Method for regenerating an exhaust particulate filter

Abstract

The invention relates to a method for regenerating an exhaust particulate filter of a motor vehicle, wherein a course of a simulated regeneration is varied at different starting points in a predicted driving route of the motor vehicle. In order to carry out the regeneration, a starting point is selected at which a pre-given optimization criterion for the regeneration can be best met.

Description

Technical Field

[0001] The present invention relates to a method for regenerating an exhaust particulate filter of a motor vehicle. The present invention further relates to a computer program for implementing each step of the method and a machine-readable storage medium storing the computer program. Finally, the present invention relates to an electronic control device configured to implement the method. Background Art

[0002] In order to comply with emission regulations, a diesel particulate filter is required in the exhaust pipe of a motor vehicle with a diesel engine. The particulate filter must be cleaned of its soot deposits at certain time intervals so that its flow resistance does not reduce the engine power. For this purpose, the soot layer is burned off, where carbon dioxide and water vapor are formed from the soot. To burn the soot, an exhaust gas temperature of usually more than 550 °C is required. These temperatures are not reliably reached during vehicle operation, so additional measures are taken for regeneration. For this purpose, energy is additionally introduced into the particulate filter, for example by heating the particulate filter with an electric heating disk, using a fuel burner or re-injecting fuel into the engine combustion chamber. The choice of the time point for initiating particulate filter regeneration is oriented, for example, towards the section of the motor vehicle's journey and the pressure difference caused by the particulate filter. Additionally, certain boundary conditions such as a sufficient engine temperature or exhaust gas temperature must be ensured. It must also be ensured that appropriate conditions prevail during the entire regeneration. Usually, regeneration is ended when the soot accumulation in the particulate filter drops below a pre-given threshold. This is called complete regeneration.

[0003] It is disadvantageous in terms of energy to start a regeneration that cannot be ended due to the end of the motor vehicle journey. It should also be noted that the regeneration of the particulate filter is an exothermic process. Therefore, when the motor vehicle transitions to idling, there is a risk that the exhaust gas mass flow decreases in the case of a highly loaded particulate filter and that the temperature in the particulate filter increases when the oxygen partial pressure increases simultaneously, and this temperature increase may cause damage to the particulate filter. Therefore, JP 2003314250 A proposes estimating from the data of the motor vehicle navigation system how much time is still available until the end of the journey. Additionally, estimating from the data of earlier regenerations how long the regeneration will probably last. If the comparison of these data should result in the particulate filter regeneration no longer being able to be terminated before reaching the end of the journey, the start of the regeneration is suppressed. Summary of the Invention

[0004] A method for regenerating an exhaust particulate filter of a motor vehicle provides for predicting the driving route of the motor vehicle. For example, this can be done based on user input into the vehicle navigation system. However, it is also possible to apply a method for predicting the driving route that is independent of user input. The regeneration process is simulated at different starting time points on the predicted driving route. For the actual start of the regeneration, the starting time points are then selected at which the pre-given optimization criteria for the regeneration can be best met.

[0005] For this purpose, the regeneration process has been simulated in the past while driving on the said driving route. The regeneration is then simulated at each of the starting time points, where parameters from the current operating data of the motor vehicle can be supplied to the simulation respectively. If a later prediction of the driving route of the motor vehicle shows that the motor vehicle will move again on the driving route for which the regeneration process has been simulated, in the case of the required regeneration of the exhaust particulate filter, the best regeneration starting time point can be selected from the existing simulation data.

[0006] When simulating the regeneration process at different starting time points, at least one soot accumulation of the exhaust particulate filter, the speed of the motor vehicle, and the exhaust gas temperature of the motor vehicle are preferably considered as parameters. For this purpose, the soot accumulation can be expressed as a soot mass. In the first step of the simulation, the soot mass is set to a value at which regeneration usually starts. As the exhaust gas temperature, the exhaust gas temperature upstream of the exhaust particulate filter and particularly preferably also upstream of the turbine of the exhaust gas turbocharger of the motor vehicle is preferably used. This value can in particular be measured by means of a temperature sensor not far downstream of the internal combustion engine.

[0007] In particular, at each simulation, a waiting time related to the exhaust mass flow and the exhaust gas temperature can be waited for before starting the simulation. This takes into account the fact that after the start of the actual regeneration, it takes a certain amount of time until the exhaust system is preheated to such an extent that the soot is actually burned off.

[0008] Preferably, different starting time points are selected such that each starting time point has a pre-given minimum interval from the previous starting time point and, moreover, is at a time point at which there is no prohibition of the start of regeneration. Ideally, all the simulated regenerations start in this way at intervals from one another that correspond to the pre-given minimum interval. Thereby, a uniform simulation series is achieved, where on the one hand the minimum interval should be chosen so short that a large selection of starting time points is available, one of which can be used for the actual start of regeneration, and on the other hand not so many simulations are carried out that an unacceptably high computational effort would be incurred in this case. However, on the other hand, simulations of regenerations that cannot actually be carried out are also avoided, because the starting time points of such regenerations, for example, are during a parking state of the motor vehicle, which is a prohibition criterion for starting regeneration due to the low exhaust mass flow during idling.

[0009] In a preferred embodiment of the method, the optimization criterion is the time period required to reduce the soot accumulation in the exhaust particulate filter to a pre-given value. This pre-given value is in particular the value of the soot accumulation that is stored as a threshold in the control device of the motor vehicle, in the case of which the actual regeneration being carried out will also be aborted.

[0010] As an alternative to a pure optimization based on duration, in another embodiment of the method, preferably, the optimization criterion is the value F, which is calculated at least from the time period required to reduce the soot accumulation in the exhaust particulate filter to a pre-given value and from the amount of energy required for the regeneration. This calculation can be carried out according to Equation 1:

[0011] (Equation 1)

[0012] Here, ∆t represents the time period and E represents the amount of energy. f1 is an applicable cost factor for the regeneration duration, and f2 is an applicable cost factor for the amount of energy used. It is particularly preferred to incorporate other addends into the value F according to Equation 1 in order to obtain a more refined optimization criterion. In particular, the formation of nitrogen oxides and oil dilution during regeneration can be considered here. Again, a separate cost factor is assigned to each of these values.

[0013] From the simulation of the regeneration change process, it is also possible to identify from which point in time it may no longer be possible to fully execute regeneration on the predicted driving route. "Fully execute" is understood here to mean that the soot accumulation can be reduced to the value set for aborting the regeneration. Preferably, the starting point at which regeneration may not be fully executable is not selected, so as to thereby avoid strong heating of the exhaust particulate filter, which on the one hand can no longer be used for regeneration in the parked state of the motor vehicle due to the lack of exhaust mass flow, and on the other hand poses a risk of damaging the exhaust particulate filter.

[0014] In principle, different starting time points on the predicted driving route can be determined, for example, by means of a segment index or based on the sections of the motor vehicle's driving. However, preferably, the different starting time points are selected at the same straight-line intervals from each other. To simplify the calculations required therefor, it is furthermore preferred to perform the prediction of the driving route such that successive points are provided at the same straight-line intervals from each other on the driving route. Thus, the driving route can be defined by several points related to further prediction and stored in this way with a small amount of data.

[0015] The computer program is set up to perform each step of the method, especially when the computer program runs on a computing device or an electronic control device. This makes it possible to implement different embodiments of the method on the electronic control device without having to make structural changes to it.

[0016] By installing (Aufspielen) the computer program onto a conventional electronic control device, an electronic control device is obtained which is set up to perform the regeneration of the exhaust particulate filter of the motor vehicle by means of this method. Description of the Drawings

[0017] Embodiments of the present invention are shown in the drawings and are described in more detail in the following description.

[0018] Figure 1 A schematic diagram showing selected elements of a motor vehicle, the exhaust particulate filter of which can be regenerated by means of a method according to an embodiment of the present invention.

[0019] Figure 2 Schematically shows the implementation of selected calculation steps in a method according to an embodiment of the present invention.

[0020] Figure 3 The time courses of the vehicle speed and the soot accumulation of the exhaust particulate filter in an embodiment of the method according to the present invention are shown in two figures.

[0021] Figure 4 A flowchart showing an embodiment of the method according to the present invention is shown. Detailed implementation mode

[0022] Figure 1 An internal combustion engine 10 is shown, which is currently implemented as a diesel engine. The internal combustion engine has an exhaust gas turbocharger 20. The compressor 21 of the exhaust gas turbocharger 20 is arranged in the air supply device 11 of the internal combustion engine 10. The intake pipe 12 of the internal combustion engine 10 is located between the compressor 21 and the internal combustion engine 10. The exhaust gas of the internal combustion engine 10 is discharged into the exhaust pipe line 13. The turbine 22 of the exhaust gas turbocharger 20 is arranged in this exhaust pipe line. A temperature sensor 14 for measuring the exhaust gas temperature is located in the exhaust pipe line 13 between the turbine 22 and the internal combustion engine 10. An exhaust particulate filter 15 is arranged in the exhaust pipe line 13 downstream of the turbine 22. The internal combustion engine 10 is controlled by an electronic control device 16.

[0023] In an embodiment of the method according to the invention, each time the motor vehicle passes through a driving route, a large number of regenerations of the exhaust particulate filter 15 are simulated on this driving route. For this purpose, the driving route is divided into sequences with the same linear intervals between each other. The start and end of each sequence are stored as data points using their GPS data. Each simulation is performed in multiple traversals. As Figure 2 shown, in each traversal (Durchlauf), the soot accumulation mSot of the exhaust particulate filter 15 is used as an input parameter. Then, for each other traversal, the output parameter of the previous traversal is used as an input parameter. The soot accumulation mSot is fed to a first characteristic curve 31. In addition, the currently measured temperature T3 in the exhaust pipe line 13 upstream of the turbine 22 by means of the temperature sensor 14 is used as another input parameter for the calculation and is fed to a second characteristic curve 32. The speed Vehv of the motor vehicle is used as a third input parameter and is fed to a third characteristic curve 33. The values obtained from the three characteristic curves 31, 32, and 33 are multiplied by each other to determine the burned soot mass dmSotBurn. This soot mass is subtracted from the current soot accumulation mSot in order to obtain a new value of the soot accumulation mSot.

[0024] Figure 3 Shows the variation of the vehicle speed Vehv over time t for the driving route passed through within a time period of 1900 seconds. Each simulation of the regeneration starts at a fictional soot accumulation mSot of 25 g. Currently, this is the following soot accumulation, in which case the regeneration of the exhaust particulate filter would start in the conventional operation of the motor vehicle without using the method according to the invention. Then, according to Figure 2The simulated traversal until the soot accumulation mSot has been reduced to 10 g. This is the value at which the regeneration of the exhaust particulate filter is aborted during motor vehicle operation because the attempt to burn off additional soot would no longer be energy-efficient. The regeneration that reduces the soot accumulation mSot to 10 g is thus understood as a complete regeneration.

[0025] To perform the simulation, the minimum interval for the current pre-given simulation start point is 50 seconds. As long as there are no conditions due to which the start of the regeneration of the exhaust particulate filter 15 would be prohibited, the simulation starts at this minimum interval. However, due to the existence of prohibition conditions, the time interval between individual simulation starts can also increase. Therefore, the first simulation does not start at motor vehicle startup, but only starts after a time t of 125 seconds because the minimum speed Vehv of the motor vehicle has not been reached for the start of regeneration until then. In fact, some other time points that would apply to the start pattern due to the minimum interval are also not used because the vehicle speed Vehv is too low at the respective time points.

[0026] From Figure 3 it can be seen that a complete regeneration can be achieved when the regeneration starts for the last time (letztmals) after 775 seconds. All simulations of regenerations starting later end due to the motor vehicle stopping after 1800 seconds of driving with the soot accumulation mSot being greater than 10 g. The simulation results are stored together with the driving route. For this purpose, for each stored driving route, on the one hand, the following information is available, namely from which starting time point of the regeneration it can no longer be considered a complete regeneration until the end of the drive (last mile home), and on the other hand, for each starting time point of the regeneration, an estimate can be made: how long it will take until the value of the soot accumulation mSot is reduced to 10 g and thus the regeneration has been completely terminated. If the regeneration duration is used as an optimization criterion, the best starting time point of the regeneration can be selected in this way under possible regenerations.

[0027] In another embodiment of the method, the best starting time point is not selected solely based on the shortest possible regeneration duration. Instead, a value F is calculated for each simulated regeneration according to formula 1, which value depends on the regeneration duration and on the other hand depends on the energy E used for the regeneration. Then the starting time point of the regeneration for which the value F becomes the smallest is considered the best.

[0028] In one embodiment of the method according to the invention, after starting the motor vehicle, an attempt is made to predict the driving route of the motor vehicle. If the driver has not entered his driving destination into the navigation system of the motor vehicle, the starting position of the motor vehicle is compared with the starting position of the previous driving route of the motor vehicle. If a consistency is found here, an estimate is made based on the time and weekday when the stored driving route started in the past and the current weekday and current time: which of these driving routes the driver will most likely pass through, and this driving route is used as the predicted driving route. If a predicted driving route cannot be achieved in this way, the method according to the invention is ended, and the motor vehicle returns to its conventional regeneration strategy stored in the electronic control device 16 for its exhaust particulate filter 15. If, however, the prediction of the driving route is successful, a check is made: whether the soot accumulation mSot has become so large that there is a regeneration requirement for the current driving of the motor vehicle. If this is not the case, the method is also ended due to the return to the conventional regeneration strategy. If there is a regeneration requirement, a further check is made: whether the soot accumulation mSot has reached the threshold value for overloading the exhaust particulate filter 15 with soot. If this should be the case, regeneration needs to be introduced immediately, and the regeneration is started. If the soot accumulation mSot is high enough so that the exhaust particulate filter 15 should have been regenerated during the preceding driving, although the soot accumulation is not so high that immediate regeneration would be required, a further check is made: whether it will be possible to completely terminate the regeneration on the predicted driving route. If this is not possible, the regeneration is actively inhibited and the regeneration is postponed in this way. Return to step 40, in which it is checked whether the route is still being announced as before, whether the motor vehicle is therefore on the predicted route, or whether the motor vehicle has deviated from this predicted route. If the regeneration has not been inhibited, it is then checked: whether the optimal regeneration starting point determined based on the simulation of the possible regeneration starting points has been reached. If this is not the case, the start of the regeneration is also temporarily inhibited. Otherwise, the regeneration is started.

[0029] Conventional regeneration strategies that can be stored in the control device 16 already include a so-called measure for the regeneration benefit as a parameter for starting regeneration, in addition to the soot accumulation mSot. The value of this measure can be used to start regeneration more frequently at beneficial points than at unfavorable points. Here, for example, the benefit is determined based on the road type stored in the navigation system, where driving on a highway is considered beneficial for regeneration, while driving on an urban road is considered unfavorable for regeneration. In the currently described embodiment of the method according to the invention, regeneration is started by intervening in the conventional regeneration strategy. For this purpose, when the check 44 determines that the optimal starting position for regeneration has been reached, the measure of the benefit is set to its maximum value by the process of the method according to the invention, and regeneration is triggered in this way. For inhibition 53, the measure is set to "very unfavorable". If the soot mass should rise to a very high value, the electronic control device 16 will start an "emergency regeneration" even in a "very unfavorable" situation, which contributes to the robustness of the solution. In particular, error handling in the solution according to the invention is also saved in this way, because in case of doubt, the conventional logic circuit simply takes over. This enables the implementation of this embodiment of the method according to the invention in the electronic control device 16 with the already existing regeneration software, without having to completely replace the regeneration software with new software.

Claims

1. A method for regenerating (52) an exhaust particulate filter (15) of a motor vehicle, wherein a course of the regeneration is simulated at different starting time points on a predicted driving route of the motor vehicle, and in order to perform the regeneration (52), a starting point is selected at which a pre-given optimization criterion for the regeneration is best met, wherein the optimization criterion is a value calculated at least from the time period required to reduce the soot accumulation (mSot) of the exhaust particulate filter (15) to a pre-given value and from the energy required for the regeneration, i.e., F = f1·Δt + f2·E, where F is the value of the optimization criterion, Δt is the time period, and E is the energy, f1 is an applicable cost factor for the regeneration duration, and f2 is an applicable cost factor for the energy used, and wherein the starting time point is regarded as optimal according to the regeneration for which the value F becomes minimum.

2. The method according to claim 1, wherein For the predicted driving route, the time courses of the soot accumulation (mSot) of the exhaust particulate filter (15), the speed (Vehv) of the motor vehicle, and the exhaust gas temperature (T3) of the motor vehicle have been respectively determined when the driving route was previously traveled, and these parameters (mSot, Vehv, T3) are used when simulating the course of the regeneration at different starting time points.

3. The method according to claim 1 or 2, characterized in that, Different starting time points are selected such that each starting time point has a pre-given minimum interval from the previous starting time point and is located at a time point at which there is no prohibition for the start of the regeneration (52).

4. The method according to claim 1 or 2, characterized in that, The optimization criterion is the time period required to reduce the soot accumulation (mSot) of the exhaust particulate filter (15) to a pre-given value.

5. The method according to claim 1 or 2, characterized in that, A starting point that may not be able to fully perform the regeneration (52) on the predicted driving route is not selected.

6. The method according to claim 1 or 2, characterized in that, On the predicted driving route, different starting time points are selected at the same linear interval.

7. The method according to claim 6, characterized in that, The prediction of the driving route is carried out such that successive points are provided on the driving route at the same linear interval from each other.

8. A computer program product having a computer program, the computer program being configured to perform each step of the method according to any one of claims 1 to 7.

9. A machine-readable storage medium having stored thereon a computer program, the computer program being configured to perform each step of the method according to any one of claims 1 to 7.

10. An electronic control device (16), the electronic control device being configured to perform the regeneration (52) of an exhaust particulate filter (15) of a motor vehicle by means of the method according to any one of claims 1 to 7.

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