EP3717757B1 - Method for operating an exhaust aftertreatment system of an internal combustion engine and exhaust aftertreatment system - Google Patents

Description

The present invention relates to a method for operating an exhaust gas aftertreatment system of an internal combustion engine, in particular a diesel engine, which has a combined SCR particle filter arranged in an exhaust line and a device for targeted, defined changing of the NH ₃ and / or NOx concentration in the exhaust gas mass flow upstream Has SCR particle filter.

In particular, vehicles with diesel internal combustion engines (diesel engine), but increasingly also vehicles with Otto internal combustion engines (gasoline engine), nowadays have a particle filter (DPF, PF) to avoid particles (soot, fine dust) in the exhaust emissions as well as a so-called SCR catalytic converter ( Catalytic converter with selective reduction) to reduce the NOx content in the exhaust emissions. A combined filter / catalytic converter, hereinafter referred to as SCR particle filter or with the abbreviation SC-PF, is increasingly being used, which is a particle filter with SCR function, ie a particle filter that has an additional coating a NO _x / NH ₃ conversion material. In other words, this is a particle filter with an integrated SCR function.

With an SCR catalytic converter, adding an aqueous urea solution to the exhaust gas produces NH ₃ (ammonia), which reacts with the NOx in the exhaust gas to form elemental nitrogen (N ₂ ) and water.

The legislature is always lowering the emission limit values of the exhaust gases from vehicles with internal combustion engines (internal combustion engines) continues and issues regulations to monitor their proper functioning. This also applies in particular to the so-called OBD diagnosis (on-board diagnosis, ongoing, automatic self-diagnosis during normal operation of the vehicle) in such vehicles. Nowadays, SCR particulate filters must also be subjected to such frequent and precise OBD diagnostics.

It is known to carry out such a diagnosis with respect to the particle emissions with a so-called PM sensor (Particulate Matter Sensor). If the PM emission measured by the particle sensor after the particle filter is higher than a threshold value, the particle filter is diagnosed as faulty. However, a relatively long period of time is required for such a diagnosis. Furthermore, the diagnosis is limited to the particle emission and the accuracy of the diagnosis is also not good enough to meet the requirements of even lower emission threshold values in the future.

From the US 2013/0202506 A1 a method for operating an exhaust gas aftertreatment system is known in which an SCR catalytic converter is diagnosed. This involves a targeted, defined induction of a change in the NH ₃ concentration and / or a change in the NO _x concentration in the exhaust gas mass flow upstream of the SCR catalytic converter and the measurement of the NH ₃ and / or NO _x concentration change in the exhaust gas mass flow after the SCR catalytic converter with the help of a concentration sensor. However, this publication does not relate to an SCR particulate filter.

Similar diagnostic procedures for SCR catalytic converters are based on the WO 2013/147653 A1 and the US 2016/0069243 A1 emerged.

Also from the WO 2007/037730 A1 a diagnostic method for an exhaust gas aftertreatment system is known which has an SCR catalytic converter. the DE 10 2013 200 623 A1 shows a diagnostic method for breakthroughs in substrates of particle filters with an SCR-catalytic coating on the basis of sensor-detected changes in NOX concentration downstream of the SCR particle filter.

The present invention is therefore based on the object of creating a method and a corresponding exhaust gas aftertreatment system of an internal combustion engine that enable particularly rapid and precise monitoring of an SCR particle filter with regard to its NO _x / NH ₃ conversion and the particle filtering during operation of the internal combustion engine .

This object is achieved according to the invention with a method and an exhaust gas aftertreatment system according to claims 1 and 14. According to the invention, a method for operating an exhaust gas aftertreatment system of an internal combustion engine is presented, the exhaust gas aftertreatment system having an exhaust line for guiding an exhaust gas mass flow and an SCR particle filter arranged in the exhaust line and with a device for targeted, defined changing of the NH ₃ and / or NOx concentration is arranged in the exhaust gas mass flow upstream in front of the SCR particle filter, and at least one first concentration sensor, in the exhaust gas mass flow downstream after the SCR particle filter.

• Zunächst wird die Brennkraftmaschine auf eine Diagnosebetriebsart eingestellt, wobei bestimmte maßgebliche Diagnose-Betriebsparameter der Brennkraftmaschine auf Übereinstimmung mit Diagnose-Vorgabewerten verifiziert, eingestellt oder eingeregelt werden.
• Bei Vorliegen der Diagnosebetriebsart erfolgt eine gezielte, definierte Herbeiführung einer NH₃-Konzentrationsänderung und/oder einer NOx-Konzentrationsänderung im Abgasmassenstrom stromaufwärts des SCR-Partikelfilters, in Bezug auf die in der Diagnosebetriebsart vorliegenden Werte der NH₃-Konzentration und oder der NOx-Konzentration.
• Anschließend erfolgt das Messen der NH₃- und/oder NOx-Konzentrationsänderung im Abgasmassenstrom nach dem SCR-Partikelfilter innerhalb eines, unmittelbar auf die vorgenannte NH₃- und/oder NOx-Konzentrationsänderung vor dem SCR-Partikelfilter folgenden, festgelegten Zeitfensters, mittels des zumindest einen ersten Konzentrationssensors, der ein entsprechendes erstes Konzentrationsmesssignal abgibt, und das
• Bereitstellen eines korrelierenden Konzentrations-Vergleichswertes zumindest auf Basis des ersten Konzentrationsmesssignals.
• Anhand des jeweiligen Konzentrations-Vergleichswertes und vorgegebener Grenzwerte erfolgt eine Bewertung der innerhalb des festgelegten Zeitfensters gemessenen NH₃- und/oder NOx-Konzentrationsänderung nach dem SCR-Partikelfilter.
• Schließlich erfolgt ein Diagnostizieren des SCR-Partikelfilters als schadhaft aufgrund von Durchbrüchen im Filtersubstrat, wenn die Bewertung ergibt, dass der Konzentrations-Vergleichswert zumindest einen vorgegebenen Grenzwert überschritten hat.

The method according to the invention serves to identify breakthroughs in the filter substrate of the SCR particle filter and has the following steps:

• First of all, the internal combustion engine is set to a diagnostic operating mode, with certain relevant diagnostic operating parameters of the internal combustion engine being verified, set or regulated for compliance with predetermined diagnostic values.
• When the diagnostic mode is present, a targeted, defined induction of a change in the NH ₃ concentration and / or a change in the NOx concentration in the exhaust gas mass flow upstream of the SCR particle filter takes place in relation to the values of the NH ₃ concentration and / or the NOx concentration in the diagnostic mode .
• The change in NH ₃ and / or NOx concentration in the exhaust gas mass flow downstream of the SCR particle filter is then measured within a _{specified time window immediately following the aforementioned change in NH 3} and / or NOx concentration upstream of the SCR particle filter, by means of the at least a first concentration sensor which emits a corresponding first concentration measurement signal, and that
• Providing a correlating concentration comparison value at least on the basis of the first concentration measurement signal.
• On the basis of the respective concentration comparison value and specified limit values, an assessment of the change in NH ₃ and / or NOx concentration measured within the specified time window takes place after the SCR particle filter.
• Finally, the SCR particle filter is diagnosed as defective due to breakthroughs in the filter substrate if the assessment shows that the comparison value for the concentration has exceeded at least a predetermined limit value.

The invention also relates to an exhaust gas aftertreatment system of an internal combustion engine, which has an SCR particle filter arranged in an exhaust line and at least one device for targeted, defined changing of the NH ₃ and / or NOx concentration in the exhaust gas mass flow upstream in front of the SCR particle filter, and at least one concentration sensor , for measuring the NH ₃ and / or NOx concentration in the exhaust gas mass flow downstream after the SCR particle filter.

This exhaust gas aftertreatment system is characterized in that it has an electronic computing and control unit which is set up for targeted, defined changing of the NH ₃ and / or NOx concentration in the exhaust gas mass flow upstream of the SCR particle filter by means of the device for targeted, defined changing of the NH ₃ and / or NOx concentration and for detecting a first concentration measurement signal output by the at least one concentration sensor. The electronic computing and control unit is also set up to implement the method for operating an exhaust gas aftertreatment system of an internal combustion engine in accordance with one of the embodiments of the method according to the invention described above and below.

It can thus be summarized that the basic idea of the invention is to use a NOx and / or NH ₃ sensor downstream of an SCR particle filter to be used in conjunction with a change in NH ₃ concentration and / or a change in NOx concentration in the exhaust gas mass flow upstream of the SCR particle filter to subject the SCR particle filter to a functional check, in particular a performance diagnosis. For example, a wall-flow filter with a suitable SCR coating is used as the SCR particle filter.

Function-influencing damage to SCR particle filters usually consists of breakthroughs or holes in the substrate of the filter, the number or cross-sectional area of which determine the degree of damage and through which a corresponding part of the exhaust gas can pass unfiltered and untreated. If the total cross-section of the breakthroughs or open holes is above a Threshold value, the corresponding particulate emissions exceed a diagnostic threshold value (OBD threshold value).

In order to detect this state, the system is preferably in a steady or stationary operating state, for example idling, at a quasi-constant SCR particle filter temperature at which the NOx concentration signal and / or the NH ₃ concentration signal after the SCR particle filter varies slightly , for example below 1 ppm / sec, the addition amount of the urea solution and / or the NOx raw emission preferably increased in one step, for example by 200 ppm NH ₃ / NO _{x based} on the previously given NH ₃ addition amount or NOx raw emission, and the course of the NOx and / or NH ₃ signal is observed (measurement of the corresponding increase in concentration). If the SCR particle filter is now within the emission limit, it can be assumed that the entire cross section of openings in the filter substrate is so small that the added urea or the increased NOx concentration is initially stored for the most part in the SCR particle filter. Therefore, the NOx or NH ₃ signal measured after the filter has only a slight increase over a short period of time, for example 3 seconds, depending on the air mass flow. After that, the corresponding signal is stable and has a much lower gradient (less than 1 ppm / sec) than an SCR particle filter that is too badly damaged.

However, if the threshold value is exceeded, the entire cross section of openings in the filter substrate is so large that the added urea or. the increased NOx concentration flows through the SCR particle filter untreated to a large extent and almost without delay, so that the corresponding sensors after the SCR particle filter an immediate, increased NH ₃ - / NO _x concentration increase within the specified, immediately following time window register what the corresponding signal again assumes a more stable state with a lower gradient.

It has been shown that the ratio between the change in NOx and / or NH ₃ concentration after the SCR particle filter and the change in NOx and / or NH ₃ concentration before the SCR particle filter is directly proportional to the total cross-section of the openings in the filter substrate of the SCR -Particle filter is. If this ratio is above a certain threshold or limit, the filter is classified as defective in terms of particulate conversion.

A corresponding change in the NOx concentration upstream of the SCR particle filter can be carried out, for example, by reducing the exhaust gas recirculation rate (EGR rate), in particular with high pressure exhaust gas recirculation, but also with low pressure exhaust gas recirculation. Here, too, it can be seen that the change in NOx concentration after the SCR particle filter in relation to the change in NOx concentration before the SCR particle filter is directly proportional to the total cross-section of the openings in the filter substrate of the SCR particle filter. In the context of the method, a concentration comparison value is determined on the basis of the concentration measurement signal provided by means of the at least one concentration sensor. In its simplest form, this concentration comparison value can, for example, represent the maximum deflection of the concentration measurement signal within the defined time window. The concentration comparison value can, however, also be a ratio between the NH ₃ and / or NOx concentration change before and after the SCR particle filter. Likewise, the concentration comparison value can be determined on the basis of several successive changes in concentration and the respective gradients of the changes in concentration can also be used, as will be explained below. Here can the change in concentration is understood to mean both an increase in concentration and a reduction in concentration or both in succession.

_{The named concentration sensor is an NH 3} sensor or a NOx sensor, depending on whether the NH ₃ or NOx concentration is changed to carry out the method. While an NH ₃ sensor is only suitable for measuring the NH ₃ concentration, the aforementioned NOx sensor, on the other hand, can _{measure both the NH 3} and the NOx concentration, i.e. consequently also a combination of NOx and NH ₃ . In this case, it is a combined NH ₃ / NO _x concentration sensor. Depending on the desired measurement, the sensors suitable for this can therefore be provided.

The present invention also relates to an exhaust gas aftertreatment system of an internal combustion engine, in particular a diesel engine, which has an SCR particle filter arranged in an exhaust line and at least one device for targeted, defined changing of the NH ₃ and / or NO _x concentration in the exhaust gas mass flow upstream before the SCR. Particle filter, and at least one first concentration sensor, for measuring the NH ₃ and / or NOx concentration in the exhaust gas mass flow downstream after the SCR particle filter. This exhaust gas aftertreatment system is characterized by the fact that it has an electronic computing and control unit which is set up for targeted, defined changing of the NH ₃ and / or NOx concentration in the exhaust gas mass flow upstream of the SCR particle filter by means of the device for targeted, defined Changing the NH ₃ and / or NOx concentration and for detecting a first concentration measurement signal output by the at least one first concentration sensor. According to the invention, the electronic computing and control unit is also set up to use the method for operating a Exhaust aftertreatment system of an internal combustion engine, as shown in the preceding and the following explanations.

• Figur 1 eine schematische Darstellung einer Ausführung einer erfindungsgemäßen Abgasnachbehandlungsanlage;
• Figur 2 ein Blockdiagramm zur Darstellung des Verfahrensablaufs einer Ausführung des erfindungsgemäßen Verfahens;
• Figur 3 eine qualitative Darstellung von Verlaufskurven der NO_x/NH₃-Konzentration vor und nach dem SCR-Partikelfilter bei intaktem und defektem SCR-Partikelfilter; und
• Figur 4 eine qualitative Darstellung von Verlaufskurven der NO_x/NH₃-Konzentration vor und nach dem SCR-Partikelfilter bei aufeinanderfolgenden NO_x/NH₃-Konzentrationsänderungen.

The invention and further advantageous exemplary embodiments and developments of the invention are explained in detail below with reference to the figures. Show it:

• Figure 1 a schematic representation of an embodiment of an exhaust gas aftertreatment system according to the invention;
• Figure 2 a block diagram to illustrate the process sequence of an embodiment of the method according to the invention;
• Figure 3 a qualitative representation of course curves of the NO _x / NH ₃ concentration before and after the SCR particle filter with an intact and defective SCR particle filter; and
• Figure 4 a qualitative representation of course curves of the NO _x / NH ₃ concentration before and after the SCR particle filter with successive changes in the NO _x / NH ₃ concentration.

Objects with the same function and name are identified throughout the figures with the same reference symbols.

Figure 1 shows schematically in a simplified representation an embodiment of an exhaust gas aftertreatment system according to the invention of an internal combustion engine, for example a diesel engine. The exhaust gas mass flow 10 coming from the internal combustion engine (not shown here) is guided in the direction of the arrow through an exhaust pipe 1 and passes an SCR particle filter 3 (SC-PF), which is designed, for example, as a wall-flow filter with an SCR coating and is arranged in the exhaust pipe 1 .

For the targeted, defined bringing about a change in the NH ₃ concentration in the exhaust gas mass flow 10 upstream of the SCR particle filter 3, there is an NH ₃ supply device 7 on the exhaust pipe 1 upstream of the SCR particle filter 3 for supplying an NH ₃ solution 7d into the Exhaust pipe 1 arranged. In _{this exemplary embodiment, the NH 3} supply device 7 has a storage container 7a for storing a suitable aqueous NH ₃ solution 7d, which is also referred to as urea solution. The storage container 7a is connected via a supply line to a metering device 7b, for example an injection valve, which in turn is arranged on the exhaust gas line 1 and is set up _{to dispense defined quantities of the NH 3} solution into the exhaust gas mass flow 10. The supplied NH ₃ solution produces NH ₃ , which converts the NOx contained in the exhaust gas into nitrogen and water. The SCR particulate filter therefore fulfills its function as a diesel particulate filter and at the same time reduces the NOx content in the exhaust gas.

Furthermore, an exhaust gas recirculation device 2, a so-called high-pressure exhaust gas recirculation system, which branches off from the exhaust pipe 1 upstream of the SCR particle filter 3 and branches off from the exhaust gas line 1 upstream of the SCR particle filter 3, is arranged for a targeted, defined change in the NOx concentration in the exhaust gas mass flow 10, via which a first part Exhaust gas mass flow 10a of the exhaust gas mass flow 10 emitted by the internal combustion engine is returned to the intake region of the internal combustion engine via a first exhaust gas recirculation line 2a. The size of the recirculated first partial exhaust gas mass flow 10a can be set via a first exhaust gas recirculation valve 2b arranged in the first exhaust gas recirculation line 2a. The junction of this exhaust gas recirculation device 2 is expediently arranged on the exhaust gas line 1 upstream of the NH ₃ feed device 7, since the _{supplied NH 3} solution 7d is to be supplied completely to the SCR particle filter 3 for NOx reduction.

In a further expansion stage of the exhaust gas aftertreatment system according to the invention, as in Figure 1 shown, an exhaust gas recirculation device 8, a so-called low-pressure exhaust gas recirculation system, is arranged upstream of the SCR particle filter 3 upstream of the SCR particle filter 3 for the targeted, defined bringing about a change in the NOx concentration in the exhaust gas mass flow 10, via which a further part Exhaust gas mass flow 10b of the exhaust gas mass flow 10 emitted by the internal combustion engine is returned to the intake area of the internal combustion engine via a further exhaust gas recirculation line 8a. The size of the recirculated further partial exhaust gas mass flow 10b can be set via a further exhaust gas recirculation valve 8b arranged in the further exhaust gas recirculation line 8a.

The mode of operation of such exhaust gas recirculation devices for reducing emissions, in particular for influencing the raw NOx emissions of the internal combustion engine, that is to say the NOx concentration in the exhaust gas, is known to the person skilled in the art from the prior art and will not be explained further here.

Although the in Figure 1 The maximum expansion stage of the exhaust gas aftertreatment system _{according to the invention shown has both an NH 3} supply device 7 and a first exhaust gas recirculation device 2 as well as a further exhaust gas recirculation device 8, then the presence of one of these devices is sufficient for an embodiment of the exhaust gas aftertreatment system according to the invention. Likewise, two or all three of these devices can also be used in combined operation and, as it were, become one device for targeted, defined bringing about a change in the NH ₃ concentration and / or a change in the NOx concentration in the exhaust gas mass flow 10 upstream of the SCR particle filter 3.

As an indispensable component for the method according to the invention, at least one first concentration sensor 6 for measuring the NH ₃ and / or NOx concentration in the exhaust gas mass flow 10 is arranged downstream, after the SCR particle filter 3, in the exhaust gas mass flow 10. This first concentration sensor 6 emits a corresponding first concentration measurement signal 110, on the basis of which a correlating concentration comparison value (VgW) can be provided.

Furthermore, the embodiment of the exhaust gas aftertreatment system according to the invention shown here has, according to a further expansion stage, an additional concentration sensor 5 arranged in the exhaust gas mass flow 10 upstream in front of the SCR particle filter 3 for measuring the NH ₃ and / or NOx concentration upstream of the SCR particle filter 3 on. This is expediently arranged in the exhaust gas mass flow 10 downstream of the NH ₃ feed device 7 and the junction of the first exhaust gas recirculation device 2, directly in front of the SCR particle filter 3, so that with this additional concentration sensor 5, both the NH ₃ and the NOx concentration change can be detected in front of the SCR particle filter 3, that is to say the targeted change in the NH ₃ and / or NOx concentration. This additional concentration sensor 5 also emits a corresponding second concentration measurement signal 100 which can also be used to provide a concentration comparison value (VgW).

In this way, an actually measured value for the change in the NH ₃ concentration can be used to carry out the method and / or the NOx concentration change in the exhaust gas mass flow 10 upstream of the SCR particle filter 3 can be used, for example, to provide a concentration comparison value (VgW), which increases the reliability of the diagnosis of the SCR particle filter. Otherwise, if only the concentration sensor 6 arranged downstream of the SCR particle filter 3 is available, for example the default value for the targeted, defined change in concentration is assumed as the actual value, it being assumed that the device for the targeted, defined change of the respective concentration value is functioning correctly .

Furthermore, the in Figure 1 The illustrated embodiment of the exhaust gas aftertreatment system according to the invention has an electronic computing and control unit 15 (ECU). This is set up for the targeted, defined changing of the NH ₃ and / or NOx concentration in the exhaust gas mass flow 10 upstream of the SCR particle filter 3, by means of at least one of the above-mentioned devices for the targeted, defined changing of the NH ₃ and / or NOx concentration and for detecting a first concentration measurement signal (110) output by the at least one concentration sensor 6 and, in a further expansion stage, a second concentration measurement signal. For this purpose, the electronic computing and control unit 15 is electrically connected via signal lines 2c, 5c, 6c, 7c and 8c to the system components first exhaust gas recirculation valve 2b, additional concentration sensor 5, first concentration sensor 6, metering device 7b and further exhaust gas recirculation valve 8b in order to send control signals to the corresponding system components give or receive signals, in particular measurement signals, from the corresponding system components.

The electronic computing and control unit 15 is also set up to use the method according to the invention for operating a Execute exhaust gas aftertreatment system of an internal combustion engine according to one of the embodiments according to the invention on the basis of a first concentration measurement signal of the first concentration sensor 6 or on the basis of the two concentration measurement signals of the first and the additional concentration sensor 6, 5. For this purpose, the sequence of the method, corresponding calculation algorithms, and the required default values for controlling the exhaust gas aftertreatment system and the internal combustion engine are stored in the form of executable program code in the electronic control unit 15 or in associated electronic storage units.

An embodiment of the exhaust gas aftertreatment system, as described above, is characterized in that the electronic computing and control unit 15 is an integral part of a central control unit (CPU) 16 of the internal combustion engine, the method to be carried out being part of an on-board diagnostic system for monitoring the exhaust-relevant functional units of the internal combustion engine is in normal operation.

An embodiment of the method according to the invention for operating an exhaust gas aftertreatment system of an internal combustion engine in one of the embodiments described above is illustrated in FIG Figure 2 The simplified block sequence program shown in the essential procedural steps.

After the start of the process, in the first process step marked with "D-BP_set", the internal combustion engine is set to a diagnostic operating mode, with certain relevant diagnostic operating parameters (D-BP) of the internal combustion engine being in accordance with diagnostic default values (D-BP_set) verified, adjusted or adjusted.

• Die Motordrehzahl (RPM) der Brennkraftmaschine wird auf einen Wert zwischen 1100 und 1900 Umdrehungen/Minute eingeregelt.
• Die Betriebstemperatur (T-SC-PF) des SCR-Partikelfilters 3 wird auf einen Wert zwischen 250°C und 350°C eingeregelt.
• Eine Druckdifferenz des Abgasmassenstroms (ΔP_SCR-PF) über den SCR-Partikelfilter 3 zwischen 3 bar und 7 bar wird verifiziert.
• Weiterhin wird verifiziert, dass eine NH₃-Speichermenge (SM_SC-PF) im SCR-Partikelfilter 3 über einem vordefinierten Schwellenwert liegt.
• Ergänzend kann die NH₃-Zugabemenge auf einen, in Bezug auf die stromaufwärts des SCR-Partikelfilters im Abgas vorliegende NOx-Konzentration, stöchiometrischen Wert eingeregelt werden, das heißt, dass die NH₃-Zugabemenge einer Menge entspricht, die zur vollständigen Umsetzung des NOx-Anteils im Abgas im SCR-Partikelfilter erforderlich ist. Die Vorgabe dieser Betriebsparameter gewährleistet einen stabilen Betrieb der Brennkraftmaschine, reduziert Störeinflüsse auf das Verfahren und erhöht somit die Sicherheit der Aussagekraft der Diagnose des SCR-Partikelfilters.

In one embodiment variant of the method, the diagnostic mode is characterized by at least one of the following diagnostic operating parameters:

• The engine speed (RPM) of the internal combustion engine is regulated to a value between 1100 and 1900 revolutions / minute.
• The operating temperature (T-SC-PF) of the SCR particle filter 3 is regulated to a value between 250 ° C and 350 ° C.
• A pressure difference in the exhaust gas mass flow (ΔP_SCR-PF) across the SCR particle filter 3 between 3 bar and 7 bar is verified.
• It is also verified that an NH ₃ storage amount (SM_SC-PF) in the SCR particle filter 3 is above a predefined threshold value.
• In addition, the _{amount of NH 3} added can be adjusted to a stoichiometric value in relation to the NOx concentration present in the exhaust gas upstream of the SCR particulate filter, _{i.e. the amount of NH 3} added corresponds to an amount that is necessary for complete conversion of the NOx -Part of the exhaust gas in the SCR particle filter is required. The specification of these operating parameters ensures stable operation of the internal combustion engine, reduces disruptive influences on the method and thus increases the reliability of the informative value of the diagnosis of the SCR particle filter.

The corresponding diagnostic default values are for this purpose in an electronic memory of the electronic computing and control unit (ECU), which is shown in Figure 2 is marked with "E_Sp1" and can be easily read out and used to carry out this process step.

Since the adjustment, setting and verification of the diagnostic operating parameters can take a certain amount of time, the following process step, which is marked with "D-BP = D-BP_set", checks whether the current diagnostic operating parameters match the diagnostic default values to match. As long as this is not the case, attempts are made to adjust the diagnostic operating parameters (D-BP) to the diagnostic default values (D-BP_set). If the desired diagnostic operating parameters are available, the next method step can follow.

In the following _{process step, marked with "NO x} / NH ₃ ", the targeted, defined induction of a change in the NH ₃ concentration and / or a change in the NOx concentration in the exhaust gas mass flow 10 upstream of the SCR particle filter 3 takes place, depending on the design of the exhaust gas aftertreatment system by appropriate individual or combined control of one or more of the devices: NH ₃ feed device 7, first exhaust gas recirculation device 2 and further exhaust gas recirculation device 8; as in Figure 2 shown with dashed lines. Thus, depending on the design of the exhaust gas aftertreatment system, a change in the NH ₃ concentration or a change in the NOx concentration or a combined or superimposed change in the NOx / NH ₃ concentration can be brought about by means of a corresponding control of the devices mentioned for the targeted, defined induction of the NH ₃ and / or NOx concentration change, by the electronic computing and control unit (ECU) 15.

Thus, in one embodiment of the method, the defined change in NOx concentration upstream of the SCR particle filter 3 can consist of an increase or a reduction in the NOx concentration, which is achieved, for example, by a defined reduction or increase in an exhaust gas recirculation rate, with an additional support here further operating parameters of the internal combustion engine can be influenced in the sense of an increase in the NOx concentration in the exhaust gas. The exhaust gas recirculation rate can be determined by means of the first exhaust gas recirculation device 2 or the further exhaust gas recirculation device 8 or the two exhaust gas recirculation devices 2, 8 in combination. This is done, for example, by appropriate control of the first exhaust gas recirculation valve 2b or the second exhaust gas recirculation valve 8b or a combined control of the first and second exhaust gas recirculation valve 2b, 8b by means of the electronic computing and control unit (ECU) 15.

Furthermore, in one embodiment of the method, the defined change in the NH ₃ concentration upstream of the SCR particle filter 3 can _{consist of a defined increase or reduction in the NH 3} concentration, which is achieved by a defined increase or reduction in the amount of NH ₃ solution 7d added by means of the NH ₃ feed device 7 is set. This takes place in particular by appropriate activation of the metering device 7b by means of the electronic computing and control unit (ECU) 15.

In the further course of the method according to the invention will now be in accordance with the "NO _x / NH ₃ _Sig" step marked, the NH ₃ - and / or NO _x -Konzentrationsänderung in the exhaust gas mass flow 10 after the SCR particle filter 3 within a directly on the aforementioned NH ₃ - and / or NO _x concentration change before the SCR particle filter 3 following, measured time window (TW). This takes place by means of the at least one first concentration sensor 6, which emits a corresponding first concentration measurement signal 110, which is fed via the signal line 6c to the electronic computing and control unit for further processing.

_{In one embodiment of the method, the change in the NH 3} and / or NO _x concentration upstream, in front of the SCR particle filter, is also measured in the same time window (TW) as part of the aforementioned method step. For this purpose, an additional concentration sensor 5 is used to arrange the exhaust gas mass flow 10 upstream in front of the SCR particle filter 3 is, a _{second concentration measurement signal 120 correlating to the NH 3} and / or NO _x concentration change in the exhaust gas mass flow 10 upstream of the SCR particle filter 3 is provided and fed to the electronic computing and control unit ECU via a signal line 5c. This not only enables the relative consideration of the change in concentration before and after the SCR particle filter 3 and an associated increase in the diagnostic reliability of the method, but also the possibility of assessing the function of the exhaust gas recirculation _{devices 2, 8 and the NH 3} feed device 7.

In the following _{method step labeled “(NO x} / NH ₃ ) VGW”, a correlating concentration comparison value (VgW) is provided at least on the basis of the first concentration measurement signal (110). As a concentration comparison value (VgW), for example, in different versions of the method, a respective maximum value or minimum value of the change in concentration reached within the defined time window (TW) and / or a concentration change gradient determined within the defined time window (TW) can be used.

In a further embodiment of the method, provided that the NH ₃ and / or NOx concentration change is also measured upstream in front of the SCR particle filter, the concentration comparison value (VgW) can be applied to the respective NH determined within the defined time window ₃ - and / or NOx concentration changes after and before the SCR particle filter 3 are based. For this purpose, for example, in a further embodiment of the method, the values of the NH ₃ and / or NOx concentration changes determined within the defined time window at a certain point in time and / or the gradients of these concentration changes, in each case before and after the SCR particle filter 3, can be combined compared or put in relation to each other. This enables a particularly reliable concentration comparison value (VgW) to be provided and increases the diagnostic reliability of the method, since incorrect diagnoses due to possibly defective devices for changing the NH ₃ and / or NOx concentration can be ruled out.

In the following process step, marked with "VgW - GW", the change in NH ₃ and / or NOx concentration measured within the specified time window TW after the SCR particle filter (3) is evaluated on the basis of the respective concentration comparison value (VgW) and specified limit values (GW). As already mentioned above, a respective maximum or minimum value of the change in concentration and / or a determined gradient of the change in concentration or also comparison or ratio values based on the respective before and after the SCR particle filter can be used as the concentration comparison value, depending on the execution of the method, as already mentioned above 3 measured values or gradients of the change in concentration can be used. This enables a wide range of variance in the design of the method according to the invention and the adaptation to the needs of the respective application. In accordance with the concentration comparison value to be used, correspondingly adapted limit values must then be specified. These can, for example, be determined beforehand empirically or by means of model calculation and are, for example, stored in an electronic memory area of the electronic computing and control unit and called up from there to evaluate the change in concentration. Such an electronic storage area is in Figure 2 , marked with E_Sp2 and contains the corresponding limit values, which are shown as "(NO _x / NH ₃ ) GW".

On the basis of the previously described evaluation of the change in concentration after the SCR particle filter 3, the following method step, marked with “VGW≥GW”, diagnoses the SCR particle filter 3 as defective, “SCR-PF = nok” if the evaluation results that the concentration comparison value (VgW) has exceeded at least a predetermined limit value (GW). Otherwise, the SCR particle filter is diagnosed as functional "SCR-PF = ok" if the concentration comparison value has not reached or exceeded a limit value. This concludes the method according to the invention.

In order to ensure a permanently error-free operation of the exhaust gas aftertreatment system, the method according to the invention can be repeated in certain cycles during operation, these cycles being based on a certain operating time, a certain operating performance or on requirement values determined during operation.

A further embodiment of the method is characterized in that in the context of the change in NH ₃ and / or NOx concentration, there is initially an increase in concentration and an immediately subsequent reduction in concentration. In this case, after the concentration increase for a specific first period of time, the concentration is reduced to a value selected in this way and for a second period selected in this way, so that an average value of the NH ₃ and / or NOx resulting over the duration of the increase in concentration and the reduction in concentration takes place. Concentration downstream of the SCR particle filter, which corresponds to the value of the NH ₃ and / or NOx concentration prevailing before the concentration increase. In this way it is ensured that over the duration of the procedure, on average over time, there is no increase in pollutant emissions caused by the procedure. Another embodiment of the method is characterized in that _{a combined concentration sensor 6 is used to measure the change in NH 3} and / or NOx concentration in the exhaust gas mass flow 10, which measures the change in NH ₃ and / or NOx in a combined concentration measurement signal 110 summarizes. This can apply both to the first concentration sensor 6, downstream of the SCR particle filter 3, and to the second concentration sensor 5, upstream of the SCR particle filter 3. This advantageously makes it possible to _{specify both a change in NH 3} concentration and a change in NOx concentration as well as a combined change in NH ₃ / NO _x concentration for carrying out the method and thus also opens up a greater scope for the extent of the predetermined change in concentration.

In a further embodiment of the method, the respective fixed time window (TW) for measuring the change in NH ₃ and / or NO _x concentration in the exhaust gas mass flow 10 after and / or in front of the SCR particle filter 3 has a duration of less than or equal to 5 seconds, in particular less than or equal to 3 seconds. The length of this time window ensures that only a rapid change in the NH ₃ and / or NO _x concentration after the SCR particle filter 3, as occurs only when the SCR particle filter 3 is defective, when determining the concentration comparison value and so on the diagnosis of the SCR particulate filter shows the effect.

Figure 3 shows an example of the curves of the NO _x / NH ₃ concentration over time, which were recorded with the aid of combined NO _x / NH ₃ concentration sensors upstream and downstream of the SCR particulate filter. The curve 100 shows the NO _x / NH ₃ concentration upstream of the SCR particulate filter, starting from an in the NO _x / NH ₃ concentration regulated at approx. 40 ppm at time T1, a defined change in concentration by approx. 100 ppm to 140 ppm is brought about. _{The curve 110 shows the NO x} / NH ₃ concentration recorded downstream of the SCR particle filter in the case of a defective SCR particle filter. _{An increased value of the NO x} / NH ₃ concentration at approx. 15 ppm can already be seen here in the phase of the diagnostic operating mode. At time T1, the NO _x / NH ₃ concentration begins to rise with a gradient G1 within time window TW and rises to a maximum concentration KM1 at time T2, at the end of time window TW.

In contrast, the profile curve 120 shows the NO _x / NH ₃ concentration recorded downstream of the SCR particle filter in the case of an intact SCR particle filter. Here, in the phase of the diagnostic operating mode, there is _{a minimum value for the NO x} / NH _{3 concentration.} At the point in time T1, the NO _x / NH ₃ concentration also begins to rise within the time window TW, but with a significantly smaller gradient G2 compared to the curve 110. Accordingly, only a significantly smaller maximum concentration KM2 is reached up to time T2, at the end of time window TW.

As can be seen from the aforementioned exemplary embodiments, the maximum concentration MK1, MK2 reached up to a certain point in time within the time window TW or at the end of the time window TW or the respective gradient G1, G2 of the NO _x - / NH ₃ concentration increase within the time window TW can be used. Furthermore, it is possible to consider the concentration values determined downstream of the SCR particle filter and the concentration values specified or determined upstream in combination and to use them therefrom to determine a comparison value. The NO _x / NH ₃ concentration values upstream of the SCR particle filter can be based on the default values, determined with the aid of model considerations or measured by means of a concentration sensor (if available).

To determine a concentration comparison value VgW, in one embodiment the gradient of the increase in concentration downstream of the SCR particle filter determined within the time window TW can be divided by the jump value of the change in concentration upstream of the SCR particle filter. The result is used as the concentration comparison value VgW. For example, if the gradient of the increase in concentration downstream of the SCR particle filter is 11.3 ppm / s and the jump value for the change in concentration upstream of the SCR particle filter is 480 ppm (paying attention to the sign), the result is a comparison value of: $$\left(11.3\mathrm{ppm}/\mathrm{s}\right)/480\mathrm{ppm}=0.024/\mathrm{s}\mathrm{.}$$

If there is a limit value GW of, for example, 0.016 / s, then this would be exceeded (VgW ≥ GW) and the SCR particle filter would have to be assessed as defective (SCR-PF = nok).

This procedure increases the robustness of the method against interfering influences.

Another embodiment of the method is characterized in that the change in NH ₃ and / or NO _x concentration has an increase in concentration and an immediately following reduction in concentration, and the values and / or the gradients of the increase in concentration and the reduction in concentration in each case after and before the SCR particle filter 3 can be used in combination with one another to evaluate the measured change in NH ₃ and / or NO _x concentration after the SCR particle filter 3.

For example, a ratio of the gradient of the concentration increase downstream and the grade value of the concentration increase upstream of the SCR particle filter as well as the gradient of the subsequent concentration drop downstream and the associated grade value of the concentration reduction upstream of the SCR particle filter can be formed and their sum can be calculated.

This is qualitatively in Figure 4 shown. Shown is the curve 100 of the NH ₃ - / NO _x concentration upstream and the resulting curve 110 of the NH ₃ - / NO _x concentration downstream of the SCR particle filter. The curve 100 shows a deliberately and defined sudden increase in concentration + KSp1 by a certain amount at time T1 and a persistence of the increased NH ₃ - / NO _x concentration over the time window TW1 up to time T2. This is followed by an equally targeted and defined sudden concentration reduction -KSp2 by the same amount, that is to say a complete reduction in the concentration increase, at time T2. The resulting course of the NH ₃ - / NO _x concentration downstream of the SCR particle filter shows an increase following time T1 with the gradient + G1a, within the time window TW1 immediately following the change in concentration + KSp1, up to time T2 and a subsequent drop in the NH ₃ - / NO _x concentration with a gradient -G1b within the time window TW2 immediately following the change in concentration -KSp2, which lasts up to time T3. According to the above scheme, the concentration comparison value VgW can be determined according to the following relationship: $$\left(+\mathrm{G1a}/+\mathrm{KSp1}\right)+\left(-\mathrm{G1b}/-\mathrm{KSp2}\right)=\mathrm{VgW}$$

For example, there is a gradient of +7.3 ppm / s downstream with a jump value of the concentration increase of +480 ppm upstream of the SCR particle filter and then a gradient of -11.3 ppm / s downstream with a jump value of the concentration reduction of -480 ppm / s this is how the concentration comparison value is calculated as follows: $$\begin{array}{l}\left(\left(+7.3\mathrm{ppm}/\mathrm{s}\right)/+480\mathrm{ppm}\right)+\left(\left(-11.3\mathrm{ppm}/\mathrm{s}\right)/-480\mathrm{ppm}\right)=\\ 0.015/\mathrm{s}+0.024/\mathrm{s}=0.039/\mathrm{s}.\end{array}$$

If there is a limit value GW of, for example, 0.026 / s, then this would be exceeded (VgW ≥ GW) and the SCR particle filter would have to be assessed as defective (SCR-PF = nok).

This procedure further increases the robustness of the method against interfering influences.

In a further embodiment of the method, after the diagnosis of the SCR particle filter 3, the targeted, defined change in the NH ₃ and / or NO _x concentration in the exhaust gas mass flow 10 upstream of the SCR particle filter 3 is withdrawn, the diagnostic mode is ended and the NH ₃ - and / or NOx concentration is again set or regulated as a function of the current operating point of the internal combustion engine.

How out Figure 2 As can be seen, different further measures can now be initiated on the basis of and as a function of the diagnosis result.

If the diagnosis shows that the SCR particle filter is intact and working properly (SCR-PF = ok), the internal combustion engine can continue to operate in the normal operating mode after the method has been carried out, i.e. after the functionality of the SCR particle filter 3 has been diagnosed , this is shown in the process step marked "BP_Norm".

However, if the diagnosis reveals that the SCR particle filter is defective (SCR-PF = nok), emergency operation of the internal combustion engine can be initiated instead, which, for example, still enables a workshop to be visited when the engine output is reduced. At the same time, an error message can be output to the vehicle driver with the request to visit the nearest workshop immediately or to initiate the repair. This is in Figure 2 in the process step marked with "BP_Not".

Claims (17)

1. Method for operating an exhaust-gas aftertreatment system of an internal combustion engine, which exhaust-gas aftertreatment system has an exhaust-gas line (1) for conducting an exhaust-gas mass flow (10) and has an SCR particle filter (3) arranged in the exhaust-gas line (1), wherein a device for targeted, defined variation of the NH₃ and/or NO_x concentration is arranged in the exhaust-gas mass flow (10) upstream of the SCR particle filter (3), and at least one first concentration sensor (6) is arranged in the exhaust-gas mass flow (10) downstream of the SCR particle filter (3), in order to detect apertures in the filter substrate of the SCR particle filter (3), having the following steps:

   - setting the internal combustion engine to a diagnostic operating mode, wherein certain relevant diagnostic operating parameters (D-BP) of the internal combustion engine are verified for, or set or adjusted to, correspondence with diagnostic default values (D-BP_set);
   in the presence of the diagnostic operating mode,

   - targeted, defined inducement of an NH₃ concentration change and/or of an NO_x concentration change in the exhaust-gas mass flow (10) upstream of the SCR particle filter (3) in relation to the values of the NH₃ concentration and/or of the NO_x concentration that are present in the diagnostic operating mode;

   - measuring the NH₃ and/or NO_x concentration change in the exhaust-gas mass flow (10) downstream of the SCR particle filter (3) within a specified time window (TW), which directly follows the abovementioned NH₃ and/or NO_x concentration change measured upstream of the SCR particle filter (3), by means of the at least one first concentration sensor (6), which outputs a corresponding first concentration measurement signal (110); and

   - providing a correlating concentration comparison value (VgW) at least on the basis of the first concentration measurement signal (110);

   - evaluating the NH₃ and/or NO_x concentration change downstream of the SCR particle filter (3) measured within the specified time window (TW) on the basis of the respective concentration comparison value (VgW) and predefined limit values (GW); and

   - diagnosing the SCR particle filter (3) as defective owing to apertures in the filter substrate if the evaluation yields that the concentration comparison value (VgW) has overshot at least one predefined limit value (GW) .
2. Method according to Claim 1, in which the device for targeted, defined inducement of the NH₃ and/or NO_x concentration change in the exhaust-gas mass flow (10) upstream of the SCR particle filter (3) has an NH₃ feed device (7) for the feed of an NH₃ solution (7d) into the exhaust-gas line (1) and/or has a first exhaust-gas recirculation device (2) which branches off from the exhaust-gas line (1) upstream of the SCR particle filter (3) and/or has a further exhaust-gas recirculation device (8) which branches off from the exhaust-gas line (1) downstream of the SCR particle filter (3).
3. Method according to Claim 1 or 2,
   wherein the diagnostic operating mode is characterized by at least one of the following diagnostic operating parameters:

   - engine speed (RPM) of the internal combustion engine between 1100 and 1900 revolutions/minute;

   - operating temperature (T-SC-PF) of the SCR particle filter (3) between 250°C and 350°C;

   - pressure difference of the exhaust-gas mass flow (ΔP_SCR-PF) across the SCR particle filter (3) of between 3 bar and 7 bar;

   - stored NH₃ quantity (SM_SC-PF) in the SCR particle filter (3) lies above a predefined threshold value;

   - added NH₃ quantity adjusted to a value which is stoichiometric in relation to the NO_x concentration in the exhaust gas upstream of the SCR particle filter.
4. Method according to either of Claims 2 and 3,
   wherein the defined NO_x concentration change upstream of the SCR particle filter (3) consists in an increase or a reduction of the NO_x concentration that is set as a result of a defined reduction or increase of an exhaust-gas recirculation rate of the first exhaust-gas recirculation device (2) and/or of the further exhaust-gas recirculation device (8).
5. Method according to one of Claims 2 to 4,
   wherein the defined NH₃ concentration change upstream of the SCR particle filter (3) consists in a defined increase or reduction of the NH₃ concentration that is set as a result of a defined increase or reduction of the added quantity of the NH₃ solution (7d) by means of the NH₃ feed device (7) .
6. Method according to one of Claims 1 to 5,
   wherein, in the evaluation of the NO_x concentration change and/or NH₃ concentration change downstream of the SCR particle filter (3) measured within the specified time window (TW), a respective maximum value or minimum value, attained within the defined time window (TW), of the concentration change and/or a gradient, determined within the defined time window (TW), of the concentration change is used as concentration comparison value (VgW).
7. Method according to any of Claims 1 to 6, characterized in that, in the course of the NH₃ and/or NO_x concentration change, a concentration increase and an immediately subsequent concentration reduction occur, wherein, after the concentration increase for a particular first period of time, the concentration reduction occurs to such a selected value, and for such a selected second period of time, that a resulting mean value of the NH₃ and/or NO_x concentration over the duration of the concentration increase and of the concentration reduction corresponds to the value of the NH₃ and/or NO_x concentration prevailing before the concentration increase.
8. Method according to one of Claims 1 to 7,
   wherein, for the measurement of the NH₃ and/or NO_x concentration change in the exhaust-gas mass flow (10),
   use is made in each case of a combined concentration sensor (6) which combines the NH₃ and/or NO_x concentration change in a combined concentration measurement signal (110) .
9. Method according to any of Claims 1 to 8, characterized in that the respective specified time window (TW) has a duration of less than or equal to 5 seconds, in particular less than or equal to 3 seconds.
10. Method according to any of Claims 1 to 9, characterized in that, after the diagnosis of the SCR particle filter (3), the targeted, defined NH₃ and/or NO_x concentration change in the exhaust-gas mass flow (10) upstream of the SCR particle filter (3) is withdrawn and, in a manner dependent on the diagnosis result, the internal combustion engine is transferred back into the normal working operating mode (BP_Norm) and continues to be operated, or is restricted to emergency operation (BP_Not).
11. Method according to any of Claims 1 to 10, characterized in that an additional concentration sensor (5) is arranged in the exhaust-gas mass flow (10) upstream of the SCR particle filter (3), by means of which additional concentration sensor a second concentration measurement signal (100) which correlates with the NH₃ and/or NO_x concentration change in the exhaust-gas mass flow (10) upstream of the SCR particle filter (3) is provided, wherein the concentration comparison value (VgW) used for the evaluation of the measured NH₃ and/or NO_x concentration change downstream of the SCR particle filter (3) is based on the respective NH₃ and/or NO_x concentration changes downstream and upstream of the SCR particle filter (3) determined within the defined time window (TW).
12. Method according to Claim 11, characterized in that the values of the NH₃ and/or NO_x concentration changes determined within the defined time window at a particular point in time, and/or the gradients of said concentration changes, in each case upstream and downstream of the SCR particle filter (3) are compared with one another or set in relation to one another.
13. Method according to Claim 12, characterized in that the NH₃ and/or NO_x concentration change has a concentration increase and an immediately subsequent concentration reduction, and the values and/or the gradients of the concentration increase and of the concentration reduction in each case upstream and downstream of the SCR particle filter (3) are used in combination with one another for the evaluation of the measured NH₃ and/or NO_x concentration change downstream of the SCR particle filter (3).
14. Exhaust-gas aftertreatment system of an internal combustion engine, which exhaust-gas aftertreatment system has an SCR particle filter (3) arranged in an exhaust-gas line (1) and has at least one device for targeted, defined variation of the NH₃ and/or NO_x concentration in the exhaust-gas mass flow (10) upstream of the SCR particle filter (3) and has at least one first concentration sensor (6) for measuring the NH₃ and/or NO_x concentration in the exhaust-gas mass flow (10) downstream of the SCR particle filter (3), characterized in that the exhaust-gas aftertreatment system has an electronic processing and control unit (15) which is configured for targeted, defined variation of the NH₃ and/or NO_x concentration in the exhaust-gas mass flow (10) upstream of the SCR particle filter (3) by means of at least one of the devices for targeted, defined variation of the NH₃ and/or NO_x concentration and for detecting a first concentration measurement signal (110) output by the at least one concentration sensor (6), wherein the electronic processing and control unit (15) is furthermore configured to execute the method for operating an exhaust-gas aftertreatment system of an internal combustion engine according to any of Claims 1 to 10.
15. Exhaust-gas aftertreatment system according to Claim 14, characterized in that it has an additional concentration sensor (5) which is arranged in the exhaust-gas mass flow (10) upstream of the SCR particle filter (3) and which serves for measuring the NH₃ and/or NO_x concentration upstream of the SCR particle filter (3), wherein the electronic processing and control unit (15) is configured to execute the method for operating an exhaust-gas aftertreatment system of an internal combustion engine according to any of Claims 11 to 13.
16. Exhaust-gas aftertreatment system according to Claim 14 or 15, in which the device for targeted, defined variation of the NH₃ and/or NO_x concentration in the exhaust-gas mass flow (10) upstream of the SCR particle filter (3) has an NH₃ feed device (7) for the feed of an NH₃ solution (7d) into the exhaust-gas line (1) and/or has a first exhaust-gas recirculation device (2) which branches off from the exhaust-gas line (1) upstream of the SCR particle filter (3) and/or has a further exhaust-gas recirculation device (8) which branches off from the exhaust-gas line (1) downstream of the SCR particle filter (3).
17. Exhaust-gas aftertreatment system according to any of Claims 14 to 16, characterized in that the electronic processing and control unit (15) is an integral constituent part of a central control unit (16) of the internal combustion engine, and the method for being executed is part of an on-board diagnostic system for monitoring the exhaust-gas-relevant functional units of the internal combustion engine during intended operation.

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