Method for performing on-board diagnosis of an exhaust gas catalytic converter

Abstract

The invention relates to a method for carrying out on-board diagnosis of an exhaust gas catalytic converter in an exhaust gas aftertreatment system of an internal combustion engine of a vehicle. The exhaust gas aftertreatment system comprises an exhaust gas catalytic converter and at least one NOx sensor arranged downstream of the exhaust gas catalytic converter. Firstly, after starting the internal combustion engine, at which the exhaust gas catalytic converter has a temperature below its light-off temperature, the start of a first conversion of nitrogen oxides starting after starting is determined by measuring the NOx concentration in the exhaust gas with the NOx sensor. Subsequently, a parameter is determined, which characterizes the start of the first conversion. The determined parameter is compared with an expected value for the parameter and a state of the exhaust gas catalytic converter dependent on the comparison is determined based on the comparison.

Description

Technical Field

[0001] The invention relates to a method for carrying out on-board diagnosis of an exhaust gas catalytic converter in an exhaust gas aftertreatment system of an internal combustion engine of a vehicle. The invention further relates to a vehicle which is configured to carry out on-board diagnosis of an exhaust gas catalytic converter. Background Art

[0002] The exhaust gas regulations that are becoming increasingly stringent now and in the future place high demands on the original emissions of engines and require highly efficient exhaust gas aftertreatment (ANB) of internal combustion engines. Here, the further stringency of the exhaust gas specifications in view of the permitted nitrogen oxide emissions in accordance with the requirements for further reduced consumption is a challenge for engine developers. In gasoline engines (Ottomotor, Otto engine), exhaust gas cleaning is carried out in a known manner via a three-way catalytic converter and other catalytic converters arranged before or after the three-way catalytic converter. In diesel engines, current exhaust gas aftertreatment systems are used, which have an oxidation catalytic converter, a catalytic converter for selective catalytic reduction of nitrogen oxides (SCR catalytic converter) and a particle filter for separating carbon black particles and, if applicable, other catalytic converters. The common feature is therefore an exhaust gas catalytic converter, which includes a catalytic coating, by means of which the emission of harmful substances (HC, CO and NOx) is reduced.

[0003] Exhaust gas catalytic converters have the property of increasing the speed of certain reactions without consuming any of the gases themselves. By suitable selection of the catalytic converter material or catalytic converter coating, it is possible to complete the oxidation reaction for CO and HC at relatively low temperatures in the presence of oxygen and the reduction reaction for nitrogen oxides NOx in the presence of reduced components (CO, H2, HC) in the exhaust gas.

[0004] For this purpose, Pt, Pd and Rh have been used as catalyst materials. In order to achieve high conversion rates, the noble metals are dispersed on a carrier oxide with a large surface area. The carrier oxide is usually an inorganic material with a complex pore structure (e.g., aluminum oxide), which is applied as an aqueous solution (coating) to a honeycomb monomer (substrate) made of ceramic or metal.

[0005] The exhaust catalytic converter is first heated by the engine exhaust gas. In order to convert the pollutant components (HC, CO, NOx), the exhaust catalytic converter requires a minimum temperature, which is called the light-off temperature. Measures are often taken to shorten the phase until the catalyst is started (light-off). The shortening of the heating time can be achieved by optimizing the catalyst heating measures on the engine side, such as delayed ignition, increased engine speed, camshaft adjustment, lambda curve, and, if necessary, by secondary air supply. In addition, there are active catalyst heating measures, including the so-called E-Kat (electrically heatable catalyst). It can significantly shorten the start time.

[0006] The exact determination of the start of the first initial conversion of pollutant emissions, in other words the determination of the light-off of the exhaust gas catalytic converter during its heating phase, cannot currently be determined unambiguously. With the aid of a lambda probe, only an indirect determination is possible with the aid of the oxygen storage capacity (OSC) of the exhaust gas catalytic converter. However, this is slow on the one hand and inaccurate on the other. However, an accurate determination ensures the advantage of an improved, appropriate control and regulation of the evaluation of the state of the exhaust gas catalytic converter (e.g. aging or contamination, sometimes also called poisoning) and of measures for shortening the heating time of the exhaust gas catalytic converter.

[0007] DE 10 2017 214 444 A1 relates to a method for operating an exhaust gas aftertreatment device, which further comprises a three-way catalytic converter and a NOx sensor arranged downstream. During operation, the NOx emissions are continuously measured by the sensor. If the NOx emissions increase because the three-way catalytic converter loses its efficiency due to a lower catalyst temperature, further measures are implemented, such as delayed ignition and / or electrical heating of the catalyst.

[0008] DE 10 2019 006 426 A1 includes a NOx sensor arranged downstream of a catalyst for monitoring the NOx reduction capacity of the catalyst. During lean operation at an exhaust gas temperature of 600° C. or higher, the engine switches to a rich operating state at a point in time when the air-fuel ratio present downstream of the catalyst reaches a threshold value. When the air-fuel ratio present downstream in the rich operating state reaches a threshold value, the engine switches again to a lean operating state. The diagnostic element compares the NOx concentration in the rich operating state with a diagnostic threshold value in order to thereby diagnose the degree of degradation of the NOx reduction capacity of the catalyst.

[0009] DE 10 2017 218 327 A1 describes a method for operating a combustion engine. In the exhaust system of the combustion engine, there is a three-way catalytic converter with lambda control, which is followed by a NOx sensor with an integrated lambda probe. By measuring the lambda value and the NH3 value in combination with the NOx sensor with an integrated lambda probe, a lambda target value is determined upstream of the three-way catalytic converter. Summary of the invention

[0010] The present invention is based on the object of providing a method for carrying out on-board diagnosis of an exhaust gas catalytic converter in an exhaust gas aftertreatment system of an internal combustion engine of a vehicle and a corresponding vehicle, by means of which the state of the exhaust gas catalytic converter can be determined.

[0011] This object is achieved by a method for performing on-board diagnosis of an exhaust gas catalytic converter in an exhaust gas aftertreatment system of an internal combustion engine of a vehicle and a vehicle with an internal combustion engine and an exhaust gas aftertreatment system, wherein the exhaust gas aftertreatment system comprises the exhaust gas catalytic converter and at least one NOx sensor arranged downstream of the exhaust gas catalytic converter, characterized in that the vehicle is set up to implement the method for performing on-board diagnosis of the exhaust gas catalytic converter.

[0012] According to the invention, a method for carrying out on-board diagnosis of an exhaust gas catalytic converter in an exhaust gas aftertreatment system of an internal combustion engine of a vehicle is provided. In this case, the exhaust gas aftertreatment system comprises an exhaust gas catalytic converter and at least one NOx sensor arranged downstream of the exhaust gas catalytic converter. Firstly, after starting the internal combustion engine, at which the exhaust gas catalytic converter has a temperature below its light-off temperature, the start of a first start-up-initiated conversion of nitrogen oxides is determined by measuring the NOx concentration in the exhaust gas with the NOx sensor. Subsequently, a parameter is determined which characterizes the start of the first-initiated conversion. The determined parameter is compared with an expected value for the parameter and, as a function of the comparison, the state of the exhaust gas catalytic converter is determined as a function of the comparison.

[0013] The NOx sensor preferably comprises a sensor unit and a control unit. The control unit is designed to provide measurement values ​​so that they are then transmitted to the engine controller. The NOx sensor is circulated by the exhaust gas and can thus measure nitrogen and oxygen concentrations. The acquired measurement signals are transmitted to the on-board diagnostics. The on-board diagnostics usually monitor the engine and the emission-related elements of the exhaust gas aftertreatment permanently and during vehicle operation.

[0014] The method comprises a starting process of a cold internal combustion engine, wherein during the starting process the temperature of the exhaust gas catalytic converter is below its light-off temperature. By operating the exhaust gas catalytic converter with hot exhaust gas and the resulting loading, the exhaust gas catalytic converter is supplied with energy by heat conduction, thereby increasing its temperature until it is finally above the light-off temperature. The heating is supported by the initial catalytic converter activity itself, i.e. by the exothermic conversion reaction taking place in the catalytic converter.

[0015] The “light-off temperature” is understood to be the catalytic converter temperature at which 50% of the inflowing pollutants, in this case nitrogen oxides NOx, are catalytically converted. The specific height of the light-off temperature depends on the individual catalytic converter coating.

[0016] The NOx sensor is used in this case to determine whether the conversion of nitrogen oxides has begun, that is, the conversion of NOx into nitrogen, by measuring the nitrogen oxide concentration or its change. It can thus be determined whether the ignition temperature has been reached and the conversion of the pollutant emissions of the exhaust gas has taken place.

[0017] According to a preferred embodiment, the start of the first conversion of nitrogen oxides by the catalyst, which begins after starting, is determined by comparing the NOx concentration measured by a NOx sensor downstream of the catalyst with the NOx concentration present upstream of the catalyst, i.e. the amount of NOx flowing into the catalyst. The latter can be measured by a further NOx sensor upstream of the exhaust gas catalyst or preferably modeled as a function of the operating point of the internal combustion engine. The modeling is usually carried out with the aid of a performance map which presents the raw NOx emissions of the engine as a function of its operating point (load, speed).

[0018] Furthermore, the state of the exhaust gas catalytic converter can be determined by means of the determined parameter which characterizes the start of the first, initially initiated switch-over by comparison with an expected value for the parameter, depending on the comparison.

[0019] Thus, it is possible to first determine basically whether the exhaust gas catalytic converter is usable or damaged. According to the present invention, the proof of the conversion capacity no longer has to be carried out indirectly with the aid of the oxygen storage capacity (OSC) of the exhaust gas catalytic converter with the aid of a lambda probe, but is now carried out directly and substantially more accurately. In addition, according to the present invention, a much more accurate determination of the exact starting point of the initial conversion can be achieved. This assessment is preferably carried out with each start-up process of the internal combustion engine, in which the temperature of the exhaust gas catalytic converter is below its ignition temperature and reaches or exceeds the ignition temperature due to operation. The conventional costly lambda adjustment can thus be omitted. In addition, a prediction of the aging state of the exhaust gas catalytic converter can occur. The possible pollution state of the exhaust gas catalytic converter can also be evaluated by this method. The exhaust gas catalytic converter and its coating are subjected to extremely aggressive conditions, caused by harmful substances in the exhaust gas and high temperatures and temperature differences. The basic dangers for the exhaust gas catalytic converter include thermal overload and pollution. Heat, especially through rapid thermal change stress, can damage not only the catalyst carrier but also the coating. In the case of high and rapidly changing exhaust gas temperatures, the carrier material can lose its strength. In addition, sintering processes can occur in the area of ​​the coating and the coating, so that the active catalytic surface is reduced. In addition to thermal overload, the catalytic coating can also be deactivated by harmful substances. Such substances are Pb, Hg and Cd. They introduce chemical connections and thus form irreversible inactive alloys. Similarly, SO2 and P can be absorbed by the catalytic layer and prevent further reactions. This mechanism is partially reversible and can be degraded by heat. Through the state determination caused by the method according to the invention, it is possible to introduce suitable measures on the one hand in order to regenerate the catalytic layer. On the other hand, it can be determined that in addition to the reversible damage, other irreversible damage has occurred, which, if necessary, makes other measures or even the replacement of the catalyst necessary.

[0020] Suitable catalytic converters that can be used for the assembly or are the subject of the method are generally all components that have a catalytic coating. This can be, for example, a pure exhaust gas catalytic converter, such as a three-way catalytic converter, an oxidation catalytic converter, a NOx storage catalytic converter or an SCR catalytic converter. In addition, catalytically coated particle filters are considered (especially in the first position), that is, particle filters that are equipped with the above-mentioned catalyst coating. In the case of particle filters equipped with a three-way catalytic coating, four-way catalytic converters are also mentioned.

[0021] In a preferred embodiment of the invention, it is provided that the parameter characterizing the start of the first initiated conversion is the time or time equivalent that elapses between the start process and the first initiated conversion. Driving behavior (and therefore engine speed, load, etc.) has a significant influence on the dynamics of the heating of the exhaust gas catalytic converter, which can accordingly have an influence on the start of the first initiated conversion and the expected value of the parameter. Therefore, on the one hand, the use of time as a parameter can be realized, which is measured between the start of the internal combustion engine and the start of the first initiated conversion. Its expected value can be determined, for example, via a model in the form of a comprehensive characteristic curve, which provides information about the expected value of the time depending on the operating mode. In this case, the engine speed and load can be variable, based on which the exactly associated expected value can be determined. Particularly preferably, the parameter is a time equivalent, which advantageously simplifies the determination of the expected value, because the information about driving behavior and the like is often already inherent to the time equivalent. By using time or a time equivalent, in addition to predicting the usual functionality of the exhaust gas catalytic converter, an evaluation of intermediate states can also be performed. Depending on the deviation of the measured value of the parameter from the expected value of the parameter, the current state and efficiency of the exhaust gas catalytic converter can be determined. A defective or damaged exhaust gas catalytic converter starts the conversion with a delay or completely stops the conversion in terms of time or a time equivalent.

[0022] In a further preferred embodiment of the invention, it is provided that the time equivalent is the integrated (cumulative) exhaust gas mass flow, the integrated (cumulative) amount of exhaust gas components (NOx, HC, CO . . . ), the integrated (cumulative) amount of energy input into the catalytic converter, the amount of fuel consumed by the internal combustion engine or the travelled distance. Thus, different suitable possibilities are available, which take into account the driving behavior or operating mode of the vehicle, which influences how much heat is input into the exhaust gas catalytic converter for its heating, in order to achieve an even more accurate state determination of the exhaust gas catalytic converter. The integrated mass flow is incorporated into the driving behavior, for example, in such a way that the fuel supply changes depending on the engine speed and load. Thus, the starting point of the first start of the conversion of the exhaust gas catalytic converter can be distinguished from each other in time in different driving modes. By taking into account the mass flow integrated between the engine start and the start of the conversion over time, the driving behavior is inherently observed and the comparability of the duration between the engine start and the start point of the conversion is ensured. The integrated mass flow can be calculated or modeled simply and with high accuracy, in particular via the engine operating point (load, speed) or cylinder filling. Alternatively, however, there are several possibilities for measuring the mass flow. Likewise, the integrated exhaust gas components, the amount of energy input or the travelled distance are advantageous time equivalents, which can likewise be calculated or measured in known ways.

[0023] In another advantageous embodiment of the method according to the invention, the parameter is the temperature of the exhaust gas catalytic converter or of the exhaust gas downstream of the exhaust gas catalytic converter at the start of the first initial conversion of nitrogen oxides. By determining the temperature as a parameter and comparing it with a desired value, the state or intermediate states of the exhaust gas catalytic converter can be predicted. Thus, for example, the pollution state acts on the catalytic coating of the exhaust gas catalytic converter and influences it with the following consequences: delayed conversion, which only starts at a higher catalytic converter or exhaust gas temperature. By observing and comparing the temperature as a parameter, this and other states can be detected and identified.

[0024] For an even more accurate and more comprehensive assessment of the state of the exhaust gas catalytic converter, preferably the time or a time equivalent and the temperature of the exhaust gas catalytic converter or of the exhaust gas can be used in combination with one another.

[0025] Preferably, the temperature of the exhaust gas catalytic converter or the exhaust gas downstream of the exhaust gas catalytic converter is calculated via a model. Since the lambda probe and the NOx sensor system as well as the knowledge about the internal combustion engine and the control of its air and fuel supply are available, a very accurate model of the temperature development of the exhaust gas catalytic converter or the exhaust gas downstream of the exhaust gas catalytic converter can be generated in conjunction with other component-specific parameters such as, for example, the thermal conductivity, which is dependent on the operating behavior of the vehicle. This can then be used to determine the temperature when starting the first conversion of the exhaust gas catalytic converter.

[0026] According to another preferred embodiment of the invention, the temperature of the exhaust gas catalytic converter or of the exhaust gas downstream of the exhaust gas catalytic converter is measured by a temperature sensor. This can also be done by determining the thermal resistance of the NOx sensor. This allows a very accurate temperature determination to be performed.

[0027] Preferably, the expected value of the parameter is determined as a function of the operating point of the internal combustion engine. As already mentioned, the actual driving behavior and thus the operating mode influence the parameter to be measured and also its expected value. Therefore, for qualitative and quantitative high-value predictions about the state of the exhaust gas catalytic converter, it is advantageous to take into account the operating point of the internal combustion engine. This can be done, for example, by using a comprehensive characteristic curve. The comprehensive characteristic curve can here be an expected value that depends on the engine speed and load of the internal combustion engine. Alternative comprehensive characteristic curves can also be used. The comprehensive characteristic curve can be two-dimensional or multi-dimensional and thus also contain characteristic curves.

[0028] As a result of the evaluation of the comparison of the determined parameter with the expected value of the parameter, the state of the catalytic converter is determined. The state of the catalytic converter is preferably determined by an onboard computer and / or a control unit of the vehicle. If the difference between the determined parameter and the expected value is above a predetermined threshold value, a damaged or severely aged catalytic converter is determined and an error signal is generated by the onboard computer and / or the control unit of the vehicle. In this way, different warning levels can be realized and certain error tolerances can also be calculated.

[0029] Another preferred embodiment of the present invention relates to a vehicle which is a hybrid vehicle. The method is then carried out after the switch from electric motor operation to internal combustion engine operation and after the internal combustion engine has been restarted. In hybrid vehicles which include an electric motor as a traction motor in addition to the internal combustion engine and which are distinguished by reduced emissions of pollutants, it is particularly advantageous for the switched electric motor and internal combustion engine operation to monitor the state of the exhaust gas catalytic converter. After a distance achieved by the electric motor, during the period when the internal combustion engine is not in operation, the catalytic converter can be cooled to its light-off temperature. After the (re)start of the internal combustion engine, the method according to the present invention is suitable for detecting the first initial conversion and the catalytic converter state determined thereby.

[0030] Advantageously, the determined state of the exhaust gas catalytic converter is used to control and / or regulate the exhaust gas catalytic converter measures. By determining the state in accordance with the method of the invention, it can be determined whether and which exhaust gas catalytic converter measures should be implemented. In addition, engine-side catalytic converter heating measures such as delayed ignition, increased engine speed, camshaft adjustment or lambda adjustment can be performed. In addition, there are catalytic converter heating measures outside the engine, which include electrical heating of electrically heatable catalytic converters (so-called E-Kat) or secondary air supply. A significant proportion of the total harmful substance emissions comes from the following phase in which the exhaust gas aftertreatment system is not yet activated, that is, the phase after starting the internal combustion engine. By using the determined state, the mentioned measures can be ideally pre-planned and optimized, so that the start time and the harmful substances determined here can be reduced. Here, the knowledge of the catalytic converter state also allows the necessary matching of the measures. As long as, for example, it is determined that the ignition temperature of a previously damaged or slightly aged catalytic converter is shifted to a higher temperature relative to a new catalytic converter, the intensity and / or duration of the heating measures can be increased.

[0031] Unless otherwise explained in detail, the different embodiments of the invention mentioned in the present application can be advantageously combined with one another. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The invention is explained below in an exemplary embodiment with reference to the accompanying drawings.

[0033] Figure 1 shows the system construction of the exhaust gas aftertreatment system according to the present invention;

[0034] Figure 2 A flow chart of a method for carrying out on-board diagnosis of an exhaust gas catalytic converter according to one embodiment of the present invention is shown. DETAILED DESCRIPTION

[0035] The invention is then implemented according to an embodiment of the invention, for example its use in a vehicle. However, the method is by no means restricted to this application.

[0036] exist Figure 1 1 shows an exhaust gas aftertreatment system 1 according to an embodiment of the invention, which is connected downstream of an internal combustion engine 2 of a vehicle (not shown in further detail otherwise). An exhaust gas catalytic converter 3 is arranged downstream of the internal combustion engine 2, which is designed as a three-way catalytic converter 3 in this example.

[0037] Arranged downstream of the three-way catalytic converter 3 is a NOx sensor 4 which projects into the exhaust gas line, whereby the NOx sensor 4 is circulated by the exhaust gas 6 (indicated by arrows) and measures the NOx concentration or changes therein. Also arranged downstream of the three-way catalytic converter 3 is a flow meter 8 which is designed to measure the exhaust gas mass flow 6 .

[0038] Furthermore, the exhaust gas aftertreatment system 1 comprises a temperature sensor 7. It is located downstream of the three-way catalytic converter 3 and measures the temperature of the exhaust gas escaping from the three-way catalytic converter 3. Another possibility for measuring the exhaust gas temperature is to use the NOx sensor 4 by determining its thermal resistance. Alternatively, the temperature sensor 7 can also be arranged directly at or in the three-way catalytic converter 3 in order to measure the catalyst temperature.

[0039] Furthermore, the vehicle comprises an onboard computer 5 , which is used, among other things, to prepare and evaluate signals which originate, among other things, from the NOx sensor 4 , the flow meter 8 and the temperature sensor 7 .

[0040] Furthermore, the exhaust gas aftertreatment system 4 of the exemplary embodiment shown comprises an electrical catalytic converter heating device 9 which is arranged in the immediate vicinity of the three-way catalytic converter 3 and is designed to heat the three-way catalytic converter 3 .

[0041] Subsequently, according to Figure 2 Explain for example Figure 1 A method according to the invention for a vehicle.

[0042] The method starts in block 10, where the internal combustion engine 2 is started. Before starting the internal combustion engine 2 or at the time of starting the internal combustion engine 2, the three-way catalytic converter 3 has a temperature below its light-off temperature. This temperature is acquired by the temperature sensor 7. Alternatively, the catalyst temperature is modeled. After a longer engine standstill, it is conceivable, for example, that the catalyst temperature corresponds to the ambient temperature.

[0043] According to this embodiment, in addition to the temperature as a parameter, in particular also a time equivalent is used as a parameter to be measured. In this case, the time equivalent is the integrated exhaust gas mass flow. Accordingly, the measurement of this time equivalent is carried out in block 11 directly after the internal combustion engine 2 is started, in other words, the measurement of the exhaust gas mass flow is carried out by means of the flow meter 8 and its integration with the advancing time. Alternatively, the current exhaust gas mass flow is modeled and integrated on a comprehensive characteristic curve depending on the operating point of the internal combustion engine 2.

[0044] In block 12, the nitrogen oxides in the exhaust gas 6 and their changes are measured by means of the NOx sensor 4. At the same time, the NOx concentration flowing into the catalytic converter 3, i.e. the NOx raw emissions of the internal combustion engine 2, is determined. This is preferably done by modeling supported by a map of the NOx raw emissions depending on the operating point of the internal combustion engine 2.

[0045] In block 13, a check is made by the onboard computer 5 whether the NOx concentration acquired by the NOx sensor 4 deviates from the NOx concentration flowing into the catalytic converter 3. If there is no deviation, the conversion by the catalytic converter 3 has not yet started and the method returns to block 12, where the NOx concentration downstream of the catalytic converter 3 is measured again and the current NOx raw emissions of the internal combustion engine 2 are determined, so that the query in block 13 is then repeated.

[0046] If, on the other hand, a deviation of the NOx concentration detected by the NOx sensor 4 from the NOx concentration flowing into the catalytic converter 3 is detected, the conversion of pollutants, in particular nitrogen oxides, present in the exhaust gas 6 is started in the three-way catalytic converter 3. In this case, the determination of this first conversion, which starts after the internal combustion engine 2 is started, is carried out in block 14.

[0047] The onboard computer 5 determines the temperature currently present in the exhaust gas 6 and therefore in the three-way catalytic converter 3 based on the signal of the temperature sensor 7. It also completes the integrated flow measurement (block 15) of the exhaust gas mass flow 6. Thus, a suitable time equivalent is present via the integrated exhaust gas mass flow 6, with which the start of the first initiated conversion can be characterized and compared.

[0048] Based on the performance map, the onboard computer 5 determines the expected value of the characteristic parameter for an undamaged exhaust gas catalytic converter that is like new. By means of the driving mode or operating mode, which takes place from the start of the internal combustion engine 2 and the beginning of the first initial conversion, the expected value can be determined based on the performance map, which can be expected for this specific situation for an exhaust gas catalytic converter that is like new. In block 16, the onboard computer 5 then compares the parameter determined by the measurement for the three-way catalytic converter 3 with the expected value of this parameter determined by the performance map. Since the integrated exhaust gas mass flow is used as a time equivalent in this example (for example, in the measurement of mass), the expected value is also the integrated exhaust gas mass flow, which can be expected for a three-way catalytic converter that is like new between the engine start and the start of the conversion. In addition, the measured temperature of the three-way catalytic converter 3 during the first initial conversion also affects the comparison. The expected value for the temperature of the three-way catalytic converter 3 (from which the conversion can theoretically be expected in the three-way catalytic converter 3 that is like new) can also be determined from the performance map.

[0049] In block 17, the state of the catalytic converter 3 is determined as a function of this comparison. This is done by evaluating the deviation between one or more measured parameters and one or more of their expected values. Threshold values ​​can be defined which take into account certain tolerances and fluctuations. By combining the two parameters (time equivalent and temperature), the state of the three-way catalytic converter 3 can be evaluated particularly accurately. This can be done using average values ​​from the temperature parameter and the time equivalent parameter, wherein the averaging can be converted by different weightings of the two parameters.

[0050] In order to operate the three-way catalytic converter 3 efficiently and keep the emission of pollutants as low as possible, the determined catalytic converter state can also be used to implement and adjust the exhaust gas catalytic converter measures. By way of example, according to the embodiment according to the invention, E-Kat is used. The onboard computer 5 controls the catalytic converter heating device 9 for this purpose. By using the determined state, the catalytic converter heating device 9 is ideally pre-planned and optimized, so that the start time and the pollutants determined here can be reduced, which can be compensated by the catalytic converter heating device, for example, if a reduced efficiency is determined.

[0051] Reference Symbols List

[0052] 1 Exhaust gas aftertreatment system

[0053] 2 Internal combustion engine

[0054] 3 Three-way catalytic converter

[0055] 4 NOx sensor

[0056] 5 Onboard computer

[0057] 6 Exhaust gas / exhaust gas mass flow

[0058] 7 Temperature Sensor

[0059] 8 Flow Meter

[0060] 9 Catalytic converter heating.

Claims

1. A method for performing on-board diagnosis of an exhaust gas catalytic converter (3) in an exhaust gas aftertreatment system (1) of an internal combustion engine (2) of a vehicle, wherein: The exhaust gas aftertreatment system (1) comprises the exhaust gas catalyst (3) and at least one NOx sensor (4) arranged downstream of the exhaust gas catalyst (3), and comprises the following steps: After starting the internal combustion engine (2), wherein the exhaust gas catalytic converter (3) has a temperature below its light-off temperature, the start of a first conversion of nitrogen oxides starting after the start is determined by measuring the NOx concentration in the exhaust gas (6) with the NOx sensor (4), determining parameters characterizing the onset of the first initiated transformation, The determined parameter is compared with the expected value of that parameter, and The state of the exhaust gas catalytic converter (3) is determined as a function of the comparison.

2. The method according to claim 1, wherein: The parameter is the time or time equivalent that elapses between the start-up process and the first initiated conversion.

3. The method according to claim 2, wherein: The time equivalent is the integrated exhaust gas mass flow, the integrated exhaust gas component quantity, the energy quantity input, the fuel quantity consumed or the travelled distance.

4. The method according to claim 1, wherein: The parameter is the temperature of the exhaust gas catalytic converter (3) or the temperature of the exhaust gas (6) downstream of the exhaust gas catalytic converter (3) at the beginning of the first initial conversion of the nitrogen oxides.

5. The method according to claim 4, wherein: The temperature of the exhaust gas catalytic converter (3) or of the exhaust gas (6) downstream of the exhaust gas catalytic converter (3) is calculated via a model or measured by a temperature sensor (7).

6. The method according to any one of claims 1 to 5, wherein: The desired value is determined from a performance map which is dependent on the operating point of the internal combustion engine (2).

7. The method according to any one of claims 1 to 5, wherein: If the difference between the determined parameter and the desired value lies above a predetermined threshold value, an error signal is generated in the on-board computer (5) and / or in the control unit.

8. The method according to any one of claims 1 to 5, wherein: The vehicle is a hybrid vehicle and the method is carried out after starting the internal combustion engine (2) after switching from electric motor operation to internal combustion engine operation.

9. The method according to any one of claims 1 to 5, wherein: The determined state of the exhaust gas catalytic converter (3) is used for opening and / or regulating exhaust gas catalytic converter measures.

10. A vehicle with an internal combustion engine (2) and an exhaust gas aftertreatment system (1), wherein: The exhaust gas aftertreatment system (1) comprises the exhaust gas catalytic converter (3) and at least one NOx sensor (4) arranged downstream of the exhaust gas catalytic converter (3), characterized in that the vehicle is configured to implement a method according to any one of claims 1 to 9 for performing on-board diagnosis of the exhaust gas catalytic converter (3) in the exhaust gas aftertreatment system (1) of an internal combustion engine (2) of the vehicle.

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