EP2469061A2 - Method and control equipment for determining a carbon black loading of a particulate filter - Google Patents

Abstract

The method involves determining a soot entry of a particulate filter (22) to determine soot loading in the filter during transient operating phase. The soot entry is corrected in stationary operating phase such that deviation of soot entry in transient operating phase is considered. The deviation of soot entry is determined as a function of preset boost pressure setting point and actual value of charging pressure. An independent claim is included for control unit for determining soot loading of particulate filter in internal combustion engine.

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.

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.

If the soot entry as a function of the engine operating point is determined according to the map, this corresponds to the nominal state for a system in the stationary steady state, in which the einzuregelnden operating parameters, such as supplied air and fuel mass, EGR rate, etc. and thus the air-fuel ratio lambda to coincide with the actual 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 are a consequence of unsteady and therefore difficult to detect engine operating states is. 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 valid for different engine operating modes and is therefore 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, which is operated with a predetermined fuel mass setpoint and with an air mass corresponding to a predetermined boost pressure setpoint. 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 at least as a function of the predetermined boost pressure setpoint and a measured boost pressure actual value is determined, wherein in a preferred embodiment additionally a measured lambda actual value flows into the determination.

The advantage of this procedure is that the method works exclusively with (in principle exact) measured and calculated values and is able to take into account the influence of a lambda deviation (Δλ) of a stationary lambda (lambda reference value) on the soot emission of the engine without the lambda reference value having to be derived from operating point dependent maps to be determined empirically. Rather, the lambda deviation mainly responsible for the transient deviation of the soot emission is determined exclusively mathematically and only from the lambda deviation a soot emission value is determined, for which a simple, empirically determined characteristic curve is sufficient. As a result, the method is characterized by a very high accuracy. In addition, the thus derived influence of the lambda deviation on the soot emission is valid for each operating mode of the internal combustion engine.

In the context of the present invention, the term "charge pressure" is understood in a broad sense and includes a pressure of the internal combustion engine supplied and present in front of the intake valve combustion air regardless of the Luftzuführungsart. In particular, it comprises the charge pressure generated by a charge air charger, for example an exhaust gas turbocharger, with which the internal combustion engine is operated. However, the term also includes - in the case of uncharged engines - the intake pressure. The term "charge pressure" is thus to be understood as "charge or intake pressure".

In a preferred embodiment of the invention, it is provided that a lambda reference value is determined as a function of the predetermined boost pressure setpoint value, the measured boost pressure actual value and the measured lambda actual value, and a soot emission reference value or a value correlating therewith as a function of the lambda Reference value is determined and this value is included in the correction. In this case, the lambda reference value can be determined according to the following equation: $${\mathit{\lambda }}_{\mathit{REF}}={\mathit{\lambda }}_{\mathit{is}}\cdot \frac{p\_L_{\mathit{Should}}}{p\_L_{\mathit{is}}}\mathrm{,}$$

As already stated above, this lambda reference value requires no derivation via empirically determined operating point-dependent maps and is valid for each engine operating mode.

In a further preferred embodiment of the invention, provision is made for a soot emission actual value or a value correlating therewith to be dependent on the measured lambda actual value is determined and this value is included in the correction. In this case, the soot emission reference value and the actual value of the soot emissions can be read from an empirically determined characteristic curve as a function of the lambda reference value or lambda actual value.

In a preferred embodiment, a (first) correction factor is determined from the ratio of the soot emission actual value and the soot emission reference value or from the corresponding correlating values, 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.

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 lambda-dependent characteristic curve which maps a soot emission value or a correlating value, in particular a dimensionless soot emission characteristic, as a function of lambda.

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

Figur 1

schematisch eine Verbrennungskraftmaschine mit zugeordneten Abgastrakt;

Figur 2

logisches Blockschaltbild eines Verfahrens gemäß Stand der Technik zur Ermittlung einer Beladung eines Partikelfilters;

Figur 3

einen detaillierten Ausschnitt des Blockschaltbildes nach Figur 2;

Figur 4

logisches Blockschaltbild eines Verfahrens zur Ermittlung einer Beladung eines Partikelfilters gemäß einer bevorzugten Ausführung der vorliegenden Erfindung;

Figur 5

einen detaillierten Ausschnitt des Blockschaltbildes nach Figur 4 und

Figur 6

schematisch Lambda-Rußemissions-Kennlinie.

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

FIG. 1

schematically an internal combustion engine with associated exhaust tract;

FIG. 2

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

FIG. 3

a detailed section of the block diagram after FIG. 2 ;

FIG. 4

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;

FIG. 5

a detailed section of the block diagram after FIG. 4 and

FIG. 6

schematically lambda soot emission characteristic.

FIG. 1 shows a total of 10 designated internal combustion engine, which is in particular a diesel engine. The internal combustion engine 10 comprises a plurality of cylinders 12 to which fuel is supplied via a fuel injection system 14 by means of a premixing, but usually directly. Further, the cylinders 12 are connected to an intake manifold 16, for example, via an intake manifold, not shown, via which an air supply into the combustion chambers of the cylinder 12 takes place to represent therein an ignitable air-fuel mixture corresponding to a desired LambdaSollwert. For this purpose, the intake pipe 16 may optionally contain a controllable adjusting element 18, for example a throttle valve.

On the other side (not shown) outlet openings of the cylinder 12, usually via an exhaust manifold, also not shown, connected to an exhaust passage 20, in which the exhaust gas of the internal combustion engine 10 flows. The exhaust passage 20 includes a particulate filter 22, in particular a diesel particulate filter DPF. In addition, further exhaust gas purifying components may be disposed in the exhaust passage 20, wherein FIG. 1 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 FIG. 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 divert a partial flow of exhaust gas from the exhaust duct 20 in a known manner and lead it back to the combustion process of the engine 10 by being introduced approximately into the intake manifold 16 or into the exhaust manifold. In this way, combustion temperatures can be lowered and thus reduce the formation of nitrogen oxides. Exhaust gas turbochargers comprise a turbine arranged in the exhaust duct 20, which - driven by the kinetic energy of the exhaust gas - drives a compressor arranged in the intake pipe via a shaft in order to thus compress the charge air of the internal combustion engine 10 and thereby achieve higher outputs.

The internal combustion engine 10 and its components also have a control and regulating system whose central element is an engine control unit 26, on the one hand via Signal lines (in FIG. 1 shown with dashed arrows) receives signals from various sensors 28, 30 and on the other hand via control lines (solid arrows) various actuators 14, 18 controls. In detail, the control unit 26 receives a signal from a lambda probe 28 arranged in the exhaust duct 20, which correlates with an oxygen content of the exhaust gas and thus with the lambda actual value λ _actual . The lambda probe should preferably be designed as a broadband probe and is preferably installed at a position close to the engine upstream of the first catalytic converter 24. Further, a pressure sensor 30 in the intake pipe 16 or the intake manifold is arranged, which detects a boost pressure actual value p_L _{i s t} and transmitted to the engine control unit 26. In the presence of a turbocharger, which supplies the internal combustion engine 10 with compressed air, the pressure sensor 30 is preferably arranged downstream of the compressor, in particular downstream of an air charging radiator. Other sensors (not shown) typically include a speed sensor that measures engine speed n and a sensor (eg, a pedal encoder) that provides a signal corresponding to engine load L to engine control unit 26. 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.

In dependence on the read-in signals, the control unit 26 determines, using stored characteristic maps 32, operating parameters of the internal combustion engine 10 and corresponding control signals for the actuators in order to represent desired setpoint values. In this context, the control unit 36 determines a current operating point of the internal combustion engine 10, in particular in the form of the speed n and the engine load L, and determined from a stored map depending on the operating point a fuel mass setpoint m_K _{Sol /} and controls the fuel injection system 14, for example with a corresponding opening time signal to supply the engine 10, the desired fuel mass. Further, the control unit 26 determines from a further stored map as a function of the operating point (n, L) a boost pressure setpoint p_L _{S o //} and controls the throttle valve 18 and / or the compressor of the turbocharger with a corresponding position signal to the desired boost pressure to represent in the intake manifold. The boost pressure p_L and the fuel mass m_K are controlled in the closed loop by the measured actual value p_L _lst 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, to restore its original loading capacity and thus its filter function. In order to determine the filter loading, approaches are known in the art which continuously determine and integrate soot input and soot discharge into and out of the DPF 22 by soot mass simulation models, thus resulting in a cumulative load that can be compared to the load threshold ,

Such a known in the art model is in the block diagram of FIG. 2 shown schematically. This model takes into account four influences that either increase the load or reduce the 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 FIG. 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 FIG. 2 ). This is mainly caused by the transient deviations of the current lambda value λ _lst from the stationary lambda value λ _REF at the current operating point. In this case, input variables are, in addition to the rotational speed and the torque, the measured lambda actual value. Details for determining the transient soot mass flow according to this prior art will be described below in connection with FIG. 3 explained.

As a further influence on the soot loading of the DPF 22, a NO _x regeneration is taken into account in order to reduce the load, with the assumption of sufficient exhaust gas temperatures that the soot in the particulate filter burns off due to the nitrogen oxides such as NO _{2 present} in the exhaust gas (branch c in FIG FIG. 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 FIG. 2 ). Since the thermal regeneration with consumption of oxygen of the exhaust gas as the oxidant takes place, as input variables for determining the Rußaustragsrate next to the speed, the torque and the exhaust gas temperature and the lambda value.

Corresponding maps are used for all components a) to d), which indicate the soot entry into the DPF or the soot discharge from the DPF, for example in the form of soot mass flows with the unit mg / m ³ or mg / h, depending on the input variables mentioned depict. 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. To illustrate this procedure for determining the transient Rußottrags is in FIG. 3 a detailed excerpt from the procedure FIG. 2 shown.

According to FIG. 3 the lambda actual value is detected by measurement in the exhaust gas flow. Furthermore, from the current operating point, which is read in the form of the current rotational speed and the current torque, a stationary lambda reference value is determined, which is taken from an empirically determined characteristic map (lambda reference characteristic map) as a function of the rotational speed and the 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.

The basic defect of this known procedure is that the lambda reference map is only valid for a single operating mode of the internal combustion engine. Diesel engines of the most modern type, which have an exhaust aftertreatment system for nitrogen oxides, such as a NO _x storage catalytic converter, but are driven with at least six and sometimes more different modes, including for example normal operation, Oxidation Catalyst Heating Operation, DPF Preheating, DPF Regeneration, NO _x Storage Catalyst Regeneration, NO _x Storage Catalyst Desulfurization, and possibly others. This means that a lambda reference characteristic field for determining the lambda reference value for all operating points must be determined empirically for each of these operating modes. The application and administration effort is thus very high. In addition, corrections in the combustion process resulting from changing environmental conditions such as air pressure, air temperature, cooling water temperature, etc., and having an influence on the steady-state air-fuel ratio can not be mapped in a lambda reference map. This has the consequence that the known method for taking into account transient lambda deviations in the DPF loading calculation in many operating situations of the engine is inaccurate and no longer meets the above requirements of diesel engines of the latest design.

In order to overcome these problems, another approach is chosen according to the invention, namely by evaluating deviations of the soot entry due to the transient operating situation by taking into account the boost pressure control deviation and incorporated into the modeling of soot mass emissions of the internal combustion engine to determine the DPF loading. In particular, the transient deviation of the soot entry is determined at least as a function of the predetermined boost pressure setpoint and a measured, actual instantaneous boost pressure actual value, preferably also as a function of the measured, actual instantaneous lambda 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. Preferably, a lambda reference value λ _REF in response to the predetermined charge pressure setpoint p_l _setpoint, the measured charging pressure actual value p_ L _{/ st} and the measured actual lambda value λ _{/ st} determined and a Rußemissions reference value or a hereby correlated value depending the lambda reference value λ _REF determined. The lambda reference value λ _REF corresponds to the lambda value which would occur if the control variable of the boost pressure p_L were regulated to its desired value, ie if steady-state conditions existed. In contrast to that on the basis of Figures 2 and 3 In the state of the art in which λ _{REF is determined} as a function of the operating point (rotational speed, torque) from empirically determined lambda reference characteristic curves, exclusively measured values (actual lambda value and boost pressure actual value) flow into the lambda reference value λ _REF used _according to the invention Calculated value of the boost pressure setpoint. Since these measured and calculated values, including all influences on the boost pressure set value (such as changing ambient pressure etc.) represent the current operating situation of the engine, the method according to the invention λ _REF regardless of individual operating modes, but generally valid for all operating modes of the engine. In addition, the measured and calculated variables are available anyway in every step of the electronic engine control unit. Also, the method requires no complex calibration, but results solely by the inventive calculation approach.

An overview of the principle of the inventive method is in FIG. 4 shown, wherein the branches a), c) and d) basically according to conventional methods, as already associated with FIG. 2 could be determined. Significant difference to known methods is here so the procedure for taking into account the transient influences on the soot emission of the engine in branch b), depending on the boost pressure feedback and the boost pressure setpoint and optionally also the lambda feedback, the current speed and the current torque is determined. From these quantities, a correction factor is finally formed which, by multiplication with the stationary soot emission from branch a), leads to a soot mass flow (or soot entry) which maps the actual unsteady soot mass flow with very good accuracy.

In principle, different mathematical calculation methods can be used to implement the determination according to the invention of the soot loading of the particulate filter. However, particularly preferred is a simplified approach shown below, which has advantages in view of limitations of the computing power and the available space in the engine control unit 26 and thus allows the load determination in real time. The approach is also characterized by a minimum effort for the calibration. The simplified approach can be derived as follows.

In the approach simplifying it is assumed that the transient deviations in the air-fuel ratio (lambda) are essentially due to control deviations of the boost pressure, ie a difference between the actual currently existing boost pressure (the boost pressure actual value) from the boost pressure target value (the controlled variable). This approach is justified by the fact that the boost pressure control has particularly large inertia, whereby at a dynamic load point change of the vehicle, the actual boost pressure systematically "lags behind" the setpoint. For this reason, the control deviation of the boost pressure contributes by far the most to lambda deviations and thus to differences in transient and stationary soot emissions. The approach favored here accordingly ignores system deviations of the fuel supply, which has significantly lower inertias.

The air-fuel ratio lambda λ is defined by the relationship of equation (1), where m_L is the air mass, m_K is the fuel mass and r is the stoichiometric ratio for complete conversion of the oxygen content. $$\mathit{\lambda }=\frac{m\_L}{r\cdot \mathrm{m\_}K}\mathit{With}r\approx 14.7$$

The actual air mass in a cylinder of the internal combustion engine is proportional to the boost pressure actual value at an operating point of the engine. The same applies to the corresponding setpoints. It is therefore possible, the relationship of equation (2) can be prepared, wherein M_L _{l s t} of air mass actual value (measured value), M_L _If the air mass setpoint value (controlled variable), p_l _lst the charging pressure actual value (measured variable) and p_l _{S o ll} mean the boost pressure setpoint (controlled variable). $$\frac{m\_L_{\mathit{is}}}{m\_L_{\mathit{Should}}}=\frac{p\_L_{\mathit{is}}}{p\_L_{\mathit{Should}}}$$

The lambda reference value λ _REF , which would be set stationary at an adjusted boost pressure (ie p_L _{I s t} = p_L _setpoint ) at an operating point of the engine, can be determined as a function of the current transient lambda actual _value λ _{l s t} (for p_L _lst ≠ p_L _setpoint ) with equation (3) under the simplification m_K _ls = m_K _setpoint . $${\mathit{\lambda }}_{\mathit{REF}}=\frac{m\_L_{\mathit{Should}}}{r\cdot m\_K_{\mathit{Should}}}=\frac{m\_L_{\mathit{is}}\cdot \frac{p\_L_{\mathit{Should}}}{p\_L_{\mathit{is}}}}{r\cdot m\_K_{\mathit{is}}}={\lambda }_{\mathit{is}}\cdot \frac{p\_L_{\mathit{Should}}}{p\_L_{\mathit{is}}}$$

Thus, for the desired lambda deviation of the lambda actual value Δλ λ _lst from the stationary lambda reference value _REF λ, the relationship can be formulated according to equation (4). $$\mathrm{\Delta }\mathit{\lambda }={\mathit{\lambda }}_{\mathit{REF}}-{\mathit{\lambda }}_{\mathit{is}}={\mathit{\lambda }}_{\mathit{is}}\cdot \left(\frac{p\_L_{\mathit{Should}}}{p\_L_{\mathit{is}}}-1\right)$$

Thus, the lambda control deviation Δλ depends exclusively on the lambda actual value _λ, p _ L s and p _oll from the charging pressure actual value _ L _is the boost pressure setpoint value. The lambda actual value λ _can be measured in a known manner by means of a lambda probe in the exhaust gas. Similarly, the actual value Labedruck p _ L can _by means of a pressure sensor in the intake tract can be detected, for example, in or in front of an intake manifold. After all, it is the labed pressure setpoint

p_L _{should be able} to be predetermined in a known manner by a calculated value, which may be dependent on the operating point, for example as a function of the current engine speed and the current engine torque, for example from empirically determined and stored in the engine control maps. Since in diesel engines, the boost pressure is usually the control variable for the control of the air mass supplied to the engine, its setpoint and its actual value are always determined anyway and are therefore always present in the engine control unit.

Details of the preferred approach according to the invention for determining the transient soot emission are disclosed in US Pat FIG. 5 shown.

The stationary soot emission can - as usual in the art - with the input variables speed, torque and optional ambient pressure from stored emission maps, which have been determined empirically under stationary conditions for the individual operating points represented (branch a).

In order to determine a correction factor for the transient influence, the lambda actual value λ _ist in the exhaust gas with the lambda probe 28 (p. FIG. 1 ) detected in the exhaust gas. The lambda actual value λ _actual is the input value of a characteristic _{curve_1} , which maps the soot emission or a value correlated _{therewith as} a function of lambda. To illustrate the basic relationship, an example of such a characteristic is shown schematically in FIG FIG. 6 shown here, wherein according to a preferred embodiment, the soot emission in the form of a dimensionless normalized Ruße.missionskennwerts is shown. Output variable of this process step is thus a Rußemissionskennwert (soot emission actual value) for the actually measured lambda value λ _lst .

In a further or parallel process step, the pressure sensor 30 (FIG. FIG. 1 ) in the intake system measured _charge pressure actual value p_L _lst and in particular the characteristic map as a function of speed and torque determined boost pressure setpoint p_L _Soll read and calculated by dividing the ratio of the two. This ratio is then multiplied by the lambda actual value λ _lst to obtain the lambda reference value λ _REF according to equation (3). The lambda reference value λ _REF is the input _{quantity of} the characteristic curve_1 according to FIG FIG. 6 from which a soot emission characteristic value (soot emission reference value) for the lambda reference value λ _{REF is} determined.

By dividing the actual value of the soot emission and the reference value of the soot emission, a correction factor 1 is obtained, which mathematically takes into account the lambda deviations Δλ in transient operating situations. The correction factor_1 can be applied in a simple embodiment of the invention without further modification by multiplication on the stationary soot emission from branch a) and thus lead 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 FIG. 5 ) introducing an operating point dependent sensitivity (gain). In this embodiment, depending on the current operating point, in particular as a function of the rotational speed and the torque, a second correction factor (correction factor_2) is 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 FIG. 5 the correction factor is obtained, with which the calculated stationary soot emission is multiplied. Strictly speaking, it is after FIG. 5 the deviation of the correction factor_1 of 1 amplifies according to: $$\mathrm{correction\; factor}\mathrm{=}\left(\mathrm{Korrekturfaktor\_}\mathrm{1}\mathrm{-}\mathrm{1}\right)\mathrm{*}\mathrm{Korrekturfaktor\_}\mathrm{2}\mathrm{+}\mathrm{1}$$

Thus, in quasi-stationary operating conditions of the engine, in which the boost pressure setpoint is _compensated ( p_L _lst = p_L _setpoint ) , the correction factor is identical 1 irrespective 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

Fuel injection system

16

air intake pipe

18

Actuator / throttle

20

exhaust duct

22

Particulate filter (DPF)

24

catalyst

26

Engine control unit

28

lambda probe

30

pressure sensor

32

Maps / characteristic curves

n

Engine speed

L

engine load

λ

Air-fuel ratio lambda

λ _lst

Lambda actual value

λ _REF

Lambda reference value

M_L

air mass

m_L _lst

Air mass actual value

m_L _target

Air mass setpoint

m_K

Fuel mass

m_K _lst

Fuel mass value

m_K _Soll

Fuel mass setpoint

p_l

boost pressure

p_L _lst

Charging pressure actual value

p_L _setpoint

Boost pressure setpoint

Claims (10)

Method for determining a soot load of a particulate filter (22), which is arranged in an exhaust path of an internal combustion engine (10), which is operated with a predetermined fuel mass setpoint ( m_K _setpoint ) and with an air mass corresponding to a predetermined boost pressure setpoint ( p_L _setpoint ) wherein a soot ingress is detected in the particulate filter (22) for determining the soot charge in a transient operation situation by the soot ingress for a corresponding steady-state operating point is determined and this is corrected so that a deviation of the Rußeintrags is taken into account as a result of transient operating situation, characterized in that in that the deviation of the soot entry due to the transient operating situation is determined at least as a function of the predetermined boost pressure setpoint ( p_L _setpoint ) and a measured boost pressure actual value ( pL _actual ). A method according to claim 1, characterized in that the transient deviation of the Rußeintrags depending on the predetermined boost pressure setpoint ( p_L _setpoint ) , the measured boost pressure actual value ( p_L _actual ) and a measured lambda actual value ( λ _lst ) is determined. A method according to claim 2, characterized in that a lambda reference value ( λ _REF ) in dependence on the predetermined boost pressure setpoint ( p _L _setpoint ) , the measured boost pressure actual value ( p_L _lst ) and the measured lambda actual value ( λ _lst ) determined and a Rußemissions reference value or a value correlated therewith in accordance with the lambda reference value ( λ _REF ) is determined and this value is included in the correction. A method according to claim 3, characterized in that the lambda reference value ( λ _REF ) is determined according to the following equation: $${\mathit{\lambda }}_{\mathit{REF}}={\mathit{\lambda }}_{\mathit{is}}\cdot \frac{p\_L_{\mathit{Should}}}{p\_L_{\mathit{is}}}\mathrm{,}$$

Method according to one of the preceding claims, characterized in that a soot emission actual value or a value correlated _{therewith is} determined as a function of the measured lambda actual value ( λ _actual ) and this value is included in the correction. Method according to one of Claims 3 to 5, characterized in that a first correction factor is determined from the ratio of the carbon black emission actual value and the carbon black emission reference value or from the corresponding correlating values and the first correction factor is included in the correction. Method according to one of Claims 3 to 6, characterized in that a stored lambda-dependent characteristic curve is used for determining the soot emission reference value and the soot emission actual value or the corresponding correlating values. Method according to one of the preceding claims, characterized in that a second correction factor in dependence on a 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 (26) for determining a soot load of a particulate filter (22), which is adapted to carry out a method according to one of claims 1 to 8. Control device (26) according to claim 9, comprising a stored lambda-dependent characteristic curve, which maps a soot emission value or a correlating value, in particular a dimensionless soot emission characteristic as a function of lambda.

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