DE102017219185A1 - A method of determining a condition of a catalyst and exhaust aftertreatment device - Google Patents

Abstract

The invention relates to a method for determining a state of a catalytic converter (4) of a motor vehicle (1), in which a content of oxygen in the exhaust gas upstream of the catalytic converter (4) and by means of a second sensor (7) is detected by means of a first sensor (6) Content of oxygen in the exhaust gas downstream of the catalyst (4) is detected. The contents of oxygen in the exhaust gas are detected after a change in operating conditions of an internal combustion engine (2) of the motor vehicle (1) arranged upstream of the catalytic converter (4), in which following a operation of the internal combustion engine (2) with a rich air-fuel Mixture operation is adjusted with a lean air-fuel mixture. Based on measured values of the content of oxygen in the exhaust gas detected by the sensors (6, 7), an oxygen storage capacity of the catalyst (4) is determined. At least one further quantity relating to the exhaust gas is determined, and based on a relationship between the oxygen storage capacity and the at least one further variable, the condition of the catalytic converter (4) is determined. Furthermore, the invention relates to an exhaust aftertreatment device for a motor vehicle (1).

Description

The invention relates to a method for determining a state of a catalytic converter of a motor vehicle, in which by means of a first sensor, a content of oxygen in the exhaust gas upstream of the catalyst and by means of a second sensor, a content of oxygen in the exhaust gas downstream of the catalyst is detected. Furthermore, the invention relates to an exhaust aftertreatment device for a motor vehicle.

Components of an exhaust aftertreatment device of a motor vehicle such as catalytic converters are monitored in their function and mode of operation as part of an on-board diagnostic (OBD). These components are reported as faulty as soon as a defined threshold of emissions is exceeded.

In the DE 10 2013 010 562 A1 For example, a method is described for determining a conversion ability of hydrocarbons of a catalyst which utilizes the oxygen storage capacity of oxidation catalysts. In this case, an engine arranged upstream of the catalytic converter is initially operated for a relatively long time with a rich air-fuel ratio, so that the exhaust gas has a low residual oxygen content and a high proportion of hydrocarbons. As a result, the catalyst is almost completely eliminated by oxygen. Subsequently, the engine is operated lean, so that its exhaust gas has a high residual oxygen content and a low content of hydrocarbons at the engine outlet. In the case of an intact oxidation catalyst, the breakthrough from rich to lean is measured with a high time delay by a lambda probe arranged behind the oxidation catalytic converter. Because the oxygen initially fills the oxygen storage of the catalyst, and only then is an increased oxygen content at the catalyst outlet measurable. With increasing aging of the catalyst, the breakdown from rich to lean is measured progressively earlier because the oxygen storage capacity of the catalyst is reduced by aging or defect.

The DE 10 2013 010 562 A1 however, does not describe the oxygen storage ability diagnosis as very reliable in operation, and therefore proposes to determine the hydrocarbon conversion ability of a catalyst by means of an oxygen-sensitive sensor downstream of the catalyst which has cross-sensitivity to hydrocarbons.

However, it is desirable to use the oxygen storage capability of the catalyst to monitor a catalyst. Because the oxygen storage capacity can be easily detected after leaps in the combustion air ratio lambda from rich to lean by means of corresponding sensors, for example in the form of lambda probes upstream and downstream of the catalyst.

In this context, it is currently customary for a driver of the motor vehicle, which is equipped with the catalytic converter, to signal a defect in the catalytic converter by lighting up an engine control lamp if a specific limit value is undershot during the measurement of the oxygen storage capability. Furthermore, in such a case, a corresponding fault memory entry is stored in an error memory of the motor vehicle.

However, in prior art processes in which the oxygen storage capacity of the catalyst is measured from rich to lean after the combustion air ratio has jumped, it may happen that a fully functional catalyst is identified as being defective or a defective catalyst has been identified as having been diagnosed is classified as functional.

It is therefore an object of the present invention to provide such a method and an exhaust gas aftertreatment device suitable for carrying out the method, which or which permits a more reliable statement about the state of the catalytic converter.

This object is achieved by a method having the features of patent claim 1 and by an exhaust gas aftertreatment device having the features of patent claim 9. Advantageous embodiments of the invention are the subject of the dependent claims and the description.

In the method according to the invention for determining a state of a catalytic converter of a motor vehicle, a content of oxygen in the exhaust gas upstream of the catalytic converter is detected by means of a first sensor. By means of a second sensor, a content of oxygen in the exhaust gas downstream of the catalyst is detected. The contents of oxygen in the exhaust gas are detected after varying operating conditions of an internal combustion engine of the motor vehicle arranged upstream of the catalytic converter. In the variation, operation with a lean air-fuel mixture is set subsequent to operation of the rich-air-fuel mixture internal combustion engine. Based on measured values of the content of oxygen in the exhaust gas detected by the sensors, an oxygen storage capacity of the catalyst is determined. Furthermore, at least one further quantity relating to the exhaust gas is determined. The condition of the catalyst is based on a relationship between the oxygen storage capacity and the at least one further size determined.

This is based on the finding that the diagnosis of the oxygen storage capacity is highly dependent on dynamic effects, which can be taken into account due to the relationship between the at least one further variable relating to the exhaust gas and the oxygen storage capacity. As a result, the method allows a more reliable statement about the state of the catalyst. The result of the catalyst monitoring, that is to say the determined state of the catalyst, is so much more reliable than is the case if the relationship between the at least one further variable and the oxygen storage capacity is not established and considered.

Furthermore, it is thus possible to make a qualitative statement about a degree of aging of the catalyst. In addition, a user of the motor vehicle, in particular the driver of the motor vehicle, can be informed preventively about an imminent defect in the catalytic converter. Overall, so the monitoring of the function of the catalyst is improved, which is based on the measurement of the oxygen storage capacity of the catalyst. In this case, the measured oxygen storage capacity is not simply compared with a fixed limit value, but evaluated as a function of the at least one further variable.

In the operation of the internal combustion engine with the rich air-fuel mixture is in a respective combustion chamber of the internal combustion engine, a combustion air ratio λ, which sets the actual air mass available for combustion in relation to the stoichiometric, required for complete combustion air mass of λ < 1 before (lack of air). So it takes less air in the combustion part, as would be necessary for the stoichiometric reaction of all located in the combustion chamber fuel molecules with atmospheric oxygen. When operating with the lean air-fuel mixture, on the other hand, there is a combustion air ratio λ> 1 (excess air). Thus, more air participates in the combustion than would be necessary for the stoichiometric reaction of all the fuel molecules with the atmospheric oxygen.

Preferably, a temperature of the exhaust gas in the catalyst is determined as the at least one further variable. The temperature can be measured here or derived from the operating conditions of the internal combustion engine. This is based on the finding that the oxygen storage capacity of the catalyst increases with increasing temperature in the temperatures occurring during operation of the catalytic converter. Thus, if the relationship between the oxygen storage capacity and the temperature of the exhaust gas in the catalyst is known, it can be determined very reliably whether, for example, a comparatively low oxygen storage capacity of the catalyst is due to aging thereof or to a low temperature. This makes the determination of the state of the catalyst particularly reliable.

Alternatively, but preferably additionally, a mass flow of the exhaust gas is determined as the at least one further variable. Because the oxygen storage capacity of the catalyst also depends on the exhaust gas mass flow. Especially at higher temperatures, the oxygen storage capacity of the catalyst is higher with a lower exhaust gas mass flow than with a higher exhaust gas mass flow and the same temperature. The consideration of the exhaust gas mass flow thus contributes to increasing the reliability in the statement about the state of the catalyst.

Preferably, the relationship between the oxygen storage capacity of the catalyst and the mass flow of the exhaust gas at different temperatures of the exhaust gas is determined. Thus, the circumstance can be taken into account that both the mass flow of the exhaust gas and the temperature of the exhaust gas in the catalyst have an influence on its oxygen storage capacity.

It has also proven to be advantageous if the relationship between the oxygen storage capacity and the at least one further variable is determined at least for a first catalyst having a first aging state and for a second catalyst having a second aging state different from the first aging state. Hereby, an aging state of the catalytic converter is concluded on the basis of the oxygen storage capacity determined on the basis of the measured values of the oxygen content in the exhaust gas. By first determining the relationship for at least two differently aged catalysts, the aging state of the catalyst, the condition of which is to be assessed for instance in the context of an on-board diagnosis, can be determined by interpolation or extrapolation based on this relationship. It is therefore very easy to draw conclusions about the aging state of the catalyst to be assessed.

Preferably, as the first catalyst, a catalyst is used in a new state. As the second catalyst, a catalyst in a limit state is preferably used. When the limit state is reached, the catalyst must be replaced. The catalyst is then namely no longer able to sufficiently remove pollutants from the exhaust or convert. If the relationship between the oxygen storage capacity and the at least one further variable determined on the one hand for the catalyst when new and on the other for the catalyst in the limit state, it can be concluded in a particularly reliable manner lying between these two aging levels, respective aging stages of the catalyst.

Preferably, the relationship between the oxygen storage capacity and the at least one further quantity is determined for at least one further catalyst having a third state of aging which is different from the new state and the limit state. By such intermediate values, the inference to the actual aging stage of the catalyst, at the input and output of which during driving the content of oxygen in the exhaust gas is determined, is particularly precise.

Finally, it has proven to be advantageous if a warning device is actuated which communicates an imminent defect of the catalytic converter to a user of the motor vehicle. For example, in the motor vehicle equipped with the catalytic converter, a warning light can alert the user, in particular the driver, to the impending failure of the catalytic converter. Additionally or alternatively, a corresponding message can be displayed on a display of the motor vehicle and / or an acoustic warning message can be output by the warning device. The user can be informed in time so that a defect of the catalyst is imminent. This allows the user to take countermeasures in good time, such as checking, maintaining or replacing the catalytic converter.

The exhaust gas aftertreatment device according to the invention for a motor vehicle comprises a catalytic converter, which is arranged downstream of an internal combustion engine of the motor vehicle. The exhaust aftertreatment device comprises a first sensor for detecting a content of oxygen in the exhaust gas upstream of the catalyst and a second sensor for detecting a content of oxygen in the exhaust gas downstream of the catalyst. A control device of the exhaust gas aftertreatment device is designed to determine a state of the catalytic converter. Furthermore, the control device is designed to effect a change of operating conditions of the internal combustion engine of the motor vehicle. In changing the operating conditions, an operation with a lean air-fuel mixture is set subsequent to an operation of the internal combustion engine with a rich air-fuel mixture. The control device is designed to determine an oxygen storage capacity of the catalytic converter based on measured values of the content of oxygen in the exhaust gas detected by the sensors. In a memory device of the exhaust gas aftertreatment device, data values are stored which indicate a relationship between the oxygen storage capacity and at least one variable concerning the exhaust gas. The control device is designed to determine the state of the catalyst based on the context. Consequently, the inventive method can be carried out by means of the exhaust gas aftertreatment device. Accordingly, the exhaust aftertreatment device allows a more reliable statement about the state of the catalyst.

The data values can be stored in the memory device, in particular in the form of at least one characteristic curve or in the form of a characteristic diagram. The memory device can be designed in particular as a data memory of the control device.

The advantages and preferred embodiments described for the method according to the invention also apply to the exhaust aftertreatment device according to the invention and vice versa.

Further features of the invention will become apparent from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively indicated combination but also in other combinations or in isolation.

• 1 schematisch ein Kraftfahrzeug mit einer Verbrennungskraftmaschine, in deren Abgasstrang ein Katalysator angeordnet ist, wobei ein Steuergerät des Kraftfahrzeugs dazu ausgebildet ist, anhand von Messwerten einer Sauerstoffspeicherfähigkeit des Katalysators einen Zustands des Katalysators zu ermitteln;
• 2 einen Graphen, in welchem Kurven schematisch einen Zusammenhang zwischen der Sauerstoffspeicherfähigkeit und einer Temperatur eines Katalysators für einen ersten Katalysator und einen zweiten, stärker gealterten Katalysator angeben; und
• 3 einen Graphen, in welchem Kurven schematisch den Einfluss der Temperatur und des Abgasmassenstroms auf die Sauerstoffspeicherfähigkeit eines Katalysators angeben.

The invention will now be explained in more detail with reference to a preferred embodiment and with reference to the drawings. Show it:

• 1 schematically a motor vehicle with an internal combustion engine, in the exhaust gas line of a catalyst is arranged, wherein a control device of the motor vehicle is adapted to determine a state of the catalyst based on measured values of an oxygen storage capacity of the catalyst;
• 2 a graph in which curves indicate schematically a relationship between the oxygen storage capacity and a temperature of a catalyst for a first catalyst and a second, more aged catalyst; and
• 3 a graph in which curves indicate schematically the influence of temperature and the exhaust gas mass flow on the oxygen storage capacity of a catalyst.

In 1 is schematically a motor vehicle 1 shown which is an internal combustion engine 2 having. In an exhaust system 3 the internal combustion engine 2 is a catalyst 4 arranged. The catalyst 4 which may be, for example, a 3-way catalyst, a nitrogen oxide storage catalyst, a catalytic coating on a particulate filter or an oxidation catalyst has the ability to store oxygen. In particular, cerium oxides may be the catalyst 4 give the ability to store oxygen.

In the present case, a control device monitors approximately in the form of a control device 5 , in particular an engine control unit, the function of the catalyst 4 by measuring the oxygen storage capacity of the catalyst 4 , For this causes the controller 5 as part of an on-board diagnosis, a change in operating conditions upstream of the catalyst 4 arranged internal combustion engine 2 , This is the internal combustion engine 2 initially operated with a rich air-fuel mixture, so that in the catalyst 4 contained oxygen is consumed. Subsequently, the internal combustion engine 2 operated with a lean air-fuel mixture.

A corresponding change in the composition of the internal combustion engine 2 emitted exhaust gas is by means of a first sensor approximately in the form of a first lambda probe 6 detects which upstream of the catalyst 4 , ie the input side of the catalyst 4 is arranged. By means of a second sensor, for example in the form of a second lambda probe 7 The content of oxygen in the exhaust gas downstream of the catalyst 4 , that is, at the exit of the catalyst 4 detected. In an alternative embodiment, the second sensor may be located upstream of the exit, and thus downstream of the catalyst 4 or catalyst section located between the two sensors. For example, the second sensor may be placed in a gap which is between a first monolith of the catalyst 4 and a second monolith of the catalyst 4 is provided. Alternatively, the sensor may be introduced into a bore formed in one of the monoliths to measure the oxygen content directly in the monolith.

The increased oxygen content in the exhaust gas upstream of the catalyst 4 due to the operation of the internal combustion engine 2 with the lean air-fuel mixture is from the first lambda probe 6 immediately after changing the operating conditions of the internal combustion engine 2 detected. In contrast, detects the second lambda probe 7 an increased oxygen content in the exhaust later. Because initially, due to the oxygen storage capacity of the catalyst 4 the oxygen storage of the catalyst 4 refilled. The breakthrough from rich to lean, so the increased oxygen content in the exhaust also downstream of the catalyst 4 However, with increasing aging of the catalyst 4 measured earlier. Because of the aging of the catalyst 4 (or due to a defect of the catalyst 4 ) decreases the oxygen storage capacity of the catalyst 4 from.

To the state, in particular the state of aging, of the catalyst 4 determine determines the present case, the controller 5 based on that of the lambda probes 6 . 7 measured oxygen oxygen content in the exhaust gas, the oxygen storage capacity (OSC) of the catalyst 4 ,

In the present case, the monitoring of the function of the catalyst 4 by measuring the oxygen storage capacity of the catalyst 4 but especially reliable. Because the measured oxygen storage capacity is not compared with a fixed limit, but as a function of the temperature of the exhaust gas in the catalyst 4 and the mass flow of the exhaust gas through the catalyst 4 rated. The temperature of the exhaust gas in the catalyst 4 can by means of a temperature sensor 8th be determined. The exhaust gas mass flow is preferably based on that of the control unit 5 given operating conditions of the internal combustion engine 2 certainly.

The dependence of the oxygen storage capacity of the catalyst 4 from the temperature and the aging of the catalyst 4 should be related to 2 be illustrated. In an in 2 shown graph is on an ordinate 9 the oxygen storage capacity is plotted in milligrams and on an abscissa 10 the temperature in degrees Celsius. A first turn 11 illustrates a relationship between the temperature of the exhaust gas in a catalyst and the oxygen storage capacity of the catalyst for a still comparatively little aged catalyst. A second turn 12 illustrates the temperature dependence of the oxygen storage capacity of another, more aged catalyst.

Both catalysts are preferably operated such that the catalysts are first heated at a high exhaust gas mass flow of, for example, about 115 kilograms per hour become. Then, for example, reduced to about 50 kilograms per hour reduced mass flow through the catalysts. In this constant exhaust gas mass flow, respective measurements of the oxygen storage capacity of the respective catalytic converter are carried out over a predetermined period of time. Due to the lower mass flow, both the less aged catalyst (curve 11 ) as well as the more aged catalyst (curve 12 ) increasingly. This temperature decrease is in 2 through an arrow 13 qualitatively illustrated.

It can be seen that at a given temperature, the oxygen storage capacity of the less aged, through the curve 11 illustrated catalyst is greater than the oxygen storage capacity of the more aged, through the curve 12 illustrated catalyst. Such relationships between the aging of the catalyst and the temperature-dependent oxygen storage capacity are present in the form of data values in a memory 14 stored, which for example as a memory device of the control unit 5 can be trained.

For the catalysts, based on which the curves 11 . 12 In addition, nitrogen oxide emissions were recorded in the New European Driving Cycle (NEDC). This revealed that the through the curve 11 Catalyst complied with the limit of 60 milligrams of NOx per kilometer and also the one through the curve 12 more aged catalyst exceeded this limit by less than 50 percent. Accordingly, also by the curve 12 Catalyst illustrated no aging state, in which an excessively high exceedance of the limit value is present.

Preference is given to determining the in the memory 14 For example, data values to be stored in the form of characteristic curves or characteristic diagrams use a first catalyst which is in a not yet aged new state and a second catalyst which is in a limit state. The limit state of the catalyst describes the aging state of the same, in which the catalyst should be replaced, because this catalyst is no longer able to meet the permissible emission levels. In such catalysts, which have very different aging states, the temperature-dependent oxygen storage capacities are even more different than is the case with the catalysts for which the curve is 11 and the curve 12 in 2 qualitatively illustrate this relationship.

The data values for the characteristic curves and characteristic diagrams which describe the dependency of the oxygen storage capacity on the temperature can be determined in particular on a test bench. However, the corresponding relationships describable by the data values will be those in the motor vehicle 1 arranged catalyst 4 transferred when the control unit 5 while driving the condition of the catalyst 4 of the motor vehicle 1 determined.

In another, in 3 shown graph is also on the ordinate 9 the oxygen storage capacity in milligrams and on the abscissa 10 the temperature is plotted in degrees Celsius. Based on 3 However, the dependence of the oxygen storage capacity of a particular aging state having catalyst on the one hand and the mass flow of the exhaust gas on the other hand should be illustrated. A first, in the graph according to 3 illustrated curve 15 illustrates the dependence of the oxygen storage capacity of the catalyst on the temperature at a first, comparatively small exhaust gas mass flow, for example at an exhaust gas mass flow of about 50 kilograms per hour. To get the metrics to create the curve 15 To obtain the catalyst is first applied to a high exhaust gas mass flow of, for example, about 115 kilograms per hour and thus increases the temperature of the catalyst. Subsequently, the measurement of the oxygen storage capacity of the catalyst takes place during cooling thereof and at a constant mass flow, for example at the mass flow rate of 50 kilograms per hour. The decrease in the temperature or the cooling of the catalyst charged with the lower exhaust gas mass flow is in 3 by a first arrow 16 illustrated. Accordingly, as the temperature decreases, the oxygen storage capacity of the catalyst decreases.

The same catalyst is then again subjected to an increased exhaust gas mass flow, for example with an exhaust gas mass flow of between about 115 kilograms per hour to about 120 kilograms per hour. Accordingly, the temperature in the catalyst increases again. This is in 3 by another arrow 17 qualitatively illustrated. A second, in the graph of 3 illustrated curve 18 illustrates the increase in oxygen storage capacity of the catalyst traversed by the higher exhaust gas mass flow as the temperature increases. Here, therefore, an increase in the oxygen storage capacity with the rise in temperature can be seen. At temperatures of less than 500 degrees Celsius, however, may look like 3 it can be seen that the oxygen storage capacity of the catalyst be greater when it is charged with the larger exhaust gas mass flow is, as if this is acted upon by the lower exhaust gas mass flow. This is due to the fact that at relatively low temperatures of the exhaust gas, the oxygen storage capacity of the catalyst has not yet started.

Data values indicating the corresponding dependencies of the oxygen storage capacity of catalysts having at least two different aging stages at different temperatures and different exhaust gas mass flows are present in the memory 14 stored and from the control unit 5 in judging the condition of the catalyst 4 considered. For example, one may be in the memory 14 of the control unit 5 stored characteristic map based on the measured oxygen storage capacity of the catalyst 4 at a known temperature of the catalyst 4 and known exhaust mass flow through the catalyst 4 a conclusion on the state of aging or the degree of aging of the catalyst 4 to be pulled. A result of monitoring the catalyst 4 through the control unit 5 is thus much more resilient than comparing the measured oxygen storage capacity of the catalyst 4 with a single, fixed limit.

In addition, not only a statement can be made about whether the catalyst 4 is functional or defective, but also about how strong the aging of the catalyst 4 has progressed. A user of the motor vehicle 1 For example, the driver of the motor vehicle 1 , can thus be informed in time if a defect of the catalyst 4 imminent. For example, the controller 5 a warning device 19 of the motor vehicle 1 control the driver of the impending failure of the catalyst 4 communicated. An increased emissions of pollutants with the catalyst 4 equipped motor vehicle 1 can be avoided this way.

LIST OF REFERENCE NUMBERS

1

motor vehicle

2

Internal combustion engine

3

exhaust gas line

4

catalyst

5

control unit

6

lambda probe

7

lambda probe

8th

temperature sensor

9

ordinate

10

abscissa

11

Curve

12

Curve

13

arrow

14

Storage

15

Curve

16

arrow

17

arrow

18

Curve

19

warning device

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102013010562 A1 [0003, 0004]

Claims (9)

Method for determining a state of a catalytic converter (4) of a motor vehicle (1), in which by means of a first sensor (6) a content of oxygen in the exhaust gas upstream of the catalyst (4) and by means of a second sensor (7) a content of oxygen in Exhaust gas downstream of the catalyst (4) is detected, wherein the contents of oxygen in the exhaust gas after changing operating conditions of an upstream of the catalyst (4) arranged internal combustion engine (2) of the motor vehicle (1) are detected, in which following an operation of Internal combustion engine (2) with a rich air-fuel mixture is set to operate with a lean air-fuel mixture, characterized in that based on detected by the sensors (6, 7) measured values of the content of oxygen in the exhaust gas, an oxygen storage capacity of the Catalyst (4) is determined, wherein at least one further size of the exhaust gas is determined and bas Based on a relationship between the oxygen storage capacity and the at least one further variable, the state of the catalyst (4) is determined. Method according to Claim 1 , characterized in that as the at least one further variable, a temperature of the exhaust gas in the catalyst (4) is determined. Method according to Claim 1 or 2 , characterized in that as the at least one further variable, a mass flow of the exhaust gas is determined. Method according to Claim 3 , characterized in that the relationship between the oxygen storage capacity and the mass flow of the exhaust gas at different temperatures of the exhaust gas is determined. Method according to one of the preceding claims, characterized in that the relationship between the oxygen storage capacity and the at least one further variable is determined at least for a first catalyst having a first aging state and for a second catalyst having a second, different from the first aging state aging state based on the determined on the basis of the measured values of the content of oxygen in the exhaust gas oxygen storage capacity on an aging condition of the catalyst (4) is concluded. Method according to Claim 5 , characterized in that as the first catalyst a catalyst is used in the new state and as the second catalyst, a catalyst in a limit state, upon reaching a replacement of the catalyst is to be made is used. Method according to Claim 6 , characterized in that the relationship between the oxygen storage capacity and the at least one further variable for at least one further catalyst is determined with a third, different from the new state and the limit state aging state. Method according to one of the preceding claims, characterized in that a warning device (19) is actuated, which communicates to a user of the motor vehicle (1) an imminent defect of the catalytic converter (4). Aftertreatment device for a motor vehicle (1), comprising a catalytic converter (4), which is arranged downstream of an internal combustion engine (2) of the motor vehicle (1), with a first sensor (6) for detecting a content of oxygen in the exhaust gas upstream of the catalytic converter (4 ) and a second sensor (7) for detecting a content of oxygen in the exhaust gas downstream of the catalyst (4), and with a control device (5), which is designed for determining a state of the catalyst (4), wherein the control device (5) is adapted to cause a change in operating conditions of the internal combustion engine (2) of the motor vehicle (1), in which following an operation of the internal combustion engine (2) with a rich air-fuel mixture, an operation with a lean air-fuel Mixture is set, characterized in that the control device (5) is adapted to, based on the sensors (6, 7) measured values of the content of oxygen in the exhaust gas to determine an oxygen storage capacity of the catalyst (4), wherein in a memory device (14) of the exhaust gas aftertreatment device data values are stored, which indicate a relationship between the oxygen storage capacity and at least one size of the exhaust gas, said Control device (5) is designed to determine based on the context of the state of the catalyst (4).

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