthermore, optionally, but for example, the catalytic converter temperature, the exhaust gas mass flow and the NO _x mass flow upstream of the catalytic converter can also be used singly or in combination for limiting.

For all such conditions it is possible in the limit to temporarily deactivate the integrator and thus "freeze" the diagnosis, so that certain phases of modeling inaccuracy do not affect the diagnosis at all and the diagnosis is then resumed in part.

It is equally reasonable and possible to consider the temperature gradient of the catalytic converter for weighting. In the case of high temperature gradients, competition occurs between the NO _x reaction and NH ₃ absorption in the SCR catalytic cleaner, which makes modeling difficult. To take this into account, the current temperature gradient may be compared to a threshold value. If the threshold is exceeded within a certain time, the integrator may be reset to a previously stored value, which corresponds, for example, to the value when the threshold of the temperature gradient is exceeded for the first time. In this way, imprecise phases are not taken into account in the case that the diagnosis is not completely prevented with each brief increase in the temperature gradient.

For other of the mentioned grant conditions, a corresponding interruption of the diagnosis can in principle also be made in a similar manner, wherein the integrator either continues to run after the interruption or is reset to a previously determined previous value.

If NH ₃ is emitted from the catalytic converter due to an increase in temperature, there is a further limitation on the diagnosability of the catalytic converter. This process may result in ammonia slip in the case of an undamaged catalytic converter (WPA) being greater than in the case of a damaged catalytic converter (BPU) in which less NH ₃ has been stored. The measured combined sensor value downstream of the catalytic converter may thus be greater in the case of an undamaged catalytic converter than in the case of a damaged catalytic converter. According to the described diagnostic method, the integral will thus rise and the measured signal will be mistakenly regarded as an indicator of a reduced storage capacity, so that this may lead to a (false) diagnosis of a damaged catalytic converter. To prevent this, the ammonia leakage of the catalytic converter may be modeled for a model of the WPA catalytic converter taking into account temperature. If the modeled NH ₃ slip is above the threshold, the diagnosis or integration of the difference may be correspondingly re-stopped. Alternatively, the modeled NH ₃ signal for WPA states may be compared to the modeled NH ₃ signal for BPU states. If the modeled WPA value is higher than the modeled BPU value, the approval of the diagnosis based thereon is not reasonable and may be re-correspondingly frozen (in the case of using the value stored before the temperature rise) or discarded.

Furthermore, the accuracy of the diagnosis or modeling used may also depend on the accuracy of the modeled NH ₃ level of the catalytic converter. If it is expected that the modeled NH ₃ level cannot be determined with sufficient accuracy in one case, then the diagnosis can be throttled or stopped again correspondingly in these cases. For this purpose, for example, two different additional catalytic converter models can be modeled, wherein the first additional model is based on tolerance characteristics of the fill level, which lead to a maximum NH ₃ fill level, and the second additional model is based on tolerance characteristics, which lead to a minimum NH ₃ fill level. From the absolute or relative difference of the two model values, a trust factor can be determined, which corresponds to the current tolerance characteristic with respect to the NH ₃ level. The difference between the modeled and measured exhaust gas values may then be multiplied by the trust factor in order to achieve a throttling or further weighting of the diagnostic method with respect to the accuracy of the NH ₃ level.

Fig. 4 shows a flow chart of method steps of an exemplary embodiment of the invention. It is not necessary here to use all the illustrated steps in the method according to the invention, but other steps or interventions, which are not depicted here, can likewise be carried out.

After starting the diagnostic part (step 100), it is checked in step 102 whether the approval conditions for the diagnosis are met, i.e. whether, as described above, for example, approval conditions for the sensor are present, or whether the temperature gradient is below a certain threshold as described. If this is not the case, the diagnosis is continued or carried out when the re-check of these grant conditions is successful.

Next, in step 104, a trust factor is calculated for the current value difference. Also, other weighting factors may be determined in this step, which are applied to the corresponding differences, for example, to throttle the potential impact. Here, certain conditions may also be used not only for checking alignment approval but also for weighting, or different conditions and effects may be involved.

In step 106, the integrator that integrates the difference between the model and the measured value and the catalytic converter model used are updated based on the previous steps.

In step 108, it is checked whether the predefined monitoring period has ended. If not, the diagnostic process continues in that the loop is traversed again from the beginning (step 100) and the conditions and weighting values are checked again correspondingly and applied to the differences to be integrated, and the integrator is updated again with these values (step 106).

If it is ascertained in step 108 that the monitoring period ends, i.e., that a predefined period of time expires or a predefined criterion for determining the monitoring period is met, for example, the monitoring phase ends and the obtained integrator value is now compared with a threshold value in step 110. If the integrator value exceeds the determined predetermined threshold value, it can be concluded that the diagnosed catalytic converter is damaged (step 112), and if the threshold value is not exceeded, the reason is that the catalytic converter is not damaged (step 114). The condition of the threshold depends on the modeling used.

A further monitoring phase can then be introduced, which correspondingly provides a new integrator value for comparison with the threshold value.

It is also possible to first evaluate a plurality of such integrator values and then to infer whether the catalytic converter is undamaged or damaged and that the diagnostic system (e.g. OBD) is causing a corresponding alarm, for which purpose, for example, a minimum number of results may be specified that must be successively or discontinuously higher than the threshold value. As already seen in fig. 3, the precise integrated value, although possibly differing in value for a determined catalytic converter state, is generally within a narrow range and above or below a defined threshold value, enabling clear and robust resolvable of WPA and BPU states.

It will be readily appreciated that the factors and conditions described with respect to throttling or weighting the diagnosis or with respect to stopping, discarding or freezing the diagnosis may be used alone or in combination with each other. The order in which certain conditions are checked may or may not be as described herein, and certain steps may be omitted, depending on the implementation.

In another embodiment it is also possible to replace the NO _x sensor which is cross-sensitive to NH ₃, for example using a so-called multi-gas sensor which is able to output separate signals of NO _x and NH ₃. It is also conceivable to use sensors without or with negligible cross sensitivity in the case of the method according to the above embodiment, which sensors can thus essentially individually output the mass flow or concentration of the exhaust gas component. In these cases, the method steps according to the invention can also be applied to the respective single signals of NO _x and/or NH ₃, namely the modeling of the values, the differentiation from measured values and model values, and the subsequent integration of the obtained differences and the checking of the threshold values for these integrated values.

It is also possible in the case of the described method to monitor only a single catalytic converter or also a system of a plurality of catalytic converters one after the other, as is shown for example in fig. 1. In this case, in a system of several catalytic converters, the difference and the sum can be carried out individually after each catalytic converter, or a combined model of several catalytic converters under consideration can be used, so that only the exhaust gas measured values at the sensors downstream of the last catalytic converter of these catalytic converters under consideration are used as measured values. In principle, the invention can be used in all exhaust systems with SCR catalytic converters and metering units.

Preferably, the described method steps and calculations are implemented in one or more control units. The same control unit, preferably an engine control device, can be used for all steps, sensor data and control processes.

These steps can be implemented electronically or preferably in software in a corresponding control unit, such as a processor or microcontroller, so that it is possible in a simple manner to equip the control unit with the diagnostic system according to the invention as long as a corresponding interface to the sensor is present. The software modules on the control unit can also be combined with other corresponding hardware elements, such as microcontrollers and FPGAs, in order to implement certain parts of the embodiments according to the invention. The connection of a plurality of control units is likewise possible.

Claims

1. A method for monitoring the status of a catalytic converter (12, 13) for reducing nitrogen oxides, the method comprising:

Calculating (31) at least one modeled exhaust gas measurement value for a predetermined state of a model catalytic converter;

detecting (30) at least one corresponding measured exhaust gas measurement value after the catalytic converter (12, 13); and

determining whether the catalytic converter (12, 13) is intact or damaged based on the at least one modeled exhaust gas measurement and the at least one measured exhaust gas measurement,

Wherein determining whether the catalytic converter (12, 13) is intact or damaged based on the at least one modeled exhaust gas measurement value and the at least one measured exhaust gas measurement value comprises:

Calculating (34) a difference (Δc) between the at least one measured exhaust measurement value and the at least one modeled exhaust measurement value;

Calculate (36) the integral value of the integral of a plurality of difference values (Δc) within a predetermined time period;

comparing the integrated value with a threshold value (110); and

Based on the comparison, it is determined whether the catalytic converter (12, 13) is intact or damaged.

2 . The method of claim 1 , wherein the at least one measured exhaust measurement and the at least one modeled exhaust measurement are one of: a nitrogen oxide measurement, an ammonia measurement, or a combined nitrogen oxide-ammonia measurement.

3. The method of claim 1 or 2, wherein the at least one measured exhaust measurement value and the at least one modeled exhaust measurement value describe a concentration or a mass flow of an exhaust component, respectively.

4. The method according to claim 1 or 2, wherein the measured exhaust gas value is detected by means of a nitrogen oxide sensor (17, 18) which has a cross-sensitivity to ammonia.

5 . The method according to claim 1 , wherein each difference value (Δc) is multiplied by a weighting factor before the integration, wherein the weighting factor is determined based on predefined operating conditions of the catalytic converter.

6. The method according to claim 5, wherein the predetermined operating conditions for determining the weighting factor include at least one of the following operating conditions: tolerance characteristics of the ammonia level of the catalytic converter; the temperature of the catalytic converter; the temperature gradient of the catalytic converter; the permissible conditions of the sensor used; the exhaust gas mass flow; the nitrogen oxide mass flow.

7. The method according to claim 1 or 2, further comprising:

Before using the difference to calculate the integral, a permissive condition is checked (102); and

Only when the admission condition is met is the associated difference used to form the integral.

8 . The method of claim 7 , wherein the permissive conditions include a modeled maximum ammonia slip after the catalytic converter and/or a maximum temperature gradient in the catalytic converter.

9. The method according to claim 1 or 2, wherein the calculation of the at least one modeled exhaust gas measurement value is performed based on a reaction kinetic model or a data-based model.

10. The method according to claim 1 or 2, wherein the model catalytic converter is a WPA catalytic converter or an intermediate layer catalytic converter between a WPA catalytic converter and a BPU catalytic converter.

11. A method for monitoring the status of a catalytic converter (12, 13) for reducing nitrogen oxides, the method comprising:

The integrated exhaust gas measurement values are respectively calculated according to the integration of a plurality of exhaust gas measurement values within a predetermined time period;

respectively calculating the integrated modeled exhaust gas measurement values according to the integration of a plurality of modeled exhaust gas measurement values within the predetermined time period;

Calculating the difference between the integrated exhaust gas measurement value and the integrated modeled exhaust gas measurement value;

comparing the difference with a threshold value;

12. The method of claim 11, wherein the at least one measured exhaust measurement and the at least one modeled exhaust measurement are one of: a nitrogen oxide measurement, an ammonia measurement, or a combined nitrogen oxide-ammonia measurement.

13. The method of claim 11 or 12, wherein the at least one measured exhaust measurement and the at least one modeled exhaust measurement describe a concentration or a mass flow of an exhaust component, respectively.

14. The method according to claim 11 or 12, wherein the measured exhaust gas value is detected by means of a nitrogen oxide sensor (17, 18) which has a cross-sensitivity to ammonia.

15. The method according to claim 11 or 12, wherein the calculation of the at least one modeled exhaust gas measurement value is performed based on a reaction kinetic model or a data-based model.

16. The method according to claim 11 or 12, wherein the model catalytic converter is a WPA catalytic converter or an intermediate layer catalytic converter between a WPA catalytic converter and a BPU catalytic converter.

17. A computing unit (19) which is configured to carry out all method steps of the method according to one of the preceding claims.

18 . A computer program product comprising a computer program which, when executed on a computing unit, causes the computing unit to execute all method steps of the method according to claim 1 .

19 . A machine-readable storage medium having a computer program stored thereon, which, when executed on a computing unit, causes the computing unit to execute all method steps of the method according to claim 1 .