DE102018209811A1 - Method for determining a state of a catalytic converter and exhaust gas 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 temperature of the catalytic converter (4) is increased by operating an internal combustion engine (2) of the motor vehicle (1) arranged upstream of the catalytic converter (4) , Downstream of an inlet (5) of the catalytic converter (4), at least one measured value is detected by means of at least one sensor (6), which correlates with an oxygen content in the exhaust gas of the internal combustion engine (2). A greater change in the measured values is recorded in a first measured value range than in at least one further measured value range adjacent to the first measured value range. A temperature of the catalyst (4) present in the first measured value range is determined. The state of the catalytic converter (4) is determined on the basis of the temperature present in the first measured value range. The invention further relates to an exhaust gas 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 a temperature of the catalytic converter is increased by operating an internal combustion engine of the motor vehicle arranged upstream of the catalytic converter. Downstream of an inlet of the catalytic converter, at least one measured value is recorded by means of at least one sensor, which correlates with an oxygen content in the exhaust gas of the internal combustion engine. Furthermore, the invention relates to an exhaust gas aftertreatment device for a motor vehicle.

To comply with legal requirements with regard to the emissions of an internal combustion engine of a motor vehicle, on the one hand, the internal combustion engine or the engine must be set correctly. In addition, however, exhaust gas aftertreatment by means of at least one catalytic converter is also required in order to comply with emission limit values. The effectiveness of the at least one catalyst strongly depends on its aging. In order to ensure the functionality of the catalytic converter in the motor vehicle, the aging of the catalytic converter is therefore regularly determined. A measurement is usually carried out for this purpose in order to determine the oxygen storage capacity of the catalyst.

For example, the DE 102 48 842 A1 a method for determining the aging state of an exhaust gas catalytic converter, in which a light-off temperature of the catalytic converter and its oxygen storage capacity are ascertained to determine the aging state. According to the DE 102 48 842 A1 oxygen sensors are used to control the lambda of the internal combustion engine when the internal combustion engine is warmed up. In fact, when the internal combustion engine is warming up, a control oscillation of a certain amplitude and frequency of the combustion air ratio is impressed with which the combustion takes place in the internal combustion engine. The vibrations of the combustion air ratio on the inlet side of the catalytic converter are smoothed out as they pass through the catalytic converter due to its oxygen storage capacity. This means that if the catalytic converter has a high oxygen storage capacity, it is no longer possible to detect any oscillation of the combustion air ratio by means of an oxygen sensor serving as a diagnostic probe.

Furthermore, it is possible to temporarily reduce the combustion air ratio with which the internal combustion engine is operated from a value of Ä = 1 to a value of Ä <1. A lambda probe arranged downstream of the catalytic converter then also measures a reduced oxygen content in the exhaust gas downstream of the catalytic converter with a certain time delay. The greater this time delay between the setting of a reduced value of the combustion air ratio λ and the reaction of the lambda sensor downstream of the catalytic converter, the greater the oxygen storage capacity of the catalytic converter. This relationship is usually used to infer the aging of the catalyst.

However, there may be a deterioration in the emission results downstream of the catalyst even though the catalyst has good oxygen storage capacity. Some damage mechanisms, such as oil poisoning, act more on the oxygen storage in the coating than on the precious metals contained in the coating. These components of the catalytic converter can thus be impaired, even if the components of the catalytic converter responsible for the storage of oxygen hardly show any aging. It is therefore not always possible to infer the emission results and consequently the aging of the catalyst directly from the oxygen content or from the oxygen storage capacity of the catalyst.

Furthermore, the case may occur that the oxygen storage capacity of the catalytic converter is impaired, but the catalytic conversion of exhaust gas components, which is caused by noble metal components of the catalytic converter, hardly shows any deterioration. For this reason too, there is not necessarily a direct connection between the oxygen storage capacity of the catalytic converter and its performance with regard to the conversion of exhaust gas components.

In addition, it has been shown that measurement results for determining the oxygen storage capacity of the catalyst can vary widely. So two successive measurements can show different results. This also makes it difficult to deduce the aging of the catalyst from the oxygen storage capacity.

If the oxygen storage capacity of the catalytic converter is used to determine the aging of the catalytic converter, on the one hand the associated large spread of aging is disadvantageous. A further disadvantage is that there may not be a good correlation between the measurement result for the quality of the oxygen storage of the catalytic converter and the emissions of the motor vehicle equipped with the catalytic converter, since this is the case Consideration of other influences can be neglected. This applies in particular to the aging of the noble metals of the catalyst.

It is an object of the invention to provide a method and an exhaust gas aftertreatment device which is suitable for carrying out the method and which enables a particularly reliable determination of the state of the catalytic converter.

This object is achieved according to the invention by a method with the features of patent claim 1 and by an exhaust gas aftertreatment device with 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 temperature of the catalytic converter is increased by operating an internal combustion engine of the motor vehicle arranged upstream of the catalytic converter. The behavior of the catalytic converter warming up from the cold state is therefore considered. Downstream of an inlet of the catalytic converter, at least one measured value is recorded by means of at least one sensor. The at least one measured value correlates with an oxygen content in the exhaust gas of the internal combustion engine. A greater change in the measured values is recorded in a first measured value range than in at least one further measured value range adjacent to the first measured value range. A temperature of the catalytic converter present in the first measured value range is determined. The state of the catalytic converter is determined on the basis of the temperature present in the first measured value range.

This is based on the knowledge that there is a first connection between the emission results which are achieved in the operation of the warmed up or heated catalyst with regard to the conversion of pollutants, and the course of the measured values, which are recorded by means of the sensor. The sudden or strong change in the measured values occurring in the first measured value range correlates with an equally comparatively sudden increase in the conversion of pollutants in the catalytic converter. A second relationship exists between this first relationship and the ignition temperature or light-off temperature of the catalytic converter. This light-off temperature is in turn dependent on the aging of the catalyst.

Depending on the condition or aging condition of the catalytic converter, the catalytic converter starts up, that is, at least 50 percent conversion of at least one pollutant under consideration occurs at a lower temperature or at a higher temperature. Starting or igniting the catalyst in turn means that the conversion of the pollutants increases suddenly or suddenly. However, this abrupt improvement in the catalyst with regard to the conversion of the pollutants occurs essentially simultaneously with the rapid or sudden change in the measured values in the first measured value range. By looking at the temperature of the catalytic converter present in the first measured value range, the condition of the catalytic converter can thus be determined particularly reliably or assessed realistically.

The corresponding relationships, namely on the one hand between the sudden improvement in the emission results and the sudden change in the measured values and on the other hand between this correlation and the light-off temperature of the catalytic converter, have proven to be particularly reliable in series of tests for realistically determining the condition of the catalytic converter. In addition, there is very little variation in the results. Aging effects of components of the catalyst such as precious metals in a catalytically active surface of the catalyst are implicitly considered in this process. Because these aging effects relate directly to the emission results of the catalyst and its light-off temperature. As a result, the method enables a particularly reliable determination of the state of the catalytic converter.

In the method, the behavior of the entire catalyst is advantageously considered and not only the behavior of the oxygen-storing components of the catalyst, that is to say of cerium components and / or zirconium components of the catalyst. The catalytic converter of the motor vehicle can in particular be designed as a three-way catalytic converter and / or as an oxidation catalytic converter or the like.

A change in the measured values as a function of time is preferably recorded in the first measured value range. This is because the sudden or abrupt change in the measured values compared to a less pronounced change in the measured values can be determined in the at least one further measured value range in a simple and reliable manner. This applies in particular if a change in the measured values is also recorded as a function of time in the further measured value ranges.

The change occurring in the first measured value range is preferably the Measured values detected an increase in electrical voltage. This is because a lambda probe which is to be provided anyway to check the functionality of the catalytic converter and which is arranged downstream of the inlet of the catalytic converter can be used to record the at least one measured value. The time course of the voltage of this lambda probe can be used particularly easily to determine the state of the catalytic converter.

The temperature of the catalytic converter present in the first measured value range can be determined by measuring a temperature of the exhaust gas in the catalytic converter. A temperature sensor can be used for this. In this way, the temperature can be determined particularly reliably.

Additionally or alternatively, the temperature of the catalytic converter present in the first measured value range can be determined based on operating conditions of the internal combustion engine. The temperature can therefore also be determined using a model, so that the effort associated with the provision of a temperature sensor can be dispensed with.

However, the temperature, which is modeled, that is to say determined based on operating conditions of the internal combustion engine, can also be checked for its plausibility by means of a temperature sensor.

To determine the state of the catalytic converter, the temperature of the catalytic converter present in the first measured value range is preferably compared with reference values of the temperature stored in a memory. Such a comparison with reference values stored in the memory of a control device, such as a control device or an on-board computer, for example in a table, enables the state of the catalytic converter to be determined with little effort and in a reliable manner. In particular, the temperature of the catalytic converter present in the first measured value range can be assigned to a respective state of the catalytic converter by interpolation or extrapolation.

An aging state of the catalyst is preferably determined as the state of the catalyst. Because the ability of the catalytic converter to convert pollutants contained in the exhaust gas into other, harmless exhaust gas components depends on the aging of the catalytic converter.

Finally, it has proven to be advantageous if a warning device is activated which communicates an impending defect in the catalytic converter to a user of the motor vehicle. For example, in the motor vehicle which is equipped with the catalytic converter, a warning lamp can inform the user, in particular the driver, of the impending defect in the catalytic converter. Additionally or alternatively, a corresponding message can be shown 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 good time that a catalytic converter defect is imminent. In this way, the user can have countermeasures taken in good time, such as a check, maintenance or replacement of 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 in an exhaust line of the motor vehicle. The exhaust gas aftertreatment device comprises at least one sensor arranged downstream of an inlet of the catalytic converter for detecting at least one measured value, which correlates with a content of oxygen in the exhaust gas of the internal combustion engine. A control device of the exhaust gas aftertreatment device is designed to determine a state of the catalytic converter. The control device is designed to detect a greater change in the measured values in a first measured value range than in at least one further measured value range adjacent to the first measured value range. The control device is further designed to determine the state of the catalytic converter based on a temperature of the catalytic converter present in the first measured value range.

Consequently, the method according to the invention can be carried out by means of the exhaust gas aftertreatment device. Accordingly, the exhaust gas aftertreatment device enables a particularly reliable determination of the state of the catalytic converter.

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

Further features of the invention result from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively specified combination but also in other combinations or on their own.

• 1 stark schematisiert ein Kraftfahrzeug mit einer Verbrennungskraftmaschine, in deren Abgasstrang ein Katalysator angeordnet ist, wobei ein Steuergerät des Kraftfahrzeugs dazu ausgebildet ist, anhand des Spannungsverlaufs einer Lambdasonde und der Anspringtemperatur des Katalysators einen Zustand des Katalysators zu ermitteln;
• 2 einen Graphen, in welchem die Konvertierung von Schadstoffen mittels des neuen, nicht gealterten Katalysators in Abhängigkeit von der Temperatur des Katalysators anhand dreier Kurven dargestellt ist, wobei zusätzlich der Verlauf der mittels der Lambdasonde erfassten Spannung dargestellt ist; und
• 3 einen weiteren Graphen, in welchem drei Kurven die Konvertierung von Schadstoffen mittels des Katalysators angeben sowie weitere Kurven den Spannungsverlauf der Lambdasonde, wobei in 3 die Verhältnisse für einen Katalysator mit Alterungserscheinungen dargestellt sind.

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

• 1 highly schematized a motor vehicle with an internal combustion engine, in the exhaust line of which a catalytic converter is arranged, a control device of the motor vehicle being designed to determine a state of the catalytic converter on the basis of the voltage profile of a lambda probe and the light-off temperature of the catalytic converter;
• 2 a graph in which the conversion of pollutants by means of the new, non-aged catalytic converter as a function of the temperature of the catalytic converter is shown on the basis of three curves, the course of the voltage detected by means of the lambda probe also being shown; and
• 3 a further graph in which three curves indicate the conversion of pollutants by means of the catalytic converter and further curves the voltage curve of the lambda sensor, wherein in 3 the conditions for a catalyst are shown with signs of aging.

In 1 is a highly schematic motor vehicle 1 shown which is an internal combustion engine 2 having. In an exhaust line 3 the internal combustion engine 2 is a catalyst 4 arranged. The catalyst 4 can be designed, for example, as a three-way catalytic converter, as an oxidation catalytic converter or the like. Downstream of an inlet 5 of the catalyst 4 is a sensor 6 arranged, which in the present case is designed as a lambda probe. By means of the sensor 6 Accordingly, measured values are recorded which contain oxygen in the exhaust gas of the internal combustion engine 2 correlate. The sensor 6 can be designed as a voltage step probe or as a broadband probe.

In 1 is shown schematically that the sensor 6 downstream of an outlet 7 of the catalyst 4 in the exhaust line 3 is arranged. The catalyst 4 However, it can also have a plurality of blocks or monoliths, for example a first monolith and a second monolith, each of which has a catalytically active surface. Then it can also be provided that the sensor 6 , downstream of the first monolith and upstream of the second monolith, the measured values in the catalyst 4 detected.

The means of the sensor 6 Measured values are sent to a control device, for example in the form of a control unit 8th of the motor vehicle 1 transmitted. With the sensor 6 Measured values recorded are values of an electrical voltage, which depends on the oxygen content in the exhaust gas, with which an electrode of the sensor 6 is applied when the catalyst 4 from the exhaust gas of the internal combustion engine 2 is flowed through.

Behavior of the catalytic converter is present 4 viewed from the cold state. Accordingly, the initially cold catalyst 4 by operating the internal combustion engine 2 heated. However, a heater can also be provided around the catalyst 4 bring it up to its operating temperature more quickly, at which a conversion of pollutants contained in the exhaust gas takes place to a desired extent.

In one in 2 shown graphs 9 illustrate several curves 10 . 11 . 12 the conversion of pollutants in the catalyst 4 depending on the temperature of the catalyst 4 , Accordingly, the curve illustrates 10 the conversion of hydrocarbons (CH) using the catalyst 4 , the curve 11 the conversion of carbon monoxide (CO) and the curve 12 the conversion of nitrogen oxides (NOx) using the catalyst 4 , It is from the graph 9 in 2 can be seen that with the three curves 10 . 11 . 12 As the temperature of the exhaust gas increases, the conversion rates of hydrocarbons, carbon monoxide and nitrogen oxides, given in percent, increase suddenly or suddenly. This happens when the catalyst 4 has reached its so-called light-off temperature or ignition temperature.

In the graph in 2 is the temperature of the catalyst 4 or that in the catalyst 4 located exhaust gas on an abscissa 13 applied. On respective sections of a first ordinate 14 are in the graph 9 according to 2 in contrast, the conversion rates of the exemplified pollutants in the form of hydrocarbons, carbon monoxide and nitrogen oxides. On another ordinate 15 is in the graph 9 according to 2 by means of the sensor 6 recorded voltage is plotted. Here, a first curve illustrates 16 by means of the sensor 6 captured readings of voltage when the sensor 6 downstream of the first monolith of the catalyst 4 is arranged. A second curve 17 illustrates this using the sensor 6 captured readings of voltage when the sensor 6 as in 1 shown downstream of the outlet 7 of the catalyst 4 is arranged. In both curves 16 . 17 is in a first range of measured values 18 a particularly large change in the measured values of the voltage can be detected. The one through the curves 16 . 17 The specified time profile of the measured values of the voltage thus points in this first measured value range 18 a jump or rise. In contrast, the first, measured value range 18 adjacent measured value ranges 19 . 20 of the curves 16 . 17 the changes in the measured values of the voltage are significantly less.

From the graph 9 in 2 , which shows the conditions for the new, not yet aged catalyst 4 is a correlation between those shown by the curves 10 . 11 . 12 illustrated emission results of the catalyst 4 and the time course of the sensor 6 measured voltage. Accordingly, there is a first connection between the emission results and the voltage profile of the lambda sensor or the sensor 6 ascertainable. Another connection exists between this first connection and the light-off temperature or ignition temperature of the catalytic converter 4 ,

For this purpose, the starting behavior of the warm-up catalytic converter 4 viewed from the cold state. In the in 2 shown graphs 9 which are the ratios for the new, unused catalyst 4 illustrates, on the one hand, there is a clear relationship between the emission measurements and the voltage at the sensor 6 seen. The catalytic converter starts or ignites 4 takes place here, for example, at a temperature 21 of around 280 degrees Celsius. In the area of this temperature 21 at which the conversion rates of the catalyst 4 have already risen sharply, is also the sudden change in the sensor 6 detected voltage observable. The temperature 21 is based on the abscissa 13 in the first measurement range 18 ,

There is therefore the first connection between the performance of the catalytic converter 4 with regard to the reduction of pollutants in the exhaust gas and thus with regard to the emissions of the motor vehicle 1 and that by means of the sensor 6 measured voltage. This relationship has proven to be particularly reliable in test series, and a scattering of the same in tests carried out in succession on the same catalyst 4 is very low. The second relationship is formed by the first relationship and the light-off temperature or ignition temperature of the catalytic converter 4 , in in 2 shown example, the first relationship and the temperature 21 , Here, too, tests and measurements have shown reliable values, and the spread is very small.

With particular reference to one in 3 shown further graphs 22 should be the reliability in determining the aging condition of the catalyst by looking at the measured values of the sensor 6 on the one hand and the light-off temperature of the catalyst 4 on the other hand, are illustrated again.

Again are in the graph 22 on the first ordinate 14 in respective sections the conversion rates in percent for hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) are plotted, and on the abscissa 13 the temperature of the exhaust gas in the catalytic converter 4 in degrees Celsius. On the further or second ordinate 15 is the one with the sensor 6 recorded voltage is plotted. The in 3 shown graph 22 however illustrates the conditions for the catalyst 4 , if it is aged, i.e. shows signs of aging.

In 3 accordingly illustrates a curve 32 the effectiveness of the aged catalyst 4 after a cold start in terms of hydrocarbon conversion, a curve 23 in terms of carbon monoxide conversion and a curve 24 with regard to the conversion of nitrogen oxides. It can be seen that a sudden increase in the conversion rates and thus an improvement in the emission results occurs only at a higher temperature than that for the new, non-aged catalyst 4 according to 2 the case is. Furthermore illustrate in 3 respective curves 25 . 26 the time course of the sensor 6 measured voltage. The curve 25 shows the conditions when the sensor 6 is arranged downstream of the first monolith, and the curve 26 illustrates the relationships when the sensor 6 the voltage downstream of the outlet 7 of the catalyst 4 recorded (compare 1 ).

Even with the aged catalyst 4 occurs in a first range of measured values 27 a sudden increase in using the sensor 6 recorded measured values of the voltage. There will also be one in this first measurement range 27 present temperature 28 of the catalyst 4 certainly. With that through the graph 22 in 3 exemplified aged catalyst 4 is this temperature 28 , i.e. the light-off temperature of the catalyst 4 , but significantly higher at around 360 degrees Celsius.

Even with the aged catalyst 4 is a clear correlation between the performance of the catalyst 4 with regard to the conversion of pollutants and the time course of using the sensor 6 detected voltage recognizable. However, that occurs in the first measurement range 27 noticeable jump in the measured values of the voltage later, namely at the higher temperature 28 on than this according to the graph 9 at the in 2 illustrated, new or not yet aged catalyst 4 the case is.

By considering on the one hand the sudden increase of the sensor 6 detected voltage and on the other hand the light-off temperature of the catalyst 4 the aging of the catalyst 4 determine particularly reliably. Because further aging effects are implicitly considered here, because aging effects of the catalytic converter 4 direct impact on using the catalyst 4 achievable reductions in pollutant emissions. These emission results in turn correlate with those using the lambda probe or the sensor 6 detected voltage.

While driving the motor vehicle 1 can thus at the start of the same and the subsequent heating of the catalyst 4 the aging of the catalyst 4 directly from the jump of using the sensor 6 or the voltage detected by the lambda probe. For this, the value of the temperature 21 . 28 in the area of the jump of the signal of the lambda probe in the on-board computer or in the control unit 8th can be compared with reference values. The reference values can be stored in a memory, for example 29 be stored, for example in one in the memory 29 of the control unit 8th deposited table.

To the value of the temperature 21 . 28 can determine a temperature sensor 30 can be used (compare 1 ). The value of the temperature 21 . 28 can also be modeled, for example, based on the operating conditions of the internal combustion engine 2 be determined. By comparing the value of the temperature 21 . 28 , in which both the sudden improvement in the emission values of the catalyst 4 occurs as well as the sudden increase in the level of the sensor 6 detected voltage with that in the memory 29 especially the control unit 8th stored reference values of temperature can particularly easily and reliably aging the catalyst 4 be determined.

A user of the motor vehicle 1 , for example the driver of the motor vehicle 1 , can thus be informed in good time if a defect in the catalytic converter 4 imminent. For example, the control device 8th a warning device in the form of a warning lamp 31 control which the driver the impending or already occurred defect of the catalyst 4 communicated.

LIST OF REFERENCE NUMBERS

1

motor vehicle

2

Internal combustion engine

3

exhaust gas line

4

catalyst

5

inlet

6

sensor

7

outlet

8th

control unit

9

graph

10

Curve

11

Curve

12

Curve

13

abscissa

14

ordinate

15

ordinate

16

Curve

17

Curve

18

Measuring range

19

Measuring range

20

Measuring range

21

temperature

22

Curve

23

Curve

24

Curve

25

Curve

26

Curve

27

Measuring range

28

temperature

29

Storage

30

temperature sensor

31

warning light

32

Curve

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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.

Patent literature cited

• DE 10248842 A1 [0003]

Claims (9)

Method for determining a state of a catalytic converter (4) of a motor vehicle (1), in which a temperature of the catalytic converter (4) is increased by operating an internal combustion engine (2) of the motor vehicle (1) arranged upstream of the catalytic converter (4), and in which Downstream of an inlet (5) of the catalytic converter (4), at least one measured value is detected by means of at least one sensor (6), which correlates with a content of oxygen in the exhaust gas of the internal combustion engine (2), characterized in that a larger one is in a first measured value range The change in the measured values is recorded as in at least one further measured value range adjacent to the first measured value range, a temperature of the catalyst (4) present in the first measured value range being determined and the state of the catalyst (4) being determined based on the temperature present in the first measured value range becomes. Procedure according to Claim 1 , characterized in that a change in the measured values as a function of time is recorded in the first measured value range. Procedure according to Claim 1 or 2 , characterized in that an increase in an electrical voltage is detected as the change in the measured values occurring in the first measured value range. Method according to one of the preceding claims, characterized in that the temperature of the catalyst (4) present in the first measured value range is determined by measuring a temperature of the exhaust gas in the catalyst (4). Method according to one of the preceding claims, characterized in that the temperature of the catalytic converter (4) present in the first measured value range is determined based on operating conditions of the internal combustion engine (2). Method according to one of the preceding claims, characterized in that, in order to determine the state of the catalyst (4), the temperature of the catalyst (4) present in the first measured value range is compared with reference values of the temperature stored in a memory (21). Method according to one of the preceding claims, characterized in that an aging state of the catalyst (4) is determined as the state of the catalyst (4). Method according to one of the preceding claims, characterized in that a warning device (31) is actuated, which communicates an impending defect in the catalytic converter (4) to a user of the motor vehicle (1). Exhaust gas aftertreatment device for a motor vehicle (1), with a catalytic converter (4), which is arranged downstream of an internal combustion engine (2) of the motor vehicle (1) in an exhaust line (3) of the motor vehicle (1), with at least one downstream of an inlet (5) of the catalytic converter (4) arranged sensor (6) for detecting at least one measured value, which correlates with a content of oxygen in the exhaust gas of the internal combustion engine (2), and with a control device (8), which is used for determining a state of the catalytic converter (4) is formed, characterized in that the control device (8) is designed to detect a greater change in the measured values in a first measured value range than in at least one further measured value range adjacent to the first measured value range, the control device (8) being further designed to based on a temperature of the catalytic converter present in the first measured value range rs (4) to determine the state of the catalyst (4).

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