HK1220241B - Method for operating an exhaust gas aftertreatment device - Google Patents

Description

Method for operating an exhaust gas aftertreatment device

Technical Field

The invention relates to a method for operating an exhaust gas aftertreatment device with a diesel particle filter and a device for controlling the exhaust gas aftertreatment device. The invention also relates to an exhaust gas aftertreatment device and an internal combustion engine.

Background Art

The prior art discloses the use of diesel particle filters for cleaning exhaust gases of soot particles. Diesel particle filters can have a microporous structure (e.g., a ceramic structure or a microporous steel fabric structure, as described in US 2007151231 A), whose walls separate the soot particles. It is also known to regenerate diesel particle filters. A distinction is made here between passive regeneration and active regeneration, in which soot particles are burned at predetermined time intervals and/or after a predefined trigger signal.

Exhaust gas aftertreatment systems with passively regenerating diesel particulate filters utilize the aforementioned CRT effect (Continuous Regeneration Trap), and in this sense, the diesel particulate filter regenerates continuously, particularly without a fixed, pre-set trigger signal. In passive regeneration technology, the engine's exhaust gas temperature is sufficient during normal operating conditions for continuous soot removal in the diesel particulate filter. Regeneration can optionally be assisted by ongoing measures under unusual weather conditions or during prolonged, constant low-load operation. For example, the engine's exhaust gas temperature, and thus the combustion of soot, can be significantly increased temporarily. US 2010031638 A, for example, describes increasing the engine load to enable passive regeneration. US 2011265456 A describes increasing the exhaust gas temperature by changing the combustion cycle to improve soot combustion.

To determine the appropriate time for regeneration, various, sometimes complex, calculation methods and simulation or estimation methods have been described to determine the soot loading of the diesel particle filter. WO 05/116413 discloses training a neural network to determine the loading state from the operating state of the engine, the differential pressure across the diesel particle filter, and exhaust gas values. While these calculation methods are relatively complex, they also avoid requiring additional, specific measurements of the filter state.

This means that in order to determine the load of the diesel particle filter (DPF) or the appropriate time for a regeneration step based on the load state of the diesel particle filter, it has proven useful to determine the load using a differential pressure measurement (ΔP) across the diesel particle filter. In the simplest case, regeneration can be initiated, for example, by the aforementioned thermal management measures, if a predetermined or calculated reference value for the differential pressure (ΔP) is exceeded.

However, it turns out that the causes of the differential pressure are relatively complex. This is because the differential pressure increases over the life of a diesel particle filter not only due to the soot load, but also due to the soot load; the generation of the soot load is fundamentally life-limiting for the diesel particle filter. Soot essentially has a combustible carbon component, while soot is defined as the incombustible component of the filter load that can hardly be removed (and in any case not without effort) during operation. Therefore, measures for reducing the soot content are described in DE 1 002 951.

However, the increase in differential pressure caused by soot loading during operation initially results in the reference value for initiating regeneration, which relates to the differential pressure, being reached progressively earlier, or the reference value calculated from combustion proving to be too low. Consequently, in passive regeneration systems, this leads to thermal management being initiated more frequently than is actually appropriate, i.e., even though the soot loading of the diesel particle filter is not yet critical, thermal management is often initiated. For example, DE 12034 340 A1 discloses performing a combustion calculation for a known fuel specification, which also takes into account the soot residues in the diesel particle filter. Furthermore, an improved method and a device for operating an exhaust gas aftertreatment device are desirable, by means of which the influence of soot on the differential pressure of the diesel particle filter in an exhaust gas aftertreatment device in the case of a passively regenerated diesel particle filter can be taken into account, in particular, determined.

Summary of the Invention

The present invention provides an improved and relatively simple method and a device by means of which the influence of soot on the differential pressure across a diesel particle filter of an exhaust gas aftertreatment device in the case of a passively regenerated diesel particle filter can be taken into account, in particular ascertained. In particular, the method and the device should be usable with relatively little effort and reliability during operation.

The method object is achieved by the invention with a method for operating an exhaust gas aftertreatment device, wherein the diesel particle filter is passively regenerated during operation and the method comprises the following steps:

- measuring the differential pressure across the diesel particle filter at the current exhaust gas volume flow and determining a current correction factor for the differential pressure;

- calculate the corrected differential pressure from the differential pressure and the current correction factor,

According to the invention, it is provided that the current correction factor is determined by means of the following steps:

- determining a lower differential pressure at a predetermined time interval at a determined exhaust gas volume flow;

- Compare the lower differential pressure with a pre-set current reference value.

According to the invention, a new correction factor is calculated based on the comparison, or the previous correction factor is retained as the current correction factor. The comparison of the lower differential pressure with a predefined current reference value is decisive for whether a new correction factor, which is decisive for the load on the lower part, can be calculated as a (new) current correction factor (with a new value), or whether the previous correction factor can be retained as a (previously) current correction factor (with a previous value).

The present invention is based on the concept that, for passively regenerating diesel particle filters, the magnitude of the differential pressure caused solely by soot loading (i.e., in the absence of soot loading) cannot actually be known at any time. According to this concept, there is no definable time during the operation of the exhaust gas aftertreatment device at which the diesel particle filter is free of soot. This is a key difference from active regeneration methods, in which, after thermal management initiated by a trigger signal (i.e., at a definable time), it can be determined that the soot loading reaches a local minimum over time. Consequently, in passive regeneration systems, there is no need for a correction pressure that would account for the differential pressure caused by soot loading so that the measured, particularly current, differential pressure can be corrected. However, in active regeneration methods, the need for such a concept is eliminated.

However, the present invention now recognizes that the measured differential pressure can still be meaningfully corrected by determining a lower differential pressure at predetermined time intervals during operation of the exhaust gas aftertreatment device at a predetermined exhaust gas volume flow. During this time period, this lower differential pressure can, according to knowledge, be attributed in any case to a soot load with a lower, additional soot load. According to the present invention, this lower load is then assigned to a current correction factor. Thus, when a lower differential pressure is present, the current differential pressure can be corrected using the current correction factor determined in this manner.

The object with respect to the device is achieved by a control device according to claim 13. The control device is designed to operate an exhaust gas aftertreatment device, in particular an exhaust gas aftertreatment device with a passively regenerated diesel particle filter, while determining a corrected differential pressure, and is designed to initiate an additional regeneration step.

This object also relates to the exhaust gas aftertreatment device according to claim 14. In another advantageous development, the control device is integrated into the exhaust gas aftertreatment device. The control device can of course also be designed independently of the exhaust gas aftertreatment device.

Finally, the invention relates to an internal combustion engine, in particular a diesel internal combustion engine, with a motor, a diesel particulate filter and the described exhaust gas aftertreatment device according to claim 15 .

Although the concept is particularly advantageous in passively regenerating diesel particle filters, or is motivated by problems arising therein, it is not limited to use therein. In principle, the concept can also be used in actively regenerating diesel particle filters, i.e., in particular, diesel particle filters that regenerate after a fixed, predefined trigger signal, to correct the differential pressure or to check parameters of the active regeneration method or the like; in particular, it contributes to optimizing the time intervals for thermal management in active regeneration methods.

The present invention advantageously provides for determining the corrected differential pressure on a relatively reliable basis and enables a relatively simple method for determining the corrected differential pressure. In particular, the present invention finds a suitable compromise between reliability or accuracy and realizability or real-time capability of the method for determining the corrected differential pressure.

Advantageous developments of the invention can be seen from the dependent claims and are described in individual advantageous embodiments, which implement the above-described solution within the scope of the task stated and with further advantages.

In particular, the exhaust gas volume flow can be kept within a predetermined exhaust gas volume flow interval around a certain exhaust gas volume flow; usually, within the framework of system requirements, it is ensured that the differential pressure is determined, for example at the same value of the exhaust gas volume flow, in order to be able to determine comparable values of the differential pressure.

Based on the corrected differential pressure, in one embodiment, it is then possible to initiate subsequent processes at the correct time, which are dependent on the soot loading of the diesel particle filter. This can, for example, include incorporating the corrected differential pressure into the mechanism for controlling the exhaust gas aftertreatment device, thereby enabling, for example, thermal management to be performed in an improved manner and/or with an optimized time sequence. This can generally prevent diesel particle filters with passive regeneration from initiating harsh or soft thermal management too frequently, thereby avoiding unnecessary additional losses caused by thermal management.

Furthermore, in addition or as an alternative, the corrected differential pressure can also be made available to a central engine control unit (ECU) in order, for example, to correct a characteristic map, a control or regulation process or a general process for which the differential pressure across the diesel particulate filter is used as a manipulated variable.

In the context of a particularly preferred embodiment, it is provided that the dependency of the further process on the comparison comprises the following steps:

- If the lower differential pressure is above a predefined current reference value, then: a new correction factor is calculated from the previous correction factors, wherein the new correction factor is assigned to the current correction factor for correspondence, and/or

If the lower differential pressure lies below a predefined current reference value, then: the previous correction factor is retained, wherein the current correction factor corresponds to the previous correction factor.

In particular, the current differential pressure is measured continuously, in particular continuously. In this way, the lower differential pressure can be determined from the current differential pressure continuously, that is, regularly according to a predefined schedule; for example, by means of a continuous minimum value, wherein the respective minimum value means "if current differential pressure < lower differential pressure (old), then lower differential pressure (new) = current differential pressure." The lower differential pressure is preferably a minimum differential pressure, in particular a local minimum over time and/or an absolute minimum over time.

The measured current differential pressure value is advantageously filtered and validated before it is taken into account for determining the correction factor or the corrected differential pressure. This prevents the correction from being based on abnormal or erroneous measured values in the measured values.

Advantageously, a minimum value is determined therefrom. In particular, it is provided that the lower differential pressure is a local minimum in time and/or an absolute minimum in time differential pressure.

Preferably, the lower differential pressure is subjected to a trustworthiness check, wherein a trustworthy value of the lower differential pressure is used for comparison. This advantageously stabilizes the process, which is preferably used under fixed and sufficiently reliable physical operating conditions of the exhaust gas aftertreatment device. In particular, it can be provided that the lower differential pressure has a trustworthy value (if this value has been determined) which, given the current exhaust gas volume flow value, is constant as a function of time for a first predetermined trustworthiness period, in particular corresponding to a specific exhaust gas volume flow value, in particular the current exhaust gas volume flow value lies around the specific exhaust gas volume flow value within a predetermined exhaust gas volume flow interval. Additionally or alternatively, it can be provided that the lower differential pressure remains essentially constant as a function of time for a second predetermined trustworthiness period.

In other words, the ascertained minimum value is trustworthy, in particular if the system is operated within a predefined exhaust gas volume flow for a sufficient time and/or the ascertained minimum value does not change for a sufficient time.

In particular, within the scope of a particularly preferred embodiment, the determined and trusted minimum value is compared with a reference. The reference particularly preferably corresponds to the differential pressure of the diesel particle filter in a brand new state within a predetermined exhaust gas volume flow. If the determined minimum value is greater than the reference, the correction factor is adapted.

In one advantageous embodiment, the correction factor is adapted in fixed steps. This prevents overly frequent adjustments and prevents excessive corrections. It is particularly advantageous to ensure that a predetermined operating time and a predetermined number of measured values are reached before the correction factor is adapted, in order to initiate the adaptation.

A particularly preferred embodiment provides for assigning a correction factor, which is multiplied by the exhaust gas volume flow, to the differential pressure correction for soot. It is particularly advantageous to perform the following steps to determine the corrected differential pressure: A current correction value (ΔP_K_actual [mbar]) is calculated as the product of the current correction factor (ΔP_K) and the current exhaust gas volume flow (Abgasvolume_actual). Furthermore, the corrected differential pressure is preferably calculated by subtracting the current correction value from the measured differential pressure. This allows for a simple correction of the measured differential pressure.

Advantageously, the current correction factor (AscheΔP_K) can be calculated when a reference value is exceeded as the sum of the previous correction factor (AscheΔP_K[n-1]) and a defined constant. Considering the service life of the diesel particle filter, precisely one constant can be used for each exhaust gas volume flow. It is also advantageous to store different constants for different total operating times of the diesel particle filter. The method can thus be easily transferred to different diesel particle filter embodiments and corresponding motors with regard to the selection of suitable constants.

In an advantageous embodiment of the method, after the current reference value is exceeded by the lower differential pressure, a new reference value (Ref-Wert) is calculated, which is obtained from the sum of the current reference value (Ref-Wert_neu) and the product of the current correction factor (AscheΔP_K) and the determined exhaust gas volume flow (AscheΔP_K * Abgasvolumenstrom_Bereich). The reference value is adapted to take into account the increased soot loading of the diesel particle filter, so that suitable reference values can be used during repeated execution of the method.

This is accordingly explained as follows within the framework of a particularly preferred equation summary:

AscheΔP_K_akluell [mbar] =AscheΔP_K * Abgasvolumenstrom_aktuell

If the reference value is exceeded, then:

AscheΔP_K = AscheΔP_K [n-1] + const.

and

Ref-Wert = Ref-Wert_neu + AscheΔP_K * Abgasvolumenstrom_Bereich

Preferably, to determine the lower differential pressure, the measured differential pressure values are continuously recorded, and the lower differential pressure is determined from these differential pressure values at predetermined time intervals at a predetermined exhaust gas volume flow. This ensures continuous monitoring of the differential pressure, and the monitoring results can simultaneously be used to correct the differential pressure.

In one advantageous embodiment, the method additionally includes a control step in which the corrected differential pressure ΔP is compared with a predetermined threshold value and, if exceeded, a regeneration step of the diesel particle filter is initiated. This method thereby allows a regeneration step to be initiated as soon as the soot load necessitates it, without requiring premature and therefore unnecessary initiation of such a step based on the soot load of the diesel particle filter. Particularly preferred is thermal management as a regeneration step. Here, the combustion of soot in the diesel particle filter is increased by simply increasing the exhaust gas temperature of the engine. Overall, the present invention thus avoids excessive thermal management of the engine and thus saves unnecessary additional energy.

Embodiments of the present invention are now described below with reference to the accompanying drawings. These figures do not necessarily represent the embodiments to scale; rather, they are presented schematically and/or slightly distorted for purposes of explanation. With regard to supplementary concepts directly apparent from the drawings, reference is made to the relevant prior art. It should be noted that various variations and modifications in the form and details of the embodiments are possible without departing from the general concept of the invention. The features of the invention disclosed in the description, drawings, and claims may be essential for the various modifications of the invention, both individually and in any combination. Furthermore, all combinations of at least two of the features disclosed in the description, drawings, and/or claims fall within the scope of the invention. The general concept of the invention is not limited to the exact form or details of the preferred embodiments shown and described below, nor to the content, which is limited by comparison with the content claimed in the claims. Within the described measurement ranges, values within the stated limits are also disclosed as limit values and may be used and claimed as desired. For simplicity, identical or similar parts or parts with identical or similar functions are denoted by the same reference numerals below.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the invention can be gathered from the following description of preferred embodiments and with the aid of the accompanying drawings, which illustrate them in the following figures:

1 is a schematic diagram of a preferred embodiment of an internal combustion engine with a system of a motor, a supercharging unit, an exhaust gas aftertreatment device for a diesel particle filter, and a mechanism for passive regeneration of the diesel particle filter;

FIG. 2 is a schematic diagram of the differential pressure profile across a diesel particle filter in an exhaust gas aftertreatment system as shown for the internal combustion engine of the example in FIG. 1 as a function of the age of the diesel particle filter;

FIG3 is a schematic diagram of the measured differential pressure curve as a function of the exhaust gas volume in an exhaust gas aftertreatment device, as shown for the internal combustion engine of the example in FIG1 , wherein the differential pressure curve is measured at different times during the life of the diesel particulate filter;

FIG4 is a flow chart of an embodiment of a method for operating an exhaust gas aftertreatment device in an infrastructure;

FIG. 5 : Flow chart of another specific embodiment of a method for operating an exhaust gas aftertreatment device in a modified design.

DETAILED DESCRIPTION

FIG1 shows an internal combustion engine 1000 having a motor 100, a supercharging unit 200, and a symbolically illustrated exhaust gas aftertreatment system 300 including a diesel particulate filter (DPF). The DPF can be charged via a control unit GCU with temperature management; this serves to passively regenerate the DPF. The exhaust gas aftertreatment system control unit GCU is currently installed as a module in a system comprising the exhaust gas aftertreatment system, the DPF, and the control unit GCU. The control unit for controlling the passive regeneration of the DPF (symbolized by arrow 301) is currently connected to a central control unit ECU of internal combustion engine 1000 via a data and control bus CAN. The central control unit ECU is also configured to control the motor 100 and the supercharging unit, as symbolized by arrows 301 and 302. In this case, the motor 100 is a diesel motor with several cylinders Z, shown only by way of example and symbol, formed in a motor block. These cylinders can be supplied, for example, via a common rail system with corresponding injection of fuel (not shown).

The supercharging section 200 is connected to the engine block via corresponding intake and exhaust manifolds in the charge air ducts 101L and 101A, respectively, for supplying charge air LL and discharging exhaust gas AG. In the current configuration, the supercharging section 200 comprises a first supercharging stage 200I and a second supercharging stage 200II, each of which comprises a corresponding turbocharger arrangement with compressors 201.1 and 202.1 and turbines 201.2 and 202.2, respectively, in the charge air LL and exhaust gas AG circuits. Charge air coolers 201.3 and 202.3 are connected downstream of the compressors 201.1 and 202.1, respectively. The supercharging stages, compressors, turbines, and coolers can also be described as low-pressure or high-pressure compressors, turbines, or coolers. Internal combustion engine 1000 or supercharging system 200 shown here merely represents an example of an internal combustion engine for a system with exhaust gas aftertreatment device 300 and an explanation of the system.

The present invention also encompasses exhaust gas aftertreatment systems for motors 100 without a supercharging unit or with only a single-stage supercharging unit. In the present case, the supercharging unit is actually designed as a two-stage supercharging unit for a large diesel engine, whose high-pressure stage (second supercharging stage 200II) can be closed by means of a wastegate 202.4 in the exhaust gas bypass line 101B. For load control, a throttle flap 202.5 is arranged in the charge air duct 101L of the internal combustion engine 1000. This throttle flap can be activated in conjunction with the wastegate 202.4 to appropriately control the supercharging stages 200II, 200I depending on the load state of the motor 100.

In addition, internal combustion engine 1000 is currently provided with an exhaust gas recirculation system 400, wherein an exhaust gas recirculation valve 401 and an exhaust gas cooler 402 for treating the recirculated exhaust gas AG are arranged in exhaust gas recirculation line 101R. The supercharging unit 200 and the exhaust gas recirculation system 400 are activated by activating the exhaust gas recirculation valve 401 or the waste gate 202.4, respectively, as indicated by arrow 302.

The characteristics of the differential pressure ΔP across the diesel particle filter DPF are then described as a function of the soot and ash loading of the diesel particle filter, based on the lifespan T_L of the diesel particle filter or as a function of the exhaust gas volume flow V_AG. It is shown that, as is apparent from the concept, knowledge of these values of the differential pressure ΔP can be advantageously used to illustrate an advantageous method and arrangement for controlling exhaust gas aftertreatment device 300. For further details, see the descriptions of FIG. 2 , FIG. 3 , or FIG. 4 and FIG. 5 .

FIG2 shows a schematic diagram of the differential pressure profile in a diesel particle filter over its lifespan T_L. The vertical axis (ordinate) shows the differential pressure ΔP, while the horizontal axis (abscissa) shows the lifespan T_L. Without a load of soot or dust, the differential pressure ΔP in the diesel particle filter theoretically remains constant over the entire lifespan T_L. This profile is shown in curve 110. However, in actual operation, the diesel particle filter is loaded with soot and dust.

In active regeneration systems, soot combustion occurs at predetermined intervals, typically using additional burners or by re-injecting fuel. The resulting increase in exhaust gas temperature allows the excess oxygen in the exhaust gas to be used to oxidize diesel soot present in the diesel particle filter. This soot combustion typically occurs completely. In other words, sufficient information is available for operating a system with active regeneration to identify a time after active regeneration at which no soot is present in the diesel particle filter, making it easier to measure the effects of soot. Curve 120 shows the course of the differential pressure in such an active regeneration system. The differential pressure course in an active regeneration system shows different minima 121 and 122, which characterize the time after complete soot combustion. At this time, the diesel particle filter is free of soot and is loaded solely with soot. During engine operation, there is always a state (after active regeneration) in which it is known that no soot is present in the diesel particle filter. The magnitude of the effect on the differential pressure caused by soot can be determined at this time. Accordingly, all these minimum values for the pure soot-laden and non-soot-laden insults lie on the hypothetical profile of the differential pressure in the diesel particle filter (shown in curve 130). After complete soot combustion, the profile of the differential pressure in the diesel particle filter with pure soot loading can be determined in an active system based on the maximum differential pressure. A correction value for the differential pressure ΔP during soot loading is also derived from the differential pressure value after complete soot combustion.

For passive regeneration systems, there's no predetermined time at which complete soot combustion occurs. Only a state with soot and ash exists. Therefore, it's impossible to measure only the effect of soot on the differential pressure ΔP at a single moment. In particular, in passive regeneration systems, it's unknown where in the diesel particle filter the soot is deposited. Accordingly, the effect of soot on the differential pressure ΔP can vary from system to system. Curve 140 illustrates the differential pressure profile in a diesel particle filter with passive regeneration. Because soot combustion in passive regeneration systems occurs continuously, rather than cyclically, there are no states in passive regeneration diesel particle filters where the differential pressure ΔP caused solely by soot can be reliably measured. This eliminates the need for simple correction of the measured differential pressure using the differential pressure after complete soot combustion, as is the case with active systems. Threshold 150 for the differential pressure ΔP specifies the differential pressure ΔP at which additional regeneration of the diesel particle filter must be initiated in order to achieve increased soot combustion. If the differential pressure limit 150 is exceeded, thermal management is activated. Without differential pressure correction, this would trigger regeneration too frequently (or continuously). As can be seen from the diagram, this threshold is reached more quickly due to soot loading than it would be under pure soot loading. Without providing a correction factor AscheΔP_K for the differential pressure ΔP, an additional regeneration step would be initiated prematurely and unnecessarily. This results in unnecessary fuel consumption and unnecessary loading of the diesel particulate filter. In this case, according to the current concept, the measured differential pressure is shifted downward by AscheΔP_K, the current correction factor. Only the effects due to soot are then taken into account. The differential pressure ΔP is plotted in the diagram shown for a predetermined exhaust gas flow.

According to the embodiment of the invention described here, the correction value for the differential pressure ΔP can be determined by the soot loading (in particular for passive regeneration systems), without the need for a time during operation at which the differential pressure ΔP is influenced only by the soot loading and not by the dust loading.

According to the embodiment of the present invention, such a correction factor is determined by determining the lower differential pressure ΔP-MIN at a predetermined exhaust gas volume flow V_AG at predetermined time intervals and comparing this lower differential pressure ΔP-MIN with a predetermined current reference value. If the lower differential pressure ΔP-MIN exceeds the predetermined current reference value, a new correction factor is calculated from the previous correction factor, and the current correction factor then corresponds to this new correction factor. If the lower differential pressure ΔP-MIN falls below the current reference value, the previous correction factor is retained, and the current correction factor then corresponds to the previous correction factor. It is shown that the lower differential pressure ΔP-MIN can be reliably determined, for example, at a local minimum 141 and a local saddle point 142 over time.

FIG. 3 shows a representation of the dependence of the measured differential pressure on the exhaust gas volume at different times during the life phase of a diesel particle filter.

The differential pressure increase caused by soot is plotted along a symbolic timeline 240 (which currently extends over a year). At time A on timeline 240, as shown in curve 210, the diesel particle filter is still largely free of soot. In the example shown, at time B, represented by curve 220, eight months after time A, the differential pressure ΔP across the diesel particle filter is significantly greater than the differential pressure at time A. The differential pressures shown in this diagram were measured in the soot-free state of the diesel particle filter. Four months later, at time C, shown in curve 230, a further increase in differential pressure is observed due to the increased soot load. As can be seen from the diagram, the differential pressure increase caused by soot is proportional to the exhaust gas volume. The regeneration interval (for example, for softer or harder thermal management) is related to the differential pressure ΔP across the diesel particle filter. This differential pressure ΔP increases over the life of the diesel particle filter due to soot, as shown in FIG3 . As a result, the regeneration intervals are shorter, since the differential pressure ΔP always reaches its limit value earlier.

If the influence of soot is determined and/or calculated (in a particularly advantageous manner according to the approach explained here), the regeneration interval can be optimized, for example kept constant. Consequently, unnecessary additional consumption due to overly frequent regeneration is a hindrance.

FIG4 shows a flow chart of a first embodiment of the method according to the present invention. This follows the following idea:

- Evaluation of the time-dependent differential pressure in relation to the volume flow;

- The time-dependent change in differential pressure is a measure of soot content;

- It should not matter how much soot is deposited where and what oil is used.

Accordingly, in step 310 , the current differential pressure ΔP is measured as a function of the exhaust gas volume flow V_AG. The measured value can be filtered and possibly limited and validated beforehand in step 311 in order to prevent the subsequent method from being based on abnormal measured values in the measurement results.

In step 320, a lower differential pressure, in particular a minimum value, for a specific exhaust gas flow is determined from the measured values within a predetermined time interval. This lower differential pressure ΔP is compared with a predetermined current reference value in step 330, and a current correction factor is determined in step 340 based on the result of the comparison between the lower differential pressure ΔP and the reference. In other words, a comparison (differentiation) with the reference is first performed in step 330, and then a slope or correction factor is calculated in step 340. The current correction factor is determined in step 340 as follows:

If the lower differential pressure ΔP-MIN is greater than a predefined current reference value, a new correction factor is calculated from the previous correction factors and used as the current correction factor. If the lower differential pressure ΔP is less than the current reference value Ref_Wert, the previous correction factor is retained, meaning the current correction factor corresponds to the previous correction factor. One possible approach to determining the current correction factor when the lower differential pressure ΔP exceeds the reference value is to add a predetermined constant to the previous correction factor. Another possible approach to calculating the current correction factor is to record the lower differential pressures for different exhaust gas volume flows at predetermined time intervals, record the lower differential pressures as a function of the exhaust gas volume flow, form a straight line from the determined points, determine the slope of the straight line, and finally subtract the slope of the reference straight line from this slope. In an advantageous embodiment of the method according to the present invention, in step 350, a correction value for the differential pressure ΔP is determined for the current exhaust gas volume flow V_AG from the previously determined current correction factor and the corresponding current exhaust gas volume flow V_AG. In step 360, this correction value is subtracted from the current differential pressure ΔP, and the result of this subtraction is output as the corrected differential pressure ΔP. This corrected differential pressure ΔP can be compared, for example, with a predetermined threshold value in a subsequent step (not shown here), and if this threshold value is exceeded, an additional regeneration step of the diesel particulate filter can be initiated.

FIG5 shows a flow chart of another embodiment of the method according to the present invention. In addition to the method steps shown in FIG4 , step 480 precedes the execution of steps 330 to 360 . In this step, a certain operating duration of the diesel particle filter and a certain number of measured values in steps 310 and 320 must be reached before the lower differential pressure ΔP for a certain exhaust gas volume flow V_AG is declared reliable within a predetermined time interval in step 481 . Simultaneously, a comparison of the lower differential pressure with the current reference value in step 330 is initiated in step 482 . Step 480 serves, on the one hand, to ensure the reliability of the lower differential pressure determined within the predetermined time interval and, on the other hand, to ensure that the requirements for a certain operating duration do not occur too frequently, thereby avoiding frequent system corrections. Step 480 preferably includes a "learning complete" detection (a learning threshold value determined for x hours plus a certain number of values has been learned).

Claims (24)

1. A method for operating an exhaust aftertreatment device (300), wherein a diesel particulate filter (DPF) is passively regenerated during operation, the method comprising the steps of: - Given the current exhaust gas volume flow V_AG_aktuell, measure the current differential pressure (ΔP) on the diesel particulate filter (DPF) and determine the current correction factor AscheΔP_K for the current differential pressure (ΔP); - Calculate the corrected differential pressure from the current differential pressure (ΔP) and the current correction factor AscheΔP_K; - The corrected differential pressure is compared with a predetermined threshold, and if the threshold is exceeded, the regeneration step of the diesel particulate filter is initiated; The feature is that the current correction factor AscheΔP_K is determined by at least the following steps: - Determine the differential pressure ΔP-MIN at predetermined time intervals given a defined exhaust gas volume flow (V_AG); - Compare the differential pressure ΔP-MIN with the preset current reference value Ref-Wert, and based on this, determine a new correction factor or keep the current correction factor AscheΔP_K[n-l] as the current correction factor AscheΔP_K. 2. The method according to claim 1, characterized in that, - If the lower differential pressure ΔP-MIN is above the pre-set current reference value Ref-Wert, then: calculate a new correction factor from the current correction factor AscheΔP_K[n-l], where the new correction factor is assigned to the current correction factor AscheΔP_K for correspondence, and/or - If the differential pressure ΔP-MIN is below the preset current reference value Ref-Wert, then: maintain the correction factor AscheΔP_K[n-l] up to now, where the current correction factor AscheΔP_K corresponds to the correction factor AscheΔP_K[n-l] up to now. 3. The method according to claim 1 or 2, characterized in that the current differential pressure (ΔP) is filtered and/or confirmed, wherein the filtered and/or confirmed value of the current differential pressure (ΔP) is considered in order to determine the correction factor. 4. The method according to claim 1 or 2, characterized in that the lower differential pressure ΔP-MIN is provided for a reliability test, wherein a reliable value of the lower differential pressure ΔP-MIN is considered for comparison. 5. The method according to claim 4, characterized in that the lower differential pressure ΔP-MIN has a reliable value when it is obtained under the following conditions: - The current exhaust gas volume flow V_AG_aktuell value is constant as a function of time with respect to a predetermined first confidence time period, and/or - The differential pressure ΔP-MIN remains essentially constant as a function of time for a predetermined second confidence period. 6. The method according to claim 4, wherein the lower differential pressure ΔP-MIN is the local minimum and/or the absolute minimum differential pressure in time. 7. The method according to claim 1 or 2, characterized in that the preset current reference value Ref-Wert is the reference differential pressure value of the diesel particulate filter (DPF) in a brand new state or in the load state of the diesel particulate filter (DPF). 8. The method according to claim 1 or 2, characterized in that the corrected differential pressure is calculated from the current differential pressure (ΔP) and the current correction factor AscheΔP_K, the method comprising the following steps: - Calculate the current correction value AscheΔP_K_aktuell as the product of the current correction factor AscheΔP_K and the current exhaust gas volume flow V_AG_aktuell, and - The corrected differential pressure is calculated by subtracting the current correction value from the current differential pressure (ΔP). 9. The method according to claim 1 or 2, characterized in that, if the lower differential pressure ΔP-MIN is above a pre-set current reference value Ref-Wert, a new correction factor is calculated from the sum of the correction factors AscheΔP_K[n-l] up to now and the determined constant const. 10. The method according to claim 1 or 2, characterized in that, if the lower differential pressure ΔP-MIN is above a pre-set current reference value Ref-Wert, a new reference value is calculated, which is obtained from the sum of the product of the current correction factor AscheΔP_K and the determined exhaust gas volume flow (V_AG) and the current reference value Ref-Wert_neu. 11. The method according to claim 1 or 2, characterized in that the current differential pressure (ΔP) is continuously measured. 12. The method according to claim 1 or 2, wherein the regeneration includes thermal management. 13. The method according to claim 1, characterized in that the differential pressure ΔP-MIN is determined in a predetermined time interval within a predetermined exhaust gas volume flow interval around a determined exhaust gas volume flow (V_AG). 14. The method according to claim 3, wherein the correction factor is a corrected differential pressure. 15. The method according to claim 4, characterized in that the lower differential pressure ΔP-MIN has a reliable value when it is obtained under the following conditions: - The current exhaust gas volume flow V_AG_aktuell value corresponds to the determined exhaust gas volume flow (V_AG) value, and/or - The differential pressure ΔP-MIN remains essentially constant as a function of time for a predetermined second confidence period. 16. The method according to claim 4, characterized in that the lower differential pressure ΔP-MIN has a reliable value when it is obtained under the following conditions: - The current exhaust gas volume flow V_AG_aktuell value is within a predefined exhaust gas volume flow interval located around a defined exhaust gas volume flow (V_AG) value, and/or - The differential pressure ΔP-MIN remains essentially constant as a function of time for a predetermined second confidence period. 17. The method according to claim 11, characterized in that the current differential pressure (ΔP) is continuously measured. 18. The method according to claim 11, characterized in that, in order to determine the lower differential pressure ΔP-MIN, the current value of the differential pressure (ΔP) is continuously recorded, and the lower differential pressure ΔP-MIN is determined from the recorded value of the current differential pressure (ΔP) at predetermined time intervals under a determined exhaust gas volume flow (V_AG). 19. The method according to claim 18, characterized in that, in order to determine the lower differential pressure ΔP-MIN, the current value of the differential pressure (ΔP) is continuously recorded. 20. A mechanism for controlling an exhaust aftertreatment device with a diesel particulate filter (DPF), characterized in that the mechanism is configured to perform the method according to any one of claims 1 to 19. 21. The apparatus according to claim 20, characterized in that the exhaust gas aftertreatment device is an exhaust gas aftertreatment device with a passively regenerable diesel particulate filter (DPF). 22. An exhaust gas aftertreatment device (300) having a diesel particulate filter (DPF) and the mechanism according to claim 20 or 21. 23. The exhaust gas aftertreatment device (300) according to claim 22, characterized in that the diesel particulate filter (DPF) is a passively regenerable diesel particulate filter (DPF). 24. An internal combustion engine (1000) having a motor (100) and an exhaust aftertreatment device (300) according to claim 22 or 23.