Method for operating a drive device for a motor vehicle, drive device for a motor vehicle and computer program product

Abstract

Method for operating a drive device (1) for a motor vehicle, which has a drive unit (2) generating exhaust gas, an exhaust gas aftertreatment device (12) designed as a vehicle catalyst for aftertreating the exhaust gas, a broadband lambda probe arranged upstream of the exhaust gas aftertreatment device (12), a jump lambda probe arranged downstream of the exhaust gas aftertreatment device (12), and a pollutant sensor (15) reacting to nitrogen oxide and ammonia, arranged downstream of the exhaust gas aftertreatment device (12), 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,wherein 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), wherein the first operating range (16) and the second operating range (17) are characterized by a mass flow of the exhaust gas, wherein the first operating range (16) is recognized if a mass flow of the exhaust gas lies within a first mass flow range, characterized in that the second operating range (17) is recognized if the mass flow of the exhaust gas lies within a second mass flow range, wherein the first mass flow range comprises smaller values ​​than the second mass flow range,wherein the first operating range (16) and the second operating range (17) are additionally characterized by a first combustion air ratio in the exhaust gas upstream of the exhaust gas aftertreatment device (12) and a second combustion air ratio in the exhaust gas downstream of the exhaust gas aftertreatment device (12), wherein a range of at least 0.95 and at most 1.05 is used for the first combustion air ratio and a Nernst voltage of at least 0.68 V to at most 0.75 V is used for the second combustion air ratio.

Description

[0001] 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 catalyst for aftertreating the exhaust gas, a broadband lambda probe arranged upstream of the exhaust gas aftertreatment device, a jump lambda probe arranged downstream of the exhaust gas aftertreatment device, and a pollutant sensor reacting to nitrogen oxide and ammonia arranged downstream of the exhaust gas aftertreatment device 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, wherein the sensor offset is determined only in a first operating range of the drive unit and a catalyst condition parameter is determined only in a second operating range of the drive unit that is different from the first operating range,The first operating range and the second operating range are characterized by a mass flow of the exhaust gas, and the first operating range is recognized if a mass flow of the exhaust gas lies within a first mass flow range. The invention further relates to a drive device for a motor vehicle and a computer program product.

[0002] For example, the prior art document USUS 2023 / 0 112 942 A1 is known. This document describes methods and systems for adjusting an ammonia sensor output using measured values ​​from a nitrogen oxide sensor, wherein the nitrogen oxide sensor has a cross-sensitivity to ammonia. For example, a gain value of the ammonia sensor is determined and updated while no nitrogen oxide is detected to calculate a corrected ammonia sensor output value. An offset value of the ammonia sensor is determined and updated while no ammonia is detected to set the ammonia sensor to zero when no nitrogen oxide is detected.

[0003] The document DE 102 23 385 A1 describes a method for determining an offset correction of a NOx sensor. In a first step, during a predetermined release interval prior to a measurement interval, the values ​​of at least one sensor operating parameter are determined and compared with an assigned release value. In a second step, depending on the comparison result, a decision is made as to whether the NOx signal of the NOx sensor should be released to determine the offset correction value in the subsequent measurement interval.

[0004] The German patent document DE 199 53 601 A1 relates to a method for testing an exhaust catalytic converter of an internal combustion engine. To test the exhaust catalytic converter when the engine is at operating temperature, a NOx sensor is used to determine the NOx concentration downstream of the exhaust catalytic converter to be diagnosed. During the diagnosis period, the oxygen loading of the exhaust catalytic converter is increased, and the NOx concentration measured during several lambda controller oscillations is used to determine the conversion properties of the exhaust catalytic converter.

[0005] Furthermore, the prior art documents DE 198 28 609 A1, DE 103 39 062 A1, DE 198 52 240 A1, DE 199 11 664 A1 and US 2017 / 0 030 244 A1 are known.

[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 precise determination of a state of the vehicle catalyst.

[0007] This is achieved according to the invention with a method for operating a drive device for a motor vehicle with the features of claim 1. It is provided that the second operating range is detected if the mass flow of the exhaust gas lies within a second mass flow range, wherein the first mass flow range comprises smaller values ​​than the second mass flow range, wherein the first operating range and the second operating range are additionally characterized by a first combustion air ratio in the exhaust gas upstream of the exhaust gas aftertreatment device and a second combustion air ratio in the exhaust gas downstream of the exhaust gas aftertreatment device, wherein a range of at least 0.95 and at most 1.05 is used for the first combustion air ratio and a Nernst voltage of at least 0.68 V to at most 0.75 V is used for the second combustion air ratio.

[0008] Advantageous embodiments with useful further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments explained in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are feasible.

[0009] The drive device serves to drive the motor vehicle, i.e. to provide 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 or a diesel 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. In addition, the fresh gas can comprise exhaust gas, provided that exhaust gas recirculation is implemented, in which the exhaust gas generated by the drive unit is at least partially recirculated into the drive unit, namely 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 reacted in the drive unit.

[0010] 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.

[0011] The exhaust gas aftertreatment device 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 efficiency of the exhaust gas aftertreatment device, with which the pollutants are converted into less hazardous products, depend in particular on the composition of the exhaust gas supplied to the exhaust gas aftertreatment device and / or on the oxygen loading of the exhaust gas aftertreatment device, which in turn is related to the composition of the exhaust gas. Preferably, the conversion efficiency also depends on the catalyst condition parameter, which describes the condition of the vehicle catalytic converter.

[0012] To operate the drive device, a first combustion air ratio and a second combustion air ratio are preferably used, among other things. 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 a first lambda probe, and the second combustion air ratio is measured using a 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.

[0013] 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. Ultimately, the fuel-fresh gas mixture, or its composition, is adjusted, at least temporarily, depending on the first combustion air ratio and the second combustion air ratio.

[0014] Due to the ever-increasing stringent regulations for exhaust emissions, these must be monitored ever more closely. For this reason, a pollutant sensor is provided, particularly in addition to the two lambda sensors, which reacts to nitrogen oxide and ammonia. The pollutant sensor is preferably a nitrogen oxide sensor that is cross-sensitive to ammonia. The measured value of the nitrogen oxide sensor is therefore influenced by both the nitrogen oxide content and the ammonia content in the exhaust gas. In particular, the measured value of the nitrogen oxide sensor results in a sum of the nitrogen oxide content and the ammonia content present in the exhaust gas downstream of the exhaust gas aftertreatment device. Nitrogen oxide is understood here to mean, in particular, only nitrogen monoxide, only nitrogen dioxide, or - preferably - both nitrogen monoxide and nitrogen dioxide, i.e. the totality of nitrogen monoxide and nitrogen dioxide.The pollutant sensor is located downstream of the exhaust gas aftertreatment device and therefore measures the pollutant content in the exhaust gas downstream of the exhaust gas aftertreatment device.

[0015] The pollutant content is determined using the pollutant sensor, namely using the measured value from the pollutant sensor. The sensor offset is also taken into account, which describes any deviation of the measured value from the actual pollutant content as precisely as possible. In particular, the pollutant content is equal to the sum of the measured value of the pollutant sensor and the sensor offset, or the pollutant content is the result of the measured value minus the sensor offset. In either case, the pollutant content is a function of the measured value and the sensor offset. The pollutant content or the respective content is a content indication or content variable and specifies the content of the respective substance, in particular the pollutant, in the exhaust gas. The content is specified, for example, as a mass fraction, amount fraction or volume fraction. However, it can also be given as a mass concentration, amount concentration or volume concentration.

[0016] The pollutant content is used to determine the catalyst condition parameter, which describes the condition of the vehicle's catalyst, particularly its conversion efficiency. The catalyst condition parameter is a parameter that is only determined periodically and therefore does not need to be permanently available. For example, the catalyst condition parameter describes an age-related change in the vehicle's catalyst, i.e., a change, particularly a reduction, in conversion efficiency due to age or age-related influences. The catalyst condition parameter is therefore only determined periodically.

[0017] The catalyst condition parameter preferably serves as an input variable for a catalyst model, by means of which an output content of at least one exhaust gas component is determined from an input content. The input content is present upstream and the output content downstream of the vehicle catalyst in the exhaust gas. The catalyst model is preferably used continuously during operation of the drive unit to determine the output content from the input content. The input content is understood, in particular, to be a content of the at least one exhaust gas component in raw emissions from the drive unit. The raw emissions or the input content can be measured using a sensor or determined using a model.

[0018] However, based on the measured value or the pollutant content determined from it, it is not possible to distinguish between a change in the pollutant content due to the changing catalyst condition parameter and a change in the sensor offset. Thus, the pollutant sensor can indicate a high pollutant content 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 content itself does not allow any conclusions to be drawn about the background of the measured value.

[0019] For this reason, it is provided to differentiate between different operating ranges of the drive unit and, depending on the respective operating range of the drive unit, to determine either the sensor offset or the catalyst state parameter, but not the other variable. 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 operating range. In other words, in the first operating range only the sensor offset is determined, but not the catalyst state parameter, and in the second operating range only the catalyst state parameter is determined, but not the sensor offset. This means that the sensor offset is only determined in the first operating range and the catalyst state parameter is only determined in the second operating range. The two operating ranges are different from one another.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 one another or—preferably—are spaced apart from one another.

[0020] The first operating range is selected such that there is no or only a lower dependence of the pollutant content or the measured value on the catalyst condition parameter than in the second operating range. Conversely, the second operating range is selected such that the pollutant content or the measured value therein shows a stronger dependence on the catalyst condition parameter than in the first operating range. Thus, the pollutant content measured using the pollutant sensor or its change can be clearly assigned to the sensor offset in the first operating range and to the catalyst condition parameter in the second operating range. This enables both an accurate determination of the sensor offset and precise detection of the condition of the vehicle's catalyst.

[0021] A further development of the invention provides that the first operating range and the second operating range are additionally characterized by at least one of the following operating parameters: a mass flow gradient of the exhaust gas and a temperature of the exhaust gas aftertreatment device. It may be provided 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.

[0022] The first combustion air ratio is determined using the aforementioned first lambda probe, and the second combustion air ratio is determined using the second lambda probe. The first combustion air ratio lies in a first range for the first operating range and in a second range for the second operating range. Analogously, the second combustion air ratio lies in a (further) first range for the first operating range and in a (further) second range for the second operating range. The mass flow describes the amount of exhaust gas per unit of time that flows through the exhaust gas aftertreatment device. In this respect, the mass flow is a throughput of the exhaust gas through the exhaust gas aftertreatment device. The mass flow gradient describes a change in the mass flow over time. The temperature of the exhaust gas aftertreatment device is preferably measured using a sensor.However, it can of course also be determined using a temperature model.

[0023] The exhaust gas mass flow lies within a first mass flow range for the first operating range and a second mass flow range for the second operating range. The mass flow gradient lies within a first mass flow gradient range for the first operating range and a second mass flow gradient range for the second operating range. The temperature of the exhaust gas aftertreatment system lies within a first temperature range for the first operating range and a second temperature range for the second operating range. The use of these operating parameters enables targeted differentiation between the operating ranges.

[0024] A further development of the invention provides that the operating parameter is a first operating parameter which comprises different value ranges for the first operating range and the second operating range, and that a second operating parameter selected from the operating parameters comprises identical value ranges for the first operating range and the second operating range. It has already been mentioned that several of the aforementioned operating parameters can be used to characterize the operating ranges. The two operating ranges are preferably different from one another with regard to the first operating parameter, but agree with regard to the second operating parameter. This means that in the two operating ranges the first operating parameter lies in different value ranges, but the value ranges for the second operating parameter agree.In other words, the conditions between the operating ranges differ for the first operating parameter, while they are identical for the second operating parameter.

[0025] The first operating parameter is, for example, the mass flow of the exhaust gas, whereas the second operating parameter is one of the aforementioned operating parameters that differs from the mass flow. Provision can be made for several second operating parameters to be used, each of which lies in identical value ranges for the two operating ranges. Particularly preferred is the mass flow, which lies in different value ranges for the two operating ranges, to be used as the first operating parameter. For the second operating parameters, however, the operating ranges are characterized by identical value ranges. The described procedure ensures that the catalyst condition parameter is reliably determined.

[0026] The invention provides that the first operating range and the second operating range are recognized, in particular only if or precisely if the mass flow of the exhaust gas lies within a respective specific mass flow range. The mass flow is the instantaneous mass flow of the exhaust gas through the exhaust gas aftertreatment device. This means that the mass flow for the first operating range lies in a mass flow range assigned to the first operating range and for the second operating range in a mass flow range assigned to the second operating range. The mass flow range assigned to the first operating range can also be referred to as the first mass flow range and the mass flow range assigned to the second operating range as the second mass flow range. The two mass flow ranges are different from one another, in particular they do not overlap.They are therefore, for example, directly adjacent to one another or – preferably – spaced apart from one another.

[0027] According to the invention, the first mass flow range comprises smaller values ​​than the second mass flow range, i.e., it is below the latter. For example, the first mass flow range is smaller than the second mass flow range; for example, a circumference of the first mass flow range is at most 60%, at most 50%, or at most 40% of a circumference of the second mass flow range. A distance between the mass flow ranges is preferably at least 30%, at least 20%, or at least 10% of the circumference of the first mass flow range and / or at least 20%, at least 10%, or at least 7.5% of the circumference of the second mass flow range.

[0028] For example, the first mass flow range used is a range from more than 0 kg / h to a maximum of 225 kg / h, from at least 5 kg / h to a maximum of 200 kg / h, or from at least 10 kg / h to a maximum of 175 kg / h. The second mass flow range is preferably a range of at least 225 kg / h, at least 250 kg / h, or at least 275 kg / h. Additionally, the second mass flow range can be a maximum of 700 kg / h, a maximum of 600 kg / h, or a maximum of 500 kg / h. This procedure enables the sensor offset and the catalyst condition parameter to be determined with high accuracy.

[0029] 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 at least one of the following conditions is additionally met: the mass flow gradient lies within a respective specific gradient range and the temperature of the exhaust gas aftertreatment device lies within a respective specific temperature range.

[0030] The use of the first combustion air ratio and the second combustion air ratio to characterize the operating ranges has already been mentioned. The two combustion air ratio ranges, i.e., the first combustion air ratio range and the second combustion air ratio range, are selected independently of each other but may overlap. It may be provided that the combustion air ratios for each operating range are considered separately.

[0031] It is therefore assumed that the first operating range exists 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.

[0032] 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 ratio lies within a second combustion air ratio range assigned to the second operating range. It can be provided that the combustion air ratio ranges are identical for both operating ranges. Thus, the presence of both the first operating range and the second operating range 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.

[0033] According to the invention, 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, preferably for both operating ranges. For the second combustion air ratio, according to the invention, 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 used, preferably likewise for both operating ranges.

[0034] The mass flow gradient is the gradient of the mass flow of the exhaust gas over time, i.e., the first derivative of the mass flow. The first mass flow gradient range and the second mass flow gradient range are preferably identical and amount to a maximum of 40 kg / h / s, a maximum of 30 kg / h / s, or a maximum of 25 kg / h / s. 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. The respective operating range is only recognized if the respective variable lies within the respective range. Preferably, this applies to several or even all of the aforementioned variables.This again results in particularly high accuracy.

[0035] A further development of the invention provides that it is assumed that the first operating range and / or the second operating range exists, in particular only if or precisely if the respective condition is met over a respective period of time. For each of the stated conditions used to check the respective operating range, a respective period of time is therefore defined. Only if the corresponding condition applies over this period of time is the condition considered to be met. This prevents detection of the respective operating range if the respective variable is only within the required range for a short period of time. This prevents influence from transient behavior of the drive unit and achieves a high level of accuracy.

[0036] It is particularly preferred that the first operating range is detected and the sensor offset is determined, in particular only if or precisely if one or more of the following conditions apply, in particular all of the conditions mentioned: - The first combustion air ratio lies over a first period of time within the specific first combustion air ratio range assigned to the first operating range, - the second combustion air ratio lies within the specific second combustion air ratio range assigned to the first operating range over a second period of time, - the mass flow of the exhaust gas lies within the specific mass flow range assigned to the first operating range over a third period of time, - the mass flow gradient lies within the specific gradient range assigned to the first operating range over a fourth time period, and - the temperature of the exhaust gas aftertreatment device is within the specific temperature range assigned to the first operating range over a fifth period of time.

[0037] Additionally or alternatively, the second operating range is detected and the sensor offset is determined, in particular only if or precisely if one or more of the following conditions apply, in particular all of the conditions mentioned: - The first combustion air ratio lies over a first period of time within the specific first combustion air ratio range assigned to the second operating range, - the second combustion air ratio lies within the specific second combustion air ratio range assigned to the second operating range over a second period of time, - the mass flow of the exhaust gas lies within the specific mass flow range assigned to the second operating range over a third period of time, - the mass flow gradient lies within the specific gradient range assigned to the second operating range over a fourth time period, and - the temperature of the exhaust gas aftertreatment device is within the specific temperature range assigned to the second operating range over a fifth period of time.

[0038] 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.

[0039] A further development of the invention provides that the first combustion air ratio range contains 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 each other. The stoichiometric combustion air ratio occurs at λ = 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 ratio range. The described procedure enables high accuracy in determining the sensor offset and the catalyst condition parameter.

[0040] A further development of the invention provides that a temperature range above a light-off temperature of the exhaust gas aftertreatment system is used as the temperature range, particularly for both operating ranges. The light-off temperature of the exhaust gas aftertreatment system is understood to be the temperature above which the exhaust gas aftertreatment system has a conversion efficiency of 50% for the pollutants to be converted, in particular for nitrogen oxide. To ensure that the exhaust gas aftertreatment system's conversion efficiency for nitrogen oxide 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 downwards, i.e., toward 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.

[0041] 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 content and / or the ammonia content, 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.

[0042] 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 λ = 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 the trim control or the step-down lambda sensor. This allows the composition of the fuel / fresh gas mixture to be adjusted with high precision.

[0043] 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 in order to determine the sensor offset, and then, by operating the drive unit in the second operating range, the catalyst state parameter is determined using the previously determined sensor offset. Thus, it is provided to first determine the sensor offset before subsequently determining the catalyst state parameter at a time interval therefrom. For example, it is provided to operate the drive unit specifically in the first operating range and determine the sensor offset. The drive unit is then specifically operated in the second operating range, and the catalyst state parameter is determined.

[0044] However, it can also be provided that the drive unit is controlled solely as a function of a default value specified by a user of the motor vehicle, for example a default value specified 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 operating range or in the second operating range. If it is determined that the drive unit is operating in the first operating range, the measured value of the pollutant sensor is evaluated and the sensor offset is determined. If, on the other hand, it is determined that the drive unit is operating in the second operating range, the measured value of the pollutant sensor is recorded.

[0045] For example, it is provided to calculate the catalyst condition parameter directly using the available sensor offset. However, this is preferably only provided if the last determination of the sensor offset occurred no longer than a certain period of time ago. If this period of time is exceeded, the system first waits until the drive unit is operating in the first operating range. In this case, the sensor offset is determined, and this sensor offset is immediately calculated to determine the catalyst condition parameter from the measured value recorded during operation of the drive unit in the second operating range. This achieves a high level of accuracy.

[0046] 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 condition parameter. The aging parameter describes the condition of the vehicle catalyst over time. In particular, the oxygen storage capacity of the vehicle catalyst directly depends on the aging parameter or is described by it. Additionally or alternatively, the aging parameter describes the conversion performance, in particular the maximum achievable conversion performance using the vehicle catalyst.

[0047] For example, the aging parameter is used in a catalyst model that mathematically describes the vehicle catalyst. The catalyst model is preferably used permanently to determine an output content of at least one exhaust gas component present downstream of the vehicle catalyst from an input content of at least one pollutant component present upstream of the vehicle catalyst. The exhaust gas component can be nitrogen oxide, but also an exhaust gas component other than nitrogen oxide, such as carbon oxide, in particular 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 drive system or drive unit.The catalyst condition parameter incorporated into the catalyst model is only adjusted or corrected periodically. This approach enables particularly precise determination of pollutant emissions and corresponding monitoring.

[0048] 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 broadband lambda probe arranged upstream of the exhaust gas aftertreatment device, a jump lambda probe arranged downstream of the exhaust gas aftertreatment device 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 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 device is provided and designed 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 is different from the first operating range, wherein the first operating range and the second operating range are characterized by a mass flow of the exhaust gas, wherein the drive device is provided and designed to detect the first operating range if a mass flow of the exhaust gas lies within a first mass flow range.It is further provided that the second operating range is detected if the mass flow of the exhaust gas lies within a second mass flow range, wherein the first mass flow range comprises smaller values ​​than the second mass flow range, wherein the first operating range and the second operating range are additionally characterized by a first combustion air ratio in the exhaust gas upstream of the exhaust gas aftertreatment device and a second combustion air ratio in the exhaust gas downstream of the exhaust gas aftertreatment device, wherein a range of at least 0.95 and at most 1.05 is used for the first combustion air ratio and a Nernst voltage of at least 0.68 V to at most 0.75 V is used for the second combustion air ratio.

[0049] The advantages of such a procedure or such a design of the drive system have already been pointed out. Both the drive system for the motor vehicle and the method for its operation can be further developed according to the explanations in this description, so reference is made to these in this regard.

[0050] 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.

[0051] 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.

[0052] The invention will be explained in more detail below with reference to the exemplary embodiments shown in the drawings, without limiting the invention. In the drawings: Fig. 1 a schematic representation of a drive device for a motor vehicle, Fig. 2 a diagram in which a conversion performance of a vehicle catalyst is plotted, for which a catalyst condition parameter has a first value, and Fig. 3 a diagram in which the conversion performance is plotted for a vehicle catalyst for which the catalyst condition parameter has a second value.

[0053] The Fig. Figure 1 shows a schematic representation of a drive device 1 comprising 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.

[0054] 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.

[0055] Upstream of the exhaust 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 location. Downstream of the exhaust 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 aftertreatment device 12 is a pollutant sensor 15, which reacts to nitrogen oxide and ammonia and serves to determine a pollutant content in the exhaust gas. The pollutant sensor 15 is shown integrated into the second lambda probe 14 by way of example.

[0056] The pollutant content in the exhaust gas is determined by measuring a measured value using pollutant sensor 15. The measured value is subjected to a sensor offset. This results in the pollutant content. The pollutant content is therefore, for example, equal to the sum of the measured value and the sensor offset. It can also be specified that the pollutant content is equal to the measured value minus the sensor offset.

[0057] The Fig. Figure 2 shows a diagram in which a conversion efficiency η is plotted against a catalyst temperature T and an exhaust gas mass flow m. The exhaust gas aftertreatment device 12 corresponds to a vehicle catalyst with a first value of a catalyst condition parameter. In particular, an aging parameter of the vehicle catalyst is used as the catalyst condition 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 condition parameter, the conversion efficiency is approximately at the same level in both operating ranges 16 and 17.

[0058] The Fig.3 shows the diagram in which the conversion performance η is again plotted against the temperature T and the mass flow ṁ, namely for an exhaust gas aftertreatment device 12 for which the catalyst state parameter has a second value that is different from the first value. While the first value of the catalyst state parameter indicates a newer vehicle catalyst, the second value represents an older or more aged vehicle catalyst. Accordingly, the conversion performance is lower overall. When comparing the diagrams for the different values ​​of the catalyst state parameter, it is particularly noticeable that the conversion performance is almost the same in the first operating range, whereas it differs significantly or more significantly in the second operating range.

[0059] It follows that a sensor offset of the pollutant sensor 15 can be detected more reliably in the first operating range 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 condition parameter. Preferably, the operating ranges of the drive unit 2 differ only with regard to a mass flow of the exhaust gas flowing through the exhaust gas aftertreatment device 12. For example, the mass flow for the first operating range is at least 5 kg / h and at most 200 kg / h, and for the second operating range is at least 250 kg / h and at most 600 kg / h. The described procedure enables reliable determination of both the sensor offset and the catalyst condition parameter. LIST OF REFERENCE SYMBOLS: 1 drive device 2 drive unit 3 Exhaust system 4 cylinders 5 Inlet valve 6 exhaust valve 7 Fresh gas tract 8 compressors 9 exhaust gas turbocharger 10 turbines 11 Exhaust pipe 12 Exhaust aftertreatment system 13 1. Lambda sensor 14 2. Lambda sensor 15 pollutant sensor 16 1. Operating area 17 2. Operating area

Claims

[1] Method for operating a drive device (1) for a motor vehicle, which has a drive unit (2) generating exhaust gas, an exhaust gas aftertreatment device (12) designed as a vehicle catalyst for aftertreating the exhaust gas, a broadband lambda probe arranged upstream of the exhaust gas aftertreatment device (12), a jump lambda probe arranged downstream of the exhaust gas aftertreatment device (12), and a pollutant sensor (15) reacting to nitrogen oxide and ammonia arranged downstream of the exhaust gas aftertreatment device (12) 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,wherein 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), wherein the first operating range (16) and the second operating range (17) are characterized by a mass flow of the exhaust gas, wherein the first operating range (16) is recognized if a mass flow of the exhaust gas lies within a first mass flow range, , characterized bythat the second operating range (17) is detected if the mass flow of the exhaust gas lies within a second mass flow range, wherein the first mass flow range comprises smaller values ​​than the second mass flow range, wherein the first operating range (16) and the second operating range (17) are additionally characterized by a first combustion air ratio in the exhaust gas upstream of the exhaust gas aftertreatment device (12) and a second combustion air ratio in the exhaust gas downstream of the exhaust gas aftertreatment device (12), wherein a range of at least 0.95 and at most 1.05 is used for the first combustion air ratio and a Nernst voltage of at least 0.68 V to at most 0.75 V is used for the second combustion air ratio. [2] Method according to claim 1, characterized bythat the first operating range (16) and the second operating range (17) are additionally characterized by at least one of the following operating parameters: 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, characterized by 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 claim 2, characterized bythat the first operating range (16) and / or the second operating range (17) is detected if at least one of the following conditions is additionally met: the mass flow gradient lies within a respective specific gradient range and the temperature of the exhaust gas aftertreatment device (12) lies within a respective specific temperature range. [5] Method according to one of the preceding claims, characterized by that it is assumed that the first operating range (16) and / or the second operating range (17) exists if the respective condition is fulfilled over a respective period of time. [6] Method according to one of the preceding claims, characterized byin that, in order to determine the catalyst state parameter, the drive unit (2) is first operated in the first operating range (16) in order 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. [7] Method according to one of the preceding claims, characterized by that an ageing parameter of the vehicle catalyst describing an oxygen storage capacity is used as the catalyst condition parameter. [8] 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 a drive unit (2) generating exhaust gas, an exhaust gas aftertreatment device (12) designed as a vehicle catalyst for aftertreating the exhaust gas, a broadband lambda probe arranged upstream of the exhaust gas aftertreatment device (12), a jump lambda probe arranged downstream of the exhaust gas aftertreatment device (12), and a pollutant sensor (15) reacting to nitrogen oxide and ammonia arranged downstream of the exhaust gas aftertreatment device (12) 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, wherein the drive device (1) is provided and designed toto determine the sensor offset only in a first operating range (16) of the drive unit (2) and a catalyst condition parameter only in a second operating range (17) of the drive unit (2) that is different from the first operating range (16), wherein the first operating range (16) and the second operating range (17) are characterized by a mass flow of the exhaust gas, wherein the drive device (1) is further provided and designed to detect the first operating range (16) if a mass flow of the exhaust gas lies within a first mass flow range, characterized bythat the second operating range (17) is detected if the mass flow of the exhaust gas lies within a second mass flow range, wherein the first mass flow range comprises smaller values ​​than the second mass flow range, wherein the first operating range (16) and the second operating range (17) are additionally characterized by a first combustion air ratio in the exhaust gas upstream of the exhaust gas aftertreatment device (12) and a second combustion air ratio in the exhaust gas downstream of the exhaust gas aftertreatment device (12), wherein a range of at least 0.95 and at most 1.05 is used for the first combustion air ratio and a Nernst voltage of at least 0.68 V to at most 0.75 V is used for the second combustion air ratio. [9] Computer program product comprising instructions which cause the drive device (1) according to claim 8 to carry out the method steps according to one or more of claims 1 to 7.

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