METHOD FOR OPERATING A DRIVE DEVICE FOR A MOTOR VEHICLE, DRIVE DEVICE FOR A MOTOR VEHICLE AND COMPUTER PROGRAM PRODUCT

Description

[0001] The invention relates to a method for operating a drive unit for a motor vehicle, which comprises an exhaust gas-generating drive unit, an exhaust gas aftertreatment device designed as a vehicle catalyst for aftertreating the exhaust gas, and a pollutant sensor arranged downstream of the exhaust gas aftertreatment device that reacts to nitrogen oxides and ammonia for determining a pollutant content in the exhaust gas, wherein the pollutant content is determined from a measured value of the pollutant sensor and a sensor offset. The invention further relates to a drive unit for a motor vehicle and a computer program product.

[0002] For example, prior art includes US patent 2023 / 0112942 A1. This patent describes methods and systems for adjusting an ammonia sensor output using readings from a nitrogen oxide sensor, where the nitrogen oxide sensor has cross-sensitivity to ammonia. For example, an ammonia sensor gain value is determined and updated while no nitrogen oxide is detected to calculate a corrected ammonia sensor output value. An ammonia sensor offset value is determined and updated while no ammonia is detected to set the ammonia sensor to zero when no nitrogen oxide is detected.

[0003] The object of the invention is to propose a method for operating a drive unit for a motor vehicle which has advantages over known methods, in particular enabling an accurate determination of the state of the vehicle catalyst.

[0004] 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 the sensor offset is determined only in a first operating range of the drive unit and a catalyst state parameter is determined only in a second operating range of the drive unit that differs from the first operating range.

[0005] 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.

[0006] The drive system serves to propel the motor vehicle, thus providing the drive torque directed towards propelling the motor vehicle. To provide this drive torque, the drive system comprises the drive unit. The drive unit is preferably an internal combustion engine, in particular a gasoline engine or a diesel engine. During operation of the drive system, fuel and fresh gas are supplied to the drive unit at least intermittently, the fresh gas containing fresh air at least intermittently. Additionally, the fresh gas may contain exhaust gas if exhaust gas recirculation is implemented, whereby 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.

[0007] During operation of the engine, exhaust gas is produced due to the chemical reaction between fuel and fresh air. This exhaust gas is discharged towards the outside environment of the engine or vehicle. Since the exhaust gas generated by the engine contains pollutants, it is first routed to an exhaust aftertreatment system before being released into the environment. 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 released into the environment.

[0008] The exhaust aftertreatment system is a vehicle catalytic converter, preferably a three-way catalytic converter. The vehicle catalytic converter can be integrated with a particulate filter. For this purpose, the particulate filter is, for example, provided with a catalytic coating. The conversion rate, and thus the conversion efficiency of the exhaust aftertreatment system, which converts the pollutants into less harmful products, depends in particular on the composition of the exhaust gas supplied to the system and / or on the oxygen content of the exhaust aftertreatment system, which in turn is related to the composition of the exhaust gas. Preferably, the conversion efficiency also depends on the catalyst state parameter, which describes the state of the vehicle catalytic converter.

[0009] To operate the drive unit, a first air-fuel ratio and a second air-fuel ratio are preferably used. The first air-fuel ratio corresponds to the air-fuel ratio in the exhaust gas upstream of the exhaust aftertreatment system, i.e., in terms of flow dynamics, between the drive unit and the exhaust aftertreatment system. The second air-fuel ratio is the air-fuel ratio present in the exhaust gas downstream of the exhaust aftertreatment system. The first air-fuel ratio is preferably measured using a first lambda sensor, and the second air-fuel ratio using a second lambda sensor. For this purpose, the first lambda sensor is arranged upstream of the exhaust aftertreatment system, and the second lambda sensor is arranged downstream of the exhaust aftertreatment system.

[0010] For example, the two air-fuel ratios, the first and second air-fuel ratios, are used to implement lambda control. Specifically, the composition of the fuel-air mixture is adjusted based on the first air-fuel ratio, while the second air-fuel ratio is used to correct the first air-fuel ratio as part of a trim control system. Ultimately, the fuel-air mixture, or rather its composition, is adjusted, at least temporarily, depending on the first and second air-fuel ratios.

[0011] Due to increasingly stringent regulations on exhaust emissions, monitoring must be ever more precise. Therefore, a pollutant sensor is provided, particularly in addition to the two lambda sensors, which reacts to nitrogen oxides and ammonia. Preferably, the pollutant sensor is a nitrogen oxide sensor that exhibits cross-sensitivity to ammonia. The measured value of the nitrogen oxide sensor is therefore influenced by both the nitrogen oxide and ammonia content in the exhaust gas. In particular, the measured value of the nitrogen oxide sensor results in the sum of the nitrogen oxide and ammonia content present in the exhaust gas downstream of the exhaust aftertreatment system. Here, nitrogen oxide refers specifically to nitrogen monoxide, nitrogen dioxide, or—preferably—to both nitrogen monoxide and nitrogen dioxide, i.e., the total of nitrogen monoxide and nitrogen dioxide.The pollutant sensor is located downstream of the exhaust aftertreatment system, thus measuring the pollutant content in the exhaust gas downstream of the exhaust aftertreatment system.

[0012] The pollutant concentration is determined using the pollutant sensor, specifically by utilizing the sensor's measured value. Additionally, the sensor offset is taken into account, which describes any deviation of the measured value from the actual pollutant concentration as precisely as possible. In particular, the pollutant concentration is equal to the sum of the pollutant sensor's measured value and the sensor offset, or it is the measured value minus the sensor offset. In either case, the pollutant concentration is a function of the measured value and the sensor offset. The pollutant concentration, or the respective concentration, is a measure of concentration and indicates the amount of the respective substance, especially the pollutant, in the exhaust gas. This concentration is expressed, for example, as a mass fraction, mole fraction, or volume fraction. It can also be expressed as mass concentration, molar concentration, or volume concentration.

[0013] The catalyst state parameter is determined from the pollutant content. This parameter describes the condition of the vehicle's catalytic converter, particularly its conversion efficiency. The catalyst state parameter is specifically a parameter that is only determined periodically and therefore does not need to be continuously available. For example, the catalyst state parameter describes age-related changes in the vehicle's catalytic converter, specifically a change in its conversion efficiency, particularly a reduction, due to age or age-related influences. Therefore, the catalyst state parameter is only determined periodically.

[0014] Preferably, the catalyst state parameter serves as an input for a catalyst model, which determines the output concentration of at least one exhaust gas component from an input concentration. The input concentration is present upstream and the output concentration downstream of the vehicle catalyst in the exhaust gas. Preferably, the catalyst model is used continuously during operation of the powertrain to determine the output concentration from the input concentration. The input concentration is understood to be, in particular, the concentration of the at least one exhaust gas component in the raw emissions of the powertrain. The raw emissions or the input concentration can be measured by a sensor or determined using a model.

[0015] However, the measured value, or the pollutant concentration determined from it, does not allow for a distinction between a change in pollutant concentration due to a changing catalyst state parameter and a change in sensor offset. Thus, the pollutant sensor can indicate a high pollutant concentration and consequently a low conversion efficiency both when a corresponding sensor offset is present and when the conversion efficiency is actually low. The measured pollutant concentration alone does not allow for any conclusions to be drawn about the underlying cause of the measured value.

[0016] For this reason, it is planned to distinguish between different operating ranges of the drive unit and, depending on the respective operating range, to determine either the sensor offset or the catalyst state parameter, but not the other. More precisely, two operating ranges of the drive unit are defined, with the sensor offset being determined in the first operating range and the catalyst state parameter in the second. In other words, only the sensor offset, but not the catalyst state parameter, is determined in the first operating range, and only the catalyst state parameter, but not the sensor offset, is determined in the second operating range. This means that the sensor offset is determined only in the first operating range and the catalyst state parameter only in the second operating range. The two operating ranges are distinct from each other.This means that at least one parameter describing them has different values ​​in the two operating ranges. In particular, the two operating ranges do not overlap with respect to the parameter, but at most border each other or – preferably – are spaced apart.

[0017] The first operating range is selected such that the pollutant content or the measured value exhibits no or only a weaker dependence on the catalyst state parameter than in the second operating range. Conversely, the second operating range is selected such that the pollutant content or the measured value shows a stronger dependence on the catalyst state parameter than in the first operating range. Thus, the pollutant content measured by the pollutant sensor, or its change, can be clearly attributed to the sensor offset in the first operating range and to the catalyst state parameter in the second operating range. This enables both an accurate determination of the sensor offset and a precise assessment of the vehicle catalyst's condition.

[0018] A further development of the invention provides that the first operating range and the second operating range are characterized by at least one of the following operating parameters: a first air-fuel ratio in the exhaust gas upstream of the exhaust gas aftertreatment device, a second air-fuel ratio in the exhaust gas downstream of the exhaust gas aftertreatment device, a mass flow rate of the exhaust gas, a mass flow gradient of the exhaust gas, and a temperature of the exhaust gas aftertreatment device. It is possible that only one of the aforementioned operating parameters is used to characterize the two operating ranges. Preferably, however, several or even all of the aforementioned parameters are used.

[0019] The first air-fuel ratio is determined using the aforementioned first lambda sensor, and the second air-fuel ratio is determined using the second lambda sensor. The first air-fuel ratio lies within a first range for the first operating range and within a second range for the second operating range. Similarly, the second air-fuel ratio lies within a (further) first range for the first operating range and within a (further) second range for the second operating range. The mass flow rate describes the amount of exhaust gas per unit of time that flows through the exhaust aftertreatment system. The mass flow rate is thus a throughput of the exhaust gas through the exhaust aftertreatment system. The mass flow rate gradient describes the change in mass flow rate over time. The temperature of the exhaust aftertreatment system is preferably measured using a sensor.However, it can of course also be determined using a temperature model.

[0020] The exhaust gas mass flow rate lies within a first mass flow rate range for the first operating range and within a second mass flow rate range for the second operating range. The mass flow rate gradient lies within a first mass flow rate gradient range for the first operating range and within a second mass flow rate gradient range for the second operating range. The temperature of the exhaust aftertreatment system lies within a first temperature range for the first operating range and within a second temperature range for the second operating range. The use of these operating parameters allows for targeted differentiation between the operating ranges.

[0021] A further development of the invention provides that the operating parameter is a first operating parameter that comprises different value ranges for the first and second operating ranges, and a second operating parameter selected from the operating parameters comprises identical value ranges for the first and second operating ranges. It has already been mentioned that several of the aforementioned operating parameters can be used to characterize the operating ranges. Preferably, the two operating ranges differ from each other with respect to the first operating parameter, but are identical with respect to the second operating parameter. This means that the first operating parameter lies within different value ranges in the two operating ranges, but the value ranges for the second operating parameter are the same.In other words, the conditions between the operating ranges differ for the first operating parameter, while they are identical for the second operating parameter.

[0022] The first operating parameter is, for example, the exhaust gas mass flow rate, whereas the second operating parameter is a different parameter from the aforementioned operating parameters. It is possible to use several second operating parameters, each with identical value ranges for both operating ranges. Particularly preferred is the use of the mass flow rate as the first operating parameter, which has different value ranges for the two operating ranges. For the second operating parameters, however, the operating ranges are characterized by identical value ranges. The described procedure ensures that the catalyst state parameter is reliably determined.

[0023] A further development of the invention provides that the first operating range and / or the second operating range is detected, in particular only if or precisely if the mass flow rate of the exhaust gas lies within a respective specific mass flow rate range. The mass flow rate is the instantaneous mass flow rate of the exhaust gas through the exhaust aftertreatment system. This means that the mass flow rate for the first operating range lies within a mass flow rate range assigned to the first operating range, and for the second operating range, within a mass flow rate range assigned to the second operating range. The mass flow rate range assigned to the first operating range can also be referred to as the first mass flow rate range, and the mass flow rate range assigned to the second operating range can be referred to as the second mass flow rate range. The two mass flow rate ranges are preferably distinct from each other; in particular, they do not overlap.They are therefore, for example, directly adjacent to each other or – preferably – spaced apart from each other.

[0024] Preferably, the first mass flow range comprises smaller values ​​than the second mass flow range, i.e., it is smaller than the second mass flow range. For example, the first mass flow range is smaller than the second mass flow range; for instance, the extent of the first mass flow range is at most 60%, at most 50%, or at most 40% of the extent of the second mass flow range. The distance between the mass flow ranges is preferably at least 30%, at least 20%, or at least 10% of the extent of the first mass flow range and / or at least 20%, at least 10%, or at least 7.5% of the extent of the second mass flow range.

[0025] For example, the first mass flow rate range is used to be more than 0 kg / h up to a maximum of 225 kg / h, at least 5 kg / h up to a maximum of 200 kg / h, or at least 10 kg / h up to a maximum of 175 kg / h. The second mass flow rate range is preferably at least 225 kg / h, at least 250 kg / h, or at least 275 kg / h. Additionally, the second mass flow rate range can be at most 700 kg / h, at most 600 kg / h, or at most 500 kg / h. This approach enables the sensor offset and the catalyst state parameter to be determined with high accuracy.

[0026] A further development of the invention provides that the first operating range and / or the second operating range is recognized, in particular only if or exactly if at least one of the following conditions is met: the first combustion air ratio is within a respective specific first combustion air ratio range, the second combustion air ratio is within a respective specific second combustion air ratio range, the mass flow gradient is within a respective specific gradient range, and the temperature of the exhaust aftertreatment device is within a respective specific temperature range.

[0027] The use of the first and / or second combustion air ratios to characterize the operating ranges has already been mentioned. The two combustion air ratio ranges, i.e., the first and second combustion air ratio ranges, are selected independently of each other but may overlap. It may be possible to consider the combustion air ratios for each operating range separately. Thus, the first operating range is assumed to exist if the first combustion air ratio lies within a first combustion air ratio range assigned to the first operating range and / or the second combustion air ratio lies within a second combustion air ratio range assigned to the first operating range.

[0028] Additionally or alternatively, the presence of the second operating range is assumed if the first combustion air ratio lies within a first combustion air ratio range assigned to the second operating range and / or the second combustion air ratio lies within a second combustion air ratio range assigned to the second operating range. It may be provided that the combustion air ratio ranges are identical for both operating ranges. Thus, the presence of both the first and second operating ranges is assumed if the first combustion air ratio lies within the first combustion air ratio range and / or the second combustion air ratio lies within the second combustion air ratio range, and any further conditions are met.

[0029] For the first combustion air ratio range, for example, a range of at least 0.95 and at most 1.05, at least 0.97 and at most 1.03, or at least 0.98 and at most 1.02 is used, preferably for both operating ranges. For the second combustion air ratio, a Nernst voltage of at least 0.68 V to at most 0.75 V, of at least 0.69 V to at most 0.74 V, or of at least 0.70 V to at most 0.73 V, or the combustion air ratio corresponding to this Nernst voltage, is preferably used, also preferably for both operating ranges.

[0030] The mass flow gradient is the gradient of the exhaust gas mass flow rate over time, i.e., the first derivative of the mass flow rate. The first mass flow gradient range and the second mass flow gradient range are preferably identical and are at most 40 kg / h / s, at most 30 kg / h / s, or at most 25 kg / h / s, respectively. The temperature of the exhaust aftertreatment system is, for example, the temperature of a honeycomb structure of the exhaust aftertreatment system through which the exhaust gas is routed to the aftertreatment stage, or the temperature of a housing of the exhaust aftertreatment system in which the honeycomb structure is located. The honeycomb structure is, in particular, provided with the catalytic coating. The respective operating range is only recognized if the respective parameter lies within that range. Preferably, this is necessary for several or even all of the aforementioned parameters. This again results in particularly high accuracy.

[0031] A further development of the invention provides that the first operating range and / or the second operating range is assumed to exist, in particular only or precisely if the respective condition is fulfilled for a specific period of time. For each of the conditions used to verify the respective operating range, a specific period of time is defined. Only when the corresponding condition is met for this period of time is the condition considered fulfilled. This prevents the detection of the respective operating range if the respective parameter is only within the required range for a short period. This prevents interference from transient behavior of the drive unit and achieves high accuracy.

[0032] It is particularly preferred that the first operating range is detected and the sensor offset is determined, especially only if or precisely if one or more of the following conditions are met, in particular all of the following conditions: The first combustion air ratio lies within the defined first combustion air ratio range assigned to the first operating range for a first time period, the second combustion air ratio lies within the defined second combustion air ratio range assigned to the first operating range for a second time period, the exhaust gas mass flow rate lies within the defined mass flow rate range assigned to the first operating range for a third time period, the mass flow gradient lies within the defined gradient range assigned to the first operating range for a fourth time period, and the exhaust gas aftertreatment device temperature lies within the defined temperature range assigned to the first operating range for a fifth time period.

[0033] Additionally or alternatively, the second operating range is detected and the sensor offset is determined, in particular only if or exactly if one or more of the following conditions apply, in particular all of the following conditions: The first combustion air ratio lies within the specified first combustion air ratio range assigned to the second operating range over a first time period, the second combustion air ratio lies within the specified second combustion air ratio range assigned to the second operating range over a second time period, the exhaust gas mass flow rate lies within the specified mass flow rate range assigned to the second operating range over a third time period, the mass flow gradient lies within the specified gradient range assigned to the second operating range over a fourth time period, and the temperature of the exhaust gas aftertreatment device lies within the specified temperature range assigned to the second operating range over a fifth time period.

[0034] Preferably, the following time intervals are used: the first time interval has a length of preferably at least 1 s, at least 2 s, or at least 3 s. Additionally or alternatively, the second time interval has a length of at least 2 s, at least 3 s, or at least 4 s. The third time interval can have a length of 0 s, as can the fourth time interval, additionally or alternatively. However, the third and / or the fourth time interval can also be longer than 0 s, in particular having a length of at least 1 s, at least 2 s, or at least 3 s. The fifth time interval, for example, has a length of at least 2 s, at least 3 s, or at least 4 s.

[0035] A further development of the invention provides that the first air-fuel ratio range and / or the second air-fuel ratio range each contain a stoichiometric air-fuel ratio. The stoichiometric air-fuel ratio is understood to be the air-fuel ratio at which the fuel and fresh gas contained in the fuel-air mixture react completely with each other. The stoichiometric air-fuel ratio is present at λ = 1. For example, at least one of the air-fuel ratio ranges is symmetrical with respect to the stoichiometric air-fuel ratio, with the stoichiometric air-fuel ratio being located at its midpoint. This applies in particular to the first air-fuel ratio range, but optionally also to the second air-fuel ratio range.The described procedure enables high accuracy in determining the sensor offset and the catalyst state parameter.

[0036] A further development of the invention provides that a temperature range above the light-off temperature of the exhaust aftertreatment system is used, particularly for both operating ranges. The light-off temperature of the exhaust aftertreatment system is understood to be the temperature at which the system achieves a conversion efficiency of 50% for the pollutants to be converted, especially for nitrogen oxides. To ensure that the conversion efficiency of the exhaust aftertreatment system for nitrogen oxides is sufficient to determine the sensor offset with good accuracy, the temperature range is selected such that a lower limit lies above the light-off temperature. Preferably, the temperature range is limited at the bottom, i.e., towards lower temperatures, by a lower limit that is at least 50 K, at least 100 K, or at least 150 K higher than the light-off temperature.For example, the lower limit is at least 450 °C, at least 500 °C, or at least 550 °C. This approach achieves the advantages already mentioned.

[0037] A further development of the invention provides that a lambda sensor integrated into the pollutant sensor is used as the second lambda sensor. The pollutant sensor, which measures the nitrogen oxide content and / or the ammonia content, also serves to measure the second air-fuel ratio. For this purpose, a corresponding design of the pollutant sensor or the lambda sensor is implemented. This results in a particularly compact design.

[0038] A further development of the invention provides that a wideband lambda sensor is used as the first lambda sensor and a narrowband lambda sensor as the second lambda sensor. The wideband lambda sensor enables the detection of the residual oxygen content or the corresponding air-fuel ratio over a wider measuring range than the narrowband lambda sensor. The wideband lambda sensor is preferably used to perform the aforementioned lambda control and, accordingly, to adjust the composition of the fuel-air mixture with which the engine is operated. The narrowband lambda sensor has a narrower measuring range than the wideband lambda sensor; in particular, it is used (only) for detecting an air-fuel ratio of λ = 1. However, the measuring accuracy of the narrowband lambda sensor is higher than that of the wideband lambda sensor.Deviations and errors of the wideband lambda sensor are preferably compensated for at least partially using the trim control or, alternatively, the jump lambda sensor. This allows for highly accurate adjustment of the fuel-air mixture composition.

[0039] A further development of the invention provides that, to determine the catalyst state parameter, the drive unit is first operated in the first operating range to determine the sensor offset, and then the catalyst state parameter is determined by operating the drive unit in the second operating range using the previously determined sensor offset. Thus, it is provided that the sensor offset is determined first, before the catalyst state parameter is subsequently determined at a later time interval. For example, it is provided that the drive unit is deliberately operated in the first operating range and the sensor offset is determined. Subsequently, the drive unit is deliberately operated in the second operating range, and the catalyst state parameter is determined.

[0040] However, it is also possible for the drive unit to be controlled solely based on a preset value specified by the vehicle user, for example, a preset value entered using a control element. In this case, there is no targeted approach to the respective operating range. Instead, the drive unit is monitored to determine whether it is operating in the first or second operating range. If it is determined that the drive unit is operating in the first operating range, the measured value from the pollutant sensor is evaluated and the sensor offset is determined. Conversely, if it is determined that the drive unit is operating in the second operating range, the measured value from the pollutant sensor is recorded.

[0041] For example, it is possible to calculate the catalyst state parameter directly using the available sensor offset. However, this is preferably only possible if the sensor offset was last determined within a certain time period. If this time period has been exceeded, the system waits until the drive unit is operating in the first operating range. In this case, the sensor offset is determined and then used to calculate the catalyst state parameter directly from the measured value acquired during operation of the drive unit in the second operating range. This achieves high accuracy.

[0042] A further development of the invention provides that an aging parameter of the vehicle catalyst, describing its oxygen storage capacity, is used as the catalyst state parameter. The aging parameter describes the state of the vehicle catalyst over time. In particular, the oxygen storage capacity of the vehicle catalyst depends directly on, or is described by, the aging parameter. Additionally or alternatively, the aging parameter describes the conversion performance, in particular the maximum conversion performance achievable with the vehicle catalyst.

[0043] For example, the aging parameter is used in a catalyst model that mathematically describes the vehicle catalyst. This catalyst model is preferably used continuously to determine the output concentration of at least one exhaust component downstream of the vehicle catalyst, based on an input concentration of at least one pollutant component present upstream. The exhaust component can be nitrogen oxide (NOx), but it can also be a different exhaust component, such as carbon oxide, particularly carbon monoxide and / or carbon dioxide. Thus, while the catalyst condition parameter is only determined periodically, the catalyst model is used continuously to monitor the pollutant emissions of the propulsion system or drive unit.The catalyst state parameter incorporated into the catalyst model is only adjusted or corrected periodically. This approach enables particularly precise determination and monitoring of pollutant emissions.

[0044] The invention further relates to a drive unit for a motor vehicle, in particular for carrying out the method as described in this description, wherein the drive unit comprises an exhaust gas-generating drive unit, an exhaust gas aftertreatment device designed as a vehicle catalyst for aftertreating the exhaust gas, and a pollutant sensor arranged downstream of the exhaust gas aftertreatment device that reacts to nitrogen oxides and ammonia for determining a pollutant content in the exhaust gas, wherein the pollutant content is determined from the measured value of the pollutant sensor and a sensor offset. The drive unit is designed and configured to determine the sensor offset only in a first operating range of the drive unit and a catalyst state parameter only in a second operating range of the drive unit that differs from the first operating range.

[0045] The advantages of such a procedure or such a design of the drive system have already been mentioned. Both the drive system for the motor vehicle and the method for operating it can be further developed as described in this document, and reference is made to these details.

[0046] Furthermore, the invention relates to a computer program product comprising commands that cause the drive device to execute the described process steps as outlined in this description. For the advantages and possible advantageous embodiments, reference is made to the description in its entirety.

[0047] 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.

[0048] The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The drawing shows: Figure 1 is a schematic representation of a drive unit for a motor vehicle, Figure 2 is a diagram in which a conversion power of a vehicle catalyst is plotted, for which a catalyst state parameter has a first value, and Figure 3 is a diagram in which the conversion power for a vehicle catalyst is plotted, for which the catalyst state parameter has a second value.

[0049] The Figure 1Figure 1 shows a schematic representation of a drive unit 1, which comprises a drive unit 2, in this case an internal combustion engine, and an exhaust system 3. In the illustrated embodiment, the drive unit 2 has several cylinders 4, each with a combustion chamber. Each cylinder 4 has at least one intake valve 5 and at least one exhaust valve 6. Fresh gas from a fresh gas tract 7 can be supplied to the respective cylinder 4 via each of the intake valves 5, whereas exhaust gas can be discharged from the corresponding cylinder 4 through each of the exhaust valves 6, namely towards the exhaust system 3.

[0050] Fresh gas is supplied to the inlet valves 5 by means of a compressor 8, which is part of an exhaust gas turbocharger 9. In addition to the compressor 8, the exhaust gas turbocharger 9 has a turbine 10, which is fluidically connected to the outlet valves 6 via an exhaust line 11, which is part of the exhaust system 3. Downstream of the turbine 10 is an exhaust aftertreatment system 12, which here is designed as a vehicle catalyst, specifically a three-way catalyst. Downstream of the exhaust aftertreatment system 12, the exhaust system 3 opens into the external environment of the drive unit 1, for example via a tailpipe. It should be noted that the exhaust gas turbocharger 9 is purely optional. It can therefore be omitted.

[0051] Upstream of the exhaust aftertreatment system 12, a first lambda sensor 13 is located to determine the first residual oxygen content and, correspondingly, the first air-fuel ratio of the exhaust gas. Downstream of the exhaust aftertreatment system 12, a second lambda sensor 14 serves to determine a second residual oxygen content and, correspondingly, a second air-fuel ratio of the exhaust gas. Also downstream of the exhaust aftertreatment system 12, a pollutant sensor 15 is located, which reacts to nitrogen oxides and ammonia and serves to determine the pollutant content in the exhaust gas. The pollutant sensor 15 is shown integrated into the second lambda sensor 14 as an example.

[0052] The pollutant content in the exhaust gas is determined by measuring a value using the pollutant sensor 15. This value is then subjected to a sensor offset. The pollutant content is derived from this. For example, the pollutant content is equal to the sum of the value and the sensor offset. Alternatively, the pollutant content can be calculated as the value minus the sensor offset.

[0053] The Figure 2Figure 1 shows a diagram plotting the conversion rate η against a catalyst temperature T and an exhaust gas mass flow rate m. The exhaust aftertreatment system 12 corresponds to a vehicle catalyst with a first value of a catalyst state parameter. In particular, an aging parameter of the vehicle catalyst is used as the catalyst state parameter. A first operating range 16 and a second operating range 17 are roughly indicated in the diagram. For the vehicle catalyst with the first value of the catalyst state parameter, the conversion rate is approximately the same in both operating ranges 16 and 17.

[0054] The Figure 3The diagram, which plots the conversion rate η against the temperature T and the mass flow rate ṁ, shows the conversion rate for an exhaust aftertreatment system 12 for which the catalyst state parameter has a second value that differs from the first. While the first value of the catalyst state parameter indicates a newer vehicle catalyst, the second value represents an older or more heavily aged vehicle catalyst. Accordingly, the overall conversion rate is lower. A comparison of the diagrams for the different values ​​of the catalyst state parameter reveals that the conversion rate is almost identical in the first operating range, whereas it differs significantly, or even more significantly, in the second operating range.

[0055] It follows that in the first operating range, the sensor offset of the pollutant sensor 15 can be detected more reliably than in the second operating range. In the second operating range 17, however, the measured value of the pollutant sensor 15, in conjunction with the sensor offset, can be used to determine the catalyst state parameter. Preferably, the operating ranges of the drive unit 2 differ only with respect to the mass flow rate of the exhaust gas flowing through the exhaust aftertreatment device 12. For example, the mass flow rate for the first operating range is at least 5 kg / h and at most 200 kg / h, and for the second operating range at least 250 kg / h and at most 600 kg / h. The described procedure enables a reliable determination of both the sensor offset and the catalyst state parameter. REFERENCE MARK LIST:

[0056] 1. Drive unit 2. Drive assembly 3. Exhaust system 4. Cylinder 5. Inlet valve 6. Exhaust valve 7. Fresh gas system 8. Compressor 9. Exhaust gas turbocharger 10. Turbine 11. Exhaust pipe 12. Exhaust gas aftertreatment system 13. 1st lambda sensor 14. 2nd lambda sensor 15. Pollutant sensor 16. 1st operating range 17. 2nd operating range

Claims

1. Method for operating a drive device (1) for a motor vehicle, which has an exhaust gas-producing drive unit (2), an exhaust gas aftertreatment device (12) configured as a vehicle catalytic converter for the aftertreatment of the exhaust gas, and a pollutant sensor (15) arranged downstream of the exhaust gas aftertreatment device (12) and reacting to nitrogen oxide and ammonia for determining a pollutant content in the exhaust gas, wherein the pollutant content is determined from a measured value of the pollutant sensor (15) and a sensor offset, characterised in that the sensor offset is determined only in a first operating range (16) of the drive unit (2) and a catalyst state parameter is determined only in a second operating range (17) of the drive unit (2) that is different from the first operating range (16).

2. Method according to claim 1, characterised in that the first operating range (16) and the second operating range (17) are characterised by at least one of the following operating parameters: a first air-fuel ratio present in the exhaust gas upstream of the exhaust gas aftertreatment device (12), a second air-fuel ratio present in the exhaust gas downstream of the exhaust gas aftertreatment device (12), a mass flow of the exhaust gas, a mass flow gradient of the exhaust gas, and a temperature of the exhaust gas aftertreatment device (12).

3. Method according to one of the preceding claims, characterised in that the operating parameter is a first operating parameter which comprises different value ranges for the first operating range (16) and the second operating range (17), and a second operating parameter selected from the operating parameters comprises identical value ranges for the first operating range (16) and the second operating range (17).

4. Method according to one of the preceding claims, characterised in that the first operating range (16) and / or the second operating range (17) is detected if the mass flow of the exhaust gas is within a respective specified mass flow range.

5. Method according to one of the preceding claims, characterised in that the first operating range (16) and / or the second operating range (17) is detected if at least one of the following conditions is met: the first air-fuel ratio is within a respective specified first air-fuel ratio range, the second air-fuel ratio is within a respective specified second air-fuel ratio range, the mass flow gradient is within a respective specified gradient range, and the temperature of the exhaust gas aftertreatment device (12) is within a respective specified temperature range.

6. Method according to one of the preceding claims, characterised in that it is assumed that the first operating range (16) and / or the second operating range (17) is present if the respective condition is met over a respective period of time.

7. Method according to one of the preceding claims, characterised in that, in order to determine the catalyst state parameter, the drive unit (2) is first operated in the first operating range (16) to determine the sensor offset and then, by operating the drive unit (2) in the second operating range (17), the catalyst state parameter is determined using the previously determined sensor offset.

8. Method according to one of the preceding claims, characterised in that an ageing parameter of the vehicle catalytic converter describing an oxygen storage capacity is used as the catalytic converter state parameter.

9. Drive device (1) for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive device (1) has an exhaust gas-producing drive unit (2), an exhaust gas aftertreatment device (12) configured as a vehicle catalytic converter for the aftertreatment of the exhaust gas, and a pollutant sensor (15) arranged downstream of the exhaust gas aftertreatment device (12) and reacting to nitrogen oxide and ammonia for determining a pollutant content in the exhaust gas, wherein the pollutant content is determined from a measured value of the pollutant sensor (15) and a sensor offset, characterised in that the drive device (1) is provided and configured to determine the sensor offset only in a first operating range (16) of the drive unit (2) and a catalyst state parameter only in a second operating range (17) of the drive unit (2) that is different from the first operating range (16).

10. Computer program product comprising instructions that cause the drive device (1) according to claim 9 to carry out the method steps according to one or more of claims 1 to 8.