Method for operating a drive device for a motor vehicle, drive device for a motor vehicle, and computer program product
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-22
- Publication Date
- 2026-04-08
AI Technical Summary
Existing methods for determining the sensor offset of pollutant sensors in motor vehicle drive devices are imprecise, especially due to the cross-sensitivity of nitrogen oxide sensors to ammonia concentrations, and are challenging to calibrate accurately, particularly during overrun operations which are rare in modern vehicles.
The sensor offset of the nitrogen oxide sensor is determined only when the exhaust gas aftertreatment device's conversion performance for nitrogen oxide meets a specific threshold and the ammonia concentration downstream is below a certain value, using a method that adjusts the offset based on measured pollutant concentrations and expected values within defined combustion air ratio, mass flow, and temperature ranges.
This approach allows for a highly accurate determination of the sensor offset, ensuring precise pollutant concentration measurement by ensuring specific operating conditions are met, thereby enhancing the accuracy of pollutant concentration determination.
Smart Images
Figure EP2024064082_05122024_PF_FP_ABST
Abstract
Description
[0001] Method for operating a drive device for a motor vehicle, drive device for a motor vehicle and computer program product
[0002] DESCRIPTION:
[0003] The invention relates to a method for operating a drive device for a motor vehicle, which has a drive unit generating exhaust gas, an exhaust gas aftertreatment device designed as a vehicle catalytic converter for aftertreating the exhaust gas, a first lambda probe arranged upstream of the exhaust gas aftertreatment device for measuring a first combustion air ratio in the exhaust gas, a second lambda probe arranged downstream of the exhaust gas aftertreatment device for measuring a second combustion air ratio in the exhaust gas, and a pollutant sensor arranged downstream of the exhaust gas aftertreatment device, which reacts to nitrogen oxide and ammonia and is used to determine a pollutant concentration in the exhaust gas, wherein the pollutant concentration is determined from a measured value of the pollutant sensor and a sensor offset. The invention further relates to a drive device for a motor vehicle and a computer program product.
[0004] For example, the prior art document DE 10 2017 204 301 A1 is known. This document describes a method for correcting an offset of an ammonia sensor arranged downstream of at least one SCR catalyst in an SCR system. The method comprises the following steps: First, ammonia slip is detected using the ammonia sensor, then a modeled ammonia fill level is set to a maximum ammonia fill level, and subsequently, an underdosing of a reducing agent for the SCR system is carried out. When the modeled ammonia fill level has returned to a nominal ammonia fill level, the underdosing is terminated. A current offset is then determined, and the offset is corrected using a difference between the current offset and a predicted offset.
[0005] Furthermore, the document DE 198 10 483 A1 discloses a method for determining the sensor offset for HC and / or NO x Sensors located in the exhaust system of an internal combustion engine with a catalytic converter. The sensor signal is read and stored as an offset signal in operating states of the internal combustion engine and the catalytic converter in which no HC and / or NOx emissions occur. Specifically, the sensor signal is read and stored as an offset signal when the engine is cold or during regeneration of a NOx storage catalyst with a rich air-fuel mixture.
[0006] It is an object of the invention to propose a method for operating a drive device for a motor vehicle, which has advantages over known methods, in particular enables a very precise determination of the sensor offset of the pollutant sensor.
[0007] This is achieved according to the invention with a method for operating a drive device for a motor vehicle having the features of claim 1. It is provided that the sensor offset of the nitrogen oxide sensor is determined, in particular only when or precisely when an operating state of the drive device exists in which a conversion performance of the exhaust gas aftertreatment device for nitrogen oxide corresponds at least to a specific conversion performance threshold value and an ammonia concentration downstream of the exhaust gas aftertreatment device is less than a concentration threshold value.
[0008] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims. It is pointed out that the exemplary embodiments explained in the description are not restrictive; rather, any variations of the features disclosed in the description, the claims and the figures are feasible. The drive device serves to drive the motor vehicle, thus providing a drive torque directed towards driving the motor vehicle. To provide the drive torque, the drive device has the drive unit. The drive unit is preferably in the form of an internal combustion engine, in particular a gasoline internal combustion engine. During operation of the drive device, fuel and fresh gas are supplied to the drive unit at least temporarily, wherein the fresh gas contains fresh air at least temporarily.Additionally, the fresh gas may contain exhaust gas, provided exhaust gas recirculation is implemented, in which the exhaust gas generated by the drive unit is at least partially recirculated back into the drive unit, namely as a component of the fresh gas. The fuel and the fresh gas supplied to the drive unit form a fuel-fresh gas mixture with a specific composition, which is reacted in the drive unit.
[0009] During operation of the drive unit, the chemical reaction between fuel and fresh gas produces exhaust gas, which is discharged to the environment outside the drive system or the motor vehicle. Since the exhaust gas generated by the drive unit contains pollutants, the exhaust gas is first fed to the exhaust aftertreatment system before being released into the environment. In the exhaust aftertreatment system, the pollutants are at least partially converted into less hazardous products. Only after passing through the exhaust aftertreatment system is the exhaust gas discharged to the environment outside.
[0010] The exhaust gas 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, for example, is provided with a catalytic coating. The conversion rate and thus the conversion performance of the exhaust gas aftertreatment system, with which the pollutants are converted into harmless products, depend in particular on the composition of the exhaust gas supplied to the exhaust gas aftertreatment system and / or on the oxygen loading of the exhaust gas aftertreatment system, which in turn is related to the composition of the exhaust gas.
[0011] The first combustion air ratio and the second combustion air ratio, among other things, are used to operate the drive system. The first combustion air ratio corresponds to a combustion air ratio in the exhaust gas upstream of the exhaust aftertreatment device, i.e., in terms of flow, between the drive unit and the exhaust aftertreatment device. The second combustion air ratio is a combustion air ratio present in the exhaust gas downstream of the exhaust aftertreatment device. The first combustion air ratio is measured using the first lambda probe, and the second combustion air ratio is measured using the second lambda probe. For this purpose, the first lambda probe is arranged upstream of the exhaust aftertreatment device, and the second lambda probe is arranged downstream of the exhaust aftertreatment device.For example, the two combustion air ratios, i.e., the first combustion air ratio and the second combustion air ratio, are used to implement lambda control. In particular, the composition of the fuel-fresh gas mixture is adjusted based on the first combustion air ratio, whereas the second combustion air ratio is used to correct the first combustion air ratio as part of a trim control.
[0012] Due to the ever-stricter regulations for exhaust emissions, these must be monitored with increasing precision. Therefore, in addition to the two lambda sensors, a pollutant sensor is provided, which reacts to nitrogen oxide and ammonia. Preferably, the pollutant sensor is a nitrogen oxide sensor, which is cross-sensitive to ammonia. The measured value of the nitrogen oxide sensor is therefore influenced by both the nitrogen oxide concentration and the ammonia concentration in the exhaust gas. In particular, the measured value of the nitrogen oxide sensor results in a sum of the nitrogen oxide concentration and the ammonia concentration present in the exhaust gas downstream of the exhaust gas aftertreatment device. Nitrogen oxide here means nitrogen monoxide, nitrogen dioxide, or - preferably - the combination of nitrogen monoxide and nitrogen dioxide.
[0013] The pollutant concentration is determined using the pollutant sensor's measured value. The sensor offset, which describes any deviation of the measured value from the actual pollutant concentration as precisely as possible, is also taken into account. Specifically, the pollutant concentration is equal to the sum of the pollutant sensor's measured value and the sensor offset, or the pollutant concentration 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.
[0014] For example, it is intended to use the pollutant concentration temporarily as the nitrogen oxide concentration and temporarily as the ammonia concentration. The pollutant concentration is preferably used as the nitrogen oxide concentration if the drive system is operated in an operating state in which there is a high probability that no or only a small amount of ammonia is present in the exhaust gas. This is particularly the case when the drive system is operated with a fuel-fresh gas mixture in which there is an excess of oxygen, i.e., with a combustion air ratio of greater than one.
[0015] Conversely, the pollutant concentration is preferably used as the ammonia concentration when the drive system is in an operating state in which there is a certain probability that there is no or only a small amount of nitrogen oxide in the exhaust gas. This is particularly the case when operating with a fuel-fresh gas mixture with a lack of oxygen, i.e. when the combustion air ratio is less than one. In addition, it can be provided to determine both the nitrogen oxide concentration and the ammonia concentration from the pollutant concentration. For this purpose, one of the concentrations is preferably determined using a model, for example the ammonia concentration. The other of the concentrations, in particular the nitrogen oxide concentration, is then calculated from the pollutant concentration and the concentration determined using the model.
[0016] To determine the pollutant concentration as accurately as possible, it is necessary to determine the sensor offset with high precision. However, this is challenging because even during overrun of the engine, the exhaust gas contains not only fresh air but also outgassing from the cylinder crankcase. Thus, overrun is not suitable for reliably calibrating the pollutant sensor by determining the sensor offset. Furthermore, overrun occurs only rarely in modern drive systems, so there is no possibility of using overrun.
[0017] For this reason, the sensor offset is determined in the operating state of the drive system in which, on the one hand, the conversion performance of the exhaust gas aftertreatment system for nitrogen oxide corresponds at least to the conversion performance threshold value and, on the other hand, the ammonia concentration is less than the concentration threshold value. The sensor offset is therefore only determined in this operating state. The sensor offset is preferably determined by determining the measured value of the pollutant sensor in the operating state of the drive system by measuring and setting the sensor offset equal to the measured value, or by comparing the determined pollutant concentration with an expected pollutant concentration and adjusting the sensor offset by a difference between the determined pollutant concentration and the expected pollutant concentration. The expected pollutant concentration is, for example, equal to zero.By taking into account both the nitrogen oxide conversion capacity of the exhaust gas aftertreatment device and the ammonia concentration downstream of the exhaust gas aftertreatment device, the determined sensor offset is highly accurate, so that the pollutant concentration can subsequently be determined or is determined with high accuracy. A further development of the invention provides that it is assumed that the operating state of the drive device exists, in particular only if or precisely if the following conditions are met: the first combustion air ratio lies within a specific first combustion air ratio range, and the second combustion air ratio lies within a specific second combustion air ratio range.Therefore, it is not necessary to actually determine the conversion efficiency of the exhaust gas aftertreatment system or the ammonia concentration. Rather, it is assumed that both of these conditions are met if the combustion air ratios are within the combustion air ratio ranges.
[0018] As soon as just one of the combustion air ratios lies outside the associated combustion air ratio range, it is assumed that either the conversion performance of the exhaust gas aftertreatment system is insufficient or the ammonia concentration is too high, and the sensor offset is not determined. In other words, the operating state of the drive direction is only assumed to exist if the aforementioned conditions are met. Consequently, the sensor offset of the pollutant sensor is only determined if these conditions are met. It is therefore necessary that all of the aforementioned conditions are met in order to conclude that the operating state of the drive device is present and to determine the determining sensor offset. Using the described procedure, the sensor offset is determined with high accuracy.
[0019] In other words, the invention also relates to a method characterized in that the sensor offset of the nitrogen oxide sensor is determined, in particular only when or precisely when the following conditions are met: the first combustion air ratio lies within a specific first combustion air ratio range, and the second combustion air ratio lies within a specific second combustion air ratio range. Reference is made to the further explanations of this description.
[0020] A further development of the invention provides that it is assumed that the operating state of the drive device exists, in particular only if or precisely if at least one of the following conditions is met: a mass flow of the exhaust gas lies within a certain mass flow range, a mass flow gradient lies within a certain gradient range and a temperature of the exhaust gas aftertreatment device lies within a certain temperature range. The conditions relating to the combustion air conditions are also referred to in this description as first conditions and the conditions now mentioned are also referred to as second conditions. Preferably, it is only assumed that the operating state of the drive direction exists if or precisely if at least one of the second conditions is met, in particular several of the second conditions or even all of the second conditions.
[0021] The second conditions relate to the mass flow, the mass flow gradient, and the temperature of the exhaust gas aftertreatment device. The mass flow is the instantaneous mass flow of the exhaust gas through the exhaust gas aftertreatment device, and the mass flow gradient is its gradient over time, i.e., the first derivative of the mass flow. The temperature of the exhaust gas aftertreatment device is, for example, a temperature of a honeycomb body of the exhaust gas aftertreatment device, through which the exhaust gas is guided to the exhaust gas aftertreatment, or a temperature of a housing of the exhaust gas aftertreatment device in which the honeycomb body is arranged. The honeycomb body is, in particular, provided with the catalytic coating.
[0022] For example, the mass flow range is limited downwards by a first limit which is at least 5 kg / h, at least 10 kg / h or at least 15 kg / h, additionally or alternatively at most 30 kg / h, at most 25 kg / s or at most 20 kg / s. The mass flow range is limited upwards by a second limit which is at least 100 kg / h, at least 110 kg / h or at least 120 kg / h, additionally or alternatively at most 150 kg / h, at most 140 kg / h or at most 130 kg / h. The gradient range is preferably only limited upwards, for example to at most 30 (kg / h) / s, at most 25 (kg / h) / s or at most 20 (kg / h) / s. The temperature range is preferably only limited downwards, in particular to at least 400 °C, at least 450 °C or at least 500 °C.
[0023] Preferably, it is only assumed that the operating state of the drive device is present and the determination of the sensor offset can be carried out, in particular only if or precisely if both the first conditions and at least one of the second conditions, preferably several of the second conditions or all of the second conditions, are met. As part of the check as to whether the operating state of the drive device is present, the mass flow is compared with the mass flow range and / or the mass flow gradient with the gradient range and / or the temperature with the temperature range. If the mass flow, the mass flow gradient or the temperature is outside the respective range, the corresponding condition is not met. The described procedure, in turn, enables the determination of the sensor offset with extremely high accuracy.
[0024] A further development of the invention provides that it is assumed that the operating state of the drive direction exists, preferably only if or precisely if the respective condition is fulfilled over a respective time period. For each of the stated conditions used to check for the existence of the operating state, a respective time period is therefore defined. Only when the corresponding condition applies over this time period is the condition considered fulfilled. This prevents the sensor offset from being determined if the operating state only exists over a short period of time, which does not ensure the accuracy of the sensor offset. Conversely, the described procedure achieves a high level of accuracy in determining the sensor offset.It is therefore assumed that the operating state of the drive device exists, in particular only if or precisely if one or more of the following conditions apply, in particular all of the conditions mentioned:.
[0025] - the first combustion air ratio lies within the determined first combustion air ratio range over a first period of time,
[0026] - the second combustion air ratio lies within the determined second combustion air ratio range over a second period of time,
[0027] - the mass flow of the exhaust gas is within the specified mass flow range over a third period of time,
[0028] - the mass flow gradient lies within the specified gradient range over a fourth time period, and
[0029] - the temperature of the exhaust aftertreatment device remains within the specified temperature range over a fifth period of time.
[0030] The following time periods are preferably used: The first time period has a length of preferably at least 1 s, at least 2 s or at least 3 s. Additionally or alternatively, the second time period has a length of at least 2 s, at least 3 s or at least 4 s. The third time period can have a length of 0 s, additionally or alternatively likewise the fourth time period. However, the third time period and / or the fourth time period can also be longer than 0 s, in particular have a length of at least 1 s, at least 2 s or at least 3 s. The fifth time period has, for example, a length of at least 2 s, at least 3 s or at least 4 s. A development of the invention provides that the time period for the condition relating to the second combustion air ratio is selected to be longer than the time period for the condition relating to the first combustion air ratio.The second combustion air ratio must remain within the second combustion air ratio range for a longer period than the first combustion air ratio in the first combustion air ratio range in order to determine the presence of the operating state of the drive device. Preferably, the second time period for the second combustion air ratio is longer than the first time period for the first combustion air ratio by a factor of at least two, at least three, or at least four. This achieves particularly high accuracy in determining the sensor offset.
[0031] A further development of the invention provides that the first combustion air ratio range and / or the second combustion air ratio range each contain a stoichiometric combustion air ratio. The stoichiometric combustion air ratio is understood to be the combustion air ratio at which the fuel contained in the fuel-fresh gas mixture and the fresh gas contained therein react completely with one another. The stoichiometric combustion air ratio occurs at X = 1. For example, at least one of the combustion air ratio ranges is symmetrical with respect to the stoichiometric combustion air ratio, with the stoichiometric combustion air ratio thus being centrally located within it. This applies in particular to the first combustion air ratio range, but optionally also to the second combustion air ratio range.
[0032] 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 as the first combustion air ratio range. 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. The described procedure enables high accuracy in determining the sensor offset.
[0033] A further development of the invention provides that a temperature range lying above a light-off temperature of the exhaust gas aftertreatment device is used as the temperature range. The light-off temperature of the exhaust gas aftertreatment device is understood to be the temperature above which the exhaust gas aftertreatment device has a conversion efficiency of 50% for the pollutants to be converted, in particular for nitrogen oxide. To ensure that the conversion efficiency of the exhaust gas aftertreatment device for nitrogen oxide is sufficient to determine the sensor offset with good accuracy, the temperature range is selected such that its lower limit lies above the light-off temperature. Preferably, the temperature range is limited downwards, i.e. towards lower temperatures, by a lower limit which 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.
[0034] A further development of the invention provides for a lambda sensor integrated into the pollutant sensor to be used as the second lambda sensor. The pollutant sensor, which measures the nitrogen oxide concentration and / or the ammonia concentration, also serves to measure the second combustion air ratio. For this purpose, a corresponding design of the pollutant sensor or the lambda sensor is implemented. This results in a particularly compact design.
[0035] A further development of the invention provides that a broadband lambda probe is used as the first lambda probe and a step-type lambda probe is used as the second lambda probe. The broadband lambda probe enables the detection of the residual oxygen content or the corresponding combustion air ratio over a wider measuring range than the step-type lambda probe. The broadband lambda probe is preferably used to carry out the aforementioned lambda control and, accordingly, to adjust the composition of the fuel / fresh gas mixture with which the drive unit is operated. The step-type lambda probe has a narrower measuring range than the broadband lambda probe; in particular, it is used (only) to detect a combustion air ratio of X = 1. However, the measuring accuracy of the step-type lambda probe is higher than that of the broadband lambda probe.Deviations and errors in the wideband lambda sensor are preferably at least partially compensated for using a trim control or the step-down lambda sensor. This allows the composition of the fuel / fresh gas mixture to be adjusted with high precision.
[0036] The invention further relates to a drive device for a motor vehicle, in particular for carrying out the method according to the statements in the context of this description, wherein the drive device has a drive unit generating exhaust gas, an exhaust gas aftertreatment device designed as a vehicle catalyst for aftertreating the exhaust gas, a first lambda probe arranged upstream of the exhaust gas aftertreatment device for measuring a first combustion air ratio in the exhaust gas, a second lambda probe arranged downstream of the exhaust gas aftertreatment device for measuring a second combustion air ratio in the exhaust gas and a pollutant sensor arranged downstream of the exhaust gas aftertreatment device, which reacts to nitrogen oxide and ammonia and is for determining a pollutant concentration in the exhaust gas, wherein the pollutant concentration is determined from a measured value of the pollutant sensor and a sensor offset.
[0037] The drive device is provided and designed to determine the sensor offset of the pollutant sensor when an operating state of the drive device exists in which a conversion performance of the exhaust gas aftertreatment device for nitrogen oxide corresponds at least to a specific conversion performance threshold value and an ammonia concentration downstream of the exhaust gas aftertreatment device is less than a concentration threshold value.
[0038] The advantages of such a drive system design and such a procedure have already been pointed out. Both the drive system for the motor vehicle and the method for operating it can be further developed according to the explanations in this description, so reference is made to these in this regard.
[0039] Furthermore, the invention relates to a computer program product comprising instructions that cause the drive device to execute the explained method steps according to the embodiments of this description. Regarding the advantages and possible advantageous developments, reference is made to the entire description.
[0040] The features and feature combinations described in the description, in particular the features and feature combinations described in the following description of the figures and / or shown in the figures, can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments are also considered to be encompassed by the invention that are not explicitly shown or explained in the description and / or the figures, but which follow from or can be derived from the explained embodiments.
[0041] The invention is explained in more detail below with reference to exemplary embodiments illustrated in the drawings, without limiting the invention. In the drawings:
[0042] Figure 1 shows a schematic representation of a drive device for a motor vehicle. Figure 1 shows a schematic representation of a drive device 1 having a drive unit 2, which here is in the form of an internal combustion engine, and an exhaust tract 3. In the illustrated embodiment, the drive unit 2 has a plurality of cylinders 4, each with a combustion chamber. Each of the cylinders 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 from the corresponding cylinder 4 can be discharged through each of the exhaust valves 6, namely in the direction of the exhaust tract 3.
[0043] The fresh gas is provided to the intake 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 fluidly connected to the exhaust valves 6 via an exhaust line 11, which is a component of the exhaust tract 3. Downstream of the turbine 10 is an exhaust gas aftertreatment device 12, which here is designed as a vehicle catalytic converter, in particular as a three-way catalytic converter. Downstream of the exhaust gas aftertreatment device 12, the exhaust tract 3 opens into an external environment of the drive device 1, for example via a tailpipe. It should be noted that the exhaust gas turbocharger 9 is purely optional. It can also be omitted accordingly.
[0044] Upstream of the exhaust gas aftertreatment device 12 is a first lambda probe 13 for determining a first residual oxygen content and, accordingly, a first air-combustion ratio of the exhaust gas at this point. Downstream of the exhaust gas aftertreatment device 12, a second lambda probe 14 is used to determine a second residual oxygen content and, accordingly, a second air-combustion ratio of the exhaust gas. Also downstream of the exhaust gas aftertreatment device 12 is a pollutant sensor 15 that reacts to nitrogen oxide and ammonia and serves to determine a pollutant concentration in the exhaust gas. The pollutant sensor 15 is shown integrated into the second lambda probe 14 by way of example. The pollutant concentration in the exhaust gas is determined by measuring a measured value using the pollutant sensor 15. The measured value is subjected to a sensor offset. This results in the pollutant concentration.For example, the pollutant concentration is equal to the sum of the measured value and the sensor offset. It can also be specified that the pollutant concentration is equal to the measured value minus the sensor offset.
[0045] In order to determine the sensor offset as accurately as possible, an operating state of the drive device 1 is waited for in which the conversion performance of the exhaust gas aftertreatment device 12 for nitrogen oxide corresponds at least to a specific conversion performance threshold value and, in addition, an ammonia concentration downstream of the exhaust gas aftertreatment device 12 is less than a concentration threshold value. Only when these conditions are met or when this operating state exists is the sensor offset determined, for example, by setting it equal to a measured value of the pollutant sensor 15 measured in the operating state of the drive device 1. It can also be provided that the operating state is approached deliberately, in particular by adjusting the drive device 1 accordingly.In any case, the sensor offset is determined with high accuracy, so that the subsequent determination of the pollutant concentration is also carried out with high accuracy.
[0046] LIST OF REFERENCE SYMBOLS:
[0047] 1 drive device
[0048] 2 Drive unit 3 Exhaust tract
[0049] 4 cylinders
[0050] 5 Inlet valve
[0051] 6 exhaust valve
[0052] 7 Fresh gas tract 8 Compressor
[0053] 9 exhaust gas turbocharger
[0054] 10 turbines
[0055] 11 Exhaust pipe
[0056] 12 Exhaust aftertreatment system 13 1. Lambda probe
[0057] 14 2. Lambda sensor
[0058] 15 pollutant sensor
Claims
PATENT CLAIMS:
1. A method for operating a drive device (1) for a motor vehicle, which has an exhaust gas-generating drive unit (2), an exhaust gas aftertreatment device (12) designed as a vehicle catalyst for aftertreating the exhaust gas, a first lambda probe (13) arranged upstream of the exhaust gas aftertreatment device (12) for measuring a first combustion air ratio in the exhaust gas, a second lambda probe (14) arranged downstream of the exhaust gas aftertreatment device (12) for measuring a second combustion air ratio in the exhaust gas, and a pollutant sensor (15) arranged downstream of the exhaust gas aftertreatment device (12) for determining a pollutant concentration in the exhaust gas, wherein the pollutant concentration is determined from a measured value of the pollutant sensor (15) and a sensor offset, characterized in that the sensor offset of the pollutant sensor (15) is determined,if an operating state of the drive device (1) exists in which a conversion performance of the exhaust gas aftertreatment device (12) for nitrogen oxide corresponds to at least a certain conversion performance threshold value and an ammonia concentration downstream of the exhaust gas aftertreatment device (12) is less than a concentration threshold value.
2. Method according to claim 1, characterized in that it is assumed that the operating state of the drive device (1) is present if the following conditions are met: the first combustion air ratio is within a specific first combustion air ratio range and the second combustion air ratio is within a specific second combustion air ratio range.
3. Method according to one of the preceding claims, characterized in that it is assumed that the operating state of the drive device (1) is present if at least one of the following conditions is met: a mass flow of the exhaust gas is within a certain mass flow range, a mass flow gradient lies within a certain gradient range and a temperature of the exhaust gas aftertreatment device (12) lies within a certain temperature range.
4. Method according to one of the preceding claims, characterized in that it is assumed that the operating state of the drive device (1) is present if the respective condition is fulfilled over a respective period of time.
5. Method according to one of the preceding claims, characterized in that the time period for the condition relating to the second combustion air ratio is selected to be longer than the time period for the condition relating to the first combustion air ratio.
6. Method according to one of the preceding claims, characterized in that the first combustion air ratio range and / or the second combustion air ratio range each contain a stoichiometric combustion air ratio.
7. Method according to one of the preceding claims, characterized in that a temperature range above a light-off temperature of the exhaust gas aftertreatment device is used as the temperature range.
8. Method according to one of the preceding claims, characterized in that a lambda probe integrated into the pollutant sensor (15) is used as the second lambda probe (14).
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 generating drive unit (2), an exhaust gas aftertreatment device (12) designed as a vehicle catalyst for aftertreating the exhaust gas, a a first lambda probe (13) arranged upstream of the exhaust gas aftertreatment device (12) for measuring a first combustion air ratio in the exhaust gas, a second lambda probe (14) arranged downstream of the exhaust gas aftertreatment device (12) for measuring a second combustion air ratio in the exhaust gas, and a pollutant sensor (15) arranged downstream of the exhaust gas aftertreatment device (12) which reacts to nitrogen oxide and ammonia and is used to determine a pollutant concentration in the exhaust gas, wherein the pollutant concentration is determined from a measured value of the pollutant sensor (15) and a sensor offset, characterized in that the drive device (1) is provided and designed to determine the sensor offset of the pollutant sensor (15) when an operating state of the drive device (1) exists,in which a conversion performance of the exhaust gas aftertreatment device (12) for nitrogen oxide corresponds to at least a certain conversion performance threshold value and an ammonia concentration downstream of the exhaust gas aftertreatment device (12) is less than a concentration threshold value.
10. Computer program product comprising instructions which 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.