Monitoring the status of catalytic converters for reducing nitrogen oxides

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

Technical Field

[0001] The invention relates to a method for monitoring the state of a catalytic converter for reducing nitrogen oxides, as well as to a computing unit for carrying out the method and to a computer program for carrying out the method. Background Art

[0002] In the vehicle field, in order to reduce nitrogen oxides (NO x ), in particular an SCR catalytic converter (Selective Catalytic Reduction) can be used. Nitrogen monoxide NO and nitrogen dioxide NO2 are collectively referred to as nitrogen oxides. The basic principle of an SCR catalytic converter is that nitrogen oxide molecules are reduced to elemental nitrogen on the surface of the catalytic converter in the presence of ammonia (NH3) as a reducing agent. The reducing agent is usually provided in the form of an aqueous urea solution (HWL) that releases NH3, which is provided via a controlled metering device upstream of the SCR catalytic converter.

[0003] At present, the use of SCR catalytic converters also requires the use of at least one nitrogen oxide sensor. However, two nitrogen oxide sensors are often used, one in front of the SCR catalytic converter and one behind the SCR catalytic converter. In many markets, regulations for vehicle diagnostics (OBD, OnBoard-Diagnostics) require very precise monitoring of the system and especially the SCR catalytic converter. If the catalytic converter ages and is no longer able to adequately convert nitrogen oxides, the corresponding warning light must be reliably activated and the catalytic converter must be replaced before the required limit value is exceeded.

[0004] The aging and / or damage of the SCR catalytic purifier can be monitored by evaluating nitrogen oxides with the help of appropriate sensors in front of and behind the catalytic purifier. For this purpose, in the passive diagnostic method, the nitrogen oxide concentration, nitrogen oxide mass flow or nitrogen oxide conversion rate is usually measured at the following stage, at which stage it is possible to fully distinguish between an undamaged SCR catalytic purifier and a damaged SCR catalytic purifier. Here, the diagnostic conditions are usually selected so that the nitrogen oxide conversion of the undamaged SCR catalytic purifier is high and the nitrogen oxide conversion of the damaged catalytic purifier (boundary part) to be identified is as low as possible. In the case of such identification, the still undamaged SCR catalytic purifier or its state is also referred to as a WPA (worst performing acceptable) catalytic purifier, and the damaged state is referred to as a BPU (best performing unacceptable). The greater the difference between these states under the current conditions, the more robust the diagnostic method based on them.

[0005] Because conventional nitrogen oxide sensors are cross-sensitive to ammonia, they display NO x The so-called ammonia slip after the SCR catalytic converter can lead to a significant reduction in efficiency because the ammonia also leads to an increased sensor signal, which can be erroneously interpreted as an increase in nitrogen oxides. This makes it easier to identify the BPU catalytic converter on the one hand, because it appears to be worse than it actually is; on the other hand, the WPA components also appear to be erroneously worse, making it difficult to distinguish between the states. Therefore, these methods usually have the goal of selecting conditions so that no ammonia slip occurs.

[0006] If this passive method is not accurate enough, an active method can be used, which determines the ammonia storage capacity of the SCR catalytic converter by means of intervention in the dosage of the urea solution. This ammonia storage capacity correlates very well with thermal or chemical damage to the SCR catalytic converter. Summary of the invention

[0007] According to the invention, a method for monitoring the state of a catalytic converter, as well as a computing unit for carrying out the method and a computer program for carrying out the method are proposed. Advantageous embodiments are the subject of the following description.

[0008] The present invention utilizes the following measures: measured values ​​detected after (downstream of) the catalytic converter are compared with exhaust gas measured values ​​modeled for a predetermined state of the model catalytic converter or respectively derived or filtered therefrom, for example integrated or summed; and based on the comparison, it is determined whether the catalytic converter is intact or damaged.

[0009] By using the model as a comparison, all operating conditions can be physically depicted and thus taken into account during the diagnosis. Instead of the previous determination of the efficiency and emissions of the catalytic converter, this direct determination of the catalytic converter aging thus makes it possible to better distinguish between catalytic converter damage and damage or malfunctions of other components.

[0010] Here, at least one measured exhaust gas measurement value and at least one modeled exhaust gas measurement value can be, in particular, a nitrogen oxide measurement value, an ammonia measurement value or a combined nitrogen oxide-ammonia measurement value, respectively, and can, for example, respectively indicate the concentration or mass flow of exhaust gas components such as the mentioned nitrogen oxides or ammonia. For this purpose, no structural changes are required relative to conventional exhaust gas lines, and common sensors can be used. In particular, the measured exhaust gas values ​​can be detected by means of a nitrogen oxide sensor, which has a cross-sensitivity to ammonia. Here, this cross-sensitivity is advantageously incorporated into the diagnostic method by taking into account two aging mechanisms of the catalytic converter - a lower storage capacity for ammonia and a poorer conversion of nitrogen oxides in terms of quantity.

[0011] This makes it possible to avoid active interventions in metering that would affect efficiency and emissions. In addition, intact catalytic converters can be distinguished more precisely from damaged catalytic converters, so that the robustness and resolution of the diagnosis are improved.

[0012] Preferably, the determination of whether the catalytic converter 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 includes: finding the difference between the at least one measured exhaust gas measurement value and the at least one modeled exhaust gas measurement value; finding the integral value of the integral of multiple differences within a predetermined time period; comparing the integral value with a threshold value; and determining whether the catalytic converter is intact or damaged based on the comparison. It is easy to understand that finding the integral value will be implemented as a sum in practice. In this embodiment, it is very easy to infer whether the catalytic converter works better or worse than the model based on the sign of the integral value. It is also possible to first integrate the model value and the measurement value separately and then find the difference.

[0013] According to one embodiment, each difference value can also be multiplied by a weighting factor before integration, wherein the weighting factor is determined based on predefined operating conditions of the catalytic converter. In this way, phases with high modeling and / or measurement accuracy can have a greater influence on the diagnosis, while the influence of values ​​that may be inaccurately determined or modeled can be limited.

[0014] 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 of the catalytic converter; temperature gradient of the catalytic converter; permissible conditions of the sensor used; exhaust gas mass flow; nitrogen oxide mass flow.

[0015] Furthermore, according to one embodiment, before using the difference value for integration, a further permission condition can be checked, and only if the permission condition is met can the associated difference value be used for integration. This does not force the entire diagnosis to be discarded, and it is still ensured that values ​​with insufficient evidence have no influence on the evaluation. In this way, the evaluation frequency and the resolution accuracy are further improved. The permission condition can include, for example, the maximum ammonia slip after modeling behind the catalytic converter and / or the maximum temperature gradient in the catalytic converter, because, for example, the emission of ammonia at high temperatures can lead to evaluation distortions, or high temperature gradients caused by changes in the reaction process can lead to modeling difficulties.

[0016] The calculation of at least one modeled exhaust gas measurement value can be implemented, for example, based on a reaction kinetic model or a data-based model (that is, a comprehensive characteristic curve model). Known models can also be found in the literature, such as "Unsteady analysis of NO Reduction over Selective Catalyst Reduction-De-NOxMonolith Catalysts", E Tronconi, A. Cavanna, P. Forzatti, Ind. Eng. Chem. Res 1998, No. 37, pp. 2341-2349. These models can be implemented in modern motor vehicle (Kfz) control devices and not only depict the NO reduction of the SCR catalytic converter, but also the NO reduction of the SCR catalytic converter. x The NH3 slip is converted and depicted.

[0017] A computing unit according to the present invention, for example a control unit of a motor vehicle, is set up, in particular by means of programming, to carry out the method according to the present invention.

[0018] In particular, when the implementing control device is also used for other tasks and is therefore always present, the implementation of the method according to the invention in the form of a computer program or computer program product with program code for executing all method steps is also advantageous, because this results in particularly low costs. In particular, suitable data carriers for providing the computer program are magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs and others. It is also possible to download the program via a computer network (Internet, intranet, etc.).

[0019] Further advantages and embodiments of the invention are apparent from the description and the accompanying drawings.

[0020] The invention is schematically illustrated in the drawings with the aid of exemplary embodiments and is described below with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 An exemplary catalytic purification system is schematically shown, which is suitable for embodiments of the present invention;

[0022] Figure 2 The principle of catalytic converter diagnosis according to one embodiment of the present invention is depicted;

[0023] Figure 3 An exemplary diagram of the integrated difference for an undamaged (WPA) catalytic converter and a damaged (BPU) catalytic converter according to one embodiment of the present invention is shown; and

[0024] Figure 4 Exemplary method steps according to embodiments of the present invention are shown. DETAILED DESCRIPTION

[0025] Figure 1An exemplary system is shown in which an embodiment of the present invention can be applied. Here, one or more catalytic purifier elements are arranged in the exhaust gas line, and the exhaust gas flow 10 is introduced from the internal combustion engine into the one or more catalytic purifier elements for exhaust gas treatment. In the figure, a diesel oxidation catalytic purifier (DOC) 11 is first shown, and two SCR catalytic purifier elements 12 and 13 are connected to the downstream of the diesel oxidation catalytic purifier, and these two SCR catalytic purifier elements can also include a particle filter with an SCR coating (SCRF) 12, for example. In front of each SCR catalytic purifier element 12, 13, a dosing module 14 and 15 are arranged respectively, which is used to introduce a urea aqueous solution (HWL) into the system in a dosing manner. Each dosing module 14, 15 is controlled by a control unit 19, wherein preferably all modules of the same unit, such as 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 positions of the system.

[0026] In particular, a nitrogen oxide sensor and / or an ammonia sensor can be installed before and / or after each catalytic converter element 11, 12 / 13, which measures the concentration and / or conversion rate and / or mass flow of the corresponding components in the exhaust gas flow. x sensor, the NO x The sensor is also cross-sensitive to ammonia (NH3), or may involve a multi-gas sensor that can output NO separately. x Similarly, the corresponding positions 16, 17, and 18 in the exhaust gas flow can also be arranged for NO x The measured values ​​of all sensors are forwarded to the control unit 19 for processing. Of course, other sensors not shown here can also be used, such as temperature sensors, oxygen sensors, air mass flow meters and other sensors at different locations in the system.

[0027] In order to identify the state of the SCR catalytic converters 12, 13 in such systems or similar systems, i.e. to be able to carry out a diagnosis with regard to damage or aging of the catalytic converters, according to one embodiment of the present invention, the measured exhaust gas values ​​are compared with modeled exhaust gas values ​​and integrated over a certain period of time.

[0028] In this case, a theoretical catalytic converter model can be used, which models the expected values ​​of nitrogen oxides and ammonia in the exhaust gas flow behind the catalytic converter or in a determined predetermined state, for example in the still intact WPA state (worst performing acceptable) of the catalytic converter. The model can be, for example, a reaction kinetic model or a data-based model, which is basically known in the art. As relevant variables for modeling and measurement, the concentrations of exhaust gas components, i.e., in particular NH3 and NO x Alternatively, the mass flow of these variables can also be used. It is also possible to model the exhaust gas values ​​using a model based on a comprehensive characteristic curve.

[0029] Figure 2 The principle of a catalytic converter diagnosis for a catalytic converter according to one embodiment of the present invention is depicted. Based on a suitable model 31 of the SCR catalytic converter, the modeled NO x concentration And the modeled NH3 concentration For this purpose, the ammonia concentration before the catalytic converter, i.e. As input variables influencing model 31 , the ammonia concentration can be determined based on the activation of the corresponding metering module; and the nitrogen oxide concentration upstream of the catalytic converter As an input variable influencing 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 a model as a function of the operating state of the engine.

[0030] Next, the calculated sum signal 32 of these two modeled variables

[0031]

[0032] can be connected to the NO x The signals measured at the sensors are compared.

[0033] In this embodiment, the measured sensor signal is NO x The sensor value, the NO x The sensor is cross-sensitive to NH3 and is arranged downstream of the catalytic converter 30, where both components cause one signal. In fact, the measured signal indicates that NO x and a combined value of the corresponding concentrations of NH 3 , which corresponds substantially to the sum of the concentrations present downstream of the catalytic converter 30 ,

[0034]

[0035] Next, to compare the measured value with the modeled value, the difference between the two summed values ​​can be calculated 34,

[0036]

[0037] That is, from the NOx after the catalytic converter x The summed value 32 modeled for the catalytic converter output is subtracted from the summed value measured for NH3 and NH3.

[0038] The difference obtained here The integral is performed over a predefined evaluation period, for example by an integrator 36 , and the integral obtained is compared with a threshold value. This comparison is then evaluated by a diagnostic system 38 , for example an OBD diagnostic software.

[0039] If a WPA catalytic converter is used as model 31, then in the case of a still intact catalytic converter being measured, ie a WPA catalytic converter, the following applies:

[0040]

[0041] This means that the difference between the model value and the measured value fluctuates around zero and the integral obtained is also close to 0. In the case of an aged or damaged catalytic converter (BPU)

[0042]

[0043] That is, the measured signal is higher than the modeled value, i.e. the integral rises above a threshold value. It can be provided that, as soon as the threshold value is exceeded in the comparison of the integral value with the threshold value, the catalytic converter 30 is classified as damaged with respect to the OBD diagnosis 38, and as long as the obtained signal is below the threshold value, the catalytic converter 30 is classified as still not damaged.

[0044] The difference between the measured value and the modeled value, which is increased in the case of a damaged catalytic converter (and thus also the integral exceeding the threshold value), can be explained essentially on the basis of two effects: about half is related to ammonia (NH 3 ), which can no longer be stored sufficiently in a damaged catalytic converter compared to a WPA catalytic converter; the other half is due to the nitrogen oxides NO x , which can no longer be sufficiently converted by a damaged catalytic converter and therefore also occur in increasing quantities downstream of the catalytic converter. This results in two main aging effects, namely reduced NH3 storage capacity and lower NO x The conversion is taken into account as the only monitored variable for diagnosing the catalytic converter.

[0045] Replacement of WPA catalytic converter, for exhaust gas values ​​after the catalytic converter and For the modeling 31 of , a so-called intermediate layer catalytic converter between the WPA state and the BPU state can also be considered. In this case, the integrator 36 will run positively in the case of the measured BPU catalytic converter and will run negatively in the case of the WPA.

[0046] Figure 3 An exemplary statistical evaluation of a plurality of integral values, that is to say the integrated difference values ​​for diagnostic measurements on BPU components and WPA components, and modeling of such an intermediate layer catalytic converter is shown, wherein the integral values ​​are plotted against the time t [s]. In this case, the points above the diagram (greater than 0) are the integral values ​​in the case of a damaged catalytic converter (BPU), while the values ​​below (less than 0) indicate the integral values ​​in the case of an intact catalytic converter (WPA).

[0047] For example, based on NO x Integration, can use standardized time periods as evaluation time points or lengths of individual monitoring phases for diagnosis, so that diagnosis is made in NO x The amount is evaluated after reaching, for example, 2 grams.

[0048] The accuracy of this diagnosis depends strongly 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 individually for each round or for each difference and multiplied by the difference. As a result, the expected phases with high model accuracy can be taken into account to a greater extent, while the expected phases with lower accuracy only conditionally or not at all influence the diagnosis.

[0049] For example, general operating conditions can be used, such as for NO x The sensor and the permission of the dosing module of the urea-water solution are used as these weighted conditions. In addition, for example, the catalytic converter temperature, the exhaust gas mass flow and the NO x Mass flow, used for restriction.

[0050] For all such conditions, it is possible in the extreme case to temporarily deactivate the integrator and thus “freeze” the diagnosis, so that certain phases of inaccurate modeling have no influence on the diagnosis at all and to subsequently resume the diagnosis partly.

[0051] It is also reasonable and possible to take into account the temperature gradient of the catalytic converter for weighting. In the case of high temperature gradients, in the SCR catalytic converter, the NOx Competition between the reaction and the NH3 absorption occurs, which makes modeling difficult. In order to take this into account, the current temperature gradient can be compared with a threshold value. If the threshold is exceeded within a certain time, the integrator can be reset to a previously stored value, which corresponds, for example, to the value at the first time the temperature gradient threshold was exceeded. In this way, inaccurate phases are not taken into account, in which the diagnosis is not completely prevented at each brief increase in the temperature gradient.

[0052] For the other of the mentioned release conditions, a corresponding interruption of the diagnosis can in principle also be carried out in an analogous manner, wherein the integrator either continues to operate after the interruption or is reset to a previously determined previous value.

[0053] If NH3 is emitted from the catalytic converter due to the increase in temperature, there is a further limitation on the diagnosability of the catalytic converter. This process may result in: the ammonia leakage in the case of an undamaged catalytic converter (WPA) is greater than the ammonia leakage in the case of a damaged catalytic converter (BPU), in which less NH3 is already stored. By this, the measured combined sensor value behind the catalytic converter may 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 therefore increase and the measured signal will be mistakenly regarded as a sign of reduced storage capacity, so that this may lead to a (wrong) diagnosis of a damaged catalytic converter. In order to prevent this, the ammonia leakage of the catalytic converter can be modeled for the model of the WPA catalytic converter taking into account the temperature. If the modeled NH3 leakage is higher than a threshold value, the diagnosis or the integration of the difference can be temporarily stopped accordingly. Alternatively, the modeled NH3 signal for the WPA state can be compared with the modeled NH3 signal for the BPU state. If the modeled WPA value is higher than the modeled BPU value, the granting of a diagnosis is not plausible on this basis and can be correspondingly frozen again (when using the value stored before the temperature increase) or discarded.

[0054] In addition, the accuracy of the diagnosis or the modeling used may also depend on the accuracy of the modeled NH3 level of the catalytic converter. If it is expected that the modeled NH3 level cannot be determined with sufficient accuracy in one case, the diagnosis can therefore be correspondingly throttled or stopped again 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 the following tolerance characteristic of the level, which leads to a maximum NH3 level, and the second additional model is based on the following tolerance characteristic, which leads to a minimum NH3 level. Based on the absolute or relative difference between the two model values, a trust factor can be determined, which corresponds to the current tolerance characteristic with respect to the NH3 level. Subsequently, the difference between the modeled exhaust gas value and the measured exhaust gas value can be multiplied by the trust factor in order to achieve throttling or further weighting of the diagnostic method with respect to the accuracy of the NH3 level.

[0055] Figure 4 The flowchart shows the method steps of an exemplary embodiment of the present invention. In this case, not all of the steps shown need to be used in the method according to the present invention, but other steps or interventions that are not shown here can also be carried out.

[0056] After the diagnostic part is started (step 100), it is checked in step 102 whether the diagnostic permission conditions are met, i.e., whether, as described above, permission conditions exist for the sensor, for example, or whether the temperature gradient is below a certain threshold, as described. If this is not the case, the diagnosis is only continued or carried out if the recheck of these permission conditions is successful.

[0057] Next, in step 104, a confidence factor is calculated for the current value difference. In this step, other weighting factors can also be determined, which are applied to the corresponding difference values, for example, in order to moderate potential influences. Certain conditions can also be used not only for the check of permission but also for weighting, or different conditions and influences can be involved.

[0058] In step 106 , an integrator that integrates the difference between the model and the measured value and the used catalytic converter model are updated based on the previous steps.

[0059] In step 108, it is checked whether the predefined monitoring time period has expired. If it has not expired, the diagnostic process is continued by the loop being traversed again from the beginning (step 100) and the conditions and weighting values ​​being checked again accordingly and applied to the difference to be integrated, and the integrator being updated again with these values ​​(step 106).

[0060] If it is ascertained in step 108 that the monitoring period has ended, i.e., for example, a predetermined period has expired or a predetermined criterion for determining the monitoring period has been met, 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); if the threshold value is not exceeded, the cause is that the catalytic converter is not damaged (step 114). The situation of the threshold value depends on the modeling used.

[0061] Subsequently, a further monitoring phase can be initiated, which correspondingly provides a new integrator value for comparison with the threshold value.

[0062] It is also possible to first evaluate a number of such integrator values ​​and then infer whether the catalytic converter is intact or damaged, and for the diagnostic system (for example OBD) to trigger a corresponding alarm; for this purpose, for example, a minimum number of results that must exceed the threshold value successively or also discontinuously can be specified. Figure 3 As has already been seen in , the exact integral value for a specific catalytic converter state may differ in value, but generally lies within a narrow range and lies above or below a defined threshold value, so that a clear and robust distinction between WPA and BPU states is possible.

[0063] It is easy to understand that the factors and conditions described for throttling or weighting the diagnosis or for stopping, discarding or freezing the diagnosis can be used individually or in combination with each other. Here, the order in which certain conditions are checked can be as described here or can also be different; depending on the implementation method, certain steps can also be omitted.

[0064] In another embodiment, it is also possible to replace NO which is cross-sensitive to NH3 x Sensors, such as so-called multi-gas sensors, are used which are able to output NO x It is also conceivable that in the case of the method according to the above embodiments, sensors with no cross-sensitivity or negligible cross-sensitivity are used, which sensors can therefore output the mass flow or concentration of the exhaust gas components essentially individually. In these cases, the method steps of the invention can also be applied individually to NO x and / or a corresponding single signal of NH 3 , namely modeling of the values, differentiation of the measured values ​​from the model values, and subsequent integration of the obtained difference values ​​and checking of threshold values ​​for these integrated values.

[0065] It is also possible that, in the method described, only a single catalytic converter is monitored, or also a system consisting of a plurality of catalytic converters arranged one after another, as in Figure 1 In this case, in a system with multiple catalytic converters, the difference and sum can be performed separately after each catalytic converter, or a combined model consisting of multiple catalytic converters under consideration can be used, so that only the exhaust gas measured value at the sensor after the last catalytic converter under consideration is used as the measured value. In principle, the present invention can be used in all exhaust gas systems with SCR catalytic converters and metering units.

[0066] Preferably, the described method steps and calculations are implemented in one or more control units. Here, for example, the same control unit, preferably an engine control unit, can be used for all steps, sensor data and regulation processes.

[0067] These steps can be implemented electronically or preferably software-based in a corresponding control unit, such as a processor or microcontroller, so that as long as a corresponding interface to the sensor is present, it is possible to equip the control unit with the diagnostic system according to the invention in a simple manner. In this case, the software module on the control unit can also be combined with other corresponding hardware elements, such as a microcontroller and an FPGA, in order to implement certain parts of the embodiment according to the invention. The connection of multiple control units is also 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 value downstream of 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 on the basis of 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 according to claim 7, wherein the permission conditions include: A modeled maximum ammonia slip downstream of 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: 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 value downstream of 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: 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; Based on the comparison, it is determined whether the catalytic converter (12, 13) is intact or damaged.

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 .

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