EP3215725A1

EP3215725A1 - Method for determining a soot load on a particulate filter provided with a selectively catalytic coating

Info

Publication number: EP3215725A1
Application number: EP15786870.4A
Authority: EP
Inventors: Berthold Keppeler; Thorsten Woog
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2014-11-05
Filing date: 2015-10-28
Publication date: 2017-09-13
Also published as: WO2016070972A1; US20170335730A1; DE102014016347A1

Abstract

The invention relates to a method for determining a soot load (65) on a particulate filter (5) provided with a selectively catalytic coating, said method comprising the following steps: determining a nitrogen oxide conversion (45) on the particulate filter (5); and determining a soot load (65) on the particulate filter (5) from the determined nitrogen oxide conversion (45).

Description

A method of determining soot loading of a particulate filter provided with a selectively catalytic coating

The invention relates to a method for determining a soot loading of a particle filter provided with a selectively catalytic coating.

According to current and future emission guidelines, clear limits are provided for emissions from internal combustion engines, especially with regard to hydrocarbon, carbon monoxide, nitrogen oxide and particulate emissions. Due to the

Increasing fuel economy savings in the operation of internal combustion engines, exhaust gas temperatures, which are available for the catalytic exhaust aftertreatment, continue from. For this reason, close-coupled SCR (Selective Catalytic Reduction) systems (SCR) featuring a particle filter with integrated selective catalytic coating or SCR coating close to the engine (SDPF) are playing an increasingly important role in future exhaust aftertreatment concepts in order to meet the increased requirements , It is important for the operating strategy of such an exhaust aftertreatment system, the

Soot loading of the particulate filter to determine as accurately as possible. It turns out that too frequent triggering of a regeneration leads to an increased aging of the applied on the filter catalytic coating and in addition has a higher carbon dioxide and pollutant emission of the internal combustion engine result. On the other hand, if the regeneration is initiated too late, very high temperature gradients can occur within the particle filter, which can lead to its mechanical damage.

European Patent Application EP 2 749 745 A1 discloses a method for determining a soot charge of a particle filter provided with a selectively catalytic coating, in which two different determination methods are combined with one another. On the one hand, a soot emission model or loading model used, which depending on various motor parameters a

Soot emission calculated as well as deposited in the particulate filter and determined by the continuous Rußabbrand with nitrogen dioxide (N0 ₂ ) degraded mass. A further model is used which calculates the soot load by measuring a differential pressure in the exhaust gas flow dropping across the particulate filter (differential pressure model).

The disadvantage of this is that the regeneration of the particulate filter for safety reasons - always for reasons of component protection - is always triggered when one of the two models reaches a maximum allowable deposited in the control unit of the internal combustion engine load limit. It shows that the determination of the soot load from the differential pressure is very inaccurate, especially after a regeneration that has not been completed, which is also called partial regeneration. The soot emission model, for its part, shows very great fluctuations in accuracy depending on the operating point of the internal combustion engine, so that ultimately it becomes too powerful

Deviations between the calculated by the two models soot load values for the particulate filter can come. Overall, this results in a premature regeneration of the particulate filter without it actually being necessary at the time it appears indexed according to one of the models.

The invention has for its object to provide a method which does not have the disadvantages mentioned.

The object is achieved by providing a method having the features of claim 1. Advantageous embodiments emerge from the subclaims.

The object is achieved in particular by a method for determining a

Soot loading of a provided with a selectively catalytic coating particulate filter, namely a particulate filter with a coating which acts selectively catalytically for the reduction of nitrogen oxides, is provided with the following steps: It is determined - especially momentary - nitrogen oxide conversion at the particulate filter, and it is from the certain nitrogen oxide conversion determined - especially momentary - soot loading of the particulate filter. In particular, the soot loading of the particulate filter is determined as a function of the determined nitrogen oxide conversion. Of the

Nitrogen oxide conversion can also be determined by averaging individual within a predetermined time interval of for example a few seconds to a few minutes

Nitrogen conversion values are determined. In that regard, it has been shown that at a provided with a selective catalytic coating particle filter by the spatial combination of the selective catalytic reduction function on the one hand and the particle filter function on the other hand interactions between the soot load of the filter and the nitrogen oxide in the filter wall. Based on this dependence, it is possible to infer from the nitrogen oxide conversion on the soot load of the particulate filter. This method has very high accuracy at least in certain operating ranges and is therefore suitable for determining a highly accurate soot load, which can then be used as the basis for deciding on a regeneration measure without fear of premature regeneration.

In particular, this can also be combined with at least one further determination of the soot load on the basis of at least one further model, this being the case here

addressed, very accurate method can be used in particular to correct a determined based on the further model soot loading, or to correct or adapt the other model itself.

The method is preferably carried out in an exhaust system of an internal combustion engine, wherein the exhaust system is preferably an oxidation catalyst,

in particular a diesel oxidation catalyst (DOC), and / or a nitrogen oxide storage catalyst (NSK). Downstream of the oxidation catalyst and / or the nitrogen oxide storage catalyst seen in the flow direction of the exhaust gas downstream of a system for the selective catalytic reduction of nitrogen oxides is arranged, which has the selective catalytic coating having particle filter. In one embodiment of the method, it is possible for this to be carried out for an SCR system which, in addition to the particle filter provided with the selectively catalytic coating, also has a catalyst for selective catalytic reduction (SCR catalyst) without a particle filter function. This is then preferably arranged downstream of the particle filter provided with the selectively catalytic coating.

Preferably, an exhaust gas recirculation device is additionally used. Particularly preferred is a multi-way exhaust gas recirculation device is used, which is a

Has high pressure exhaust gas recirculation line and a low pressure exhaust gas recirculation line.

In a preferred embodiment of the method, the soot loading from the determined nitrogen oxide is determined by the specific nitrogen oxide is compared with a - preferably stored in a map - nitrogen oxide conversion, which has the provided with the selectively catalytic compound particulate filter, if he is not laden with soot, for example when new or after a complete regeneration. In particular, by comparison with this reference value of the

Particulate filter without soot loading, the current soot load can be determined very accurately.

An embodiment of the method is preferred, which is characterized in that the soot load is determined with the procedure described here, if a - in particular instantaneous - exhaust gas temperature, which is preferably measured by means disposed in the exhaust line upstream of the particulate filter temperature sensor - greater than or equal a predetermined minimum temperature and less than or equal to a predetermined maximum temperature. It has been shown that a clear and in particular clearly evaluable relationship between the nitrogen oxide conversion and the soot load of the particulate filter is given in particular in a certain temperature range for the exhaust gas temperature upstream of the particulate filter. Therefore, the method can be performed with particularly high accuracy in this temperature range. It turns out that the minimum temperature is preferably from at least 175 ° C to at most 210 ° C. Alternatively or additionally, the maximum temperature is preferably from at least 240 ° C to at most 280 ° C. In a preferred embodiment of the method, the soot loading is preferably determined when the exhaust gas temperature upstream of the particulate filter is from at least 150 ° C to at most 300 ° C, preferably from at least 175 ° C to at most 280 ° C, preferably from at least 175 ° C to at most 240 ° C, preferably from at least 210 ° C, to at most 280 ° C, preferably from at least 210 ° C to at most 240 ° C, is. The temperature ranges mentioned here represent particularly suitable ranges for a highly accurate determination of the soot load on the basis of the determined nitrogen oxide conversion. The minimum temperature and / or the maximum temperature can preferably be specified variably in a control unit of an internal combustion engine.

It is also an embodiment of the method is preferred, which is characterized in that for determining the soot load from the specific nitrogen oxide a - especially momentary - ratio of nitrogen dioxide concentration to a total nitrogen oxide concentration in the exhaust gas, which is the sum of the nitrogen dioxide concentration and a nitric oxide concentration (NO), is used upstream of the particulate filter. It has in fact been shown that the

Dependence of the nitrogen oxide conversion on the soot load itself in addition to the ratio of the nitrogen dioxide concentration to the total nitrogen oxide concentration in Exhaust gas depends. In particular, the nitrogen oxide conversion increases with increasing ratio of nitrogen dioxide to total nitrogen oxide with increasing carbon black loading. A very accurate evaluation of the soot loading on the basis of the nitrogen oxide conversion can therefore be carried out if the ratio of nitrogen dioxide to total nitrogen oxide in the exhaust gas is taken into account.

An embodiment of the method is also preferred, which is characterized in that the soot loading is determined when the ratio of the nitrogen dioxide concentration to the total nitrogen oxide concentration in the exhaust gas upstream of the particulate filter is greater than a predetermined minimum value. This can be defined so that in any case a very accurate determination of the soot loading based on the nitrogen oxide conversion is possible. As the sensitivity of the process increases with the increasing ratio of nitrogen dioxide to total nitrogen oxide, it is possible to ensure very high accuracy over a suitable definition of the predetermined minimum value. An embodiment of the method is preferred in which the predetermined minimum value is from at least 10% to at most 50%, preferably from at least 20% to at most 40%, and particularly preferably from at least 30% to at most 50%. In these areas is a highly accurate evaluation of the soot load depending on the particular

Nitric oxide sales ensured.

An embodiment of the method is preferred, which is characterized in that the nitrogen oxide conversion at the particle filter is determined by means of nitrogen oxide sensors arranged upstream and downstream of the particle filter. Such sensors are preferably already provided in the exhaust system, so that it requires no additional, expensive elements for the implementation of the method. The method is therefore very inexpensive feasible. At the same time, the nitrogen oxide conversion at the particulate filter can be determined very accurately using the sensors provided upstream and downstream thereof. In this case, preferably a differential measurement of the total nitrogen oxide concentration in the exhaust gas is carried out between the measuring point upstream and the measuring point downstream of the particle filter. The nitrogen oxide conversion can be determined very easily and very accurately at the same time.

A nitrogen oxide sensor arranged downstream of the particulate filter can also be arranged downstream of an additional SCR catalytic converter provided downstream of the particulate filter and without a particulate filter function. An embodiment of the method is also preferred, which is characterized in that the ratio of the nitrogen dioxide concentration to the total nitrogen oxide concentration in the exhaust gas upstream of the particulate filter based on the - in particular momentary - exhaust gas temperature upstream of the particulate filter or upstream of - in particular upstream of the particulate filter arranged - oxidation catalyst , an exhaust gas mass flow over the oxidation catalyst, and / or an aging state of the oxidation catalyst is determined. The ratio of nitrogen dioxide to total nitrogen oxide is particularly preferably read from a characteristic field as a function of at least one of the parameters mentioned. This is particularly preferably deposited in a control unit of the internal combustion engine which has the exhaust gas line in which the method is carried out. Each of the parameters mentioned here alone characterizes the one mentioned here

Ratio, in particular, the said parameters together allow a very accurate determination of the ratio, so that they are suitable to open a map for the ratio.

An embodiment of the method is also preferred, which is characterized in that the soot loading is compared by comparing the determined nitrogen oxide conversion with a predetermined nitrogen oxide conversion of the unloaded particulate filter, ie without soot loading. The method performed in this way achieves a particularly high accuracy, which has already been described in detail above. In this case, the predetermined nitrogen oxide conversion of the unloaded particulate filter is preferably in

Dependence of an exhaust gas mass flow over the particulate filter, the exhaust gas temperature upstream of the particulate filter, the ratio of nitrogen dioxide to total nitrogen oxide upstream of the particulate filter, a reducing agent loading,

in particular an ammonia loading (NH ₃ ) of the particulate filter, an aging state of the particulate filter and / or an operating point of an internal combustion engine whose exhaust gas line has the particulate filter determined. Particularly preferably, the predetermined nitrogen oxide conversion is read out as a function of at least one of the parameters mentioned here from a characteristic map stored in particular in a control device for the internal combustion engine. Each of the parameters mentioned here is already characteristic of the predetermined nitrogen oxide conversion.

In particular, however, the parameters mentioned here in combination with each other are characteristic of the predetermined nitrogen oxide conversion, so that they are particularly suitable for building up a characteristic diagram for the predetermined nitrogen oxide conversion. In particular, the nitrogen oxide conversion of the non-carbon black is preferred

Particle filter as a function of the exhaust gas mass flow through the particulate filter, the Temperature upstream of the particulate filter, the nitrogen dioxide to nitrogen oxide ratio before the particulate filter, the reducing agent loading of the particulate filter and the

Aging condition of the particulate filter deposited in the control unit and read based on the factors mentioned for the current operating condition of the internal combustion engine. The reducing agent loading of the particulate filter is preferably determined using a suitable model, in particular calculated.

At least one of the aging states of the oxidation catalyst and / or the particulate filter are preferably determined as an aging factor, in particular depending on the factors temperature over time. In particular, a temperature-time integral can be formed for at least one of the abovementioned exhaust-gas treatment elements, from which an aging state is then determined.

An embodiment of the method is also preferred, which is characterized in that the soot loading of the particulate filter in addition to the previously described procedure in the context of the method by means of a loading model and further additionally with reference to a falling over the particulate filter

Differential pressure - in particular via a differential pressure model - is determined. There are then three possibilities for determining the soot load available that can be used mutually to correct the determined soot load and so in combination with each other a particularly high accuracy of the determination of the

Ensure soot loading. Preferably, regeneration of the particulate filter is performed when one of the detection methods returns soot loading as a result that reaches or exceeds a predetermined maximum soot loading value. Thus, it can be ensured that the particulate filter is always regenerated, if this is indicated.

An embodiment of the method is also preferred, which is characterized in that the soot loading is determined on the basis of the nitrogen oxide conversion, if a first loading value determined on the basis of the loading model for the

Soot loading and a determined based on the differential pressure, the second load value for the soot load have a difference that reaches or exceeds a predetermined differential limit. The very precise method described here for determining the soot loading via the determined nitrogen oxide conversion is thus preferably used when the other two determination methods yield strongly differing results, this being an indication that at least one of the determination methods currently does not provide reliable load values. In a preferred According to an embodiment of the method, the soot loading determined on the basis of the nitrogen oxide conversion is preferably used to correct the first and / or the second load value, and / or to correct the load values

Used investigation methods. This is based on the idea that the soot loading determined by means of the process from the nitrogen oxide conversion - at least in certain operating ranges - represents the most accurately determinable soot load. This can therefore be used in a particularly favorable manner for the correction of the load values determined elsewhere and / or the determination method for determining these load values. It is possible that a regeneration of the particulate filter is postponed, although this is indicated by one of the models, namely, if the method according to which the soot loading is determined based on the specific nitrogen oxide conversion, does not indicate regeneration. In this case, rather, the one

Regeneration indexing determination method and / or the determined using this determination method load value using the determined by the method described here loading value corrected.

Finally, an embodiment of the method is preferred, which is characterized in that by controlling an exhaust gas recirculation device and / or by means of active heating of an oxidation catalyst targeted conditions are set, under which the soot loading of the particulate filter from the determined nitrogen oxide conversion can be determined. In this case, preferably an exhaust gas recirculation device is used which has a high-pressure exhaust gas return path and a low-pressure exhaust gas recirculation path. A strategy for controlling the exhaust gas recirculation device can then be adjusted as needed so that the exhaust gas recirculation takes place completely via the high pressure exhaust gas recirculation path, whereby the best possible formation of nitrogen dioxide is achieved at the oxidation catalyst. Furthermore, additionally or alternatively, a desired temperature range for the exhaust gas temperature can be adjusted in a targeted manner by a change in an overall exhaust gas recirculation rate and / or by active heating of the oxidation catalytic converter, in particular by means of an electrical heating device. Overall, it is thus possible to create conditions with respect to the exhaust gas temperature or with respect to the ratio of nitrogen dioxide to total nitrogen oxide in the exhaust gas, in which a very accurate determination of the soot loading is possible by means of the method described here.

The targeted setting of such favorable conditions is preferably carried out in particular when the other two methods of determination, that is to say in particular the loading model and the differential pressure model, have greatly different load values return, wherein a difference between the load values preferably reaches or exceeds a predetermined differential limit.

The invention also includes a control device for an internal combustion engine, which is set up to carry out a preferred embodiment of the method. It is possible that the control unit is the engine control unit (ECU) of the internal combustion engine. Alternatively, it is also possible that a separate control unit is provided for carrying out the method.

It is possible that the method is implemented directly in an electronic structure, in particular a hardware, of the control device. Alternatively or additionally, it is possible that in any case certain method steps, preferably the entire method, is given as a computer program product. In that regard, a computer program product is preferably loaded into the control unit, which comprises steps on the basis of which an embodiment of the method is carried out when the computer program product is running on the control unit.

The invention also includes an internal combustion engine which is set up to carry out an embodiment of the method, and / or which has a control unit which is set up to carry out the method. In this case, the internal combustion engine is in particular assigned an exhaust gas line with at least one of the exhaust gas aftertreatment elements described in the context of the method.

The invention finally also includes a motor vehicle having an internal combustion engine according to one of the previously described embodiments. The motor vehicle is preferably designed as a passenger car, as a truck or as a commercial vehicle.

The invention will be described in more detail below with reference to the drawings. Showing:

1 shows a schematic representation of an internal combustion engine together with exhaust gas line, for which an embodiment of the method for determining a soot load can be carried out;

Fig. 2 is a schematic representation of the relationship between the

Nitrogen oxide conversion on one with a selectively catalytic coating provided particulate filter and the soot loading thereof as a function of the temperature;

Fig. 3 is a schematic representation of the relationship between the

Nitrogen oxide conversion and soot loading as a function of a ratio of a nitrogen dioxide concentration to a total nitrogen oxide concentration in the exhaust gas upstream of the particulate filter, and

Fig. 4 is a schematic representation of an embodiment of the method.

Figure 1 shows a schematic representation of an embodiment of a

Internal combustion engine 1 with an exhaust line 3, for which the method described here is preferably carried out. The exhaust gas line 3 has a particle filter 5 provided with a selectively catalytic coating, which is set up in order, on the one hand, to filter soot particles from the exhaust gas flow of the internal combustion engine 1 and, on the other hand, to selectively reduce catalytic nitrogen oxides present in the exhaust gas. Such a particulate filter 5 is also commonly referred to as SDPF. Downstream of the particulate filter 5, an SCR catalyst 7 is additionally arranged in the embodiment shown here, which is also adapted for the selective catalytic reduction of nitrogen oxides, but it has no particulate filter function.

Upstream of the particle filter 5, a metering device 9 for a reducing agent is arranged, which can be metered into the exhaust gas flow by means of the metering device 9, where it is then reacted with the nitrogen oxides on the selectively catalytic coating of the particle filter 5 and the SCR catalyst 7, whereby the nitrogen oxides reduced to nitrogen.

As reducing agent, a urea-water solution is preferably injected into the exhaust gas stream via the metering device 9, the urea reacting with the hot exhaust gas and decomposing to form ammonia, which then acts as the actual reducing agent in the particle filter 5 and preferably in the SCR catalyst 7 acts.

In order to be able to determine the nitrogen oxide conversion at the particle filter 5, in the exemplary embodiment illustrated here, a first nitrogen oxide sensor 11 is arranged upstream of the metering device 9, with a second nitrogen oxide sensor immediately downstream of the particle filter 5 -in particular between the particle filter 5 and the SCR catalytic converter 7 13 is arranged. The second nitrogen oxide sensor 13 may also be arranged downstream of the SCR catalytic converter 7. About a difference measurement of the signals of the two nitrogen oxides 1 1, 13, in particular taking into account Signal of the first nitrogen oxide sensor 11, a momentary absoltur or relative

Nitrogen oxide conversion on the particle filter 5 determinable.

In the exemplary embodiment illustrated here, an oxidation catalytic converter 15 is arranged upstream of the particle filter 5 and in particular also upstream of the metering device 9. Instead of the oxidation catalyst 15 or in addition to the

Oxidation catalyst 15, it is possible that upstream of the particulate filter 5 and in particular upstream of the metering device 9, a nitrogen oxide storage catalyst (NSK) is arranged.

In the present case, the oxidation catalytic converter 15 has a heating device 17, which is preferably designed as an electrical heating device.

The internal combustion engine 1 also has a charge air line 19, via which charge air can be supplied. In per se known manner, a compressor 21 is arranged in the charge air line, which is drivable by a arranged in the exhaust line 3 turbine 23. It is insofar realized a turbocharger device in the embodiment shown here.

The illustrated embodiment also has an exhaust gas recirculation device 25, which here has a high-pressure exhaust gas recirculation path 27 and a low-pressure exhaust gas recirculation line 29. In this case, the high-pressure exhaust gas recirculation path 27 branches off the high-pressure region of the exhaust line 3 upstream of the turbine 23, wherein it opens into the high-pressure region of the charge air line 19 downstream of the compressor 21. The low-pressure exhaust gas recirculation line 29 branches off downstream of the SCR catalytic converter 7 from the low-pressure region of the exhaust line 3 and flows upstream of the compressor 21 into the low-pressure region of the charge air line 19.

In the context of the method, the heating device 17 is preferably selectively controlled in order to bring the exhaust gas temperature into a range in which the method can be carried out with high accuracy. Alternatively or additionally, the exhaust gas recirculation device 25 is preferably also controlled in such a way that conditions are created in which the method can be carried out with high accuracy. In this case, provision is made in particular for the total recirculation of the exhaust gas to be switched over to the high-pressure exhaust gas recirculation path 27, so that the highest possible formation of nitrogen dioxide on the oxidation catalytic converter 15 is achieved. Additionally or alternatively, it is possible for a total exhaust gas recirculation rate to be influenced in a targeted manner in order to reduce the exhaust gas Temperature - in addition to or as an alternative to the control of the heater 17, is brought into a range in which the method is particularly efficient and feasible with high accuracy. For determining the exhaust gas temperature, by the way, a temperature sensor, not shown in FIG. 1, is preferably provided, with which the exhaust gas temperature upstream of the particulate filter 5 can be detected.

Figure 2 shows a schematic, diagrammatic representation of a dependence of the nitrogen oxide conversion U (NO _x ) - plotted against the exhaust gas temperature T upstream of the particulate filter 5 - of the soot loading of the particulate filter 5. It is with a solid curve 31 of the nitrogen oxide conversion at the particulate filter 5 at a the first, higher soot load of the particulate filter 5 is shown, wherein the nitrogen oxide conversion is applied to the particulate filter 5 at a second, lower soot loading against the temperature of the exhaust gas before the particulate filter 5 with a second, dashed curve 33. It is also indicated in FIG. 2 that a temperature range exists between a minimum temperature T _min and a maximum temperature T _max , in which the method with particularly high sensitivity can be used, because curves which determine the nitrogen oxide conversion U (NO _x ) as a function of the temperature Describe T for different soot loadings of the particulate filter 5, comparatively large distances from each other. In particular, no curve intersections result in this temperature range, so that an unambiguous assignment of the nitrogen oxide conversion U (NOx) to the soot charge is possible. This applies in particular when - as is preferably carried out - the instantaneous nitrogen oxide conversion is compared with a reference value for the unloaded particulate filter 5 and to that extent with a baseline or base curve.

Figure 3 shows schematically and diagrammatically the dependence of the nitrogen oxide conversion U (NOx) - plotted against the temperature T of the exhaust gas upstream of the

Particulate filter 5 - from a ratio of a nitrogen dioxide concentration to a total nitrogen oxide concentration in the exhaust gas. In this case, a first curve pair 35 is shown in the diagram of Figure 3, which represents nitrogen oxide sales at a first, higher ratio of nitrogen dioxide to total nitrogen oxide in the exhaust gas. In this case, a first curve 37, which is shown in solid lines, shows the temperature dependence of the nitrogen oxide conversion for a first, higher soot load of the particulate filter 5, wherein a second dash-dotted curve 39 this curve for a second, lower

Soot loading of the particulate filter 5 shows. A second pair of curves 39 is shown correspondingly for a second, lower ratio of nitrogen dioxide to total nitrogen oxide in the exhaust gas. This second pair of curves 39 has a third curve 41, shown in dashed lines which represents the nitrogen oxide conversion as a function of the temperature for the first, larger soot load of the particulate filter 5, wherein the second pair of curves 39 has a fourth, dotted curve 43 which the nitrogen oxide conversion as a function of the temperature for the second, lower soot loading of Particulate filter 5 represents. The curve pairs 35, 39 are based on the identical first and second soot loadings. From Figure 3 is thus immediately clear that a clearer separation of the nitrogen oxide conversion depending on the soot loading of the particulate filter 5 then exists when the ratio of nitrogen dioxide to total nitrogen oxide is higher. The method can be carried out with particularly high accuracy with a comparatively high ratio of nitrogen dioxide to total nitrogen oxide, in particular if a predetermined minimum value for the ratio is exceeded. This is between at least 10% to at most 50%, preferably between at least 20% to at most 40% and more preferably between at least 30% to at most 50%.

Figure 4 shows a schematic representation of an embodiment of the method in the manner of a flow chart. In the context of the method, the instantaneous nitrogen oxide conversion 45 at the particle filter 5 is preferably determined by means of the nitrogen oxide sensors 11, 13. From a map 47 is the reference value of the load-free nitrogen oxide 49, which the particulate filter 5 has when it is not loaded with soot, so either new or completely regenerated has. The map 47 is spanned by an aging factor 51 for the particulate filter 5, the ratio 53 of the nitrogen dioxide concentration to the total nitrogen oxide concentration upstream of the particulate filter 5 in the exhaust gas, the temperature 55 upstream of the particulate filter 5 in the exhaust gas, an exhaust gas mass flow 57 via the particulate filter 5, and a Reducing agent loading 59, in particular an ammonia loading of the particulate filter. 5

Accordingly, the load-free nitrogen oxide conversion 49 is read in dependence on the parameters shown on the left of the map 47. Preferably, the aging factor 51 and the nitrogen dioxide concentration ratio 53 are

Total nitrogen oxide concentration dimensionless. The temperature 55 is preferably given in ° C, the exhaust gas mass flow 57 preferably in kg / h, and the reducing agent loading 59 preferably in g.

The aging factor 51 is preferably determined as a function of the temperature and time factors, in particular as a temperature-time integral. The ratio of nitrogen dioxide to total nitrogen oxide in the exhaust gas is preferably determined based on the temperature of the exhaust gas upstream of the oxidation catalyst 15 or the temperature upstream of the particulate filter 5, the exhaust gas mass flow over the oxidation catalyst, and the aging state of the oxidation catalyst 15 - also from a map not shown here. The reducing agent loading 59 preferably results from a model calculation.

In a differential element 61, a difference 62 between the instantaneous nitrogen oxide conversion 45 and the charge-free nitrogen oxide conversion 49 is now preferably formed. This difference 62 enters into a determination element 63, into which, in addition, the ratio 53 of the nitrogen dioxide concentration to the total nitrogen oxide concentration preferably enters. From this ratio 53 and the difference 62 determined in the difference 62, the current soot load 65 of the

Particulate filter 5 is calculated. This represents a very accurate value for the soot loading of the particulate filter 5, in particular in the optimum temperature range for the method and at a predetermined minimum value ratio 53. In this case, it is possible to correct this value for correcting other determination methods, in particular a soot loading model and / or a differential pressure model, to use.

Overall, it can be seen that, with the help of the procedure, in particular a premature one

Regeneration of the particulate filter 5 can be avoided. This will do that

Regeneration interval of the particulate filter 5 extends, resulting in a saving of fuel and a reduced thermal load of the catalytic coating of the

Exhaust aftertreatment system has the consequence.

Claims

claims

A method of determining a soot load (65) one having a selective one

catalytic filter-coated particle filter (5), comprising the following steps: determining a nitrogen oxide conversion (45) on the particle filter (5) and determining a soot loading (65) of the particle filter (5) from the determined nitrogen oxide conversion (45).

2. The method according to claim 1,

characterized in that

the soot load (65) is determined when an exhaust gas temperature (55) in an exhaust line (3) upstream of the particulate filter (5) is greater than or equal to a predetermined minimum temperature (T _min ) and less than or equal to one

predetermined maximum temperature (T _max ), preferably the

Minimum temperature (T _min ) of at least 175 ° C to at most 210 ° C and / or the maximum temperature (T _max ) of at least 240 ° C to at most 280 ° C, or wherein the exhaust gas temperature (55) upstream of the particulate filter (5) preferably from at least 150 ° C to at most 300 ° C, preferably from at least 175 ° C to at most 280 ° C, preferably from at least 175 ° C to 240 ° C, preferably from at least 210 ° C to at most 280 ° C, preferably from at least 210 ° C to not more than 240 ° C.

3. The method according to any one of the preceding claims,

characterized in that

for determining the soot load (65) from the determined nitrogen oxide conversion (45) a ratio (53) of a nitrogen dioxide concentration to a Total nitrogen concentration in the exhaust gas upstream of the particulate filter (5) is used.

4. The method according to any one of the preceding claims,

characterized in that

the soot load (65) is determined when the ratio (53) of the

Nitrogen dioxide concentration to the total nitrogen oxide concentration in the exhaust gas upstream of the particulate filter (5) is greater than a predetermined minimum value, preferably the minimum value of at least 10% to at most 50%, preferably from at least 20% to at most 40% or from at least 30% to at most 50% is.

5. Method according to one of the preceding claims,

characterized in that

the nitrogen oxide conversion (45) on the particle filter (5) is determined by means of nitrogen oxide sensors (11, 13) arranged upstream and downstream of the particle filter.

6. The method according to any one of the preceding claims,

characterized in that

the ratio (53) of the nitrogen dioxide concentration to the

Total nitrogen oxide concentration based on the exhaust gas temperature (55) upstream of the particulate filter (5) or an exhaust gas temperature upstream of a

Oxidation catalyst (15), an exhaust gas mass flow (57) above the

Oxidation catalyst (15), and / or an aging state of the

Oxidation catalyst (15) is determined.

7. The method according to any one of the preceding claims,

characterized in that

the soot load (65) is compared to a predetermined nitrogen oxide conversion (49) of the unloaded particulate filter (5) by comparing the determined nitrogen oxide conversion (45), the predetermined nitrogen oxide conversion (49) of the particulate filter (5) preferably being dependent on an exhaust gas mass flow (57). above the particulate filter, the exhaust gas temperature (55) upstream of the particulate filter (5), the ratio (53) of the nitrogen dioxide concentration to the Total nitrogen oxide concentration upstream of the particulate filter (5), a

Reducing agent loading of the particulate filter (5), an aging state of the particulate filter (5), and / or in dependence on an operating point of a

Internal combustion engine (1), which has the particle filter (5) is determined.

8. The method according to any one of the preceding claims,

characterized in that

the soot loading (65) of the particulate filter (5) additionally by means of a

Loading model and based on a dropping across the particulate filter (5) differential pressure, preferably a regeneration is performed when one of these detection methods returns a soot load as a result that reaches or exceeds a predetermined maximum value.

9. The method according to any one of the preceding claims,

characterized in that

the soot load is determined on the basis of the nitrogen oxide conversion (45) if a first load value determined on the basis of the load model and a second load value determined on the basis of the differential pressure have a difference that reaches or exceeds a predetermined differential limit, whereby the determination based on the nitrogen oxide conversion (45) Soot loading preferably for correcting the first and / or the second load value and / or for correcting at least one of these load values underlying

Investigation methods, namely the loading model and / or the

Differential pressure model, is used.

10. The method according to any one of the preceding claims,

characterized in that

by means of activation of an exhaust gas recirculation device (25) and / or by means of active heating of an oxidation catalyst (15), conditions are specifically set, under which the soot loading (65) of the particulate filter (5) from the nitrogen oxide conversion (45) can be determined.