AT521117A1 - Method for functional testing of SCR catalysts of an SCR system - Google Patents

Abstract

The invention relates to a method for functional testing of individual SCR catalysts (5, 6) of an exhaust aftertreatment system, wherein the SCR system comprises two SCR catalysts, wherein in the SCR system, a fuel is metered in which contains a reducing agent or converted into a reducing agent is stored, and wherein the reducing agent is at least temporarily stored in at least one SCR catalyst (5, 6), wherein first the SCR catalysts (5, 6) are emptied, then, if necessary, the SCR system is tempered, then a metered predetermined diagnostic amount of the fuel, which defines a reducing agent amount, wherein the reducing agent amount is smaller than the maximum of the first SCR catalyst (5) in a functional condition storable amount of reducing agent, wherein, if during the dosing of the diagnostic amount, no reducing agent slip after the second SCR catalyst (6) is detected, the temp the first SCR catalyst (5) is raised to or above its desorption temperature, and wherein the second SCR catalyst (6) is defined as being defective when, during the elevation of the temperature of the first SCR catalyst (5), to or above its desorption temperature, a reductant slip after the second SCR catalyst (6) is detected.

Description

The invention relates to a method for checking the function of individual SCR catalysts (5, 6) of an exhaust aftertreatment system, wherein the SCR system comprises two SCR catalysts, wherein the SCR system is metered into a working substance which contains a reducing agent or is converted into a reducing agent, and wherein the reducing agent is at least temporarily stored in at least one SCR catalyst (5, 6), first deflating the SCR catalysts (5, 6), then, if necessary, tempering the SCR system, then a predetermined diagnostic amount of the working fluid wherein the amount of reducing agent is smaller than the maximum amount of reducing agent that can be stored by the first SCR catalytic converter (5) in a functional state, if no reductant slip after the second SCR catalytic converter () during the dosing of the diagnostic quantity 6) is detected, the temper nature of the 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 raising the temperature of the first SCR catalyst (5) to or above its desorption temperature a reductant slip after the second SCR catalyst (6) is detected.

Fig. 2 / 32nd

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AVL List GmbH

Method for functional testing of SCR catalysts of an SCR system

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

From the prior art, different methods for functional testing of SCR components of an exhaust aftertreatment system of

Internal combustion engines known. For example, methods are known in which a case of damage of the SCR system is detected if a deviation between real NOx measured values and modeled NOx measured values occurs after the exhaust gas aftertreatment system. In conventional methods, since it is not possible to detect which of the two SCR components is not functional, in practice it may be necessary to swap all SCR components or only the second SCR component to repair the damage.

The object of the invention is to overcome the disadvantages of the prior art. In particular, it is an object of the invention to provide a method by means of which the faulty SCR catalyst can be determined simply and quickly in order to avoid unnecessary replacement of non-defective catalysts. This determination should be made without the use of additional sensors and / or additional components, i. H. So done using the vehicle's sensors and / or components, which quickly, easily and inexpensively faulty

Catalysts can be found and selectively exchanged.

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

The invention relates to a method for functional testing of individual SCR catalysts of an SCR system of an exhaust aftertreatment system of a

Internal combustion engine, the SCR system along the

Exhaust aftertreatment plant serially comprises a first SCR catalyst and a second SCR catalyst, wherein in the SCR system in normal operation, which corresponds to the intended operation, a fuel is metered / 32

PP31558AT

AVL List GmbH wherein the operating material contains a reducing agent or is converted into a reducing agent, and wherein the reducing agent is at least temporarily stored in at least one SCR catalyst of the SCR system.

According to the invention, the method comprises the following steps: activating a diagnostic operation, then emptying the SCR catalysts by stopping or reducing the fuel supply until no reducing agent is stored in the SCR catalysts, then, if necessary,

Tempering, in particular heating, the SCR system, so that the temperature of the SCR system and in particular the SCR catalysts is within a predetermined temperature window, and then a predetermined diagnostic amount of the fuel is metered, which defines a reducing agent amount, wherein the reducing agent amount is less than the maximum amount of reducing agent that can be stored by the first SCR catalytic converter in a functional state, wherein if no diagnostic dose is available during dosing

Reductant slip after the second SCR catalyst is detected, the temperature of the first SCR catalyst is increased to or above its desorption temperature, wherein the second SCR catalyst is defined as defective when during the increase of the temperature of the first SCR catalyst on or over its Desorption is a Reduktionsmittelschlupf after the second SCR catalyst is detected, and where appropriate, a status information on the function of the first SCR catalyst and / or the second SCR catalyst is output and / or stored, and that the diagnostic operation may be terminated.

If appropriate, it is provided that during normal operation, in particular during operation, a feedstock suitable for selective catalytic reduction, such as, in particular, a urea-containing mixture, a urea solution or AdBlue®, is metered in before the SCR catalyst. The operating substance may contain a reducing agent, in particular ammonia NH 3, or be convertible into a reducing agent, in particular NH 3. A urea-containing mixture, in particular a urea-water solution, such as, for example, AdBlue®, is preferably used as the operating material, the fuel / 32

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If necessary, AVL List GmbH is converted into the reducing agent, in particular NH 3, by reactions described below:

Thermolysis: (NH2) 2CO NH3 + HNCO

Hydrolysis: HNCO + H2O NH3 + CO2

In a first step, during the thermolysis reaction, the urea (NH 2) 2 CO can be converted into ammonia NH 3 and isocyanic acid HNCO. In a second

Step in the hydrolysis reaction, the isocyanic acid HNCO can be converted with water H2O into ammonia NH3 and carbon dioxide CO2.

If appropriate, the reducing agent, in particular NH 3, can be stored and / or stored at least temporarily in at least one SCR catalytic converter. Optionally, the ammonia attaches to the active sites of the SCR catalyst. The at least temporarily stored reducing agent, in particular the ammonia NH3, can then reduce nitrogen oxides NOx, in particular nitric oxide NO and nitrogen dioxide NO2.

The metering of the operating material can take place via a metering device, in particular via an injector or via an injection nozzle. In particular, it is provided that the operating material is introduced before the first SCR catalyst.

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 catalysts may be based on the fact that the reducing agent still contained in the SCR catalyst is consumed by the reduction of nitrogen oxides NOx, whereby the SCR catalysts, in particular completely, can be emptied.

Optionally, it may be provided that the reducing agent still contained in the SCR catalyst is carried out by a discharge operation, for example a temperature increase of the SCR catalyst.

After the SCR catalysts have been emptied, the SCR system and in particular the SCR catalysts can be tempered, in particular heated, in order to bring the SCR catalysts to a predetermined temperature. This / 32

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Temperierungsschritt can be omitted if the temperature of the SCR catalysts is already in a predetermined temperature window.

Subsequently, a predetermined amount of the operating material, a so-called diagnostic amount, are metered. Preferably, the amount of reducing agent introduced by the diagnostic amount can be smaller than that amount that can be stored at least temporarily by a first functional SCR catalytic converter.

As a result, it can be ensured that the amount of reducing agent introduced by the diagnostic quantity can optionally be recorded at least temporarily, in particular completely, by the first SCR catalytic converter and / or stored at least temporarily, in particular completely. This means that, if appropriate, a predefined reductant storage level in a first functional SCR catalytic converter can be achieved by the diagnostic amount.

Optionally, it is provided that during the diagnostic operation after metering in the diagnostic amount of fuel, in particular continuously, so much fuel is metered in that the predefined reductant storage level can be maintained. That is, where appropriate, exactly as much fuel is metered in, as is consumed by the occurring NOx emissions and their implementation, and thus the reducing agent storage level in the SCR catalysts and / or in one of the two SCR catalysts remains substantially constant.

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

Subsequently, the temperature of the first SCR catalyst can be raised to or above its desorption temperature. Preferably, the second SCR catalyst is defined as defective and / or non-functional, if during the temperature increase of the first SCR catalyst on or about his /

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Desorption a reductant slip after the second SCR catalyst is detected. In other words, the reductant slip after the second SCR catalyst occurs in the above-described temperature increase of the first SCR catalyst only when desorbed from the first SCR catalyst

Reducing agent without at least temporary storage can pass the second SCR catalyst. As a result, it can be stated that the second SCR catalyst is not functional because it has little or no effect

Having reducing agent storage capacity.

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

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

Desorption the reducing agent is expelled from the SCR catalyst and / or leaves the SCR catalyst.

The reducing agent slip, in particular the NH3 slip, can be detected by at least one sensor, in particular a NOx sensor or NH3 sensor.

The at least one sensor may be arranged after the SCR catalysts or the SCR system. If necessary, the NH3 slip is detected by an increased measured value of the NOx sensor, since the concentration of NH3 can have an influence on a NOx sensor.

In the context of the present disclosure, an SCR system can be understood in particular to mean a system which comprises an sDPF catalyst, a

SCR catalyst and / or an ASC catalyst or is formed from a sDPF catalyst, an SCR catalyst and / or an ASC catalyst. Preferably, the SCR system also includes the device for metering in the operating material and optionally also the operating material as such.

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In the context of the present disclosure, an SCR catalyst may be understood as an sDPF catalyst, an SCR catalyst, an ASC catalyst and / or an SCR-ASC catalyst combination.

Optionally, the determined functionality of the

Exhaust after-treatment system output as status information and / or stored. If appropriate, the status information can also be stored in a storage system of the internal combustion engine and / or of a motor vehicle.

Subsequently, the diagnostic operation may be terminated.

In the context of the present disclosure, diagnostic operation means an operation in which the method steps of the method follow one another, as described above. This means that optionally first the SCR catalysts, in particular completely, are emptied, then the SCR catalysts optionally tempered, then a predetermined diagnostic amount of the fuel is metered, then optionally the temperature of the first SCR catalyst and optionally connect the temperature of the second SCR catalyst is increased.

Optionally, it is provided that, in particular, subsequently the temperature of the second SCR catalyst is increased up to or above its desorption temperature, wherein the first SCR catalyst is defined as defective if, during the elevation of the temperature of the second SCR catalyst, to or above its

Desorption is a reducing agent slip after the second SCR catalyst is detected, and that the diagnostic operation is terminated if necessary.

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 SCR25 catalytic converter without at least temporarily being stored and / or received therein. This means that, if appropriate, the introduced amount of reducing agent is taken up at least temporarily directly by the second SCR catalytic converter, if this is functional. Now, when the second SCR catalyst is brought to or above its desorption temperature, the / 32 leaves

PP31558AT

AVL List GmbH optionally stored reducing agent, the second SCR catalyst and a reducing agent slip is detectable.

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

Optionally, it is provided that both SCR catalysts are defined as defective if a reduction agent slip after the second SCR catalytic converter is detected during metering in of the diagnostic quantity, and that the diagnostic operation is terminated, if appropriate.

If both SCR catalysts are not functional, no reducing agent or only a very small amount of reducing agent can be at least temporarily stored in the SCR catalysts. This means that, if appropriate, the amount of reducing agent introduced by the diagnostic quantity passes through the two SCR catalysts of the SCR system without at least temporarily being stored in it.

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

Optionally, it is contemplated that the SCR catalysts are heated sequentially or staggered in time by first heating the first SCR catalyst to or above its desorption temperature, and then heating the second SCR20 catalyst to or above its desorption temperature.

If appropriate, it is provided that the temperatures of the SCR catalysts are increased by increasing the exhaust gas temperature.

Optionally, it can be provided that the individual SCR catalysts are heated separately. This means that optionally the first and second SCR25 catalysts can be brought independently of one another to their desorption temperature, in particular desorption temperatures.

It is preferably provided that the increase in the temperature of the SCR catalysts takes place by increasing the exhaust gas temperature. This means that if necessary / 32

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By increasing the exhaust gas temperature, AVL List GmbH first heats the first SCR catalyst and then subsequently the second SCR catalyst to or above its desorption temperature. In particular, it is provided that the

Exhaust after-treatment system, in particular the SCR catalysts, by a

Motor measure to be brought to the desired temperature.

Optionally, it is provided that the diagnostic mode is activated when previously a reduced efficiency, in particular a reduced overall efficiency of the SCR system is detected in a pre-diagnostic or in the normal overall efficiency monitoring while driving, the detection in particular by an on-board diagnostic system or a Workshop diagnostic system is performed.

In particular, it can be provided that the diagnostic operation, in particular the relevant method steps of the diagnostic operation, be carried out, if previously a reduced efficiency, in particular a reduced NOx conversion rate, is detected. That is, if necessary, if a reduced

Overall efficiency, in particular a reduced total NOx conversion rate, the SCR system is detected in a pre-diagnostic or normal driving, the diagnostic operation is performed and / or information on the status of the SCRSystems is output.

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

Optionally, it is provided that the predetermined diagnostic quantity of fuel for the diagnostic operation is dimensioned such that in a functional first SCR catalyst introduced by the diagnostic amount of fuel reducing agent can be stored at least temporarily in the first SCR catalyst.

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

This prevents any reductant slip from occurring after the second SCR catalyst, although the first SCR catalyst is still functional. That is, if necessary, this prevents overcharging of a first functional SCR catalyst, thereby reducing detection errors.

Optionally, it is provided that the predetermined diagnostic quantity of fuel for the diagnostic operation is dimensioned such that in a functional first and / or second SCR catalyst introduced by the diagnostic amount of fuel reducing agent stored at least temporarily in the first and / or second SCR catalyst can be.

The diagnostic amount of fuel is in particular determined / calculated by means of test experiments in which e.g. with a given dosage of fuel a good and bad system tested and the system behavior in

Maps / thresholds is deposited. The diagnostic amount is then chosen so that the best differentiability between good and bad system is given.

Optionally, it is provided that the emptying of the SCR catalysts by stopping or reducing the fuel supply takes place until a parameter is detected, which provides information that no reducing agent is stored in the SCR catalysts, this parameter in particular by at least a NOx sensor is detected.

If appropriate, 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 between the before and According to the SCR catalysts detected emissions is at emptied SCR catalysts below a predetermined differential value and in particular is zero.

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This can be used to judge whether the emptying of the SCR catalysts has been completed. In particular, it is provided that, if substantially 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 catalysts are considered empty. In this case, no reducing agent is stored in the SCR catalysts, whereby no NOx emissions can be implemented.

The first NOx sensor is optionally after the internal combustion engine and the second NOx sensor optionally after the exhaust aftertreatment system, that is optionally after the last SCR catalyst arranged.

If appropriate, it is provided that the reactions of the SCR system, in particular of the SCR catalysts, which are decisive for the method are calculated in addition to the real operation in a kinetic model, the kinetic model in particular corresponding to a mathematical mapping of the physical model of the SCR system used ,

The relevant reactions for the process can be calculated in a mathematical and / or physical model. For example, such a kinetic model is disclosed in Applicant's AT 512 514 B1. It is preferably provided that the relevant reactions are mapped mathematically and physically by the kinetic models. The responses may thus be based on physical conditions, which may reduce estimates and / or uncertainties and increase the accuracy of the modeled values. For example, the kinetic models can also be used to image the oxidation of the reducing agent, in particular the oxidation of NH 3. In conventional methods without kinetic models, the oxidation of reducing agent, if taken into account at all, can usually only be estimated, which is associated with large uncertainties or is inaccurate.

Optionally, it is provided 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 if this is functional.

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It can preferably be provided that the amount 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 reductant slippage is prevented by overcharging the first SCR catalyst.

Optionally, it is provided that the determination of the defective SCR catalytic converter takes place by a comparison of the reducing agent slip actually occurring with reference values, such as measured data, simulation data, characteristic diagrams or empirical values.

Optionally, it is provided that the determination of the defective SCR catalytic converter is effected by a comparison of the time profile and / or the amplitude of the reducing agent slip actually occurring with reference values, such as measured data, simulation data, characteristic diagrams or empirical values.

In particular, measured data, simulation data, maps or empirical values can be compared with the reducing agent slip actually occurring. In particular, it is provided that the time course, ie the time when the

Reductant slip occurs with pre-recorded measurement data

Simulation data, maps or even compared with experience.

The timing of reductant slip may be significantly dependent on which of the two SCR catalysts is inoperative.

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

If the first SCR catalyst is functional and the second SCR catalyst is not functional, the reductant may be stored at least temporarily by the first SCR catalyst. This means that, if appropriate, no reduction agent slip is detected immediately after the dosage of the diagnostic amount. Only when the first SCR catalyst over or on his / 32

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Desorption is heated, a reducing agent slip after the second SCR catalyst can be detected.

If the first SCR catalyst is not functional and the second SCR catalyst is functional, the reducing agent can only be temporarily stored by the second SCR catalyst. That is, no reductant slip may be detected immediately after metering of the feedstock and, optionally, no reductant slip after heating to or above the desorption temperature of the first SCR catalyst. Only when the second SCR catalyst has been heated to or above its desorption temperature can a reductant slip after the second SCR catalyst be detected in this case.

Optionally, it is provided that the diagnostic operation deviates from the regular operation of the internal combustion engine.

Optionally, it is provided that the prediagnosis operation deviates from the regular operation of the internal combustion engine.

If appropriate, 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 one before the SCR catalysts and one after the SCR Catalysts arranged NOx sensor and / or NH3 sensor is performed.

Due to the fact that no additional and / or external measuring technology is required for carrying out the method, that is to say for assessing which of the two SCR catalysts, the assessment is simple, quick and inexpensive to carry out. In particular, it is provided that only vehicle-specific sensors, in particular the vehicle's own NOx sensors, are used for the assessment. It is preferably provided that a maximum of two on-vehicle NOx sensors are used.

Optionally, it is provided that the status information on the functionality of the first SCR catalytic converter and / or the second SCR catalytic converter is activated by means of activation

PP31558AT

AVL List GmbH is issued a lamp and / or as information on a display, whereby a person is informed about the status of the functionality of the first SCR catalyst and / or the second SCR catalyst.

This allows the user to be informed about the status of the SCR system.

In particular, it is provided that the status information informs the person about the

Functionality of SCR catalysts informed. This means that the person on the basis of the activation of a lamp and / or as information on a display gets the information which of the two SCR catalysts is not functional.

This means that, if appropriate, the functionality of the first SCR catalytic converter and / or the second SCR catalytic converter can also be assessed while driving, that is to say without a workshop visit.

The invention will now be further illustrated by way of example, non-exclusive, exemplary embodiments.

1 shows a schematic representation of a first embodiment of an exhaust aftertreatment system, FIGS. 2a, 2b and 2c show the schematic curves of the temperature, the load and the detected NOx / NH3 measurement value of the second NOx sensor over time during the diagnostic operation for a functional one FIGS. 3a, 3b and 3c show the diagrammatic profiles of the temperature, the charge and the detected NOx / NH3 measurement value of the second NOx sensor over time during the diagnostic operation for an SCR system, wherein the first SCR25 catalyst is not functional, and 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 over time during the diagnostic operation for an SCR system, where the second SCR catalyst is not functional tig is.

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Unless otherwise indicated, the reference numerals correspond to the following components: internal combustion engine 1, first NOx sensor 2, metering device 3, second NOx sensor 4, first SCR catalyst 5, second SCR catalyst 6, diesel oxidation catalyst 7, diesel oxidation catalyst temperature 8, first SCR catalyst temperature 9, second SCR catalyst temperature 10, temperature in degrees Celsius 11, reductant loading in grams per liter 12, first reductant load 13, second reductant load 14, detected NOx / NH3 reading 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 aftertreatment system. The exhaust aftertreatment system of the internal combustion engine 1 comprises a first NOx sensor 2, a diesel oxidation catalyst 7, a metering 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 aftertreatment system, the first SCR catalytic converter 5 comprises an sDPF or the first SCR catalytic converter 5 is designed as an sDPF. Further, according to this first embodiment, the second SCR catalyst 6 comprises an SCR catalyst and an ASC catalyst, and the second SCR catalyst 6 is formed as an SCR-ASC combination catalyst.

In normal operation, that is, in normal operation, a fuel is metered via the metering device 3 before the first SCR catalyst 5. The fuel contains a reducing agent or is convertible into a reducing agent.

The reducing agent, in particular ammonia NH3, is stored at least temporarily in at least one SCR catalytic converter 5, 6.

FIGS. 2 a, 2 b and 2 c show the diagrammatic profiles of the temperature, the charge and the detected NO x / NH 3 measurement value of the second NO x sensor 4 for various components of the exhaust aftertreatment system during the diagnostic operation for a functioning 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 the case of a non-functional SCR system.

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

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 are on the y-axis, the reducing agent loading in grams per liter 12 and on the x-axis, the time in seconds 18 shown schematically. In FIG. 2c, the y-axis is the detected NOx / NH3 measured value 17 of the second SCR catalytic converter 6, and the time in seconds 18 is shown schematically on the x-axis.

From the schematic progressions, the measured data can be seen that in the

Diagnostic operation, first, the SCR catalysts 5, 6 are emptied, whereby the reducing agent charge 13, 14 of the first SCR catalyst 5 and the second SCR catalyst 6 is reduced to substantially zero. According to this embodiment, the emptying of the SCR catalysts 5, 6 is effected by a reduction or interruption of the fuel supply.

According to this embodiment, the two SCR catalysts 5, 6 already have a temperature 9, 10, which lies within a predetermined temperature window, and thus need not be tempered.

Subsequently, a predetermined diagnostic amount of the fuel is metered in before the first SCR catalyst 5. The diagnostic amount of fuel brings a quantity of reducing agent into the exhaust aftertreatment system, which can be stored at least temporarily in a functional first SCR catalytic converter 5. As a result, an overcharge of the first SCR catalytic converter 5 is prevented by the introduction of the diagnostic amount.

In the case illustrated in FIGS. 2 a, 2 b and 2 c, both the first SCR catalytic converter 5 and the second SCR catalytic converter 6 are functional and serve, for example, for determining measured data. This means that the amount of reducing agent introduced by the diagnostic quantity in the first SCR catalytic converter 5 can be stored at least temporarily. Immediately after the dosage of the diagnostic amount, the reducing agent loading of the first SCR catalyst 5, / 32 increases

PP31558AT

AVL List GmbH the so-called first reducing agent loading 13, leaps and bounds. In this case, no reduction agent slip after the second SCR catalytic converter 6 occurs immediately after the dosage of the diagnostic quantity.

Subsequently, the first SCR catalytic converter 5 is brought to or above its desorption temperature by engine measures, in particular by increasing the exhaust gas temperature. By increasing the exhaust gas temperature rise

Diesel oxidation catalyst temperature 8, the first SCR catalyst temperature 9 and the second SCR catalyst temperature 10 at.

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 desorbs. Since both the first 5 and the second SCR catalytic converter 6 are functional in the measurement data generation, no reduction agent slip after the second SCR catalytic converter 6 is thereby detected.

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. Only when the second SCR catalyst 6 is heated to or above its desorption temperature, a reducing agent slip after the second SCR catalyst 6 is detected.

This second detected NO x / NH 3 measured value 17 is shown in FIG. 2 c. The first detected NOx / NH3 measured value 16 of 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. Preferably, a first NOx sensor 2 is arranged only before the first SCR catalytic converter 5, in particular in front of the diesel oxidation catalytic converter 7, ie immediately after the internal combustion engine 1, and after the second SCR catalytic converter 6, ie after the exhaust gas aftertreatment system, a second NOx sensor 4 ,

According to this embodiment, the SCR catalysts 5, 6 are heated with a time lag. That is, first the first SCR catalyst 5 is heated to or above its desorption temperature and then the second SCR catalyst 6 is heated to or above its desorption temperature.

FIGS. 3 a, 3 b and 3 c show the schematic curves of the temperature, the charge and the detected NO x / NH 3 measurement value of the second NO x sensor 4 for / 32

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AVL List GmbH various components of the exhaust aftertreatment system during the diagnostic operation for an SCR system, wherein the first SCR catalyst 5 is not functional.

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

Before the diagnostic mode is activated in the, in particular real, operation, a reduced overall efficiency of the SCR system must be detected. The

Overall efficiency of the SCR system can be detected in a pre-diagnostic mode or by normal overall efficiency monitoring while driving. In particular, the detection may be performed by an on-board diagnostic system or a workshop diagnostic system.

Now, if the diagnostic operation is activated, the method steps, as described in particular in Figures 2a, 2b and 2c, executed first.

This means that after the emptying of the SCR catalysts 5, 6, a predetermined diagnostic quantity of fuel is metered in via the metering device 3 before the first SCR catalytic converter 5. According to this embodiment, the emptying of the SCR catalysts 5, 6 is effected by a reduction or interruption of 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 catalysts 5, 6. In particular, it is provided that the emptying is considered complete when the NOx measured value of the first NOx sensor 2 and the NOx measured value of the second NOx sensor 4 substantially do not deviate or only slightly from one another. When the two SCR catalysts 5, 6 are empty, substantially no reducing agent is present in the SCR catalysts 5, 6 and NOx emissions can no longer be reduced.

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According to this embodiment, the predetermined diagnostic quantity of fuel is such 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, during the diagnostic operation after metering in the diagnostic amount of fuel, in particular continuously, so much fuel is metered in that the predefined reductant storage level can be maintained. That is, substantially as much fuel is metered in as consumed by the NOx emissions occurring and their conversion, thus keeping the reductant storage level in the first SCR catalyst 5 substantially constant.

Moreover, it is provided that the reactions of the first SCR catalytic converter 5 and of the second SCR catalytic converter 6, which are decisive for the method, are calculated in addition to the actual operation in a kinetic model. The kinetic model according to this embodiment is a mathematical and / or physical mapping of the real system.

In particular, according to this embodiment, it is provided that the predetermined quantity of diagnostic fuel is determined or calculated by the kinetic model of the first SCR catalytic converter 5. That is, according to the model calculation, the predetermined diagnosis quantity can be stored at least temporarily in the first SCR catalytic converter 5 if it is functional.

Subsequently, the exhaust gas temperature is increased by a motor measure and the SCR catalysts 5, 6 heated in time.

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 amount of reducing agent is thus stored at least temporarily immediately after the metering in the second SCR catalytic converter 6.

This is shown in FIG. 3b, since the reducing agent charge of the second SCR catalytic converter 6, the so-called second reducing agent charge 14, increases abruptly after the diagnostic quantity has been metered in. This means that in this case no / 32

PP31558AT

AVL List GmbH

Reductant slip is detected by the second NOx sensor 4 immediately after the dosing of the diagnostic amount.

Now, when the first SCR catalyst 5 has been heated to or above its desorption temperature, according to this embodiment, no reductant slip is detected by the second NOx sensor 4 because substantially no reducing agent is stored in the first SCR catalyst 5.

Only when the second SCR catalytic converter 6 is heated to or above its desorption temperature does the reducing agent stored therein at least temporarily desorb, and the second NOx sensor 4 can detect a reducing agent slip, a so-called second detected NOx / NH 3 measured value 17.

By comparing the reduction agent slip actually occurring with reference values, such as measurement data, simulation data, characteristic maps or empirical values, it can be determined which of the two SCR catalysts 5, 6 is not functional. The measured data can be determined on the basis of a functional SCR15 system, as shown for example in FIG.

Moreover, 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 / NH3 measured value 17.

The diagnostic mode can be used in a workshop or in the workshop without additional measuring technology

Driving operation to be performed. In particular, it is provided that the method, in particular the diagnostic operation, requires only the vehicle-specific sensors, in particular the NOx sensors 2, 4 and / or the NH3 sensors, to be carried out. In particular, it is provided that only the two on-vehicle NOx sensors 2, 4 are used for the method according to the invention.

In order to remedy the damage, in this case only the first SCR catalytic converter 5 has to be replaced in order to be able to meet the legal requirements, in particular the legal requirements regarding NOx emissions. An unnecessary replacement of the second SCR catalyst 6 is prevented by the method, whereby time and cost can be reduced.

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PP31558AT

AVL List GmbH

FIGS. 4 a, 4 b and 4 c show the diagrammatic profiles of the temperature, the charge and the detected NO x / NH 3 measurement value of the second NO x sensor 4 for various components of the exhaust aftertreatment system during the diagnostic operation for an SCR system, the second SCR catalytic converter 6 is not functional.

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

Now, if the diagnostic operation is activated, the method steps, as described in particular in Figures 2a, 2b, 2c, 3a, 3b and 3c, executed first.

In contrast to FIG. 3, in the case illustrated here the first SCR catalytic converter 5 is functional and the second SCR catalytic converter 6 is not functional. That is, the amount of reducing agent introduced by the diagnostic amount is stored in the first SCR catalyst 5. Thus, no reduction agent slip after the second SCR catalyst 6 is detectable immediately after the dosage of the diagnostic amount.

As soon as the first SCR catalytic converter 5 is heated to or above its desorption temperature, the gas stored in it, at least temporarily, is desorbed

Reducing agent. Since the second SCR catalyst 6 is not functional, the desorbed reducing agent can not be stored in this. Thereby, the desorbed reducing agent passes through the second SCR catalyst 6 without delay and immediately after the first SCR catalyst 5 becomes its

Desorption has reached or exceeded a Reduktionsmittelschlupf after the second SCR catalyst 6 detected.

In order to remedy 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, in particular the legal requirements regarding NOx emissions. An unnecessary / 32

PP31558AT

AVL List GmbH

Replacement of the first SCR catalyst 5 is prevented by the method, whereby time and cost can be reduced.

According to an embodiment not shown, a reduction agent slip after the second SCR5 catalyst 6 is detected immediately after the dosage of the diagnostic amount. This is the case when both SCR catalysts 5, 6 are not functional. In this case, both the first SCR catalyst 5 and the second SCR catalyst 6 can substantially store no reducing agent.

In order to remedy the damage, in this case both SCR catalytic converters 5, 6 have to be replaced in order to meet the legal requirements, in particular the legal requirements

Specifications regarding NOx emissions.

Claims (17)

1. Method for functional testing of individual SCR catalysts (5, 6) of a SCR system of an exhaust aftertreatment system of an internal combustion engine, - wherein the SCR system along the exhaust aftertreatment plant serially comprises a first SCR catalyst (5) and a second SCR catalyst (6), wherein a fuel is metered into the SCR system in normal operation, which corresponds to the intended operation, wherein the operating material 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, comprising the following steps: - activate a diagnostic operation, - then emptying the SCR catalysts (5, 6) by stopping or reducing the fuel supply until no reducing agent is stored in the SCR catalysts (5, 6), Thereafter, if necessary, tempering, in particular heating, of the SCR system, so that the temperature of the SCR system and in particular of the SCR catalysts (5, 6) within a predetermined Temperature window is located, characterized - That then a predetermined diagnostic amount of the fuel is metered, which defines a reducing agent amount, wherein the reducing agent amount is smaller than the maximum of the first SCR catalyst (5) in a functional condition storable amount of reducing agent, if the temperature of the first SCR catalyst (5) is not increased to or above its desorption temperature, when no reductant slip after the second SCR catalyst (6) is detected during the dosing of the diagnostic amount, the second SCR catalyst (6 ) when 23/32 PP31558AT AVL List GmbH is defined defective, if during the increase of the temperature of the first SCR catalyst (5) to or above its desorption temperature, a reducing agent slip after the second SCR catalyst (6) is detected, and if necessary, status information about the function of the first SCR catalytic converter (5) and / or the second SCR catalytic converter (6) is output and / or stored, - and that the diagnostic operation is terminated if necessary. 2. The method according to claim 1, characterized - That, in particular subsequently, the temperature of the second SCR catalyst (6) is increased up to or above its desorption temperature, wherein the first SCR catalyst (5) is defined as defective when during the increase in the temperature of the second SCR catalyst (6 ) is detected at or above its desorption temperature, a reducing agent slip after the second SCR catalyst (6), - and that the diagnostic operation is terminated if necessary. 3. The method according to claim 1 or 2, characterized - That both SCR catalysts (5, 6) are defined as defective if during the dosing of the diagnostic amount of a reducing agent slip after the second SCR catalyst (6) is detected, - and that the diagnostic operation is terminated if necessary. 4. The method according to any one of claims 1 to 3, characterized that the SCR catalysts (5, 6) are heated successively or with a time offset, first that the first SCR catalyst (5) is heated to or above its desorption temperature, - And then that the second SCR catalyst (6) is heated to or above its desorption temperature. 24/32 PP31558AT AVL List GmbH 5. The method according to any one of the preceding claims, characterized in that the temperatures of the SCR catalysts (5, 6) are increased by increasing the exhaust gas temperature. 6. The method according to any one of the preceding claims, characterized in that the diagnostic operation is activated when previously a reduced efficiency, in particular reduced overall efficiency of the SCR system is detected in a pre-diagnosis operation or in the normal overall efficiency monitoring while driving, the detection in particular performed by an on-board diagnostic system or a workshop diagnostic system. 7. The method according to any one of the preceding claims, characterized in that the predetermined diagnostic amount of fuel for the diagnostic operation is such that in a functional first SCR catalyst (5) introduced by the diagnostic amount of fuel reducing agent at least temporarily in the first SCR -Catalyst (5) can be stored. 8. The method according to any one of the preceding claims, characterized in that the emptying of the SCR catalysts (5, 6) by stopping or reducing the fuel supply takes place until a parameter is detected, which provides information that no reducing agent in more the SCR catalysts (5, 6) is stored, this parameter is detected in particular by at least one NOx sensor. 9. The method according to claim 8, characterized the parameter is a difference between an emission recorded before the SCR catalysts (5, 6), in particular a NOx emission, and an emission recorded after the SCR catalysts, in particular a NOx emission, 25/32 PP31558AT AVL List GmbH - And that the difference of the before and after the SCR catalysts (5, 6) detected emissions with empty SCR catalysts (5, 6) is below a predetermined differential value and in particular zero. 10. The method according to any one of the preceding claims, characterized in that the decisive for the process reactions of SCRSystems, in particular the SCR catalysts (5, 6), in addition to the real operation in a kinetic model are calculated, the kinetic model in particular a mathematical mapping of the physical model of the SCR system used. 11. The method according to claim 10, characterized in that the predetermined diagnostic amount of fuel is determined or calculated by the kinetic model and in particular corresponds to an amount of reducing agent, which can be stored according to the model calculation entirely at least temporarily in the first SCR catalytic converter (5), if this is functional. 12. The method according to any one of the preceding claims, characterized in that the determination of the defective SCR catalyst (5, 6) by comparing the actually occurring reducing agent slip with reference values, such as measurement data, simulation data, maps or empirical values, takes place. 13. The method according to any one of the preceding claims, characterized - That the determination of the defective SCR catalyst (5, 6) by a Comparison of the time course and / or the amplitude of the reducing agent slip actually occurring with reference values, such as measured data, Simulation data, maps or empirical values, takes place. 14. The method according to any one of the preceding claims, characterized in that the diagnostic operation deviates from the control mode of the internal combustion engine. 26/32 PP31558AT AVL List GmbH 15. The method according to any one of claims 6 to 14, characterized in that the Vordiagnosebetrieb deviates from the control mode of the internal combustion engine. 16. The method according to any one of the preceding claims, characterized - that the process is carried out in a workshop without additional measurement technology, and / or that the method is carried out exclusively with the vehicle's own sensors, - And / or that the method is performed exclusively with a front of the SCR catalysts (5, 6) arranged and after the SCR catalysts (5, 6) arranged NOx sensor and / or NH3 sensor. 17. The method according to any one of the preceding claims, characterized in that the status information on the functionality of the first SCR catalyst (5) and / or the second SCR catalyst (6) by means of activation of a lamp and / or output as information on a display whereby a person is informed about the status of the functionality of the first SCR catalyst (5) and / or the second SCR catalyst (6).