DE102016207474A1 - A method of operating an exhaust aftertreatment system, exhaust aftertreatment system, and internal combustion engine having such an exhaust aftertreatment system - Google Patents

Abstract

The invention relates to a method for operating an exhaust aftertreatment system (3), which comprises an exhaust line (7) with an SCR catalytic converter (9), a metering device (11) for introducing reducing agent into the exhaust line (7) upstream of the SCR Catalyst (9), and with - a breakthrough detection means (13) for detecting a breakdown of the SCR catalyst (9), wherein - depending on at least one HC load of the SCR catalyst (9) representing parameter to one of the Breakthrough detection means (13) recognized breakthrough of the SCR catalyst (9) towards a) in a first mode (29) at least one measure in response to the HC loading of the SCR catalyst (9), or b) in a second mode (31 ) at least one measure for adjusting the operation of the exhaust gas line (7) to an aging of the SCR catalyst (9) is performed.

Description

The invention relates to a method for operating an exhaust aftertreatment system, an exhaust aftertreatment system, and an internal combustion engine having such an exhaust aftertreatment system.

In internal combustion engines, which have an exhaust aftertreatment system with a catalyst for the selective catalytic reduction of nitrogen oxides (SCR catalyst), there is the problem that in operating conditions in which increasingly unburned hydrocarbons (HC) occur in the exhaust gas, catalytically active, active centers of the SCR Catalyst can be coated with hydrocarbons. An achievable with the SCR catalyst conversion rate for the reduction of nitrogen oxides is then significantly reduced. However, this reduction of the conversion rate is reversible, since the HC storage capacity of the SCR catalyst decreases with increasing temperature. Especially at temperatures above 350 ° C, the hydrocarbons are desorbed from the catalyst material of the SCR catalyst, which after some time, at least approximately or even completely recover its original maximum conversion rate. To delineate this is an aging of the SCR catalyst, whereby its maximum conversion rate decreases over time due to aging effects. This is not reversible. It is therefore important for the operation of the exhaust aftertreatment system to differentiate between aging effects on the one hand and HC loading of the SCR catalyst on the other hand, in particular a dosing strategy for a reducing agent for the reaction on the SCR catalyst may depend on whether the maximum conversion rate reversible is reduced by HC loading or irreversibly due to aging. Existing exhaust aftertreatment systems can be improved, especially with regard to this distinction.

The invention has for its object to provide a method for operating an exhaust aftertreatment system, an exhaust aftertreatment system and an internal combustion engine with such an exhaust aftertreatment system, wherein said disadvantages do not occur.

The object is achieved by providing the subject matters of the independent claims. Advantageous embodiments emerge from the subclaims.

The object is achieved, in particular, by providing a method for operating an exhaust gas aftertreatment system, which will also be referred to as AGN system for short, and which includes an exhaust gas line with an SCR catalytic converter and a metering device for introducing reducing agent into the exhaust gas line upstream of the exhaust gas treatment system SCR catalyst has. The AGN system also includes a breakthrough detection means for detecting a breakdown of the SCR catalyst. It is provided that, depending on at least one parameter representing the HC loading of the SCR catalytic converter, in a first operating mode, a breakthrough of the SCR catalytic converter detected by the breakthrough detection means is at least one measure in response to the HC loading of the SCR catalytic converter is carried out. Furthermore, depending on the at least one parameter representing the HC loading of the SCR catalytic converter, at least one measure for adapting the operation of the exhaust gas line to aging of the SCR catalytic converter is carried out in a second operating mode. The method has advantages over the prior art. In particular, based on an estimate of the HC load by means of the at least one parameter, it is possible to make a distinction as to how to respond to a breakthrough of the SCR catalyst detected by the breakthrough detection means. If this estimation points to a specific HC loading of the SCR catalytic converter, at least one suitable measure can be taken in the first operating mode. If, on the other hand, due to the estimation of the HC load, it is unlikely that the breakthrough is due to the HC load, at least one measure can be taken in the second operating mode to adapt the operation of the exhaust line to aging of the SCR catalytic converter. Thus, not only does the method distinguish between HC loading and aging of the SCR catalyst, it also provides a suitable response to these cases. In particular, the first operating mode or the second operating mode is selected on the basis of or depending on the parameter representing the HC loading of the SCR catalytic converter.

Increased HC emissions occur more intensively during a cold start and cold ambient conditions of internal combustion engines. Other conditions in which increased HC emissions occur, for example, long periods of operation under no-load conditions, such as ships, which use at least one internal combustion engine while lying in the harbor to generate electricity. In principle, such increased HC emissions can not be avoided; in particular, the associated operating states can not be completely avoided. Because of the occurring in such operating conditions, low exhaust gas temperatures, there is an HC loading of the SCR catalyst, while the hydrocarbons can desorb at higher exhaust gas temperatures again from the catalyst material of the SCR catalyst.

An exhaust aftertreatment system is understood to mean, in particular, a system which is adapted for the passage of exhaust gas, in particular from an exhaust gas source, in particular an internal combustion engine, to an exhaust gas outlet, in particular an exhaust, and secondarily for the aftertreatment of the exhaust gas, in particular for removal of unwanted, if appropriate toxic or environmentally harmful substances and / or particles or the like from the exhaust gas.

An exhaust system is understood in particular to mean a conduit or pipe system for the passage of the exhaust gas, including exhaust gas aftertreatment devices provided along this line or pipe system. Under exhaust aftertreatment devices are understood in particular means that are suitable to after-treat exhaust gas, in particular catalysts, particulate filters, metering devices and the like.

A metering device for introducing reducing agent into the exhaust gas system is understood in particular to mean a device which is suitable and adapted to introduce a reducing agent into the exhaust gas line and, in particular, into the exhaust gas flow, in particular to inject or inject it. The metering device is preferably set up for controlling the amount of reducing agent introduced into the exhaust gas line, in particular per unit time, thus for metering the reducing agent. In this case, a quantity control can in particular be pulse width modulated, but can also be carried out in another suitable manner. The metering device is designed in particular controllable, preferably for metering the reducing agent.

A reducing agent is understood in particular to mean a medium which is suitable for reacting with nitrogen oxides on the catalyst material of the SCR catalytic converter in such a way that the nitrogen oxides are reduced, but the reducing agent is oxidized. The term "reducing agent" is understood in a broader sense such that it also means a reducing agent precursor product which is metered into the exhaust gas line and only reacts or disintegrates in contact with the hot exhaust gas to form an actual reducing agent.

In a preferred embodiment of the method can be introduced as a reducing agent in particular a urea-water solution in the exhaust line, said urea-water solution in the exhaust line to ammonia and water decomposes, the ammonia as the actual reducing agent in the strict sense at the SCR -Catalyst acts. It reacts there with nitrogen oxides contained in the exhaust gas to nitrogen and water.

An SCR catalyst is understood in particular to mean a device which has a catalytic material, preferably on a carrier substrate, which is set up and / or suitable for the selective catalytic reduction of nitrogen oxides, in particular for the selective catalytic conversion of nitrogen oxides with a reducing agent, in particular ammonia , to a reduced product, especially nitrogen.

A breakthrough of the SCR catalyst is understood to mean a state in which the reducing agent supplied to the SCR catalyst is not completely reacted, in particular oxidized, but rather unreacted reducing agent emerges from the SCR catalyst. Such a breakthrough can occur, for example, when a maximum conversion rate of the SCR catalyst is reduced, wherein the metered amount of reducing agent is not tuned to this reduced maximum conversion rate. It is possible that then more reducing agent is metered into the exhaust system, as can be implemented on the SCR catalyst. Accordingly, unreacted reducing agent escapes from the SCR catalyst so that the catalyst is in breakthrough. The maximum conversion rate of the SCR catalyst can be reduced for example by an HC loading, but also by aging.

By a breakthrough detection means is meant in particular a device which is suitable and adapted to detect a breakthrough of the SCR catalyst. In particular, the breakthrough detection means comprises a suitable sensor arranged downstream of the SCR catalyst and arranged to detect unreacted reducing agent in the exhaust gas. This may be a reducing agent sensor, for example an ammonia sensor. If ammonia is used as a reducing agent in the narrower sense, it can also be a nitrogen oxide sensor, since nitrogen oxide sensors typically have a cross-sensitivity to ammonia. In order to be able to recognize a breakthrough in more detail, it is possible for a suitable sensor, in particular in each case a nitrogen oxide sensor, to be provided both upstream of the SCR catalytic converter and downstream of the SCR catalytic converter. The signals from these sensors can then be used, in a manner known per se, to detect a breakthrough. The breakthrough detection means may further comprise an evaluation or control device or be part of a control device which is adapted to detect a breakthrough on the basis of at least one sensor signal.

The detection of a breakdown of the SCR catalyst is preferred performed as in the German patent specification DE 10 2011 011 441 B3 describe is. The same patent also describes a possibility of determining a maximum conversion rate of an SCR catalyst. In the present process, preferably, the maximum conversion rate of the SCR catalyst is also determined in the manner described in the German Patent DE 10 2011 011 441 B3 is described. The teaching laid down in this publication is expressly referred to here.

Preferably, an estimate of an HC loading of the SCR catalyst is carried out on the basis of the at least one parameter, which means that the HC load is estimated either on the basis of a model or an invoice, or at least implicitly on the basis of at least one other variable is determined approximately. The HC loading is thus preferably not measured directly in particular, but estimated on the basis of the at least one parameter representing it, wherein it is not absolutely necessary to estimate the HC load itself as a separate variable. Rather, an implicit estimate by determining or estimating another variable that correlates with HC loading is also possible. In particular, it is possible for the parameter representing the HC loading of the SCR catalyst itself to be used as an estimate.

A parameter representing the HC loading of the SCR catalyst is understood to be a physical quantity which correlates with the HC loading of the SCR catalyst and thus is suitable for giving an indication of the HC loading of the SCR catalyst. There is no need for a direct causal connection between the HC loading on the one hand and the parameter that represents itself on the other hand. On the contrary, there may be a connection such that, given the presence of a specific value or a specific value range of the parameter-in particular over a specific time-it is possible to conclude that there is a specific HC load on the SCR catalytic converter.

Within the scope of the method, at least two parameter ranges of the parameter are preferably differentiated, wherein the exhaust gas aftertreatment system is operated in a first parameter range in the first operating mode and in a second parameter range in the second operating mode. In this case, the first parameter range is preferably assigned a larger HC load than the second parameter range.

The first operating mode is also referred to below as a trial operation. In particular, it is assigned an area of the HC loading in which it makes sense to take at least one measure in response to the HC loading, in particular with the aim of avoiding, if possible, further breakthroughs of the SCR catalyst and preferably at the same time the HC To reduce the load. The second operating mode is in particular assigned an HC load which is so low that a detected breakthrough is very likely not due to the HC load, but rather due to aging of the SCR catalytic converter. It then makes sense to take at least one measure to adapt the operation of the exhaust line to the aging of the SCR catalyst. The second operating mode is also referred to below as normal operation.

In the first operating mode, no measure is preferably taken to adapt the operation of the exhaust gas line to aging of the SCR catalytic converter; the operation of the exhaust system is therefore explicitly not adapted to aging of the SCR catalyst. This makes sense because the detected breakthrough is most likely due exclusively to the HC load, so there is no knowledge about a possible aging of the SCR catalyst. Aging in this mode could therefore lead to mismatch.

According to one embodiment of the invention, it is provided that, depending on the at least one parameter representing the HC loading of the SCR catalytic converter, the metering device is either activated in order to introduce reducing agent into the exhaust gas line or else it is not actuated. It can therefore be decided in an advantageous manner on the basis of the at least one parameter, if any reducing agent is introduced into the exhaust system, or whether rather the introduction of reducing agent is omitted in the exhaust system.

In the above-mentioned first and second modes, reducing agent is preferably introduced into the exhaust gas line. Only in this way can a breakthrough of the SCR catalytic converter occur at all, which then reacts appropriately in the operating modes. It is preferably provided a third mode in which no reducing agent is introduced into the exhaust line, thus the metering device is not activated. This third operating mode is in particular associated with a third parameter range of the parameter, in which, in particular, such a high HC loading of the SCR catalytic converter is estimated that metering in of reducing agent does not make sense, because this could not be implemented, at least to a very substantial extent. In the first mode, also called Trying operation is called, on the other hand - in particular repeated - reducing agent can be introduced into the exhaust line to test whether the HC loading is still so large that a breakthrough occurs. Thus, in particular, it can be observed and ascertained whether and to what extent the HC load has possibly already been reduced. In the third operating mode, which is also referred to as normal operation, on the other hand, reducing agent is introduced into the exhaust gas line on the basis of a conventional quantity control, wherein any breakthrough detected is attributed to aging of the SCR catalytic converter, after which a suitable measure is taken.

Preferably, also in the trial operation, thus the first mode of operation, regular dosing is performed on the basis of conventional quantity control of the reducing agent, but a detected breakthrough is treated differently than in the second mode, namely due to a detected breakthrough to one or re-existing HC loading of the SCR catalyst is closed, whereupon the at least one measure is taken in response to the HC loading.

The first operating mode is therefore used in particular in a middle region of the HC loading. The second mode is used in a lower range of HC loading, with HC loading being smaller in this smaller range than in the middle range. Finally, the third operating mode is used in the area of a higher HC load, the higher HC load being greater than the mean HC load.

According to one embodiment of the invention, it is provided that a calculated loading of the SCR catalyst with hydrocarbons is used as the at least one parameter representing the HC loading of the SCR catalyst. In this case, in particular, an HC loading computer can be used. Preferably, a model is used to calculate the HC loading, which is suitable for at least approximately calculating a current loading state of the SCR catalytic converter with hydrocarbons. In this case, for example, a model of the raw hydrocarbon emissions of an internal combustion engine at different boundary conditions of the operation, for example in a cold start, idling, under part load, under full load, and the like, are used. The model preferably describes a time course of adsorption, desorption and HC conversion in the SCR catalyst. This may in particular be a physically motivated model. On the basis of the model, in particular a time profile of the HC load can be calculated. Different threshold values for the HC loading can be defined, for example an HC loading threshold beyond which no conversion of nitrogen oxides to the SCR catalyst is possible, an HC loading threshold above which only a reduced conversion is possible, and / or optionally an HC loading threshold below which a regular operation of the SCR catalyst with undiminished or hardly reduced conversion is possible. While such a HC load calculator may have high accuracy, it does require elaborate modeling and parameterization of various effects to achieve desired accuracy.

Additionally or alternatively, it is possible that as the at least one parameter a result of a temporal evaluation of an operating state of the exhaust gas line is used. This allows a comparatively simple plausibility check of the HC loading of the SCR catalytic converter by a temporal assessment of the operating state of the exhaust gas line and / or in particular of an operating state of an internal combustion engine having the exhaust gas line. In this case, for example, an operation at low load and / or low exhaust gas temperatures can be integrated in time, wherein in particular a weighting can be used. For example, it can be taken into account here that the longer the load has to be traveled at higher loads in order to compensate for a HC load that has been charged, the colder the previous operation was. Such integral value formed may also be down-integrated by operating at higher load and / or higher exhaust gas temperature. Again, thresholds for the integral thus formed can be defined to select the various modes of operation. Preferably, parameters for a weighting function are determined for the integration of the operating states in tests. This results in comparison to a HC loading computer a significantly lower parameterization effort at the same time reduced computing costs during operation. At the same time, however, if necessary - at least in comparison to a well-parameterized loading computer - an achievable accuracy is lower.

As far as here and in the following operating states of the exhaust system are addressed, are also preferred at the same time also operating states of the exhaust system having internal combustion engine meant. Thus, as a rule, high exhaust-gas temperatures and high loads-in particular at high speeds-of the internal combustion engine can be correlated with one another, so that corresponding operating states are likewise correlated with one another. In particular, the term "operating state of the exhaust gas line" can accordingly also include and include a corresponding operating state of the internal combustion engine.

Additionally or alternatively, it is possible for the result of an evaluation of a course of measures to adapt the operation of the exhaust gas line to the aging of the SCR catalytic converter to be used as the at least one parameter. A simple method of age adaptation is, for example, a replacement of a value for a maximum conversion rate of the SCR catalyst by a new, lower value. For example, if a breakthrough is detected, it can be checked which maximum turnover rate has been reached by the time of detection. It can then be further examined which maximum conversion rate would correspond to the breakthrough just identified. For large changes detected maximum conversion rates compared to stored, previous maximum conversion rates, the cause of the breakthrough can be assessed as HC loading, so then the first mode can be selected. This is consistent with the recognition that aging is usually not sudden, but rather approximately continuous and comparatively slow, while HC loading typically can lead to faster jumps in maximum turnover rate. If an HC load is detected as the cause of the breakthrough, preferably the determined new maximum turnover rate is not stored and thus no aging adjustment is performed. If the HC loading is reduced as a result, at least approximately the original maximum conversion rate of the SCR catalytic converter can be reached again during operation. An aging adjustment would therefore lead to errors and would have to be considered a mismatch. In addition, a simple logic can be implemented such that after a start of an internal combustion engine, which has the exhaust line, initially starting from a possible HC loading, only when the first time the maximum conversion rate of the SCR Catalyst has been reached, a detected breakthrough interpreted as aging and then the second mode is performed.

If a course of measures for adapting the operation of the exhaust gas line to aging of the SCR catalyst is evaluated in order to obtain the at least one parameter, this means a comparatively simple procedure since measures for aging adaptation are preferably provided anyway. It therefore only requires a new, appropriate evaluation of these measures in the context of the procedure. On the other hand, this method is relatively inaccurate compared to the previously described methods.

Additionally or alternatively, it is preferably provided that a time duration for at least one specific operating state or operating state region of the exhaust gas line is used as the at least one parameter. As already stated above, an operating state or operating state region of an internal combustion engine can be used, which has the exhaust gas line. In this case, it is possible, for example, after a certain period of time, during which high temperatures prevailed in the exhaust gas line, to safely attribute an opening to an aging of the SCR catalytic converter, because after this specific period of time at the corresponding temperatures an approximately previously existing HC load of the SCR Catalyst is considered to be degraded with high probability. On the other hand, prior to the expiry of this predetermined period of time, it is possible, for example, to assume an HC loading of the SCR catalytic converter if a breakthrough is detected. This approach is very easy to implement; however, it does harbor the least certainty with regard to a clear assignment of the breakthrough recognition to a specific effect of all the methods described so far, in particular because of its extremely indirect approach.

According to one embodiment of the invention, it is provided that as the at least one measure in response to the HC loading for a predetermined shutdown period, an introduction of reducing agent is omitted in the exhaust system. In the first operating mode, the so-called trial operation, this takes into account the fact that a recognized breakthrough is apparently due to a still or re-existing HC loading of the SCR catalyst, in view of the reduced maximum conversion rate, a further dosage of reducing agent in the At least initially exhaust gas train is not useful. On the other hand, it is assumed in this mode of operation that the HC load is not too high and can be reduced in a certain time, in particular depending on the current operating conditions of the exhaust line. The introduction of reducing agent is therefore not completely adjusted, but only for the predetermined shutdown time, after the expiration again a contribution of reducing agent takes place, so that it can be festgesellt whether further breakthrough occurs. If this is the case, the introduction of reducing agent can be interrupted again for the predetermined switch-off period. This can be continued, for example, until a breakthrough is no longer detected when the introduction of reducing agent is restarted. The operation can then, for example, go into normal operation, and thus into the second operating mode.

Alternatively or additionally, it is possible that as the at least one measure for adjusting the operation of the exhaust gas line to an aging the SCR catalyst an aging map is changed, wherein the aging map is used to control the introduction of reducing agent in the exhaust line, in particular for quantity control. For example, in the aging characteristic curve, maximum conversion rates for the SCR catalyst can be stored, for example as a function of at least one further parameter, in particular the temperature of the SCR catalytic converter or the exhaust gas temperature in the region of the SCR catalytic converter. The values for the maximum conversion rate in the aging map can then be adapted, in particular to smaller values, if a breakthrough is recognized and assigned to an aging of the SCR catalytic converter. As a result, the quantity control for the introduction of reducing agent can be adapted gradually to the aging of the SCR catalyst and its age-related reduced sales. The aging map is thus preferably changed in particular to a reduced maximum conversion rate.

According to a development of the invention, it is provided that the predetermined switch-off time duration is selected in the first operating mode as a function of a temperature in the region of the SCR catalytic converter. This is based on the finding that the desorption of hydrocarbons from the SCR catalyst is faster the higher the temperature in its range. Thus, the predetermined turn-off period can be made shorter at a higher temperature, and is more preferably selected at a lower temperature. Preferably, the predetermined turn-off period is selected depending on a current temperature in the region of the SCR catalyst. The temperature in the region of the SCR catalyst is preferably a temperature of the SCR catalyst itself, which is preferably measured on or in the SCR catalyst, or an exhaust gas temperature upstream, in particular immediately upstream of the SCR catalyst used.

The predetermined switch-off time period is preferably read from a characteristic map or a characteristic line in which the switch-off time duration is stored as a function of the temperature in the region of the SCR catalytic converter.

According to one embodiment of the invention, it is provided that in the first operating mode, a regeneration time period is detected, during which there is at least one operating state of the exhaust gas line which is suitable for regeneration of the SCR catalytic converter. The first mode is exited, and it is preferred to change to the second mode when the regeneration period reaches or exceeds a predetermined maximum value. The detection of the regeneration period is in particular started when the operation of the exhaust aftertreatment system in the first mode is started or changed to the first mode. A time counter provided for the regeneration period is preferably set to zero. Times of regeneration are then detected as regeneration times, for which there is an operating state of the exhaust gas line which is suitable for reducing the HC load of the SCR catalytic converter, that is to say regenerating it. In particular, times are detected at which a torque of an internal combustion engine, which has the exhaust aftertreatment system, depending on a speed of the internal combustion engine above a first predetermined limit characteristic. Thus, in particular, the instantaneous torque and the instantaneous speed of the internal combustion engine are detected and checked as to whether these lie above the first specific limit characteristic in a characteristic map spanned by the rotational speed on the one hand and the torque on the other hand.

Additionally or alternatively, times can be detected as regeneration times, to which a temperature in the range of the SCR catalyst, in particular an exhaust gas temperature upstream of the SCR catalyst or a temperature measured directly at or in the SCR catalyst, depending on an exhaust gas mass flow above a second certain limit characteristic lies. In this case, the instantaneous temperature in the region of the SCR catalytic converter on the one hand and the instantaneous exhaust gas mass flow through the SCR catalytic converter on the other hand are preferably detected and checked in this case as to whether a corresponding instantaneous value pair lies above the second specific limit characteristic curve in one by the temperature lies in the region of the SCR catalyst on the one hand and the exhaust gas mass flow on the other hand spanned map.

Both of the aforementioned criteria are characteristic of operating conditions in which a HC loading in the SCR catalyst can be reduced, in particular because they describe - indirectly or directly - conditions in which a temperature in the range of the SCR catalyst and in particular a temperature of the the SCR catalyst flowing through the exhaust stream is high enough to desorb adsorbed in the SCR catalyst hydrocarbons.

Times when there are operating conditions of the exhaust gas line that are not suitable for regeneration of the SCR catalyst, for example because they are either neutral with respect to the HC loading or rather lead to a build-up of an HC load, are not preferred recorded as regeneration times and added to the regeneration period. The regeneration period is therefore a measure of in which Scope a regeneration of the SCR catalyst, that is, in particular a desorption of hydrocarbons, has taken place.

According to a preferred embodiment of the method, it is possible that only a continuous time interval is detected as a regeneration period, in which for the regeneration of the SCR catalyst suitable operating conditions of the exhaust line are present, wherein the detection of the regeneration period is aborted when an operating state occurs, not is suitable for the regeneration of the SCR catalyst. The detection of the regeneration period can then be restarted if there is again an operating state which is suitable for the regeneration of the SCR catalytic converter, wherein preferably then the previously detected value of the regeneration period is set to zero.

If the regeneration time duration reaches or exceeds the predetermined maximum value, it can be assumed that the SCR catalytic converter is regenerated at least to the extent that a change to the second operating mode, and therefore to normal operation, makes sense. The first mode is then preferably terminated, and it is changed to the second mode.

This algorithm proposed here with the detection of the regeneration time duration in the first mode of operation is intended to bring about in an advantageous manner in an operation of the exhaust system with higher exhaust gas temperatures and / or an internal combustion engine with higher loads connected to the exhaust line after a predetermined maximum period in the regular operation is changed. It is thus effectively avoided that the first mode is continued ad infinitum. However, if operating conditions of the exhaust gas line, in which a HC load is established again, or the engine goes back to a very low load point, can also be changed back to the first mode, or it can be at operating conditions that a very high load of SCR catalyst with hydrocarbons suggest, also the dosage of the reducing agent completely switched off again, thus be changed to the third mode.

According to one development of the invention, it is provided that a first degree of loading of the SCR catalyst with lighter hydrocarbons is estimated, wherein a second degree of loading of the SCR catalyst with heavier hydrocarbons is estimated. In particular, the terms "lighter" and "heavier" refer to lighter hydrocarbons having shorter chain hydrocarbon molecules than heavier hydrocarbons, the heavier hydrocarbons having longer chain molecules than the lighter hydrocarbons. Analogously, the terms may also refer to a molecular weight or density of hydrocarbons, with lighter hydrocarbons having a low molecular weight or density than heavier hydrocarbons. A boundary between lighter hydrocarbons and heavier hydrocarbons with respect to the chain length, the molecular weight and / or the density may be suitably drawn depending on the direction of the process, concrete operating conditions of the internal combustion engine and / or the exhaust line, and a fuel used to operate the internal combustion engine become.

The first degree of loading and the second degree of loading are preferably calculated, in particular by means of an HC loading computer and / or a preferably physically motivated model of the HC load.

The exhaust gas train is preferably operated in the first operating mode if both the first load level and the second load level are smaller than a first load limit value, wherein at least one load level selected from the first load level and the second load level is greater than a second load limit value.

The exhaust gas train is preferably operated in the second operating mode if both the first load level and the second load level are smaller than the second load limit value.

Alternatively or additionally, it is preferable to refrain from introducing reducing agent into the exhaust gas line, that is, in particular not actuating the metering device in the third operating mode if at least one degree of loading, selected from the first loading level and the second loading level, is greater than the first loading limit value.

In this case, the first loading limit value is greater than the second loading limit value.

With this logic, and by properly selecting the first loading threshold and the second loading threshold, the following is achieved:
If at least one of the loading levels is greater than the first, larger loading limit value, it is assumed that there is such a high HC loading that it does not make sense to introduce reducing agent into the exhaust gas line. It would then only very high reductant emissions occur downstream of the SCR catalyst, because due to the HC loading no adequate nitrogen oxide conversion can be achieved. Therefore, will dispensed with a contribution of reducing agent in the exhaust system, so the third mode selected.

If the first loading limit value and the second loading limit value are both smaller than the second, smaller loading limit value, it is assumed that there is only a very small HC loading of the SCR catalytic converter, so that a regular operation or normal operation can be carried out, hence the second operating mode makes sense is. Triggering the breakthrough detection is then attributed to aging of the SCR catalyst as the cause, and a suitable measure is taken.

If, on the other hand, at least one of the loading limit values is greater than the second, smaller loading limit value and, at the same time, both loading limit values are smaller than the first, larger loading limit value, it can be assumed that an HC loading of the SCR catalytic converter is present, but this is within one range which justifies the execution of the first operating mode, and thus the trial operation. In particular, it is then possible to start a regular metering of the reducing agent, although triggering the breakthrough recognition is interpreted as indicating that the HC load is still too high. As a result, a suitably appropriate measure is then taken; in particular, the metering of the reducing agent for the predetermined switch-off period is then omitted. After expiry of the shutdown period, reductant can again be metered into the exhaust gas line, in particular to check whether the HC load is still too high. The execution of the first mode of operation may be continued until either no breakthrough is detected, in which case the regular dosage of the reducing agent is continued, or until the detected regeneration period reaches or exceeds its predetermined maximum value, in which case it is possible to change to the second mode.

It is possible that exactly two load levels are used. Alternatively, it is also possible that more than two degrees of loading are used, with a finer subdivision of the hydrocarbons and the loading of the SCR catalyst is possible. The previously discussed logic may then be extended accordingly to account for the finer subdivision of the load levels.

According to a preferred, simpler embodiment of the method, it is also possible, instead of a plurality of degrees of loading, which are assigned to different types of hydrocarbons, to use only an overall degree of loading and to use them in the sense of the logic explained above. In this case, it is preferably provided that an overall degree of loading of the SCR catalytic converter with hydrocarbons is estimated, wherein the exhaust line is operated in the first mode, when the total load level is less than a first total load limit and at the same time greater than a second total Load limit is. The first total loading limit value is greater than the second total loading limit value.

Alternatively or additionally, the exhaust line is operated in the second mode when the total load level is less than the second total load threshold.

Alternatively or additionally, the metering device is not actuated if the total degree of loading is greater than the first total loading limit value.

In this context, a total degree of loading is understood as meaning, in particular, a degree of loading of the SCR catalyst integrated as it were over all hydrocarbons, in which no distinction is made between different chain lengths, molar masses, densities or the like.

As already indicated, this corresponds to the logic already explained above in connection with the first and second degrees of loading, according to which a very high HC load can be assumed, applied to the total loading level on which the loading is based, if the overall load factor is greater as the first, larger total load limit, so that a dosage of reducing agent in the exhaust line is not useful. If, on the other hand, the total degree of loading is less than the first, larger overall loading limit value and, at the same time, greater than the second, smaller total loading limit value, there is an HC loading in which the first operating mode and thus the trial operation make sense. It can be checked whether there is still a relevant HC loading, and this can be reduced if necessary. If, on the other hand, the total degree of loading is less than the second, smaller total loading limit value, it can be assumed that the HC load is very low, so that operation of the exhaust line in the second operating mode and thus normal operation makes sense.

According to one embodiment of the invention, it is provided that the temporal evaluation of the operating state of the exhaust gas line is carried out in which a temperature in the range of the SCR catalyst - that is, in particular a temperature measured on or in the SCR catalyst, or preferably immediately upstream of the SCR catalyst measured exhaust gas temperature - is detected as a function of time, wherein a value for a switch-off duration is determined as a function of the detected temperature. In particular, an instantaneous temperature in the region of the SCR catalytic converter is detected and, depending on this, an instantaneous value for the switch-off duration is determined in each case. The thus determined values for the switch-off duration are integrated in time to an integral switch-off duration, in particular added up. In this way, the integral switch-off duration can be used as an index or characteristic parameter for an evaluation of the previous operation of the exhaust gas line, wherein, as will be explained in more detail below, it allows an estimation of the HC load of the SCR catalytic converter. The instantaneous values for the switch-off duration are preferably read from a characteristic in which values for the switch-off duration are stored as a function of the temperature. In particular, it is provided that lower temperatures are assigned higher values for the switch-off duration, while higher temperatures are assigned lower values for the switch-off duration. On the basis of the integral switch-off duration, it is thus possible in particular to determine how long and / or to what extent high temperatures have prevailed in the region of the SCR catalytic converter that are suitable for preventing or reducing HC load. In this case, it is also possible, in particular, for temperatures which are suitable for reducing the HC charge of the SCR catalytic converter, which in particular therefore represent suitable operating states of the exhaust gas line for regeneration of the SCR catalytic converter, to be assigned negative values for the switch-off duration. An integral turn-off duration built up by summing up positive values of the turn-off duration can then be reduced or integrated down at temperatures suitable for the regeneration of the SCR catalyst. In this case, due to the weighting carried out by means of the characteristic curve, in particular the colder the previously prevailing temperatures of the SCR catalytic converter, the longer the higher temperatures have to be achieved in order to reduce the HC load that has occurred.

The integral turn-off duration is preferably limited to zero down. This makes sense, because otherwise it would be possible to achieve a large integral negative switch-off duration that is so great in terms of its magnitude during prolonged operation of the exhaust gas line at high temperatures that it could not be brought into positive range even if conditions exist cause a very high HC loading of the SCR catalyst. As a result, even a very high HC loading of the SCR catalyst could no longer be reliably detected. Therefore, although negative values are preferably allowed for the current turn-off duration, the integral turn-off duration must not become less than zero.

According to one development of the invention, it is provided that the exhaust gas line is operated in the first operating mode when the integral switch-off duration is less than a first switch-off duration limit and at the same time greater than a second switch-off duration limit value.

Alternatively or additionally, the exhaust gas line is preferably operated in the second operating mode if the integral switch-off duration is less than the second switch-off duration limit value.

Alternatively or additionally, an introduction of reducing agent into the exhaust gas line is omitted, and therefore in particular the metering device is not activated if the integral switch-off time is greater than the first switch-off time limit value.

In this case, the first switch-off duration limit is greater than the second switch-off duration limit value.

This corresponds to the logic already explained above in connection with the degree of loading, according to which a very high HC load can be assumed, applied to the shutdown duration considered here, if the integral turn-off time is greater than the first, larger turn-off duration limit, so that metering of reducing agent in the exhaust system does not make sense. If, on the other hand, the integral switch-off duration is shorter than the first, larger switch-off duration limit and, at the same time, greater than the second, smaller switch-off duration limit value, there is an HC load in which the first operating mode and thus the trial operation make sense. It can be checked whether there is still a relevant HC loading, and this can be reduced if necessary. If, however, the integral switch-off duration is shorter than the second, smaller switch-off duration limit value, it can be assumed that the HC load is very low, so that operation of the exhaust gas line in the second operating mode and thus normal operation make sense.

It is possible that the integral turn-off duration is also used at the same time as the predetermined turn-off period in the first operating mode, for which an introduction of reducing agent into the exhaust gas line is omitted if a break-through is detected. However, it is also possible for the integral switch-off duration to be used merely as a measure of the HC charge of the SCR catalytic converter, wherein the predetermined switch-off time duration for the first operating mode is chosen to be different from and especially independent of the integral switch-off duration.

According to a simpler embodiment of the method, it is possible, the HC loading of the SCR catalyst by simple temporal evaluation of the operating state or the Estimate operating conditions of the exhaust system or make it plausible, with a weighting is omitted. In this case, for example, an operation of the exhaust system at low exhaust gas temperatures - in particular below a certain exhaust gas temperature limit - are integrated in time, and this can be used as a measure of the HC load. A corresponding integral can also be integrated down with higher exhaust gas temperatures during operation of the exhaust gas system.

Additionally or alternatively, it is possible aufintegrieren only operating times at higher temperatures above a predetermined exhaust gas limit temperature and compare the integral or the sum in particular with a maximum duration determined for this purpose, wherein a detected breakthrough after this predetermined maximum duration of aging of the SCR catalyst are assigned and the exhaust system is operated in the second mode, is assumed before the expiry of this predetermined maximum duration of a possible HC load, and the exhaust system is operated in particular in the first mode.

The various limit values and / or threshold values described here can preferably be parameterized, with particular preference still being able to be set during operation of the exhaust gas aftertreatment system, either during operation or, if appropriate, during maintenance or inspection. In this way, the method with high flexibility is feasible.

The object is also achieved by providing an exhaust aftertreatment system having an exhaust line with an SCR catalyst, a metering device for introducing reductant into the exhaust line upstream of the SCR catalyst, and a breakthrough detection means for detecting a breakdown of the SCR catalyst. The AGN system preferably has estimating means for estimating HC loading of the SCR catalyst based on at least one parameter representing the HC loading of the SCR catalyst. The exhaust gas aftertreatment system is set up in a first operating mode at least in response to the at least one parameter, in particular as a function of the estimation of the HC loading of the SCR catalytic converter by the estimation means, in response to a breakthrough of the SCR catalytic converter detected by the breakthrough detection means perform a measure in response to the HC loading of the SCR catalyst, or perform in a second mode at least one measure to adjust the operation of the exhaust line to an aging of the SCR catalyst. The system is preferably configured to carry out one of the previously described embodiments of the method. In connection with the exhaust aftertreatment system, in particular, the advantages that have already been explained in connection with the method.

The exhaust aftertreatment system preferably has a control device, which preferably has the estimation means. Preferably, the control device is operatively connected to the metering device and is set up to control the metering device as a function of the at least one parameter representing the HC loading of the SCR catalytic converter. The control device may in particular be the control unit of an internal combustion engine to which the exhaust aftertreatment system is assigned, or the control device may be part of the control unit of the internal combustion engine or cooperate with the control unit of the internal combustion engine. But it is also possible that the control device is provided as a separate, independent of the control unit of the internal combustion engine control device of the exhaust aftertreatment system.

According to a preferred embodiment, it is provided that the exhaust aftertreatment system is free of an oxidation catalyst upstream of the SCR catalyst in the exhaust line, and / or that the exhaust aftertreatment system is free of a blocking catalyst downstream of the SCR catalyst in the exhaust line. In particular, a barrier catalyst is understood as meaning a catalyst which is set up for the oxidation of unreacted reducing agent in order to reduce or prevent reductant emissions into the environment. In particular, the barrier catalyst may be adapted to oxidize ammonia to nitrogen oxides. Such a barrier catalyst is also referred to as anti-slip catalyst (ASC).

Thus, the exhaust aftertreatment system particularly preferably does not have an oxidation catalytic converter arranged upstream of the SCR catalytic converter and no barrier catalytic converter arranged downstream of the SCR catalytic converter. In particular, in such an exhaust aftertreatment system, the advantages of the method and of the exhaust-gas aftertreatment system described here are realized, since operation of such an exhaust-gas aftertreatment system is very critical with regard to HC loading of the SCR catalyst and reductant breakthrough. Namely, an oxidation catalyst provided upstream of the SCR catalyst usually reduces the entry of hydrocarbon emissions into the SCR catalyst in certain temperature ranges because hydrocarbon molecules are reacted in the oxidation catalyst. A barrier catalyst mitigates the effects of HC loading by a breakthrough Reductant emissions that emerge from the SCR catalyst are reacted in the barrier catalyst at least to some extent in other substances, in particular nitrogen oxides and nitrogen.

But it is also possible that the exhaust aftertreatment system comprises an oxidation catalyst upstream of the SCR catalyst and / or a barrier catalyst downstream of the SCR catalyst. Even then, the implementation of the method and the previously described embodiment of the exhaust aftertreatment system is useful and advantageous.

According to one embodiment of the invention, it is provided that the SCR catalyst comprises iron zeolite or is made of iron zeolite. It is also possible that the SCR catalyst has vanadium or is made of vanadium or vanadium-based. In this case, the advantages of the process and the exhaust aftertreatment system are realized in a special way, because especially those SCR catalysts show a strong tendency to HC adsorption and have a high HC storage capacity.

According to one embodiment of the invention, it is provided that the exhaust aftertreatment system has a switchable exhaust gas bypass path to the SCR catalyst. In particular, depending on the operating point, at least a portion of the exhaust gas stream can be conducted past the SCR catalytic converter along the exhaust gas bypass path. In particular, during low load operation, exhaust gas can be routed around and thus not around the SCR catalyst to avoid build up of HC loading in the SCR catalyst as much as possible. For this purpose, preferably corresponding actuators, in particular exhaust valves, and additional line sections are required. However, such exhaust valves are usually not completely sealed. It can therefore exhaust gas leakage pass into the SCR catalyst, so that nevertheless an HC loading can be established. This can then be suitably reacted within the scope of the method and with the exhaust aftertreatment system proposed here.

Finally, the object is also achieved by providing an internal combustion engine having an exhaust aftertreatment system according to one of the embodiments described above. In particular, the advantages that have already been explained in connection with the method and the exhaust-gas aftertreatment system are realized in connection with the internal combustion engine.

The internal combustion engine is preferably designed as a reciprocating engine. It is possible that the internal combustion engine is arranged to drive a passenger car, a truck or a commercial vehicle. In a preferred embodiment, the internal combustion engine is used to drive in particular heavy land or water vehicles, such as mine vehicles, trains, the internal combustion engine is used in a locomotive or a railcar, or ships. It is also possible to use the internal combustion engine to drive a defense vehicle, for example a tank. An exemplary embodiment of the internal combustion engine is preferably also stationary, for example, used for stationary power supply in emergency operation, continuous load operation or peak load operation, the internal combustion engine in this case preferably drives a generator. A stationary application of the internal combustion engine for driving auxiliary equipment, such as fire pumps on oil rigs, is possible. Furthermore, an application of the internal combustion engine in the field of promoting fossil raw materials and in particular fuels, for example oil and / or gas, possible. It is also possible to use the internal combustion engine in the industrial sector or in the field of construction, for example in a construction or construction machine, for example in a crane or an excavator. The internal combustion engine is preferably designed as a diesel engine, as a gasoline engine, as a gas engine for operation with natural gas, biogas, special gas or another suitable gas. In particular, when the internal combustion engine is designed as a gas engine, it is suitable for use in a cogeneration plant for stationary power generation.

The description of the method on the one hand and the exhaust aftertreatment system and the internal combustion engine on the other hand are to be understood as complementary to one another. Features of the exhaust aftertreatment system and the internal combustion engine that have been explained explicitly or implicitly in the context of the method are preferably individually or combined with each other features of a preferred embodiment of the internal combustion engine or the exhaust aftertreatment system. Method steps which have been explicitly or implicitly described in connection with the exhaust aftertreatment system or the internal combustion engine are preferably individually or combined with each other steps of a preferred embodiment of the method. This is preferably characterized by at least one method step, which is due to at least one feature of an inventive or preferred embodiment of the exhaust aftertreatment system or the internal combustion engine. The internal combustion engine and / or the exhaust gas aftertreatment system are preferably characterized by at least one feature which is characterized by at least one Process step of an inventive or preferred embodiment of the method is conditional.

The invention will be explained in more detail below with reference to the drawing. Showing:

1 a schematic representation of an embodiment of an internal combustion engine with an exhaust aftertreatment system;

2 a schematic overview of an embodiment of the method;

3 a schematic detail of an embodiment of the method;

4 a schematic detail of another embodiment of the method, and

5 a detailed representation of another embodiment of the method.

1 shows a schematic representation of an embodiment of an internal combustion engine 1 with an exhaust aftertreatment system 3 , where here is an engine block 5 the internal combustion engine 1 with an exhaust system 7 the exhaust aftertreatment system 3 connected such that the exhaust gas of the internal combustion engine 1 from the engine block 5 along the exhaust line 7 , in particular in the direction of an arrow P, can be performed. The exhaust system 7 has an SCR catalyst 9 which is set up for the selective catalytic reduction of nitrogen oxides. Upstream of the SCR catalyst 9 is in the exhaust system 7 a metering device 11 arranged, which is adapted to reducing agent, which is also a reducing agent precursor product, in particular a urea-water solution, understood, in the exhaust line 7 contribute.

The AGN system 3 has a breakthrough detection means 13 which is set up for a breakthrough of the SCR catalyst 9 that is, in particular, an emission of unreacted reducing agent from the SCR catalyst 9 to recognize. The breakthrough detection means 13 preferably has a control device 15 acting as a control unit for the internal combustion engine 1 designed and for controlling the engine block 5 can be operatively connected with this, as well as at least a first exhaust gas sensor element 17 on, which can be configured as a reducing agent sensor for measuring a reducing agent concentration in the exhaust gas, but preferably in particular as a nitrogen oxide sensor. Namely, by means of a nitrogen oxide sensor, namely, the reducing agent concentration in the exhaust gas can be measured, if ammonia as a reducing agent in the SCR catalyst 9 is used because nitrogen oxide sensors have a cross-sensitivity to ammonia. The control device 15 is with the first exhaust gas sensor element 17 operatively connected. The first exhaust gas sensor element 17 is downstream of the SCR catalyst 9 in the exhaust system 7 arranged.

In addition, a second exhaust gas sensor element is preferred 19 along the exhaust line 7 disposed upstream of the SCR catalyst, wherein the second exhaust gas sensor element 19 can be designed as a reducing agent sensor or as a nitrogen oxide sensor. The second exhaust gas sensor element 19 is also with the controller 15 operatively connected. Breakthrough detection can in particular be done by evaluating measuring signals of the first exhaust gas sensor element 17 , but preferably by evaluating measuring signals of both the second exhaust gas sensor element 19 as well as the first exhaust gas sensor element 17 be performed. The control device 15 is also with the metering device 11 operatively connected to the control and in particular to a quantity control of the dosage of the reducing agent, wherein also in the control device 15 present control information for the metering device 11 to detect a breakthrough of the SCR catalyst 9 can be used.

The exhaust aftertreatment system 3 preferably has an estimation means 21 for estimating HC loading of the SCR catalyst 9 based on at least one of the HC loading of the SCR catalyst 9 representing parameters. Here is the estimator 21 here in the controller 15 integrated, in particular as a hardware module part of the control device 15 or as a software-based estimation means, in particular as a software module, in the control device 15 can be implemented.

Immediately upstream of the SCR catalyst 9 is still a temperature sensor 23 for measuring an exhaust gas temperature in the exhaust line 7 arranged, which is also connected to the control device 15 is operatively connected, so that the exhaust gas temperature immediately upstream of the SCR catalyst 9 - Especially as a temperature in the range of the SCR catalyst 9 - By the controller 15 is detectable.

The exhaust aftertreatment system 3 is set to one of the breakthrough detection means 13 recognized breakthrough of the SCR catalyst 9 depending on the at least one HC loading of the SCR catalyst 9 representative parameters in a first mode at least one measure in response to the HC loading of the SCR catalyst 9 but at least in a second mode at least one measure for adjusting the operation of the exhaust line 7 to an aging of the SCR catalyst 9 perform.

The control device 15 is with the metering device 11 in particular operatively connected and adapted to control the same as a function of the at least one, the HC loading of the SCR catalyst 9 representing parameters.

The embodiment of the exhaust aftertreatment system shown here 3 is particularly free from an oxidation catalyst upstream of the SCR catalyst 9 so it does not have an oxidation catalyst upstream of the SCR catalyst 9 on. The exhaust aftertreatment system 3 is also free of a barrier catalyst downstream of the SCR catalyst 9 Thus, in particular it does not have a barrier catalyst downstream of the SCR catalyst 9 on.

The SCR catalyst 9 It preferably has iron zeolite or vanadium, or it is made of iron zeolite or vanadium.

Only schematically indicated here is that the exhaust aftertreatment system 3 prefers an exhaust gas bypass path 25 around the SCR catalyst 9 wherein the exhaust bypass path 25 is formed switchable, that operating point dependent, in particular dependent on a load point of the internal combustion engine 1 , Exhaust gas around the SCR catalyst 9 can be conducted around. It is particularly preferably provided that at low load points and / or at low exhaust gas temperatures, the highest possible proportion of the exhaust gas flow, preferably the complete exhaust gas flow, along the switchable Abgasumgehungspfads 25 is directed to the SCR catalyst 9 if possible keep unburned hydrocarbons in the exhaust gas. As a complete flow around the SCR catalyst 9 However, in principle can not be guaranteed, it makes sense nevertheless, the method proposed here also in connection with an exhaust aftertreatment system 3 perform such a exhaust bypass path 25 having.

But it is also very well an embodiment of the exhaust aftertreatment system 3 possible, in which no exhaust gas bypass path 25 is provided.

2 shows a first schematic overview of an operation of a first embodiment of the method for operating the exhaust aftertreatment system 3 , in particular the exhaust aftertreatment system 3 according to 1 , Schematically, here is the breakthrough detection means 13 presented as well as a decision-making tool 27 which decides in what way to a detected breakthrough of the SCR catalyst 9 should be reacted. The decision-making tool 27 may be part of the estimator 21 be or with this interaction. It may be the decision-making tool 27 the exhaust aftertreatment system 3 in particular switching between the first mode schematically indicated here 29 and also indicated second mode 31 , wherein in the first mode 29 at least one measure in response to a detected HC loading of the SCR catalyst 9 is performed, wherein in the second mode 31 at least one measure to adjust the operation of the exhaust line 7 to an aging of the SCR catalyst 9 is carried out. The decision between the first mode 29 and the second mode 31 in particular, a decision as to whether the detected breakthrough of increased HC loading of the SCR catalyst 9 or aging of the SCR catalyst 9 is assigned. In the first mode, in response to a detected breakthrough, introduction of reductant into the exhaust line 7 preferably refrain for a predetermined shutdown period. In the second mode 31 For example, in response to a detected breakthrough, an aging map is preferably changed, in particular to a reduced maximum conversion rate, the aging map for controlling the introduction of reducing agent into the exhaust gas line 7 is used, in particular for quantity control.

A third mode in which no reducing agent in the exhaust line 7 is introduced is in 2 therefore not shown, because in this case no breakthrough on the SCR catalyst 9 can be detected, so this case for the schematic representation according to 2 is not relevant.

The decision-making tool 27 makes the decision between the first mode 29 and the second mode 31 in particular as a function of at least one of the HC loading of the SCR catalyst 9 representing parameters. In particular, this parameter can be a calculated loading of the SCR catalyst 9 be hydrocarbons; In this respect, here is schematically a HC loading computer 33 implied, its result in the decision of the decision-making 27 can flow into it. The parameter may additionally or alternatively also be a result of a temporal evaluation of an operating state of the exhaust gas line 7 In this respect, schematically here a first evaluation means 35 is shown, which is set up to an operating history of the exhaust system 7 and the decision-making tool 27 to provide a corresponding result for decision.

The parameter may additionally or alternatively also be a result of an evaluation of a course of measures for adjusting the operation of the exhaust gas line 7 an aging of the SCR catalyst; In this respect, here is schematically a second evaluation 37 illustrated, which is configured to evaluate a corresponding course of measures, the second evaluation means 37 is set up in particular to evaluate changes in the aging map. The second evaluation means 37 is set up to be the decision-making tool 27 to provide a result of its evaluation for decision making.

Finally, it is alternatively or additionally possible for the parameter to be a time duration for at least one specific operating state or operating state region of the exhaust gas line 7 is. In that regard, here is a control 39 which is set up to detect such a time duration and to transmit corresponding information to the decision-making means 27 or to control the decision-making means 27 depending on this period of time.

In the first mode 29 and in the second mode 31 Reducing agent is in the exhaust system 7 introduced, the metering device 11 is thus activated for the introduction of reducing agent. However, it is possible that, depending on the at least one parameter, introduction of reducing agent into the exhaust gas line 7 is omitted, the metering device 11 then in particular - in the third mode - is not driven, which will be explained in more detail below.

3 shows a schematic representation of a detail of an embodiment of the method. Identical and functionally identical elements are provided with the same reference numerals, so that reference is made to the preceding description. Here again is the breakthrough detection means 13 shown, as well as the first mode 29 symbolizing arrow, the result of the breakthrough detection means 13 Whether in the positive case, a breakthrough was detected or in the negative case, no breakthrough was detected, as well as the answer to the question whether - in the positive case - the first mode is currently present, or whether this - in the negative case - is not present here a first digestive limb 41 be linked together in the sense of a logical AND connection. Is both the first mode 29 before and at the same time a breakthrough was detected, in a first step S1, the introduction of reducing agent in the exhaust system 7 for the predetermined shutdown time t _D omitted. In an in 3 1, it is shown that the predetermined switch-off time period t _{D is} preferably read from a first characteristic curve K 1, which values for the predetermined switch-off time period t _D as a function of the temperature T in the region of the SCR catalytic converter 9 includes. The temperature T is preferred with the in 1 illustrated temperature sensor 23 or alternatively directly on or in the SCR catalyst 9 measured.

After the predetermined switch-off period t _D has elapsed, the regular metering of the reducing agent into the exhaust gas line is preferably carried out 7 restarted, being - as long as the first mode 29 If there is a breakthrough once again, the dosage for the predetermined switch-off time period t _{D is} omitted.

4 shows a further detailed representation of an embodiment of the method. Identical and functionally identical elements are provided with the same reference numerals, so that reference is made to the preceding description. It is shown here that the HC loading computer 33 a first degree of loading 45 for the loading of the SCR catalyst 9 with lighter hydrocarbons and a second degree of loading 47 calculated for a loading of the SCR catalyst with heavier hydrocarbons, in which lighter hydrocarbons in particular have a shorter average chain length than heavier hydrocarbons. Alternatively or additionally, the terms "lighter" and "heavier" may also refer to a molecular weight and / or a density of the hydrocarbons. The first degree of loading 45 and the second degree of loading 47 be in a comparison step 49 each with a first loading limit 51 and with a second loading limit 53 compared. The first loading limit 51 is greater than the second loading limit 53 , The results of the comparison with the first loading limit 51 go into a second digestive tract 55 a, wherein the results of the comparison with the second loading limit 53 in a first Veroderungsglied 57 received.

The results of the second digestive tract 55 and the first verifier 57 go again into a third Verundungsglied 59 in, in which additionally a Dosierfreigabe 61 for the reducing agent is received. This dosing release 61 has the truth value "true" when the exhaust line 7 and / or the internal combustion engine 1 be operated in an operating condition, which generally allows a dosage of reducing agent. This is particularly responsive to an exhaust gas temperature, which must be above a certain exhaust gas threshold, so that in principle the dosage of the reducing agent can be released. Only if the dosing release 61 has the truth value "true", reducing agent can be metered at all, a metering of reducing agent but may be due to further circumstances be omitted. The result of the third digestive tract 59 goes into a fourth Verundungsglied 63 which also includes a regeneration time period evaluation 65 enters, whose truth value is "true", as long as a predetermined maximum value for a regeneration period is not reached, which will be explained in more detail below.

First, but the regeneration time duration evaluation 65 and the fourth digestive limb 63 disregard to explain the basic operation of the remaining logic. Thus, in the following, a representation of this mode of operation will be given which, for the sake of simplified illustration, assumes that the fourth rounding element 63 and the regeneration time period evaluation 65 would not be present: This shows that the result of the second Verundungsglieds 55 then "true" is when both the first degree of loading 45 as well as the second degree of loading 47 are smaller than the first loading limit 51 , In any other case, the result is the second digestive device 55 "not correct". The result of the first Veroderungsglieds 57 is then "true" if at least one degree of loading selected from the first degree of loading 45 and the second degree of loading 47 , greater than the second loading limit 53 , or if both load levels 45 . 47 are greater than the second loading limit 53 , On the other hand, are both load levels 45 . 47 less than the second loading limit 53 , is the result of the first Veroderungsglieds 57 "not correct".

In combination with the third digestive limb 59 and under the proviso that the dosing 61 is positive, then the following logic results: The first mode 29 is selected if, on the one hand, the first load level 45 and the second degree of loading 47 both are smaller than the first load limit 51 , Wherein at least one degree of loading, selected from the first degree of loading 45 and the second degree of loading 47 , greater than the second loading limit 53 ,

Not explicitly shown in 4 in that preferred in the second mode 31 is switched when the first load level 45 and the second degree of loading 47 both are smaller than the second load limit 53 , In this case, it is assumed that the HC loading of the SCR catalyst 9 either not present or at least so low that the exhaust system 7 can be operated in normal operation, with a detected breakthrough aging of the SCR catalyst 9 can be assigned.

Also not explicitly shown in 4 in that it is preferred to switch to the third operating mode, that is to say to introduce reducing agent into the exhaust gas line 7 completely dispensed with or the metering device 11 is not controlled if at least one of the load levels 45 . 47 is greater than the first load limit 51 , In this case it is assumed that the HC loading of the SCR catalyst 9 is so high that a dosage of reducing agent does not make sense.

The loading limits 51 . 53 are preferably parameterizable. In particular, they are selected such that the previously explained logic can be usefully carried out, in particular the first loading limit value 51 an HC loading of the SCR catalyst 9 depicts, at or above which no dosage of reducing agent makes more sense, the second loading limit 53 a loading threshold for the SCR catalyst 9 below which a normal operation and an assignment of a breakthrough to an aging of the SCR catalyst 9 makes sense.

The following is now closer to the meaning of the fourth Verundungsglieds 63 as well as the regeneration time period evaluation 65 received: Is or is the first mode 29 Namely, a regeneration time period is preferably detected while one for a regeneration of the SCR catalyst 9 suitable operating state of the exhaust system 7 is present. This is when the result of the third digestive 59 "True" becomes an evaluation 67 the operating state of the exhaust system 7 and / or the internal combustion engine 1 started, in particular a load point of the internal combustion engine 1 can be evaluated. But it is also possible that here in particular from the temperature sensor 23 measured temperature T is evaluated. A combination of these types of evaluation is possible. Anyway, in the evaluation 67 checked whether the current operating state for the regeneration of the SCR catalyst 9 is suitable, that is to say, conditions exist because of which hydrocarbons from the SCR catalyst 9 be desorbed. At the same time as the start of the evaluation 67 In a second step S2, a time counter is also set to zero, so that a time detection for the regeneration time period restarts. In a third step S3, the times are respectively recorded in which for a regeneration of the SCR catalytic converter 9 suitable operating conditions of the exhaust system 7 present, these times are combined into a regeneration period. The regeneration period is compared with a predetermined maximum value, and as a regeneration period evaluation 65 is returned, whether the regeneration period has not reached or exceeded the predetermined maximum value. The truth value of the regeneration time period evaluation 65 is "true" as long as the predetermined maximum value has not yet been reached or is exceeded, it is "wrong" as soon as the predetermined maximum value is reached or exceeded.

This leads in connection with the fourth rounding member 63 ultimately, that the first mode 29 is executed as long as the regeneration period has not yet reached or exceeded the predetermined maximum value, wherein the first mode 29 is left when the regeneration period reaches or exceeds the predetermined maximum value. Preferably, in this latter case then in the second mode 31 changed.

In a second diagram D2 and in a third diagram D3 are criteria for the evaluation 67 shown. According to the second diagram D2 are suitable operating states of the internal combustion engine 1 and at the same time the exhaust system 7 in particular those in which a pair of values comprising the torque M of the internal combustion engine 1 and whose speed n, above a second characteristic K2, which represents in particular a first specific limit characteristic is. Suitable operating conditions of the internal combustion engine 1 and / or the exhaust line 7 are according to the third diagram D3 and those in which a pair of values, including the temperature T in the range of the SCR catalyst 9 , in particular the means of the temperature sensor 23 measured temperature, and an exhaust gas mass flow dm in the region of the SCR catalyst 9 , above a third characteristic K3, which in particular represents a second specific limit characteristic. Preferably, both of the conditions mentioned here are evaluated, with a time being recorded as a contribution to the regeneration period if at least one of the conditions mentioned is met at that time.

5 shows a further detailed representation of an embodiment of the method. Identical and functionally identical elements are provided with the same reference numerals, so that reference is made to the preceding description. Here is the first evaluation 35 shown, which is set up for temporal evaluation of an operating state of the exhaust system 7 , In the first evaluation means 35 the temperature T is in the range of the SCR catalyst 9 preferred by the temperature sensor 23 is measured, a. The first evaluation device 35 In particular, there is a characteristic curve or weighting curve 69 which comprises values for a switch-off duration t _A as a function of the detected temperature T. By the first evaluation means 35 Now the temperature T is detected time-dependent, using the weighting curve 69 A value for the switch-off duration t _{A is} assigned to the detected temperature T at any point in time, the values for the switch-off duration t _{A determined in this} way being integral with an integral switch-off duration 71 be integrated. In this case, lower measured values of the temperature T are assigned higher values of the switch-off duration t _A than higher measured values of the temperature T. In particular, it is possible that high values of the temperature T, in particular values above 350 ° C., are assigned negative values for the switch-off duration t _A , This is based on the idea that an HC loading of the SCR catalyst 9 occurs more intensively when the exhaust gas temperature T is low, wherein the HC load can be reduced when a higher exhaust gas temperature T is present. The turn-off duration t _A can thus also be integrated down in particular during high-temperature operation T.

The integral switch-off duration 71 is, however, by means of a limiter 73 limited down to zero, to avoid that there is a very strong negative value for the integral turn-off 71 builds up, in which case hardly any actually existing HC-loading of the SCR catalyst 9 could be detected. The so limited integral turn-off 75 is in a second comparison step 77 both with a first shutdown limit 79 as well as with a second shutdown limit 81 wherein the first cut-off duration limit 79 is greater than the second shutdown limit 81 , This is the limited integral switch-off duration 75 less than the first cut-off duration limit 79 and - which is not explicitly shown here - greater than the second cut-off duration limit 81 , will be in the first mode 29 connected. On the other hand, it is the limited integral switch-off time 75 less than the second exhaust duration limit 81 is - initially for the sake of simpler representation, disregarding a second Veroderungsglieds 83 - in the second mode 31 connected. It is not shown explicitly that it is preferred to switch to the third operating mode if the limited integral switch-off duration 75 is greater than the first shutdown limit 79 , The switch-off duration limits 79 . 81 So comes the importance of which in connection with the embodiment according to 4 for the loading limits 51 . 53 was explained. Accordingly, the first shutdown duration limit corresponds 79 preferably also a limit that such a high loading of the SCR catalyst 9 with hydrocarbons that a dosage of reducing agent no longer makes sense, with the second shutdown limit 81 a loading of the SCR catalyst 9 with hydrocarbons that is so low that in any case below this second cut-off duration limit value 81 a normal operation can be performed, wherein a detected breakthrough aging of the SCR catalyst 9 can be assigned. The shutdown duration limits 79 . 81 are preferably parameterizable.

In this embodiment of the method, a possibility is also preferably provided the first mode 29 when the regeneration time period has reached or exceeded a predetermined maximum value, in this embodiment in this case positive as a possibility to change to the second operating mode 31 is shown. For this purpose, in particular the already indicated, second Veroderungsglied 83 intended.

In particular, the temperature T is here in a third comparison step 85 with a limit temperature 87 , which may for example be 350 ° C, compared, in which case when the measured temperature T is the limit temperature 87 exceeds the evaluation 67 is started, here in connection with 4 explained steps of the evaluation 67 and the second step S2 and the third step S3 are shown together. Thus, a regeneration time period is also detected here, while one for a regeneration of the SCR catalytic converter 9 suitable operating state of the exhaust system 7 and / or the internal combustion engine 1 is present, where - as in connection with 4 explains - from this the regeneration time duration evaluation 65 results. This, however, is here in a negative 89 denies or inverts, and the corresponding value is then the second Vererterungsglied 83 fed. According to this logic is now so in the second mode 31 changed if either the limited integral turn-off time 75 becomes smaller than the second cut-off duration limit 81 or when the predetermined maximum value for the regeneration period has been reached or exceeded. This leads - just as in connection with 4 explained, only in slightly different implementation - to that the first mode 29 then leave and especially in the second mode 31 is changed when the predetermined maximum value for the Regeneration period has been reached or exceeded.

For the evaluation 67 can turn - as related to 4 explained - the diagrams D2 and D3 are used.

Overall, it turns out that with the method proposed here and the exhaust aftertreatment system 3 during operation of an SCR catalyst 9 responds properly to its hydrocarbon loading and thus reducing agent emissions can be avoided.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102011011441 B3 [0015, 0015]

Claims (15)

Method for operating an exhaust aftertreatment system ( 3 ), which - an exhaust line ( 7 ) with an SCR catalyst ( 9 ), - a metering device ( 11 ) for introducing reducing agent into the exhaust gas line ( 7 ) upstream of the SCR catalyst ( 9 ), and with - a breakthrough detection means ( 13 ) for detecting a breakthrough of the SCR catalyst ( 9 ), wherein - depending on at least one HC loading of the SCR catalyst ( 9 ) to one of the breakthrough detection means ( 13 ) recognized breakthrough of the SCR catalyst ( 9 ) a) in a first operating mode ( 29 ) at least one measure in response to the HC loading of the SCR catalyst ( 9 ), or b) in a second mode ( 31 ) at least one measure for adjusting the operation of the exhaust line ( 7 ) to an aging of the SCR catalyst ( 9 ) is carried out. A method according to claim 1, characterized in that depending on the at least one of the HC loading of the SCR catalyst ( 9 ) representing the metering device ( 11 ) a) is activated in order to introduce reducing agent into the exhaust gas line ( 7 ) or b) is not activated. Method according to one of the preceding claims, characterized in that as the at least one (the HC loading of the SCR catalyst 9 a) a calculated loading of the SCR catalyst ( 9 ) with hydrocarbons; b) a result of a temporal evaluation of an operating state of the exhaust gas line ( 7 ); c) a result of an evaluation of a course of measures to adjust the operation of the exhaust gas system ( 7 ) to an aging of the SCR catalyst ( 9 ), and / or d) a period of time for at least one specific operating state of the exhaust gas line ( 7 ) is used. Method according to one of the preceding claims, characterized in that a) as the at least one measure in response to the HC loading of the SCR catalyst ( 9 ) for a predetermined shut-off period (t _D ) a contribution of reducing agent in the exhaust line ( 7 ) and / or that b) as the at least one measure to adjust the operation of the exhaust line ( 7 ) to an aging of the SCR catalyst ( 9 ) an aging map is changed, which is used to control the introduction of reducing agent in the exhaust line. Method according to one of the preceding claims, characterized in that the predetermined switch-off time duration (t _D ) depends on a temperature (T) in the region of the SCR catalyst ( 9 ) is selected. Method according to one of the preceding claims, characterized in that in the first operating mode ( 29 ) a regeneration period is detected while the one for a regeneration of the SCR catalyst ( 9 ) suitable operating state of the exhaust line ( 7 ), the first mode ( 29 ) when the regeneration period reaches or exceeds a predetermined maximum value. Method according to one of the preceding claims, characterized in that a first degree of loading ( 45 ) of the SCR catalyst ( 9 ) is estimated with lighter hydrocarbons, wherein a second degree of loading ( 47 ) of the SCR catalyst ( 9 ) is estimated with heavier hydrocarbons, wherein a) the exhaust gas line ( 7 ) in the first mode ( 29 ) when both the first degree of loading ( 45 ) as well as the second degree of loading ( 47 ) are smaller than a first loading limit ( 51 ), and at least one degree of loading, selected from the first degree of loading ( 45 ) and the second degree of loading ( 47 ), is greater than a second loading limit ( 53 ), and / or wherein b) the exhaust gas line ( 7 ) is operated in the second mode when the first degree of loading ( 45 ) and the second degree of loading ( 47 ) are smaller than the second loading limit ( 53 ), and / or wherein c) the metering device ( 11 ) is not activated, if at least one degree of loading, selected from the first degree of loading ( 45 ) and the second degree of loading ( 47 ), is greater than the first loading limit ( 51 ), the first loading limit ( 51 ) is greater than the second loading limit ( 53 ). Method according to one of the preceding claims, characterized in that a total degree of loading of the SCR catalyst ( 9 ) is estimated with hydrocarbons, wherein a) the exhaust gas line ( 7 ) in the first mode ( 29 ) is operated when the total degree of loading is less than a first total loading limit and at the same time greater than a second total loading limit, and / or b) the exhaust line ( 7 ) is operated in the second mode when the total load level is smaller than the second total loading limit, and / or where c) the metering device ( 11 ) is not driven when the total load level is greater than the first total load threshold, wherein the first total load threshold is greater than the second total load threshold. Method according to one of the preceding claims, characterized in that the temporal evaluation of the operating state of the exhaust gas line ( 7 ) is carried out by - a temperature (T) in the region of the SCR catalyst ( 9 ) is detected as a function of time, wherein - a value for a switch-off duration (t _A ) is determined as a function of the detected temperature (T), wherein - the determined values for the switch-off duration (t _A ) coincide with an integral switch-off duration ( 71 ), where - the integral switch-off duration ( 71 ) is preferably limited to zero down. A method according to claim 9, characterized in that a) the exhaust gas line ( 7 ) in the first mode ( 29 ) is operated when the integral switch-off duration ( 71 ) is at the same time smaller than a first cut-off duration limit value ( 79 ) and greater than a second cut-off duration limit ( 81 ), and / or wherein b) the exhaust gas line ( 7 ) in the second mode ( 31 ) is operated when the integral switch-off duration ( 71 ) is less than the second cut-off duration limit ( 81 ) and / or wherein c) the metering device ( 11 ) is not triggered if the integral switch-off duration ( 71 ) is greater than the first cut-off duration limit ( 79 ), where the first cut-off duration limit ( 79 ) is greater than the second cut-off duration limit ( 81 ). Exhaust aftertreatment system ( 3 ), with - an exhaust line ( 7 ), with - an SCR catalyst ( 9 ), - a metering device ( 11 ) for introducing reducing agent into the exhaust gas line ( 7 ) upstream of the SCR catalyst ( 9 ), and with - a breakthrough detection means ( 13 ) for detecting a breakthrough of the SCR catalyst ( 9 ), wherein - the exhaust aftertreatment system ( 3 ) is arranged in dependence on at least one of the HC loading of the SCR catalyzer ( 9 ) to one of the breakthrough detection means ( 13 ) recognized breakthrough of the SCR catalyst ( 9 ) a) in a first operating mode ( 29 ) at least one measure in response to the HC loading of the SCR catalyst ( 9 ), or b) in a second mode ( 31 ) at least one measure for adjusting the operation of the exhaust line ( 7 ) to an aging of the SCR catalyst ( 9 ), the exhaust aftertreatment system ( 3 ) is preferably configured to carry out a method according to one of claims 1 to 10. Exhaust aftertreatment system ( 3 ) according to claim 11, characterized by a control device ( 15 ), which with the metering device ( 11 ) is operatively connected and set up to control the metering device ( 11 ) depending on the at least one of the HC loading of the SCR catalyst ( 9 ) representing parameters. Exhaust aftertreatment system ( 3 ) according to one of claims 11 and 12, characterized in that the exhaust aftertreatment system ( 3 ) is free from a) an oxidation catalyst upstream of the SCR catalyst ( 9 ), and / or of b) a barrier catalyst downstream of the SCR catalyst ( 9 ). Exhaust aftertreatment system ( 3 ) according to one of claims 11 to 13, characterized by a switchable exhaust gas bypass path ( 25 ) around the SCR catalyst ( 9 ). Internal combustion engine ( 1 ), with an exhaust aftertreatment system ( 3 ) according to any one of claims 11 to 14.

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