DE102017110234B4 - Nitrogen oxide reduction for lean-burn engines with SCR storage model - Google Patents

Abstract

Exhaust gas aftertreatment system (10) for an internal combustion engine comprising an SCR catalytic converter (16) with a feed passage (11) and a follow-up passage (13), with a current feed nitrogen oxide content (cPre) in the feed passage (11 ) and a current post-nitrogen oxide content (cPost) in the post-run passage (13) are determined and a reducing agent injector (15) is arranged upstream of the SCR catalytic converter (16) in order to inject a reducing agent that is in the SCR catalytic converter (16) is stored and nitrogen oxides (NOx) is reduced, and wherein the exhaust gas aftertreatment system (10) comprises a control unit (20) which is connected to the reducing agent injector (15) and controls the current addition amount (Qi) of the reducing agent , wherein the control unit (20) comprises a multi-part simulation model (21) and a pilot control (22) and is designed to carry out the following steps: - In the control unit (20), a setpoint value (Qi *) for the current Redukt The quantity of added ionizing agent is determined on the basis of a precontrol value (Qpre) and a storage management value (Qstr); - The precontrol value (Qpre) is determined by the precontrol (22) on the basis of the feed nitrogen oxide content (cPre); - The storage management value (Qstr) is determined by the multi-part simulation model (21) as a function of an estimated reducing agent content (cRed ') in the SCR catalytic converter (16) so that the estimated reducing agent content (cRed') approximates a target value (cRed *) - The simulation model (21) comprises at least a first element in the form of a reducing agent addition model (31) and a second element in the form of a reducing agent storage model (32), on the basis of which the reducing agent content (cRed ') is estimated - an actual efficiency of the nitrogen reduction is determined on the basis of the leading nitrogen oxide content (cPre) and the trailing nitrogen oxide content (cPost); - in a learning process, if an efficiency is determined nz deviation (dEff) compared to a target efficiency (rEff *) of the nitrogen oxide reduction, a correction value adjustment (27) is carried out in at least two members (31, 32, 33, 34) of the simulation model (21); - characterized in that, that the efficiency deviation (dEff) is distributed according to a weighting key to the correction value adjustment (27) in the at least two members (31, 32, 33, 34) of the simulation model by dividing the deviation value (dEff) into two or more parts.

Description

The disclosure relates to an exhaust gas aftertreatment system for an internal combustion engine with an SCR catalytic converter and a reducing agent injector as well as a method for determining the cause of an efficiency deviation of the nitrogen oxide reduction in the exhaust gas aftertreatment system.

Out GELBERT, G. et al. ("NH3 level control for SCR catalysts based on real-time physical models", MTZ 78 (02/2017), p.61-66) , REIF, K. et al. ("Exhaust technology for internal combustion engines", Wiesbaden, Springer, 2015, p.64-p.68, ISBN 978-3-658-09521-5) and DE 10 2005 050 709 A1 It is known to reduce nitrogen oxides in the exhaust gas of internal combustion engines, especially lean-burn engines, by adding a reducing agent to nitrogen and other harmless reaction products. For this purpose, the reducing agent is added to the exhaust gas and stored in an SCR catalytic converter. The SCR catalytic converter is a catalytic converter for selective catalytic reduction, in which the added reducing agent is deposited on a catalytic surface by adsorption and reacts there with nitrogen oxides in the exhaust gas.

The reducing agent content (stored amount) in the SCR catalytic converter should be in a predetermined range of values so that the reduction reaction takes place at a desired efficiency. If the reducing agent content is too low or goes back to zero, nitrogen oxides can break through the SCR catalytic converter. If the reducing agent content becomes too high, the added and possibly toxic reducing agent can no longer accumulate in the SCR catalytic converter or it partially desorbs again. In both cases, reducing agent can escape from the SCR catalytic converter and enter the outside atmosphere, or it is necessary to take additional measures to remove the excess reducing agent.

The exhaust gas aftertreatment systems known to date are not optimally designed. They are particularly susceptible to certain malfunctions, so that the efficiency of the nitrogen oxide reduction is not guaranteed over the entire service life of the exhaust gas aftertreatment system and in all operating states.

It is a first object of the present disclosure to provide an improved exhaust aftertreatment system. A second object of the disclosure is to show an improved method for determining the cause of an efficiency deviation of the nitrogen oxide reduction. The claimed invention achieves at least one of these objects by the features of the main claim.

The present disclosure comprises several main aspects that can be used alone or in any combination.

A first major aspect of the present disclosure relates to an exhaust aftertreatment system. The exhaust gas aftertreatment system is provided for an internal combustion engine and can in particular be fed with the exhaust gas from the internal combustion engine. It comprises at least one SCR catalytic converter with a pre-flow passage and a post-flow passage. In the exhaust gas aftertreatment system, a (momentary) lead nitrogen oxide content in the flow direction of the exhaust gas upstream of the SCR catalytic converter, ie in the lead passage, and a (momentary) trailing nitrogen oxide content in the flow direction after the SCR catalytic converter, ie in determined by the trailing passage. In other words, the upstream passage is arranged upstream of the SCR catalytic converter in the flow direction of the exhaust gas and the downstream passage is arranged downstream of the SCR catalytic converter in the flow direction of the exhaust gas.

A reducing agent injector, which preferably adds or injects a reducing agent into the exhaust gas, is arranged upstream of the SCR catalytic converter. The reducing agent (together with the exhaust gas) is fed to the SCR catalytic converter and stored in the SCR catalytic converter. Nitrogen oxides in the exhaust gas are reduced by the stored reducing agent. A nitrogen oxide sensor for detecting the feed nitrogen oxide content is particularly preferably arranged upstream of the SCR catalytic converter and further upstream of the reducing agent injector.

The exhaust gas aftertreatment system comprises a control unit which is connected to the reducing agent injector and controls the current addition amount of the reducing agent. The control unit has a special design and enables a learning process to be carried out in order to detect a detected deviation of the actual efficiency of the nitrogen oxide reduction from a target value and to make multiple suitable corrections in order to compensate for several interfering influences together. This enables a significantly improved adaptation of the control, which in particular overcomes the disadvantages of previously known, one-dimensional adaptations.

In the exhaust gas aftertreatment system according to the present disclosure, the control unit comprises a multi-element simulation model and a pilot control. The control unit is designed to carry out the steps described below.

A setpoint value for the current amount of reducing agent added (injection amount) is established on the basis of a pilot control value and, in addition, a storage control value. The pre-control value is determined on the basis of the (current) feed nitrogen oxide content. It represents the amount of reducing agent that is to be added to the exhaust gas in order to reduce the currently detected amount of nitrogen oxides in the exhaust gas. The pilot control works particularly quickly and can perform the essential part of the control task in steady-state conditions of the internal combustion engine or the exhaust gas aftertreatment system in order to ensure the efficiency of the nitrogen oxide reduction.

The storage guide value is determined by the multi-element simulation model as a function of an estimated reducing agent content in the SCR catalytic converter in such a way that the estimated reducing agent content is approximated to a target value. The storage management value thus indicates which positive or negative amount of reducing agent is to be added compared to the pilot control value in order to keep the reducing agent content in the SCR catalytic converter in such a value range that the nitrogen oxide reduction is carried out with the desired and preferably maximum efficiency. Adjustments can thus be made via the storage management value, which compensate for the various disruptive influences or inadequacies of the precontrol in the event of changes in the exhaust gas aftertreatment system (transient system states).

For example, it is possible through the learning process on the one hand to determine whether a (determined) deviation in efficiency of the nitrogen oxide reduction is based on an excess of reducing agent or a shortage of reducing agent in order to increase or decrease the amount of reducing agent in the SCR catalytic converter to approach a target value. In other words, it can be determined that the actual reducing agent content in the SCR catalytic converter deviates from an estimated reducing agent content. The estimated reducing agent content can then be adjusted to the value which was determined by the learning method, i.e. a value which represents a reducing agent excess or a reducing agent shortage. The estimated reducing agent content then again represents the actual state in the SCR catalytic converter. According to the deviation between the (updated) estimated value of the reducing agent content, a storage guide value is generated which instructs an increased or decreased addition of reducing agent, so that the estimated reducing agent content is then approximated to the target value.

Various disruptive influences can occur temporarily or permanently in the exhaust gas aftertreatment system, which reduce the efficiency of the nitrogen oxide reduction or other negative events such as overfilling of the SCR catalytic converter (excess reducing agent) and the resulting breakthrough of the reducing agent or emptying of the SCR catalytic converter (reducing agent deficiency) and the resulting nitrogen oxide breakthrough. Different states can be recognized by the learning process and an adaptation can be made in the multi-part simulation model in order to compensate for the disturbances. These adaptations are preferably carried out in addition to the above-described approximation of the estimated reducing agent content to the target value. If, for example, it is repeatedly determined in several passes of the learning process that there is a shortage of reducing agent, this can indicate that the actual amount added by the reducing agent injector, for example due to drift, deviates from the control specification (target amount added / injection command), which is caused by an adaptation of the simulation model can be compensated.

If it is determined at the same time that there is only a small efficiency deviation despite the lack of reducing agent, this can indicate an error or a drift in the sensor signal that is output by a feed nitrogen oxide sensor. In other words, the comparison of the Results from several rounds of the learning process are determined as to whether a compensatory action (adaptation in the simulation model) was sufficient or effective. If an insufficient reduction in the efficiency deviation or even an increase in the efficiency deviation is determined, another adaptation strategy can be selected.

Any chemical substance that is suitable for reducing nitrogen oxides in the SCR catalytic converter can be used as the reducing agent. It can particularly preferably be an aqueous urea solution (urea solution) which decomposes to ammonia in the exhaust gas. Ammonia (NH3) is the one actually reducing substance and a toxic gas, which according to the legal regulations may only get into the outside atmosphere in certain concentrations.

If an excess of reducing agent is added to the exhaust gas aftertreatment system, the reducing agent content in the SCR catalytic converter can rise above a specified target value and even above the current storage capacity, with the proportion of the reducing agent that can no longer be stored or gradually Desorbed portion of the reducing agent passes through the SCR catalytic converter. In exhaust gas aftertreatment systems known to date, in which there may be a significant breakthrough of the reducing agent, a further filter or catalytic device must be provided downstream of the SCR catalytic converter in order to remove the excess reducing agent from the exhaust gas act as a so-called ammonia slip catalyst.

• - Abweichung der Ist-Beigabemenge an Reduktionsmittel von der Soll-Beigabemenge, beispielsweise durch Alterung oder Verschleiß des Reduktionsmittel-Injektors oder unzureichende Versorgung des Reduktionsmittel-Injektors;
• - Abweichung der tatsächlich durch chemische Reaktion umgesetzten Menge an Reduktionsmittel in dem SCR-Katalysator von einer geschätzten umgesetzten Menge, beispielsweise aufgrund eines (noch nicht detektierten) Reduktionsmittel-Überschusses oder Reduktionsmittel-Mangels oder bei sich stark ändernden Betriebsbedingungen des Verbrennungsmotors (schwankende Abgastemperatur / schwankender Stickoxid-Gehalt / schwankende Abgas-Strömungsgeschwindigkeit usw.);
• - Desorption von Reduktionsmittel aus dem SCR-Katalysator ohne chemische Umsetzung, beispielsweise durch hohe Strömungsgeschwindigkeit des Abgases, zu niedrige oder zu hohe Abgastemperatur, etc.;
• - Abweichung der Ist-Konzentration des beizugebenden Reduktionsmittels von einer Soll-Konzentration;
• - Abweichung des Versorgungs-Drucks, mit dem Reduktionsmittel zu dem Reduktionsmittel-Injektor gespeist wird, von einem Soll-Druck;
• - Unzureichende Wirksamkeit von Maßnahmen zur Vor-Umsetzung des Reduktionsmittels, beispielsweise unzureichende Ozon-Beigabe zur erhöhten Umsetzung von Harnstoff in Ammoniak;
• - Fehlerhafte Bestimmung von Eingangs-Parametern der Steuerung, insbesondere durch Kreuz-Sensitivität oder Drift an Sensoren, zeitliche Verzögerungen in der Messwert- oder Simulationswerterfassung, etc;
• - Inhomogene Speicherung des Reduktionsmittels im SCR-Katalysator.

The disruptive influences that can lead to insufficient or excessive addition of reducing agent include the following in particular:

• Deviation of the actual addition amount of reducing agent from the target addition amount, for example due to aging or wear of the reducing agent injector or insufficient supply of the reducing agent injector;
• - Deviation of the amount of reducing agent actually converted by chemical reaction in the SCR catalytic converter from an estimated converted amount, for example due to an (as yet undetected) reducing agent excess or reducing agent shortage or if the operating conditions of the internal combustion engine change significantly (fluctuating exhaust gas temperature / fluctuating Nitrogen oxide content / fluctuating exhaust gas flow rate, etc.);
• - Desorption of reducing agent from the SCR catalytic converter without chemical conversion, for example due to the high flow velocity of the exhaust gas, too low or too high an exhaust gas temperature, etc .;
• - Deviation of the actual concentration of the reducing agent to be added from a target concentration;
• Deviation of the supply pressure with which the reducing agent is fed to the reducing agent injector from a setpoint pressure;
• Insufficient effectiveness of measures for the pre-conversion of the reducing agent, for example insufficient addition of ozone to the increased conversion of urea into ammonia;
• - Incorrect determination of input parameters of the control, in particular due to cross-sensitivity or drift on sensors, time delays in the measurement or simulation value acquisition, etc;
• - Inhomogeneous storage of the reducing agent in the SCR catalytic converter.

According to the present disclosure, a design of the multi-part simulation model in combination with a learning method is proposed, which is suitable for compensating for several of the aforementioned negative influences.

The simulation model estimates the current reducing agent content in the SCR catalytic converter and calculates or estimates the various influences that lead to an increase or decrease in the reducing agent content in the SCR catalytic converter. These are in particular the adsorption of reducing agent in the SCR catalytic converter and the actually added amount of reducing agent. In addition, the desorption of reducing agents (without chemical reaction) and the conversion of reducing agents by chemical reaction can be calculated or modeled.

The simulation model thus comprises at least a first element in the form of a reducing agent addition model and a second element in the form of a reducing agent storage model, on the basis of which the reducing agent content in the SCR catalytic converter is estimated.

An actual efficiency of the nitrogen oxide reduction is determined on the basis of the upstream nitrogen oxide content and the downstream nitrogen oxide content. In the learning process, when an efficiency discrepancy between the actual efficiency and a target efficiency of the nitrogen oxide reduction is determined, a correction value adjustment is carried out in at least two elements of the simulation model, for example by changing correction values in relation to the estimate of the addition of reducing agent as well as the estimation of the reducing agent storage. A correction value can be, for example, a gain factor or an offset value or a substitute value to which a variable of the simulation model is to be changed. By distributing the correction value adjustment to several parameters, it can be adjusted to different parameters Interfering influences are reacted so that the efficiency of the nitrogen oxide reduction remains within the permissible limits over the entire service life of the exhaust gas aftertreatment system or its components.

A second main aspect of the present disclosure relates to a method for determining the cause of an efficiency discrepancy in the nitrogen oxide reduction.

Nitrogen oxide sensors used in practice have a cross-sensitivity for nitrogen oxides and unreacted reducing agent or for reducing agent passing through the SCR catalytic converter. In other words, they show a positive measurement deflection both when they come into contact with nitrogen oxides ( NOx ) as well as, for example, with ammonia (NH3).

Out US 2003/0 046 928 A1 a description of the cross-sensitivity of a nitrogen oxide sensor and a method are known by which a distinction is to be made between a nitrogen oxide-based measured value and a reducing agent-based measured value in an exhaust gas aftertreatment system with SCR catalytic converter and reducing agent injector. The exhaust aftertreatment system is operated there with an aggressive addition scheme. The stoichiometric equilibrium amount is added as the nominal injection amount of reducing agent and the SCR catalytic converter is continuously operated at a maximum reducing agent content. Reducing agent in the exhaust gas that breaks through the SCR catalytic converter must therefore, if necessary, be removed by separate devices.

In a stationary state of the exhaust gas aftertreatment system according to US 2003/0 046 928 A1 an overdosed reducing agent pulse (injection pulse with test injection quantity greater than the nominal injection quantity) is added according to a predetermined scheme and a reaction of the nitrogen oxide measured value, which is recorded downstream of the SCR catalytic converter, is evaluated. If the nitric oxide reading increases in response to the overdosed injection pulse, it is concluded that the sensor has reacted to reducing agents (ammonia / urea). If, on the other hand, the nitric oxide reading drops in response to the overdosed injection pulse, it is concluded that the sensor has detected nitric oxide ( NOx ) responded. This form of conclusion is based on a simplified consideration of the processes in the SCR catalytic converter. The assumption can be summarized as follows: If there is an insufficient addition of reducing agent, all of the added reducing agent would react and nitrogen oxides would break through the SCR, so that only nitrogen oxide reaches the sensor. If an overdosed reducing agent pulse is added in such a case, this should compensate for the previous deficiency so that less nitrogen oxide reaches the sensor and the measured value drops. On the other hand, if there is an excessive addition of reducing agent, all of the nitrogen oxide would react, so that only unreacted reducing agent breaks through the SCR catalytic converter and reaches the sensor. If an overdosed reducing agent pulse is then added, this should increase the excess so that even more reducing agent reaches the sensor and the measured value rises.

According to the revelation in US 2003/0 046 928 A1 it is also provided that an underdosed reducing agent pulse (injection pulse with a test injection quantity less than the nominal injection quantity) is added, with it being determined for each pulse whether the nitrogen oxide measured value downstream of the SCR catalytic converter rises or falls in response to a pulse . If the pulse direction and the direction of change of the sensor value have the same direction, it is concluded that the sensor reacts to reducing agents (ammonia / urea). If the pulse direction and the direction of change of the sensor value are opposite to each other, it is concluded that the sensor is on nitrogen oxide ( NOx ) responded. For each reducing agent pulse, exactly one change in the sensor value as a result of the pulse is recorded according to a predetermined time rule. In fact, however, the processes in the SCR catalytic converter are of a very complex nature and the simplified assumption can lead to incorrect interpretations.

In order to obtain a more reliable result, therefore, in US 2003/0 046 928 A1 suggested executing several pulses one after the other and adding or integrating the results of the pulses. However, this method has disadvantages which have made it unreliable or lead to undesirable side effects for exhaust gas aftertreatment systems that are operated with a conservative addition scheme.

In the case of a conservative addition scheme, the storage of reducing agent in the SCR catalytic converter is not maximized, but is managed in accordance with a predetermined target value for the reducing agent content. For this reason, storage effects in the SCR catalytic converter have an increased influence on the change in the post-flow nitrogen oxide content. An excess of reducing agent in the SCR catalytic converter can no longer simply be determined. Furthermore, a value can be used as the nominal injection quantity in a pilot control which corresponds to the amount of reducing agent that is presumably reacted in the nitrogen oxide reduction according to the current initial nitrogen oxide content - this amount is referred to below as the estimated reaction amount.

It should be avoided as far as possible that unreacted reducing agent breaks through the SCR catalytic converter so that no additional cleaning of the exhaust gas has to be carried out by separate devices. It is therefore associated with a certain risk or undesirable to execute a larger number of overdosed reducing agent pulses one after the other. This is because the case could arise that a reducing agent breakthrough would only be generated or provoked by the overdosed pulses.

The nitrogen oxide reduction does not take place 100% (even with a correctly set reducing agent content in the SCR catalytic converter), but at a current maximum efficiency. In other words, the nitrogen oxide reduction has an efficiency of less than 1. If the stoichiometric equilibrium amount is specified as the nominal injection amount, then a certain proportion of the added reducing agent cannot react due to the efficiency. In other words, a gradual overfilling of the SCR catalytic converter is enforced. If the SCR catalytic converter is already being operated at a maximum reducing agent content, the unreacted portion of the stoichiometric equilibrium amount cannot be stored and thus leads to an undesired reducing agent breakthrough. The addition of several overdosed reducing agent pulses for testing or learning purposes would further strengthen this reducing agent breakthrough. It is therefore desirable to achieve a reliable result with just one or a few test pulses. This is achieved by the method disclosed here by means of a multiple response analysis, which is explained further below.

The estimated reaction amount takes into account the efficiency of the SCR catalytic converter and provides, for example, as the nominal injection amount, the product of the stoichiometric equilibrium amount and the estimated reduction efficiency, i.e. a value that is lower than with an aggressive addition scheme. In other words, in the conservative addition scheme according to the present disclosure, the pilot control adds (only at most) as much reducing agent as is necessary to compensate for the decrease in the reducing agent content caused by a reduction reaction in the SCR catalytic converter.

The main advantage of the conservative addition scheme lies in the avoidance of a (creeping) overfilling of the SCR catalytic converter and the resultant breakthrough in the reducing agent. Further advantages are the simplification of the exhaust gas aftertreatment system and reduced consumption of reducing agent.

It has been shown that a conservative addition scheme causes some deviations in the measurable behavior of the exhaust gas aftertreatment system that have not yet been fully clarified. In particular, it was recognized that the US 2003/0 046 928 A1 described method can lead to significant erroneous detections because it does not take into account storage effects in the SCR catalytic converter and the different kinetics (conversion rate) of adsorption, desorption and reaction processes under different operating conditions of the exhaust gas aftertreatment system. There are various operating parameters that can have different and even opposite effects on the kinetics of the adsorption, desorption and reaction processes. For example, falling temperatures and a falling volume flow increase the adsorption of reducing agents in the SCR catalytic converter. On the other hand, falling temperatures also inhibit the chemical reaction.

The reaction of a sensor for detecting the trailing nitrogen oxide content to a reducing agent pulse takes place with a conservative addition scheme with an unpredictable dynamic, so that a distinction between a positive or negative change in the trailing nitrogen oxide content according to time rules or alone occurs Low-pass filtering leads to misinterpretations.

It is assumed that, due to the conservative addition scheme, the adsorption and desorption of reducing agent in the SCR catalytic converter takes place locally differently, ie spatially inhomogeneously. On the one hand, in the SCR catalytic converter, surface areas at the front in the flow direction of the exhaust gas appear to react more quickly and more directly to a change in the addition of reducing agent than areas at the rear. On the other hand, in the cross section of the SCR catalytic converter, depending on the flow velocity, pressure, temperature and volume flow of the exhaust gas, some areas appear to be more involved in the adsorption, desorption and reaction processes and some areas to a lesser extent. After a transient operation (state with changing operating parameters) it is not possible to predict the extent to which the inhomogeneous storage of reducing agent is pronounced in the SCR catalytic converter. It seems that it is at the same time in some areas of the SCR catalytic converter leads to an excess of reducing agent (overflow) and in other areas to a shortage of reducing agent (idling), with the two processes superimposing one another.

The method according to the second main aspect of the present disclosure makes it possible (independently of a time prediction) to determine the cause of an efficiency discrepancy in the nitrogen oxide reduction. The method is preferably carried out in the exhaust gas aftertreatment system described above and comprises the following steps.

A momentary feed nitrogen oxide content in the feed passage is determined. The determination can take place on the basis of a measurement by a feed nitrogen oxide sensor and / or on the basis of a model-based estimation or calculation of the feed nitrogen oxide content. Because of the above-mentioned cross-sensitivity, a measurement of the flow nitrogen oxide content is preferably carried out in the flow direction of the exhaust gas upstream of the reducing agent injector, so that the flow nitrogen oxide sensor cannot come into contact with the added reducing agent. Furthermore, a momentary wake nitrogen oxide content in the wake passage is determined by a wake nitrogen oxide sensor, which has a cross-sensitivity for nitrogen oxides ( NOx ) and the added reducing agent (ammonia / urea).

If a steady state of the exhaust gas aftertreatment system is determined, the control unit causes the reducing agent injector to execute a positive or negative injection pulse, ie an injection pulse with a test addition amount that is significantly above or below a nominal addition amount, which according to the current flow rate Nitric oxide content is determined. The nominal addition amount can be determined according to an aggressive or preferably according to a conservative addition scheme.

The measurement signal of the tracking nitrogen oxide sensor is recorded and evaluated with several separate partial responses in a time segment after the injection pulse and before any further injection pulse. The evaluation can be done in any way and is explained below.

A decision about the cause of the efficiency discrepancy is made on the basis of an overall consideration of the multiple partial responses and any changes in direction of the partial responses that have been recorded.

The disclosed method has several advantages. By evaluating the measurement signal with partial responses, the analysis of the measurement signal can be carried out essentially independently of the dynamics (speed) of the reaction. In particular, the time window for an interpretation of the responses to a pulse can be essentially indefinite. The same measurement method can therefore be used for both fast and slow reactions.

An efficiency of the nitrogen oxide reduction is preferably calculated on the basis of the leading nitrogen oxide content and the trailing nitrogen oxide content. The calculated efficiency is compared with an estimated efficiency or a target value for the efficiency in order to determine a deviation. The execution of an injection pulse can depend on the condition that the calculated efficiency deviates from the target value by an impermissible amount, or that there is a minimum deviation. Alternatively, an injection pulse can be carried out without a previous determination of an efficiency deviation.

The multiple partial responses can particularly preferably be compared with decision patterns. There can be simple decision-making patterns that allow a quick initial interpretation of the cause of a change in efficiency. These decision patterns can be meaningful for those cases in which storage effects do not come into play, or only to a small extent, and where the dynamics are essentially rapid. In addition, more complex decision patterns can be defined, which can differentiate between early partial answers and opposing later partial answers.

Further advantageous embodiments of the invention are specified in the subclaims, the following description and the drawings.

• 1: eine schematische Darstellung des Abgasnachbehandlungssystems gemäß der vorliegenden Offenbarung;
• 2: Ein erster Satz von Entscheidungsmustern zur Bestimmung der Ursache einer Effizienz-Abweichung der Stickoxid-Reduktion;
• 3: Vorgänge in einem SCR-Katalysator unter Soll-Bedingungen bei konservativer Beigabe von Reduktionsmittel;
• 4A u. 4B: Vorgänge in einem SCR-Katalysator unter Soll-Bedingungen auf einen positiven und einen negativen Injektionspuls;
• 5 u. 6: Mögliche Vorgänge in einem SCR-Katalysator bei Reduktionsmittel-Mangel auf einen negativen Injektionspuls;
• 7 u. 8: Mögliche Vorgänge in einem SCR-Katalysator bei Reduktionsmittel-Mangel auf einen positiven Injektionspuls;
• 9 u. 10: Mögliche Vorgänge in einem SCR-Katalysator bei Reduktionsmittel-Überschuss auf einen negativen Injektionspuls;
• 11 u. 12: Mögliche Vorgänge in einem SCR-Katalysator bei Reduktionsmittel-Mangel auf einen positiven Injektionspuls;
• 13: Mögliche Vorgänge in einem SCR-Katalysator auf eine positiven Injektionspuls, wenn der Reduktionsmittel-Gehalt unterhalb eines Soll-Werts liegt;
• 14: Ein zweiter Satz von Entscheidungsmustern zur Bestimmung der Ursache einer Effizienz-Abweichung der Stickoxid-Reduktion;
• 15: Beispielhafte Analyse des Mess-Signals des Nachlauf-Stickoxid-Sensors nach einem positiven Injektionspuls
• 16: Ein Beispiel für die Ausführung des Lernverfahrens gemäß der vorliegenden Offenbarung in mehreren Durchgängen.

The invention is shown schematically and by way of example in the drawings. These show:

• 1 : a schematic representation of the exhaust aftertreatment system according to the present disclosure;
• 2 : A first set of decision patterns for determining the cause of an efficiency deviation of the nitrogen oxide reduction;
• 3 : Processes in an SCR catalytic converter under target conditions with conservative addition of reducing agent;
• 4A and . 4B: processes in an SCR catalytic converter under target conditions for a positive and a negative injection pulse;
• 5 u . 6: Possible processes in an SCR catalytic converter in the event of a shortage of reducing agent in response to a negative injection pulse;
• 7 u . 8: Possible processes in an SCR catalytic converter in the event of a shortage of reducing agent in response to a positive injection pulse;
• 9 u . 10: Possible processes in an SCR catalytic converter in the event of an excess of reducing agent on a negative injection pulse;
• 11 u . 12: Possible processes in an SCR catalytic converter in the event of a shortage of reducing agent in response to a positive injection pulse;
• 13th : Possible processes in an SCR catalytic converter in response to a positive injection pulse if the reducing agent content is below a target value;
• 14th : A second set of decision patterns for determining the cause of an efficiency deviation of the nitrogen oxide reduction;
• 15th : Exemplary analysis of the measurement signal of the tracking nitrogen oxide sensor after a positive injection pulse
• 16 : An example of the execution of the learning method according to the present disclosure in multiple passes.

The exhaust aftertreatment system ( 10 ) according to the present disclosure is in 1 outlined. In the lower area there is a catalysis section ( 12th ) shown, which is preceded by a passage ( 11 ) and a follow-up passage ( 13th ) connected is. Through the forward passage ( 11 ) an exhaust gas is sent to the catalysis section ( 12th ) supplied. The exhaust gas contains nitrogen oxides ( NOx ). The one from the catalysis section ( 12th ) escaping and nitrogen oxides ( NOx ) largely cleaned exhaust gas is passed through the after-run passage ( 13th ) discharged.

In the catalysis section ( 12th ) is at least one SCR catalytic converter ( 16 ) arranged, which may have a known structure. With the SCR catalytic converter ( 16 ) a filter ( 17th ) be connected, in particular a soot particle filter. Alternatively or additionally, a separate filter can be installed in the exhaust gas aftertreatment system ( 10 ) be provided, in particular downstream of the SCR catalytic converter ( 16 ).

In the example of 1 is upstream of the SCR catalyst ( 16 ) a diesel oxidation catalyst ( 14th ) provided as an optional element. Furthermore, upstream of the SCR catalytic converter ( 16 ) a reducing agent injector ( 15th ), which can also have a known structure. The reducing agent injector ( 15th ) is in the example of 1 in the direction of flow of the exhaust gas directly in front of the SCR catalytic converter ( 16 ) arranged. Alternatively, it can be arranged at any other point, for example upstream of a turbine and / or an exhaust gas mixer (not shown), which improves the mixing of the reducing agent and exhaust gas.

The reducing agent injector ( 15th ) is preferably supplied with a liquid reducing agent that is supplied with a delivery pressure. In the context of the present disclosure, for reasons of simplified representation, no distinction is made between whether the reducing agent is injected as a preliminary product (urea / urea), which is only converted into the reducing substance (ammonia), or whether it is a finished product. The amount of reducing agent added means the amount of the preliminary product or reducing substance that is required according to the underlying chemical reaction to generate a certain amount of nitrogen oxides ( NOx ) to reduce. In the case of ammonia, the following chemical equations can be used to determine the required amount to be added: 4 NO + 4 NH ₃ + O ₂ -> 4 N ₂ + 6 H ₂ O, 2 NO ₂ + 4 NH ₃ + O ₂ -> 3 N ₂ + 6 H ₂ O.

If when determining the nitrogen oxide content ( cPre , cPost ) is not differentiated between the different oxide types (NO, NO2, NO3 ...), the simplified sum formula can be used: NO + NO ₂ + 2 NH ₃ -> 2 N ₂ + 3 H ₂ O.

As a result, in a simplified view, a stoichiometric ratio of 1 to 1 between nitrogen oxides ( NOx ) and ammonia (NH3) can be assumed. The presumed ratio of nitrogen monoxide (NO), nitrogen dioxide (NO2) and other nitrogen oxide compounds ( NOx ) can possibly be determined by model-based calculation or on the basis of characteristic maps etc. depending on the operating state of the internal combustion engine in order to determine the stoichiometric equilibrium amount even more precisely, i.e. which amount of reducing agent is to be provided according to the chemical equations for converting the detected amount of nitrogen oxides . If another reducing agent is used, different formulas must be used accordingly.

The reducing agent injector ( 15th ) is connected to the control unit ( 20th ) of the exhaust aftertreatment system ( 10 ) and is connected via an injector driver ( 24 ) charged with energy. The injector driver ( 24 ) can be arranged at any point, e.g. as part of the control unit ( 20th ) (please refer 1 ) or as part of the reducing agent injector ( 15th ).

Through the injector driver ( 24 ) is calculated according to a setpoint ( Qi * ) an injection command for adding the reducing agent ( CQ ) with which the reducing agent injector ( 15th ) is applied. The injection command ( CQ ) in particular, an activation current for an electrical actuator of the reducing agent injector ( 15th ) being.

The through the reducing agent injector ( 15th ) (actually) added amount ( Qi ) of reducing agent is supplied to the SCR catalytic converter ( 16 ) supplied. In the enlarged section of 1 some processes are outlined by which the (actual) reducing agent content ( cRed ) rises or falls in the SCR catalytic converter. That part of the added amount ( Qi ) on reducing agent, which is adsorbed on the catalytic wall, is with ( Qad ) marked. Due to the (currently) adsorbed amount ( Qad ) of reducing agent, the reducing agent content or the stored amount of reducing agent increases ( cRed ).

That part of the stored quantity ( cRed ) of the reducing agent, which is produced by chemical reaction with nitrogen oxides ( NOx ) is implemented, the reaction amount ( Qr ) marked. The (currently) reacted crowd ( Qr ) of reducing agent lowers the reducing agent content ( cRed ) in the SCR catalytic converter. In simplified terms, it can be assumed that only reducing agents adsorbed on the catalytic wall lead to a chemical conversion of nitrogen oxides ( NOx ) contributes, ie it is first necessary that a reducing agent component is adsorbed on the wall so that it can subsequently participate in the reduction reaction. A direct conversion of nitrogen oxides ( NOx ) due to the reducing agent present in the exhaust gas does not occur or occurs at negligible conversion rates.

The amount desorbed ( Qde ) of reducing agent indicates how much reducing agent is removed from the catalytic wall without chemical conversion. You can also state what excess portion of the actually added amount ( Qi ) of reducing agent leaves the SCR catalytic converter without chemical conversion, for example if the SCR catalytic converter is overfilled and no adsorption on the catalytic wall is possible for this proportion.

The addition of reducing agent is controlled in such a way that, on the one hand, the reducing agent content ( cRed ) is kept so high in the SCR catalytic converter that the desired efficiency of nitrogen oxide reduction is achieved and that, on the other hand, the SCR catalytic converter is not overfilled or empty ( 16 ) enter. The target value ( cRed * ) for the reducing agent content in the SCR catalytic converter ( 16 ) represents such an amount of stored reducing agent that the aforementioned goals are achieved. The target value ( cRed * ) is adapted to the current operating state of the exhaust gas aftertreatment system, for example, to take account of the changing storage capacity with rising and falling temperatures and with rising or falling volume flows.

The target value for the amount of reducing agent added ( Qi * ) can be defined in any way, for example as an injection rate (amount added per time interval). The reducing agent additives ( Qi ) can occur continuously or intermittently, e.g. with a constant or variable injection rate, whereby different individual injection quantities are specified for each injection or in groups in order to achieve the specified injection rate or the target value ( Qi * ) to reach. With an increased specification of the target value ( Qi * ), injections can be carried out with an increased amount and vice versa. Alternatively, uniform individual injection quantities can be specified in each case, whereby the addition quantity per time interval can be changed by specifying an injection frequency an adjustment to the target value ( Qi * ) to reach. Again alternatively, mixtures of a change in the individual injection quantity and a change in the injection frequency are possible. In the following, for the sake of simplicity, it is assumed that a target value ( Qi * ) (per time interval) for the addition of reducing agent, which, for example, depends on the state parameters of the exhaust gas aftertreatment system ( 10 ) into concrete injection commands ( CQ ) is implemented for single injections.

While the reducing agent addition ( Qi ) occurs rather intermittently, the chemical reaction takes place rather continuously. The storage of the reducing agent leads to a buffer effect, which enables a balance between the intermittent addition of reducing agent and the continuous reducing agent conversion.

The setpoint ( Qi * ) for the addition of reducing agent is determined by a target value calculation ( 23 ) provided and at least based on the input control value ( Qpre ) and the memory management value ( Qstr ) calculated for the addition of reducing agent. The underlying calculation can be of any type. In a simple version, the current pre-control value ( Qpre ) and the current memory management value ( Qstr ) can be added. The memory management value ( Qstr ) can be positive, negative, or zero. Alternatively or additionally, more complex calculations can be used which, for example, allow the addition of reducing agent to be temporarily prevented with subsequent compensation, that is to say a time shift of the amounts added between (adjacent) time intervals. It may be necessary to temporarily prevent the addition of reducing agents, for example, in those time intervals in which the operating state of the internal combustion engine or the exhaust gas aftertreatment system changes very significantly.

The pre-tax value ( Qpre ) is controlled by the feedforward ( 22nd ), i.e. in an open control loop, provided and based on the current nitrogen oxide content of the flow ( cPre ) definitely. The feed nitrogen oxide content ( cPre ) can be determined in any way. In the example of 1 is a feed nitrogen oxide sensor ( 40 ) in the forerunner passage ( 11 ) provided, which determines the feed nitrogen oxide content ( cPre ) recorded directly. Alternatively or additionally, a feed nitrogen oxide content ( cPre ) be provided as an estimated value by another control component, in particular by an engine controller with a combustion model, which determines the current nitrogen oxide emissions from a combustion chamber of the internal combustion engine. Both a measured value and an estimated or calculated value of the feed nitrogen oxide content ( cPre ) are available, whereby these values can be checked for consistency with one another and adapted if necessary. Again, alternatively or additionally, a total amount of nitrogen oxides ( NOx ) and the types of nitrogen oxides contained (NO, NO2, NO3 etc.) can be determined via an estimate or calculation. In the following, it is assumed, in simplified form, that the feed nitrogen oxide content ( cPre ) is detected by sensors.

The multi-part simulation model ( 21 ) explained in more detail. In the drawings, estimated or calculated values which represent an actual variable in the control are each marked by a line and target values by an asterisk. ( Qi ) denotes the actual amount of reducing agent added, which as a rule cannot be determined directly, while ( Qi * ) the target value and ( Qi * ) give an estimated value for the added amount. ( cRed ) gives the actual reducing agent content in the SCR catalytic converter ( 16 ), which cannot be determined directly either, while ( cRed * ) a target value and ( cRed * ) give an estimated value of the reducing agent content, etc.

The memory management value ( Qstr ) is preferred as a deviation of the estimated reducing agent content ( cRed ' ) from the setpoint ( cRed * ) calculated. The setpoint ( cRed * ) can be specified in any way. According to a simple embodiment, it can be defined as a static value and, for example, a maximum storage capacity of the SCR catalytic converter ( 16 ) under normal operating conditions. Alternatively and preferably, the setpoint ( cRed * ) be set dynamically, e.g. depending on the state parameters of the exhaust gas aftertreatment system ( 10 ) and / or the internal combustion engine. The definition can in particular depending on the temperature of the SCR catalytic converter ( 16 ) and / or the temperature of the exhaust gas and / or an age of the SCR catalytic converter ( 16 ) respectively. Furthermore, the flow velocity or the volume flow of the exhaust gas can be used to adjust the setpoint value ( cRed * ) conditional.

The target value ( cRed * ) for the reducing agent content according to a predetermined addition scheme.

In the context of the present disclosure, a distinction is made between at least one aggressive and one conservative addition scheme, whereby the specification of the target value ( cRed * ) for the reducing agent content is preferably carried out according to the conservative addition scheme.

A conservative addition scheme provides that the target value ( cRed * ) for the reducing agent content in the SCR catalytic converter ( 16 ) is significantly lower than the (current) maximum storage capacity of the SCR catalytic converter ( 16 ) for reducing agents. A conservative addition scheme, for example, sees the target value ( cRed * ) in a range of 30% to 80% of the (current) maximum storage capacity. This prevents undesired overfilling of the SCR catalytic converter ( 16 ) and prevented a reducing agent breakthrough caused by it.

In the case of an aggressive addition scheme, the target value ( cRed * ) set in a range of greater than 80% or greater than 90% of the (current) maximum storage capacity, which is also possible, but may require that an ammonia slip catalyst (not shown) or another element for downstream of the SCR catalyst Removal of an excess reducing agent is provided in the exiting exhaust gas.

The aforementioned value ranges are given purely by way of example and can vary depending on the size and effectiveness of the SCR catalytic converter ( 16 ) to change.

In the multi-part simulation model ( 21 ) according to 1 contains various elements that depend on the state parameters of the exhaust gas aftertreatment system ( 10 ) and especially the SCR catalytic converter ( 16 ) estimate or calculate by which influences the current reducing agent content ( cRed ) rises or falls. The number and design of the links can depend on the design of the exhaust gas aftertreatment system ( 10 ) and especially the catalysis section ( 12th ) be modified.

In the example of 1 includes the multi-part simulation model ( 21 ) a first link ( 31 ) in the form of a reducing agent addition model. This determines depending on an actuation ( Qi * / CQ ) of the reducing agent injector ( 15th ) an estimated amount ( Qi ' ) of added reducing agent. In other words, the reducing agent addition model calculates ( 31 ) an estimate ( Qi ' ) for the actually added amount ( Qi ) of reducing agent. The actuation of the reducing agent injector ( 15th ) can be characterized by any system variable, preferably by the target value ( Qi * ) for adding reducing agent or by the injection command ( CQ ).

• - Konzentration der reduzierenden Substanz oder eines Vorprodukts im Speise-Fluid des Reduktionsmittel-Injektors;
• - Speise-Druck des Reduktionsmittel-Injektors;

The estimated amount ( Qi ' ) of the added reducing agent can also depend on the following parameters:

• - Concentration of the reducing substance or a precursor in the feed fluid of the reducing agent injector;
• - Feed pressure of the reducing agent injector;

15th shows an example of the course of the maximum storage capacity (cMax), the target value ( cRed * ) as well as the estimated value ( cRed ' ) for the reducing agent content compared to the actual reducing agent content ( cRed ). The actual reducing agent content ( cRed ) cannot be measured directly and is therefore not known to the control. In the time range shown, there are three stationary states ( S1 , S2 , S3 ), between which there are unsteady or transient states. In each of the three stationary states ( S1 , S2 , S3 ) there is a different operating state of the exhaust gas aftertreatment system ( 10 ) so that there are different maximum storage capacities (cMax). Accordingly, for each of the stationary states ( S1 , S2 , S3 ) another target value ( cRed * ) for the reducing agent content.

In the first steady state, the addition of reducing agent and storage management take place correctly. The estimated value ( cRed ' ) the reducing agent content corresponds to the actual reducing agent content ( cRed ) and there is no impermissible deviation between the estimated reducing agent content ( cRed ') and the target value ( cRed * ) in front. Accordingly, it is to be expected that the nitrogen oxide reduction occurs with the correct efficiency.

In the second steady state ( S2 ) there is a different operating state of the exhaust gas aftertreatment system ( 10 ), which is why a higher storage capacity (cMax) of the SCR catalytic converter ( 16 ) and a correspondingly higher target value ( cRed * ) are available for the reducing agent content. The addition of reducing agent and storage management are also carried out correctly.

During the transition to the third steady state, i.e. in the transient transition, there is a discrepancy between the estimated reducing agent content ( cRed ' ) and the actual reducing agent content ( cRed ) on. The estimated reducing agent content ( cRed ) is wrongly at the level of the target value ( cRed * ). In fact, however, there is an excess of reducing agent which, according to the measured values of the post-flow nitrogen oxide content ( cPost ) leads to a reduction in the efficiency of nitrogen oxide reduction. So there is a breakthrough in reducing agent.

When the learning process below is carried out for the first time, the excess reducing agent is recognized. Various phenomena can be considered as the reason for the occurrence of the excess reducing agent. On the one hand, the reducing agent injector ( 15th ) an actual amount ( Qi ) added reducing agent that was greater than the target amount ( Qi * ). On the other hand, more reducing agent could actually have been adsorbed in the SCR catalytic converter or less reducing agent reacted than was estimated in the simulation model. Ie the estimated amount of adsorption ( Qad ) could have been smaller than the actual amount of adsorption ( Qad ' ) and the estimated response amount ( Qr ' ) could have been smaller than the actual response amount ( Qr ).

As a countermeasure, the estimated reducing agent content ( cRed ' ) adjusted to the value (cMax). In addition, further correction value adjustments can be carried out in the simulation model, which are explained below.

If the estimated reducing agent content ( cRed ' ) is adapted to the value (cMax), the impermissible deviation from the target value ( cRed * ) recorded by the control for the reducing agent content. Accordingly, a negative memory management value ( Qstr ), which leads to lower target injection quantities ( Qi * ) and thus causes the estimated reducing agent content ( cRed ' ) back to the target value ( cRed * ) is approximated.

In the example of 16 after the first implementation (L1) of the learning process, the simulation model assumes that the estimated reducing agent content ( cRed ' ) on the target value ( cRed * ) remain. In fact, in the example shown, a deviation occurs again that leads to an excess of reducing agent, i.e. the actual reducing agent content ( cRed ) is again above the target value ( cRed * ) and drifts towards the value of (cMas). The reason for this could be that the actual amount added ( Qi ) is greater than the target value ( Qi * ), which, on the one hand, is due to a measurement error in the feed nitrogen oxide sensor ( 40 ) or an error in the injector ( 15th ) could be traceable.

If the learning process is carried out further (L2), the renewed excess reducing agent can be recognized, whereby the estimated reducing agent content ( cRed ' ) is changed again to a suitable value, and further adaptations can be made in the simulation model in order to reduce the recorded drift of the reducing agent content ( cRed ) to compensate. Appropriate measures are explained below.

On or in the reducing agent addition model ( 31 ) any correction value ( W1 ) can be provided, which can be adapted when a learning process is carried out. In the example of 1 for the sake of simplicity it is assumed that the correction value W1 is a multiplicative factor that gives the estimated value ( Qi ' ) the added amount increased or decreased compared to a basic calculation. As an alternative or in addition, other correction values can be provided which, for example, provide one or more specific adaptations with regard to the above-mentioned influencing parameters.

• - Momentaner (geschätzter) Reduktionsmittel-Gehalt (cRed') im SCR-Katalysator (16) - entspricht Besetzungs- bzw. Füllungsgrad der Katalysatorwandung;
• - Momentane (geschätzte) Beigabemenge (Qi') an Reduktionsmittel - bezogen vom Reduktionsmittel-Beigabemodell (31);
• - Temperatur des SCR-Katalysators (16);
• - Temperatur des zugeführten Abgases;
• - Konzentration der reduzierenden Substanz im zugeführten Abgas;
• - Durchmischungsgrad von Reduktionsmittel und Abgas stromaufwärts zu SCR-Katalysator, beispielsweise abhängig von Anordnung des Reduktionsmittel-Injektors und Betrieb oder Last einer zwischen dem Reduktionsmittel-Injektor (15) und dem SCR-Katalysator (16) etwaig angeordneten Turbine;
• - Strömungsgeschwindigkeit bzw. Volumenstrom des Abgases, bspw. bezogen von einem Strömungssensor (nicht dargestellt) oder von einer Motorsteuerung.

The second link ( 32 ) of the simulation model ( 21 ) is a reducing agent storage model ( 32 ). This estimates depending on the condition parameters of the exhaust gas aftertreatment system ( 10 ), whitch amount ( Qad ' ) of reducing agent currently in the SCR catalytic converter ( 16 ) is stored by adsorption. The estimated amount ( Qad ' ) can depend on the following status parameters:

• - Current (estimated) reducing agent content ( cRed ' ) in the SCR catalytic converter ( 16 ) - corresponds to the degree of occupation or filling of the catalyst wall;
• - Current (estimated) amount added ( Qi ' ) of reducing agent - based on the reducing agent addition model ( 31 );
• - temperature of the SCR catalytic converter ( 16 );
• - temperature of the supplied exhaust gas;
• - Concentration of the reducing substance in the supplied exhaust gas;
• - Degree of mixing of reducing agent and exhaust gas upstream of the SCR catalytic converter, for example depending on the arrangement of the reducing agent injector and the operation or load of one between the reducing agent injector ( 15th ) and the SCR catalytic converter ( 16 ) possibly arranged turbine;
• - Flow velocity or volume flow of the exhaust gas, for example obtained from a flow sensor (not shown) or from an engine control.

In the example of 1 it is assumed for the sake of simplicity that a correction value ( W2 ) on or in the reducing agent storage model ( 32 ) is a multiplicative factor that gives the value ( Qad ' ) increased or decreased compared to a basic calculation. As an alternative or in addition, other correction values can be provided which, for example, provide one or more specific adaptations with regard to the above-mentioned influencing parameters.

This in 1 summation element shown separately ( 25th ), which shows the estimated reducing agent content ( cRed ' ) can also be part of the reducing agent storage model ( 32 ) being. Correspondingly, the correction value ( W2 ) - as an alternative or in addition to the above options - a multiplicative factor, an offset value or a substitute value for the estimated reducing agent content ( cRed ' ) being. It is particularly preferably an offset value.

• - Momentaner (geschätzter) Reduktionsmittel-Gehalt (cRed') im SCR-Katalysator (16) - entspricht Besetzungs- bzw. Füllungsgrad der Katalysatorwandung;
• - Temperatur des SCR-Katalysators (16);
• - Temperatur des zugeführten Abgases;
• - Konzentration der Stickoxide (NOx) im zugeführten Abgas;
• - Strömungsgeschwindigkeit des Abgases.

The third link ( 33 ) of the simulation model ( 21 ) is in the example of 1 a reaction model ( 33 ), which depends on the state parameters of the exhaust gas aftertreatment system ( 10 ) estimates what proportion ( Qr ' ) of the reducing agent stored in the SCR catalytic converter is removed or converted by chemical reaction. The estimated amount ( Qr ' ) of the reducing agent converted by reaction can depend on the following state parameters:

• - Current (estimated) reducing agent content ( cRed ' ) in the SCR catalytic converter ( 16 ) - corresponds to the degree of occupation or filling of the catalyst wall;
• - temperature of the SCR catalytic converter ( 16 );
• - temperature of the supplied exhaust gas;
• - concentration of nitrogen oxides ( NOx ) in the supplied exhaust gas;
• - flow velocity of the exhaust gas.

In the example of 1 it is assumed for the sake of simplicity that a correction value ( W3 ) on or in the reaction model ( 33 ) is a multiplicative factor that gives the estimated value ( Qr ' ) increased or decreased compared to a basic calculation. As an alternative or in addition, other correction values can be provided which, for example, provide one or more specific adaptations with regard to the above-mentioned influencing parameters. In particular, a correction value ( W3 ) be a multiplicative factor and / or an offset value that determines the feed nitrogen oxide content ( cPre ) compared to the measured value of the feed nitrogen oxide sensor ( 40 ) increased or decreased. A correction value adjustment in relation to the measured value of the inlet nitrogen oxide sensor ( 40 ) can also have an effect on the feedforward control ( 22nd ) and thus the pre-tax value ( Qpre ) for adding reducing agents. This means that a correction value adjustment can be made in addition to the changes in the multi-part simulation model ( 21 ) a correction value ( W3 ) for or in the feedforward control ( 22nd ) to change.

• - Momentaner (geschätzter) Reduktionsmittel-Gehalt (cRed') im SCR-Katalysator (16) - entspricht Besetzungs- bzw. Füllungsgrad der Katalysatorwandung;
• - Momentane (geschätzte) Beigabemenge (Qi') an Reduktionsmittel - bezogen vom Reduktionsmittel-Beigabemodell (31);
• - Temperatur des SCR-Katalysators (16);
• - Temperatur des zugeführten Abgases;
• - Strömungsgeschwindigkeit des Abgases.

The fourth link in the simulation model ( 21 ) is a desorption model ( 34 ), which depends on the state parameters of the exhaust gas aftertreatment system ( 10 ) calculates which proportion ( Qde ' ) the reducing agent stored in the SCR catalytic converter is desorbed without chemical conversion. The estimated amount ( Qde ' ) of the desorbed reducing agent can also be a proportion of the estimated added amount ( Qi ' ) that cannot be adsorbed in the SCR catalytic converter. The estimated amount ( Qde ' ) can depend on the following status parameters:

• - Current (estimated) reducing agent content ( cRed ') in the SCR catalytic converter ( 16 ) - corresponds to the degree of occupation or filling of the catalyst wall;
• - Current (estimated) amount added ( Qi ' ) of reducing agent - based on the reducing agent addition model ( 31 );
• - temperature of the SCR catalytic converter ( 16 );
• - temperature of the supplied exhaust gas;
• - flow velocity of the exhaust gas.

In the example of 1 it is assumed for the sake of simplicity that a correction value ( W4 ) on or in the desorption model ( 33 ) is a multiplicative factor that gives the value ( Qde ' ) increased or decreased compared to a basic calculation. As an alternative or in addition, other correction values can be provided which, for example, provide one or more specific adaptations with regard to the above-mentioned influencing parameters.

The control concept according to the present disclosure provides that the pre-control value ( Qpre ) a significant proportion of the target quantity ( Qi * ) of the reducing agent to be added depending on the current nitrogen oxide content ( cPre ) is set. This can be done with a very small time delay. In other words, (almost) as much reducing agent is always used according to the pre-control value ( Qpre ) added that the loss of reducing agent in the SCR catalytic converter ( 16 ) is compensated due to the chemical conversion. Thus, the feedforward control ( 22nd ) a basic adjustment of the addition of reducing agent to the current demand.

By specifying the storage management value ( Qstr ), which is dependent on a simulation of the processes in the SCR catalytic converter ( 16 ) is set, which leads to an increase or decrease in the current reducing agent content ( cRed ), can lead to unsteady states of the internal combustion engine or the exhaust gas aftertreatment system ( 10 ) a compensating or even finer control of the addition of reducing agent takes place. The underlying calculations and estimates may be due to the temporal buffer effect of the SCR catalytic converter ( 16 ) take place with a longer time delay.

In the following, the implementation of a learning process is explained as an example.

A comparator ( 26th ) compares the current nitrogen oxide content ( cPre ) (estimated and / or measured) and the current trailing nitrogen oxide content ( cPost ) (measured) and uses this to calculate an instantaneous efficiency of nitrogen oxide reduction. The comparator ( 26th ) compares the current efficiency with a target value ( rEff * ) and calculates an efficiency deviation from this ( dEff ).

An efficiency discrepancy occurs in particular when the SCR catalytic converter ( 16 ) has a reduced effectiveness, is overfilled or runs empty. Reduced effectiveness can, for example, be due to aging of the SCR catalytic converter ( 16 ), which reduce the efficiency. Overfilling or emptying of the SCR catalytic converter can, for example, be due to a temporary or permanent deviation in the actual amount added ( Qi ) from the target value ( Qi * ), or insufficient adsorption ( Qad ) are based.

The efficiency deviation ( dEff ) is adjusted by a correction value adjustment ( 27 ) used to in at least two of the terms ( 31 , 32 , 33 , 34 ) of the simulation model ( 21 ) to make a correction, in particular by changing the correction values ( W1 , W2 , W3 , W4 ). In addition, a correction of the estimated reducing agent content ( cRed ' ) respectively.

The efficiency deviation ( dEff ) according to a weighting key ( SW ) to two or more correction values ( W1-W4 ) in the at least two terms ( 31-34 ) of the simulation model ( 21 ) distributed, in particular by dividing the deviation value ( dEff ) in two or more percentages.

In or for the correction value adjustment ( 27 ) two or more alternative weighting keys are preferred ( SW ) are predefined, from which a suitable weighting key ( SW ) is selected. The selection can be made on the basis of any criteria, for example on the basis of the success of a previous learning process. Alternatively or additionally, the selection can be made on the basis of further status parameters of the exhaust gas aftertreatment system ( 10 ) take place, for example, a determined inconsistency between a model-based determined value and a measured value for the feed nitrogen oxide content ( cPre ). A correction value ( W1 - w4 ) as an alternative or in addition to the above options, a gain for a measured value or a calculated value can be provided, which the simulation model ( 21 ) is supplied. This includes, in particular, a measured value from an upstream nitrogen oxide sensor, a downstream nitrogen oxide sensor, an exhaust gas temperature sensor and a catalytic converter temperature sensor.

A weighting key ( SW ) at the same time an adaptation of at least one correction value ( W1 ) in or on the reducing agent addition model ( 31 ) and additionally a correction value ( W2 ) in or on the reducing agent storage model ( 32 ) performed.

In the example of 16 the correction value ( W2 ) adjusted, e.g. by adding an offset value to the estimated reducing agent content ( cRed ') updated. In other words, a weighting key is applied that allows 100% adjustment for the correction value ( W2 ) provides.

The representation in 16 is chosen purely by way of example in order to show possible courses of the calculated quantities ( cRed * , cRed ' ) to illustrate the actual changes in the physical quantities in the simulation model and, based on this, to explain an example for the multiple implementation of a learning process. The local fluctuations in the actual reducing agent content ( cRed ) are purely explanatory and do not reflect the timing or number of single injections.

In the second pass (L2) of the learning procedure it is determined that the pure adjustment of the estimated reducing agent content ( cRed ' ) was not sufficient. Another efficiency deviation is determined with an unexpectedly short time delay. On the one hand, the efficiency deviation can now lead to a renewed adjustment of the correction value ( W2 ) can be used to determine the estimated reducing agent content ( cRed ' ) to update with an offset value. For this purpose, a weighting of, for example, 50% of the efficiency deviation can be provided. The other 50% of the efficiency deviation can be used for a change in the correction value ( W1 ) can be used to calculate the estimated amount added ( Qi ' ) to increase compared to the base value. This compensates for the injector ( 15th ) maybe compared to the target value ( Qi * ) too large an actual amount ( Qi ) adds.

After adjusting the estimated reducing agent content ( cRed ' ) there is again a deviation from the target value ( cRed * ) recorded. So a negative memory management value ( Qstr ), through which a lowering of the reducing agent content ( cPre , cPre ' ) is achieved.

After the second implementation (L2), it is initially assumed that the estimated reducing agent content ( cRed ' ) the target value ( cRed * ) is equivalent to. In fact, however, a reducing agent deficiency gradually occurs, which - now with a somewhat larger time delay from L2 to L3 - leads to a renewed deviation in efficiency of the nitrogen oxide reduction.

In a new learning process (L3), the reducing agent shortage is determined and new adjustments are made in the simulation model. In this example, the correction values ( W1 , W2 ) changed. This time, however, with a different weighting key of e.g. 75% weighting for the adjustment of the correction value ( W2 ) or the estimated reducing agent content ( cRed ' ) and 25% for the correction value ( W1 ) or the estimated amount added ( Qi ' ).

After the third pass (L3) of the learning process, the system returns to the desired state, so that no inadmissible deviations in efficiency of the nitrogen oxide reduction are detected.

If the learning process is carried out multiple times, results from a previous implementation (adaptation was quickly successful / slowly successful / unsuccessful) can be used to determine the adaptations in the current implementation. In other words, the selection of a weighting key ( SW ) depending on a time delay between two implementations (L1, L2) of the learning process or between two determined efficiency deviations of the nitrogen oxide reduction. It can also depend on whether the same or different causes of the efficiency deviation (reducing agent excess or reducing agent shortage) were found between two executions (L1, L2, L3) of the learning process.

• - Sensorisch erfasster Vorlauf-Stickoxid-Gehalt (cPre);
• - Temperatur des Abgases, insbesondere in der Vorlauf-Passage;
• - Drehzahl des Verbrennungsmotors;
• - Strömungsgeschwindigkeit des Abgases;
• - Massenstrom des Abgases;
• - Effizienz der Stickoxid-Reduktion;
• - Geschätzte Beigabemenge (Qi') an Reduktionsmittel;
• - Druck im Ansaugkrümmer;

A learning process can be carried out at any point in time. According to a preferred variant, a learning process is only carried out when a specific precondition for carrying out a correction value adjustment is present. Such a precondition can in particular be that a steady state of the exhaust gas aftertreatment system ( 10 ) and / or the internal combustion engine. The parameters for determining the existence of a steady state can depend on the type and design of the internal combustion engine or the exhaust gas aftertreatment system ( 10 ) depend. Preset absolute value ranges and time intervals can preferably be defined as a yardstick for the parameters mentioned below, which can be used individually or in any combination to define a steady state:

• - Sensor-recorded feed nitrogen oxide content ( cPre );
• - temperature of the exhaust gas, especially in the flow passage;
• - speed of the internal combustion engine;
• - flow rate of the exhaust gas;
• - mass flow of the exhaust gas;
• - efficiency of nitrogen oxide reduction;
• - Estimated amount added ( Qi ' ) of reducing agent;
• - pressure in the intake manifold;

The correction value adjustment ( 27 ) or the selection of a weighting key ( SW ) can further alternatively or additionally depending on the cause of an ascertained efficiency deviation ( dEff ) respectively. The cause of the efficiency discrepancy ( dEff ) can be determined in any way. It can at least determine whether there is a shortage of reducing agent or an excess of reducing agent, ie whether the SCR catalytic converter is overfilled or has run empty. A shortage of reducing agent can be determined, for example, by detecting a nitrogen oxide breakthrough. An excess of reducing agent can be determined when a reducing agent breakthrough is detected. This is explained below using various examples. In addition, however, other causes of an ascertained efficiency discrepancy ( dEff ) that can be determined in other ways. For example, a reduction in the efficiency of the SCR catalytic converter ( 16 ) can be determined if the correction values ( W1 , W2 ) or the estimated reducing agent content ( cRed ') and the estimated amount added ( Qi ' ) Although long delays between the detection of a reducing agent excess or a reducing agent deficiency are recorded, there are still large efficiency deviations in the nitrogen oxide reduction ( dEff ) compared to the target value ( rEff * ) are available. Another indication of a reduction in the efficiency of the SCR catalytic converter ( 16 ) it may be that in a process to determine the cause of an efficiency deviation it is determined that, despite the specification of a conservative addition scheme, a reaction of the measurement signal of the run-on nitrogen oxide sensor ( 41 ) is determined that would fit an aggressive addition scheme, e.g. because there is a trend towards creeping overfilling of the SCR catalytic converter ( 16 ) is determined.

Embodiments of the method for determining the cause of an efficiency deviation (dEFF) of the nitrogen oxide reduction according to the second main aspect of the present disclosure are described below with reference to FIG 2 until 15th explained. First, with reference to FIG 3 , 4A and 4B Processes in an SCR catalytic converter under target conditions explained.

3 shows a simplified phase representation of the processes in the SCR catalytic converter when the nitrogen oxide reduction and the addition of reducing agent operate under target conditions. On the basis of this state, reference is made below to 4th until 13th deviating states and their effects on the measured value ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) described. The figures use a uniform representation that includes phase diagrams and reaction diagrams. A phase diagram is always indicated by the respective phase number 2 ( P0 , P1 , P2 , P3 ), which determine the order of the phases (but not their duration). The phase diagrams and reaction diagrams include summary representations for processes that take place gradually in an unknown time reference. In the figures, the processes are shown as a progressive sequence and are divided into phases and subsequent reactions in order to simplify understanding. Even if the presentation of the diagrams in the 3 until 13th are arranged one behind the other, this does not mean that the processes also take place in this order in reality.

To the left of 3 is an output phase ( P0 ) is shown, in which a feed nitrogen oxide sensor ( 40 ) a forerun nitric oxide content ( cPre ) is recorded. In the SCR catalytic converter ( 16 ) is a certain amount of reducing agent as the current reducing agent content ( cRed ) contain. Furthermore, the injector ( 15th ) in each phase 2 ( P0 , P1 ) an actual amount of reducing agent ( Qi ) and by the run-on nitrogen oxide sensor ( 41 ) in each phase 2 ( P0 , P1 ) a momentary trailing nitrogen oxide content ( cPost ) determined as a measured value. The run-on nitrogen oxide sensor is cross-sensitive for unreacted nitrogen oxides and unreacted reducing agent. For the sake of simplicity, no distinction is made below between the actual post-run nitrogen oxide content and that from the post-run nitrogen oxide sensor ( 41 ) differed. From the measured value ( cPost ) alone is for control anyway not recognizable whether the run-on nitrogen oxide sensor ( 41 ) only reacted to nitrogen oxides, only to unreacted reducing agent, or to both.

In the 3 until 13th boxes and circles are shown in different numbers to illustrate the different units of quantity of nitrogen oxides and reducing agents that are present in the SCR catalytic converter in the respective phase at a certain point and the change in these quantities as a result of the respective measures. A unit of quantity of nitrogen oxides is represented in each case by a square box. A unit of quantity of reducing agent is represented by a circle. The number of units of measure is used to clarify the approximate changes in quantity that can occur. In practice, different quantities and proportions may occur.

In the middle diagram of 3 reactions are shown that are caused by the measures in phase ( P0 ) enter. In reality, the reactions take place gradually and at different speeds or dynamics. The reaction diagram shows a summary of the reactions as a summary.

In the illustration on the right, a state is in a following phase ( P1 ) shown. The state shown follows on the one hand from the reaction in the SCR catalytic converter to the measures in phase ( P0 ). On the other hand, a new momentary measurement of the lead nitrogen oxide content takes place in the phase ( cPre ) as well as an additional amount ( Qi ) of reducing agents, which are essentially independent of the processes in phase ( P0 ) are. The processes of adsorption, reaction (chemical conversion) and desorption shown in the reaction diagram as well as the resulting change in the reducing agent content ( cRed ) in the SCR catalytic converter take place with unpredictable dynamics. Thus, the reactions to the measures in the initial phase ( P0 ) already at the beginning of the phase ( P1 ) to be finished. But it is also possible that some of the processes shown only after the phase ( P1 ) will take place (not shown for the sake of simplicity). The processes shown thus only show qualitative processes without specifying a specific time reference. Nevertheless, they help to understand the processes in the SCR catalytic converter, on the basis of which the cause of an efficiency deviation can be determined.

The (actual) reducing agent content ( cRed ) is below target conditions according to phase ( P0 ) in 3 on the target value ( cRed * ). The actual amount added ( Qi ) corresponds to the target value ( Qi * ), ie the nominal amount added (Qn). It is assumed here that the nominal addition amount (Qn) according to the conservative addition scheme of the estimated reaction amount ( Qr ' ) is equivalent to. It is also assumed that, as a result of a correctly working simulation model, the estimated reaction quantity ( Qr ' ) the actual amount of reaction ( Qr ) is equivalent to.

The reaction diagram of 3 includes in the upper area a representation of the supplied amount of nitrogen oxides, i.e. the amount that was used in the previous phase ( P0 ) has been detected by the flow nitrogen oxide sensor. Below this is the amount of reducing agent added ( Qi ) represented as a block, i.e. the amount that was used in the previous phase ( P0 ) through the injector ( 15th ) has been added. The amount of reducing agent stored in the SCR catalytic converter is shown in the lower area of the reaction diagram. Boxes filled with black in the reaction diagram indicate reacted nitrogen oxides ( NO ), ie the amount of nitrogen oxides that is reduced by chemical reaction with the reducing agent. Black filled circles indicate the amount of reducing agent actually converted by the reaction ( Qr ). Unfilled boxes in the reaction diagram indicate the unreacted nitrogen oxides, which will be used in the following phase ( P1 ) lead to a nitric oxide breakthrough.

In the example of 3 will the amount ( Qi ) of reducing agents in the phase ( P0 ) is added, completely adsorbed on the catalytic wall in the middle reaction diagram. Thus the actual amount of adsorption is ( Qad ) equal to the actual added amount ( Qi ). Furthermore, in the transition from the phase ( P0 ) to phase ( P1 ) just as much reducing agent ( Qad ) adsorbed, as in the sum consideration by reaction ( Qr ) is taken from the SCR catalytic converter. For this reason, the reducing agent content ( cRed ) in the phases ( P0 ) and ( P1 ) equal.

The efficiency of the nitrogen oxide reduction is 80% in the example for a simplified representation, ie of the in phase ( P0 ) supplied ten units of nitrogen oxide, eight units of measure are reacted ( NO ) and two units of measure ( NS ) are in the phase ( P1 ) as trailing nitrogen oxide content ( cPost ) recorded.

In the following, it is assumed, purely as an example, that the efficiency of 80% is the target efficiency of the SCR catalytic converter and that the target value ( rEff * ) for the nitrogen oxide reduction. In practice other values can occur.

As shown in 3 As can be seen, the same stable result can be achieved again and again if a steady state continues with an essentially continuous supply of ten units of quantity of nitrogen oxides and the addition of eight units of quantity of reducing agent.

4A and 4B show possible reactions to a positive and a negative injection pulse when it is connected to an SCR catalytic converter ( 16 ) is executed under target conditions. It is also assumed that the reducing agent content ( cRed ) in the phase ( P0 ) the target value ( cRed * ) is equivalent to. It is also assumed that, according to the conservative addition scheme, the nominal injection quantity (Qn) basically corresponds to the estimated reaction quantity ( Qr ' ), which in turn, assuming the existence of target conditions with the actual reaction amount ( Qr ) matches.

In the example of 4A a positive injection pulse ( I + ) for test purposes. With the positive injection pulse ( I + ) is the injection quantity ( Qi ) in the phase ( P0 ) by a considerable amount (dQ) greater than the nominal injection quantity (Qn). For the sake of simplicity, no distinction is made here between estimated and actual values of the added amount.

As shown in the reaction diagram below, the ten units of quantity supplied are reacted in the same proportion of nitrogen oxides ( NO ) as shown in the illustration 3 , although there is more reducing agent in the SCR catalytic converter than in the state after 3 . The reason for this is that the reduction reaction in the SCR catalytic converter primarily depends on the amount of reducing agent stored ( cRed ) and only indirectly through the added amount ( Qi ) being affected. Accordingly, stay with the example of 4A in phase ( P1 ) also two unresponsive units of measure ( NS ) of nitrogen oxide as trailing nitrogen oxide content ( cPost ) left over. Since the reducing agent content ( cRed ) the target value ( cRed * ) and is therefore less than the maximum storage capacity (cMax), the excess (dQ) of added reducing agent (here six units of quantity) can be completely absorbed in the SCR catalytic converter ( 16 ) are adsorbed (Qad = Qi). As a result, the positive injection pulse ( I + ) in the phase ( P1 ) does not lead to a noticeable change in the efficiency of the nitrogen oxide reduction. The measured value ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) remains essentially unchanged. This illustrates the buffer effect that is brought about by the storage effect in the SCR catalytic converter.

4B analogously shows a negative injection pulse ( I- ), which is carried out under the same starting conditions. So here is in the phase ( P0 ) the added amount ( Qi ) of reducing agent by a certain amount (dQ) less than the nominal amount added (Qn). As can be seen from the reaction diagram, the added amount ( Qi ) are completely adsorbed on reducing agent (Qad = Qi) and the reduction reaction takes place at the expected (maximum) efficiency, so that the measured value ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) does not change.

From the representations of 3 , 4A and 4B a first decision rule can be derived, which can be summarized as follows: If there is a positive or negative injection pulse ( I + , I- ) in a steady state no significant change in the tail nitrogen oxide content ( cPost ) can be determined, this indicates that the actual reducing agent content ( cRed ) not inadmissible from the target value ( cRed * ) differs. If there is nevertheless an efficiency deviation ( dEff ) the nitrogen oxide reduction is determined, causes other than a reducing agent excess or a reducing agent shortage could come into question, in particular a sensor drift of the leading nitrogen oxide sensor or the trailing nitrogen oxide sensor or a general reduction in efficiency of the SCR catalytic converter. This knowledge can be used on its own or in combination with the results of other runs of the test method in order to make a suitable change to the simulation model.

• Wenn auf einen positiven Injektionspuls (I+) eine (eindeutige) negative Änderung des Messwerts (cPost) des Nachlauf-Stickoxidsensors (41) folgt, kann auf einen Reduktionsmittel-Mangel (cRed--) geschlossen werden. Ist hingegen eine (eindeutige) positive Änderung des Messwerts (cPost) feststellbar, kann auf einen Reduktionsmittel-Überschuss (cRed++) geschlossen werden.

As already explained above, the kinetics of the processes in the SCR catalytic converter and the resulting dynamics of the change in the measured value ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) not sufficiently constant or predictable. For this reason it is usually not possible to establish a clear separation between the phases ( P0 , P1 ) and the reactions that take place in between. For example, it is possible that adsorption ( Qad ) of the added reducing agent takes place very quickly. In this case there is a prompt and easily detectable change in the measured value ( cPost ) of the run-on nitrogen oxide sensor ( 41 ). In such a case, the interpretations known from the prior art can be used that in 2 as simple decision rules ( 42 ) are shown. These can be summarized as follows:

• If on a positive injection pulse ( I + ) a (clear) negative change in the measured value ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) follows, it can be concluded that there is a deficiency of reducing agent (cRed--). If, on the other hand, there is a (clear) positive change in the measured value ( cPost ) can be determined, it can be concluded that there is an excess of reducing agent (cRed ++).

If the injection pulse is negative ( I- ) the interpretation is exactly the opposite. If a (unambiguous) negative change in the measured value is determined, it can be concluded that there is an excess of reducing agent (cRed ++), while a (unambiguous) positive change in the measured value indicates a shortage of reducing agent (cRed--).

With reference to the 5 until 12th further processes in the SCR catalytic converter explained, which can occur in the event of a shortage of reducing agent or an excess of reducing agent, but not according to the simple decision rules 2 or the state of the art.

the 5 until 8th go to the phase ( P0 ) assume a reducing agent deficiency (cRed--) and show possible reactions to a negative reaction pulse ( I- ) and a positive reaction pulse ( I + ) with subsequent addition of reagent ( Qi ) according to a conservative addition scheme (Qn = Qr) ( 5 and 7th ) as well as according to an aggressive addition scheme (Qn = Qs) ( 6th and 8th ).

Shown are in analogy to the representations of 3 , 4A and 4B an initial situation in the initial phase ( P0 ) with the following reaction diagram and subsequent state in the phase ( P1 ). In addition, subsequent changes are to be made in a further reaction diagram and a further phase ( P2 ), ( P3 ) with the respective effects on the measured value ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) shown.

At the bottom left of the figures, for a better overview, it is shown whether a positive or negative injection pulse ( I + , I- ) is present. Furthermore, the absolute measured values ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) in the phases ( P0 ) until ( P3 ) shown. The bar chart above shows the relative changes (dC) in the measured value ( cPost ) compared to the pre-pulse value ( cAvg ) shown. The pre-pulse value is the measured value ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) in the phase ( P0 ).

5 shows an initial situation in the phase ( P0 ) with reducing agent deficiency (cRed--). A negative injection pulse ( I- ) executed. In the reaction diagram between the phases ( P0 ) and ( P1 ) Due to the insufficient amount of stored reducing agent, only a small amount of nitrogen oxides ( NO ) respond. A significant proportion ( NS ) the nitrogen oxides are not reacted and emerge from the SCR catalytic converter. Accordingly, it is a significantly increased measured value ( cPost ) in the phase ( P1 ) detectable.

In the phase ( P1 ) the nominal amount (Qn) of reducing agent added by the injector ( 15th ) injected. The reducing agent content ( cRed ) is due to the small amount added (Qi = Qn-dQ) in the phase ( P0 ) fell even further, ie the shortage of reducing agents has increased. Accordingly, in the following phase ( P2 ) an even higher measured value ( cPost ) of the run-on nitrogen oxide sensor. However, in phase ( P1 ) again increased added amount (Qi = Qn = Qr) of reducing agent also to a relative recovery of the reducing agent content ( cRed ) in the SCR catalytic converter. Accordingly, until the following phase ( P3 ) already have a higher amount of nitrogen oxides ( NO ) reacts and the measured value ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) falls in the phase ( P3 ) again, but to a value that is higher than under the setpoint conditions 2 is to be expected. The reducing agent content ( cRed ) can differ from the phase ( P2 ) to phase ( P3 ) have recovered a little.

6th shows to 5 analogous processes assuming an aggressive addition scheme, ie that the nominal addition amount here corresponds to the stoichiometric equilibrium amount (Qn = Qs).

A comparison of the 5 and 6th shows that the results are essentially identical to 5 are. It can only be a somewhat faster recovery of the reducing agent content ( cRed ) take place in the SCR catalytic converter, but in the example shown this does not result in a change in the measured values ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) is reflected.

7th shows processes in response to a positive injection pulse ( I + ) assuming a conservative addition scheme (Qn = Qr). The initial situation in the phase ( P0 ) corresponds to the representations in 5 and 6th .

In the phase ( P0 ) an increased amount of reducing agent (Qi = Qn + dQ) is added. However, because of the delayed adsorption, this does not yet lead to an improvement in the nitrogen oxide reduction. Accordingly, in the phase ( P1 ) initially an increased measured value ( cPost ) of the run-on nitrogen oxide sensor ( 41 ). However, the increased amount added (Qi = Qn + dQ) leads to a significantly faster recovery of the reducing agent content in the further course ( cRed ) in the SCR catalytic converter. Accordingly, in the transition to phase ( P2 ) already a considerably larger proportion ( NO ) the nitrogen oxides are converted so that in the phase ( P2 ) the measured value ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) drops considerably. However, there is still a shortage of reducing agents, so that in phase ( P3 ) still essentially the same measured value ( cPost ) is present.

8th shows that too 7th analogous scenario assuming an aggressive addition of reducing agent (Qn = Qs ). Here there is an even faster and somewhat stronger recovery of the reducing agent content ( cRed ) instead, so that in phase ( P3 ) compared to 7th an even lower reading ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) is achieved. Otherwise, the processes are essentially identical.

9 shows in phase ( P0 ) an initial situation with excess reducing agent (cRed ++). A negative injection pulse (I-, Qi = Qn - dQ) is carried out, whereupon a nominal amount (Qn = Qr ') is added according to the conservative addition scheme.

Since the SCR catalytic converter is in phase ( P0 ) is well filled, the reduction of nitrogen oxides in the first reaction diagram can take place at maximum efficiency. Thus, in analogy to the processes in 2 eight units of nitric oxide ( NO ) reacts, whereby the reaction amount ( Qr ) of the stored reducing agent is eight units of measure. However, only the two units of quantity of reducing agent added according to the negative induction pulse are available for adsorption. Thus, more reducing agent is used in the transition from phase ( P0 ) to phase ( P1 ) degraded in the SCR catalytic converter than is absorbed again by adsorption. This reduces the excess of reducing agent. In the phase ( P1 ) the measured value is ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) two units of measure. In the previous phase ( P0 ) he had still carried four units of measure because a reducing agent breakthrough was recorded there as a result of the excess reducing agent.

In the transition to the further phases ( P2 , P3 ) as a result of the conservative addition of reducing agent, essentially the reducing agent content ( cRed ) kept at a constant level, which is lower than in the initial phase ( P0 ). The measured value ( cPost ) thus remains at the low level.

In the example of 10 based on an excess of reducing agent (cRed ++) finds a negative injection pulse ( I- ), although an aggressive addition scheme (Qn = Qs) is used.

The negative injection pulse ( I- ) is initially in the phase ( P1 ) In analogy to the previous example, the excess reducing agent is reduced because the amount of reaction ( Qr ) is greater than the added and thus absorbable amount (Qad = Qi). The reducing agent content ( cRed ), however, remains at an increased level, which is why the further aggressive addition up to the phase ( P3 ) there is again such a reducing agent excess that a unit of quantity ( Qde ) in phase ( P2 ) added amount ( Qi ) can no longer be adsorbed and in the phase ( P3 ) as the reducing agent breakthrough the measured value ( cPost ) increased again. This means that the measured value tends to be higher ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) than in the example of 9 .

11 again shows an example based on an excess of reducing agent in phase ( P0 ). A positive injection pulse ( I + ) with a conservative addition scheme (Qn = Qr ').

Due to the overfilling of the SCR catalytic converter, a considerable part (Qde> 0) of the in phase ( P0 ) added amount ( Qi ) are not adsorbed (Qad <Qi) and leaves the SCR catalytic converter in a reducing agent breakthrough. Accordingly, in the phase ( P1 ) to an increase in the measured value ( cPost ). The subsequent conservative addition (Qi = Qn) also results in the following phases ( P2 , 3) a reducing agent breakthrough occurs, either due to incomplete adsorption (the added amount (Qad <Qi) or due to renewed detachment or desorption of an already stored unit of measure of the reducing agent is based. Accordingly, the phases ( P2 , P3 ) an increased reading ( cPost ) detected.

12th also shows an excess of reducing agent (cRed ++) in the initial state ( P0 ) and a positive injection pulse ( I + ). In the following phases (P1-P3), however, an aggressive addition scheme (Qn = Qs) is used. The result is qualitatively similar to the previous example of 11 . However, in the example of 12th in the phases ( P2 , P3 ) an even more increased reading ( cPost ), which is based on the relatively higher amount added (Qs> Qr). Because the one in the phase ( P1 ) already significantly overfilled SCR catalytic converter can no longer absorb the slightly oversized amount added (Qi = Qs), so that the desorption amount ( Qde ) continues to rise.

13th shows a special case of the possible processes in the SCR catalytic converter, which was determined when a conservative addition scheme was used. In the phase ( P0 ) there is an initial state in which the reducing agent content ( cRed ) in the SCR catalytic converter is well above the target value shown as a dashed line ( cRed * ) lies. However, the SCR catalytic converter is not yet overfilled. This condition can be viewed as a moderate excess of reducing agent.

When using a conservative scheme for determining the target value ( cRed * ) for the reducing agent content ( cRed ) A state can occur in the SCR catalytic converter in which the target value for the efficiency of the nitrogen oxide reduction ( rEff * ) is below the maximum efficiency. In the phase ( P0 ) a positive injection pulse ( I + ) executed. Amazingly, according to the reaction diagram in the transition from phase ( P0 ) to phase ( P1 ) an increased reduction of nitrogen oxides takes place very early, the cause of which has not yet been clarified (possible local reducing agent deficiency and rapid adsorption, which increases the conversion efficiency) Compared to the example of 11 and 12th so the number increases ( NO ) of the reacted units of nitrogen oxide. Accordingly, the run-on nitrogen oxide sensor ( 41 ) in the phase ( P1 ) fewer nitrogen oxides found than in phase ( P0 ) so that the measured value ( cPost ) sinks. In addition, some of the activities in phase ( P0 ) added amount ( Qi ) is not adsorbed (Qad <Qi), but causes a reducing agent breakthrough ( Qde ) (local excess of reducing agent), which leads to an increase in the measured value ( cPost ) leads. In the phases ( P1 , P2 ) according to the conservative addition scheme, the nominal addition quantity (Qn = Qr ') is injected, which can also lead to a reducing agent breakthrough due to the constant excess of reducing agent, which occurs in the phases ( P2 , P3 ) to an increase in the measured value ( cPost ) leads.

The change (dC) shown in the measured value ( cPost ) in 13th can be even more pronounced. As a result of the unpredictable kinetics of the processes, it can happen that, based on the state in phase ( P0 ) when executing the positive injection pulse ( I + ) initially a very marked drop in the measurement result ( cPost ) takes place, while subsequently an even higher reduction agent breakthrough takes place. This could possibly be due to only temporary storage of the data in phase ( P0 ) be due to too much injected proportions of reducing agent, initially an excessive adsorption takes place, which is then compensated by a creeping desorption.

A comparison of the possible changes (dC) in the measured value ( cPost ) in the 5 until 13th that can actually occur in the event of a shortage of reducing agent or an excess of reducing agent or moderate excess of reducing agent, with the decision rules 2 illustrates the risk of misinterpretation mentioned above. A first reaction of the measurement signal ( cPost ) can (e.g. as a result of storage effects in the SCR catalytic converter) lead to an interpretation that is contrary to the actual state.

14th shows the relative changes in the measured value ( cPost ) for those in the 5 until 13th cases presented as possible reactions to a negative injection pulse ( I- ) and a positive injection pulse ( I + ) using a conservative addition scheme (Qn = Qr ') or an aggressive addition scheme (Qn = Qs).

In addition, partial responses are presented as successive increases in the measured value ( cPost ), which are explained in detail below.

15th shows exemplary curves of a feed nitrogen oxide content ( cPre ), an additional amount ( Qi ), a measured value ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) as well as a response characteristic ( R. ).

In the example of 15th a steady state is present. The feed nitrogen oxide content ( cPre ) lies within a tolerance band during the steady state ( T ). If the feed nitrogen oxide content ( cPre ) the tolerance band ( T ) would leave, this could be recorded as the end of the steady state.

As in the course of the added amount ( Qi ) can be seen, a positive injection pulse ( I + ) as the first injection pulse ( I1 ) executed. The positive injection pulse ( I + ) can be performed with a single increased dose or with a contiguous group of injections at an increased injection rate. A pre-pulse value ( cAvg ) the trailing nitrogen oxide content ( cPost ) is recorded, which takes a measured value from the run-on nitrogen oxide sensor ( 41 ) before or at the beginning of the execution of the first injection pulse ( I1 ) reproduces. The pre-pulse value ( cAvg ) be a mean value obtained in a time window prior to the execution of the injection pulse ( I1 ) is recorded. This time window is in 15th as averaging zone ( Zavg ) marked.

The measurement signal ( cPost ) of the run-on nitrogen oxide sensor ( 41 ) is given in a (indefinite duration) period of time after the injection pulse or from the start of the injection pulse ( I + ) and before any further injection pulse ( 12th ) with several separate partial answers ( R1-R13 ) rated. The partial answers can be set according to any evaluation scheme in order to ensure a successive relative change in the measured value ( cPost ) capture. According to a preferred embodiment, a first partial answer ( R1 ) set when the measurement signal ( cPost ) compared to the pre-pulse value ( cAvg ) increases or decreases by a certain amount. Another partial answer each time ( R2-R13 ) is set when the measurement signal ( cPost ) compared to the value of the measurement signal ( cPost ) to the end of the previous partial answer ( R1 ) increases or decreases by a certain amount, in particular the same amount.

In the example of 15th are used for each successive falling change in the measurement signal ( cPost ) a negative partial answer ( R1-R5 ) and with every successive positive change in the measurement signal ( cPost ) a positive partial answer ( R6-R13 ) set.

The 5 until 13th Representative courses of the partial responses for the processes shown in the SCR catalytic converter are shown. The representative courses of the partial responses are also in the decision patterns in 2 and 14th shown.

From the evaluation of the measuring signal ( cPost ) with partial responses, an easily analyzable qualitative change in the measurement signal ( cPost ), which is largely independent of the dynamics of the change. A pattern can be identified from the sequence, the distribution and, if applicable, the ratio of negative and positive partial responses, which can be evaluated to determine the cause of the efficiency deviation.

The multiple partial answers are preferred ( R1-R13 ) with decision patterns ( 42 ) compared (cf. 2 and 14th ), the representative curves of partial responses and / or changes (dC) of the measurement signal ( cPost ) to a cause (reducing agent excess (cRed ++), reducing agent deficiency (cRed--). From the pattern comparison, even if only a single injection pulse ( I1 ) or fewer injection pulses ( 11 , 12th ) Interpretations are made about the cause of an efficiency discrepancy, whether there is an excess of reducing agent or a shortage of reducing agent. The results of the pattern comparison are usually more precise and reliable than those results that can be achieved with previously known analysis methods. For example, the detected pattern can correspond to an aggressive addition scheme, although the control system provided a conservative addition scheme. This can indicate that the nominal addition amount (Qn) was incorrectly determined, i.e. at a value that is greater than the reaction amount ( Qr ) lies. To compensate, a correction value adjustment can be made in the feedforward control, if necessary paired with a change in the estimated reducing agent content ( cRed ') by an offset value.

The analysis period for the evaluation of the measurement signal ( cPost ) after or from the start of an injection pulse ( I1 ) does not need to be defined and, in particular, does not need to be divided into phases according to time rules. Rather, it is possible to carry out an assessment until either the steady state ends, a pattern comparison is finally impossible due to excessive deviations, or a new injection pulse ( 12th ) is performed. The evaluation period can therefore be variable and, for example, up to 15s (seconds) or 30s or even longer. This means that even particularly sluggish adsorption and desorption processes and thus particularly strong storage effects of the SCR catalytic converter can also be evaluated.

On the other hand, it is possible to use one or more previous partial answers ( R1-R5 ) a preliminary ruling ( D1 ) to meet about the cause. This can take place in particular if one of the simple decision rules is initially in accordance with 2 a high level of agreement with the response characteristics ( R. ) having. If the steady state ends early, the preliminary decision can be adopted as the final decision, which can be a correct decision for a significant number of the cases that occur.

If, on the other hand, the steady state persists and further partial answers ( R6-R13 ) no longer match the decision pattern that the preliminary ruling ( D1 ), a different final decision ( D2 ) are made if there is also a match to one of the other decision patterns ( 42 ) is recorded. This is exemplified in 15th shown. In the example there, the first five partial answers ( R1-R5 ) a match with a decision pattern 2 on. From the partial answer (R6) the match is lost. From around the partial answer (R9 / R10) onwards, a new match with a decision pattern emerges 14th determines that to the in 13th operations described. Accordingly, the final decision ( D2 ) that the identified cause in the present example is a moderate excess of reducing agent (cRed> cRed *).

A decision pattern ( 42 ) can therefore provide that one or more early partial answers ( R1-R5 ) in a first direction and one or more late partial answers ( R6-R13 ) are available in the opposite direction. If necessary, ratios can be provided for the respective number of partial responses in the first direction and in the opposite direction.

In addition, a decision pattern can provide that the measurement signal ( cPost ) in the area of at least one late partial answer ( R6-R13 ), which go in the opposite direction to the one or more partial answers ( R1-R5 is present to a limit value ( K ) from the pre-pulse value ( cAvg ) must deviate, whereby the deviation must be in the direction of the late partial answer. In other words, in some cases with an early drop in the measured value ( cPost ), which leads to a match with a first decision pattern, a turn to another decision pattern can only take place if, in the further course, such a sharp increase in the measured value ( cPost ) occurs that the measured value ( cPost ) by a definable limit value ( K ) above the level of the pre-pulse value ( cAvg ) increases - and vice versa.

If necessary, one or more subsequent injection pulses ( 12th , 13th ), preferably within the same steady state, with the test addition amount ( Qi ) or the direction of the following injection pulse (I2 = I- or I2 = I +) and, if applicable, the duration of the following injection pulse ( 12th ) depending on the result of the previous injection pulse ( I1 ) be determined. For example, after a first positive detection of a cause, a specific cross-check or a specific confirmation test can be carried out. As a result of the targeted specification, the total number of injection pulses required can be significantly reduced, so that the risk of generating a reducing agent breakthrough is minimized by the test method.

Modifications of the invention are possible in various ways. In particular, all of the features described, shown, claimed or otherwise disclosed in relation to the exemplary embodiments can be combined with one another in any way, replaced with one another or omitted.

The internal combustion engine can preferably be a direct injection diesel engine.

The definition of the pre-tax value ( Qpre ) can be done in any way. It can preferably be adapted as a function of an addition scheme, in particular according to a conservative addition scheme. Then the pre-control value ( Qpre ) chosen so that it is lower than the stoichiometric equilibrium amount. In other words, with a conservative addition scheme, slightly less reducing agent is used on the basis of the pre-control value ( Qpre ) added than would be necessary for the complete reduction of the amount of nitrogen oxide, which according to the feed nitrogen oxide content ( cPre ) currently the SCR catalytic converter ( 15th ) is supplied. With a conservative addition scheme, the pre-control value ( Qpre ) still be set below the estimated reaction amount (Qr ').

Alternatively, the pre-control value ( Qpre ) according to a balanced addition scheme, 95% to 100% of the stoichiometric equilibrium amount correspond to the current nitrogen oxide content ( cPre ) is determined. In the case of an aggressive addition scheme, the pre-control value ( Qpre ) are at or above the equilibrium stoichiometric amount, which may also require an ammonia slip catalyst or similar component to be installed downstream of the SCR catalyst ( 16 ) is arranged.

The addition scheme can be adapted as a function of an operating state of the internal combustion engine and / or the exhaust gas aftertreatment system. For example, if a steady state is determined, a conservative addition scheme can be selected. If an unsteady state in the direction of an increasing load or in the direction of increased combustion temperatures is determined, however, a balanced or aggressive addition scheme can be provided temporarily.

List of reference symbols

10 Exhaust aftertreatment system Exhaust gas after treatment system 11 Forward passage Upstream passage 12th Catalysis section Catalytic section 13th Follow-up passage Downstream passage 14th Diesel oxidation catalyst Diesel oxidation catalyst 15th Reducing agent injector Reductant injector 16 SCR catalytic converter SCR Catalyst 17th filter filter 18th Forward NOx sensor Upstream NOx sensor 19th Run-on NOx sensor Downstream NOx sensor 20th Control unit Control unit 21 Multi-part simulation model Multi-segment simulation model 22nd Feedforward Pre control 23 Setpoint calculation Target value calculation 24 Injector driver Injector Driver 25th Summation term Summation segment 26th Comparator Comparator 27 Weighting element / correction value adjustment Weighting segment / correction value adaptation 28 Conditional check Condition check 31 Reducing agent addition model Reductant addition model 32 Reducing agent storage model Reductant storage model 33 Reaction model Reaction model 34 Desorption model Desorption model 40 Feed nitrogen oxide sensor Upstream nitrogen oxide sensor 41 Run-on nitrogen oxide sensor Downstream nitrogen oxide sensor 42 Decision pattern Decision pattern cAvg Pre-pulse value / pre-pulse mean value Pre-pulse value / pre-pulse average value cPre Lead nitric oxide content Upstream nitrogen oxide content cPost Follow-up nitrogen oxide content Downstream nitrogen oxide content cRed Actual reducing agent content Actual reductant content cRed ' Estimated reducing agent content Estimated reductant content cRed * Setpoint for reducing agent content Target value for reductant content dEff Efficiency deviation of the nitrogen oxide reduction Efficiency deviation of nitrogen oxide reduction rEff * Target value for nitrogen oxide reduction Target value for nitrogen oxide reduction Cond Precondition for learning process / correction value adjustment Precondition for learning cycle / correction value adaptation CQ Injection command Injection command D1 Preliminary ruling Preliminary decision D2 final decision Final decision 1 + Positive injection pulse Positive injection pulse I- Negative injection pulse Negative injection pulse K Limit value (compared to cAvg) Threshold (wrt cAvg) NOx Nitrogen oxides Nitrogen oxides NO Reacted nitrogen oxides Reacted nitrogen oxides NS Unreacted nitrogen oxides / nitrogen oxide breakthrough Non-reacted nitrogen oxides / nitrogen oxide break through P0-P4 Phases Phases Qad Actual amount of adsorption Actual adsorbed quantity Qad ' Estimated amount of adsorption Estimated value for adsorbed quantity Qde Actual amount of desorption Actual desorbed quantity Qde ' Estimated amount of desorption Estimated desorbed quantity Qi Actual amount of reducing agent added Actual reductant addition quantity Qi * Setpoint for the amount of reducing agent added Target value for reductant addition quantity Qi ' Estimated value for the amount of reducing agent added Estimation value for reductant addition quantity Qpre Pre-control value for adding reducing agent pre control value for reductant addition Qr Amount of reducing agent actually converted by reaction / amount of reaction Actual quantity of reductant converted by chemical reaction / reaction quantity Qr ' Response amount estimate Estimated value for reacted quantity Qs Stoichiometric equilibrium amount Stoichiometric balance quantity Qstr Storage management value for adding reducing agent Storage guidance value for reductant addition R. Response characteristics Response characteristic R1-R13 separated partial responses to injection pulse Separated section responses to injection pulse S1 First steady state First steady state S2 Second steady state Second steady state S3 Third steady state Third steady state SW Weighting key Weighting ratio T Tolerance band Tolerance band W1 First correction value First correction value W2 Second correction value Second correction value W3 Third correction value Third correction value W4 Fourth correction value Forth correction value Zavg Averaging zone Averaging zone

Claims (10)

Exhaust gas aftertreatment system (10) for an internal combustion engine comprising an SCR catalytic converter (16) with a feed passage (11) and a follow-up passage (13), with a current feed nitrogen oxide content (cPre) in the feed passage (11 ) and a current post-nitrogen oxide content (cPost) in the post-run passage (13) are determined and a reducing agent injector (15) is arranged upstream of the SCR catalytic converter (16) in order to inject a reducing agent that is in the SCR catalytic converter (16) is stored and nitrogen oxides (NOx) is reduced, and wherein the exhaust gas aftertreatment system (10) comprises a control unit (20) which is connected to the reducing agent injector (15) and controls the current addition amount (Qi) of the reducing agent, the control unit (20 ) comprises a multi-part simulation model (21) and a precontrol (22) and is designed to carry out the following steps: - In the control unit (20), a target value (Qi *) for the current amount of reducing agent added is based on a precontrol value (Qpre) and set a memory management value (Qstr); - The precontrol value (Qpre) is determined by the precontrol (22) on the basis of the feed nitrogen oxide content (cPre); - The storage management value (Qstr) is determined by the multi-part simulation model (21) as a function of an estimated reducing agent content (cRed ') in the SCR catalytic converter (16) so that the estimated reducing agent content (cRed') corresponds to a target Value (cRed *) is approximated; - The simulation model (21) comprises at least a first element in the form of a reducing agent addition model (31) and a second element in the form of a reducing agent storage model (32), on the basis of which the reducing agent content (cRed ') is estimated; - an actual efficiency of the nitrogen reduction is determined on the basis of the leading nitrogen oxide content (cPre) and the trailing nitrogen oxide content (cPost); - In a learning process, when an efficiency deviation (dEff) compared to a target efficiency (rEff *) of the nitrogen oxide reduction is determined, a correction value adjustment (27) is carried out in at least two elements (31, 32, 33, 34) of the simulation model ( 21) performed; - characterized in that the efficiency deviation (dEff) is distributed according to a weighting key to the correction value adjustment (27) in the at least two members (31, 32, 33, 34) of the simulation model by dividing the deviation value (dEff) into two or more shares. Exhaust aftertreatment system after Claim 1 , with two or more alternative weighting keys (SW) being predefined, between which a change is made, in particular depending on the success of a previous learning process. Exhaust gas aftertreatment system according to one of the preceding claims, wherein a correction value adjustment (27) changes at least one correction value (W1) on or in the reducing agent addition model (31) and additionally a correction value (W2) on or in the reducing agent storage model (32). Exhaust gas aftertreatment system according to one of the preceding claims, wherein the reducing agent addition model (31) calculates an estimated addition amount (Qi ') of reducing agent as a function of an actuation (Qi * / CQ) of the reducing agent injector (15). Exhaust gas aftertreatment system according to one of the preceding claims, wherein the reducing agent storage model (32) estimates, depending on state parameters of the exhaust gas aftertreatment system (10), which amount (Qad ') of reducing agent is currently stored in the SCR catalytic converter (16) by adsorption. Exhaust gas aftertreatment system according to one of the preceding claims, wherein the target value (cRed *) for the reducing agent content in the SCR catalytic converter (16) and / or the pilot control value (Qpre) is determined according to a conservative addition scheme. Exhaust gas aftertreatment system according to one of the preceding claims, wherein it is checked as a precondition (Cond) for the implementation of a correction value adjustment (27) that a steady state of the exhaust gas aftertreatment system (10) and / or the internal combustion engine is present. Exhaust aftertreatment system according to one of the preceding claims, wherein the cause of an efficiency deviation (dEff) is determined, namely whether the deviation is based on a reducing agent shortage (nitrogen oxide breakthrough) or a reducing agent excess (reducing agent breakthrough), and the correction value Adaptation (27) takes place as a function of the cause of the efficiency discrepancy, in particular through the choice of a weighting key. Exhaust gas aftertreatment system according to one of the preceding claims, wherein a reaction model (33) and / or a desorption model (34) are provided as further elements of the simulation model (21), the reaction model (33) depending on state parameters of the exhaust gas aftertreatment system (10) estimates what proportion (Qr ') of the reducing agent stored in the SCR catalytic converter is converted by chemical reaction, and the desorption model (34) estimates which proportion (Qde') of the The reducing agent stored in the SCR catalytic converter is desorbed without chemical conversion. Exhaust gas aftertreatment system according to one of the preceding claims, wherein a correction value adaptation additionally changes a correction value (W3) for or in the pilot control (22).

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