Method for operating a drive unit for a motor vehicle and corresponding drive unit

Abstract

Method for operating a drive unit (1) for a motor vehicle, which has an exhaust gas-generating drive unit (2), wherein a preset value (4) for a quantity of fresh gas to be supplied to the drive unit (2) is determined at least temporarily from an operating point of the drive unit (2) specified by means of a control element (3) and a setpoint value (5) of the fresh gas quantity determined from the preset value (4) is set on an adjusting means of the drive unit (2), and wherein a diagnosis of at least one exhaust gas-carrying device of the drive unit (1) is carried out during a diagnostic period (12), characterized in that the setpoint value (5) is determined from the preset value (4) during the diagnostic period (12) by means of a low-pass filter (8,9).

Description

[0001] The invention relates to a method for operating a drive device for a motor vehicle having a drive unit generating exhaust gas, wherein a preset value for a fresh gas quantity to be supplied to the drive unit is determined at least temporarily from an operating point of the drive unit predetermined by means of a control element, and a target value for the fresh gas quantity determined from the preset value is set on an adjustment means of the drive unit, and wherein a diagnosis of at least one exhaust gas-carrying device of the drive device is performed during a diagnostic period. The invention further relates to a drive device having an internal combustion engine for a motor vehicle.

[0002] For example, the prior art document DE 10 2018 117 623 B3 is known. This document describes a method for performing an on-board diagnostic function of a vehicle, wherein an on-board diagnostic function of the vehicle is activated and a predefined accelerator pedal value of the vehicle is low-pass filtered to obtain a smoothed accelerator pedal value. Furthermore, a system for performing an on-board diagnostic function in a vehicle with a control unit is described, which is configured such that an on-board diagnostic function of the vehicle is activated and a low-pass filter function is activated, via which a predefined accelerator pedal value of the vehicle is low-pass filtered to obtain a smoothed accelerator pedal value.

[0003] Document DE 10 2013 202 989 A1 describes a method for controlling an engine exhaust gas using a front sensor and a rear sensor. The method includes adjusting a setpoint for the rear sensor based on a rate of change of an air mass flow upstream of the engine and adjusting the fuel injection to control the exhaust gas fuel-air ratio (FAR) at the rear sensor to the adjusted setpoint and to control the exhaust FAR at the front sensor to a setpoint of the front sensor.

[0004] Furthermore, the document DE 101 24 543 A1 is known from the prior art.

[0005] It is an object of the invention to propose a method for operating a drive device which has advantages over known methods, in particular at least temporarily upstream of an exhaust gas-carrying device achieves an exhaust gas composition which is constant or at least substantially constant over time, so that a regular and reliable diagnosis of the exhaust gas-carrying device is made possible.

[0006] This is achieved according to the invention with a method for operating a drive device for a motor vehicle having the features of claim 1. It is provided that the target value is determined during the diagnostic period by means of a low-pass filter from the specified value.

[0007] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0008] The drive device serves to drive the motor vehicle, i.e. to provide a drive torque directed towards driving the motor vehicle. The drive device has the drive unit, which is operated at least temporarily to provide the drive torque. The drive unit generates the exhaust gas at least temporarily during its operation. In addition to the drive unit, the drive device can have at least one further drive unit, which is operated additionally or alternatively to the drive unit to provide the drive torque. For example, the drive torque is provided temporarily by the drive unit, temporarily by the further drive unit, and temporarily by the drive unit and the further drive unit jointly. The further drive unit is preferably designed as an electric machine.In this case, the motor vehicle is a hybrid vehicle.

[0009] The drive unit is an air-breathing drive unit, for example, an internal combustion engine. Accordingly, fresh gas, in particular fresh air, is supplied to the drive unit. The fresh gas is preferably supplied to the drive unit from an external environment of the motor vehicle, for example, via an intake line. The intake line is fluidly connected to a combustion chamber of the drive unit via at least one inlet valve. A mixture of the fresh gas and fuel is combusted in the combustion chamber, at least temporarily. This generates the exhaust gas, which is at least temporarily discharged to the external environment of the motor vehicle.

[0010] The energy released during combustion is at least temporarily converted into mechanical energy and made available to a crankshaft of the drive unit. The drive power provided depends, among other things, on the amount of fresh gas supplied to the drive unit. The drive device or the drive unit has adjusting means for setting the amount of fresh gas. The adjusting means are in the form of a throttle valve, for example, or at least have such a valve. Additionally or alternatively, the adjusting means are in the form of a device for adjusting opening times of at least one intake valve or have such a device. The amount of fresh gas is to be understood in particular as the amount of fresh gas actually present in the combustion chamber after the end of an intake stroke.By adjusting the fresh gas flow rate, a delivery efficiency of the drive unit is set, which is directly dependent on the fresh gas flow rate. The delivery efficiency describes the ratio of the fresh gas flow rate to the theoretically maximum possible fresh gas flow rate.

[0011] The fresh gas quantity is preferably adjusted by a control unit to which the control element is connected. First, the operating point of the drive unit to be adjusted is determined. The operating point preferably describes a preset value for the drive power of the drive device. For example, a preset value for the drive torque and / or a preset value for the speed of the drive unit can be derived from the operating point. The operating point is specified, at least temporarily, via the control element. The control element is, for example, an accelerator pedal that is at least temporarily operated by a driver of the motor vehicle. In other words, the operating point is determined as a function of the position of the control element.

[0012] It should be noted, however, that the operating point does not result directly from the accelerator pedal position. Rather, the accelerator pedal position represents a driver command from which the operating point of the drive system is determined. In addition to or as an alternative to the driver command, the operating point can be influenced by further system interventions, in particular by a driver assistance system and / or a safety system. For example, the driver assistance system and / or the safety system can adjust the operating point to reduce the vehicle's speed in a manner deviating from the driver's command. Furthermore, the operating point can also take into account an individual vehicle characteristic selected by the driver, which describes, for example, sporty and / or economical driving behavior.In summary, the operating point is not necessarily constant when the control element is in a constant position.

[0013] The specified value for the fresh gas quantity is determined from the operating point. The specified value is, in particular, a fresh gas quantity that is to be supplied to the drive unit in order to operate it with the specified value for the drive torque and / or the specified value for the speed. The setpoint for the fresh gas quantity is determined from the specified value and set on the drive unit. The fresh gas quantity supplied to the drive unit is therefore not directly set to the specified value. Rather, the setpoint is first determined from the specified value. The setpoint is the fresh gas quantity actually set by means of the adjustment means, while the specified value represents the fresh gas quantity resulting from the operating point. In this respect, the specified value and the setpoint differ from one another, at least temporarily.

[0014] The exhaust gas generated by the drive unit during its operation is discharged to the outside environment. During the discharge, the exhaust gas is fed to the at least one exhaust gas-carrying device. This is a device of the drive device to which the exhaust gas is fed at least temporarily and / or through which the exhaust gas flows. Particularly preferably, the at least one exhaust gas-carrying device is an exhaust gas aftertreatment device, which is, for example, a component of an exhaust system. For example, the at least one exhaust gas-carrying device is present as a vehicle catalyst, in particular as a three-way catalyst, as an oxidation catalyst, as a NO x Storage catalyst or as an SCR catalyst. Additionally or alternatively, the at least one exhaust gas-carrying device is present as a measuring probe, in particular as an oxygen and / or nitrogen oxide probe, or has such a probe.

[0015] For the reliable function of the at least one exhaust gas-carrying device, the diagnosis must be performed, preferably regularly. During the diagnosis, for example, a functional test of the at least one exhaust gas-carrying device and / or its calibration is carried out. The diagnosis is carried out during the diagnosis period. Particularly preferably, the diagnosis is carried out over the entire diagnosis period, so that the diagnosis period begins at the start of the diagnosis and ends accordingly at the end of the diagnosis.

[0016] The diagnosis is performed while the drive unit is operating. This means that during the diagnosis period, the fresh gas is supplied to the drive unit, and the exhaust gas is generated by the drive unit, in particular during the entire diagnosis period. The diagnosis is preferably performed while the motor vehicle is in operation. Particularly preferably, the diagnosis is performed multiple times, resulting in several time-spaced diagnosis periods during which the diagnosis is performed. This ensures regular diagnosis of the at least one exhaust-carrying device and reliable operation of the drive device.

[0017] To ensure reliable diagnosis, it is advantageous if the exhaust gas composition remains as constant as possible throughout the diagnosis period. For example, it is advantageous if the oxygen content of the exhaust gas remains constant throughout the entire diagnosis period. This could be achieved by appropriately adjusting the target value for the fresh gas quantity. For example, the target value could be set to a constant value that deviates from the specified value during the diagnosis period so that the exhaust gas composition required for diagnosis is achieved. However, this would result in a corresponding deviation from the operating point specified by the control element, which would be perceived by the driver of the vehicle in particular as an undesirable interference with the driving behavior.

[0018] Alternatively, the diagnosis could only be performed when the target value for the fresh gas flow determined from the preset value is constant or at least nearly constant. In this case, however, a sufficiently long diagnosis period cannot be guaranteed, since dynamic changes in the preset value, in particular, lead to correspondingly rapid changes in the target value, meaning that reliable and regular diagnosis cannot be guaranteed.

[0019] Instead, the invention provides for the setpoint to be determined during the diagnostic period by filtering the specified value using the low-pass filter. Thus, even while the diagnosis is being performed, the setpoint set on the drive unit continues to be determined from the operating point. However, the setpoint is filtered using low-pass filtering. The low-pass filter used serves to smooth the temporal progression of the specified value. In particular, rapid changes in the specified value that lie above a cutoff frequency of the low-pass filter are filtered out. This leads to a delayed tracking of the setpoint compared to the specified value. This also smooths out peaks in the progression of the specified value that can occur during dynamic changes in the specified value.

[0020] The use of the low-pass filter during the diagnostic period leads to a significant reduction in dynamic influences on the amount of fresh gas supplied to the drive unit. This results in more uniform operation of the drive unit during the diagnostic period. In particular, the use of the low-pass filter results in a more uniform exhaust gas composition in the exhaust system than without the use of the low-pass filter. Accordingly, the use of the low-pass filter allows for a longer diagnostic period than would be the case without it.

[0021] The procedure according to the invention differs from known methods which, for example, only filter the accelerator pedal position. In such methods, interventions which influence the operating point downstream of the accelerator pedal position are not filtered. In particular, an intervention by a driver assistance device is not filtered. Furthermore, the specified value of the fresh gas quantity can change significantly even with a constant accelerator pedal position, for example if the vehicle is a hybrid vehicle and the additional drive unit, which is an electric machine, is switched on or off for efficiency reasons. In known methods, this leads to dynamic changes in the operating point during the diagnosis period, which make a successful diagnosis difficult or even impossible.The invention, however, enables a reliable implementation of the diagnosis, since the operating point is first determined and the specified value determined from this is filtered by means of the low-pass filter and set as the setpoint on the internal combustion engine, so that the interventions explained above, downstream of the control element, are also filtered.

[0022] A further development of the invention provides that the preset value is temporarily determined from the operating point and temporarily specified by a driver assistance system. The driver assistance system has already been mentioned above. The driver assistance system can be, for example, a cruise control assistant, an emergency braking assistant, a traction control system, and / or an electronic stability program.

[0023] The driver assistance system is designed to specify and / or adjust the preset value under certain conditions. In this respect, the preset value is only temporarily determined from the operating point and only temporarily specified by the driver assistance system. Alternatively, it can be provided that the operating point is temporarily specified and / or adjusted by the driver assistance system. Since the target value for the fresh gas quantity is determined from the preset value using the low-pass filter during the diagnosis period, the preset value specified by the driver assistance system is also filtered using the low-pass filter. This also smooths out interventions made by the driver assistance system that could cause undesirable rapid changes in the preset value during the diagnosis. This ensures particularly reliable diagnosis.

[0024] A further development of the invention provides that the diagnosis of the at least one exhaust gas-carrying device is only carried out when a diagnosis request is present. For reliable operation of the drive device, in particular in order to comply with legal regulations on exhaust gas aftertreatment, regular execution of the diagnosis is essential. The execution of the diagnosis is initially initiated by the existence of the diagnosis request. For example, the diagnosis request is present when the time elapsed since a last successfully performed diagnosis in the past exceeds a time threshold. Additionally or alternatively, the diagnosis request can be present when a need for diagnosis is determined, for example due to a detected malfunction of the at least one exhaust gas-carrying device.

[0025] If a diagnostic request is present, the diagnosis is performed at the earliest possible time. After the diagnosis has been performed, especially after a successful diagnosis, the diagnostic request is reset. Therefore, the diagnosis is only performed if the diagnostic request is present. The diagnosis is only performed again if the diagnostic request is present again. This procedure ensures regular diagnostic execution.

[0026] A further development of the invention provides that the diagnostic period begins when the specified value lies within a diagnostic interval defined by an upper interval limit and a lower interval limit. The interval limits of the diagnostic interval are selected such that, with a fresh gas quantity that lies within the diagnostic interval, a successful diagnosis of the at least one exhaust gas-carrying device is possible, in particular, a corresponding exhaust gas composition is present upstream of the at least one exhaust gas-carrying device.

[0027] If the specified value is within the diagnostic interval, the diagnosis begins. Preferably, the specified value remains within the diagnostic interval throughout the entire diagnostic period. Particularly preferably, the diagnosis is only performed if the specified value or the target value determined from the specified value is within the diagnostic interval and the diagnostic request is present. This procedure ensures that the diagnosis is not performed if the fresh gas quantity is outside the diagnostic interval, even if the diagnostic request is present. Thus, the diagnosis is only performed when necessary and, moreover, a successful diagnosis can be performed.

[0028] A further development of the invention provides that the diagnostic period ends after the diagnosis has been performed and / or when the target value exceeds an upper threshold and / or when the target value falls below a lower threshold, wherein the upper threshold is lower than the upper interval limit and the lower threshold is higher than the lower interval limit. The upper threshold and the lower threshold thus define a range that lies within the diagnostic interval.

[0029] After the diagnosis has been performed, particularly after a successful diagnosis, the diagnosis period ends and the diagnosis request is reset accordingly. However, actuation of the control element by the driver and / or intervention by the driver assistance system can result in the specified value being changed in such a way that the filtered target value exceeds the upper threshold or falls below the lower threshold. In this case, the diagnosis is terminated even if it has not yet been successfully completed. Accordingly, the diagnosis request is not reset, so that the diagnosis is performed again at the earliest possible time in the future.This ensures that a change in the operating point desired for safety reasons and / or by the driver is not affected, but at the same time the diagnosis is carried out as regularly as possible.

[0030] A further development of the invention provides that a gradient of the specified value is determined during the diagnostic period, wherein a first value is selected as a time constant of the low-pass filter if the gradient is greater than or equal to zero, and a second value is selected as the time constant of the low-pass filter if the gradient is less than zero, wherein the first value is less than the second value. The time constant is to be understood as a characteristic variable of the low-pass filter, which in particular determines the cutoff frequency of the low-pass filter. Furthermore, the time constant influences the temporal behavior of the low-pass filter, i.e. the smoothing resulting from filtering by means of the low-pass filter. Reducing the time constant of the low-pass filter leads to an increase in the cutoff frequency and accordingly to a reduction in smoothing.Conversely, an increase in the time constant leads to a reduction in the cutoff frequency and accordingly to a stronger smoothing.

[0031] The plan is now to adapt the time constant of the low-pass filter depending on the gradient of the preset value. For this purpose, the first and second values ​​are specified, with the first value being smaller than the second value. The smaller first value is selected as the time constant of the low-pass filter if the gradient of the preset value is greater than or equal to zero. Accordingly, the larger second value is selected as the time constant if the gradient is less than zero. As a result, if the preset value is increased, it is smoothed to a lesser extent. Accordingly, if it is reduced, the preset value is smoothed to a greater extent. This achieves behavior that the driver finds pleasant, since a delayed reaction of the drive system when the control element is operated to increase the drive power, which could be perceived by the driver as sluggish.

[0032] A further development of the invention provides that immediately after the end of the diagnostic period, the target value continues to be determined from the specified value by filtering it using the low-pass filter over a specific period of time, with the time constant of the low-pass filter being reduced towards a third value, preferably down to the third value. Therefore, there is no provision for suspending the use of the low-pass filter at the end of the diagnostic period, at least not immediately. A sudden suspension of filtering may be perceived as unpleasant by the driver. Therefore, there is provision for the target value to continue to be determined from the specified value by filtering it using the low-pass filter immediately after the end of the diagnostic period, at least over the specific period of time.

[0033] During the specified time period, however, the time constant of the low-pass filter is reduced toward the third value. The third value is preferably smaller than the first value and smaller than the second value; for example, the third value is equal to or nearly equal to zero. Preferably, the time constant of the low-pass filter is reduced to the third value during the specified time period. Thus, the smoothing is continuously reduced during the specified time period. This enables a particularly smooth termination of the diagnosis.

[0034] A further development of the invention provides that after the specified time period has elapsed, the target value is no longer determined from the preset value using the low-pass filter. In particular, the low-pass filtering is no longer applied outside the diagnostic period, but this only occurs after the specified time period has elapsed. Using the specified time period allows for rapid termination of the diagnosis without causing an unexpected and immediate change in driving behavior for the driver.

[0035] A further development of the invention provides that the drive unit is at least temporarily coupled in terms of drive technology to an electric machine of the drive device. If the diagnostic request is present and the specified value lies outside the diagnostic interval, the specified value is adjusted to a value within the diagnostic interval, and the drive device is set to the operating point by adjusting a drive power of the electric machine. The electric machine is present as the additional drive unit, as already mentioned above. The drive torque provided by the drive device is provided temporarily by the drive unit, temporarily by the electric machine, and temporarily by both jointly.

[0036] For example, the electric machine can be coupled to the drive unit via a separating clutch.

[0037] As already explained above, when a diagnostic request is present, the diagnosis is preferably only performed if the specified value lies within the diagnostic interval. Using the electric machine, the diagnosis is now also performed if the specified value lies outside the diagnostic interval. To this end, when the diagnostic request is present, the specified value is adjusted to the value within the diagnostic interval. This results in the drive unit being set to an operating point that deviates from the operating point specified via the control element. In order to nevertheless set the drive device to the specified operating point, the drive power of the electric machine is adjusted accordingly.

[0038] In other words, the drive power of the drive unit is adjusted in such a way that the diagnosis can be carried out. For example, the specified value of the drive power of the drive unit is temporarily reduced if the specified value lies above the upper interval limit, with the reduced drive power being compensated accordingly by the electric machine. Conversely, the specified value of the drive power of the drive unit is temporarily increased if the specified value lies below the lower interval limit, with the excess drive power being absorbed by the electric machine and fed into an energy storage device in the form of electrical energy. This procedure allows the diagnosis to be carried out even if the specified value for the fresh gas quantity determined from the operating point lies outside the diagnosis interval.

[0039] 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 and is provided and designed to determine a default value for a fresh gas quantity to be supplied to the drive unit at least temporarily from an operating point of the drive unit predetermined by means of an operating element, and to set a target value of the fresh gas quantity determined from the default value on an adjustment means of the drive unit, and to carry out a diagnosis of at least one exhaust gas-carrying device of the drive device during a diagnostic period. It is provided that the drive device is further provided and designed to filter the target value during the diagnostic period using a low-pass filter and to determine it from the default value.

[0040] The advantages of such a drive device design and such a procedure have already been pointed out. Both the drive device 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.

[0041] 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 and explained in the description and / or the figures, but which follow from or can be derived from the explained embodiments.

[0042] The invention will be explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. Fig. 1 a schematic representation of a drive device for carrying out the method according to the invention, and Fig. 2 a diagram of a time course to illustrate the method according to the invention.

[0043] The Fig. 1 shows a schematic representation of a drive device 1. The drive device 1 has a drive unit 2 and is part of a motor vehicle (not shown in detail). An operating point of the drive device 1 is specified, at least temporarily, by means of an operating element 3. A preset value 4 for a quantity of fresh gas to be supplied to the drive unit 2 is determined from the operating point. The operating element 3 is designed, for example, as an accelerator pedal that is actuated at least temporarily by a driver of the motor vehicle.

[0044] From the specified value 4, a target value 5 for the fresh gas quantity is determined and set on the drive unit 2. A diagnostic request 6 signals the need for a diagnosis of at least one exhaust gas-carrying device (not shown in detail) of the drive device 1. If the diagnostic request 6 is present, a diagnosis release 7 occurs and the diagnosis is carried out. During the diagnosis, the target value 5 is determined from the specified value 4 using a first low-pass filter 8. After the diagnosis has been carried out, the target value 5 is no longer determined from the specified value 4 using the first low-pass filter 8. In addition to the first low-pass filter 8, a second low-pass filter 9 is provided, which has a shorter time constant than the first low-pass filter 8.Thus, the setpoint value 5 can be temporarily filtered by means of the first low-pass filter 8, temporarily filtered by means of the second low-pass filter 9 and temporarily determined directly from the setpoint value 4.

[0045] The Fig. Figure 2 shows a time profile 10 of the specified value 4 and a time profile 11 of the desired value 5 over time. When the diagnostic request 6 is present, the diagnostic enable 7 occurs at time t0. At time t0, a diagnostic period 12 begins, during which the diagnosis is performed. The diagnosis begins when the specified value 4 lies within a diagnostic interval 13, which is delimited by an upper interval limit 14 and a lower interval limit 15. At time t1, the diagnosis is terminated, and the diagnostic period 12 ends accordingly.

[0046] During the diagnostic period 12, the target value 5 is determined from the specified value 4 by filtering it using the first low-pass filter 8. The time profile 11 of the target value 5 thus represents a smoothed profile of the time profile 10 of the specified value 4 within the diagnostic period 12. Immediately following the end of the diagnostic period 12 at time t1, a specific time period 16 follows, which in turn ends at time t2. During the specific time period 16, the smoothing of the specified value 4 is continuously reduced so that the target value 5 corresponds to the specified value 4 from time t2 at the latest. The target value 5 is approximated to the specified value 4 over the specific time period 16. For example, this is done by determining the setpoint value 5 from the default value 4 by means of the second low-pass filter 9, wherein the time constant of the second low-pass filter 9 is continuously reduced, in particular to a value of zero.

[0047] It is further provided to abort the execution of the diagnosis if the target value 5 exceeds an upper threshold value 17 and / or if the target value 5 falls below a lower threshold value 18. As can be seen from the illustrated time course 11, filtering the specified value 4 using the first low-pass filter 8 ensures that the target value 5 lies within a range 19 that is limited by the upper threshold value 17 and the lower threshold value 18. In the example illustrated, the time course 11 of the target value 5 lies within the range 19 over the entire diagnosis period 12. Dynamic changes in the specified value 4 are reduced during the diagnosis period 12 by the filtering. This leads to a constant or essentially constant exhaust gas composition upstream of the at least one exhaust gas-carrying device, so that the diagnosis can be carried out successfully. LIST OF REFERENCE SYMBOLS: 1 drive device 2 drive unit 3 Control element 4 Default value 5 Setpoint 6 Diagnostic request 7 Diagnostic release 8 first low-pass filter 9 second low-pass filter 10 Time course 11 Time course 12 Diagnosis period 13 Diagnostic interval 14 upper interval limit 15 lower interval limit 16 Time span 17 upper threshold 18 lower threshold 19 Area

Claims

[1] Method for operating a drive device (1) for a motor vehicle, which has a drive unit (2) generating exhaust gas, wherein a default value (4) for a fresh gas quantity to be supplied to the drive unit (2) is determined at least temporarily from an operating point of the drive unit (2) predetermined by means of an operating element (3), and a target value (5) of the fresh gas quantity determined from the default value (4) is set on an adjusting means of the drive unit (2), and wherein a diagnosis of at least one exhaust gas-carrying device of the drive device (1) is carried out during a diagnostic period (12), characterized by that the setpoint value (5) is determined during the diagnostic period (12) by means of a low-pass filter (8,9) filtered from the default value (4). [2] Method according to claim 1, characterized bythat the default value (4) is temporarily determined from the operating point and temporarily specified by a driver assistance device. [3] Method according to one of the preceding claims, characterized by that the diagnosis of the at least one exhaust gas-carrying device is only carried out when a diagnosis request (6) is present. [4] Method according to one of the preceding claims, characterized by that the diagnostic period (12) begins when the default value (4) lies within a diagnostic interval (13) limited by an upper interval limit value (14) and a lower interval limit value (15). [5] Method according to claim 4, characterized bythat the diagnostic period (12) ends after the diagnosis has been carried out and / or when the setpoint value (5) exceeds an upper threshold value (17) and / or when the setpoint value (5) falls below a lower threshold value (18), wherein the upper threshold value (17) is smaller than the upper interval limit value (14) and the lower threshold value (18) is larger than the lower interval limit value (15). [6] Method according to one of the preceding claims, characterized by that during the diagnostic period (12) a gradient of the default value (4) is determined, wherein a first value is selected as a time constant of the low-pass filter (8,9) if the gradient is greater than or equal to zero, and a second value is selected as the time constant of the low-pass filter (8,9) if the gradient is less than zero, wherein the first value is less than the second value. [7] Method according to one of the preceding claims, characterized bythat immediately after the end of the diagnostic period (12) the target value (5) continues to be determined from the preset value (4) by means of the low-pass filter (8,9) over a specific time period (16), wherein the time constant of the low-pass filter (8,9) is reduced in the direction of a third value, preferably down to the third value. [8] Method according to claim 7, characterized by that after the specified time period (16) has elapsed, the setpoint value (5) is no longer determined from the preset value (4) by means of the low-pass filter (8,9). [9] Method according to one of the preceding claims, characterized bythat the drive unit (2) is at least temporarily coupled in terms of drive technology to an electrical machine of the drive device (1), wherein when the diagnostic request (6) is present and the default value (4) lies outside the diagnostic interval (13), the default value (4) is adjusted to a value lying within the diagnostic interval (13) and the drive device (1) is set to the operating point by adjusting a drive power of the electrical machine. [10] Drive device 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 an exhaust gas and is provided and designed to determine a preset value (4) for a fresh gas quantity to be supplied to the drive unit (2) at least temporarily from an operating point of the drive unit (2) predetermined by means of an operating element (3) and to set a target value (5) of the fresh gas quantity determined from the preset value (4) on an adjusting means of the drive unit (2) and to carry out a diagnosis of at least one exhaust gas-carrying device of the drive device (1) during a diagnostic period (12), characterized bythat the drive device (1) is further provided and designed to determine the setpoint value (4) during the diagnostic period (12) by means of a low-pass filter (8,9) filtered from the specified value (4).

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