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

Abstract

The invention relates to a method for operating a drive unit (1) for a motor vehicle, which comprises an exhaust-generating drive unit, an exhaust aftertreatment device (2) designed as a vehicle catalyst for aftertreating the exhaust gas, and a lambda sensor (6) arranged downstream of the exhaust aftertreatment device (2) for determining a combustion air ratio in the exhaust gas, which is adjusted to a target value for setting the composition of a fuel-air mixture used to operate the drive unit. It is provided that condensate accumulating in the exhaust aftertreatment device (2) during warm-up operation is taken into account when adjusting the combustion air ratio to the target value. The invention further relates to a drive unit (1) for a motor vehicle and a computer program.

Description

[0001] The invention relates to a method for operating a drive unit for a motor vehicle, which has an exhaust gas-generating drive unit, an exhaust gas aftertreatment device designed as a vehicle catalyst for aftertreating the exhaust gas, and a lambda probe arranged downstream of the exhaust gas aftertreatment device for determining a combustion air ratio in the exhaust gas, which is set to a target value for adjusting the composition of a fuel-fresh gas mixture used to operate the drive unit, wherein condensate accumulating in the exhaust gas aftertreatment device during a warm-up operation is taken into account when adjusting the combustion air ratio to the target value, wherein the quantity of condensate present in the exhaust gas aftertreatment device is determined by balancing for the purpose of taking the condensate into account.The invention further relates to a drive direction for a motor vehicle and a computer program product.

[0002] For example, the prior art includes the publication DE 10 2020 100 158 A1.This describes a method for operating an exhaust aftertreatment system for an internal combustion engine with a catalyst comprising an oxygen storage unit and a lambda sensor arranged downstream of the catalyst in the exhaust pipe. Using a model of the catalyst, exhaust gas components downstream of the catalyst are determined. Based on these exhaust gas components, the signal of the lambda sensor arranged downstream of the catalyst in the exhaust pipe is simulated. Depending on this simulated signal, the exhaust aftertreatment system is operated when the oxygen storage unit is not active because a temperature has not reached or exceeded a threshold. The exhaust gas components downstream of the catalyst are determined using a model such that these model exhaust gas reactions at the catalyst are used as a basis, which take place without the oxygen component from the oxygen storage unit.

[0003] Furthermore, the prior art document EP 2 252 785 B1 describes a control system for an exhaust gas sensor that controls the power supply of a heating device which heats an exhaust gas sensor located in the exhaust pipe of an internal combustion engine, wherein the control system comprises: an exhaust gas temperature sensor that detects the exhaust gas temperature in the exhaust pipe; an air flow rate sensor that detects the air flow rate drawn into the internal combustion engine; and an outside air temperature sensor that detects the outside air temperature.a device for estimating the amount of condensate, which estimates the amount of condensate that has collected in the exhaust pipe using the exhaust temperature detected by the exhaust temperature sensor when the internal combustion engine is started, the airflow rate measured by the airflow rate sensor, and the outside air temperature detected by the outside air temperature sensor; a device for determining the presence of condensate, which determines whether or not condensate is present in the exhaust pipe based on the amount of condensate estimated by the device for estimating the amount of condensate;and a device for a heating device control that supplies an electric current to the heating device when the device for determining the presence of condensate determines that no condensate is present in the exhaust pipe. The device for estimating the amount of condensate is provided to calculate an estimated exhaust pipe wall temperature in the exhaust pipe, obtained sequentially using the exhaust gas temperature, the airflow rate, and the outside air temperature; and a condensation point of the exhaust pipe, determined based on the fuel-air ratio as a ratio of the airflow rate to the weight of the fuel; a relative exhaust pipe wall temperature based on an estimated wall temperature and the condensation point; and an additive amount of condensate based on the relative wall temperature and the airflow rate.and estimates the amount of condensation by summing the calculated amounts of condensation.

[0004] The object of the invention is to propose a method for operating a drive device for a motor vehicle which has advantages over known methods, in particular the adjustment of the composition of the fuel-fresh gas mixture with high accuracy.

[0005] According to the invention, this is achieved by a method for operating a drive unit for a motor vehicle with the features of claim 1. It is provided that, for the purpose of balancing, a drying rate of the condensate is determined at which condensate temporarily stored in the exhaust aftertreatment device is converted into gaseous water carried by the exhaust gas, wherein an ammonia throughput is determined based on the drying rate at which the ammonia contained in the condensate is introduced into the exhaust gas.

[0006] 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.

[0007] The method is designed for operating the drive unit. The drive unit serves to propel the motor vehicle, thus providing drive torque for propelling the motor vehicle. To provide the drive torque, the drive unit comprises the drive assembly. The drive assembly is preferably an internal combustion engine, in particular a gasoline or diesel engine. During operation of the drive unit, fuel and fresh gas are supplied to the drive assembly 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 assembly is at least partially returned to the drive assembly as a component of the fresh gas.The fuel and fresh gas supplied to the drive unit form the fuel-fresh gas mixture with a specific composition, which is then reacted in the drive unit.

[0008] During operation of the engine, exhaust gas is produced due to the chemical reaction of fuel and fresh air. This exhaust gas is discharged towards the outside environment of the engine or vehicle. 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 discharged into the environment, primarily through an exhaust pipe on the engine.

[0009] The exhaust aftertreatment system is in the form of a vehicle catalyst, in particular a three-way catalyst, oxidation catalyst, NO x The vehicle catalyst is a storage catalyst or SCR catalyst, or at least incorporates one. The vehicle catalyst is particularly preferably integrated into a particulate filter, especially a gasoline particulate filter or a diesel particulate filter. For this purpose, the particulate filter is, for example, provided with a catalytic coating. The conversion rate, and thus the conversion performance of the exhaust aftertreatment system, with which the pollutants are converted into less harmful products, depends in particular on the composition of the exhaust gas supplied to the exhaust aftertreatment system and the temperature of the exhaust aftertreatment system.

[0010] The components of the exhaust gas produced by the engine are also referred to as raw emissions. Raw emissions describe the composition of the exhaust gas upstream of the exhaust aftertreatment system, or in terms of flow characteristics, between the engine and the exhaust aftertreatment system. As the exhaust gas passes through the aftertreatment system, some of the substances contained within it are transformed, thus changing its composition. The substances present in the exhaust gas downstream of the aftertreatment system, which constitute the exhaust gas, are also referred to as tailpipe emissions, since this is the composition of the exhaust gas released into the environment through the engine's tailpipe.

[0011] As mentioned, the amount of pollutants contained in the tailpipe emissions depends on the raw emissions, but also on the conversion efficiency of the exhaust aftertreatment system. This efficiency is temperature-dependent. Specifically, the conversion efficiency decreases the further the temperature of the exhaust aftertreatment system deviates from its operating temperature; in other words, the greater the absolute difference between the temperatures. The temperature of the exhaust aftertreatment system refers specifically to the temperature of a ceramic honeycomb structure coated with the catalytic material.

[0012] Downstream of the exhaust aftertreatment system is the lambda sensor, which serves to determine the air-fuel ratio in the exhaust gas, i.e., the air-fuel ratio present downstream of the exhaust aftertreatment system. For this purpose, the lambda sensor measures, in particular, the residual oxygen content in the exhaust gas and calculates the air-fuel ratio from this. Preferably, the lambda sensor is designed as a switching lambda sensor. The air-fuel ratio determined by the lambda sensor serves as the basis for adjusting the composition of the fuel-air mixture. In particular, it is intended to adjust the composition such that the air-fuel ratio changes towards the target value, especially down to the target value. For example, the air-fuel ratio is regulated by adjusting the composition of the fuel-air mixture to the target value.

[0013] During the warm-up phase of the drive unit, the exhaust aftertreatment system has a temperature lower than its operating temperature. Specifically, at the beginning of the warm-up phase, the temperature of the exhaust aftertreatment system is approximately or exactly equal to the ambient temperature. During the warm-up phase, the exhaust aftertreatment system heats up, causing its temperature to rise towards, and ultimately reach, its operating temperature.

[0014] If the temperature of the exhaust gas aftertreatment system is still sufficiently low, gaseous water contained in the exhaust gas condenses within it, subsequently forming condensate or condensate within the exhaust gas aftertreatment system. This gaseous water can also be referred to as water vapor. If the temperature of the exhaust gas and / or the temperature of the exhaust gas aftertreatment system reaches or exceeds a certain temperature, also known as the threshold temperature, the condensate is discharged from the exhaust gas aftertreatment system by evaporation. Whenever this description refers to the evaporation of the condensate, this always includes the possibility of evaporation.

[0015] Particularly when the engine is operated with a rich fuel-air mixture, nitrogen oxide (NOx) is present in the exhaust gas upstream of the exhaust aftertreatment system. x ), particularly in the form of nitrogen monoxide (NO). This is converted into ammonia (NH3) in a side reaction within the exhaust aftertreatment system.

[0016] The ammonia dissolves in the water or steam and passes through the exhaust gas aftertreatment system along with the water. The ammonia then condenses together with the water and subsequently forms part of the condensate.

[0017] If the temperature of the exhaust aftertreatment system exceeds a certain temperature or threshold temperature, the condensate reverts to its gaseous state, again together with the ammonia. This means that additional ammonia is introduced into the exhaust gas, while the condensate evaporates. Oxygen is consumed for the oxidation of the ammonia in the exhaust aftertreatment system, according to the reaction equation. 2 NH3 + 1.5 O2 → N2 + 3 H2O.

[0018] Therefore, the exhaust gas contains less oxygen than expected. Consequently, the lambda sensor detects an excessively rich fuel-air mixture and adjusts the mixture towards a leaner mixture. This ultimately leads to an excess of oxygen in the exhaust aftertreatment system, causing nitrogen oxide emissions to increase.

[0019] The exhaust gas typically contains approximately 13% gaseous water. Even when the engine is operating with a slightly rich mixture, an ammonia yield—that is, the proportion of nitrogen oxides converted to ammonia—of more than 50% can occur. For example, if the exhaust gas contains 2,600 ppm nitrogen oxides, at least 1,300 ppm ammonia can be formed. A water content of 13% in the exhaust gas corresponds to 130,000 ppm, so the condensate is present as an approximately 1% ammonia solution. During the warm-up phase after a cold start of the engine, typically 2 g of water condense in the exhaust aftertreatment system and subsequently evaporate. At an ammonia content of one percent, this corresponds to 20 mg of ammonia.

[0020] For every 1,000 ppm NH3, 750 ppm O2 are required for oxidation according to the aforementioned reaction equation. This has a significant impact on the mixture composition. Therefore, during warm-up, the condensate produced in the exhaust aftertreatment system should be taken into account when adjusting the air-fuel ratio to the target value. Specifically, the amount of condensate that accumulates or has accumulated in the exhaust aftertreatment system is determined. The flow rate at which the condensate evaporates and subsequently flows as gaseous water towards the lambda sensor is also calculated. This allows the fuel-air mixture composition to be adjusted with very high accuracy, thus reducing overall pollutant emissions.

[0021] A further development of the invention provides that the proportion of ammonia contained in the condensate is determined based on the nitrogen oxide content of the exhaust gas upstream of the exhaust aftertreatment system. The nitrogen oxide content corresponds to the proportion of nitrogen oxide in the raw emissions and is therefore present upstream of the exhaust aftertreatment system. As already explained, the nitrogen oxide is at least temporarily and partially converted into ammonia in the exhaust aftertreatment system, which is dissolved by the water and consequently also by the condensate. The proportion of ammonia in the condensate is determined based on the nitrogen oxide content; this proportion is thus a function of the nitrogen oxide content. Using the described procedure, extremely high accuracy in mixture adjustment is achieved.

[0022] The invention provides that, for the purpose of accounting for condensate, the quantity of condensate present in the exhaust aftertreatment system is determined by balancing. Balancing is understood as a process in which both the flow rate at which the condensate is generated in the exhaust aftertreatment system (i.e., the gaseous water condenses to form condensate) and the flow rate at which the condensate evaporates in the exhaust aftertreatment system, so that it subsequently re-emerges as gaseous water are determined. Flow rate is understood as a quantity per unit of time, for example, a mass per unit of time or a volume per unit of time. Balancing is performed particularly as a function of the temperature of the exhaust aftertreatment system. Additionally, the exhaust gas mass flow rate at which the exhaust gas flows through the exhaust aftertreatment system can be taken into account.This also serves to achieve particularly high accuracy in adjusting the composition of the fuel-fresh gas mixture.

[0023] A further development of the invention provides that, for the purpose of balancing, a condensation rate is additionally determined at which gaseous water contained in the exhaust gas is separated from the exhaust gas and converted into condensate temporarily stored in the exhaust aftertreatment system. Balancing thus comprises condensation and / or drying. During condensation, the gaseous water contained in the exhaust gas is condensed, so that it subsequently exists as condensate in the exhaust aftertreatment system. Drying refers to the process in which the condensate present in the exhaust aftertreatment system evaporates and subsequently exists again as gaseous water, which is carried along by the exhaust gas towards the lambda sensor.

[0024] Condensation occurs at the condensation rate, and drying at the drying rate. Both the condensation rate and the drying rate can be understood as a throughput, i.e., a mass or volume per unit of time. Integrating the condensation rate and / or the drying rate yields the amount of condensate present in the exhaust aftertreatment system. The condensation rate describes the amount of condensate accumulating in the exhaust aftertreatment system per unit of time, while the drying rate describes the amount of condensate discharged from the exhaust aftertreatment system per unit of time. Considering one or both of these values ​​allows for precise adjustment of the mixture composition.

[0025] A further development of the invention provides that the temperature of the exhaust gas and / or the exhaust aftertreatment system is used to determine the condensation rate and / or the drying rate. The temperature is decisive in determining whether the gaseous water condenses or whether the condensate evaporates. If the temperature is lower than the threshold temperature, condensation occurs; if it is at least equal to this temperature, the condensate evaporates. In particular, the condensation rate is higher the greater the difference between the temperature of the exhaust aftertreatment system and a specific temperature. Conversely, the drying rate is higher the greater the difference between the temperature of the exhaust gas and / or the exhaust aftertreatment system and the specific temperature. The threshold temperature is, for example, approximately or exactly 56 °C.Using the current temperature of the exhaust gas and / or the exhaust aftertreatment system allows the aforementioned velocities to be determined with high accuracy.

[0026] A further development of the invention provides that the temperature balance is performed separately for successive subsections of the exhaust aftertreatment system in the direction of exhaust gas flow. These subsections are directly adjacent to one another in the direction of exhaust gas flow; the entire exhaust aftertreatment system, particularly upstream of the lambda sensor, is thus divided into a specific number of subsections. These subsections can also be referred to as catalyst discs. The temperature balance is performed separately for each subsection, with the temperature being determined separately for each subsection. The aforementioned temperature of the exhaust gas and / or the exhaust aftertreatment system therefore corresponds to the temperature for the respective subsection.

[0027] Furthermore, the proportion of gaseous water naturally decreases in the direction of flow when the exhaust aftertreatment system is cold, as it condenses in the upstream sections. Only when these upstream sections are saturated does the gaseous water enter the downstream sections. For example, it can be assumed that condensate is only introduced into one of the downstream sections if condensate has already evaporated in the section immediately upstream. This assumption allows for a relatively simple calculation model for the balancing process.

[0028] The invention provides that an ammonia throughput is determined based on the drying rate, which represents the rate at which the ammonia contained in the condensate is introduced into the exhaust gas. The ammonia throughput describes the rate at which the ammonia is reintroduced from the condensate into the exhaust gas during the drying of the condensate. The throughput refers in particular to a mass throughput or a volume throughput, i.e., a mass per unit of time or a volume per unit of time. The ammonia throughput is determined specifically based on the drying rate, which describes the rate at which the condensate present in the exhaust aftertreatment system evaporates and is thus converted into gaseous water, which is carried along by the exhaust gas towards the lambda sensor.In particular, the ammonia throughput is determined using both the drying rate and the proportion of ammonia contained in the condensate, the latter preferably calculated based on the nitrogen oxide content of the exhaust gas upstream of the exhaust aftertreatment system. Overall, this achieves a high degree of accuracy in the ammonia throughput, thus enabling precise adjustment of the fuel-air mixture composition.

[0029] A further development of the invention provides that the condensate is taken into account by adjusting the target value based on the ammonia flow rate. When adjusting the composition of the fuel-air mixture, the combustion air ratio determined by the lambda sensor is set to the target value by adjusting the composition. The target value used is adjusted in such a way that the condensate, or rather the proportion of ammonia present in it, is taken into account, so that despite the ammonia content, the mixture is precisely adjusted to the desired composition.

[0030] Preferably, the consideration of condensate when adjusting the combustion air ratio to the setpoint is only carried out during the warm-up phase. This means, in particular, that the calculations necessary for considering the condensate are only performed as long as condensate is present in the exhaust aftertreatment system. If it is determined, for example, through monitoring, that the amount of condensate present in the exhaust aftertreatment system has fallen below a threshold, especially if it is zero, then the consideration of the condensate is discontinued. This avoids unnecessary strain on the control unit used to operate the drive system, which performs the described calculations.

[0031] A further development of the invention provides that a first lambda sensor is located upstream of the exhaust aftertreatment device to measure a first air-fuel ratio in the exhaust gas, and that this lambda sensor is used as a second lambda sensor to measure the air-fuel ratio present as a second air-fuel ratio. Lambda control of the drive unit is then carried out based on the first and second air-fuel ratios. Preferably, several lambda sensors are present; in particular, the first lambda sensor is arranged upstream of the exhaust aftertreatment device and the second lambda sensor is arranged downstream of the exhaust aftertreatment device. The second lambda sensor is the lambda sensor mentioned above.

[0032] The first lambda sensor determines a first air-fuel ratio, and the second lambda sensor determines a second air-fuel ratio. 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 engine and the exhaust aftertreatment system. The second air-fuel ratio is present in the exhaust gas downstream of the exhaust aftertreatment system. These two air-fuel ratios are preferably used to operate the engine. For example, they are used to implement lambda control.In this process, the composition of the fuel-air mixture is specifically 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, lambda control is therefore based on both the first and second air-fuel ratios.

[0033] Preferably, the first lambda sensor is a wideband lambda sensor and the second lambda sensor is a narrowband lambda sensor. The wideband lambda sensor allows the residual oxygen content, or the corresponding air-fuel ratio, to be measured 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 powered.

[0034] 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, by means of the trim control or by using the narrowband lambda sensor. This enables the precise adjustment of the fuel-air mixture composition.

[0035] The invention further relates to a drive unit for a motor vehicle, in particular for carrying out the method according to the descriptions in this document, wherein the drive unit has an exhaust gas generating drive unit, an exhaust gas aftertreatment device designed as a vehicle catalyst for aftertreatment of the exhaust gas and a lambda probe arranged downstream of the exhaust gas aftertreatment device for determining a combustion air ratio in the exhaust gas, which is adjustable to a target value for adjusting the composition of a fuel-fresh gas mixture used to operate the drive unit.The drive mechanism is designed and configured to take into account condensate accumulating in the exhaust aftertreatment system during warm-up operation when adjusting the combustion air ratio to the setpoint. To account for this condensate, the quantity present in the exhaust aftertreatment system is determined by balancing. Furthermore, the drive mechanism is designed and configured to determine the drying rate of the condensate, at which the condensate temporarily stored in the exhaust aftertreatment system is converted into gaseous water carried by the exhaust gas. Based on this drying rate, an ammonia flow rate is determined, at which the ammonia contained in the condensate is introduced into the exhaust gas.

[0036] The advantages of such a design of the drive system or such a procedure have already been pointed out.

[0037] Both the drive device and the method for operating it may be further developed in accordance with the explanations in this description, so reference is made to these in this respect.

[0038] Furthermore, the invention relates to a computer program product comprising commands that cause the drive device to execute the described method as described herein. For the advantages and possible advantageous embodiments, reference is made to the description in its entirety.

[0039] 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.

[0040] 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: Fig. 1 a schematic representation of a section of a drive direction for a motor vehicle, namely an exhaust aftertreatment device, as well as Fig. 2. Several diagrams in which the trends of several quantities are plotted over time, purely as examples.

[0041] The Fig. Figure 1 schematically shows a section of a drive unit 1 for a motor vehicle. Specifically, an exhaust aftertreatment device 2 in the form of a vehicle catalyst is depicted. During operation of the drive unit 1, exhaust gas is supplied to this device. This exhaust gas is generated by an exhaust-producing engine unit of the drive unit 1. The exhaust gas flows through the exhaust aftertreatment device 2 in the direction of arrow 3, i.e., from an inlet port 4 towards an outlet port 5.

[0042] Downstream of at least part of the exhaust aftertreatment system 2, a lambda probe 6 is arranged for measuring the residual oxygen content in the exhaust gas and, correspondingly, the air-fuel ratio. The lambda probe 6 is shown here by way of example approximately in the middle of the exhaust aftertreatment system 2; however, its arrangement is fundamentally arbitrary and can therefore also be located further upstream, further downstream, or entirely downstream of the exhaust aftertreatment system 2.

[0043] The exhaust aftertreatment system 2 is divided into several successive sections 7, 8, 9, 10, and 11. The exhaust gas flows through sections 7 to 11 in numerical order, starting with section 7 and proceeding towards section 11. During the warm-up phase of the drive unit 1, condensate forms in the exhaust aftertreatment system 2, specifically through the condensation of gaseous water contained in the exhaust gas of the drive unit. This condensate contains ammonia, which is produced in the exhaust aftertreatment system 2 through a chemical by-reaction.

[0044] The condensate and the ammonia it contains are taken into account when adjusting the composition of a fuel-air mixture used to operate the drive unit. Here, sections 7 to 11 are considered separately; the exhaust aftertreatment system 2 is thus conceptually divided into these sections. Of course, any number of sections can be provided. Of particular relevance are those sections 7 to 11 that are located at least partially upstream of the lambda sensor 6; in the illustrated embodiment, these are sections 7, 8, and 9. However, to clarify the method behind considering the condensate, all sections 7 to 11 will be discussed.

[0045] The Fig.Figure 2 shows three diagrams, in which a first diagram shows temperature profiles 12, 13, 14, 15, 16 and 17, a second diagram shows mass profiles 18, 19, 20, 21 and 22, and a third diagram shows proportion profiles 23, 24, 45, 46, 27 and 28, each plotted against time. Temperature curve 12 shows the temperature of the exhaust gas at inlet connection 4, temperature curve 13 in sub-area 7, temperature curve 14 in sub-area 8, temperature curve 15 in sub-area 9, temperature curve 16 in sub-area 10, and temperature curve 17 in sub-area 11. Mass curve 18 describes the amount of condensate present in sub-area 12, mass curve 19 in sub-area 8, mass curve 20 in sub-area 9, mass curve 21 in sub-area 10, and mass curve 22 in sub-area 11.The proportion curve 23 describes the proportion of gaseous water in the exhaust gas at the inlet connection 4, the proportion curve 24 in the sub-area 7, the proportion curve 25 in the sub-area 8, the proportion curve 26 in the sub-areas 9, the proportion curve 27 in the sub-area 10 and the proportion curve 28 in the sub-area 11.

[0046] The temperature profiles 12 to 17 clearly show that the exhaust gas temperature increases only sequentially across sections 7 to 11 of the exhaust gas aftertreatment system 2 and is also influenced by the enthalpy of vaporization of the condensate present in the exhaust gas aftertreatment system 2. The mass profiles 18 to 22 show that condensate initially forms in each of the sections 7 to 11, namely through the condensation of gaseous water present in the exhaust gas; thus, the quantity (here represented: the mass) of the condensate initially increases. Once the exhaust gas temperature in the respective section 7 to 11 exceeds a threshold value, which is approximately or exactly 56 °C, the condensate evaporates, i.e., is converted back into gaseous water. Accordingly, the quantity of condensate in the respective section 7 to 11 decreases again from this point onward.

[0047] This also means that the amount of water vapor in the exhaust gas, or rather the proportion of water vapor in the exhaust gas, temporarily increases from this point onward and is correspondingly higher than the proportion present in the exhaust gas at the inlet port 4, as shown by the curve 23. Only once the condensate present in the exhaust aftertreatment system 2 has completely evaporated does the proportion of water in the exhaust gas downstream of the exhaust aftertreatment system 2, and in particular at the outlet port 5, correspond to the proportion present in the exhaust gas upstream of the exhaust aftertreatment system 2. In the illustrated embodiment, this is the case across the entire exhaust aftertreatment system 2 from approximately t = 45 s.Since the condensate and consequently also the water vapor contains ammonia, the accuracy of the setting of the fuel-fresh gas mixture used to operate the drive device 1 or its drive unit can be improved by taking the condensate into account when adjusting the composition to a target value. REFERENCE MARK LIST: 1 Drive unit 2 Exhaust aftertreatment system 3 Arrow 4 Inlet connection 5 Outlet connection 6 Lambda sensor 7 sub-area 8 sub-area 9 sub-area 10 sub-area 11 Sub-area 12 Temperature profile 13 Temperature profile 14 Temperature profile 15 Temperature profile 16 Temperature profile 17 Temperature profile 18 Mass distribution 19 Mass distribution 20 Mass distribution 21 Mass distribution 22 Mass distribution 23 Share development 24 Share development 25 Share development 26 Share development 27 Share development 28 Share development

Claims

[1] Method for operating a drive device (1) for a motor vehicle, which has a drive unit generating exhaust gas, an exhaust gas aftertreatment device (2) designed as a vehicle catalyst for aftertreating the exhaust gas, and a lambda probe (6) arranged downstream of the exhaust gas aftertreatment device (2) for determining a combustion air ratio in the exhaust gas, which is set to a desired value for adjusting a composition of a fuel-fresh gas mixture used to operate the drive unit, wherein condensate accumulating in the exhaust gas aftertreatment device (2) during warm-up operation is taken into account when setting the combustion air ratio to the desired value, wherein, for taking the condensate into account, a quantity of condensate present in the exhaust gas aftertreatment device (2) is determined by balancing, characterized bythat for the balancing a drying rate of the condensate is determined, with which condensate stored temporarily in the exhaust gas aftertreatment device (2) is converted into gaseous water carried by the exhaust gas, wherein on the basis of the drying rate an ammonia throughput is determined with which the ammonia contained in the condensate is introduced into the exhaust gas. [2] Method according to claim 1, characterized by that a proportion of ammonia contained in the condensate is determined on the basis of a nitrogen oxide proportion of the exhaust gas upstream of the exhaust gas aftertreatment device (2). [3] Method according to one of the preceding claims, characterized bythat for the balancing purpose, a condensation rate is additionally determined at which gaseous water contained in the exhaust gas is separated from the exhaust gas and converted into condensate water temporarily stored in the exhaust gas aftertreatment device (2). [4] Method according to claim 1 or 3, characterized by that a temperature of the exhaust gas and / or the exhaust gas aftertreatment device (2) is used in determining the condensation rate and / or the drying rate. [5] Method according to one of the preceding claims, characterized by that the balancing is carried out separately for successive sub-areas (7, 8, 9, 10, 11) of the exhaust gas aftertreatment device (2) in the flow direction of the exhaust gas. [6] Method according to one of the preceding claims, characterized bythat the condensate is taken into account by adjusting the setpoint taking into account the ammonia flow rate. [7] 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 generating exhaust gas, an exhaust gas aftertreatment device (2) designed as a vehicle catalyst for aftertreating the exhaust gas, and a lambda probe (6) arranged downstream of the exhaust gas aftertreatment device (2) for determining a combustion air ratio in the exhaust gas, which can be set to a desired value for setting a composition of a fuel-fresh gas mixture used to operate the drive unit, wherein the drive device (1) is provided and designed to take into account condensate accumulating in the exhaust gas aftertreatment device (2) when setting the combustion air ratio to the desired value during warm-up operation,wherein, for the purpose of taking the condensate into account, a quantity of condensate present in the exhaust gas aftertreatment device (2) is determined by balancing, , characterized by that the drive device (1) is further provided and designed to determine a drying rate of the condensate water for the balancing, with which drying rate condensate water temporarily stored in the exhaust gas aftertreatment device (2) is converted into gaseous water carried by the exhaust gas, wherein an ammonia throughput is determined on the basis of the drying rate, with which the ammonia contained in the condensate water is introduced into the exhaust gas. [8] Computer program product comprising instructions causing the drive device (1) according to claim 7 to carry out the method according to one or more of claims 1 to 6.

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