DE102008064606B4 - Functional adaptation of an exhaust gas cleaning device - Google Patents

Abstract

Method for adapting the function of an exhaust gas cleaning device (1) for cleaning an exhaust gas stream (3) of an internal combustion engine (5) of a motor vehicle (7) by means of a selective catalytic reduction, with: - operating the motor vehicle in an engine operating mode in which the exhaust gas temperature of the exhaust gas stream is at least in a medium has a constant temperature (63) between approximately 350 ° C and 500 ° C, - determining a raw NO emission (23) of the exhaust gas stream (3) of the internal combustion engine (5), - metering a reducing agent (11) into the exhaust gas stream ( 3) upstream of an SCR catalyst (9) which brings about the selective catalytic reduction, - varying an α value (39) which represents a relationship between the metered reducing agent (11) and the raw NO emission (23), - determining an NO -Measured value (17) by means of a NO sensor (15) arranged downstream of the SCR catalytic converter (9), - Determining a relationship between the NO measured value (17) and de r catalyst raw quantity (51) representing NO raw emission (23), - determining an extreme value point (57) occurring during the variation of the α value (39) at which the catalyst leading variable (51) has an extreme value, - performing the Function adaptation of the exhaust gas purification device (1) by means of the determined extreme value point (57) - determining an α value point (61) belonging to the extreme value point (57), characterized by at least one of the following: - comparing the α value point (61) with a reference α value point, which characterizes a non-aged reference exhaust gas purification device, - performing the function adjustment, so that after the function adjustment, the comparison has the smallest possible value or the α value point (61) again matches the reference α value point.

Description

The invention relates to a method for adapting the function of an exhaust gas cleaning device for cleaning an exhaust gas flow of an internal combustion engine of a motor vehicle by means of a selective catalytic reduction, and to a device for carrying out the method.

Functional adjustments can be used in so-called SCR systems (selective catalytic reduction), for example to compensate for changes in components of the SCR system that occur over a runtime of the SCR system. For the function adjustment such as a NO _x -Rohemission and other _NOx metrics can be evaluated. The DE 10 2005 062 120 A1 relates to a method for monitoring an exhaust gas aftertreatment system of an internal combustion engine with an engine block and an exhaust gas guide which has at least one catalytic converter, in which upstream of the catalytic converter a reagent required in the catalytic converter for NO _x reduction is introduced by means of an introduction device, the reducing agent rate being so at defined reference operating points it is far increased that an ammonia breakthrough is detected behind the catalytic converter in the exhaust gas flow behind the catalyst by means of an ammonia-sensitive sensor. In the DE 10 2007 006 489 A1 A method for diagnosing an exhaust gas sensor arranged in an exhaust gas area of an internal combustion engine, in which a comparison of a measure for at least one exhaust gas component with a measure of the exhaust gas component determined on the basis of a measurement is provided, and a device for carrying out the method are proposed.

From the DE 10 2004 046 640 A1 A method for adapting the function of an exhaust gas cleaning device for cleaning an exhaust gas stream of an internal combustion engine of a motor vehicle by means of a selective catalytic reduction is already known, in which a variation of an alpha value, which is related to a reducing agent to be metered and a raw NO _x emission, and also a determination of one a relationship is provided between a NO _x measurement value and the catalyst guide variable representing raw NO _x emission. Furthermore, an extreme value point occurring at the regeneration of the alpha value is determined, at which the catalyst guide variable has an extreme value, the functional adaptation of the exhaust gas purification device being carried out by means of the determined extreme value point.

Furthermore, from the DE 10 2006 021 089 A1 a method for adapting the function of an exhaust gas cleaning device is known, the nitrogen oxide conversion in the SCR catalytic converter being maximized by varying an alpha value, but without explicitly taking into account a catalytic converter guide variable.

The object of the invention is to provide an improved functional adaptation of an exhaust gas cleaning device for cleaning an exhaust gas flow of an internal combustion engine and to make it possible to carry this out as independently of an aging state of components of the exhaust gas cleaning device as possible.

The object is achieved with the features of the independent claims.

• Ermitteln einer NO_x-Rohemission des Abgasstroms des Verbrennungsmotors, Einstellen einer zumindest in einem Mittel konstanten Temperatur des Abgasstroms zwischen ungefähr 350° C und 500° C, Zudosieren eines Reduktionsmittels in den Abgasstroms stromaufwärts eines die selektive katalytische Reduktion bewirkenden SCR-Katalysators, Variieren eines einen Zusammenhang zwischen dem zudosierten Reduktionsmittel und der NO_x-Rohemission kennzeichnenden α-Werts, Ermitteln eines NO_x-Messwerts mittels eines stromabwärts des SCR-Katalysators angeordneten NO_x-Sensors, Ermitteln einer einen Zusammenhang zwischen dem NO_x-Messwert und der NO_x-Rohemission kennzeichnenden Katalysator-Leitgröße, Ermitteln einer während des Variierens des α-Werts auftretenden Extremwertstelle, an der die Katalysator-Leitgröße einen Extremwert aufweist und Durchführen der Funktionsanpassung der Abgasreinigungsvorrichtung mittels der ermittelten Extremwertstelle.

According to the invention, in a method for a functional adaptation of an exhaust gas cleaning device for cleaning an exhaust gas stream of an internal combustion engine of a motor vehicle by means of a selective catalytic reduction:

• Determining a raw NO _x emission of the exhaust gas flow of the internal combustion engine, setting a temperature of the exhaust gas flow that is at least at an average temperature between approximately 350 ° C. and 500 ° C., metering in a reducing agent into the exhaust gas stream upstream of an SCR catalytic converter which effects the selective catalytic reduction, varying one a relationship between the metered reducing agent and the NO _x -Rohemission characterizing α-value, determining a NO _x metric in by means of a downstream of the SCR catalyst disposed _NOx sensor, determining a a relationship between the NO _x value measured for and the NO _x Crude emission characterizing catalyst guide variable, determining an extreme value point occurring during the variation of the α value at which the catalyst guide variable has an extreme value and performing the function adaptation of the exhaust gas cleaning device by means of the determined extreme value point.

The functional adaptation can advantageously only be carried out by means of the determined extreme value point. Advantageously, further information, for example about an aging state of further components of the exhaust gas cleaning device and / or a fill level of the SCR catalytic converter, can be disregarded for the function adaptation. Alternatively and / or additionally, however, it is also conceivable to take such information into account.

The α value is understood to mean a value of a ratio of a reducing agent to a raw NOx emission that is actually present in the exhaust gas flow and which can be determined, for example, by means of a measurement. It is conceivable to define a target α value, which can result, for example, from a corresponding target injection quantity in relation to the raw NO _x emission. It is conceivable from the to determine the predetermined target injection quantity by means of a model of a corresponding metering device. An extreme value point can be understood to mean a pair of values from the α value and the extreme value of the catalyst guide variable. However, it is also conceivable to understand the extreme value point only as the corresponding α value at which the catalyst guide variable has the extreme value. The catalyst guide variable can be, for example, an activity and / or conversion rate of the SCR catalyst, for example to calculate (1 - NO _x measured value / NO _x raw emission). However, it is also conceivable that further variables are included in the catalyst guide variable, for example a concentration of carbon monoxide, carbon dioxide and / or ammonia, as can be determined in the exhaust gas stream before and / or after the SCR catalyst, for example by means of a model and / or corresponding sensors.

It is advantageously provided to determine an α value point belonging to the extreme value point. It has been recognized that the α value point can advantageously be determined independently of an aging state of further components of the exhaust gas cleaning device. Advantageously, an adaptation of a metering device for metering in the reducing agent can be carried out particularly easily by means of the α-value point.

The method is characterized in that a comparison of the α value point with a reference α value point, which characterizes a non-aged reference exhaust gas cleaning device and / or a performance adjustment, so that after the function adjustment, the comparison has the smallest possible value or the α-value point is again provided to match the reference α-value point. As a result, the exhaust gas cleaning device can advantageously be adapted such that it again has the functionality or as close as possible to the non-aged exhaust gas cleaning device.

It is advantageously provided that the extreme value point is determined, the catalytic converter guide variable having a maximum. If the catalyst guide variable is an activity and / or conversion rate, the SCR catalyst therefore exhibits maximum activity at the extreme value point.

It is advantageously provided that the extreme value point is determined during a regeneration stage of a regeneration of a particle filter of the exhaust gas cleaning device and / or that the extreme value point is determined immediately before or after the regeneration. The particle filter can be, for example, a diesel particle filter that has to be regenerated from time to time. Advantageously, an adaptation, in particular an increase, in the temperature of the exhaust gas stream, which is necessary anyway, can also be used for carrying out the method.

It is advantageous to set an operating mode of the internal combustion engine to set the temperature, and / or to set the operating mode by means of an internal engine post-injection of a fuel and / or by means of a shift in an ignition timing. The internal combustion engine can be a diesel engine with auto-ignition, a gasoline engine with positive ignition, or a mixed engine that has the characteristics of a diesel and a gasoline engine. The temperature can advantageously only be set by means of the operating mode of the internal combustion engine. Additional components for setting the temperature can also be used, but are not absolutely necessary.

A variation of the α value between 0.5 and 1.5 and / or a variation of the α value in the form of a ramp and / or that the NO _x sensor has a cross sensitivity to ammonia is advantageously provided. Advantageously, a ramp can be easily adjusted. The extreme value point can be limited in advance to α values between 0.5 and 1.5. With α values> 1, an ammonia slip is to be expected, which can also be detected by means of the cross sensitivity of the NO _x sensor. However, it is advantageous that only the extreme value point is determined for the function adaptation. It is therefore advantageously not necessary to make a complex distinction as to whether there is a change in the underlying measurement signal or NO _x measured value of the NO _x sensor due to a change in the NO _x content of the exhaust gas flow and / or an ammonia content of the exhaust gas flow. The catalyst guide variable can advantageously be designed in such a way that both an increase in the NO _x content and an increase in the ammonia content of the exhaust gas stream, with assumed unchanged raw NO _x emissions, brings about a mathematical reduction in the catalyst guide variable. The catalyst guide variable can advantageously be evaluated independently of an actual activity of the catalyst, namely only to determine the extreme value point, in the present case the maximum of the catalyst guide variable. It is therefore advantageously possible to determine the α-value point independently of the occurrence by means of the NO _x and / or ammonia concentration of the exhaust gas flow and to use it as the sole meaningful quantity for the function adaptation. Advantageously, due to the temperature of the exhaust gas flow set between approximately 350 ° C. and 500 ° C., further parameters, such as a loading of the SCR catalytic converter, are not necessary. The SCR catalytic converter advantageously has a comparatively low storage capacity for NH ₃ between 350 ° C. and 500 ° C. It has also been shown to be advantageous in this temperature range age-dependent increase and / or decrease in the catalyst guide variable can occur, but the α-value point does not depend on it or at least only minimally.

In a further embodiment of the method, performing the function adaptation by adapting an addition amount of the reducing agent is provided. In the course of the aging of the exhaust gas cleaning device, incorrect dosing of the reducing agent can occur. Such an incorrect metering can advantageously be prevented or at least reduced to a minimum by means of the function adaptation.

In a further embodiment of the method, the metering amount of the reducing agent is multiplied by an adaptation factor and / or the adaptation factor is determined by comparing the α value point and the reference α value point. Only a comparison of two parameters advantageously serves as the basis for the function adaptation, from which an adaptation factor for the metered quantity can be derived in a simple manner, for example by means of a proportional relationship.

In a further embodiment of the method, determination of the raw NO _x emission is provided by means of a NO _x model and / or a NO _x sensor upstream of the SCR catalytic converter. Advantageously, the raw NO _x emission can either be measured and / or determined as a model.

In a further embodiment of the method, the temperature is set by means of a burner assigned to the exhaust gas cleaning device or an external heater. It is possible that a burner or an external heater is provided in any case for the regeneration of the diesel particle filter and / or for improving the light-off behavior of the exhaust gas cleaning device, which can also advantageously be used for raising and / or adjusting the temperature.

The object is also set up in a drive arrangement of a motor vehicle with an internal combustion engine, an exhaust gas purification device connected downstream of the internal combustion engine for cleaning an exhaust gas stream of the internal combustion engine by means of a selective catalytic reduction, designed and / or constructed to carry out a previously described method. In particular, the advantages described above result.

• 1 eine Abgasreinigungsvorrichtung zur Reinigung eines Abgasstroms eines Verbrennungsmotors eines Kraftfahrzeuges;
• 2 ein Schaubild einer Variation eines α-Wertes sowie eines NO_x-Messwertes über der Zeit; und
• 3 einen funktionalen Zusammenhang einer Katalysator-Leitgröße über den α-Wert.

Further advantages, features and details emerge from the following description, in which an exemplary embodiment is described in detail with reference to the drawing. Identical, similar and / or functionally identical parts are provided with the same reference symbols. Show it:

• 1 an exhaust gas cleaning device for cleaning an exhaust gas stream of an internal combustion engine of a motor vehicle;
• 2 a graph of a variation of an α value and a NO _x measured value over time; and
• 3 a functional relationship of a catalyst guide variable via the α value.

1 shows an exhaust gas purification device 1 for cleaning an exhaust gas flow 3 of an internal combustion engine 5 of a motor vehicle shown only partially 7 , The emission control device 1 has an SCR catalyst 9 on. The SCR catalytic converter 9 is for cleaning the exhaust gas flow 3 by means of a selective catalytic reduction in the presence of a reducing agent 11 designed. The reducing agent 11 can by means of a dosing device 13 the exhaust gas flow 3 upstream of the SCR catalyst 9 be added. With the reducing agent 11 it can be, for example, ammonia or a chemical precursor of ammonia, for example urea. The urea can be, for example, in liquid form as an aqueous solution or as a solid by means of the metering device 13 the exhaust gas flow 3 be added, being in the exhaust gas stream 3 , in particular in the presence of a hydrolysis catalyst which can be released ammonia. The SCR catalytic converter 9 can have a corresponding hydrolysis precursor.

The SCR catalytic converter 9 is followed by a NO _x sensor 15 for determining a NO _x measured value 17. The NO _x measured value 17 can be from a control unit 19 , for example an engine control unit of the internal combustion engine 5 , are processed. The control unit 19 can be used to control and / or regulate the internal combustion engine 5 and / or the exhaust gas purification device 1 be designed. The control unit can accordingly 19 a control signal 21 for the dosing device 13 to generate. By means of the control unit 19 and the control signal 21 can, for example, an α value of the metering device 13 be specified according to which the reducing agent 11 the exhaust gas flow 3 can be added.

Downstream of the internal combustion engine 5 is an optional raw NO _x emission sensor 23 for generating a raw NO _x emission value 25 of the exhaust gas flow 3 assigned. The NO _x raw emission measured value 25 also becomes the control unit 19 fed. Alternatively and / or additionally, it is conceivable by means of the control unit 19 as well as this available data and a model to specify the NO _x raw emission measured value or a model-based NO _x raw emission of the Internal combustion engine 5 to represent. To control the internal combustion engine 5 and / or for transferring corresponding parameter values of the internal combustion engine 5 to or from the control unit 19 is a corresponding connection 27 intended. The parameter values can have, for example, an injection quantity, an engine torque, a speed, an engine temperature, an air quantity and / or others.

Downstream of the internal combustion engine 5 or downstream of the NO _x raw emission sensor 23 can be an oxidation catalyst 29 to implement in the exhaust gas stream 3 entrained hydrocarbons and / or carbon monoxide can be provided. Downstream of the oxidation catalyst 29 can be a diesel particulate filter 31 be arranged. Using the diesel particle filter 31 particles carried in the exhaust gas stream, for example soot particles, can be removed therefrom. Alternatively and / or additionally, it is possible to use the diesel particle filter 31 downstream of the SCR catalyst 9 to arrange. It is also conceivable to provide further exhaust gas cleaning components. For the regeneration of the diesel particle filter 31 can be a temperature of the exhaust gas flow 3 be raised. As an alternative or in addition to engine measures, the exhaust gas flow is also possible 3 upstream of the diesel particulate filter 31 a burner 33 assign. By means of the burner 33 can be a fuel in a main flow or a secondary flow 35 the exhaust gas flow 3 be metered for heating.

For those in 1 shown exhaust gas purification device 1 a function adjustment can be carried out, in particular on the dosing device 13 as well as the control signal 21 for dosing the reducing agent 11 by means of the dosing device 13 works.

Based on 2 and 3 becomes the procedure for the functional adaptation of the exhaust gas purification device 1 explained in more detail. 2 shows a graph of functional relationships over the time of a variation 37 an α-value of 39 as well as the NO _x metric in 17. For this purpose, on a first y-axis 43, a α- and a NO _x -size applied to an x-axis 41 is a time on a second y axis 45th In 2 it can be seen that the variation 37 of the α value 39 in the form of a digitized ramp increasing from bottom left to top right 47 he follows. In response to the ramp 47 the variation 37 it also turns into 2 applied NO _x measured value 17. The NO _x measured value 17 has a minimum 49 on. Since the NO _x sensor 15 can have a cross sensitivity to ammonia, it is conceivable that the right of the minimum 49 lying rise stems from an ammonia breakthrough. Regardless of this, the minimum is advantageous 49 of the NO _x measured value 17.

3 shows a catalyst guide variable 51 plotted over α. For this purpose, a catalyst activity is plotted on an x-axis 53 and on a y-axis 55. With the catalyst guide variable 51 it can be a conversion rate and / or catalyst activity in percent, which can be calculated using the formula (1 - NO _x measured value / NO _x raw emission), for example. In the 3 applied catalyst guide variable 51 has an extreme value point 57 at which the catalyst guide variable 51 an extreme value 59 or assumes a maximum. The extreme value 59 is reached at a certain value of α or an α value point 61. To determine the α value point 61, the α can be determined in accordance with the in 2 shown ramp 47 or the variation 37 can be varied. During this variation 37 For example, the NO _x measured value 17 can be determined by means of the NO _x sensor 15, and the raw NO _x emission or the NO _x raw emission measured value 25 can be determined by means of the model and / or the NO _x raw emission sensor 23 and the catalytic converter guide variable 51 by means of the control unit 19 will be charged. The extreme value point 57 be determined. From the extreme value point 57 the α-value point 61 can be determined.

The α-value point 61 can advantageously be independent of aging of the upstream oxidation catalytic converter 29 and / or the particle filter 31 and a possibly occurring HC poisoning or hydrocarbon poisoning and / or ammonia (NH ₃ ) - storage of the SCR catalyst 9 respectively. This is advantageously possible because a temperature during the implementation of the method 63 of the exhaust gas flow 3 is set to a constant value, at least constant on average. Constant on average can be understood to mean, for example, a deviation of +/- 50 ° C from an average. The temperature 63 of the exhaust gas flow 3 can be set to a value between 350 ° C and 500 ° C, especially between 400 ° C and 450 ° C. Storage capacity of the SCR catalytic converter is advantageous in this temperature range 9 relatively low, so the exhaust gas purification device 1 at these temperatures relatively quickly, that is, with comparatively small time constants, to metering amounts of the reducing agent of different sizes 11 , dosed by means of the dosing device 13 , responds. A change in the dosage of the reducing agent 11 thus causes a response of the SCR catalytic converter with comparatively small time constants and / or dead times 9 downstream NO _x sensor 15 or its NO _x measured value 17. Also advantageous is an activity or conversion rate, as described, for example, in FIG 3 by means of the catalyst guide variable 51 is shown, the SCR catalyst 9 in this temperature range almost independent of aging and / or activity of the upstream oxidation catalytic converter 29 and a setting of the nitrogen dioxide (NO ₂ ) to nitrogen oxide (NO _x ) ratio by the oxidation catalyst 29 ,

The implementation of the method or a function check or function adaptation can be carried out on an engine operating mode for keeping the temperature constant 63 of the exhaust gas flow 3 be coupled and, for example, directly after a regeneration of the diesel particle filter 31 respectively. It is advantageous for the regeneration of the particle filter 31 the temperature anyway 63 of the exhaust gas flow 3 usually raised, controlled and / or regulated. A renewed settling of the temperature does not have to be advantageous 63 , for example coming from very low temperatures. It is also conceivable to adapt the function to a regeneration stage of the diesel particle filter 31 to couple directly at the temperature 63 of the exhaust gas flow 3 within the interval 350 ° C to 500 ° C. Both processes can advantageously take place synchronously. An increase in temperature 63 of the exhaust gas flow 3 can for example by means of a motor post-injection, by means of the burner 33 , an electric heater or, in the case of a lean-burn internal combustion engine 5 by an appropriate later setting of an ignition point. The fuel used for this purpose 35 can be used advantageously for both processes. The function test and / or function adaptation can be carried out on regeneration cycles of the diesel particle filter 31 be adjusted. It is also conceivable between the regeneration cycles 31 Interconnect further functional adaptations and / or checks freely selectable. The temperature 63 can be applied directly, for example in the control unit 19 , Engine operating mode of the internal combustion engine 5 , for example the post-injection and / or later setting of the ignition point, can be applied directly.

Temperature is advantageous in the case of the constant setting, in particular in an average 63 between 350 ° C and 500 ° C as influencing factors to be considered, in particular only a mass flow of the exhaust gas flow 3 , NO _x concentrations, in the present case the NO _x measured value 17 and the NO _x raw emission of the internal combustion engine 5 , for example modeled or the NO _x raw emission measured value 25, an aging of the metering device 13 as well as a possibly occurring drift of the sensors, for example the NO _x sensor 15 and / or the NO _x raw emission sensor 23. It is advantageous that the SCR catalytic converter is laboriously loaded 9 , the oxidation catalyst 29 and / or the diesel particulate filter 31 in a reference condition compared to an aged condition is not necessary.

To carry out the function adaptation or function check, the α or the α value 39, as for example in FIG 2 shown, varies such that the NO _x sensor 15 behind the exhaust gas purification device 1 or the SCR catalytic converter 9 the activity maximum or the extreme value point 57 the catalyst guide variable 51 or activity can be detected. The α value point 61 can be determined accordingly. It is also advantageous for the function adaptation that a change in the NO _x sensor 15, that is to say the NO _x measured value 17 that can be determined by it, is caused, for example, by a drift, for example over a running time of the exhaust gas cleaning device 1 can only occur if a height, i.e. an absolute measure of the catalyst guide variable 51 or the activity of the SCR catalyst 9 is different, but the α-value point 61 remains unchanged or at least only minimally changed. A change, for example a drift, of the metering device would be advantageous 13 , shift the α-value point 61 in one direction. This can advantageously be recorded when adapting the function. On the basis of the detected change in the α-value point 61, a metered quantity or one can be made using the control signal 21 transferable setpoint of the dosing device 13 can be adapted, for example increased or decreased by means of multiplication by an adaptation factor.

Overall, there is advantageously a robust possibility of changes, for example the metering device 13 to detect and accordingly the exhaust gas purification device 1 to adapt, advantageously a data processing effort in a software of the control unit 19 to be deposited model about the catalytically active components of the exhaust gas purification device 1 can be minimized.

In addition, it is advantageously possible to dispense with complex detection of an NH ₃ slip, since the α-value point 61 can only be determined by means of the NO _x measured value 17 without taking into account any cross-sensitivity to ammonia. To this extent, the NO _x measured value 17 issues a sum signal in the exhaust gas flow 3 contained NO _x and ammonia. On a complex and complicated method to distinguish a poor implementation of the SCR catalyst 9 by, for example, an underdosing and associated increased NO _x measured values 17 due to NO _x breaking through and a high NH ₃ slip due to, for example, an overdosing and consequently a higher NO _x measured value 17 by NH ₃ breaking through can be dispensed with. It can also be advantageous by means of the constantly set temperature 63 the function adjustment can be carried out much more easily and with significantly less maintenance. A more precise and better function adaptation or correction or adaptation of the exhaust gas purification device advantageously results 1 , A filling level of the SCR catalytic converter can also be advantageous 9 be waived by a composition of the exhaust gas flow 3 and thus of a catalytic function of the upstream oxidation catalytic converter 29 and / or particle filter 31 depends.

Reference list

1

Emission control device

3

Exhaust gas flow

5

Internal combustion engine

7

Motor vehicle

9

SCR catalytic converter

11

Reducing agent

13

Dosing device

15

NO _x sensor

17

NO _x measurement

19

Control unit

21

Control signal

23

NO _x raw emission sensor

25

NO _x raw emissions measurement

27

connection

29

Oxidation catalyst

31

Diesel particulate filter

33

burner

35

fuel

37

variation

39

α value

41

X axis

43

first y axis

45

second y-axis

47

ramp

49

minimum

51

Catalyst benchmark

53

X axis

55

y axis

57

Extreme value point

59

Extreme value

61

α value digit

63

temperature

Claims (10)

Method for adapting the function of an exhaust gas cleaning device (1) for cleaning an exhaust gas stream (3) of an internal combustion engine (5) of a motor vehicle (7) by means of a selective catalytic reduction, with: - operating the motor vehicle in an engine operating mode in which the exhaust gas temperature of the exhaust gas stream is at least in a medium has a constant temperature (63) between approximately 350 ° C. and 500 ° C., - determining a raw NO _x emission (23) of the exhaust gas stream (3) of the internal combustion engine (5), - metering a reducing agent (11) into the exhaust gas stream (3) upstream of an SCR catalyst (9) which brings about the selective catalytic reduction, - varying an α value (39) which represents a relationship between the added reducing agent (11) and the NO _x raw emission (23), - determining a NO _x measured value (17) by means of a NO _x sensor (15) arranged downstream of the SCR catalytic converter (9), - determining a relationship between the NO _x -Measured value (17) and the NO _x raw emission (23) representing the catalyst guide variable (51), - Determining an extreme value point (57) occurring during the variation of the α value (39) at which the catalyst guide variable (51) has an extreme value, - performing the functional adaptation of the exhaust gas purification device (1) by means of the determined extreme value point (57) - determining an α value point (61) belonging to the extreme value point (57), characterized by at least one of the following: - comparing the α value point (61) with a reference α value point that characterizes a non-aged reference exhaust gas purification device, - performing the function adjustment so that after the function adjustment the comparison has the smallest possible value or the α value point (61) again with the reference α-value point matches. Method according to the preceding claim, comprising: - Determining the extreme value point (57), the catalyst guide variable (51) having a maximum. Method according to one of the preceding claims, with: at least one of the following: - determining the extreme value point (57) during a regeneration stage of a regeneration of a particle filter (31) of the exhaust gas cleaning device (1), - determining the extreme value point (57) immediately before or after the regeneration . Method according to one of the preceding claims, with at least one of the following: - Setting the operating mode by means of an internal engine post-injection of a fuel (35), - Setting the operating mode by shifting an ignition timing. Method according to one of the preceding claims, with at least one of the following: - varying the α value (39) between 0.5 and 1.5, - varying the α value (39) in the form of a ramp (47), - whereby the NO _x sensor (15) has a cross sensitivity to ammonia. Procedure according to Claim 1 , with: - performing the function adjustment by adjusting a metering amount of the reducing agent (11). Procedure according to Claim 6 , with at least one of the following: - multiplying the metered amount of the reducing agent (11) by an adaptation factor, - determining the adaptation factor by comparing the α value point (61) with the reference α value point. Method according to one of the preceding claims, with: at least one of the following: - determining the raw NO _x emission (23) by means of a NO _x model, - determining the raw NO _x emission (23) by means of a SCR catalytic converter (9) upstream NO _x raw emission sensor (23). Method according to one of the preceding claims, with: - Setting the temperature (63) by means of a burner (33) assigned to the exhaust gas cleaning device (1). Drive arrangement of a motor vehicle (7), with: - An internal combustion engine (5), an exhaust gas cleaning device (1) connected downstream of the internal combustion engine (5) for cleaning an exhaust gas stream (3) of the internal combustion engine (5) by means of a selective catalytic reduction, set up, designed and / or constructed for carrying out a method according to one of the previous claims.

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