AT521117B1 - Procedure for checking the function of SCR catalytic converters in an SCR system - Google Patents

Abstract

The invention relates to a method for checking the function of individual SCR catalytic converters (5, 6) in an exhaust gas aftertreatment system, the SCR system comprising two SCR catalytic converters, with a fuel being metered into the SCR system which contains a reducing agent or is converted into a reducing agent and wherein the reducing agent is stored at least temporarily in at least one SCR catalytic converter (5, 6), the SCR catalytic converters (5, 6) being emptied first, then, if necessary, the temperature of the SCR system being tempered, then one predetermined diagnostic amount of the operating fluid is metered in, which defines an amount of reducing agent, the amount of reducing agent being smaller than the maximum amount of reducing agent that can be stored by the first SCR catalytic converter (5) in the functional state, and if no slippage of reducing agent occurs during metering of the diagnostic amount after the second SCR catalytic converter (6) is detected, the temperature d it first SCR catalyst (5) is increased to or above its desorption temperature, and wherein the second SCR catalyst (6) is defined as defective if during the increase the temperature of the first SCR catalyst (5) to or above its desorption temperature, a reducing agent slip is detected downstream of the second SCR catalytic converter (6), the defective SCR catalytic converter (5, 6) being determined by comparing the course over time and/or the amplitude of the actually occurring reducing agent slip with reference values, such as measurement data, simulation data , maps or empirical values.

Description

description

PROCEDURE FOR CHECKING THE FUNCTIONALITY OF SCR CATALYTIC CONVERTERS IN AN SCR SYSTEM

The invention relates to a method according to the preamble of the independent patent claim.

Different methods for checking the function of SCR components of an exhaust gas aftertreatment system of internal combustion engines are known from the prior art. For example, methods are known in which damage to the SCR system is detected if there is a discrepancy between real NOx measured values and modeled NOx measured values after the exhaust gas aftertreatment system. Since conventional methods cannot detect which of the two SCR components is not functional, it may be necessary in practice to replace all SCR components or just the second SCR component in order to repair the damage.

The object of the invention is to overcome the disadvantages of the prior art. In particular, the object of the invention is to provide a method by means of which the faulty SCR catalytic converter can be determined simply and quickly in order to avoid an unnecessary replacement of non-defective catalytic converters. This determination is intended to be made without the use of additional sensors and/or additional components, i. H. This is done using the vehicle's own sensors and/or components, which means that faulty catalytic converters can be located quickly, easily and inexpensively and replaced in a targeted manner.

The object of the invention is achieved in particular by the features of the independent patent claim.

The invention relates to a method for checking the function of individual SCR catalytic converters of an SCR system of an exhaust aftertreatment system of an internal combustion engine, the SCR system serially comprising a first SCR catalytic converter and a second SCR catalytic converter along the exhaust aftertreatment system, with the SCR -System in regular operation, which corresponds to the intended operation, a fuel is metered, the fuel contains a reducing agent or is converted into a reducing agent, and the reducing agent is stored at least temporarily in at least one SCR catalytic converter of the SCR system.

According to the invention it is provided that the method comprises the following steps: activating a diagnostic mode, then emptying the SCR catalytic converters by stopping or reducing the supply of fuel until no more reducing agent is stored in the SCR catalytic converters, then, if necessary, tempering, in particular Heating up the SCR system, so that the temperature of the SCR system and in particular of the SCR catalytic converters is within a predetermined temperature window, with a predetermined diagnostic quantity of the fuel then being metered in, which defines a quantity of reducing agent, with the quantity of reducing agent being smaller than the maximum of the first SCR catalytic converter in functional condition storable amount of reducing agent,

wherein, if no reductant slip is detected after the second SCR catalyst during dosing of the diagnostic amount, the temperature of the first SCR catalyst is increased to or above its desorption temperature, the second SCR catalyst being defined as defective if during the increase the temperature of the first SCR catalytic converter at or above its desorption temperature, a reducing agent slip after the second SCR catalytic converter is detected, and where appropriate status information on the function of the first SCR catalytic converter and/or the second SCR catalytic converter is output and/or stored, and that the diagnostic operation is ended if necessary, the defective SCR catalytic converter being determined by comparing the course over time and/or the amplitude of the actually occurring reducing agent slip with reference values such as measured data, simulation data, characteristic diagrams or empirical values.

If necessary, it is provided that in normal operation, in particular in normal operation, a fuel suitable for selective catalytic reduction, such as in particular a mixture containing urea, a urea solution or AdBlue®, is metered in upstream of the SCR catalytic converter. The fuel can contain a reducing agent, such as ammonia NH in particular, or can be converted into a reducing agent, such as NH3 in particular. A mixture containing urea, in particular a urea-water solution, such as AdBlue®, is preferably used as the fuel, with the fuel possibly being converted into the reducing agent, in particular NH 2 , by the reactions described below:

Thermolysis: (NH2)2CO > NHs + HNCO Hydrolysis: HNCO + H2:O > NHs3 + CO»

In a first step, the urea (NH2)2CO can be converted into ammonia NHs and isocyanic acid HNCO in the thermolysis reaction. In a second step, in the hydrolysis reaction, the isocyanic acid HNCO can be mixed with water H;O in ammonia NH; and carbon dioxide CO» are converted.

The reducing agent, in particular NHgs, can optionally be stored and/or stored at least temporarily in at least one SCR catalytic converter. If necessary, the ammonia accumulates on the active centers of the SCR catalytic converter. The at least temporarily stored reducing agent, in particular the ammonia NHs3, can then reduce nitrogen oxides NOx, such as in particular nitrogen monoxide NO and nitrogen dioxide NO».

[0010] The fuel can be metered via a metering device, such as in particular via an injector or via an injection nozzle. In particular, it is provided that the fuel is introduced before the first SCR catalytic converter.

[0011] Due to the fact that the fuel supply is optionally reduced or stopped, no new reducing agent is supplied to the SCR system. The emptying of the SCR catalytic converters can be based on the fact that the reducing agent still contained in the SCR catalytic converter is consumed by the reduction of nitrogen oxides NOx, as a result of which the SCR catalytic converters can be emptied, in particular completely. If necessary, provision can be made for the reducing agent still contained in the SCR catalytic converter to be removed by means of an emptying operation, for example by increasing the temperature of the SCR catalytic converter.

[0012] After the SCR catalysts have been emptied, the SCR system and in particular the SCR catalysts can/can be tempered, in particular heated, in order to bring the SCR catalysts to a predetermined temperature. This tempering step can be omitted if the temperature of the SCR catalytic converters is already within a predetermined temperature window.

[0013] A predetermined quantity of the operating fluid, a so-called diagnostic quantity, can then be metered. The amount of reducing agent introduced by the diagnostic amount can preferably be smaller than the amount that can be stored at least temporarily by a first functional SCR catalytic converter. This can ensure that the quantity of reducing agent introduced by the diagnostic quantity can be at least temporarily, in particular completely, absorbed and/or at least temporarily, in particular completely, stored by the first SCR catalytic converter. This means that, if necessary, a previously defined reducing agent storage level can be achieved in a first functional SCR catalytic converter by means of the diagnosis quantity.

If necessary, it is provided that so much fuel is metered in during the diagnostic operation after the metering of the diagnostic amount of fuel, in particular continuously, that the previously defined reducing agent storage level can be maintained. This means that exactly as much fuel is metered in as is consumed by the NOx emissions that occur and their conversion, and thus the reducing agent storage level in the SCR catalytic converters and/or in one of the two SCR catalytic converters

essentially remains constant.

If no reducing agent slip is detected after the second SCR catalytic converter during metering of the diagnostic quantity, the introduced quantity of reducing agent can be stored at least temporarily in one of the two SCR catalytic converters or in both SCR catalytic converters together. This means that one of the two SCR catalytic converters or both SCR catalytic converters together has or have a storage capacity that is equal to or greater than the amount of reducing agent introduced.

The temperature of the first SCR catalyst can then be increased to or above its desorption temperature. The second SCR catalytic converter is preferably defined as defective and/or non-functional if a reducing agent slip after the second SCR catalytic converter is detected during the temperature increase of the first SCR catalytic converter to or above its desorption temperature. In other words, the reducing agent slip after the second SCR catalytic converter only occurs when the temperature of the first SCR catalytic converter increases as described above if the reducing agent desorbed from the first SCR catalytic converter can pass through the second SCR catalytic converter without being stored at least temporarily. This makes it possible to determine that the second SCR catalytic converter is not functional, since it has no or only very little reducing agent storage capacity.

In this case, the second SCR catalytic converter can be defined as defective and can subsequently be exchanged in a targeted manner.

In the context of the present disclosure, desorption temperature is understood to mean a temperature which corresponds to a temperature at which the at least temporarily stored reducing agent can no longer be stored and/or maintained in the SCR catalytic converter. This means that at or above the desorption temperature, the reducing agent is stored out of the SCR catalytic converter and/or leaves the SCR catalytic converter.

The reducing agent slip, in particular the NHs slip, can be detected by at least one sensor, in particular an NOx sensor or NH3: sensor. The at least one sensor can be arranged after the SCR catalytic converters or the SCR system. If necessary, the NHs slip is detected by an increased measured value of the NOx sensor, since the concentration of NH; can affect a NOx sensor.

Under an SCR system can be understood in the context of the present disclosure in particular a system which comprises an sDPF catalyst, an SCR catalyst and / or an ASC catalyst or from an sDPF catalyst, an SCR catalyst and / or an ASC catalyst is formed. The SCR system preferably also includes the device for metering in the fuel and possibly also the fuel as such.

[0021] Within the scope of the present disclosure, an SCR catalytic converter can be understood to mean an sSDPF catalytic converter, an SCR catalytic converter, an ASC catalytic converter and/or an SCR-ASC catalytic converter combination.

If necessary, the determined functionality of the exhaust aftertreatment system is output and/or stored as status information. If necessary, the status information can also be stored in a memory system of the internal combustion engine and/or a motor vehicle.

[0023] The diagnostic mode can then be ended if necessary.

[0024] In the context of the present disclosure, diagnostic operation is understood to mean operation in which the method steps of the method, as described above, follow one another. This means that if necessary the SCR catalytic converters are emptied first, in particular completely, then the SCR catalytic converters are temperature-controlled if necessary, then a predetermined diagnostic quantity of the operating fluid is metered in, then if necessary the temperature of the first SCR catalytic converter and then if necessary the temperature of the second SCR catalyst is increased.

If necessary, it is provided that in particular subsequently the temperature of the second SCR catalyst is increased to or above its desorption temperature, the first SCR catalyst being defined as defective if during the increase in the temperature of the second SCR catalyst to or a reducing agent slip after the second SCR catalytic converter is detected via its desorption temperature, and that the diagnostic operation is ended if necessary.

[0026] If the first SCR catalytic converter is no longer functional, the reducing agent introduced by the diagnostic quantity of the fuel passes through the first SCR catalytic converter without being stored and/or included in it, at least temporarily. This means that the introduced quantity of reducing agent is at least temporarily taken up directly by the second SCR catalytic converter if this is functional. If the second SCR catalytic converter is then brought to or above its desorption temperature, the reducing agent that may have been stored leaves the second SCR catalytic converter and a reducing agent slip can be detected.

In this case, the first SCR catalytic converter can be defined as defective and can subsequently be replaced in a targeted manner.

If necessary, it is provided that both SCR catalytic converters are defined as defective if a reducing agent slip after the second SCR catalytic converter is detected during metering of the diagnostic quantity,

and that the diagnostic operation is ended if necessary.

If both SCR catalytic converters are not functional, no reducing agent or only a very small amount of reducing agent can be stored at least temporarily in the SCR catalytic converters. This means that the quantity of reducing agent introduced by the diagnostic quantity may pass through the two SCR catalytic converters of the SCR system without being stored in them, at least temporarily.

In this case, the first and the second SCR catalytic converter can be defined as defective and can subsequently be exchanged in a targeted manner.

Optionally, it is provided that the SCR catalysts are heated sequentially or at different times, that first the first SCR catalyst is heated to or above its desorption temperature, and that the second SCR catalyst is then heated to or above its desorption temperature.

If necessary, it is provided that the temperatures of the SCR catalytic converters are increased by increasing the exhaust gas temperature.

If necessary, it can be provided that the individual SCR catalytic converters are heated up separately. This means that, if necessary, the first and the second SCR catalytic converter can be brought to their desorption temperature, in particular desorption temperatures, independently of one another.

It is preferably provided that the increase in the temperature of the SCR catalytic converters takes place by increasing the exhaust gas temperature. This means that, if necessary, first the first SCR catalytic converter and then the second SCR catalytic converter are heated to or above its desorption temperature as a result of an increase in the exhaust gas temperature. In particular, it is provided that the exhaust gas aftertreatment system, in particular the SCR catalytic converters, are brought to the desired temperature by an engine measure.

If necessary, it is provided that the diagnostic mode is activated if a reduced efficiency, in particular a reduced overall efficiency, of the SCR system is previously detected in a pre-diagnostic mode or during normal overall efficiency monitoring while driving, the detection being based in particular on an on -Board diagnosis system or a workshop diagnosis system is carried out.

[0036] In particular, it can be provided that the diagnostic operation, in particular the measured

applicable method steps of the diagnostic operation, are carried out if previously a reduced efficiency, in particular a reduced NOx conversion rate, is detected. This means that if a reduced overall efficiency, in particular a reduced overall NOx conversion rate, of the SCR system is detected in a pre-diagnosis mode or during normal driving, the diagnostic mode is carried out and/or information about the status of the SCR system is output.

The user can be informed by the status information that his SCR system is not functional. In particular, it can be provided that the detection and/or monitoring of the overall efficiency of the SCR system is carried out by an on-board diagnostic system, a workshop diagnostic system and/or a vehicle-internal diagnostic system.

If necessary, it is provided that the predetermined diagnostic amount of operating fluid for the diagnostic operation is dimensioned such that, with a functional first SCR catalytic converter, the reducing agent introduced by the diagnostic amount of operating fluid can be stored at least temporarily in the first SCR catalytic converter.

In particular, it can be provided that a specific amount of reducing agent is introduced by the diagnostic amount of operating fluid, which can be at least temporarily, in particular completely, stored and/or absorbed by a functional first SCR catalytic converter.

[0040] This prevents a reducing agent slippage from occurring after the second SCR catalytic converter, although the first SCR catalytic converter is still functional. This means that, if necessary, this prevents an overcharging of a first functional SCR catalytic converter, as a result of which detection errors are reduced.

If necessary, it is provided that the predetermined diagnostic quantity of operating fluid for the diagnostic operation is dimensioned in such a way that, with a functional first and/or second SCR catalytic converter, the reducing agent introduced by the diagnostic quantity of operating fluid is at least temporarily in the first and/or second SCR -Catalyst can be saved.

The diagnosis quantity of operating fluid is determined/calculated in particular from/by means of test trials in which, for example, a good and bad system is checked with specified dosage quantities of operating fluid and the system behavior is stored in characteristic diagrams/threshold values. The set of diagnostics is then selected in such a way that there is the best possible differentiation between the good and the bad system.

If necessary, it is provided that the emptying of the SCR catalytic converters takes place by stopping or reducing the fuel supply until a parameter is detected that provides information that no more reducing agent is stored in the SCR catalytic converters, this parameter is detected in particular by at least one NOx sensor.

Optionally, it is provided that the parameter is a difference between an emission recorded before the SCR catalysts, in particular a NOx emission, and an emission recorded after the SCR catalysts, in particular a NOx emission, and that the difference of the emissions detected before and after the SCR catalytic converters when the SCR catalytic converters are emptied is below a predetermined differential value and in particular is zero.

[0045] This makes it possible to judge whether the emptying of the SCR catalytic converters has been completed. In particular, it is provided that if essentially no difference is detected between the NOx measured value of the first NOx sensor and the NOx measured value of the second NOx sensor, the SCR catalytic converters are considered empty. In this case, no reducing agent is stored in the SCR catalytic converters, which means that no NOx emissions can be converted.

The first NOx sensor is possibly after the internal combustion engine and the second

The NOx sensor may be located after the exhaust aftertreatment system, that is to say after the last SCR catalytic converter.

If necessary, it is provided that the reactions of the SCR system, in particular the SCR catalysts, which are decisive for the process, are calculated in addition to real operation in a kinetic model, the kinetic model in particular being a mathematical representation of the physical model of the SCR used -System corresponds.

The reactions that are decisive for the method can be calculated in a mathematical and/or physical model. For example, such a kinetic model is disclosed in the applicant's AT 512 514 B1. Provision is preferably made for the relevant reactions to be mapped mathematically and physically by the kinetic models. The reactions can thus be based on physical conditions, which can reduce estimates and/or uncertainties and which can increase the accuracy of the modeled values. For example, the oxidation of the reducing agent, in particular the oxidation of NHe:, can also be mapped with the kinetic models. With conventional methods without kinetic models, the oxidation of reducing agent, if it is taken into account at all, can usually only be estimated, which is associated with great uncertainties or is imprecise.

If necessary, it is provided that the predetermined diagnosis amount of operating fluid is determined or calculated by the kinetic model and in particular corresponds to an amount of reducing agent which, according to the model calculation, can be stored at least temporarily in the first SCR catalytic converter when it is functional .

It can preferably be provided that the quantity of reducing agent, which can be stored at least temporarily in a functional first SCR catalytic converter, can be calculated by a kinetic model of the first SCR catalytic converter. This can ensure that a reducing agent slip is prevented by overcharging the first SCR catalytic converter.

If necessary, it is provided that the defective SCR catalytic converter is determined by comparing the actually occurring reducing agent slip with reference values, such as measured data, simulation data, characteristic diagrams or empirical values.

[0052] Provision is made for the defective SCR catalytic converter to be determined by comparing the course over time and/or the amplitude of the actually occurring reducing agent slip with reference values such as measured data, simulation data, characteristic diagrams or empirical values.

[0053] In particular, measurement data, simulation data, characteristics maps or empirical values can be compared with the actually occurring reducing agent slip. In particular, it is provided that the course over time, ie the point in time when the reducing agent slip occurs, is compared with previously recorded measurement data, simulation data, characteristic diagrams or also with empirical values.

[0054] The timing of the occurrence of the reducing agent slip can essentially depend on which of the two SCR catalytic converters is not functional.

If both SCR catalysts are not functional, the reducing agent can pass through the two SCR catalysts without being stored at least temporarily. This means that, if necessary, a slip of reducing agent is detected immediately after the diagnostic quantity has been metered in downstream of the second SCR catalytic converter.

[0056] If the first SCR catalytic converter is functional and the second SCR catalytic converter is not functional, the reducing agent can be stored at least temporarily by the first SCR catalytic converter. This means that possibly no slippage of reducing agent is detected immediately after metering in the diagnostic quantity. Only when the first SCR catalytic converter is heated above or to its desorption temperature can a reducing agent slip after the second SCR catalytic converter be detected.

If the first SCR catalyst is not functional and the second SCR catalyst is functional, the reducing agent can be stored at least temporarily only by the second SCR catalyst. This means that possibly no slip of reducing agent is detected immediately after metering in the fuel and possibly no slip of reducing agent after heating to or above the desorption temperature of the first SCR catalytic converter. In this case, a reducing agent slip after the second SCR catalytic converter can only be detected when the second SCR catalytic converter has been heated to or above its desorption temperature.

If necessary, it is provided that the diagnostic operation deviates from the normal operation of the internal combustion engine.

If necessary, provision is made for the pre-diagnosis operation to deviate from the normal operation of the internal combustion engine.

If necessary, it is provided that the method is carried out without additional measurement technology in a workshop, and / or that the method is carried out exclusively with the vehicle's own sensors, and / or that the method is arranged exclusively with a before the SCR catalysts and a is carried out after the SCR catalysts arranged NOx sensor and / or NHs sensor.

Because no additional and/or external measurement technology is required to carry out the method, ie to assess which of the two SCR catalytic converters is not functional, the assessment can be carried out easily, quickly and inexpensively. In particular, it is provided that only the vehicle's own sensors, in particular the vehicle's own NOx sensors, are used for the assessment. Provision is preferably made for a maximum of two on-board NOx sensors to be used.

If necessary, it is provided that the status information on the functionality of the first SCR catalyst and / or the second SCR catalyst is output by activating a lamp and / or as information on a display, whereby a person on the status of the functionality of the first SCR catalyst and / or the second SCR catalyst is informed.

[0063] This allows the user to be informed of the status of the SCR system. In particular, it is provided that the status information informs the person about the functionality of the SCR catalytic converters. This means that the person gets the information about which of the two SCR catalytic converters is not functional based on the activation of a lamp and/or as information on a display.

[0064] This means that, if necessary, the functionality of the first SCR catalytic converter and/or the second SCR catalytic converter can also be assessed while driving, ie without visiting a workshop.

The invention will now be explained further using the example of exemplary, non-exclusive, exemplary embodiments.

1 shows a schematic representation of a first embodiment of an exhaust gas aftertreatment system,

Figures 2a, 2b and 2c show the schematic curves of the temperature, the load and the detected NOx / NH3 measured value of the second NOx sensor over time during diagnostic operation for a functional SCR system, the curves as measurement data in methods according to the invention can be used,

Figures 3a, 3b and 3c show the schematic curves of the temperature, the loading and the detected NOx / NH3 measured value of the second NOx sensor over time during diagnostic operation for an SCR system, the first SCR catalyst not is functional, and

Figures 4a, 45 and 4c show the schematic curves of the temperature, the load and the detected NOx / NH3 measured value of the second NOx sensor over time during diagnostic operation for an SCR system, the second SCR catalyst not is functional.

Unless otherwise indicated, the reference symbols correspond to the following components: internal combustion engine 1, first NOx sensor 2, dosing device 3, second NOx sensor 4, first SCR catalytic converter 5, second SCR catalytic converter 6, diesel oxidation catalytic converter 7, diesel oxidation catalytic converter temperature 8, first SCR catalyst temperature 9, second SCR catalyst temperature 10, temperature in degrees Celsius 11, reducing agent loading in grams per liter 12, first reducing agent loading 13, second reducing agent loading 14, detected NOx/NH3 measured value in ppm 15, first detected NOx/NH3 measured value 16, second detected NOx/NH3 measured value 17 and time in seconds 18.

1 shows a first embodiment of an internal combustion engine with an exhaust gas aftertreatment system. The exhaust aftertreatment system of the internal combustion engine 1 comprises a first NOx sensor 2, a diesel oxidation catalytic converter 7, a dosing device 3, a first SCR catalytic converter 5, a second SCR catalytic converter 6 and a second NOx sensor 4.

According to this first embodiment of an exhaust gas aftertreatment system, the first SCR catalytic converter 5 comprises an sDPF or the first SCR catalytic converter 5 is designed as an SDPF. Furthermore, according to this first embodiment, the second SCR catalytic converter 6 comprises an SCR catalytic converter and an ASC catalytic converter, or the second SCR catalytic converter 6 is designed as an SCR-ASC combination catalytic converter.

In regular operation, that is to say in normal operation, a fuel is metered in via the metering device 3 upstream of the first SCR catalytic converter 5 . The fuel contains a reducing agent or can be converted into a reducing agent. The reducing agent, in particular ammonia NHs, is stored at least temporarily in at least one SCR catalytic converter 5, 6.

Figures 2a, 2b and 2c show the schematic curves of the temperature, the load and the detected NOx / NH3s measured value of the second NOx sensor 4 for various components of the exhaust gas aftertreatment system during diagnostic operation for a functional SCR system.

The curves determined in this way can be used, for example, as measurement data for determining the defective SCR catalytic converter 5, 6 in a non-functional SCR system.

This means that by comparing the measured data determined in this way with curves that actually occur in a non-functional SCR system, it is possible to conclude that the SCR catalytic converter 5, 6 is defective.

In Fig. 2a, the temperature in degrees Celsius 11 and on the x-axis the time in seconds 18 are shown schematically on the y-axis. In FIG. 2b, the reducing agent loading in grams per liter 12 is shown schematically on the y-axis and the time in seconds 18 is shown schematically on the x-axis. 2c shows the detected NOx/NH3s measured value 17 of the second SCR catalytic converter 6 on the y-axis and the time in seconds 18 on the x-axis.

From the schematic curves of the measurement data it can be seen that in diagnostic mode first the SCR catalytic converters 5, 6 are emptied, whereby the reducing agent loading 13, 14 of the first SCR catalytic converter 5 and the second SCR catalytic converter 6 is essentially the same is reduced to zero. According to this embodiment, the SCR catalytic converters 5, 6 are emptied by reducing or interrupting the fuel supply.

According to this embodiment, the two SCR catalytic converters 5, 6 already have a temperature 9, 10 which is within a predetermined temperature window and therefore do not have to be temperature-controlled.

[0080] A predetermined diagnostic quantity of the fuel is then metered in upstream of the first SCR catalytic converter 5 . The diagnostic amount of fuel introduces an amount of reducing agent into the exhaust gas aftertreatment system, which can be stored at least temporarily in a functional first SCR catalytic converter 5 . This prevents the first SCR catalytic converter 5 from being overcharged by the introduction of the diagnostic quantity.

In the case illustrated in FIGS. 2a, 2b and 2c, both the first SCR catalytic converter 5 and the second SCR catalytic converter 6 are functional and are used, for example, to determine measurement data. This means that the amount of reducing agent introduced by the diagnostic amount can be stored at least temporarily in the first SCR catalytic converter 5 . Immediately after the diagnostic quantity has been metered in, the reducing agent loading of the first SCR catalytic converter 5, the so-called first reducing agent loading 13, increases suddenly. In this case, there is no slippage of reducing agent downstream of the second SCR catalytic converter 6 immediately after the diagnostic quantity has been metered in.

The first SCR catalytic converter 5 is then brought to or above its desorption temperature by engine measures, in particular by increasing the exhaust gas temperature. Due to the increase in the exhaust gas temperature, the diesel oxidation catalytic converter temperature 8, the first SCR catalytic converter temperature 9 and the second SCR catalytic converter temperature 10 rise.

As soon as the first SCR catalytic converter 5 is heated to or above its desorption temperature, the reducing agent stored at least temporarily in the first SCR catalytic converter 5 is desorbed. Since both the first 5 and the second SCR catalytic converter 6 are functional when the measurement data is generated, no slippage of the reducing agent downstream of the second SCR catalytic converter 6 is detected as a result.

The quantity of reducing agent desorbed from the first SCR catalytic converter 5 is stored at least temporarily in the second SCR catalytic converter 6 . A reducing agent slip after the second SCR catalytic converter 6 is only detected when the second SCR catalytic converter 6 has been heated to or above its desorption temperature.

This second detected NOx/NHs measured value 17 is shown in FIG. 2c. The first detected NOx/NH3 measured value 16 in FIG. 2c can only be detected if a further NOx sensor is arranged between the first SCR catalytic converter 5 and the second SCR catalytic converter 6 . A first NOx sensor 2 is preferably arranged just upstream of the first SCR catalytic converter 5, in particular upstream of the diesel oxidation catalytic converter 7, i.e. immediately downstream of the internal combustion engine 1, and a second NOx sensor 4 is arranged downstream of the second SCR catalytic converter 6, i.e. downstream of the exhaust gas aftertreatment system.

According to this embodiment, the SCR catalytic converters 5, 6 are heated with a time delay. This means that first the first SCR catalytic converter 5 is heated to or above its desorption temperature and then the second SCR catalytic converter 6 is heated to or above its desorption temperature.

Figures 3a, 3b and 3c show the schematic curves of the temperature, the load and the detected NOx / NH3s measured value of the second NOx sensor 4 for various components of the exhaust gas aftertreatment system during diagnostic operation for an SCR system, the first SCR catalyst 5 is not functional.

In Fig. 3a, the temperature in degrees Celsius 11 is shown on the y-axis and the time in seconds 18 is shown on the x-axis. 3b shows the reducing agent loading in grams per liter 12 on the y-axis and the time in seconds 18 on the x-axis. In FIG. 3c, the detected NOx/NH3 measured value 17 of the second SCR catalytic converter 6 is shown on the y-axis and the time in seconds 18 is shown on the x-axis.

[0089] Before the diagnostic mode is activated in, in particular real, mode, a reduced overall efficiency of the SCR system must be detected. The overall efficiency of the SCR system can be detected in a pre-diagnosis mode or by normal overall efficiency monitoring during driving. In particular, the detection of an on-board

Diagnostic system or a workshop diagnostic system are carried out.

If the diagnostic mode is now activated, the procedural steps as described in particular in FIGS. 2a, 2b and 2c are carried out first.

This means that after the SCR catalytic converters 5, 6 have been emptied, a predetermined diagnostic quantity of fuel is metered in before the first SCR catalytic converter 5 via the metering device 3. According to this embodiment, the SCR catalytic converters 5, 6 are emptied by reducing or interrupting the fuel supply.

The emptying is considered complete when a parameter is detected which provides information about the amount of reducing agent in the two SCR catalytic converters 5, 6. In particular, it is provided that the emptying is considered complete when the measured NOx value of the first NOx sensor 2 and the measured NOx value of the second NOx sensor 4 essentially do not differ from one another at all or differ only slightly from one another. When the two SCR catalytic converters 5, 6 are empty, there is essentially no reducing agent in the SCR catalytic converters 5, 6 and NOx emissions can no longer be reduced.

[0093] According to this specific embodiment, the predetermined diagnostic amount of fuel is measured in such a way that it can be stored at least temporarily in a functional first SCR catalytic converter 5 and/or second SCR catalytic converter 6 .

According to this embodiment, so much fuel is metered in during the diagnostic operation after the diagnostic amount of fuel has been metered in, in particular continuously, that the previously defined reducing agent storage level can be maintained. This means that essentially just as much fuel is metered in as is consumed by the NOx emissions that occur and their conversion, with the result that the level of reducing agent stored in the first SCR catalytic converter 5 remains essentially constant.

[0095] It is also provided that the reactions of the first SCR catalytic converter 5 and the second SCR catalytic converter 6, which are decisive for the method, are calculated in a kinetic model in addition to real operation. According to this embodiment, the kinetic model is a mathematical and/or physical representation of the real system.

[0096] In particular, according to this specific embodiment, it is provided that the previously determined diagnostic quantity of fuel is determined or calculated by the kinetic model of the first SCR catalytic converter 5 . This means that the predetermined diagnostic quantity according to the model calculation can be stored entirely at least temporarily in the first SCR catalytic converter 5 if the latter is functional.

The exhaust gas temperature is then increased by an engine measure and the SCR catalytic converters 5, 6 are heated at different times.

If, as in this case, the first SCR catalytic converter 5 is not functional, the quantity of reducing agent introduced by the diagnostic quantity passes through the first SCR catalytic converter 5 without being stored in it. The quantity of reducing agent is therefore stored at least temporarily in the second SCR catalytic converter 6 immediately after metering.

[0099] This is shown in FIG. 3b, since the reducing agent loading of the second SCR catalytic converter 6, the so-called second reducing agent loading 14, increases suddenly after the diagnostic quantity has been metered in. This means that in this case no slippage of reducing agent is detected by the second NOx sensor 4 immediately after the diagnostic quantity has been metered.

If now the first SCR catalyst 5 has been heated to or above its desorption temperature, no reducing agent slip is detected by the second NOx sensor 4 according to this embodiment, since no reducing agent is stored in the first SCR catalyst 5 essentially.

Only when the second SCR catalytic converter 6 reaches or exceeds its desorption temperature

is heated, the reducing agent stored therein at least temporarily is desorbed, and the second NOx sensor 4 can detect a reducing agent slip, a so-called second detected NOx/NH3 measured value 17 .

By comparing the actually occurring reducing agent slip with reference values, such as measurement data, simulation data, characteristic diagrams or empirical values, it can be determined which of the two SCR catalytic converters 5, 6 is not functional. The measurement data can be determined using a functional SCR system, as shown for example in FIG. 2 .

In addition, it is also possible to determine the defective SCR catalytic converter 5, 6 from the time profiles of the temperatures 8, 9, 10 and the measured value of the second NOx sensor 4, the second detected NOx/NHs measured value 17.

The diagnostic operation can be carried out without additional measurement technology in a workshop or while driving. In particular, it is provided that the method, in particular the diagnostic operation, only requires the vehicle's own sensors, in particular the NOx sensors 2, 4 and/or the NHs sensors, to be carried out. In particular, it is provided that only the two vehicle NOx sensors 2, 4 are used for the method according to the invention.

In order to repair the damage, only the first SCR catalytic converter 5 has to be replaced in this case in order to be able to meet the legal requirements, in particular the legal requirements with regard to NOx emissions, again. The method prevents the second SCR catalytic converter 6 from being replaced unnecessarily, which means that time and costs can be reduced.

Figures 4a, 4b and 4c show the schematic curves of the temperature, the load and the detected NOx / NH3 measured value of the second NOx sensor 4 for various components of the exhaust gas aftertreatment system during diagnostic operation for an SCR system, the second SCR catalyst 6 is not functional.

In Fig. 4a, the temperature in degrees Celsius 11 is shown on the y-axis and the time in seconds 18 is shown on the x-axis. 4b shows the reducing agent loading in grams per liter 12 on the y-axis and the time in seconds 18 on the x-axis. In FIG. 4c, the detected NOx/NH3 measured value 17 of the second SCR catalytic converter 6 is shown on the y-axis and the time in seconds 18 is shown on the x-axis.

If the diagnostic mode is now activated, the procedural steps as described in particular in FIGS. 2a, 2b, 2c, 3a, 3b and 3c are carried out first.

In contrast to FIG. 3, in the case shown here, the first SCR catalytic converter 5 is functional and the second SCR catalytic converter 6 is not functional. This means that the quantity of reducing agent introduced by the diagnosis quantity is stored in first SCR catalytic converter 5 . Consequently, no slippage of reducing agent downstream of the second SCR catalytic converter 6 can be detected immediately after the diagnostic quantity has been metered in.

As soon as the first SCR catalytic converter 5 is heated to or above its desorption temperature, the reducing agent stored in this at least temporarily is desorbed. Since the second SCR catalytic converter 6 is not functional, the desorbed reducing agent cannot be stored in it. As a result, the desorbed reducing agent passes through the second SCR catalytic converter 6 without a time delay, and immediately after the first SCR catalytic converter 5 has reached or exceeded its desorption temperature, a slip of reducing agent downstream of the second SCR catalytic converter 6 is detected.

In order to repair the damage, only the second SCR catalytic converter 6 has to be replaced in this case in order to be able to meet the legal requirements again, in particular the legal requirements with regard to NOx emissions. The method prevents the first SCR catalytic converter 5 from being replaced unnecessarily, which means that time and costs can be reduced.

According to an embodiment that is not shown, a reducing agent slip after the second SCR catalytic converter 6 is detected immediately after the diagnostic quantity has been metered in. This is the case when both SCR catalytic converters 5, 6 are not functional. In this case, both the first SCR catalytic converter 5 and the second SCR catalytic converter 6 can essentially not store any reducing agent.

In order to repair the damage, both SCR catalytic converters 5, 6 must be exchanged in this case in order to be able to meet the legal requirements, in particular the legal requirements with regard to NOx emissions.

Claims (1)

patent claims 1. Method for checking the function of individual SCR catalytic converters (5, 6) of an SCR system of an exhaust aftertreatment system of an internal combustion engine, - Wherein the SCR system along the exhaust aftertreatment system serially one after the other comprises a first SCR catalytic converter (5) and a second SCR catalytic converter (6), - with the SCR system in regular operation, which corresponds to the intended operation, a fuel is metered, - where the fuel contains a reducing agent or is converted into a reducing agent, - and wherein the reducing agent is stored at least temporarily in at least one SCR catalytic converter (5, 6) of the SCR system, includes the following steps: - Activation of a diagnostic mode, - then emptying the SCR catalytic converters (5, 6) by stopping or reducing the fuel supply until no more reducing agent is stored in the SCR catalytic converters (5, 6), - Subsequently, if necessary, tempering, in particular heating, the SCR system, so that the temperature of the SCR system and in particular the SCR catalysts (5, 6) is within a predetermined temperature window, wherein - then a predetermined diagnostic quantity of the fuel is metered in, which defines a quantity of reducing agent, the quantity of reducing agent being smaller than the maximum quantity of reducing agent that can be stored by the first SCR catalytic converter (5) in a functional state, - If no slippage of reducing agent downstream of the second SCR catalytic converter (6) is detected during metering of the diagnostic quantity, the temperature of the first SCR catalytic converter (5) is increased to or above its desorption temperature, with the second SCR catalytic converter (6) being Defective is defined if a reducing agent slip after the second SCR catalytic converter (6) is detected while the temperature of the first SCR catalytic converter (5) is increasing to or above its desorption temperature, - and where appropriate status information on the function of the first SCR catalytic converter (5) and/or the second SCR catalytic converter (6) is output and/or stored, and where the diagnostic mode is ended if necessary, characterized, - That the defective SCR catalytic converter (5, 6) is determined by comparing the course over time and/or the amplitude of the actually occurring reducing agent slip with reference values, such as measurement data, simulation data, characteristic diagrams or empirical values. 2. The method according to claim 1, characterized in - that, in particular subsequently, the temperature of the second SCR catalyst (6) is increased to or above its desorption temperature, the first SCR catalyst (5) being defined as defective if while the temperature of the second SCR catalytic converter (6) is being increased to or above its desorption temperature, a slip of reducing agent downstream of the second SCR catalytic converter (6) is detected, - and that the diagnostic operation is ended if necessary. 3. The method according to claim 1 or 2, characterized in that - that both SCR catalytic converters (5, 6) are defined as defective if a reducing agent slip after the second SCR catalytic converter (6) is detected during metering of the diagnostic quantity, - and that the diagnostic mode is ended if necessary. 4. The method according to any one of claims 1 to 3, characterized in that the SCR catalytic converters (5, 6) are heated in succession or at different times, 10. 11. 12. 13th 14th 15 Austrian AT 521 117 B1 2022-04-15 - that first the first SCR catalytic converter (5) is heated to or above its desorption temperature, - And that then the second SCR catalyst (6) is heated to or above its desorption temperature. Method according to one of the preceding claims, characterized in that the temperatures of the SCR catalytic converters (5, 6) are increased by increasing the exhaust gas temperature. Method according to one of the preceding claims, characterized in that the diagnostic mode is activated if previously a reduced efficiency, in particular a reduced overall efficiency, of the SCR system is detected in a pre-diagnostic mode or during normal overall efficiency monitoring during driving, the detection in particular carried out by an on-board diagnosis system or a workshop diagnosis system. Method according to one of the preceding claims, characterized in that the predetermined diagnostic amount of operating fluid for the diagnostic operation is dimensioned such that with a functional first SCR catalytic converter (5) the reducing agent introduced by the diagnostic amount of operating fluid is at least temporarily in the first SCR catalytic converter (5) can be saved. Method according to one of the preceding claims, characterized in that the SCR catalytic converters (5, 6) are emptied by stopping or reducing the fuel supply until a parameter is detected which provides information that no more reducing agent is in the SCR -Catalysts (5, 6) is stored, this parameter being detected in particular by at least one NOx sensor. Method according to Claim 8, characterized in that - that the parameter is a difference between an emission recorded before the SCR catalytic converters (5, 6), in particular a NOx emission, and an emission recorded after the SCR catalytic converters, in particular a NOx emission, - And that the difference between the emissions detected upstream and downstream of the SCR catalytic converters (5, 6) when the SCR catalytic converters (5, 6) are emptied is below a predetermined difference value and in particular at zero. Method according to one of the preceding claims, characterized in that the reactions of the SCR system, in particular the SCR catalysts (5, 6), which are decisive for the method, are calculated in addition to real operation in a kinetic model, the kinetic model in particular being a mathematical mapping corresponds to the physical model of the SCR system used. Method according to Claim 10, characterized in that the predetermined diagnostic quantity of fuel is determined or calculated by the kinetic model and in particular corresponds to a quantity of reducing agent which, according to the model calculation, can be stored at least temporarily in the first SCR catalytic converter (5), if it is functional. Method according to one of the preceding claims, characterized in that the defective SCR catalytic converter (5, 6) is determined by comparing the actually occurring reducing agent slip with reference values, such as measured data, simulation data, characteristic diagrams or empirical values. Method according to one of the preceding claims, characterized in that the diagnostic operation differs from the normal operation of the internal combustion engine. Method according to one of Claims 6 to 13, characterized in that the pre-diagnosis operation differs from the normal operation of the internal combustion engine. Method according to one of the preceding claims, characterized in that the method is carried out in a workshop without additional measurement technology, - and/or that the procedure is carried out exclusively with the vehicle's own sensors, - and/or that the method is carried out exclusively with an NOx sensor and/or NHs: sensor arranged upstream of the SCR catalytic converters (5, 6) and downstream of the SCR catalytic converters (5, 6). 16. The method according to any one of the preceding claims, characterized in that the status information on the functionality of the first SCR catalytic converter (5) and / or the second SCR catalytic converter (6) is output by activating a lamp and / or as information on a display , whereby a person is informed of the health status of the first SCR catalyst (5) and/or the second SCR catalyst (6). 4 sheets of drawings