AT521760A1 - Frequency-based NH3 slip detection method - Google Patents

Abstract

The invention relates to a method and an exhaust gas aftertreatment system (2) for the functional analysis and / or optimization of an SCR system, an operating medium being metered in upstream of an SCR catalytic converter (5) of the SCR system during normal operation, the operating medium containing a reducing agent or is convertible into a reducing agent, and wherein the reducing agent is stored at least temporarily in the SCR catalytic converter, the method comprising the following steps: operating the internal combustion engine (1) so that a dynamically fluctuating NOx emission curve following a certain pattern is generated, passing the dynamically fluctuating NOx emissions of the internal combustion engine (1) by the SCR system, recording a first measurement signal (11) by a first NOx sensor (7) arranged after the SCR catalytic converter (5), checking whether in the recorded first measurement signal ( 11) of the first NOx sensor (7) the pattern of the dynamically fluctuating NOx-Em is present course, and possibly increasing or decreasing the metered amount of fuel.

Description

Frequency-based Nhh slip detection method

The invention relates to a method and an exhaust gas aftertreatment system according to the preambles of the independent claims. In particular, the invention relates to a method for functional analysis and / or optimization of an SCR system of an exhaust gas aftertreatment system of an internal combustion engine and an exhaust gas aftertreatment system of an internal combustion engine which is suitable and / or set up for carrying out the method according to the invention.

Different methods for detecting ammonia slip are known from the prior art. For example, methods are known in which an ammonia sensor is arranged after the SCR catalytic converter of an exhaust gas aftertreatment system. As a result, it is possible in conventional methods to directly detect the NHa slip. However, it must be mentioned here that the installation of an additional NHa sensor increases the costs for the exhaust gas aftertreatment system.

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 for function analysis and / or optimization of an SCR system of an exhaust gas aftertreatment system of an internal combustion engine, which does not require an NHa sensor for the detection of NOx or reducing agent slip. In other words, it is an object of the invention, based on the measured values of the NOx sensors, which are provided in conventional exhaust gas aftertreatment systems, for NOx emissions and / or reducing agent emissions, in particular NH3 emissions, to pass through the SCR catalytic converter to detect. The invention is therefore based on the object, inter alia, of creating an inexpensive exhaust gas aftertreatment system with which the emission of NOx and reducing agent is reduced or prevented.

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

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The invention relates to a method for functional analysis and / or optimization of an SCR system of an exhaust gas aftertreatment system of an internal combustion engine, an operating medium being metered in upstream of an SCR catalytic converter of the SCR system during normal operation, the operating medium containing a reducing agent or being convertible into a reducing agent , wherein the reducing agent is stored at least temporarily in the SCR catalytic converter, and wherein the method comprises the following steps: operating the internal combustion engine so that a dynamically fluctuating NOx emission curve following a certain pattern is generated, passing the dynamically fluctuating NOx emissions of the Internal combustion engine through the SCR system, recording a first measurement signal by a first NOx sensor arranged after the SCR catalytic converter, checking whether the pattern of the dynamically fluctuating NOx emission level is recorded in the recorded first measurement signal of the first NOx sensor fs is present, and if necessary increasing or decreasing the metered amount of fuel.

If appropriate, it is provided that, in the intended operation of the internal combustion engine, a fuel suitable for selective catalytic reduction, such as in particular a mixture containing urea, a urea solution or AdBlue®, is metered in before the SCR catalytic converter. The operating material can contain a reducing agent, such as, in particular, ammonia NH3, or it can be convertible into a reducing agent, such as, in particular, ammonia NH3. A urea-containing mixture, in particular a urea-water solution, such as AdBlue®, is preferably used as the operating medium, the operating medium optionally being converted into the reducing agent, in particular ammonia NH3, by the reactions shown below:

Thermolysis: (NH ^ CO NH ₃ + HNCO

Hydrolysis: HNCO + H2O NH ₃ + CO2

In a first step, the urea (NH2) 2CO can be converted into ammonia NH ₃ and isocyanic acid HNCO in the thermolysis reaction. In a second step, the isocyanic acid HNCO can be converted into ammonia NH ₃ and carbon dioxide CO2 with water H2O in the hydrolysis reaction.

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The reducing agent, in particular ammonia NH3, can optionally be stored and / or stored at least temporarily in the SCR catalytic converter of the SCR system. The ammonia NH3 may accumulate on the active centers of the SCR catalytic converter. The at least temporarily stored reducing agent, in particular the ammonia NH3, can subsequently reduce nitrogen oxides NOx, such as in particular nitrogen monoxide NO and nitrogen dioxide NO2.

The operating fluid can be dosed via a dosing device, in particular via an injector or an injection nozzle.

In the context of the present disclosure, an SCR system can in particular be understood to mean a system which comprises an sDPF catalytic converter, an SCR catalytic converter, an ASC catalytic converter and / or an LNT catalytic converter, that is to say a lean NOx trap catalytic converter which is formed from an sDPF catalyst, an SCR catalyst, an ASC catalyst and / or an LNT catalyst.

In particular, the SCR system also includes one, two or three devices for metering in the fuel, the fuel tank and / or possibly also the fuel as such. In particular, one or the metering device is arranged upstream of the SCR system, in particular upstream of the SCR catalytic converter.

It may be provided that the exhaust gas aftertreatment system one or two SCR catalysts, a diesel oxidation catalyst DOC, a diesel particle filter DPF, an ammonia slip catalyst ASC, one or two metering devices and / or one, two or three NOx sensors and / or one, comprises two or three NHs sensors, in particular an NHs sensor after the exhaust gas aftertreatment system.

If appropriate, it is provided that the exhaust gas aftertreatment system comprises a DOCK catalyst, an SCR catalyst, i.e. a catalyst set up for the selective catalytic reduction of nitrogen oxides, and / or an ASC catalyst, or that the exhaust gas aftertreatment system comprises a DOC catalyst, an SCR catalyst and / or an ASC catalyst is formed.

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If appropriate, it is provided that the exhaust gas aftertreatment system comprises a DOCK catalyst, a DPF catalyst, an SCR catalyst and / or an ASC catalyst, or that the exhaust gas aftertreatment system is formed from a DOCK catalyst, a DPF catalyst, an SCR catalyst and / or an ASC catalyst .

If appropriate, it is provided that the exhaust gas aftertreatment system comprises a DOCK catalytic converter, an sDPF catalytic converter, i.e. an SCR-coated DPF, an SCR catalytic converter and / or an ASC catalytic converter, or that the exhaust gas aftertreatment system consists of a DOC catalytic converter, an sDPF catalytic converter, an SCR -Catalyst and / or an ASC catalyst is formed.

It is optionally provided that the exhaust gas aftertreatment system comprises an SCR catalytic converter, a DOC catalytic converter, a DPF catalytic converter, an SCR catalytic converter and / or an ASC catalytic converter, or that the exhaust gas aftertreatment system consists of an SCR catalytic converter, a DOC catalytic converter, and a DPF -Catalyst, an SCR catalyst and / or an ASC catalyst is formed.

If appropriate, it is provided that the exhaust gas aftertreatment system comprises an SCR catalyst, a DOC catalyst, an sDPF catalyst, an SCR catalyst and / or an ASC catalyst, or that the exhaust gas aftertreatment system comprises an SCR catalyst, a DOC catalyst, an sDPF -Catalyst, an SCR catalyst and / or an ASC catalyst is formed.

If appropriate, it is provided that the exhaust gas aftertreatment system comprises a DPF catalytic converter, an SCR catalytic converter and / or an ASC catalytic converter, or that the exhaust gas aftertreatment system is formed from a DPF catalytic converter, an SCR catalytic converter and / or an ASC catalytic converter.

It may be provided that the exhaust gas aftertreatment system comprises an LNT catalyst, an sDPF catalyst, an SCR catalyst and / or an ASC catalyst, or that the exhaust gas aftertreatment system consists of an LNT5 / 38

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Catalyst, an sDPF catalyst, an SCR catalyst and / or an ASC catalyst is formed.

If appropriate, it is provided that the exhaust gas aftertreatment system comprises an LNT catalyst, a cDPF catalyst, that is to say a catalytic DPF, an ufSCR catalyst, that is to say an underfloor SCR, and / or an ASC catalyst, or that the exhaust gas aftertreatment system comprises an LNT catalyst, a cDPF catalyst, an ufSCR catalyst and / or an ASC catalyst is formed.

If appropriate, it is provided that the exhaust gas aftertreatment system comprises an LNT catalyst, an SCR catalyst, an sDPF catalyst and / or an ASC catalyst, or that the exhaust gas aftertreatment system is formed from an LNT catalyst, an SCR catalyst, an sDPF catalyst and / or an ASC catalyst .

It may be provided that the exhaust gas aftertreatment system comprises an LNT catalyst, an sDPF catalyst, an ufSCR catalyst and / or an ASC catalyst, or that the exhaust gas aftertreatment system is formed from an LNT catalyst, an sDPF catalyst, an ufSCR catalyst and / or an ASC catalyst .

It may be provided that the exhaust gas aftertreatment system comprises an LNT catalyst, an sDPF catalyst, an ufSCR catalyst and / or an ASC catalyst, or that the exhaust gas aftertreatment system is formed from an LNT catalyst, an sDPF catalyst, an ufSCR catalyst and / or an ASC catalyst .

If appropriate, it is provided that one, two, three, four, five or all of the catalysts of the exhaust gas aftertreatment system can be heated or heated and in particular are designed as electrically heated catalysts E-CAT.

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If necessary, it is provided that the exhaust gas aftertreatment system comprises a “passive NOx adsorber” PNA instead of the DOC catalyst and / or instead of the LNT catalyst.

It may be provided that the exhaust gas aftertreatment system includes a “passive NOx adsorber” PNA in addition to the above-mentioned catalysts.

Where appropriate, it is provided that the exhaust gas aftertreatment system includes a “pre-turbine catalyst” PTC in addition to the catalysts mentioned above.

It is optionally provided that the exhaust gas aftertreatment system comprises one or two metering devices and one, two or three NOx sensors and / or one, two or three NHa sensors, in particular an NHa sensor after the exhaust gas aftertreatment system.

In the context of the present disclosure, an SCR catalytic converter can be understood to mean an sDPF catalytic converter, an SCR catalytic converter and / or an ASC catalytic converter.

The internal combustion engine, in particular the diesel engine, can be operated in such a way that a predetermined, in particular dynamically fluctuating, nitrogen oxide emission curve or NOx emission curve is generated. This means that, if necessary, a predetermined course of NOx emissions is generated by the conventional transient operation of the internal combustion engine and / or optionally by the specific change in the operating parameters of the internal combustion engine. It may be provided that the NOx emission curve corresponds to a natural signal or a harmonic oscillation, such as a sine wave, in order to minimize the influence of combustion noises.

The dynamically fluctuating NOx emissions generated by the internal combustion engine flow through the exhaust gas aftertreatment system of the internal combustion engine and thus through the SCR system, in particular through

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The reduction of nitrogen monoxide NO essentially takes place at a reduction temperature of over 250 ° C according to the following regulation:

4NO + 4NH ₃ + O ₂ 4N ₂ + 6H ₂ O

It is also possible that when both nitrogen monoxide NO and nitrogen dioxide NO2 are present in the exhaust gas and the reduction temperature is in the range from 170 ° C to 300 ° C, a so-called "fast SCR reaction" can take place. The fast SCR reaction essentially follows the following rule:

NO + 2NH ₃ + NO ₂ - + 2N ₂ + 3H ₂ 0

The reduction of nitrogen dioxide NO2 essentially follows the following rule:

8NH ₃ + 6NO ₂ - + 7N ₂ + 12H ₂ O

This may mean that the nitrogen oxide concentration or NOx concentration in front of the SCR catalytic converter of the SCR system is higher than after the SCR catalytic converter.

According to the invention, a first NOx sensor is arranged after the SCR catalytic converter of the SCR system. This first NOx sensor can be set up to determine the NOx concentration. It is provided that a first measurement signal is recorded by this first NOx sensor.

If necessary, due to the cross-sensitivity of the NOx sensor, reducing agent emissions, in particular NHa emissions, are detected as NOx emissions, which means that pollutant emissions are caused by conventional methods

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It is provided that a check is carried out to determine whether the pattern of the nitrogen oxide emission curve or the NOx emission curve emitted by the internal combustion engine is present in the recorded first measurement signal of the first NOx sensor. This may make it possible to detect a nitrogen oxide slip or a reducing agent slip, in particular an ammonia slip.

It is optionally provided that the amount of fuel which is introduced upstream of the SCR catalytic converter is increased if a nitrogen oxide slip is detected by the method according to the invention.

It is optionally provided that the amount of fuel which is introduced upstream of the SCR catalytic converter is reduced if a slippage of reducing agent, in particular an NHa slip, is detected by the method according to the invention.

According to the invention, it is provided that a dynamic fluctuating NOx emission curve or NOx emissions is / are generated by the internal combustion engine, in particular the diesel engine, and that the NOx emissions generated after the SCR catalytic converter are detected and / or determined by means of a NOx sensor . In other words, a NOx signal is generated or generated in front of the SCR catalytic converter and this NOx signal is recorded after the SCR catalytic converter.

The internal combustion engine can be an internal combustion engine of a motor vehicle.

It is optionally provided that the method is carried out automatically, in particular in a control unit of a motor vehicle and / or controlled and / or regulated by a control unit of a motor vehicle.

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If appropriate, it is provided that the method steps of the method follow one another, as described above. This means that the internal combustion engine is first operated in such a way that a dynamically fluctuating NOx emission curve is generated. The generated NOx emissions can then be passed through an SCR catalytic converter and, after the SCR catalytic converter, a first measurement signal can be recorded using a first NOx sensor. It can then be checked whether the NOx emission curve pattern generated by the internal combustion engine is present in the recorded first measurement signal. If necessary, the amount of fuel is increased or decreased based on this result.

If necessary, provision is made for checking whether the pattern of the dynamically fluctuating NOx emission curve generated is present in the recorded first measurement signal of the first NOx sensor, in that a second measurement signal of a second NOx sensor arranged in front of the SCR catalytic converter is carried out with the first measurement signal is compared, or that the NOx emission curve to be expected from the operation of the internal combustion engine is compared with the emission curve recorded by the first NOx sensor.

The second NOx sensor can be arranged in front of the SCR catalytic converter and can be set up to detect NOx emissions. This can make it possible to detect and / or determine the dynamically fluctuating NOx emissions generated by the internal combustion engine or the NOx emission curve by means of the second NOx sensor upstream of the SCR catalytic converter and by means of the first NOx sensor downstream of the SCR catalytic converter .

It can be provided that the NOx emissions of the internal combustion engine are determined and / or determined using a kinetic model of the internal combustion engine. As a result, it may be possible to have to provide only one NOx sensor after the exhaust gas aftertreatment system, in particular after the SCR catalytic converter. This may make it possible to control the dynamically fluctuating NOx emissions or NOx10 / 38 generated by the internal combustion engine

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Determine the emission curve using the kinetic model in front of the SCR catalytic converter and using the first NOx sensor after the SCR catalytic converter.

It can therefore be favorable that only one NOx sensor is provided downstream of the SCR catalytic converter and no NOx sensor is provided upstream of the SCR catalytic converter. It can be expedient if the NOx sensor upstream of the SCR catalytic converter is represented by an empirical model.

If necessary, it is provided that the NOx emission curve to be expected from the operation of the internal combustion engine is determined in a kinetic model of the control device, which maps the relevant reactions mathematically and physically. The reactions modeled in the kinetic model can therefore be based on physical conditions.

It is optionally provided that the pattern is present in the first measurement signal of the first NOx sensor when the first measurement signal of the first NOx sensor contains the pattern of the dynamically fluctuating NOx emission curve generated with the same frequency and with the same amplitude.

If necessary, it is provided that for checking whether the pattern of the dynamically fluctuating NOx emission curve is present in the recorded first measurement signal of the first NOx sensor, the dynamic portion of the measurement signals is integrated and a NOx ratio factor of the SCR catalytic converter is calculated via the integrated values .

The dynamic portion of the measurement signals is calculated using a low-pass filtered gradient and is only taken into account if a predefined threshold value is exceeded. A NOx ratio factor is then calculated from the integrated dynamic components.

The NOx ratio factor is calculated using the following formula or calculation rule:

integrated dvn. Part of the first sensor (according to SCRA

NOx - ratio factor = -------------------—------------------------- integrated dyn. Part of the second sensor (before SCR)

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If necessary, the NOx ratio factor can also be understood as a NOx conversion factor.

If necessary, it is provided that the NOx conversion efficiency of the SCR catalytic converter is calculated via the ratio of the high-pass filtered measurement signals of the first and second NOx sensors, and / or that the NHa concentration after the SCR catalytic converter is calculated via the previously calculated NOx conversion efficiency and via the low-pass filtered measurement signals of the first and second NOx sensors is calculated.

The calculation of the conversion efficiency can be calculated via the ratio of the high-pass filtered measurement signal of the first NOx sensor to the high-pass filtered measurement signal of the second NOx sensor. Using this conversion efficiency, an expected NH3 concentration can subsequently be calculated by multiplying the conversion efficiency by the low-pass filtered measurement signal from the second NOx sensor and then subtracting this from the low-pass filtered measurement signal by the first NOx sensor.

It is optionally provided that the pattern has a frequency of 0.1 Hz to 10 Hz, in particular a frequency of 0.5 Hz to 5 Hz, preferably a frequency of 1 Hz, and / or that the dynamically fluctuating generated with the internal combustion engine NOx emission curve has a frequency of 0.1 Hz to 10 Hz, in particular a frequency of 0.5 Hz to 5 Hz, preferably a frequency of 1 Hz.

If appropriate, it is provided that the pattern has an amplitude of 5 ppm to 500 ppm, in particular an amplitude of 10 ppm to 100 ppm, preferably an amplitude of 30 ppm, and / or that the dynamically fluctuating NOx emission curve generated with the internal combustion engine exhibits a Has an amplitude of 5 ppm to 500 ppm, in particular an amplitude of 10 ppm to 100 ppm, preferably an amplitude of 30 ppm.

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The pattern and / or the dynamically fluctuating NOx emission curve generated with the internal combustion engine preferably has an amplitude of +/- 30 ppm and a frequency of 1 Hz.

In the context of the invention, amplitude can be understood to mean the maximum deflection of an alternating variable from the position of the arithmetic mean.

If appropriate, provision is made for the dynamically fluctuating NOx emission curve to be generated by changing the operating parameters of the internal combustion engine, the combustion temperature being increased to generate higher NOx emissions and the combustion temperature being reduced to generate lower NOx emissions.

By changing the operating parameters of the internal combustion engine, targeted NOx emissions can be generated and thus a predetermined NOx emission curve or a NOx emission curve pattern can be generated.

In order to dynamically increase the combustion temperature to generate higher NOx emissions or to dynamically lower the combustion temperature to generate lower NOx emissions, for example, a dynamic change in the injection course of the fuel, a variation of a multiple injection and / or a change in the injection pressure of the fuel can be carried out.

It may be provided that the injection or ignition timing is changed in time so that the NOx emissions are increased and decreased, and / or that the injection and / or ignition timing is moved backwards to generate lower NOx emissions, and / or that the injection or ignition timing is brought forward to generate higher NOx emissions.

If necessary, the specific change in the operating parameters of the internal combustion engine changes the MFB50 in relation to top dead center in order to also change NOx emissions. In the context of the present invention, MFB50 can be understood to mean a value which is the crankshaft angle

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In the context of the invention, the timing of the injection and / or ignition timing is to be understood to mean that this occurs later or is carried out later. The ignition timing can e.g. B. from 5 ° KW before top dead center to 2 ° KW before top dead center or from 2 ° KW before top dead center to 3 ° KW after top dead center. In both cases, the ignition timing is postponed later.

If necessary, it is provided that the dynamically fluctuating NOx emission curve is generated by an alternating, in particular sinusoidally alternating, shift of the injection or ignition timing by 1 ° KW to 10 ° KW, in particular by 1 ° KW to 3 ° KW, preferably by 2 ° KW, this shift takes place in particular relative to the injection or ignition timing that would normally be selected at this operating point.

If necessary, it is provided that an overdosing of the operating material, in particular an NHa slip, is detected and / or the supply of the operating material is reduced if the check shows that the pattern of the dynamically fluctuating NOx generated in the recorded first measurement signal of the first NOx sensor Emission curve is not present, and if the emission curve detected by the first NOx sensor is smoothed by the implementation of the NOx emissions of the dynamically fluctuating NOx emission curve generated in the SCR system.

If necessary, it is provided that an overdosing of the operating fluid is detected and / or the supply of the operating fluid is reduced if the check shows that the detected pattern in the recorded first measurement signal of the first NOx sensor has an amplitude of 1 ppm to 50 ppm, in particular an Amplitude less than 25 ppm, and the detected pattern has a frequency of 0.1 Hz to

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Hz, in particular from 0.5 Hz to 5 Hz, preferably a frequency of 1 Hz.

In particular, an overdose of the operating fluid is detected if the calculated NH3 concentration after the SCR is above a defined threshold value. The NH3 concentration after the SCR is determined using the low-pass filtered measurement signals of the first and second NOx sensors and the conversion efficiency of the NOx emissions of the internal combustion engine, which is calculated using the ratio of the high-pass filtered measurement signals of the first and second NOx sensors.

In particular, an overdosing of the fuel is detected if the check shows that in the recorded first measurement signal of the first NOx sensor the detected NOx emission curve has an average value that is many times smaller than the average value of the fluctuating NOx emission curve generated with the internal combustion engine.

In particular, an overdosing of the operating fluid is detected if the check shows that the detected NOx emission curve generated by the internal combustion engine is only smoothed in the recorded first measurement signal of the first NOx sensor. This means that, if necessary, an overdosing of the operating fluid is detected if there is no amplitude or an amplitude less than 5 ppm, 4 ppm, 3 ppm, 2 ppm or 1 ppm in the first measurement signal of the first NOx sensor.

In particular, an overdosing of the operating fluid is detected if the check shows that in the recorded first measurement signal of the first NOx sensor the detected NOx emission curve has an average value which is smaller than 1/20, 1/30, 1/40, 1/50, 1/100 or 1/200 of the mean value of the fluctuating NOx emission curve generated with the internal combustion engine.

In particular, an overdosing of the operating fluid is detected if the check shows that the first measurement signal of the first NOx15 / 38 recorded

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Sensor the detected NOx emission curve has an average value which is less than 40 ppm, 30 ppm, 20 ppm, 10 ppm or 5 ppm.

If necessary, provision is made for an underdosing of the operating material to be detected and / or the supply of the operating material to be increased if the check reveals that the pattern of the dynamically fluctuating NOx emission curve generated is present in the recorded first measurement signal of the first NOx sensor, the pattern with the The NOx conversion efficiency of the SCR catalytic converter determined by NOx sensors is below a certain threshold value, and / or the mean value of the NOx emissions recorded by the first NOx sensor is above a predetermined threshold value, in particular above 30 ppm.

In particular, an underdosing of the operating fluid is detected if the check shows that in the recorded first measurement signal of the first NOx sensor the detected NOx emission curve has an average value which is greater than 1/20, 1/30, 1/40 or 1/50 of the Average value of the fluctuating NOx emission curve generated with the internal combustion engine.

In particular, an underdosing of the operating fluid is detected if the check shows that in the recorded first measurement signal of the first NOx sensor the detected NOx emission curve has an average value which is greater than 40 ppm, 30 ppm, 20 ppm or 10 ppm. In particular, an underdosing of the operating fluid is detected if the expected NOx emission curve (from the SCR model) is at the same time significantly less than the measured value, for example 20 ppm instead of the measured 40 ppm.

If necessary, an underdosing of the fuel is detected if the check reveals that the NOx conversion efficiency determined is below a certain NOx conversion efficiency threshold. This means that an underdosing of the operating fluid may be detected if the NOx conversion efficiency determined is less than 95%, 96%, 97%, 98% or 99%.

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The dynamic component is calculated using the low-pass filtered gradient and is only taken into account if a predefined threshold value is exceeded. A conversion efficiency is then calculated from the integrated dynamic components.

The NOx conversion efficiency can be calculated in particular according to the following rule:

J NOXd _WSi scR, dy _n

TlsrR = 1--7 --------------- / N Ox _usSCRdyn where j] _{SCR is} the NOx conversion _efficiency , NOx _{dwsSCRidyn is} the dynamic portion of the NOx concentration after the SCR catalyst and NOx _{usSCR dyn is} the dynamic part of the NOx concentration _{upstream of} the SCR catalytic converter.

If appropriate, it is provided that the metered amount of fuel is increased and / or decreased by regulating or controlling the metering device.

If necessary, it is provided that status information on the function of the exhaust gas aftertreatment system is output by means of a MIL lamp “Malfunction Indicator Light - engine control lamp” of a vehicle, as a result of which the driver is informed about the status of the functionality of the exhaust gas aftertreatment system.

In particular, the invention relates to an exhaust gas aftertreatment system of an internal combustion engine, the exhaust gas aftertreatment system being suitable and / or set up for carrying out the method according to the invention.

Further features according to the invention may result from the claims, the description of the exemplary embodiments and the figures.

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

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1 shows a schematic graphic representation of a first embodiment of an internal combustion engine with an exhaust gas aftertreatment system according to the invention,

2a to 2e show a schematic graphic representation of diagrams to explain a first embodiment of the method according to the invention, and FIGS. 3a to 3d show a schematic graphic representation of diagrams to explain a second embodiment of the method according to the invention.

Unless otherwise stated, the reference symbols correspond to the following components:

Internal combustion engine 1, exhaust gas aftertreatment system 2, diesel oxidation catalyst 3, diesel particle filter 4, SCR catalyst 5, ammonia slip catalyst 6, first NOx sensor 7, second NOx sensor 8, fuel quantity correction factor 9, second measurement signal 10, first measurement signal 11, NOx conversion efficiency 12, NOx slip 13, NHa slip 14, metering device 15 and time 16.

1 shows a schematic graphic representation of a first embodiment of an internal combustion engine 1 with an exhaust gas aftertreatment system 2 according to the invention.

According to this embodiment, the internal combustion engine 1 is designed as a diesel engine. The exhaust gas aftertreatment system 2 includes one

Diesel oxidation catalytic converter 3, a diesel particulate filter 4, an SCR catalytic converter 5 and an ammonia slip catalytic converter 6.

Furthermore, the exhaust gas aftertreatment system 2 comprises a first NOx sensor 7 and a second NOx sensor 8. The first NOx sensor 7 is arranged after the SCR catalytic converter 5 and, according to this embodiment, after the ammonia slip catalytic converter 6. The second NOx sensor 8 is arranged after the internal combustion engine 1 and before the SCR catalytic converter 5. Alternatively, the second NOx sensor 8 can also be arranged either upstream of the diesel oxidation catalytic converter 3 or upstream or downstream of the diesel particle filter 4

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According to another embodiment, it can be provided that the NOx emission curve, which is generated by the internal combustion engine 1, is determined using a kinetic model. In this case, it may be possible to carry out the method according to the invention with only one NOx sensor after the SCR catalytic converter 5.

In all embodiments, it can be provided that a fuel, in particular a urea solution or AdBlue®, is metered in via a metering device 15 upstream of the SCR catalytic converter 5 in the intended operation.

According to this embodiment, the internal combustion engine 1 is operated in such a way that NOx emissions are generated which follow a specific pattern and result in a dynamically fluctuating NOx emission curve. After leaving the internal combustion engine 1, the NOx emissions generated by the internal combustion engine 1 flow through the exhaust gas aftertreatment system 2 and in particular through the catalysts of the exhaust gas aftertreatment system 2.

In particular, the internal combustion engine 1 generates a NOx emission curve which has a frequency of 0.1 Hz to 10 Hz, in particular a frequency of 0.5 Hz to 5 Hz, preferably a frequency of 1 Hz, and an amplitude of 5 ppm to 500 ppm, in particular an amplitude of 10 ppm to 100 ppm, preferably an amplitude of 30 ppm. To generate the NOx emission profile, the internal combustion engine 1 can be operated transiently and / or the operating parameters of the internal combustion engine 1 can be changed in a targeted manner.

According to this embodiment, a first measurement signal 11 is recorded with the first NOx sensor 7 after the SCR catalytic converter 5 and a second measurement signal 10 with the second NOx sensor 8 upstream of the SCR catalytic converter 5. The two NOx sensors 7, 8 are set up for the detection of NOx emissions.

According to the method, it is checked whether the pattern of the dynamically fluctuating NOx19 / 38 is in the recorded first measurement signal 11 of the first NOx sensor 7

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Emission curve is present, which according to this embodiment is recorded with the second NOx sensor 8 as the second measurement signal 10.

If the NOx emission curve pattern generated by the internal combustion engine 1 is present in the first measurement signal 11, a NOx slip 13 is detected and the amount of fuel may be increased.

If the NOx emission profile pattern generated by the internal combustion engine 1 is not present in the first measurement signal 11, an NHa slip 14 is detected and the amount of fuel may be reduced.

2a to 2e show a schematic graphic representation of a first embodiment of the method according to the invention using five different diagrams.

In the first of these five diagrams, the amount of fuel correction factor 9 is plotted over time 16 in seconds. In the second of these five diagrams, the second measurement signal 10 of the second NOx sensor 8 is plotted over time 16 in seconds. In the third of these five diagrams, the first measurement signal 11 of the first NOx sensor 7 is plotted over time 16 in seconds. In the fourth of these five graphs, the calculated NOx conversion efficiency 12 is plotted against time 16 in seconds. The fifth of these five diagrams shows the result of the method over time 16 in seconds. This fifth diagram shows whether or not a NOx slip 13 was detected using the method according to the invention

As can be seen from the diagrams, as long as the NOx emission curve pattern generated by the internal combustion engine 1 is present in the first measurement signal 11 of the first NOx sensor 7, a NOx slip 13 is detected.

According to this embodiment, the amount of fuel is increased to prevent and / or reduce NOx emissions. FIG. 2a shows the extent to which the amount of fuel is increased over time 16. 2c shows

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AVL List GmbH that an increasing amount of fuel, i.e. the higher the fuel quantity correction factor 9, results in a reduction in NOx emissions after SCR catalytic converter 5.

As soon as a sufficiently high amount of fuel is introduced in front of the SCR catalytic converter 5 via the metering device 15, the NOx emissions emitted by the internal combustion engine 1 can be converted to nitrogen and water to a sufficient extent in the SCR catalytic converter. In this case, the method no longer detects NOx slip 13. According to this embodiment, this is the case when the pattern of the dynamically fluctuating NOx emission curve is no longer present or in particular is only strongly attenuated in the recorded first measurement signal 11 of the first NOx sensor 7.

An underdosing of the operating material, i.e. NOx slip is detected here if the check shows that the NOx conversion efficiency 12 determined by the measurement signals of the first and second NOx sensors is below a certain NOx conversion efficiency threshold value and at the same time the conversion efficiency derived from a model is higher. According to this embodiment, a typical threshold value is approximately 97%, but it can also be significantly lower, e.g. B. at about 70%.

In particular, an underdosing of the fuel is detected if the check shows that in the recorded first measurement signal 11 of the first NOx sensor 7 the detected NOx emission curve has an average value which is greater than 1/25 of the average value of the fluctuating NOx generated with the internal combustion engine 1 Emission curve and at the same time the expected NOx emission curve of sensor 7 is significantly smaller.

In particular, an underdosing of the operating fluid is detected if the check shows that in the recorded first measurement signal 11 of the first NOx sensor 7 the detected NOx emission curve has an average value which is greater than 40 ppm and at the same time the expected NOx emission curve of the sensor 7 is significantly smaller is.

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This makes it possible, on the one hand, to reduce or prevent the occurrence of NOx emissions and, on the other hand, to protect the environment by falling below the pollutant emission laws prescribed by law, in particular the prescribed NOx emissions.

3a to 3d show a schematic graphic representation of a second embodiment of the method according to the invention using four different diagrams.

In the first of these four diagrams, the amount of fuel correction factor 9 is plotted over time 16 in seconds. In the second of these four diagrams, the second measurement signal 10 of the second NOx sensor 8 is plotted over time 16 in seconds. In the third of these four diagrams, the first measurement signal 11 of the first NOx sensor 7 is plotted over time 16 in seconds. The fourth of these four diagrams shows the result of the method over time 16 in seconds. From this fourth diagram it can be seen whether an NHa slip 14 was detected or not with the method according to the invention.

As can be seen from the diagrams, an NHa slip 14 is detected as long as the NOx emission curve pattern generated by the internal combustion engine 1 is not present in the first measurement signal 11 of the first NOx sensor 7.

In particular, it can be seen from FIGS. 3c and 3d that an NHa slip 14 is detected when the NOx emission curve generated by the internal combustion engine 1 with the superimposed alternating signal is only smoothed in the recorded first measurement signal 11. This means that, according to this embodiment, an overdosing is recognized if there is no amplitude of the alternating signal or an amplitude less than 3 ppm in the recorded first measurement signal 11 and at the same time the smoothed portion without an alternating signal is above a threshold value of approximately 10 ppm.

According to this embodiment, the amount of fuel is reduced to prevent and / or reduce NHa emissions. FIG. 3a shows

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AVL List GmbH to what extent the amount of fuel is reduced over time 16. It can be seen from FIG. 3 c that a reduced amount of fuel, that is to say the smaller the fuel quantity correction factor 9, results in a reduction in the NHa emissions after the SCR catalytic converter 5.

As soon as a sufficiently low amount of fuel is introduced upstream of the SCR catalytic converter 5 via the metering device 15, the ammonia introduced thereby can be converted to a sufficient extent in the SCR catalytic converter. In this case, the method no longer detects NHa slip 14. According to this embodiment, this is the case if the pattern of the dynamically fluctuating NOx emission curve is only present in a smoothed manner in the recorded first measurement signal 11 of the first NOx sensor 7 and has an average value which is less than 10 ppm.

An overdose of the fuel, i.e. an NHa slip is detected here in particular if the check shows that in the recorded first measurement signal 11 of the first NOx sensor 7 the detected NOx emission profile has an average value which is less than 1/90 of the average value with the internal combustion engine 1 generated fluctuating NOx emission curve.

This makes it possible, on the one hand, to reduce or prevent the occurrence of NHa emissions and, on the other hand, to protect the environment by falling below the pollutant emission laws prescribed by the legislator, in particular the NHa emissions that may be required.

If appropriate, it can be provided in all embodiments that, as part of the checking step of the method, it is checked whether in the recorded first measurement signal 11 of the first NOx sensor 7 the NOx emission curve of the internal combustion engine 1 or the NOx emission curve of the second measurement signal 10 of the second NOx -Sensor 8 is present.

The effects according to the invention can be achieved by this exemplary configuration.

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The invention is not limited to the illustrated embodiments, but encompasses any method and any exhaust gas aftertreatment system 2 according to the following patent claims.

Claims (16)

1. Method for functional analysis and / or optimization of an SCR system of an exhaust gas aftertreatment system (2) of an internal combustion engine (1), an operating medium being metered in upstream of an SCR catalytic converter (5) of the SCR system during normal operation, the operating medium containing a reducing agent or can be converted into a reducing agent, and wherein the reducing agent is stored at least temporarily in the SCR catalytic converter (5), comprising the following steps: Operating the internal combustion engine (1) so that a dynamically fluctuating NOx emission curve following a certain pattern is generated, Passing the dynamically fluctuating NOx emissions of the internal combustion engine (1) through the SCR system, Recording a first measurement signal (11) by a first NOx sensor (7) arranged after the SCR catalytic converter (5), Check whether the pattern of the dynamically fluctuating NOx emission curve is present in the recorded first measurement signal (11) of the first NOx sensor (7) and, if necessary, increase or decrease the metered amount of fuel. 2. The method according to claim 1, characterized in that checking whether the pattern of the dynamically fluctuating NOx emission curve generated is present in the recorded first measurement signal (11) of the first NOx sensor (7), in that a second measurement signal ( 10) a second NOx sensor (8) arranged in front of the SCR catalytic converter (5) is compared with the first measurement signal (11), 25/38 PP31973AT AVL List GmbH or that the NOx emission curve to be expected from the operation of the internal combustion engine (1) is compared with the emission curve recorded by the first NOx sensor (7). 3. The method according to claim 1 or 2, characterized in that the pattern in the first measurement signal (11) of the first NOx sensor (7) is present when the first measurement signal (11) of the first NOx sensor (7) the pattern of generated dynamically fluctuating NOx emission curve: with the same frequency and with the same amplitude. 4. The method according to any one of the preceding claims, characterized in that for checking whether the pattern of the dynamically fluctuating NOx emission curve is present in the recorded first measurement signal (11) of the first NOx sensor (7), the dynamic portion of the measurement signals (10, 11) is integrated and a NOx ratio factor of the SCR catalytic converter (5) is calculated via the integrated values. 5. The method according to claim 4, characterized in that a NOx conversion efficiency (12) of the SCR catalyst (5) is calculated via the ratio of the high-pass filtered measurement signals (10, 11) of the first and second NOx sensors (8), and / or that the NHa concentration after the SCR catalytic converter (5) is calculated via the previously calculated NOx conversion efficiency (12) and via the low-pass filtered measurement signals (10, 11) of the first (7) and second NOx sensor (8). 6. The method according to any one of the preceding claims, characterized in that the pattern has a frequency of 0.1 Hz to 10 Hz, in particular a frequency of 0.5 Hz to 5 Hz, preferably a frequency of 1 Hz, 26/38 PP31973AT AVL List GmbH and / or that the dynamically fluctuating NOx emission curve generated with the internal combustion engine (1) has a frequency of 0.1 Hz to 10 Hz, in particular a frequency of 0.5 Hz to 5 Hz, preferably a frequency of 1 Hz, having. 7. The method according to any one of the preceding claims, characterized in that the pattern has an amplitude of 5 ppm to 500 ppm, in particular an amplitude of 10 ppm to 100 ppm, preferably an amplitude of 30 ppm, and / or that with the Internal combustion engine (1) generated dynamically fluctuating NOx emission curve has an amplitude of 5 ppm to 500 ppm, in particular an amplitude of 10 ppm to 100 ppm, preferably an amplitude of 30 ppm. 8. The method according to any one of the preceding claims, characterized in that the generation of the dynamically fluctuating NOx emission curve takes place by changing the operating parameters of the internal combustion engine (1), the combustion temperature being increased to generate higher NOx emissions, and wherein to generate lower NOx -Emissions the combustion temperature is reduced. 9. The method according to any one of the preceding claims, characterized in that the injection or ignition timing is changed in time so that the NOx emissions are increased and decreased, and / or that to generate lower NOx emissions of the injection or. The ignition timing is moved back in time, and / or the injection or ignition timing is brought forward to generate higher NOx emissions. 27/38 PP31973AT AVL List GmbH 10. The method according to any one of the preceding claims, characterized in that the generation of the dynamically fluctuating NOx emission curve by an alternating, in particular by sinusoidally alternating, shift of the injection or ignition timing by 1 ° KW to 10 ° KW, in particular by 1 ° KW to 3 ° KW, preferably by 2 ° KW, this shift takes place in particular relative to the injection or ignition point that would normally be selected at this operating point. 11. The method according to any one of the preceding claims, characterized in that an overdosing of the operating material, in particular an NHa slip (14), is detected and / or the supply of the operating material is reduced if the check shows that in the recorded first measurement signal ( 11) of the first NOx sensor (7) the pattern of the dynamically fluctuating NOx emission curve generated is not available, and if the emission curve detected by the first NOx sensor (7) is implemented by implementing the NOx emissions of the dynamically fluctuating NOx emission curve generated is smoothed in the SCR system. 12. The method according to any one of the preceding claims, characterized in that an overdosing of the operating medium is detected and / or the supply of the operating medium is reduced if the check shows that in the recorded first measuring signal (11) of the first NOx sensor (7) the detected pattern has an amplitude of 1 ppm to 50 ppm, in particular an amplitude less than 25 ppm, and the detected pattern has a frequency of 0.1 Hz to 10 Hz, in particular 0.5 Hz to 5 Hz, preferably a frequency of 1 Hz. 13. The method according to any one of the preceding claims, characterized in that 28/38 PP31973AT AVL List GmbH that an underdosing of the operating fluid is detected and / or the supply of the operating fluid is increased if the check shows that the pattern of the dynamically fluctuating NOx emission curve generated is recorded in the recorded first measurement signal (11) of the first NOx sensor (7) is present, the NOx conversion efficiency (12) of the SCR catalytic converter (5) determined using the NOx sensors (7, 8) being below a certain threshold value, and / or the mean value of those recorded by the first NOx sensor (7) NOx emissions are above a predetermined threshold, in particular above 30 ppm. 14. The method according to any one of the preceding claims, characterized in that the increase and / or decrease in the metered amount of fuel is effected by regulating or controlling the metering device (15). 15. The method according to any one of the preceding claims, characterized in that status information on the function of the exhaust gas aftertreatment system (2) is output by means of a MIL lamp “Malfunction Indicator Light - engine control lamp” of a vehicle, whereby the driver is informed of the status of the functionality of the exhaust gas aftertreatment system ( 2) is informed. 16. exhaust gas aftertreatment system of an internal combustion engine (1), characterized in that the exhaust gas aftertreatment system (2) is suitable and / or set up for carrying out the method according to one of the claims 1 to 15.