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
- AUDI AG
- Filing Date
- 2024-06-11
- Publication Date
- 2026-04-22
Smart Images
Figure EP2024066020_19122024_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 system for a motor vehicle, which has an exhaust-generating drive unit and an exhaust gas aftertreatment system configured as a vehicle catalyst for aftertreating the exhaust gas with temperature-dependent conversion performance for pollutants contained in the exhaust gas. The invention further relates to a drive system for a motor vehicle and a computer program product.
[0004] For example, the prior art document DE 10 2021 102 240 A1 is known. This relates to a method for operating an internal combustion engine having an internal combustion engine and an exhaust system with an exhaust aftertreatment device, wherein the exhaust aftertreatment device comprises a nitrogen oxide converter and a nitrogen oxide storage device. It is provided that, at a temperature of the nitrogen oxide converter that is below its light-off temperature, the internal combustion engine is operated lean, and at a temperature of the nitrogen oxide converter that corresponds at least to the light-off temperature, the internal combustion engine is operated at least temporarily stoichiometrically, and the nitrogen oxide storage device is regenerated.
[0005] Furthermore, US Pat. No. 10,738,674 B2 discloses a device for heating a catalytic exhaust aftertreatment device. The object of the invention is to propose a method for operating a drive device for a motor vehicle that offers advantages over known methods, in particular ensuring low tailpipe emissions from the drive device.
[0006] 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 a device portion of the exhaust gas aftertreatment device is determined in which the exhaust gas aftertreatment device has a temperature which corresponds at least to an operating temperature of the exhaust gas aftertreatment device, an exhaust gas throughput threshold value is determined from the device portion and the drive unit is operated in such a way that an exhaust gas throughput of the exhaust gas generated by the drive unit corresponds at most to the exhaust gas throughput threshold value.
[0007] 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.
[0008] 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 comprises 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 at least temporarily contains fresh air. 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 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 outside environment of the drive system or 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 outside 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 outside environment, in particular through a tailpipe of the drive system.
[0010] The exhaust gas aftertreatment device is available as a vehicle catalyst, in particular as a three-way catalyst, oxidation catalyst, NO x Storage catalyst or as an SCR catalyst. The vehicle catalyst is particularly preferably integrated into a particulate filter, in particular a gasoline particulate filter or a diesel particulate filter. For this purpose, the particulate filter is provided with a catalytic coating, for example. 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 the temperature of the exhaust gas aftertreatment system.
[0011] The components of the exhaust gas produced by the drive unit are also referred to as raw emissions. Raw emissions describe the composition of the exhaust gas upstream of the exhaust aftertreatment device, or in terms of flow between the drive unit and the exhaust aftertreatment device. The substances contained in the exhaust gas are partially converted as the exhaust gas passes through the exhaust aftertreatment device, changing the composition of the exhaust gas. The substances present in the exhaust gas downstream of the exhaust aftertreatment device, which make up the exhaust gas, are also referred to as tailpipe emissions, since the exhaust gas with this composition is released into the outside environment through the tailpipe of the drive unit.
[0012] The amount of pollutants contained in the tailpipe emissions depends, as already mentioned, on the raw emissions, but also on the conversion efficiency of the exhaust aftertreatment system. This is temperature-dependent. In particular, the further the temperature of the exhaust aftertreatment system is from the operating temperature of the exhaust aftertreatment system, i.e., the greater the absolute value of the difference between the temperatures, the lower the conversion efficiency. The temperature of the exhaust aftertreatment system refers, in particular, to the temperature of a ceramic honeycomb body provided with the catalytic coating.
[0013] In particular, after a restart or a re-start of the drive unit, the temperature of the exhaust gas aftertreatment device is lower than the operating temperature, at least over part of the exhaust gas aftertreatment device. This is particularly the case if the exhaust gas itself heats up the exhaust gas aftertreatment device and no additional heat is used to heat the exhaust gas aftertreatment device apart from the heat contained in the exhaust gas. When heated up by means of the exhaust gas, upstream regions of the exhaust gas aftertreatment device are heated first, so that the temperature of regions further downstream changes more slowly towards the operating temperature. This results in regions of the exhaust gas aftertreatment device in which it has different temperatures.
[0014] Different conversion performances exist in the areas of the exhaust gas aftertreatment system with different temperatures. For example, the exhaust gas aftertreatment system has a higher conversion performance in a first area, where the temperature has already reached the operating temperature, than in a second area, where the temperature is (still) lower than the operating temperature. This reduces the ability of the exhaust gas aftertreatment system to treat the exhaust gas or to convert the pollutants contained in the exhaust gas. Accordingly, measures must be taken to prevent unacceptably high pollutant emissions into the outside environment.
[0015] For this purpose, it is intended to first determine the portion of the exhaust gas aftertreatment system in which the temperature of the exhaust gas aftertreatment system has already reached operating temperature. This portion of the system can, for example, be expressed as a distance portion over the entire extent of the exhaust gas aftertreatment system or a honeycomb body of the exhaust gas aftertreatment system in the main flow direction of the exhaust gas, or as a volume portion of the total volume of the exhaust gas aftertreatment system or at least of its honeycomb body. For example, the portion of the system is specified as a percentage.
[0016] The exhaust gas throughput threshold value is then determined from the device share determined in this way. This describes the maximum exhaust gas throughput for which the exhaust gas aftertreatment device achieves a desired conversion performance in its current state, i.e., at the temperature distribution currently prevailing in the exhaust gas aftertreatment device. Until the exhaust gas throughput threshold value is reached by an actual exhaust gas throughput through the exhaust gas aftertreatment device, it is ensured that the exhaust gas aftertreatment device achieves a conversion performance that is at least equal to or even higher than the desired conversion performance. The exhaust gas throughput is preferably understood to be a mass flow or a volume flow, i.e., an exhaust gas mass or an exhaust gas volume per unit of time. The exhaust gas throughput is expressed, for example, in the unit kg / h (mass) or in the unit m 3 / h (volume).
[0017] After determining the exhaust gas flow threshold, the drive unit is operated in such a way that the actual exhaust gas flow through the exhaust aftertreatment device of the exhaust gas generated by the drive unit corresponds at most to the exhaust gas flow threshold. For this purpose, for example, the rated power of the drive unit is limited, namely to a maximum rated power at which the exhaust gas flow corresponds at most to the exhaust gas flow threshold.
[0018] For example, it is provided that the drive device determines a specified power from a position of a control element, in particular an accelerator pedal, or adopts it from a driver assistance device which provides a corresponding specified value. From the specified power, a target power is determined and set on the drive unit, which is subsequently operated such that an actual power provided by the drive unit corresponds to the target power. Preferably, the actual power of the drive unit is regulated to the target power. To take the exhaust gas throughput threshold value into account, the target power is initially set to the specified power, but is then limited towards larger values to the maximum power at which the exhaust gas throughput corresponds to the exhaust gas throughput threshold value.The procedure described ensures that the exhaust gas discharged from the drive system into the outside environment, i.e. the tailpipe emissions of the drive system, always comply with specified values.
[0019] A further development of the invention provides that the device share is determined using a catalyst model to which at least one of the following variables is supplied as an input variable: an exhaust gas temperature, an exhaust gas flow rate, and a reaction heat generated due to the aftertreatment of the exhaust gas in the exhaust gas aftertreatment device. The catalyst model thus serves at least to determine the temperature distribution in the exhaust gas aftertreatment device and, accordingly, also the device share. In addition, the catalyst model can be used to determine the composition of the exhaust gas downstream of the exhaust gas aftertreatment device, in particular from the raw emissions, i.e. the composition of the exhaust gas generated by the drive unit upstream of the exhaust gas aftertreatment device, and the input variable.
[0020] The temperature of the exhaust gas is, in particular, a temperature that the exhaust gas has upstream of the exhaust gas aftertreatment device, preferably directly upstream of the exhaust gas aftertreatment device. As already explained, the exhaust gas throughput is understood to be the quantity of exhaust gas flowing through the exhaust gas aftertreatment device per unit of time. The reaction heat, on the other hand, describes a quantity of heat that accrues in the exhaust gas aftertreatment device itself per unit of time, namely due to the chemical reactions taking place therein during the conversion of pollutants. At least one of the aforementioned variables, but preferably several or all of the aforementioned variables, are used as an input variable for the catalyst model, which has at least the device component as an output variable.Using the procedure described, the device share and thus the exhaust gas flow threshold can be determined with high accuracy, so that the occurrence of undesirably large tailpipe emissions is reliably prevented.
[0021] A further development of the invention provides that, in addition to the device share, at least one of the following variables is taken into account when determining the exhaust gas throughput threshold: a conversion power threshold and the exhaust gas temperature. The exhaust gas throughput threshold is also determined using a model, which is available, for example, in the form of a mathematical relationship, a characteristic map, or a table. The model has the exhaust gas throughput threshold as its output variable. The conversion power threshold and / or the exhaust gas temperature are used as input variables for the model. The conversion power threshold corresponds to the minimum conversion power that the exhaust gas aftertreatment device must generate to achieve the desired tailpipe emissions.The conversion performance threshold can also be referred to as the minimum conversion performance. The temperature of the exhaust gas is preferably the temperature that the exhaust gas has upstream of the exhaust gas aftertreatment device, in particular directly upstream of the exhaust gas aftertreatment device. At least one of the aforementioned variables is taken into account as an input variable when determining the exhaust gas throughput threshold, but preferably several or both. This achieves a particularly high level of accuracy in determining the exhaust gas throughput threshold and ensures correspondingly sufficiently low tailpipe emissions.
[0022] A further development of the invention provides that a value of at least 90%, at least 95%, or at least 98% is used for the conversion performance threshold. Such a selection of the conversion performance threshold ensures particularly reliable exhaust gas aftertreatment.
[0023] A further development of the invention provides that the exhaust gas flow threshold is determined based on several characteristic maps stored for different values of the device component. The characteristic maps are stored in the drive device, for example, in a control unit of the drive device, by means of which the described method is implemented. The characteristic maps relate the variables used to determine the exhaust gas flow threshold to the latter. For example, each of the characteristic maps describes the exhaust gas flow threshold for the conversion power threshold and / or the exhaust gas temperature.
[0024] It can be provided that in each of the characteristic maps, the conversion power is plotted against the exhaust gas flow rate and / or the exhaust gas temperature. The respective characteristic map is then used to determine the exhaust gas flow rate threshold up to which the conversion power at least corresponds to the conversion power threshold. The stored characteristic maps describe different values of the device share. Using the characteristic maps, the exhaust gas flow rate threshold can be determined with high accuracy, ensuring that the desired tailpipe emissions are reliably met.
[0025] A further development of the invention provides that the characteristic maps are stored at least for values of 0% and 100% of the device's share. At a value of 0%, the temperature across the entire exhaust aftertreatment device is lower than its operating temperature; at a value of 100%, the temperature across the entire exhaust aftertreatment device corresponds to at least the operating temperature. The characteristic maps thus encompass all possible values of the device's share, so that the exhaust gas flow threshold can be easily determined, for example, by interpolation.
[0026] Preferably, the characteristic maps are available for additional values of the device component; in particular, at least 5, at least 10, or at least 20 characteristic maps are stored for different values of the device component. The values of the device component can be evenly spaced from one another. However, the distance between the values preferably decreases with increasing values, so that for smaller values, the values are further spaced from one another than for larger values. This further improves accuracy.
[0027] A further development of the invention provides that, based on the device share, a map is selected from the plurality of stored maps, and the selected map is used to determine the exhaust gas flow threshold. In particular, the map stored for a value of the device share that corresponds to or is closest to the determined device share is selected. The exhaust gas flow threshold is then determined based on this selected map. This already ensures a high level of accuracy. A further development of the invention provides that, based on the device share, a map is interpolated from the plurality of stored maps, and the interpolated map is used to determine the exhaust gas flow threshold.This procedure is particularly applicable if no map is stored for the specific device component, but rather maps are stored for values of the device component that are different from the specific device component. In this case, for example, maps are selected that are stored for values that are closest to the specific device component on opposite sides. The map is then interpolated from these maps, for example, by linear interpolation. The exhaust gas flow threshold value is then read from the interpolated map and used to control the drive unit. The described procedure further improves the accuracy of the exhaust gas flow threshold value.
[0028] The invention further relates to a drive device for a motor vehicle, in particular for carrying out the method according to the explanations in the context of this description, wherein the drive device has a drive unit generating exhaust gas and an exhaust gas aftertreatment device designed as a vehicle catalyst for aftertreating the exhaust gas with temperature-dependent conversion performance for pollutants contained in the exhaust gas.The drive device is provided and designed to determine a device portion of the exhaust gas aftertreatment device in which the exhaust gas aftertreatment device has a temperature that corresponds at least to an operating temperature of the exhaust gas aftertreatment device, to determine an exhaust gas throughput threshold value from the device portion, and to operate the drive unit such that an exhaust gas throughput of the exhaust gas generated by the drive unit corresponds at most to the exhaust gas throughput threshold value. The advantages of such a design of the drive device or such a procedure have already been pointed out. Both the drive device for the motor vehicle and the method for its operation can be further developed according to the explanations in the context of this description, so that reference is made to these in this regard.
[0029] 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.
[0030] 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.
[0031] The invention is explained in more detail below with reference to exemplary embodiments illustrated in the drawings, without limiting the invention. In the drawings:
[0032] Figure 1 is a schematic representation of a drive device for a motor vehicle, and
[0033] Figure 2 shows a characteristic map in which a conversion power of an exhaust gas aftertreatment device is plotted against an exhaust gas temperature and an exhaust gas mass. 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.
[0034] 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.
[0035] 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 combustion air ratio of the exhaust gas. 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 combustion air ratio of the exhaust gas. The two combustion air ratios are used to adjust the composition of a fuel-fresh gas mixture, which reacts chemically in the drive unit 2 to produce the exhaust gas. In the exhaust gas aftertreatment device 12, pollutants contained in the exhaust gas are converted into less hazardous products. The conversion capacity of the exhaust gas aftertreatment device 12, with which this conversion of the pollutants takes place, is temperature-dependent.The temperature dependence exists not only for the exhaust gas temperature of the exhaust gas itself, but also for a catalyst temperature of the exhaust gas aftertreatment device 12. In order to ensure that the conversion performance of the exhaust gas aftertreatment device 12 is always sufficiently high to achieve the desired tailpipe emissions, the device portion of the exhaust gas aftertreatment device 12 in which a temperature exists that corresponds at least to an operating temperature of the exhaust gas aftertreatment device 12 should first be determined.
[0036] An exhaust gas flow threshold value is then determined from this device component, and the drive unit 2 is operated in such a way that the exhaust gas flow, i.e. the exhaust gas flow rate of the exhaust gas generated by the drive unit 2, corresponds at most to the exhaust gas flow threshold value.
[0037] Figure 2 shows a characteristic map in which the conversion performance x of the exhaust gas aftertreatment device 12 is plotted against an exhaust gas mass flow rh and the temperature T, with the exhaust gas mass flow being specified in kg / h and the temperature in °C. The characteristic map is stored for a device proportion of 20%, thus indicating the conversion performance of the exhaust gas aftertreatment device 12 for a device proportion of 20%, in which the exhaust gas aftertreatment device 12 has a temperature at least corresponding to the operating temperature. Conversely, this means that the exhaust gas aftertreatment device has a temperature lower than the operating temperature over a further proportion of 80%.
[0038] It is clearly evident that the conversion efficiency decreases with decreasing temperature and increasing exhaust gas mass. For the given device proportion of the exhaust aftertreatment device 12, here 20%, the exhaust gas mass for which the conversion efficiency corresponds at least to a conversion efficiency threshold value of at least 0.9, at least 0.95, or at least 0.98 is determined for the also given exhaust gas temperature. This exhaust gas mass is then used as the exhaust gas throughput threshold value, and the drive unit 2 is operated such that the actual exhaust gas throughput is less than the exhaust gas throughput threshold value or at most corresponds to it. This ensures that the desired tailpipe emissions are achieved.
[0039] LIST OF REFERENCE SYMBOLS:
[0040] 1 drive device
[0041] 2 Drive unit 3 Exhaust tract
[0042] 4 cylinders
[0043] 5 Inlet valve
[0044] 6 exhaust valve
[0045] 7 Fresh gas tract 8 Compressor
[0046] 9 exhaust gas turbocharger
[0047] 10 turbines
[0048] 11 Exhaust pipe
[0049] 12 Exhaust aftertreatment system 13 1. Lambda probe
[0050] 14 2. Lambda sensor
Claims
PATENT CLAIMS:
1. Method for operating a drive device (1) for a motor vehicle, which drive device has a drive unit (2) generating exhaust gas and an exhaust gas aftertreatment device (12) designed as a vehicle catalyst for aftertreating the exhaust gas with temperature-dependent conversion performance for pollutants contained in the exhaust gas, characterized in that a device portion of the exhaust gas aftertreatment device (12) is determined, in which device portion the exhaust gas aftertreatment device (12) has a temperature which corresponds at least to an operating temperature of the exhaust gas aftertreatment device (12), an exhaust gas throughput threshold value is determined from the device portion and the drive unit (2) is operated in such a way that an exhaust gas throughput of the exhaust gas generated by the drive unit (2) corresponds at most to the exhaust gas throughput threshold value.
2. Method according to claim 1, characterized in that the device proportion is determined on the basis of a catalyst model to which at least one of the following variables is supplied as an input variable: a temperature of the exhaust gas, an exhaust gas throughput and a reaction heat arising due to the aftertreatment of the exhaust gas in the exhaust gas aftertreatment device (12).
3. Method according to one of the preceding claims, characterized in that in determining the exhaust gas flow rate threshold value, in addition to the device share, at least one of the following variables is taken into account: a conversion power threshold value and the temperature of the exhaust gas.
4. Method according to one of the preceding claims, characterized in that a value of at least 90%, at least 95% or at least 98% is used for the conversion performance threshold.
5. Method according to one of the preceding claims, characterized in that the exhaust gas flow threshold value is determined on the basis of several characteristic maps stored for different values of the device share.
6. Method according to one of the preceding claims, characterized in that the characteristic maps are stored at least for values of 0% and 100% of the device share.
7. Method according to one of the preceding claims, characterized in that a characteristic map is selected from the plurality of stored characteristic maps on the basis of the device share and the selected characteristic map is used to determine the exhaust gas flow rate threshold value.
8. Method according to one of the preceding claims, characterized in that a characteristic map is interpolated from the plurality of stored characteristic maps on the basis of the device component and the interpolated characteristic map is used to determine the exhaust gas flow threshold value.
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) and an exhaust gas aftertreatment device (12) designed as a vehicle catalyst for aftertreating the exhaust gas with temperature-dependent conversion performance for pollutants contained in the exhaust gas, characterized in that the drive device (1) is provided and designed to determine a device portion of the exhaust gas aftertreatment device (12) in which the exhaust gas aftertreatment device (12) has a temperature that corresponds at least to an operating temperature of the exhaust gas aftertreatment device (12), to determine an exhaust gas throughput threshold value from the device portion and to operate the drive unit (2) in such a way,that an exhaust gas flow rate of the exhaust gas generated by the drive unit (2) corresponds at most to the exhaust gas flow rate 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 of claims 1 to 8.