Methods for system diagnostics of a drive unit for a motor vehicle and corresponding drive unit

Abstract

A method for operating a drive unit for a motor vehicle, wherein the drive unit comprises an exhaust gas-generating drive unit and an exhaust gas value describing the composition of the exhaust gas is determined by means of an exhaust gas probe, and a state value describing the state of the respective system is determined for several systems of the drive unit within the framework of a system diagnostic, characterized in that for each of the several systems, at least one system defect data record indicates whether a system defect of the respective system affects the exhaust gas value, wherein, when an exhaust gas value value exceeds a range, the system defect data records of the systems are first placed on a checklist of system defect data records to be checked, and subsequently those system defect data records for which no influence on the exhaust gas value is recorded are removed from the checklist.wherein, for the system defect records remaining on the checklist, a setup diagnosis is performed to detect the system defect of the respective system based on the state value, wherein, for the system defect records remaining on the checklist, at least one linkage diagnosis is performed as part of the setup diagnosis, wherein, for at least one of the system defect records of a first of the systems, at least one linkage condition is stored which formulates a relationship between a first state value change of the state value assigned to the first system with a second state value change of the state value assigned to a second system, wherein, as part of the linkage diagnosis, those system defect records for which the respective linkage condition is not fulfilled are removed from the checklist.

Description

The invention relates to a method for operating a drive unit for a motor vehicle, wherein the drive unit comprises an exhaust gas-generating drive unit, and an exhaust gas value describing the composition of the exhaust gas is determined by means of an exhaust gas probe, and a state value describing the state of each system is determined for several systems of the drive unit within the framework of a system diagnostic. The invention further relates to a drive unit for a motor vehicle. For example, German patent application DE 10 2021 003 415 A1 is known from the prior art. This document describes a control unit for monitoring the emission behavior of a machine, whereby the monitoring is based on an initial emission influence of a component of the machine. The control unit is designed and configured to perform the following steps: determining an initial defect measure of a first component of the machine, determining an initial emission influence based on the determined initial defect measure, and monitoring the emission behavior of the machine based on the initial emission influence. The German patent application DE 10 2018 201 075 A1 relates to a method for monitoring pollutant emissions during the operation of an internal combustion engine and / or an exhaust aftertreatment system in a motor vehicle, comprising the following steps: determining one or more pollutant limit values ​​for one or more pollutant categories using a provided emission limit value model depending on one or more operating state variables of the motor vehicle; sensorially determining a pollutant concentration value for each pollutant category; determining an error in the form of an exceedance of one or more pollutant concentration values ​​for each pollutant category. The prior art documents DE 10 2007 041 848 A1 and DE 10 2010 006 728 A1 are also known. The object of the invention is to propose a method for operating a drive device which has advantages over the prior art, in particular detecting a system defect of one of the systems of the drive device with high reliability even if the system diagnostics of the respective system does not indicate such a defect. According to the invention, this is achieved by a method for operating a drive unit for a motor vehicle with the features of claim 1. It is provided that for each of the several systems, at least one system defect data record indicates whether a system defect of the respective system affects the exhaust gas value. When an exhaust gas value exceeds a specified range, the system defect data records are first placed on a checklist of system defect data records to be checked, and then those system defect data records for which no effect on the exhaust gas value is recorded are removed from the checklist. For the system defect data records remaining on the checklist, a system diagnostic is performed to detect the system defect of the respective system based on its state value.wherein, for the system defect records remaining on the checklist, at least one additional linkage diagnosis is performed as part of the setup diagnosis, wherein for at least one of the first system defect records of a first of the systems, a linkage condition is stored which formulates a relationship between a first change in the state value of the state value with a second change in the state value of the state value assigned to a second system, wherein, as part of the linkage diagnosis, those system defect records for which the respective linkage condition is not fulfilled are removed from the checklist. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments described in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are possible. The drive system serves to propel the motor vehicle, thus providing the drive torque directed towards propelling the motor vehicle. The drive system is preferably an integral part of the motor vehicle, but can, of course, also be separate from it. To provide the drive torque, the drive system comprises the drive unit, which is preferably designed as an internal combustion engine. During operation of the drive system, fuel and fresh gas are supplied to the drive unit at least intermittently, with the fresh gas containing fresh air at least intermittently. Additionally, the fresh gas may contain exhaust gas if exhaust gas recirculation is implemented, in which the exhaust gas generated by the drive unit is at least partially returned to the drive unit as a component of the fresh gas.The fuel and fresh gas supplied to the drive unit form a fuel-fresh gas mixture with a specific composition, which is then reacted within the drive unit. During operation of the engine, exhaust gas is produced due to the chemical reaction of fuel and fresh air. This exhaust gas is discharged towards the outside environment of the engine or vehicle. Preferably, before being released into the outside environment, the exhaust gas is first fed into an exhaust aftertreatment system, since it contains pollutants. In the exhaust aftertreatment system, the pollutants are at least partially converted into less harmful products. Only after passing through the exhaust aftertreatment system is the exhaust gas discharged into the outside environment. The exhaust aftertreatment system can be, for example, a vehicle catalyst, in particular a three-way catalyst, an oxidation catalyst, a NOx storage catalyst, or an SCR catalyst.However, it can also be designed as a particulate filter, in particular as a gasoline particulate filter or as a diesel particulate filter, preferably with an integrated vehicle catalyst, for example with a catalytic coating. The drive system comprises several systems, each of which constitutes a part of the drive system. These systems include, for example, components of the drive system or drive unit, as well as, or alternatively, software programs running on a control unit of the drive system. The systems thus encompass any elements of the drive system, particularly those that influence the composition and / or flow rate of the exhaust gas. Flow rate, in this context, refers to the quantity of exhaust gas per unit of time, specifically an exhaust gas mass flow or an exhaust gas volume flow. By way of example, the systems of the drive unit include one or more of the following systems: high-pressure fuel pump, fuel pressure sensor, load sensor, mixture adaptation, tank vent valve, exhaust aftertreatment system, lambda sensor, in particular pre-catalyst lambda sensor or post-catalyst lambda sensor, temperature sensor, ambient pressure sensor, turbocharger, in particular compressor and / or exhaust gas turbocharger, boost pressure sensor, intake manifold leakage test, camshaft adjuster, crankcase ventilation, EVAP system, in particular tank leakage test, expansion valve test or fuel tank shut-off valve test, cooling system, cylinder imbalance sensor, idle speed control, cold start strategy, valve lift switching, exhaust flap, knock sensor and ignition detection. System diagnostics are performed for each of the drive unit's systems, during which the status value is determined. The status value describes the condition of the respective system and is used to monitor each individual system. During system diagnostics, only one system is considered at a time; accordingly, a separate system diagnostic is performed for each system. This procedure is commonly referred to as On-Board Diagnostics (OBD). It can provide an indication of a potential system defect in individual systems. Furthermore, the exhaust gas sensor determines the exhaust gas value, which describes the composition of the exhaust gas. In particular, the exhaust gas value provides an indication of the concentration of at least one exhaust gas component. The exhaust gas sensor can be designed and positioned, for example, to measure raw emissions from the engine or to measure tailpipe emissions. In the former case, it is positioned between the engine and the exhaust aftertreatment system; in the latter case, it is positioned downstream of the exhaust aftertreatment system, i.e., between the exhaust aftertreatment system and a tailpipe through which the exhaust gas is released into the environment. The exhaust gas value allows for monitoring of the engine's emissions. For example, if an exhaust gas threshold is exceeded, the exhaust gas value indicates a malfunction in the engine. The exhaust gas value determined using the exhaust gas probe is primarily used to detect a system defect in one of the systems, particularly a defect in the system that caused the exhaust gas value to exceed the threshold. This provides a clear indication of a potential system defect without requiring, for example, the inspection of numerous systems during a drive system repair. This process can also be described as "pinpointing." Naturally, only a single exhaust gas value can be used. However, it is preferable to use several exhaust gas values, which are available for several different exhaust gas components. In this respect, it is intended to determine at least one exhaust gas value using at least one exhaust gas probe. Preferably, each of these exhaust gas values ​​is assigned to one of several exhaust gas value ranges. The procedure described for the system defect data sets is carried out, for example, if one or more of the exhaust gas values ​​leave their respective assigned exhaust gas value range. The diagnosis of all multiple systems is performed as part of a setup diagnosis. Unlike system diagnostics, this does not consider just one system, but rather several systems. The setup diagnosis provides feedback indicating which system has a system defect, or at least which system is likely to have one. To perform the setup diagnosis, it is recorded for each system whether its defect affects the exhaust gas value, specifically in a data log. For example, a marker is stored in the data log for each system, indicating a first state if the defect affects the exhaust gas value and a second state if it does not. The system defect data records serve this purpose. At least one system data record is stored for each system.However, it may also be provided that several system data records are stored for one or more of the systems, which describe different types of system defects. If the exhaust gas value now leaves the exhaust gas value range, i.e., lies outside the exhaust gas value range, the system diagnostics are performed, and only then. During the system diagnostics, all system defect data records, or at least some of them, are first added to the checklist, which specifies or lists the system defect data records to be checked. Subsequently, all those system defect data records for which no influence on the exhaust gas value is recorded are removed from the checklist; that is, those systems whose systems are not, or only with a low probability, responsible for the exhaust gas value leaving the range. Thus, only those system defect data records remain on the checklist whose systems potentially caused the exhaust gas value to deviate from the exhaust gas value range. It should be noted that this description sometimes refers to systems, system data records, and system defects in the plural. It goes without saying that any number of systems, system data records, and system defects can be present, meaning there can also be no system, no system data record, and no system defect, or only one system, only one system data record, and only one system defect. This is particularly relevant when it is stated that system data records are to be removed from the checklist. In this case, depending on whether the respective condition is met, no system data record, only one system data record, or multiple system data records can be removed from the checklist. After the checklist has been provided, the remaining system defect records are further examined during the setup diagnostics process, based on the state value assigned to their respective systems, to determine the potential system defect. The state value is used to determine the probability that the respective system caused the deviation of the exhaust gas value from the exhaust gas value range. In other words, the setup diagnostics for the corresponding system are performed for each of the remaining system defect records. It should be noted that the state values ​​of the systems used during the setup diagnostics correspond to the state values ​​determined during the system diagnostics. The state values ​​are not recalculated for the setup diagnostics; rather, the values ​​previously determined for the system diagnostics are used. Preferably, at the end of the setup diagnostics or after the setup diagnostics, a system defect is detected for one of the remaining system data records on the checklist, or for the system assigned to it, based on its respective state value. For example, this is done for the system whose state value has exceeded or is closest to a state threshold assigned to the system. In the manner described, the system responsible for the deviation of the exhaust gas value from the acceptable range can be identified with a high degree of certainty. Accordingly, the system can be replaced during routine maintenance of the drive system or the vehicle without further diagnostic effort. Optionally, the system defect records removed from the checklist can be added to a checklist. For example, the checklist is cleared beforehand. If the checklist is completely empty after the system defect records have been removed, meaning it no longer contains any system defect records, the system defect record for which the worst (usually the highest) status value is stored is preferentially selected from the checklist. The system error is then detected for this system. Preferably, this is only the case if the status value has also exceeded a threshold value assigned to the system. This threshold value is preferably chosen to be lower than the status threshold, the exceeding of which alone triggers detection of a system defect. Therefore, to detect a system defect, it is necessary that first the exhaust gas value leaves the exhaust gas value range, the checklist is empty or all system defect data records are removed from it, and additionally, the status value of the system with the worst status value exceeds the threshold value. The described procedure is preferably applied after performing the setup diagnostics. A further development of the invention provides that for each of the multiple system defect data sets, the direction in which the system defect of the respective system affects the exhaust gas value is stored. When the exhaust gas value deviates from the specified range in a particular direction, those system defect data sets for which no influence on the exhaust gas value in that specific direction is recorded are removed from the checklist. In addition to the information on whether the system defect of the respective system affects the exhaust gas value at all, the information also specifies the direction in which the exhaust gas value changes due to the system defect. Consequently, by determining with even greater accuracy which system is responsible for the change in the exhaust gas value in a specific direction or its deviation from the exhaust gas value range in that direction. For this purpose, if the exhaust gas value is outside the defined range, the direction in which it deviated from the range is determined—for example, whether the value is lower than a lower limit or higher than an upper limit. Depending on the direction in which the exhaust gas value lies outside the defined range, those system defect data records are removed from the checklist for which no influence on the exhaust gas value in that direction is recorded, or for which only an influence in the opposite direction is recorded. This further improves the accuracy of the described procedure. A further development of the invention provides that, for at least one of the systems, several system defect data sets are stored for different types of system defects and their influence on the exhaust gas value. It is possible that different types of system defects, or different system defects within the system, will result in different changes in the exhaust gas value. For example, if the high-pressure fuel pump delivers excessively high pressure, this will have a different effect on the exhaust gas value than if it delivers excessively low pressure. Depending on the exhaust gas component for which the exhaust gas value is being determined, excessively high pressure, for instance, causes a change in the exhaust gas value, while excessively low pressure has no effect or, at most, a significantly smaller effect. By storing the different types of system defects and their respective influences on the exhaust gas value, the accuracy can thus be further improved.The system is preferably listed multiple times in the checklist, namely for each of the different types of system defects. This is done in the form of multiple system defect records for the system. A further development of the invention provides that the exhaust gas value is one of several exhaust gas values ​​determined for different exhaust gas components and / or for different operating states of the drive system and / or for different configurations of the drive unit. Thus, there is not just a single exhaust gas value, but rather several exhaust gas values ​​are used for the system diagnostics. In particular, the system diagnostics are performed when one of the several exhaust gas values ​​leaves its respective assigned exhaust gas value range, i.e., lies outside of it. The exhaust gas values ​​are available, for example, for different exhaust gas components. They can be determined using different exhaust gas probes. Preferably, however, they are determined using the same exhaust gas probe, specifically by exploiting a cross-sensitivity of the exhaust gas probe.For example, the exhaust gas sensor is a NOx sensor which also exhibits cross-sensitivity to NH3. Using this exhaust gas sensor, separate exhaust gas values ​​for NOx and NH3 can be determined. Additionally or alternatively, several exhaust gas values ​​are determined for different operating states of the drive system. One exhaust gas value is determined for a first operating state, and another for a second operating state that differs from the first. The first operating state is, for example, a warm-up operating state, and the second operating state is a normal operating state.The warm-up operating state is preferably maintained as long as at least one of the following conditions is met: the exhaust aftertreatment system is heated, the temperature of the exhaust aftertreatment system is below a temperature threshold, the mass of air flowing through the exhaust aftertreatment system since the start of operation is below an air mass threshold, and the amount of heat introduced into the exhaust aftertreatment system since the start of operation is below a heat quantity threshold. For example, the warm-up state is maintained as long as at least one of the aforementioned conditions is met. However, it may also be stipulated that several or all of the aforementioned conditions must be met. If the conditions, or the conditions for the warm-up state, are no longer met, the normal operating state is maintained. Additionally or alternatively, different configurations of the drive system or drive unit can be stored for at least one of the systems. For example, if the drive unit has multiple cylinder banks, the system defects can be stored for each cylinder bank, along with their respective impact on the exhaust gas value. For this purpose, multiple system defect data sets are stored for the affected system(s). In the event that exhaust gas values ​​for two different exhaust gas components and for two different operating states of the drive system are used, a total of four exhaust gas values ​​are available. These are, for the examples mentioned above: a first exhaust gas value for NOx during the warm-up operating state, a second exhaust gas value for NOx during the normal operating state, a third exhaust gas value for NH3 during the warm-up operating state, and a fourth exhaust gas value for NH3 during the normal operating state. A separate exhaust gas value range is defined for each of these values, and the system diagnostics are performed when this range is exceeded. Furthermore, for each exhaust gas value and each system defect data set, it is recorded whether the system defect of the respective system affects the respective exhaust gas value. The described procedure enables a particularly detailed system diagnostics. A further development of the invention provides that an exhaust gas measurement is taken using the exhaust gas probe, and the exhaust gas value is determined from this measurement by accumulating it over the distance traveled by the vehicle and normalizing it using the distance traveled and / or normalizing it using a model value determined using an exhaust gas model. Thus, the exhaust gas value is not measured directly by the exhaust gas probe, but rather determined from the measured exhaust gas value. This at least partially eliminates influences resulting, for example, from different distances traveled and / or different driving styles. To determine the exhaust emission value, the exhaust emission measurement is first accumulated, i.e., summed or integrated, particularly since the vehicle started moving. "Starting moving" refers specifically to the start of the engine or drive unit after the vehicle has been switched off. The accumulated exhaust emission value is then normalized using the distance traveled since the start of driving, so that the exhaust emission value is ultimately expressed as mass or weight per unit distance, for example, grams per kilometer. Additionally or alternatively, the exhaust gas value is determined from the measured exhaust gas value by normalization using the model value. The model value is the result of the exhaust gas model, which calculates the theoretically existing exhaust gas value. For example, the exhaust gas model uses at least one operating parameter of the drive system or drive unit as an input, such as an operating point of the drive unit, which describes the current drive torque provided by the drive unit and / or the current rotational speed of the drive unit. The model value provided by the exhaust gas model as an output describes the composition of the exhaust gas in the case where all systems are fully functional. For example, the exhaust gas model assumes that all systems are in a new condition. The exhaust gas value is preferably derived from the exhaust gas measurement by accumulating it over the distance traveled by the vehicle and normalizing it using both the distance traveled and the model value. Consequently, the exhaust gas value does not directly describe the composition of the exhaust gas, but only indirectly, namely by describing the deviations of the exhaust gas composition from a modeled composition. This approach largely eliminates influences resulting from uncontrollable boundary conditions, such as driver behavior, thus enabling reliable diagnostics. A further development of the invention provides that the exhaust gas measurement is performed continuously, particularly over a driving cycle of the vehicle. The exhaust gas measurement is taken, for example, at short intervals, i.e., multiple times during the driving cycle. The driving cycle extends from the start of the journey to the end of the journey. However, it is particularly preferred that the exhaust gas value for the driving cycle is calculated only once, for example, at the beginning or end of the driving cycle. In this respect, the exhaust gas value is determined only once for each of the driving cycles in the case of multiple driving cycles. This enables reliable diagnostics. A further development of the invention provides that, at least for the system defect data records remaining on the checklist, the state value of the respective system is normalized by means of a state threshold value. Exceeding this threshold value triggers a system defect in the respective system, independent of the exhaust gas measurement. It has already been explained above that the respective state value is determined for each system. This applies at least to those systems for which system defect data records remain on the checklist, but can, of course, be implemented for all systems. Furthermore, the state threshold value is defined for each system. If the state value exceeds the state threshold value, a system defect in the respective system is detected, independent of the exhaust gas measurement. Such a procedure is particularly suitable for system diagnostics, i.e., for diagnosing the individual systems.This procedure can also be referred to as on-board diagnostics. During system diagnostics, the state threshold is preferably used to normalize the state value. The normalized state value is therefore the state value divided by the state threshold. The normalized state value provides information about the state of the respective system. During system diagnostics, the normalized state value is preferably always used instead of the state value, even if this is not explicitly stated. This procedure further improves the accuracy of the system diagnostics. A further development of the invention provides that, for the system defect data records remaining on the checklist, at least one of the following diagnostic types is additionally performed as part of the setup diagnostics: correlation diagnostics, statistical diagnostics, and intrusive diagnostics. Typically, several system defect data records remain on the checklist after evaluating the exhaust gas value. In order to further reduce the checklist and thus ultimately be able to make a plausible statement about the system defect of one of the systems, at least one of the aforementioned diagnostic types is performed before, for example, the system defect of the system is identified based on the remaining system defect data records on the checklist using the state value of the respective system. It may be provided that only a single one of the aforementioned diagnostic types is performed.Preferably, however, several diagnostic methods, in particular all diagnostic methods, are used for the system defect records remaining on the checklist. The diagnostic methods are preferably used in the specified order, but a different order is also possible in principle. The use of at least one diagnostic method enables a reliable statement about the system defect of the individual system. A further development of the invention provides that, within the framework of correlation diagnostics, a temporal correlation is performed between a temporal profile of the exhaust gas value and a temporal profile of the state value for the respective system, at least for the system defect data records remaining on the checklist. If a correlation exists for at least one of the system defect data records, all system defect data records for which the correlation is not found are removed from the checklist. The correlation diagnostics are intended to correlate the temporal profile of the exhaust gas value with the temporal profiles of the state values ​​of those systems for which at least one system defect data record remains on the checklist.Ultimately, each of the system defect data sets, or at least those remaining on the checklist, is assigned a measure of association that reflects the degree of dependence between the exhaust gas value and the state value for the respective system. This measure of association is, for example, in the form of a correlation coefficient. If, during correlation analysis, it is determined that a change in the temporal profile of the exhaust gas value coincides with a change in the temporal profile of the state value for at least one of the system defect data sets, it is assumed that the change in the exhaust gas value was caused by the respective system. Consequently, only those system defect data sets for which such a correlation is found, i.e., where the correlation coefficient exceeds a certain threshold, remain on the checklist. Those system defect data sets for which no correlation is found, i.e., whose correlation coefficient is less than or equal to the threshold, are removed from the checklist.Removal from the checklist is preferably only performed if a correlation exists for any of the system defect records. This approach typically results in a significant reduction in the number of system defect records remaining on the checklist, thus enabling efficient detection of the system defect. The invention provides that for at least one of the system defect data records of a first system, a linking condition is stored that establishes a relationship between a first change in the state value of a system and a second change in the state value of a system assigned to a second system. During the linking diagnostics, those system defect data records for which the respective linking condition is not met are removed from the checklist. The linking diagnostics utilize physical relationships to link the individual system defect data records. This is based on the observation that a first system of the first system defect data record and a second system of the second system defect data record are physically connected, so that a change in the state value of the first system must also result in a change in the state value of the second system, or vice versa.This link is formulated using the linking condition, which connects the two system defect data records. The change in the state value of the first system is also referred to as the first state value change, and the change in the state value of the second system is also referred to as the second state value change. The linking condition can be, for example, one of the following conditions: both the first state value change and the second state value change are non-zero, both the first state value change and the second state value change are non-zero and have the same sign, both the first state value change and the second state value change are non-zero and have the same amount within a certain tolerance. For example, each system defect record has a linking condition to each of the other system defect records. By way of example, the first system defect record concerns the load sensor, and the second system defect record concerns the mixture adaptation. A defect in the load sensor inevitably also affects the mixture adaptation, so a change in the state value of the load sensor also results in a change in the state value of the mixture adaptation. The described procedure enables the efficient elimination of system defect records from the checklist. A further development of the invention provides that, within the framework of statistical diagnostics, at least for the system defect data records remaining on the checklist, a distribution of the time course of the state value for the respective system is determined, and those system defect data records for which the distribution is greater are removed from the checklist. The purpose of the statistical diagnostics is to verify the accuracy of the state values. It is assumed that state values ​​for which the time course shows smaller fluctuations or a smaller control are more reliable than those for which the fluctuations or distribution are greater. For example, a standard deviation over the time course of the state value for the respective system is calculated for each of the system defect data records. It may be possible to remove all system defect records from the checklist for which the standard deviation exceeds a certain threshold. Additionally or alternatively, only the system defect record with the smallest standard deviation is retained, specifically only if the difference between the standard deviation of this system defect record and the standard deviation of the system defect record with the next smallest standard deviation is greater than a further threshold. Statistical analysis is used to verify the statistical validity of the status values. This ensures the effective execution of the system diagnostics. A further development of the invention provides that, within the framework of intrusive diagnostics, a fourth system defect data set is selected for a third system defect data set from at least those remaining on the checklist. For this fourth system defect data set, a change in the operating state of the drive unit causes a different, in particular opposing, change in the exhaust gas value and / or the state value than for the system of the third system defect data set. After the change has been made, the system defect data set for which the change in the exhaust gas value and / or the state value does not occur is removed from the checklist. The intrusive diagnostics comprise an active intervention in the operation of the drive unit, namely the change in the operating state.For example, a change in the operating state includes a change in the composition of the fuel-air mixture, a change in the provided drive torque and / or a change in the speed of the drive unit. The third and fourth system defect data sets are selected based on their differing, and often contradictory, responses to changes in operating state. The change in operating state is then implemented. Subsequently, the exhaust gas value and / or the status values ​​of the systems associated with the system defect data sets are evaluated. If the specified change in exhaust gas value or status value does not occur for one or more system defect data sets, these are removed from the checklist. This effectively eliminates further system defect data sets. Intrusive diagnostics are preferably only permitted and performed if the exhaust gas measurement exceeds a certain threshold. In this case, an error message is typically generated, and the MIL (Malfunction Indicator Lamp) is usually activated. A further development of the invention provides that, using an exhaust gas component model, the exhaust gas component concentration of at least one exhaust gas component is determined and corrected by means of a correction factor derived from the exhaust gas value. If an exhaust gas component threshold is exceeded, the exhaust gas component concentration indicates a defect in the drive unit. The exhaust gas component model serves to determine the exhaust gas component concentration, particularly in terms of flow characteristics between the drive unit and the exhaust aftertreatment system. The exhaust gas component model assumes that all systems of the drive unit are fully functional, and in particular, in new condition. The correction factor is used to account for the actual state of the systems, particularly for exhaust gas components or components for which no sensor reading is available. For this purpose, the exhaust gas value is used to determine the correction factor. This correction factor is then used to correct the exhaust gas component concentration, for example, by multiplication. If the corrected exhaust gas component concentration exceeds the exhaust gas component threshold, it is assumed that the exhaust emissions from the drive unit are no longer within the permissible range, and a corresponding defect in the drive unit is detected. This ensures reliable operation of the drive unit within the specified parameters. In other words, the exhaust gas component concentration of at least one exhaust gas component is first determined using the exhaust gas component model, specifically for a fault-free drive system in which all systems are functioning correctly and are, in particular, new. The exhaust gas component concentration is then corrected using the correction factor. The correction factor is thus used to describe the exhaust gas component concentration of an exhaust gas component for which no measured value is available. The invention further relates to a drive direction for a motor vehicle, in particular for carrying out the method according to the descriptions in this document, wherein the drive unit has an exhaust gas generating drive unit and is designed and configured to determine an exhaust gas value describing the composition of the exhaust gas by means of an exhaust gas probe and to determine a state value describing the state of the respective system for several systems of the drive unit within the framework of a system diagnosis. It is provided that for each of the several systems, at least one system defect data record indicates whether a system defect of the respective system affects the exhaust gas value. The drive unit is further designed and configured to, when an exhaust gas value exceeds a certain range, first place the system defect data records of the systems on a checklist of system defect data records to be checked, and then remove from the checklist those system defect data records for which no effect on the exhaust gas value is recorded. For the system defect data records remaining on the checklist, a setup diagnosis is performed to detect the system defect of the respective system based on the state value. For the system defect data records remaining on the checklist, at least one additional linkage diagnosis is performed as part of the setup diagnosis.wherein for at least one of the first system defect data records of a first of the systems a linking condition is stored which formulates a relationship between a first change in the state value of the state value with a second change in the state value of the state value assigned to a second system, wherein, within the framework of the linking diagnosis, those system defect data records are removed from the checklist for which the respective linking condition is not fulfilled. The advantages of such a drive system design and such a procedure have already been mentioned. Both the drive system and the method for operating it can be further developed as described in this document, and reference is made to these details. The features and combinations of features described in the description, in particular those described in the following figure description and / or shown in the figures, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention. Thus, embodiments that are not explicitly shown or explained in the description and / or the figures, but which emerge from or can be derived from the explained embodiments, are also to be considered as encompassed by the invention. The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. Figure 1, the only figure shown, is a schematic representation of a method for operating a drive unit for a motor vehicle. Figure 1 shows a schematic representation of a method for operating a drive unit for a motor vehicle. The drive unit has an exhaust-generating drive unit and an exhaust gas sensor, which determines an exhaust gas value that describes the composition of the exhaust gas from the drive unit. In module 1 of the method, a state value describing the state of each system is determined for several systems of the drive unit as part of a system diagnostic. The state values ​​obtained in this way are normalized in module 2, namely using a state threshold value assigned to the respective system. In module 3, several system defect data records are stored, which are assigned to the systems. Each system is assigned at least one of these system defect data records. It is also possible for at least one system to be assigned multiple system defect data records. In module 4, an exhaust gas measurement is determined using the exhaust gas probe and transferred to module 5. Module 5 has a further input value: a model value, which is determined in module 6. The model value is determined using an exhaust gas model and describes the composition of the exhaust gas with a fully functional drive system. In module 5, an exhaust gas value is calculated from the exhaust gas measurement and the model value. This value is therefore in a standardized form and can thus also be referred to as a standardized exhaust gas value. In module 7, a check is performed for deviations of the exhaust gas value from a defined range. If a deviation is found, module 8 removes all system defect data records from the checklist for which no influence on the exhaust gas value is recorded. Subsequently, several different diagnostics are performed as part of a setup diagnostic, which takes place in modules 9, 10, 11, and 12. Module 9 performs a correlation diagnostic, module 10 a linkage diagnostic, module 11 a statistical diagnostic, and module 12 an intrusive diagnostic. During each diagnostic, as many system data records as possible are removed from the checklist. If several system defect records remain on the checklist, the system defect record with the highest status value for its associated system is selected in a block 13. Subsequently, a system defect is detected for the system of the remaining system defect record in a block 14. Furthermore, it is preferably provided that if a threshold value is exceeded by the exhaust gas value or the exhaust gas measurement value, a device defect of the drive unit is detected directly in a block 15. It may also be provided that intrusive diagnostics are enabled only in this case by means of a block 16. Additionally or alternatively, it may be provided that the evaluation of the remaining system defect record is enabled only in this case by means of a block 17 and otherwise prevented. Finally, it may be possible to directly compare the state values ​​of multiple systems with a state threshold assigned to each system. If the state value exceeds the state threshold, a system defect in the corresponding system is immediately detected. This is indicated by arrow 18. Using the described procedure, the system with the defect is efficiently isolated. Extensive troubleshooting or system diagnostics of the other systems can therefore be avoided. REFERENCE MARK LIST: 1 Block 2 Block 3 Block 4 Block 5 Block 6 Block 7 Block 8 Block 9 Block 10 Block 11 Block 12 Block 13 Block 14 Block 15 Block 16 Block 17 Block 18 Arrow

Claims

A method for operating a drive unit for a motor vehicle, wherein the drive unit comprises an exhaust gas-generating drive unit and an exhaust gas value describing the composition of the exhaust gas is determined by means of an exhaust gas probe, and a state value describing the state of the respective system is determined for several systems of the drive unit within the framework of a system diagnostic, characterized in that for each of the several systems, at least one system defect data record indicates whether a system defect of the respective system affects the exhaust gas value, wherein, when an exhaust gas value value exceeds a range, the system defect data records of the systems are first placed on a checklist of system defect data records to be checked, and subsequently those system defect data records for which no influence on the exhaust gas value is recorded are removed from the checklist.wherein, for the system defect records remaining on the checklist, a setup diagnosis is performed to detect the system defect of the respective system based on the state value, wherein, for the system defect records remaining on the checklist, at least one linkage diagnosis is performed as part of the setup diagnosis, wherein, for at least one of the system defect records of a first of the systems, at least one linkage condition is stored which formulates a relationship between a first state value change of the state value assigned to the first system with a second state value change of the state value assigned to a second system, wherein, as part of the linkage diagnosis, those system defect records for which the respective linkage condition is not fulfilled are removed from the checklist. Method according to claim 1, characterized in that for each of the several system defect data sets, it is stored in which direction the system defect of the respective system affects the exhaust gas value, and when the exhaust gas value leaves the exhaust gas value range in a certain direction, those system defect data sets are removed from the checklist for which no influence on the exhaust gas value in the certain direction is stored. Method according to one of the preceding claims, characterized in that the exhaust gas value is one of several exhaust gas values ​​that are determined for different exhaust gas components and / or for different operating conditions of the drive device and / or for different configurations of the drive unit. Method according to one of the preceding claims, characterized in that an exhaust gas measurement value is measured by means of the exhaust gas probe and the exhaust gas value is determined from the exhaust gas measurement value by accumulating over a distance traveled by the vehicle and normalizing by means of the distance traveled and / or by normalizing by means of a model value determined using an exhaust gas model. Method according to one of the preceding claims, characterized in that, for the system defect data records remaining on the checklist, at least one of the following types of diagnosis is additionally carried out as part of the setup diagnosis: correlation diagnosis, statistical diagnosis and intrusive diagnosis. Method according to claim 5, characterized in that, within the framework of the correlation diagnosis, the existence of a temporal correlation between a temporal course of the exhaust gas value and a temporal course of the state value for the respective system is checked for at least the system defect data sets remaining on the checklist, wherein, if the correlation is found for at least one of the system defect data sets, all system defect data sets for which the correlation is not found are removed from the checklist. Method according to claim 5 or 6, characterized in that, within the framework of statistical diagnosis, at least for the system defect data records remaining on the checklist, a dispersion of the temporal course of the state value for the respective system is determined and those system defect data records for which the dispersion is greater are removed from the checklist. Method according to one of claims 5 to 7, characterized in that, within the framework of intrusive diagnostics, a fourth system defect data set is selected for a third system defect data set from at least the system defect data sets remaining on the checklist, for whose associated system a change in an operating state of the drive unit causes a different, in particular opposing, change in the state value than for the system of the third system defect data set, wherein, after making the change, the system defect data set for which the change in the state value does not occur is removed from the checklist. Drive unit for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive unit has an exhaust gas generating drive unit and is provided and designed to determine an exhaust gas value describing the composition of the exhaust gas by means of an exhaust gas probe and to determine a state value describing the state of the respective system for several systems of the drive unit within the framework of a system diagnostic, characterized in that for each of the several systems, at least one system defect data set indicates whether a system defect of the respective system affects the exhaust gas value, wherein the drive unit is further provided and designed toWhen an exhaust gas value exceeds a specified range, the system defect data records of the systems are first placed on a checklist of system defect data records to be checked, and then those system defect data records for which no influence on the exhaust gas value is stored are removed from the checklist. For the system defect data records remaining on the checklist, a setup diagnosis is performed to detect the system defect of the respective system based on the state value. For the system defect data records remaining on the checklist, at least one linkage diagnosis is performed as part of the setup diagnosis, and at least one linkage condition is stored for at least one of the first system defect data records of a first system.which establishes a relationship between a first change in the state value of the state value assigned to the first system and a second change in the state value of the state value assigned to a second system, whereby, within the framework of the linkage diagnosis, those system defect data records are removed from the checklist for which the respective linkage condition is not met.

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