METHOD FOR OPERATING A DRIVE DEVICE AND CORRESPONDING DRIVE DEVICE

Description

[0001] The invention relates to a method for operating a drive device which has a drive unit generating exhaust gas and an exhaust gas aftertreatment device for aftertreating the exhaust gas, wherein a composition of a fuel-air mixture used to operate the drive unit is determined at least temporarily by means of a lambda control on the basis of a first measured value of a first lambda probe arranged upstream of the exhaust gas aftertreatment direction and on the basis of a second measured value of a second lambda probe arranged downstream of the exhaust gas aftertreatment direction, wherein in order to adjust an oxygen fill level of an oxygen reservoir of the exhaust gas aftertreatment device to a desired fill level after an occurrence of a value of the second measured value which corresponds to a boundary value of a fill level range containing the desired fill level, the composition is adjusted in such a way thatthat the oxygen level changes by a pilot oxygen amount toward the target level. The invention further relates to a drive device.

[0002] For example, the prior art document DE 10 2018 203 399 A1 is known. This document describes a method for analyzing the oxygen storage capacity of a catalyst arranged in an exhaust system of an internal combustion engine. The method comprises decoupling the internal combustion engine from a drive train, driving the internal combustion engine by means of an electric motor, supplying a lean fuel-air mixture to the catalyst until the catalyst is completely loaded with oxygen, supplying a rich fuel-air mixture to the catalyst, determining temporal profiles of combustion air ratios upstream and downstream of the catalyst, and determining the amount of oxygen storable in the catalyst from the determined temporal profiles of the combustion air ratios.

[0003] Furthermore, the document DE 10 2005 044 729 A1 discloses a method for lambda control in an internal combustion engine with at least one catalytic converter arranged in an exhaust system of the internal combustion engine, wherein the exhaust system has a front lambda control circuit and a rear lambda control circuit with at least one rear oxygen sensor arranged downstream of the catalytic converter, wherein the rear lambda control circuit processes an output signal of the rear oxygen sensor, forms a difference value to a rear target lambda value and outputs a manipulated variable acting on the target lambda value of the front lambda control circuit.It is intended that after a change of sign of the difference value for a time interval since the change of sign, a balanced oxygen quantity is determined from the amount of oxygen introduced into and discharged from the catalyst and the manipulated variable of the rear lambda control loop is additionally selected depending on the balanced oxygen quantity.

[0004] The document DE 10 2012 019 907 A1 relates to a method for operating an internal combustion engine with an exhaust gas purification device, wherein the exhaust gas purification device has a catalyst through which an exhaust gas flow of the internal combustion engine can flow, as well as a first lambda probe arranged upstream of the catalyst in the exhaust gas flow and a second lambda probe arranged downstream of the catalyst in the exhaust gas flow.It is provided that an oxygen filling state of an oxygen storage device of the catalytic converter is determined on the basis of a first lambda signal provided by the first lambda probe and an offset value, if a lambda signal lower limit is undershot, the second lambda signal provided by the second lambda probe is set to a first value corresponding to an empty oxygen storage device and / or if a lambda signal upper limit is exceeded, the second lambda signal is set to a second value corresponding to a full oxygen storage device and immediately thereafter is controlled to a preset filling state during at least one control period, wherein at the end of the control period the offset value is adjusted on the basis of the second lambda signal.

[0005] The prior art also includes the documents DE 10 2018 251 720 A1, DE 10 2018 219 978 B3 and DE 10 2004 060 125 B4.

[0006] It is an object of the invention to propose a method for operating a drive device which has advantages over known methods, in particular enabling an oxygen filling level of an oxygen storage device of the exhaust gas aftertreatment device to be set to a desired filling level and / or an oxygen storage capacity of the oxygen storage device to be determined with high accuracy.

[0007] This is achieved according to the invention with a method for operating a drive device having the features of claim 1. It is provided that the composition is subsequently determined by means of the lambda control during a control period until the second measured value is equal to a target value corresponding to the target fill level, at least within an unavoidable tolerance, and finally the pilot oxygen quantity is corrected by an oxygen balance value determined during the control period.

[0008] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0009] The method serves to operate the drive device, which is provided and configured, for example, to drive a motor vehicle and, to that extent, to provide a drive torque directed toward driving the motor vehicle. To provide the drive torque, the drive device has the drive unit. During its operation or during the operation of the drive device, fuel and oxygen or oxygen-containing air are supplied to the drive unit, which react with one another in the drive unit. This produces exhaust gas, which is discharged from the drive unit, in particular toward an external environment of the drive device.

[0010] Since the exhaust gas contains pollutants, it is first fed to the exhaust gas aftertreatment device after being discharged from the drive unit, particularly before being released into the outside environment. The exhaust gas aftertreatment device preferably comprises at least one of the following devices: three-way catalytic converter, oxidation catalytic converter, NO x storage catalytic converter, and SCR catalytic converter. Of course, the exhaust gas aftertreatment device can comprise precisely one or more of the aforementioned devices or be present as one or more of the aforementioned devices.

[0011] With respect to a main flow direction of the exhaust gas, the first lambda probe is located upstream of the exhaust gas aftertreatment device, and the second lambda probe is located downstream of the exhaust gas aftertreatment device. The first lambda probe measures the residual oxygen content of the exhaust gas upstream of the exhaust gas aftertreatment device, while the second lambda probe measures the residual oxygen content of the exhaust gas downstream of the exhaust gas aftertreatment device. The first lambda probe provides the first measured value, and the second lambda probe provides the second measured value.

[0012] Based on both measured values, i.e., the first measured value and the second measured value, lambda control is performed, which adjusts the composition of the fuel-air mixture supplied to the power unit. In the strictest sense, lambda control is performed based on the first measured value, while trim control is performed based on the second measured value. This influences lambda control and at least partially compensates for any error in the first lambda sensor. This achieves a very high level of lambda control accuracy.

[0013] Preferably, a broadband lambda sensor is used as the first lambda sensor and a step-type lambda sensor is used as the second lambda sensor. The broadband lambda sensor enables the detection of the residual oxygen content or the corresponding lambda value over a wider measuring range than the step-type lambda sensor. The step-type lambda sensor, on the other hand, has a narrower measuring range than the broadband lambda sensor; in particular, it is used to detect a lambda value of one. However, the measuring accuracy of the step-type lambda sensor is higher than that of the broadband lambda sensor. Deviations and errors of the first lambda sensor are at least partially compensated for using the trim control or by using the second measured value of the second lambda sensor.

[0014] The exhaust gas aftertreatment system includes an oxygen storage device, which in turn includes a material that can absorb and temporarily store the oxygen contained in the exhaust gas and subsequently release it again. Specifically, when there is an excess of oxygen in the exhaust gas, oxygen from the exhaust gas is introduced into the oxygen storage device. When there is a lack of oxygen in the exhaust gas, oxygen is released from the oxygen storage device into the exhaust gas. This ensures proper functioning of the exhaust gas aftertreatment system and, above all, the effective conversion of pollutants contained in the exhaust gas into less hazardous products.

[0015] The efficiency of the exhaust gas aftertreatment system, i.e., the extent to which pollutants can be converted into less hazardous products, depends primarily on the operating conditions of the exhaust gas aftertreatment system and the oxygen level in the oxygen storage device. Operating conditions include, in particular, the operating temperature of the exhaust gas aftertreatment system. For example, the efficiency of the exhaust gas aftertreatment system is optimal at an operating temperature of the exhaust gas aftertreatment system and decreases toward lower temperatures.

[0016] To achieve optimal efficiency of the exhaust gas aftertreatment system, the oxygen fill level of the oxygen storage tank should also be between 30% and 50% (these values ​​inclusive). In any case, the oxygen storage tank must not be completely empty and not completely loaded with oxygen. In order to set the oxygen fill level to a target fill level, which in particular is at least 30% and at most 50%, it is necessary to know the oxygen storage capacity of the oxygen storage tank or at least to determine the quantity of oxygen that must be introduced into it from a completely empty oxygen storage tank or that must be removed from it from a fully filled oxygen storage tank in order to set the oxygen fill level to the target fill level.

[0017] For example, it may be provided that the drive unit is initially operated to achieve a lean exhaust gas until the second measured value from the second lambda probe indicates an oxygen excess. The drive device is then operated to generate rich exhaust gas until the second measured value indicates a lack of oxygen. From the time the drive unit switches over from operating the drive unit to generate the lean exhaust gas until the lack of oxygen is detected by the second lambda probe, the oxygen balance value is determined, which describes the amount of oxygen removed from the oxygen storage device in the specified period. The oxygen balance value is derived, for example, from the composition of the fuel-air mixture and its throughput in the drive unit or from the first measured value and the second measured value as well as an exhaust gas throughput through the exhaust gas aftertreatment device.The oxygen storage capacity of the oxygen storage is then determined from the oxygen balance value.

[0018] The reverse procedure can of course also be implemented, in which the drive unit is initially operated to generate rich exhaust gas until the second measured value indicates a lack of oxygen. The drive unit is then operated to operate lean exhaust gas, again until the second measured value indicates an excess of oxygen. The oxygen balance value is determined from the switch from rich exhaust gas to lean exhaust gas until the detection of excess oxygen. Subsequently, the oxygen storage capacity is again determined from the oxygen balance value.

[0019] However, the procedure described is based on the oxygen storage being completely emptied and then fully charged to determine the oxygen storage capacity. This can, however, be disadvantageous in terms of the fuel consumption of the drive unit and / or the resulting pollutant emissions. For this reason, a complete run through of the oxygen storage capacity should be avoided. Instead, the plan is to set the oxygen fill level directly to the target fill level starting from a completely empty oxygen storage or a fully charged oxygen storage, i.e. without the oxygen fill level overshooting, or at least without the oxygen fill level exceeding the target fill level excessively.

[0020] For this purpose, it is provided that when a value of the second measured value occurs that corresponds to the boundary value of the fill level range, the oxygen fill level is adjusted to the target fill level. The fill level range is understood to be a range that includes the target fill level. The fill level range preferably extends from a first value, which corresponds to a completely empty or discharged oxygen reservoir, to a second value, which corresponds to an oxygen reservoir that is completely filled or charged with oxygen.

[0021] The boundary value of the fill level range corresponds in particular to either a completely empty or a fully charged oxygen storage tank, i.e. an oxygen fill level of 0% or 100%. The value corresponding to the boundary value is the value of the second measured value that it assumes under the stated conditions, i.e. when the oxygen storage tank is either completely empty or fully charged. If the currently measured second measured value corresponds to this value, the oxygen storage tank is either completely empty or fully charged. Starting from this condition, the oxygen fill level should be brought to the target fill level by appropriate operation of the drive unit without the oxygen fill level (significantly) exceeding the target fill level, i.e. without overshooting or at least without pronounced overshoot.

[0022] The value of the second measured value corresponding to the boundary value occurs, for example, during overrun operation of the drive system. Overrun operation means that the drive unit is being dragged by an externally provided torque without fuel being introduced into the drive unit. This means that only air flows through the drive unit, so that the oxygen storage device is quickly fully charged with oxygen. Conversely, the second measured value can be equal to the value corresponding to the boundary value after the drive unit is operating with a rich mixture, as occurs, for example, when the drive unit is operating at high power, for example when the drive unit is operating at rated power or maximum power.

[0023] In order to set the oxygen fill level to the target level, the composition is first adjusted so that the oxygen fill level changes by the pilot oxygen quantity. The pilot oxygen quantity is a stored value which serves to set the oxygen fill level at least approximately to the target value. The pilot oxygen quantity is supplied to or removed from the oxygen reservoir by operating the drive unit with a specific composition of the fuel-air mixture over a specific period of time. The oxygen fill level can be changed by the pilot oxygen quantity in different directions. If the oxygen reservoir is empty, an oxygen quantity corresponding to the pilot oxygen quantity is added to the oxygen reservoir.When the oxygen storage is loaded, an amount of oxygen corresponding to the pilot oxygen amount is discharged from the oxygen storage.

[0024] After changing the oxygen fill level by the pilot oxygen quantity, the composition of the fuel-air mixture is determined based on the first measured value and the second measured value, more precisely using lambda control. This occurs in such a way that the second measured value changes towards a target value corresponding to the target fill level. Control is carried out until the second measured value corresponds to the target value, either exactly or at least within the unavoidable tolerance. During control, the oxygen balance value is determined; in other words, it is recorded how much oxygen is being introduced into and / or removed from the oxygen storage. It is preferably important that the oxygen fill level is changed exclusively towards the target value during the control period. In particular, changing the oxygen fill level beyond the target value is avoided.

[0025] If the second measured value reaches the target value, the pilot oxygen quantity is corrected by the oxygen balance value. If the oxygen balance value is different from zero, the input or output of the pilot oxygen quantity was not sufficient to adjust the oxygen level to the target level and the second measured value does not correspond to the target value. For example, the pilot oxygen quantity is corrected with the oxygen balance value by summing them. A new value for the pilot oxygen quantity is therefore obtained by adding the previous value of the pilot oxygen quantity to the oxygen balance value. The new value is subsequently used as the pilot oxygen quantity. The correction adjusts the pilot oxygen quantity to the actually required oxygen quantity, in particular iteratively.When the oxygen level is subsequently adjusted to the target level, the corrected pilot oxygen quantity is used, so that the adjustment is carried out with greater accuracy and the proportion of lambda control in the adjustment is smaller than before.

[0026] In particular, it is therefore provided that, given a second measured value corresponding to the fully filled or loaded oxygen storage, the composition is adjusted such that the oxygen fill level is reduced by a pilot oxygen quantity into the fill level range, then during a control period the composition is determined by means of the lambda control until the second measured value is equal to the target value corresponding to the target fill level at least within an unavoidable tolerance, and finally the pilot oxygen quantity is corrected by the oxygen balance value determined during the control period.

[0027] Additionally or alternatively, it is provided that, in the case of a second measured value which corresponds to a completely emptied or discharged oxygen storage device, the composition is adjusted in such a way that the oxygen fill level increases by a pilot oxygen quantity in the direction of the setpoint range, then during a control period the composition is determined by means of the lambda control until the second measured value corresponds to the setpoint lying in the setpoint range at least within an unavoidable tolerance and finally the pilot oxygen quantity is corrected by the oxygen balance value determined during the control period.

[0028] The described procedure allows the oxygen level of the oxygen storage tank to be adjusted to the target level without the oxygen level having to pass completely through the fill level range. This means that while adjusting the oxygen level to the target level, only a single boundary value of the fill level range is affected by the second measured value, but not both boundary values ​​that limit the fill level range. This reliably prevents unnecessary pollutant emissions from the drive system and reduces fuel consumption. Furthermore, the oxygen level is adjusted to the target level in a particularly short time.

[0029] Overall, the oxygen level is adjusted to the target level using trim control, which regulates the second measured value to the target value. This procedure is based on the realization that the second measured value can at least provide an indication of the current oxygen level in the oxygen storage. The oxygen storage capacity of the exhaust gas aftertreatment system is also optionally determined from the corrected pilot oxygen quantity, particularly as a function of the target level.

[0030] A further development of the invention provides that, within the scope of lambda control, the first measured value is regulated to a first target value, wherein the first measured value and / or the first target value are corrected with a trim value which is determined by means of a trim control on the basis of the second measured value. The composition of the fuel-air mixture is adjusted with the aid of lambda control. The first measured value is measured using the first lambda sensor and regulated to the first target value. The first measured value can therefore also be referred to as the controlled variable or as the actual value of the controlled variable, and the first target value as the reference variable of the lambda control. The composition of the fuel-air mixture serves as the manipulated variable of the lambda control.

[0031] To improve the accuracy of the lambda control, trim control is also carried out. Within the framework of trim control, the second measured value serves as the controlled variable or as the actual value of the controlled variable. The trim control uses the trim value resulting from the trim control as the manipulated variable. The trim value is used to correct the first measured value and / or the first setpoint. In any case, the trim value flows into the lambda control in such a way that a possible error in the first lambda sensor is at least partially or even completely compensated. With the help of trim control, for example, an offset error of the first lambda sensor is compensated. This significantly improves the accuracy in determining the composition of the fuel-air mixture.

[0032] A further development of the invention provides that, within the scope of the trim control, the second measured value is controlled by setting the trim value to a second setpoint corresponding to the setpoint. In the trim control, the second measured value is the controlled variable or its actual value, the second setpoint is the reference variable, and the trim value is the manipulated variable. The second setpoint is selected such that any error in the first lambda probe is compensated. For example, the second setpoint corresponds to a combustion air ratio λ of one or slightly less than one. The trim control enables an improvement in the quality of the lambda control and, accordingly, a more precise adjustment of the composition of the fuel-air mixture. The second setpoint, which is used in the trim control, corresponds to the setpoint already mentioned.

[0033] A further development of the invention provides that the fill level range is limited, on the one hand, by a first value corresponding to an oxygen reservoir completely emptied of oxygen and, on the other hand, by a second value corresponding to an oxygen reservoir completely filled with oxygen. The fill level range thus extends from an oxygen fill level of 0% to an oxygen fill level of 100%; it therefore encompasses the entire oxygen storage capacity of the oxygen reservoir. The first value limits the fill level range towards smaller values, and the second value towards larger values. The aforementioned boundary value corresponds either to the first value or the second value.

[0034] Depending on which of the values ​​corresponds to the boundary value, the oxygen storage tank is either filled with oxygen or oxygen is removed from it to adjust the oxygen level to the target level. Preferably, a case distinction is made for adjusting the oxygen level to the target level, and the procedure is selected depending on which of the values ​​corresponds to the boundary value. This means that the described procedure can be used, and is used, both when the oxygen storage tank is completely empty and when it is completely full. This achieves a particularly high degree of flexibility for the described method.

[0035] A further development of the invention provides that a fill level value is used as the target fill level which lies between the first value and the second value and is spaced apart from both values. The target fill level or the value of the target fill level is therefore greater than the first value and less than the second value. This means that the target fill level is greater than 0% and less than 100%. Preferably, the target fill level is at least 10%, at least 20% and at least 30% and / or at most 70%, at most 60% and at most 50%. In other words, the target fill level lies between 10% and 70%, between 20% and 60% or between 30% and 50% (including the aforementioned values ​​in each case). This achieves the described high conversion performance.

[0036] A further development of the invention provides that a fill level value is used as the target fill level that is closer to the first value than to the second value. It has already been explained above that the optimal conversion performance of the exhaust gas aftertreatment system is achieved at an oxygen fill level between 30% and 50% (including these values). Accordingly, it is advantageous to select the target fill level such that it describes the completely empty oxygen reservoir rather than the fully charged oxygen reservoir. This, in turn, serves to achieve a particularly high conversion performance of the exhaust gas aftertreatment system.

[0037] A further development of the invention provides that it is assumed that the second measured value is equal to the target value if a gradient of the trim value is equal to zero. It is therefore not absolutely necessary to compare the second measured value with the target value. Alternatively, the gradient of the trim value can be evaluated. If the trim value is equal to zero or at least within an unavoidable tolerance with an otherwise constant operating point of the drive unit, it can be assumed that no further intervention by the trim control will occur to change the oxygen fill level towards the target fill level. Consequently, the control period can be ended and the pilot oxygen quantity can be corrected by the oxygen balance value.

[0038] It can also be provided that the control period is only terminated when both the second measured value is equal to the target value, at least within the unavoidable tolerance, and the gradient of the trim value is equal to zero. Only under this condition is the pilot oxygen quantity corrected by the oxygen balance value, and the process for adjusting the oxygen level to the target level is terminated. This ensures particularly reliable adjustment of the oxygen level.

[0039] A further development of the invention provides that the second measured value is continuously maintained during the control period in a setpoint range corresponding to the fill level range at a distance from a further edge value opposite the edge value. The setpoint range therefore corresponds to a value range that corresponds to the fill level range. The setpoint range is limited on the one hand by a value that the second measured value has when the oxygen storage device is completely empty, and on the other hand by a value that the second measured value has when the oxygen storage device is completely full. The oxygen fill level is now adjusted to the setpoint level in such a way that the second measured value is continuously spaced from the further edge value that lies opposite the edge value or limits the setpoint range on the opposite side. This prevents the fill level range from being completely passed through.

[0040] A further development of the invention provides that the second measured value is continuously and consistently adjusted toward the target value during the control period. Lambda control is performed in such a way that the second measured value continuously changes in the same direction, namely toward the target value. In particular, the second measured value is to be prevented from changing back toward the value corresponding to the boundary value. This approach enables a particularly rapid adjustment of the oxygen level to the target level.

[0041] The invention further relates to a drive device, in particular for carrying out the method according to the embodiments in the context of this description, with a drive unit generating exhaust gas and an exhaust gas aftertreatment device for aftertreating the exhaust gas, wherein the drive device is provided and designed to determine a composition of a fuel-air mixture used to operate the drive unit at least temporarily by means of a lambda control on the basis of a first measured value of a first lambda probe arranged upstream of the exhaust gas aftertreatment direction and on the basis of a second measured value of a second lambda probe arranged downstream of the exhaust gas aftertreatment direction.

[0042] In this case, the drive device is further provided and designed to set an oxygen fill level of an oxygen reservoir of the exhaust gas aftertreatment device to a target fill level after an occurrence of a value of the second measured value which corresponds to a boundary value of a fill level range receiving the target fill level, to set the composition in such a way that the oxygen fill level changes by a pilot oxygen quantity in the direction of the target fill level, to then determine the composition by means of the lambda control during a control period until the second measured value is equal to a target value corresponding to the target fill level at least within an unavoidable tolerance and finally to correct the pilot oxygen quantity by an oxygen balance value determined during the control period.

[0043] The advantages of such a design of the drive device or 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.

[0044] 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 to be considered encompassed by the invention 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.

[0045] The invention will be explained in more detail below with reference to the exemplary embodiments shown in the drawings, without limiting the invention. In the drawings: Figure 1 shows a schematic representation of a drive device with a drive unit and an exhaust gas aftertreatment device, Figure 2 shows several diagrams in which different state variables of the drive device are plotted over time.

[0046] The Figure 1shows a schematic representation of a drive device 1, which is used, for example, to drive a motor vehicle. In general, the drive device 1 serves to provide a drive torque, namely by means of a drive unit 2. During its operation, a fuel-air mixture with a specific composition is supplied to the drive unit 2. The composition is determined using a device 3 for carrying out lambda control. During operation of the drive unit 2, exhaust gas is produced, which is discharged from the drive unit 2 and fed to an exhaust gas aftertreatment device 4. With regard to a main flow direction of the exhaust gas, upstream of the exhaust gas aftertreatment device 4 there is a first lambda probe 5 and downstream of the exhaust gas aftertreatment device 4 there is a second lambda probe 6. The two lambda probes 5 and 6 serve to detect a residual oxygen concentration in the exhaust gas.

[0047] A measured value supplied by the first lambda sensor 5 is referred to as the first measured value and a measured value supplied by the second lambda sensor 6 is referred to as the second measured value. The first measured value serves as the input variable of a first sub-device 7 of the device 3. In this sub-device, the actual lambda control of the composition of the fuel-air mixture is carried out. In the first sub-device 7, the composition is determined based on the first measured value and a default value supplied according to arrow 8. In addition, a trim value is transmitted to the first sub-device 7 according to arrow 9, which is also used in determining the composition. In particular, the first measured value and / or a first target value determined from the default value is corrected with the trim value.

[0048] The trim value is determined using a second sub-device 10 of device 3, which serves to implement a trim control. The trim control is performed using the second measured value of the second lambda probe 6 by adjusting the second measured value to a second target value, which is also determined, for example, from the specified value.

[0049] The Figure 2shows several diagrams in which different curves are plotted against time t. The upper first diagram shows the first measured value of the first lambda probe 5 in curves 11, 12 and 13. These curves 11, 12 and 13 are identical for and between the times t 1 , t 2 and t 3 and only differ from time t 3 . The middle second diagram shows curves 14, 15 and 16 for an oxygen fill level of an oxygen reservoir of the exhaust gas aftertreatment device 4. The curves 14, 15 and 16 are identical for and between the time periods t 1 and t 2 , but differ from time t 2 . The lower third diagram shows curves 17, 18 and 19 for the second measured value of the second lambda probe 6. The curves 17, 18 and 19 are identical for and between the times t 1 and t 2 , but differ from the time t 2 .

[0050] The upper diagram shows that the first measured value before time t 1 corresponds to a stoichiometric composition of the fuel-air mixture supplied to drive unit 2. From time t 1 onwards, drive device 1 or drive unit 2 is in overrun mode; drive unit 2 is thus propelled by an externally provided torque, and the fuel supply to drive unit 2 is interrupted. This means that exhaust gas with a high air content or excess oxygen enters exhaust aftertreatment device 4 through drive unit 2.

[0051] This is evident from the oxygen fill level in curves 14, 15, and 16, which increases to 100% from time t1 to time t2. The oxygen reservoir is therefore completely filled with oxygen at time t2. This circumstance can also be seen in curves 17, 18, and 19: the second measured value decreases between time t1 and time t2, starting from an initial value of, for example, approximately 0.65 V. The value to which the second measured value decreases corresponds, for example, to an edge value of a fill level range that accommodates a target fill level of the oxygen reservoir.

[0052] After such a value of the second measured value occurs, the oxygen level should be adjusted to a target level, which in the exemplary embodiment shown here is 50%. To do this, the oxygen level is first adjusted from time t 2 to time t 3 by a pilot oxygen quantity towards the target level by appropriately operating the drive unit 2. This measure is completed at time t 3. In the case of curves 11, 14, and 17, the pilot oxygen quantity is sufficient to adjust the oxygen level up to the target level. This is shown by curves 14 and 17.

[0053] Starting at time t3, the composition of the fuel-air mixture is determined using lambda control. Trim control is also performed in this context, adjusting the second measured value to a target value corresponding to the target fuel level. Curves 12 and 13 demonstrate the influence of trim control on the first measured value. For curve 12, the pilot oxygen quantity was too small, so more oxygen must subsequently be introduced into the oxygen reservoir. Curve 12 corresponds to curves 15 and 18.

[0054] For curve 13, however, the pilot oxygen quantity was too high. Accordingly, oxygen must be removed from the oxygen reservoir as part of the lambda control or trim control. Curve 13 corresponds to curves 16 and 19. It can be seen that at time t4, the second measured value reached the target value. Accordingly, curves 15 and 16 have also reached the target fill level, and according to curves 12 and 13, the trim control intervention has also decreased. The latter means, in particular, that a gradient of the trim value, which results from the trim control and is used to correct the lambda control, is zero or at least almost zero.

[0055] The described procedure enables a particularly rapid adjustment of the oxygen level to the target level, in particular without completely passing through the fill level range. This results in a reduction in fuel consumption of the drive system 1 as well as a reduction in pollutant emissions. LIST OF REFERENCE SYMBOLS:

[0056] 1Drive system 2Drive unit 3System 4Exhaust gas aftertreatment system 5First lambda probe 6Second lambda probe 7First subsystem 8Arrow 9Arrow 10Second subsystem 11Course 12Course 13Course 14Course 15Course 16Course 17Course 18Course 19Course

Claims

1. Method for operating a drive device (1), which comprises an exhaust gas generating drive unit (2) and an exhaust gas aftertreatment device (4) for the aftertreatment of the exhaust gas, wherein a composition of a fuel-air mixture used to operate the drive unit (2) is determined at least temporarily by means of a lambda control based on a first measured value of a first lambda sensor (5) arranged upstream of the exhaust gas aftertreatment device (4) and based on a second measured value of a second lambda sensor (6) arranged downstream of the exhaust gas aftertreatment device (4), wherein in order to adjust an oxygen filling level of an oxygen storage of the exhaust gas aftertreatment device (4) to a target filling level after an occurrence of a value of the second measured value, which corresponds to the boundary value of a filling level range that accommodates the target filling level, the composition is adjusted in such a way that the oxygen filling level changes by a pilot oxygen amount in the direction of the target filling level, characterized in that subsequently the composition is determined during a control period using the lambda control until the second measured value is at least within an unavoidable tolerance equal to a target value corresponding to the target filling level and finally the pilot oxygen amount is corrected by an oxygen balance value determined during the control period.

2. Method according to claim 1, characterized in that as part of the lambda control, the first measured value is regulated to a first target value, wherein the first measured value and / or the first target value are corrected with a trim value, which is determined by a trim control by means of the second measured value.

3. Method according to claim 2, characterized in that as part of the trim control, the second measured value is regulated by setting the trim value to a second target value corresponding to the target value.

4. Method according to any one of the preceding claims, characterized in that the filling level range is delimited, on the one hand, by a first value corresponding to a completely empty oxygen storage and, on the other hand, by a second value corresponding to an oxygen storage tank completely filled with oxygen.

5. Method according to claim 4, characterized in that a filling level value is used as the target filling level, which lies between the first value and the second value and is spaced from both values.

6. Method according to claim 4 or 5, characterized in that a filling level value is used as the target filling level, which is closer to the first value than to the second value.

7. Method according to claim 2 or 3, characterized in that it is assumed that the second measured value is equal to the target value if a gradient of the trim value is equal to zero.

8. Method according to any one of the preceding claims, characterized in that the second measured value during the control period is continuously held in a target value range corresponding to the filling level range at a distance from a further boundary value opposite the boundary value.

9. Method according to any one of the preceding claims, characterized in that the second measured value is continuously and consistently adjusted in the direction of the target value during the control period.

10. Drive device (1), in particular for carrying out the method according to any one or more of the preceding claims, with an exhaust gas generating drive unit (2) and an exhaust gas aftertreatment device (4) for aftertreatment of the exhaust gas, wherein the drive device (1) is provided and designed to determine a composition of a fuel-air mixture used to operate the drive unit (2) at least temporarily by means of a lambda control based on a first measured value of a first lambda sensor (5) arranged upstream of the exhaust gas aftertreatment device (4) and based on a second measured value of a second lambda sensor arranged downstream of the exhaust gas aftertreatment device (4), wherein the drive direction (1) is further provided and designed to, in order to adjust an oxygen filling level of an oxygen storage of the exhaust gas aftertreatment device (4) to a target filling level after an occurrence of a value of the second measured value, which corresponds to the boundary value of a filling level range that accommodates the target filling level, adjust the composition in such a way that the oxygen filling level changes by a pilot oxygen amount in the direction of the target filling level, characterized in that subsequently the composition is determined during a control period using the lambda control until the second measured value is at least within an unavoidable tolerance equal to a target value corresponding to the target filling level and finally the pilot oxygen amount is corrected by an oxygen balance value determined during the control period.