Method for carrying out the regeneration of a particulate filter

Abstract

A method for regenerating a particulate filter (4) arranged in the exhaust system (3) of a motor vehicle internal combustion engine (1), in which a fuel containing hydrocarbons is metered into the exhaust system (3) upstream of an oxidation catalyst (10) located upstream of the particulate filter in the exhaust system, in order to heat the particulate filter (4) to a temperature required for burning off soot accumulated in the particulate filter (4) by means of exothermic oxidation of the metered fuel in the oxidation catalyst (10), wherein the metering of the fuel is started when a temperature value relevant for the temperature of the oxidation catalyst (10) has reached a predefinable temperature threshold, characterized in that that if, after the start of the metering, the exhaust gas temperature on the outlet side of the oxidation catalyst (10) is more than a predefinable amount below a predefinable temperature setpoint, the ongoing metering of the fuel is stopped and the temperature threshold is incrementally adapted by increasing it by a predefinable incremental amount, and following the incremental adaptation of the temperature threshold, the metering of the fuel is restarted when the temperature of the oxidation catalyst (10) has reached the incrementally adapted temperature threshold, and that after a definable waiting time (t1; t2; t3; t4; t5) without incremental adaptation of the temperature threshold, the temperature threshold is decrementally adapted by lowering it by a predefinable decrement amount.

Description

[0001] The invention relates to a method for carrying out a regeneration of a particulate filter arranged in the exhaust system of a motor vehicle internal combustion engine, in which a fuel containing hydrocarbons is metered into the exhaust system upstream of an oxidation catalyst arranged upstream of the particulate filter in the exhaust system in order to heat the particulate filter to a temperature required for burning off soot accumulated in the particulate filter by means of an exothermic oxidation of the metered-in fuel in the oxidation catalyst, wherein the metering of the fuel is started when a temperature value relevant for a temperature of the oxidation catalyst has reached a predeterminable temperature threshold value.

[0002] A generic method is described, for example, in RUDELT, J., et al.: Exhaust-side fuel injection for active particulate filter regeneration, in: MTZ Motortechnische Zeitschrift, 12 / 2005. Furthermore, the method is known from US Pat. No. 8,141,348 B2. In this method, the fuel is metered into the exhaust gas, at least for a certain period of time, even when the exhaust gas temperature at the inlet side of the oxidation catalyst is below the light-off temperature of the oxidation catalyst, provided the oxidation catalyst is still sufficiently warm to oxidize the metered fuel. Furthermore, such a method is also known from US Pat. No. 9,181,841 B2.

[0003] A disadvantage of this process is that if the oxidation catalyst is insufficiently active, the oxidation reaction can cease (so-called light-out). The oxidation catalyst and / or any downstream exhaust aftertreatment components, such as an SCR catalyst downstream of the particulate filter, can then be passivated or damaged as a result of fouling with added, but not oxidatively converted, hydrocarbons.

[0004] The object of the invention is to provide a method which enables a particle filter to be reliably heated to a temperature required for soot combustion while avoiding the disadvantages mentioned.

[0005] This object is achieved by a method having the features of claim 1.

[0006] The method according to the invention provides that fuel metering for heating the particulate filter is started when a temperature value relevant for a temperature of the oxidation catalyst has reached a predeterminable temperature threshold. If, after the start of fuel metering, an exhaust gas temperature at the outlet side of the oxidation catalyst is more than a predeterminable amount below a predeterminable temperature target value, the ongoing fuel metering is stopped and the temperature threshold is incrementally adapted by increasing it by a predeterminable incremental amount. Following the incremental adaptation of the temperature threshold, fuel metering is restarted when the temperature value relevant for the temperature of the oxidation catalyst has reached the incrementally adapted temperature threshold.“Subsequently” means a comparatively short period of time of a few minutes, preferably less than 5 minutes, particularly preferably less than 1 minute.

[0007] The metered fuel is preferably the fuel that is also burned for propulsion purposes in the internal combustion engine of the motor vehicle and stored in a storage tank. This fuel is preferably fed into the exhaust gas downstream of the engine by means of a separate metering unit, such as a nozzle or an injector. The fuel can be fed into the exhaust gas in at least partially vaporized form, but it is preferably added to the exhaust gas in liquid form as a fine spray under pressure. The fuel is added upstream of the oxidation catalyst with respect to the exhaust gas flow, preferably close to the internal combustion engine. The metering can take place downstream of the turbine of an exhaust gas turbocharger, if provided. However, it can also take place upstream of such a turbine, in particular into an exhaust manifold of the internal combustion engine.

[0008] The procedure according to the invention enables an effective response to a change, in particular a reduction in the catalytic effectiveness of the oxidation catalyst with respect to oxidation of the metered fuel. This can occur, for example, if the oxidation catalyst has been passivated or partially poisoned by harmful substances or if a poorly oxidizable fuel, such as fatty acid methyl ester (FAME), was used instead of mineral diesel.

[0009] The decisive temperature value that is compared with the temperature threshold value is preferably a value for the exhaust gas temperature measured on the inlet side or upstream of the oxidation catalyst. It can of course also be provided to record the temperature of the oxidation catalyst directly using a temperature sensor introduced into the catalyst body. Furthermore, the temperature value considered decisive for the temperature of the oxidation catalyst can also be determined by mathematical simulation. In any case, when the decisive temperature value has reached the specified temperature threshold value, it is assumed that the oxidation catalyst has reached or exceeded its light-off temperature for oxidizing the added hydrocarbons, i.e. an oxidative conversion of the added hydrocarbons in the oxidation catalyst can take place to a significant extent.In this respect, the temperature threshold should be considered an assumed light-off temperature of the oxidation catalyst. Therefore, if the relevant temperature value is at least as high as the stored temperature threshold, fuel metering begins to heat the particulate filter to the required regeneration temperature—typically 400°C to 650°C—using the additional exothermic energy generated in or on the oxidation catalyst.

[0010] Since the exhaust gas temperature upstream of the oxidation catalyst typically falls below the temperature threshold during normal operation of the internal combustion engine over a wide operating range, it is usually necessary to raise the exhaust gas temperature upstream of the oxidation catalyst when there is a valid request to regenerate the particulate filter. To achieve this, engine-related measures such as adjusting injection times or injection quantities of a main or post-injection, adjusting valve opening or closing times, activating electrical consumers, throttling the combustion air supply, or similar measures can be taken. However, exhaust gas heating is also possible, particularly using an electric heater element in the exhaust system. These measures can be terminated when the increase in exhaust gas temperature achieved as a result of the oxidation of subsequently metered fuel is sufficient to cause soot burnoff in the particulate filter.The latter is ensured by comparing the exhaust gas temperature at the outlet of the oxidation catalyst with a predeterminable temperature setpoint. If this temperature exceeds the exhaust gas temperature at the outlet after dosing has started and is ongoing, the fuel dosing is preferably stopped immediately, but in any case within a short time. The temperature comparison, which is crucial for continuing or stopping fuel dosing, preferably takes place immediately or at least very quickly after the start of dosing and preferably remains active throughout the entire ongoing dosing.

[0011] Preferably, the exhaust gas temperature is measured at the outlet side of the oxidation catalyst or between the oxidation catalyst and the particulate filter. The temperature setpoint is preferably calculated as a function of the metered fuel quantity and preferably also as a function of the prevailing operating conditions of the internal combustion engine, or is taken from a corresponding characteristic map.

[0012] Comparing the exhaust gas temperature at the outlet side of the oxidation catalyst with the temperature target value makes it possible to determine whether the oxidation catalyst has sufficient catalytic activity to achieve the intended exhaust gas heating. If the exhaust gas temperature at the outlet side of the oxidation catalyst is more than a predefined amount, for example, 15 K, below a predefined temperature target value after the start of fuel metering, this is considered unrealistic, or the catalytic activity is considered insufficient, and the ongoing fuel metering is stopped. This advantageously prevents the oxidation catalyst from becoming passivated as a result of the adsorption of unreacted or currently unconvertible fuel components on its surface, or from hydrocarbons slipping through the oxidation catalyst.Any adverse impairment of the function of the oxidation catalyst or a downstream catalytically active exhaust aftertreatment component can thus be effectively avoided.

[0013] According to the invention, a catalyst activity determined to be too low is taken into account by incrementally adapting the temperature threshold by increasing it by a predeterminable increment. This means that a higher light-off temperature than the originally assumed is assumed and this temperature is increased. In this case, the engine-related or other heating measures are preferably temporarily interrupted or reduced to allow the oxidation catalyst to cool below the original temperature threshold before the increment is carried out. The regeneration process is then restarted or continued by reheating the oxidation catalyst or the exhaust gas supplied to it or heating it again or more intensively using the heating measures mentioned.Fuel dosing is subsequently restarted when the temperature value determining the oxidation catalyst temperature has reached the incrementally adapted temperature threshold. This enables a highly probable successful implementation of thermal particulate filter regeneration through soot burnoff, particularly while avoiding adverse effects caused by unburned hydrocarbons.

[0014] If, following an incremental adaptation of the temperature threshold and after resuming fuel dosing, it turns out that the required activity of the oxidation catalyst is again lacking because the predeterminable temperature target is again undershot by more than a permissible amount, the described procedure is repeated and the temperature threshold, i.e., the assumed light-off temperature, is incremented again. This takes into account, in particular, an unexpected loss of activity and enables the implementation of a subsequent successful particulate filter regeneration with a particularly high probability.

[0015] In the event of a temporary loss of activity of the oxidation catalyst, once the loss of activity has disappeared or been mitigated, it is possible and advantageous to restart fuel metering at lower temperatures to avoid unnecessary other heating measures. Such a case can occur, for example, if a relatively difficult-to-oxidize fuel is refueled with a more easily oxidized fuel. According to the invention, this is taken into account by decrementally adapting the temperature threshold by a predeterminable amount after a definable waiting period without incremental adaptation of the temperature threshold.In one embodiment of the invention, it is provided that the waiting time is determined at least by a number of particle filter regenerations and / or refueling operations carried out and / or by a quantity of fuel consumed by the internal combustion engine and / or by a distance traveled by the motor vehicle.

[0016] In a further embodiment of the invention, the waiting time is determined by a sequence and / or by a number of previous incremental and / or decremental adaptations of the temperature threshold. This makes it particularly advantageous to evaluate the history of increments and decrements performed, thereby avoiding undesirably frequent adaptation of the temperature threshold or potentially unstable behavior.

[0017] In a particularly advantageous further embodiment of the invention, the decrement amount is selected to be smaller than the increment amount. This minimizes the risk of excessive decrementation and thus an initially unsuccessful start of the particulate filter regeneration.

[0018] In a further embodiment of the method according to the invention, the increment amount is specified as a function of the exhaust gas mass flow. This takes into account the fact that the light-off temperature of the oxidation catalyst, or its change, is generally dependent on the flow rate. Specifically, an increasing increment amount can be provided for increasing exhaust gas flow rates or space velocities.

[0019] In a further embodiment, the temperature threshold is changed depending on the temperature load on the oxidation catalyst. In particular, the temperature threshold is increased by an evaluation of the operating temperatures of the oxidation catalyst, weighted in terms of duration and temperature level. This makes it possible to take into account any thermal aging that may occur. For example, based on an assessed recording of a thermal load on the oxidation catalyst, an aging index can be determined, and the temperature threshold can be continuously adjusted, i.e., increased if necessary, depending on this aging index. Preferably, the adjustment is provided in parallel with and independently of incremental and / or decremental adaptations of the temperature threshold.

[0020] In a further embodiment of the method, the temperature setpoint is calculated mathematically from the expected exhaust gas temperature increase resulting from the exothermic oxidation of the metered fuel in the oxidation catalyst. For this purpose, an exothermic model can be provided, which preferably takes into account at least the calorific value of the supplied fuel as well as heat losses and heat capacities of exhaust system components that influence exhaust gas heating, in particular the oxidation catalyst. This enables a reliable estimate of the heating effect expected from fuel oxidation, and the activity of the oxidation catalyst can be assessed particularly reliably.

[0021] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the descriptions of the figures and / or shown alone in the figures, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0022] Showing: Fig. 1 a schematic representation of an internal combustion engine with associated exhaust particulate filter, Fig. 2 a schematic representation of waiting time states in the form of a state diagram with a constant temperature threshold, and Fig. 3 an exemplary time diagram with increments and decrements of the temperature threshold value and corresponding changes of waiting time states.

[0023] In the Fig. Figure 1 shows an internal combustion engine 1 of a motor vehicle with an intake air line 2 and an exhaust system 3. The internal combustion engine 1 is preferably designed as a direct-injection diesel engine. However, the following explanations can equally apply to a spark-ignition engine, in particular a lean-burn direct-injection gasoline engine.

[0024] An oxidation catalyst 10 is arranged upstream of an exhaust particulate filter 4 in the exhaust system 3. The oxidation catalyst 10 is preferably designed as a metal or ceramic honeycomb support with an oxidation-catalytically active coating. The exhaust particulate filter 4 is preferably designed as a cordierite- or SiC-based honeycomb with flow through its wall and preferably has an oxidation-catalytically active coating or a coating that promotes soot combustion and / or a catalytic coating corresponding to an SCR catalyst.

[0025] Furthermore, pressure sensors 5, 6 are arranged in the exhaust system 3, with which a pressure loss across the exhaust particulate filter 4 can be determined. In the present case, the pressure sensors 5, 6 are arranged on the inlet and outlet sides of the exhaust particulate filter 4, whereby the pressure sensor 5 can also be provided on the inlet side of the oxidation catalyst 10. Furthermore, temperature sensors 11, 12 are provided on the inlet and outlet sides of the oxidation catalyst 10, with which a respective exhaust gas temperature can be detected. Furthermore, a secondary injection valve 13 is provided upstream of the oxidation catalyst 10, by means of which fuel can be metered into the exhaust gas. A corresponding fuel supply line is designated by the reference numeral 14. In the present case, the fuel used to drive the diesel engine 1 is supplied to the exhaust gas.

[0026] The sensors 5, 6, 11, 12, as well as the injection valve 13, are connected via signal or control lines 8 to an electronic control unit 7, which is connected to the diesel engine 1 via a preferably bidirectional control line 9 for controlling or regulating engine operation. The control unit 7 is also connected to other sensors and actuators (not shown here) for detecting and adjusting the engine operation and the driving state of the motor vehicle. It is understood that the diesel engine 1 may have other components (not shown here), such as an exhaust gas turbocharger, an exhaust gas recirculation system, or other catalytically active exhaust gas purification components upstream and / or downstream of the exhaust gas particulate filter 4, which are not separately shown here.In particular, an SCR catalyst effective for selective nitrogen oxide reduction in the presence of excess oxygen using ammonia as a reducing agent can be provided downstream of the exhaust particulate filter 4 in the exhaust system 3. The respective operating states of these components can preferably be detected via corresponding sensors and transmitted to the control unit 7.

[0027] The control unit 7 is particularly capable of intervening in engine operation, resulting in a change in the exhaust gas composition and a heating of the exhaust gas. This primarily includes changes to the injection parameters, such as the number of fuel injections per working cycle, as well as changes to their timing and duration. In this way, the combustion and exhaust gas temperatures can be influenced, as can the exhaust gas composition, in particular the NOx and particulate content. Furthermore, by changing the injection quantity, the air / fuel ratio of the air-fuel mixture processed in the diesel engine 1 can be adjusted; for this purpose, corresponding adjustment elements (not shown in detail here) are provided.Likewise, an exhaust gas recirculation rate can be changed as needed, or a vane position of a VTG exhaust gas turbocharger or a wastegate position of a wastegate turbocharger can be changed accordingly, for example, if an increase in NOx emissions is requested for soot oxidation in the exhaust particulate filter 4. The control unit 7 is thus capable of determining or adjusting all operationally relevant operating parameters of the diesel engine 1 and the exhaust system. For this purpose, characteristic maps or characteristic curves and / or calculation programs are stored in a memory of the control unit 7, from which operating variables to be adjusted can be set in a controlled or regulated manner, or from which output variables derived from input variables can be determined.

[0028] Soot particles emitted by the diesel engine 1 are filtered out of the exhaust gas supplied to it by the exhaust particulate filter 4 during operation. Depending on the operating state of the diesel engine 1, these can be oxidized to a greater or lesser extent with NO2 formed at the oxidation catalyst to CO and / or CO2 and thus removed from the exhaust particulate filter 4. During normal driving, however, the soot emission and deposition rate of soot particles in the exhaust particulate filter 4 is often greater than the oxidation rate, which is why there is usually a gradual increase in the amount of soot accumulated in the exhaust particulate filter 4. Accordingly, the flow resistance and pressure loss of the exhaust particulate filter 4 increase, which impairs engine operation.For this reason, particulate filter regenerations are carried out from time to time, during which conditions are created for accelerated oxidation of accumulated soot, particularly with the oxygen contained in the exhaust gas (soot burn-off).

[0029] The need for particulate filter regeneration is preferably determined from the pressure loss determined across the exhaust particulate filter 4 by means of sensors 5, 6, or from a value derived therefrom for the flow resistance and / or the accumulated soot quantity, and / or from a soot loading of the exhaust particulate filter 4 additionally determined from another loading model. A soot loading model preferably takes into account the existing exhaust gas temperatures, the NO2 and O2 concentrations in the exhaust gas on the inlet side of the exhaust particulate filter 4, the soot mass flow, and the temperature of the exhaust particulate filter 4 in order to continuously estimate the accumulated soot quantity. If the corresponding input variables cannot be determined by direct measurement, their determination is provided from characteristic curves or maps stored in the control unit 7 or from calculation models.During normal operation, a soot regeneration process is initiated when it is determined that the soot load or a value correlated therewith exceeds a predeterminable threshold, which typically corresponds to a soot load value of approximately 10 g / l. Depending on the operating conditions, this is the case after several hundred to several thousand kilometers of driving. However, particulate filter regenerations can also be scheduled at predefined, regular intervals or intervals dependent on the driving conditions. The conditions set for particulate filter regeneration are preferably maintained for as long as necessary to burn off the deposited soot. In accordance with the reduced soot load of the exhaust particulate filter 4, its flow resistance or the pressure loss across the exhaust particulate filter 4 decreases, so that proper operation of the diesel engine 1 is restored.

[0030] For particulate filter regeneration with accelerated oxidation of accumulated soot by oxidation with oxygen contained in the exhaust gas, the exhaust particulate filter 4 or the exhaust gas flowing into it must be heated to a temperature of 400°C to 650°C or even higher. This is achieved largely by exothermic oxidation of fuel metered into the exhaust gas via the injection valve 13 at the oxidation catalyst 10. Preferably, the metering rate is temperature-controlled such that a predeterminable target temperature downstream of the exhaust particulate filter 4 is at least largely maintained.

[0031] However, the oxidation catalyst 10 is only capable of oxidizing metered fuel to a significant extent above a so-called light-off temperature of typically 220°C to 280°C. Since these temperatures are not reached in many operating ranges of the diesel engine, it is intended that, when a request for particulate filter regeneration is made, the oxidation catalyst 10 is first heated to its light-off temperature. Once this has been achieved, fuel metering begins via the injection valve 13 in order to achieve the further required heating of the exhaust gas or the exhaust particulate filter 4 through exothermic oxidation of the metered fuel at the oxidation catalyst 10.To heat the oxidation catalyst 10 to its light-off temperature, predeterminable operating variables of the diesel engine 1, such as combustion lambda, EGR quantity, pressure, quantity, timing and progression of fuel injections, charge air temperature, and possibly other variables, are preferably adjusted, particularly depending on the driving condition and load. If it is determined that the oxidation catalyst 10 is sufficiently active to initiate or maintain soot burnoff in the particulate filter by oxidizing the metered-in fuel, the engine warm-up measures are preferably terminated or at least reduced.

[0032] In practice, it has proven difficult to reliably determine whether the oxidation catalyst 10 has reached its light-off temperature and is thus able to enable fuel oxidation to heat the exhaust gas particulate filter 4 as intended. This is particularly because the light-off temperature depends on various operating conditions, such as the exhaust gas throughput, and can also change due to difficult-to-predict circumstances, such as the occurrence of passivation or the like. For this reason, the invention provides for adapting an assumed light-off temperature of the oxidation catalyst 10 based on a first initial value, i.e. for adjusting the assumed light-off temperature under certain conditions over the course of the operating time.In this case, fuel metering via the injection valve 13 only begins when the exhaust gas temperature measured by the temperature sensor 11 arranged on the inlet side of the oxidation catalyst 10 has reached the current value for the assumed light-off temperature. In other words, a temperature value relevant to the oxidation catalyst 10 is measured by the temperature sensor 11 and compared with a predeterminable temperature threshold value as the assumed value for the light-off temperature. Fuel metering only begins when the comparison shows that the exhaust gas temperature measured at the inlet side of the oxidation catalyst 10 has reached the temperature threshold value representing the light-off temperature.

[0033] If the temperature threshold proves to be sufficiently high and thus the oxidation catalyst 10 is sufficiently active upon reaching the temperature threshold, the metered fuel can be oxidized by the oxygen present in the exhaust gas of the lean-burn diesel engine 1, releasing heat, and the particulate filter 4 can be heated. This is verified in the control unit 7 by evaluating the temperature value detected by the output temperature sensor 12. This occurs by comparing the exhaust gas temperature detected by the temperature sensor 12 at the output of the oxidation catalyst 10 with a temperature setpoint provided by the control unit 7. In this case, this temperature setpoint is calculated in real time based on a computer model or provided in the form of a pre-calculated value read from stored characteristic maps or characteristic curves.

[0034] If the comparison shows that the detected temperature value is more than a predeterminable amount below the target temperature, the heat release or temperature increase is lower than what would at least be expected based on sufficient oxidation of the metered fuel. It can therefore be assumed that the oxidation catalyst 10 had not reached its light-off temperature at the start of fuel metering, and the temperature threshold value, as the assumed value for the light-off temperature of the oxidation catalyst 10, is incrementally adapted in this case, i.e., increased by a predeterminable amount, for example, 10 K. Furthermore, the metering process that has been running since the start of fuel metering is stopped.Active engine heating measures are also at least partially and at least temporarily terminated or reduced, whereby the exhaust gas temperature measured at the inlet side of the oxidation catalyst 10 drops at least below the adapted temperature threshold, but preferably also below the temperature threshold valid before the incremental adaptation. If, upon subsequent resumption of the heating measures, the exhaust gas temperature measured by the inlet temperature sensor 11 rises again to or above the temperature threshold now increased by the incremental adaptation, the fuel metering is restarted and a renewed verification of the catalyst activity takes place as explained above. In the event that the oxidation catalyst 10 is now verified as sufficiently active, it is intended to complete the particulate filter regeneration, i.e.to maintain the particulate filter 4 at a temperature required for soot burnoff until the accumulated soot has at least largely burned off. For this purpose, fuel metering is continued for a correspondingly long period of time under temperature control. Preferably, the exhaust gas temperature detected at the outlet of the oxidation catalyst 10 is monitored throughout the entire particulate filter regeneration with fuel metering to ensure that the temperature does not fall too far below the setpoint. This enables continuous monitoring of the oxidation catalyst 10 for a possible light-out, whereupon the particulate filter regeneration can be interrupted or aborted, and the temperature threshold value can be incremented if necessary.

[0035] However, if the temperature value detected at the output of the oxidation catalyst 10 is again more than a predeterminable amount below the temperature setpoint, the initiated regeneration process can be interrupted again, and a further incremental adaptation of the temperature threshold can take place, resulting in a gradual approximation to a value that ultimately proves to be sufficiently large for the assumed light-off temperature. If more than a predeterminable number of directly consecutive incremental adaptations of the temperature threshold are required, an error message is output. In such a case, an irreparable error, such as an impermissible deactivation of the oxidation catalyst 10 or a malfunction of the metering valve 13, is assumed.Typically, however, a single incremental correction leads to stable conditions, at least for some time, so that several consecutive particulate filter regenerations can be carried out without changing the temperature threshold.

[0036] However, the inventors have recognized that an incremental adaptation of the temperature threshold may only be necessary due to a temporary deterioration in the activity of the oxidation catalyst 10. In such a case, an improvement in the activity of the oxidation catalyst 10 occurs again after some time. To take this into account and to prevent the temperature threshold from remaining permanently set unnecessarily high, which would entail corresponding fuel consumption disadvantages, it is provided to decrement the temperature threshold again after a definable waiting period without incremental adaptation of the temperature threshold. In order to exclude the unsuccessful start of a particulate filter regeneration as far as possible, the decrement is preferably selected to be smaller than the increment, with, for example, 5 K as the decrement amount.

[0037] The waiting time preferably comprises a period corresponding to a predeterminable distance traveled, for example, several thousand kilometers or a corresponding fuel consumption and / or a period corresponding to a predeterminable number of consecutive particulate filter regenerations without incremental adaptation of the temperature threshold. It has proven particularly advantageous if the waiting time is set in accordance with the history of previous incremental and / or decremental adaptations of the temperature threshold. In a particularly advantageous embodiment of the procedure according to the invention, different waiting times are set as different states in the manner of a state machine. The following is based on Fig. 2 explains an advantageous approach in more detail.

[0038] In the Fig. The state diagram schematically illustrated in Figure 2 shows operating states generally designated tx and ty as waiting times t1, t2, t3, t4, t5, within which operation with particulate filter regenerations with a constant temperature threshold occurs. Each waiting time tx is set to be shorter than a higher-indexed waiting time tx+1. Thus, waiting time t5 is longer than waiting time t4, which in turn lasts longer than waiting time t3, etc. The intention is to select waiting times t4 and t5 to be significantly longer, for example, more than four times as long as the other waiting times, since these states can be considered stable, learned states. In particular, t5 is selected to be significantly longer than t4.

[0039] If a respective waiting time tx has elapsed without an incremental adaptation of the temperature threshold having been performed, the temperature threshold is decremented and the system switches from the state with the waiting time tx to the state with the waiting time ty according to the arrows dxy. However, if an incremental adaptation of the temperature threshold proves necessary within a state with the waiting time tx, i.e., before the waiting time tx has expired, the system immediately exits the state with the waiting time tx and switches to the state with the waiting time ty with an incremental adaptation of the temperature threshold according to the arrows ixy.

[0040] Preferably directly in conjunction with the first particulate filter regeneration after initial commissioning of the exhaust gas aftertreatment system or the exhaust gas particulate filter 4 and / or the oxidation catalyst 10, an entry into the waiting state t1 occurs according to the arrow init. If this had to be aborted or interrupted because the starting value for the temperature threshold was too low, i.e. the light-off temperature of the oxidation catalyst was assumed to be too low and after reaching the temperature threshold and starting the fuel metering, the temperature detected on the output side of the oxidation catalyst 10 remained more than the predetermined amount below the temperature target value, then preferably a comparatively strong increment of the temperature threshold by, for example, 25 K is carried out.If the first particulate filter regeneration was successfully performed using the initial temperature threshold value without incrementing it, the temperature threshold is retained unchanged. This ensures that particulate filter regenerations can be successfully performed very quickly and without interruption in a new system, with a high probability.

[0041] The preferred approach described is explained below using a concrete example, for which a Fig. Reference is made to the temperature-time diagram shown in Figure 3.

[0042] In the Fig. 3, it is assumed that at time t0, particulate filter regeneration is carried out for the first time in a new exhaust system. It is further assumed that the value T0 is stored as the starting value for the temperature threshold value that determines the start of fuel metering. By way of example, it is further assumed here that after the initially stored temperature threshold value T0 is reached on the inlet side of the oxidation catalyst 10 and fuel metering begins, the exhaust gas temperature detected on the outlet side of the oxidation catalyst 10 is more than permitted below the temperature setpoint also stored in the control unit 7. It is therefore assumed that the value T0 originally assumed as the light-off temperature of the oxidation catalyst 10 is set too low. The fuel metering is then interrupted and the temperature threshold value is incrementally increased.The incrementation provided for in this case during the first particulate filter regeneration is carried out comparatively strongly, namely by 25 K in this case, and a jump into the state of the waiting time t1 takes place according to the one determined using . Fig. 2 explained procedure.

[0043] Assuming that a further incremental adaptation of the temperature threshold is not required for particle filter regenerations carried out within the waiting time t1, the temperature threshold is adapted in a decrementing manner after the waiting time t1 has elapsed, in this case by 5 K. This results in a transition to the state of waiting time t2. If, for particle filter regenerations carried out within the waiting time t2, which is longer than t1, no incremental adaptation of the temperature threshold is required, the temperature threshold is adapted again in a decrementing manner after the waiting time t2 has elapsed, again by 5 K, and a transition to the state of waiting time t3 takes place, which is again selected to be longer than t2. If, as in Fig. 3, even if particle filter regenerations have taken place within the waiting time t3, no further incremental adaptation of the temperature threshold value is required, the temperature threshold value is again adapted in a decrementing manner after the waiting time t3 has elapsed, in this case again by 5 K.

[0044] However, in the case of a state with a waiting time t3 that has been terminated by decrementing the temperature threshold, no transition to a state with a different waiting time is provided, but rather the state with the waiting time t3 is entered again and the corresponding waiting time is restarted. In contrast, in the case of an incrementing adaptation of the temperature threshold within the state with the waiting time t3, the state with the waiting time t3 is immediately left and transitioned to the state with the waiting time t4 that is longer than t3. This is shown in the diagram by Fig. This is the case at time ta in the example shown in Figure 3. The increment of the temperature threshold is 10 K, which is twice as high as the decrements. If, with the now increased temperature threshold, no increment of the temperature threshold is required within the state with the waiting time t4, then, as in Fig. 3, with a decrementing adaptation of 5K, the temperature threshold would be transitioned to the state with the further extended waiting time t5. In the case of a required increment of the temperature threshold within the state with the waiting time t4, as is the case with other increments, an immediate exit from the state would be provided. In the case of exiting the state with the waiting time t4, a transition to the state with the waiting time t1 would be provided, which is shown in the diagram of Fig. 3 is not shown, but the state diagram of Fig. 2 can be removed.

[0045] As already mentioned, the decrements are intended to be less significant than the increments. Preferably, the decrements are approximately half as large as the increments, whereby the stated values ​​of 5 K and 10 K are merely preferred values, and other values ​​can also be selected. Preferably, an increment is based on a base value of, for example, 10 K, which is changed depending on the exhaust gas mass flow, in particular, increased with increasing exhaust gas mass flow. The same can be provided for the decrement value.

[0046] In order to take into account any deterioration in the activity of the oxidation catalyst 10, which may occur, in particular gradually, as a result of thermal aging, it is provided that a thermal aging state of the oxidation catalyst 10 is continuously determined. The temperature threshold value is increased in accordance with the progressive aging, which preferably occurs gradually or in steps depending on a determined aging characteristic value. Such an aging characteristic value A can, for example, be determined as a function of the temperature T of the oxidation catalyst 10 by A=k(T)*∫Tndt where k is a predefined constant and n is a predefined exponent. The temperature threshold can be continuously adapted additively or multiplicatively, independent of any increments or decrements made, with the aging parameter A.

Claims

[1] Method for carrying out a regeneration of a particulate filter (4) arranged in the exhaust system (3) of a motor vehicle internal combustion engine (1), in which a hydrocarbon-containing fuel is metered into the exhaust system (3) upstream of an oxidation catalyst (10) arranged upstream of the particulate filter in the exhaust system, in order to heat the particulate filter (4) to a temperature required for burning off soot accumulated in the particulate filter (4) by means of an exothermic oxidation of the metered-in fuel in the oxidation catalyst (10), wherein the metering of the fuel is started when a temperature value relevant for a temperature of the oxidation catalyst (10) has reached a predeterminable temperature threshold value, characterized by , that in the event that, after the start of the dosing, an exhaust gas temperature on the outlet side of the oxidation catalyst (10) is more than a predeterminable amount below a predeterminable temperature setpoint, the ongoing dosing of the fuel is stopped and the temperature threshold is incrementally adapted by increasing it by a predeterminable incremental amount and, following the incremental adaptation of the temperature threshold, the dosing of the fuel is restarted when the temperature of the oxidation catalyst (10) has reached the incrementally adapted temperature threshold, and that after a definable waiting time (t1; t2; t3; t4; t5) without incremental adaptation of the temperature threshold value, the temperature threshold value is decrementally adapted by lowering it by a predefinable decrement amount. [2] Method according to claim 1, characterized bythat the waiting time (t1; t2; t3; t4; t5) is determined at least by a number of particle filter regenerations carried out and / or by a quantity of fuel consumed by the internal combustion engine (1) and / or by a distance traveled by the motor vehicle. [3] Method according to claim 1 or 2, characterized by that the decrement amount is chosen to be smaller than the increment amount. [4] Method according to one of claims 1 to 3, characterized by that the temperature threshold value is changed depending on a temperature load of the oxidation catalyst (10). [5] Method according to one of claims 1 to 4, characterized by that the increment amount is specified depending on the exhaust gas mass flow. [6] Method according to one of claims 1 to 5, characterized bythat the temperature setpoint is calculated from an exhaust gas temperature increase to be expected as a result of the exothermic oxidation of the metered fuel in the oxidation catalyst (10). [7] Method according to one of claims 1 to 6, characterized by that the temperature value relevant for the temperature of the oxidation catalyst (10) is determined by an exhaust gas temperature measured on the inlet side of the oxidation catalyst (10). [8] Method according to one of claims 1 to 7, characterized by that the waiting time (t1; t2; t3; t4; t5) is further determined by a sequence and / or by a number of previous incrementing and / or decrementing adaptations of the temperature threshold value.

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