DE102010055641A1 - Method for determining soot loading of particulate filter i.e. diesel particulate filter, in exhaust gas path of internal combustion engine, involves determining deviation of soot entry depending on reference and actual values - Google Patents

Abstract

The method involves supplying fuel with a predetermined injection pressure reference value (p-K-soll) of an internal combustion engine (10). A soot loading in transient operation situation is determined by determining soot entry of a particulate filter (22). The soot entry for corresponding stationary operating point is determined and/or corrected in the situation, so that deviation of the soot entry is accounted corresponding to operation situation. Deviation of the soot entry is determined depending on the reference value and measured injection pressure actual value (p-K-ist). An independent claim is also included for a controlling device for determining soot loading of a particulate filter, comprising a stored injection pressure-dependent characteristic.

Description

The invention relates to a method for determining a soot load of a particulate filter, which is arranged in an exhaust path of an internal combustion engine, which is operated with a predetermined fuel mass setpoint and with an air mass corresponding to a predetermined boost pressure setpoint. The invention further relates to a control device configured for carrying out the method.

As is known, particulate filters are used in exhaust systems of internal combustion engines, in particular diesel engines, in order to filter out soot and other particulate exhaust components from the exhaust gas. In order to maintain their filter capacity, the particulate filters must be cleaned of soot from time to time (approximately every 500 to 1500 km). To do this, the engine is switched from the normal mode to the particulate filter regeneration mode where exhaust gas temperatures of 550 to 650 ° C are generated at which the stored soot mass on the filter is consumed by consuming atmospheric oxygen. To determine the need for regeneration, the determination of the exact load of the particulate filter is of great importance. If, in fact, the soot mass actually stored in the particulate filter is greater than that determined, unacceptably high temperatures can occur during regeneration as a result of the soot overburden, which can lead to impairment of the filter. On the other hand, if the determined load is considered to be too high in the opposite case, the permissible loading capacity of the filter is not fully utilized, resulting in increased fuel consumption due to unnecessarily frequent particle filter regeneration. In addition, increased engine oil degradation can lead to increased engine wear due to increased engine oil dilution.

A known approach to determining a particulate filter loading exploits the fact that with increasing load the exhaust backpressure in front of the filter increases. Specifically, the exhaust gas backpressure or the pressure difference upstream and downstream of the filter is measured by means of pressure sensors and compared with an operating point-dependent threshold, the exceeding of which leads to the triggering of the filter regeneration. From this approach makes the example DE 10 2004 013 603 B4 Use.

DE 101 40 048 B4 describes a method for determining a particle load of a diesel particulate filter, which is connected downstream of a charged by means of an exhaust gas turbocharger diesel engine. In this case, by means of a boost pressure sensor, a current boost pressure in the intake manifold is measured and compared with an operating point-dependent reference boost pressure. The reference boost pressure corresponds to a boost pressure to be expected at the present operating point in the case of a regenerated, ie particle-free particulate filter. If the difference between the reference boost pressure and the measured boost pressure exceeds a threshold value, this is regarded as an indication of a critical fill level of the diesel particulate filter and the filter is regenerated. In an alternative, but basically analogous approach is DE 101 40 048 B4 from an exhaust gas turbocharger whose turbine blades are equipped with a regulated adjustment. In a closed loop, the vane position is regulated to a predetermined desired boost pressure. In this approach, the actual position of the turbine blades is measured and compared with an operating point-dependent reference blade position. If the difference between both exceeds a predetermined threshold value, a filter regeneration is triggered. Both approaches basically do not solve the problem of ensuring a good accuracy of the determination of the filter load in dynamic operating situations.

A fundamentally different approach to pressure or differential pressure measurement provide model-based methods that model the soot loading by the soot mass flow of the exhaust gas and thus the Rußeintrag is estimated in the filter. For this purpose, operating point-dependent maps are used which indicate the soot content of the exhaust gas as a function of the operating point, usually in the form of engine speed and engine load (which flows according to target torque or fuel mass). Taking into account the soot emissions as a result of passive and active filter regeneration, the filter loading is determined by integration.

Out DE 102 34 340 B4 It is known to determine the soot loading of a catalytic particulate filter, on the one hand, the motor soot entry is determined by map and on the other hand, the catalytic conversion of the soot with NO _{2 is} taken into account on the filter load-reducing.

In DE 10 2005 017 348 A1 A map-based approach for determining the filter load is also used. In particular, the center of gravity of fuel combustion in the cylinder, ie the crankshaft position at which 50% of the injected fuel quantity has been converted, and the fuel injection pressure are determined here. From an empirically determined characteristic map, which represents the dependence of the soot emission on the center of gravity of the fuel combustion and the injection pressure, the current soot emission is read out.

If the soot entry is determined as a function of the engine operating point according to the map, this corresponds to the nominal state for a steady-state steady state system in which the operating parameters to be adjusted, such as the supplied air and fuel mass, EGR rate, etc., and thus the air-fuel ratio lambda, coincide with those actually present. However, this is by no means the case under dynamic conditions. In particular, inertia-related control deviations lead to emissions which differ greatly from stationary soot emissions, and which are difficult to detect. This is due to the fact that, especially in highly dynamic driving cycles, the majority of the soot emissions is a consequence of unsteady and thus difficult to detect engine operating states. Under these conditions, the setpoint specifications of the air and fuel metering due to inertia of the controlled systems and actuators due to high driving dynamics are not reached in the respective current operating point of the engine (also called operating point). This is particularly true for the charge air pressure control, since this has the greatest inertia by far.

Out DE 10 2006 055 562 B4 a model-based method for determining the particulate filter loading is known, which derives the soot content of the exhaust gas from maps that use the measured or estimated lambda actual value and the current exhaust gas recirculation rate (EGR rate) as state variables for the operating point. Optionally, further state variables, in particular the rail pressure, can be taken into account. The EGR rate can be determined, for example, as a function of the quotient of the gas pressure in the intake manifold and the exhaust gas pressure upstream of the turbine of the turbocharger.

The invention is based on the object of providing a method for determining the loading of a particulate filter which has increased accuracy and is easy to implement. The determination of the load should be able to be performed in real time, for example, in the electronic engine control unit and require the least possible calibration effort. Furthermore, a control unit suitable for carrying out the method is to be provided.

These objects are achieved by a method and a control device having the features of the independent claims.

The inventive method accordingly relates to the determination of a soot loading of a particulate filter, which is arranged in an exhaust path of an internal combustion engine. The internal combustion engine has a fuel injection system, which supplies fuel with a predetermined injection pressure setpoint to the cylinders of the internal combustion engine. Preferably, the injection pressure is regulated in a closed loop. In this case, to determine the soot loading, at least in a transient operating situation, a soot entry into the particulate filter is determined by determining the soot entry for a corresponding stationary operating point and correcting it so that a deviation of the soot entry due to the transient operating situation is taken into account. According to the invention, it is now provided that the deviation of the soot entry due to the transient operating situation is determined at least as a function of the predetermined injection pressure setpoint and a measured injection pressure actual value.

The invention takes into account the fact that in a given operating point of the internal combustion engine, the stationary setpoint specifications of the fuel pressure (injection pressure) due to inertia of the controlled system and its actuators with high driving dynamics are not reached. From this transient deviation of the current (measured) injection pressure of the control specification results not only a certain error in the fuel metering, but above all, a reduced quality of the mixture preparation. Thus, the injection pressure is decisive for the available mixture formation energy. If the injection pressure setpoints can not be corrected due to the system inertia with high dynamics, the result is a suboptimal combustion process with in some cases greatly increased transient soot emissions. While previous concepts only considered a deviation of the air metering in transient operation in the form of deviations of the lambda value, deviations of the mixture preparation quality were always disregarded. However, the lambda value measured in the exhaust gas does not permit any information about the quality of the mixture preparation and the associated soot emission behavior. Consequently, by taking into account the injection pressure control rejection according to the invention for the first time, the mixture preparation quality is taken into account in the determination of a degree of loading of a particle filter, whereby the accuracy of the method is improved.

Since the injection pressure is usually subject to regulation by means of a closed control loop, the parameters required for the process according to the invention are already available in the prior art for the injection pressure setpoint and the measured actual injection pressure value. Thus, the method requires virtually no additional instrumental effort.

In the context of the present invention, the term "injection pressure" is understood in a broad sense and includes a pressure of the fuel present in front of a fuel injector, regardless of whether this, as in diesel engines usually injected directly into the cylinders or, in the case of premixing agents, into an inlet tube. Preferably, however, it is a direct-injection internal combustion engine. Furthermore, the fuel injection system of the internal combustion engine preferably has a fuel rail, in which the fuel with high (regulated) fuel pressure upstream of the injectors of the cylinder (so-called common rail concept). In this case, the injection pressure on which the method is based corresponds to the rail pressure present in the fuel rail.

In a preferred embodiment of the invention, it is provided that the transient deviation of the soot entry in dependence on the predetermined injection pressure setpoint, the measured injection pressure actual value and a current operating point of the internal combustion engine is determined. The operating or operating point can be considered in this case, in particular in the form of a current engine speed and engine load. In this way, the accuracy of the method can be further improved.

In a further preferred embodiment of the invention, it is provided that in each case a soot emission value or a value correlating therewith is determined as a function of the injection pressure setpoint and the injection pressure actual value and these soot emission values are included in the correction. In this case, the soot emission values can be read from an empirically determined stored characteristic curve as a function of the injection pressure setpoint or the injection pressure actual value, which represents the soot emission value as a function of the injection pressure. Alternatively, the use of a stored formulaic relationship between soot emission value and injection pressure is possible.

From the ratio of the soot emission value for the injection pressure actual value and the soot emission value for the injection pressure target value or from the corresponding correlating values, a (first) correction factor is determined in a preferred embodiment, which is included in the correction, in particular by multiplication with the stationary soot mass flow. Even with this very simple model, an improved accuracy over the prior art is achieved.

A further increase in the accuracy of the method is achieved in that a second correction factor is determined as a function of the current operating point of the internal combustion engine from a characteristic map and the second correction factor is included in the correction.

The subject matter of the present invention is furthermore a control device for determining a soot charge of a particle filter, which is set up to carry out the method according to the invention. The control device can be implemented in particular in an electronic engine control unit. To carry out the method, it may contain a corresponding algorithm in stored and computer-readable form and a stored injection-pressure-dependent characteristic curve which maps a soot emission value or a correlating value, in particular a dimensionless soot emission characteristic, as a function of injection pressure.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

1 schematically an internal combustion engine with associated exhaust tract;

2 Logical block diagram of a method according to the prior art for determining a load of a particulate filter;

3 1 is a logical block diagram of a method for determining a charge of a particulate filter according to a preferred embodiment of the present invention;

4 a detailed section of the block diagram after 3 and

5 schematically an injection pressure-dependent soot emission characteristic.

1 shows a total with 10 designated internal combustion engine, which is in particular a diesel engine. The internal combustion engine 10 includes a plurality of cylinders 12 which have a fuel injection system 14 Fuel is supplied by means of a premixing, but usually directly. Further, the cylinders 12 with a suction pipe 16 , For example, via an intake manifold, not shown, connected, via which an air supply into the combustion chambers of the cylinder 12 he follows; to present therein an ignitable air-fuel mixture corresponding to a desired lambda setpoint. For this purpose, the intake manifold 16 optionally a controllable actuator 18 , For example, contain a throttle.

On the other side are (not shown) outlet openings of the cylinder 12 , usually via a likewise not shown Exhaust manifold, with an exhaust duct 20 connected, in which the exhaust gas of the internal combustion engine 10 flows. The exhaust duct 20 contains a particle filter 22 , in particular a diesel particulate filter DPF. In addition, further exhaust gas purification components in the exhaust duct 20 be arranged, in 1 as an example, the DPF 22 upstream catalyst 24 is shown. The upstream catalyst 24 or other catalysts may include, for example, an oxidation catalyst, a NO _x storage catalyst or a CRT catalyst.

This in 1 shown system may, of course, further known components, such as an external exhaust gas recirculation system or an exhaust gas turbocharger have. Exhaust gas recirculation systems direct a partial exhaust gas flow from the exhaust passage in a known manner 20 and lead this back to the combustion process of the engine 10 by putting it in the intake manifold 16 or is introduced into the exhaust manifold. In this way, combustion temperatures can be lowered and thus reduce the formation of nitrogen oxides. Exhaust gas turbochargers include one in the exhaust passage 20 arranged turbine which - driven by the kinetic energy of the exhaust gas - via a shaft drives a compressor arranged in the intake manifold, thus the charge air of the internal combustion engine 10 to compress and thus bring about greater benefits.

The fuel injection system 14 has fuel injectors (injectors) 26 on, for example, each cylinder 12 one injector each 26 assigned. The injectors 26 stand with a common common rail 28 in which the fuel in highly compressed form the injectors 26 is stored upstream. Usually, the fuel is conveyed from a fuel tank by means of a feed pump and precompressed (components not in 1 shown). A high pressure point 30 then takes the compression of the fuel to a predetermined rail pressure. In the case of several cylinder banks, each bank can have its own common rail.

The internal combustion engine 10 and their components also have a control system whose central element is an engine control unit 32 is, on the one hand via signal lines (in 1 shown with dashed arrows) signals from different sensors 34 . 36 receives and on the other hand via control lines (solid arrows) various actuators 18 . 26 . 30 controls. In detail, the controller receives 26 a signal in the exhaust duct 20 arranged lambda probe 34 , which _is correlated with an oxygen content of the exhaust gas and thus a lambda actual value λ. The lambda probe should preferably be designed as a broadband probe and is preferably at a position close to the engine upstream of the first catalyst 24 Installed. Further, a pressure sensor 36 in the common rail 28 arranged, which an injection pressure actual value p_K _is detected and to the engine control unit 32 transmitted. Other sensors (not shown) typically include a speed sensor that measures engine speed n and a sensor (eg, a pedal sensor) that sends a signal corresponding to engine load L to the engine control unit 32 provides. In addition, temperature sensors for detecting the engine and / or coolant temperature, pressure sensors for detecting the ambient pressure, gas sensors for detecting exhaust gas components such as NO _x and the like may be provided.

Depending on the signals read in, the control unit determines 32 using stored maps 38 Operating parameters of the internal combustion engine 10 and corresponding control signals for the actuators to represent desired setpoints. In this context, the controller determines 32 a current operating point of the internal combustion engine 10 , in particular in the form of the rotational speed n and the engine load L, and determines from a stored map as a function of the operating point a fuel mass _desired value m_K _desired and controls the injectors 26 of the fuel injection system 14 for example, with a corresponding opening time signal to the engine 10 to supply the desired fuel mass. Furthermore, the controller determines 32 from a further stored map as a function of the operating point (n, L) a boost pressure setpoint p_L _target and controls the throttle 18 and / or the compressor of the turbocharger with a corresponding position signal to represent the desired boost pressure in the intake manifold. In addition, the controller controls 32 depending on the measured injection pressure (rail pressure) p_K _is the high-pressure pump 30 to a predetermined injection pressure setpoint p_K _Soll in the rail 28 display. The boost pressure p_L, the fuel mass m_K and the injection pressure p_K are regulated by means of closed control loops so that control deviations are minimized.

The particle filter 22 collects the soot contained in the exhaust gas and possibly other particulate constituents and must be regenerated upon reaching a critical load value in order to restore its original loading capacity and thus its filter function. In order to determine the filter loading, approaches are known in the prior art, the soot entry and the Rußaustrag in or out of the DPF 22 continuously determined by Somassmassimulations models and integrate, so that a cumulative load, the can be compared with the loading threshold results.

Such a known in the art model is in the block diagram of 2 shown schematically. This model typically takes into account four influences that either increase load or reduce load.

First of all, the soot mass flow from the engine emission flows into the model during stationary operation to increase the load (branch a in 2 ). In this case, depending on the input variables speed, torque and possibly the ambient pressure using emission maps, which were determined empirically for the respective operating point under steady state, ie constant conditions, the current soot emission of the engine determined assuming a steady state.

Furthermore, the soot mass flow from the engine emission, which also increases the load, is taken into account in unsteady, ie dynamic operation (branch b in FIG 2 ). This is mainly due to the transient variations of the current lambda value λ _is caused by the stationary lambda value λ _REF in the current operating point. In this case, input variables are, in addition to the rotational speed and the torque, the measured lambda actual value.

Another influence on the soot loading of the DPF 22 a NO _x regeneration is considered load-reducing, in which under the condition of sufficient exhaust gas temperatures, a soot burns in the particulate filter by the nitrogen oxides contained in the exhaust gas such as NO ₂ (branch c in 2 ). The NO _x regeneration usually occurs spontaneously and is triggered by high exhaust gas temperatures and not initiated arbitrarily. In addition to the speed and the torque, the input quantity is the exhaust gas temperature.

Finally, thermal soot regeneration, which is usually initiated arbitrarily when a loading threshold value is reached, is taken into account by initiating measures to increase the exhaust gas and / or filter temperature (branch d in FIG 2 ). Since the thermal regeneration takes place with consumption of oxygen of the exhaust gas as the oxidizing agent, as input variables for determining the soot discharge rate, as well as the rotational speed, the torque and the exhaust gas temperature, also enter the lambda value.

For all components a) to d) corresponding maps are used, which the soot entry into the DPF or the Rußaustrag from the DPF, for example in the form of Rußmassenströmen with the unit mg / m ³ or mg / h or mg / cycle, depending from the mentioned input values. The four individual values a) to d) are continuously calculated by addition or subtraction and integrated (accumulated) over the operating time, so that the result of the determination is an absolute soot mass or a correlated therewith size, which are compared with a predetermined critical loading threshold can.

The greatest difficulty in the effort to determine the loading of the DPF with high accuracy, the detection of soot mass flows in transient, ie dynamic operating situations for all driving cycles. It is known that the soot emissions in diesel engine greatly from the air-fuel ratio ( Lambda) depend. In particular, these are particularly high in the vicinity of the stoichiometric air-fuel ratio (lambda = 1). In the known method, therefore, a transient lambda control deviation (Δλ) is taken into account by comparing the measured instantaneous lambda value (lambda actual value) with a stationary lambda reference value, for example. The lambda actual value can be detected by measuring in the exhaust gas flow. Furthermore, according to a known procedure from the current operating point, which is read in the form of the current speed and the current torque, a stationary lambda reference value is determined, which is taken from an empirically determined map (lambda reference map) as a function of speed and torque , By subtraction formation, the lambda deviation Δλ is calculated, which together with the measured lambda actual value enter into a soot mass flow characteristic map in order to take from it the transient soot mass flow which is added to the stationary soot mass flow.

According to the invention, the control deviation of the injection pressure (rail pressure) due to the inertia of the controlled system and its actuators is evaluated and taken into account in the modeling of soot mass emissions of the internal combustion engine to determine the DPF loading in the determination of transient soot emission. In particular, the transient deviation of the soot entry is determined at least as a function of the predetermined injection pressure setpoint (rail pressure setpoint) and a measured actual actual injection pressure actual value (rail pressure actual value). In addition, the current operating point, in particular in the form of the current engine speed and the current engine torque, incorporated into the model. The consideration of the injection pressure control deviation is preferably carried out in addition to the consideration of the lambda deviation, for example according to the above in connection with branch b) of 2 executed procedure as a function of the measured actual instantaneous lambda actual value.

An overview of the principle of the inventive method is in 3 shown, wherein the branches a), b), c) and d) basically according to conventional methods, as already associated with 2 were discussed, can be performed. Significant difference to the known procedure is thus the additional consideration of the injection pressure control deviation in the determination of transient influences on the soot emission of the engine in branch e), depending on the rail pressure actual value and the rail pressure setpoint and also optionally the current speed and the current torque is determined. From these quantities, a correction factor is finally formed which, by multiplication with stationary and conventionally determined unsteady soot emission from branches a) and b), results in a soot mass flow (or soot entry) which maps the actual unsteady soot mass entry with very good accuracy.

For the implementation of the determination according to the invention of the soot loading of the particulate filter, fundamentally different calculation methods can be used. However, particularly preferred is a simplified approach shown below, the advantages in view of limitations of the processing power and the available memory space in the engine control unit 32 and thus allows the load determination in real time. The approach is also characterized by a minimum effort for the calibration.

Details of the preferred approach according to the invention for determining the transient soot emission are disclosed in US Pat 4 shown.

To determine a correction factor for the transient influence of rail pressure control deviations, the rail pressure actual value p_K _is in the common rail 28 with the pressure sensor 36 (s. 1 ) detected. The rail pressure actual value p_K _is input value is of a characteristic curve (in Kennlinie_1 4 ), which functionally maps the soot emission or a value correlated therewith from the rail pressure. To illustrate the basic relationship, an example of such a characteristic is shown schematically in FIG 5 shown here, wherein according to a preferred embodiment, the soot emission is shown in the form of a dimensionless normalized Rußemissionskennwerts. Output of this step is therefore a Rußemissionskennwert for the actually measured rail pressure _is p_K. The characteristic can be determined empirically on an engine test bench, for example, by setting different rail pressures and measuring the soot emission of the internal combustion engine.

In a further or parallel method step, the rail pressure setpoint p_K is _set by the engine control unit 32 read in and applied to the same characteristic curve (characteristic_1) to obtain a soot emission characteristic value for the rail pressure setpoint p_KSoll.

By dividing the actual value for the rail pressure _is p_K Rußemissionskennwerts map moderately obtained and Rußemissionskennwerts obtained for the rail pressure setpoint value p_K _target is a first correction factor (correction factor 1 ), which mathematically takes into account the rail pressure control deviations in transient operating situations. The correction factor_1 can in a simple embodiment of the invention without further modification by multiplication on the stationary soot emission from branch a) in 3 preferably after taking into account the lambda-dependent transient soot emission from branch b) and thus leading to a corrected, unsteady soot mass flow (not shown).

The accuracy of the method can be further improved by an empirically determined characteristic map (Kennfeld_2 in 4 ) introducing an operating point dependent sensitivity (gain). In this embodiment, depending on the current operating point, in particular as a function of the speed and the torque, a second correction factor (correction factor 2 ) determined from the map_2, which takes into account the operating point of the internal combustion engine. By multiplication of the correction factor_1 and the correction factor_2 according to 5 the correction factor is obtained, with which the calculated stationary soot emission is multiplied. Strictly speaking, it is after 4 Correction factor = (correction factor_1 - 1) · correction factor_2 + 1 Thus, in quasi-stationary operating conditions of the engine, in which the rail pressure setpoint is adjusted (p_K _ist = p_K _setpoint ), the correction factor is identical to 1 regardless of how large the operating point-dependent correction factor 2 is.

Practical application experiments have shown that the method according to the invention described above for determining the soot emission of a motor or a loading of a DPF in driving cycles with high driving dynamics provides a high level of accuracy which could not previously be achieved with the known model functions.

LIST OF REFERENCE NUMBERS

10

Internal combustion engine

12

cylinder

14

Kraftstöffeinspritzsystem

16

air intake pipe

18

Actuator / throttle

20

exhaust duct

22

Particulate filter (DPF)

24

catalyst

26

fuel injector

28

Common rail

30

high pressure pump

32

Engine control unit

34

lambda probe

36

pressure sensor

38

Maps / characteristic curves

n

Engine speed

L

engine load

λ _is

Lambda actual value

m_K _Soll

Fuel mass setpoint

p_K _is

Injection pressure value

p_K _target

Injection pressure setpoint

p_L _setpoint

Boost pressure setpoint

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102004013603 B4 [0003]
• DE 10140048 B4 [0004, 0004]
• DE 10234340 B4 [0006]
• DE 102005017348 A1 [0007]
• DE 102006055562 B4 [0009]

Claims (9)

Method for determining soot loading of a particulate filter ( 22 ), which in an exhaust path of an internal combustion engine ( 10 ), which is a fuel injection system ( 14 ), which fuel with a predetermined injection pressure setpoint (p_K _Soll ) of the internal combustion engine ( 10 ), in order to determine the soot loading in a transient operating situation, a soot entry into the particulate filter ( 22 ) is determined by the soot entry for a corresponding stationary operating point and this is corrected so that a deviation of the Rußeintrags due to the transient operating situation is taken into account, characterized in that the deviation of the soot entry due to the transient operating situation at least depending on the predetermined injection pressure Setpoint (p_K _setpoint ) and a measured injection pressure actual value (p_K _ist ) is determined. Method according to claim 1, characterized in that the fuel injection system ( 14 ) a fuel rail ( 28 ) and the injection pressure in the fuel rail ( 28 ) corresponds to the present rail pressure. Method according to one of the preceding claims, characterized in that the transient deviation of the soot entry in dependence on the predetermined injection pressure setpoint (p_K _setpoint ), the measured injection pressure actual value (p_K _is ) and a current operating point of the internal combustion engine ( 10 ) is determined. Method according to one of the preceding claims, characterized in that in each case a soot emission value or a value correlated therewith in dependence on the injection pressure setpoint (p_K _setpoint ) and the injection pressure actual value (p_K _ist ) is determined and the soot emission values are included in the correction. Method according to Claim 4, characterized in that a first correction factor is determined from the ratio of the soot emission values determined for the actual injection pressure value (p_K _ist ) and the injection pressure _desired value (p_K _setpoint ), and the first correction factor is included in the correction. Method according to one of Claims 4 to 5, characterized in that a stored injection-pressure-dependent characteristic is used to determine the soot emission values or the corresponding correlating values. A method according to claim 2, characterized in that a second correction factor as a function of the current operating point of the internal combustion engine ( 10 ) is determined from a map and the second correction factor is included in the correction. Control device ( 32 ) for determining a soot charge of a particulate filter ( 22 ) arranged to carry out a method according to one of claims 1 to 7. Control device ( 32 ) according to claim 8, comprising a stored injection-pressure-dependent characteristic ( 38 ), which maps a soot emission value or a correlating value, in particular a dimensionless soot emission characteristic, as a function of the injection pressure.

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