DE102008042819B4 - Method and device for determining a total cylinder charge and / or the current residual gas rate in an internal combustion engine with exhaust gas recirculation - Google Patents

Abstract

Method for determining an entire cylinder charge (rfrges) in cylinders of an internal combustion engine (2) with exhaust gas recirculation, with exhaust gas being recirculated at an inlet point (10) into an intake manifold (4) for feeding a gas mixture into the cylinders (3), with the entire cylinder charge (rfrges) indicates an instantaneous total amount of gas in the cylinders (3), the total cylinder charge (rfrges) depending on a sum of the gas mass flows fed to the intake manifold (4) and depending on a first dynamic correction factor (fvisrm), which determines the dynamic behavior of the Describes the intake manifold (4) with respect to the intake manifold pressure that is established there, the entire cylinder charge (rfrges) being determined as a function of a current intake manifold pressure (ps), the current intake manifold pressure (ps) being determined by integrating the with the first dynamic correction factor (fvisrm) acted upon difference between an unfiltered cylinder charge, which indicates the charge, which is through the the intake manifold (4) would set gas mass flows supplied, and the total cylinder charge (rfrges) is determined, the total cylinder charge (rfrges) as a function depending on the current intake manifold pressure (ps), depending on a current engine speed (nmot) and depending on correction factors , in particular an altitude factor (fho) for adapting to an ambient pressure and a combustion chamber temperature factor (ftbr) for taking into account the gas temperature in the cylinders (3), with exhaust gas at an inlet point (10) in an intake pipe (4) for supplying a gas mixture is fed back into the cylinder (3), the residual gas rate (rragrzw) indicating the current proportion of exhaust gas in the cylinder (3) total gas, with the following steps: - Determining the residual gas rate (rragrzw) depending on an exhaust gas partial pressure (psrext ) and depending on the current intake manifold pressure (ps), the exhaust gas partial pressure depending on an exhaust gas mass supplied to the intake manifold nstrom, depending on a second dynamic correction factor, which describes the dynamic behavior of the intake manifold (4) taking into account the introduction point (10) with regard to the resulting exhaust gas partial pressure (psrext), and is determined depending on the current exhaust gas cylinder filling.

Description

Technical area

The invention relates to an internal combustion engine with exhaust gas recirculation, which is controlled by an engine control unit, the current air charge being determined in the engine control unit as a function of the residual gas rate.

State of the art

Exhaust gas recirculations are increasingly being provided in internal combustion engines in order to reduce fuel consumption and, if necessary, to optimize exhaust emissions. Here, exhaust gas is taken from the exhaust system and metered into the fresh air of an intake manifold of an air supply system via an exhaust gas recirculation line with an exhaust gas recirculation valve.

the DE 198 30 300 A1 discloses an internal combustion engine ( 1 ) especially for a motor vehicle that is equipped with a throttle valve ( 9 ) is provided, through the air an intake pipe ( 7th ) can be supplied. An exhaust gas recirculation ( 13th , 14th ) is provided via the exhaust gas from an exhaust pipe ( 8th ) the suction pipe ( 7th ) is traceable. A control unit is available with which the internal combustion engine ( 1 ) can be controlled and / or regulated. The gas mixture in the suction pipe ( 7th ) can be divided into a fresh gas component (rffgabg), an inert gas component (rfigabg) and a fuel gas component (rfhcabg).

• - Ermitteln eines Partialdrucks des Frischgas-Anteils (ps_fg) an dem Gasmassenstrom (mp_ab) durch Aufstellen einer Massenbilanz für einen Frischgas-Massenstrom (mp_fg), und
• - Ermitteln eines Partialdrucks des Abgas-Anteils (ps_ag) an dem Gasmassenstrom (mp_ab) durch Aufstellen einer Massenbilanz für einen Abgas-Massenstrom (mp_ag).

the DE 197 56 919 A1 discloses a method for determining a gas filling of an internal combustion engine, which has an intake manifold, wherein a gas mixture of a fresh gas (fg) and an exhaust gas (ag) is located in the intake manifold, a gas mass flow (mp_ab) flowing out of the intake manifold and wherein in the Intake manifold a manifold pressure (ps) prevails, characterized by the following steps:

• - Determining a partial pressure of the fresh gas fraction (ps_fg) in the gas mass flow (mp_ab) by establishing a mass balance for a fresh gas mass flow (mp_fg), and
• - Determination of a partial pressure of the exhaust gas fraction (ps_ag) in the gas mass flow (mp_ab) by establishing a mass balance for an exhaust gas mass flow (mp_ag).

the DE 42 11 851 A1 relates to a method for controlling an internal combustion engine with an exhaust gas recirculation (EGR) system as a system for controlling harmful gas emissions. More precisely, the invention relates to a method for obtaining an accurate value for the intake air mass flow (cylinder air mass flow) of the gas as it is actually introduced into an engine cylinder when the EGR system is active; this is necessary for good engine control. The invention further relates to a method for precisely determining the amount of fuel to be injected, taking into account the transport delay of the fuel in the suction nozzle.

The exhaust gas recirculation valve is activated by the engine control unit so that a certain residual gas rate (exhaust gas recirculation rate) can be set. The admixed exhaust gas displaces the fresh air without participating in the combustion. In other words, in order to keep the engine torque constant, the throttle valve must be opened further at certain operating points when the residual gas proportion increases. The desired effect is an increase in the intake manifold pressure without the engine torque increasing. This can reduce the pumping losses of the internal combustion engine, increase efficiency and thereby lower fuel consumption.

Furthermore, by adding exhaust gas to the fresh air in the intake manifold, the combustion temperature can be lowered, which leads to a reduced formation of harmful nitrogen oxides in the exhaust gas.

In order to keep the engine torque constant, it is therefore necessary for the engine control unit to know the current air charge in the cylinders in order to be able to determine the corresponding position of the throttle valve or the corresponding injection quantity and the ignition angle based on the current air charge, so that the required engine torque is constant can be held. The relationships between the engine speed, the throttle valve position, the intake manifold pressure, the total cylinder charge and the cylinder air charge are correctly described under steady-state conditions using the functions implemented so far. Dynamic processes can also be taken into account.

In addition to the influence on the air supply system, as already mentioned above, corrections in the ignition system are also required in the case of exhaust gas recirculation. As the fuel-air mixture is diluted in the combustion chamber by recirculated exhaust gas, the combustion speed is reduced, which must be compensated for by an earlier ignition. For this, knowledge of the ratio of residual gas mass to total gas mass in the combustion chamber, the so-called exhaust gas recirculation rate, is decisive.

When taking into account the dynamic processes, it has been generally assumed that the exhaust gas introduced would be distributed homogeneously in the intake manifold, since the exhaust gas introduction point has usually been located close behind the throttle valve. However, measurements have shown that in an internal combustion engine in which the exhaust gas inlet point of the exhaust gas recirculation is very close to the inlet valves, the exhaust gas is not distributed homogeneously in the intake manifold, but rather only a very small amount on its short path from the inlet point to the cylinder inlet valve Occupies volume that is built up and reduced much faster than the total intake manifold pressure. Thus, the dynamics of the air system with regard to the recirculated exhaust gas is different from the dynamics of the air system with regard to the fresh air.

Since the engine manufacturers usually freely choose the point of introduction for the exhaust gas recirculation, the resulting different dynamics with regard to the recirculated exhaust gas and with regard to the fresh air supplied are not known. In particular, this difference becomes more serious the closer the point at which the recirculated exhaust gas is introduced to the inlet valves. The previous model, which used the same dynamic model as a basis for both the recirculated exhaust gas and the fresh air supplied and which both assume the same underlying intake manifold volume, cannot determine the current charge and the current residual gas rate in dynamic operation with sufficient accuracy.

According to the conventional method for determining the current air charge, two partial pressures can therefore be modeled for the recirculated exhaust gas and for the fresh air supplied, the addition of which results in the resulting measurable intake manifold pressure. The intake manifold dynamics are taken into account with a common dynamic correction factor, which defines the behavior of the residual gas rate and the intake manifold pressure over time. However, on the basis of the behavior observed above, this only correctly maps the case in which the introduction point of the exhaust gas recirculation takes place at or near the throttle valve.

The object of the present invention is to provide a method and a device with which, in an internal combustion engine with exhaust gas recirculation, the current air charge and / or the residual gas rate in cylinders of the internal combustion engine can be determined more precisely regardless of the point at which the exhaust gas is introduced into the intake manifold .

Disclosure of the invention

This object is achieved by the method for determining the total cylinder charge of air charge in an internal combustion engine with exhaust gas recirculation according to claim 1, the method for determining a current residual gas rate, the method for determining a current air charge and by the engine system according to the independent claims.

Further advantageous refinements of the invention are specified in the dependent claims.

According to a first aspect, a method is provided for determining an entire cylinder charge in cylinders of an internal combustion engine with exhaust gas recirculation, exhaust gas being recirculated at an introduction point into an intake manifold for supplying a gas mixture into the cylinders, the entire cylinder charge depending on a sum of the amounts supplied to the intake manifold Gas mass flows and is determined as a function of a first dynamic correction factor, which describes the dynamic behavior of the intake manifold with respect to the intake manifold pressure that is established there.

The above method enables a dynamically correct detection of the entire cylinder charge as a basis for the correct determination of the current air charge in the cylinders or the residual gas rate, taking into account the point of introduction of recirculated exhaust gas into the intake manifold.

While partial pressures are modeled in the prior art that add up to the resulting measurable intake manifold pressure, in the above method it is proposed to use the sum of the partial fillings or the partial mass flows of gas flowing into the intake manifold in order to determine the total cylinder charge.

According to one embodiment, the entire cylinder charge can be determined as a function of the current intake manifold pressure, the current intake manifold pressure being determined by integrating the difference, to which the first dynamic correction factor is applied, between an unfiltered gas mass flow fed to the intake manifold and the total gas mass flow fed to the cylinder.

Furthermore, the entire cylinder charge can be determined as a function of the current intake manifold pressure, a current engine speed and correction factors, in particular a height factor to adapt to an ambient pressure and a combustion chamber temperature factor to take into account the gas temperature in the cylinder.

• - Durchführen des obigen Verfahrens, um den momentanen Saugrohrdruck zu bestimmen;
• - Ermitteln der Restgasrate abhängig von einem Abgas-Partialdruck und abhängig von dem momentanen Saugrohrdruck, wobei der Abgas-Partialdruck abhängig von einem dem Saugrohr zugeführten Abgasmassenstrom, abhängig von einem zweiten Dynamikkorrekturfaktor, der das dynamische Verhalten des Saugrohrs unter Berücksichtigung der Einleitstelle bezüglich des sich einstellenden Abgas-Partialdrucks beschreibt, und abhängig von einer momentanen Abgas-Zylinderfüllung bestimmt wird.

According to a further aspect, a method for determining a current residual gas rate in cylinders of an internal combustion engine with exhaust gas recirculation is provided, with exhaust gas being recirculated at an introduction point into an intake manifold for feeding a gas mixture into the cylinder, the residual gas rate being the current proportion of exhaust gas in the in the Cylinder of total gas located. The process consists of the following steps:

• - Carrying out the above method in order to determine the instantaneous intake manifold pressure;
• - Determination of the residual gas rate depending on an exhaust gas partial pressure and depending on the current intake manifold pressure, the exhaust gas partial pressure depending on an exhaust gas mass flow supplied to the intake manifold, depending on a second dynamic correction factor, which determines the dynamic behavior of the intake manifold taking into account the introduction point with regard to the Exhaust gas partial pressure describes, and is determined depending on a current exhaust gas cylinder charge.

While partial pressures are modeled in the prior art that add up to the resulting measurable intake manifold pressure, it is proposed in the above method to take into account the dynamic behavior of the entire cylinder charge and the exhaust gas fraction (indicated by the residual gas rate) with different time constants.

Furthermore, the current exhaust gas cylinder filling can be determined depending on the residual gas rate and the total cylinder filling.

Furthermore, it can be provided that the exhaust gas partial pressure is achieved by integrating the difference, to which the second dynamic correction factor is applied, between the EGR filling proportion, which indicates a filling of exhaust gas in the cylinder, which would arise due to the exhaust gas mass flow currently supplied to the intake manifold, and the (actual ) Exhaust cylinder charge is determined.

• - Ermitteln der gesamten Zylinderfüllung gemäß dem obigen Verfahren;
• - Bereitstellen einer Restgasrate oder Bestimmen der Restgasrate nach dem obigen Verfahren;
• - Bestimmen der aktuellen Luftfüllung abhängig von der gesamten Zylinderfüllung und von der Restgasrate.

According to a further aspect, a method is provided for determining an instantaneous air charge in cylinders of an internal combustion engine with exhaust gas recirculation, exhaust gas being recirculated at an introduction point into an intake manifold for feeding a gas mixture into the cylinders. The process consists of the following steps:

• - Determining the total cylinder filling according to the above method;
• - Providing a residual gas rate or determining the residual gas rate according to the above method;
• - Determination of the current air charge depending on the total cylinder charge and the residual gas rate.

• - Bestimmen der momentanen Luftfüllung gemäß dem obigen Verfahren;
• - Ansteuern einer Stellung einer Drosselklappe des Verbrennungsmotors und/oder einer Einspritzmenge von Kraftstoff in ein Saugrohr des Verbrennungsmotors und/oder einen Zündwinkel zum Zünden eines Luft-/Kraftstoffgemisches abhängig von der momentanen Luftfüllung.

According to a further aspect, a method for controlling an internal combustion engine is provided. The process consists of the following steps:

• - Determination of the current air filling according to the above method;
• - Controlling a position of a throttle valve of the internal combustion engine and / or an injection quantity of fuel into an intake manifold of the internal combustion engine and / or an ignition angle for igniting an air / fuel mixture as a function of the current air charge.

Due to the dynamically correct filling detection, the adaptation of the fuel path for a correction of the fuel metering in a dynamic operating case (transition compensation) can be improved. This results in better exhaust emissions and improved drivability. Due to the dynamically correct determination of the residual gas rate, the ignition angle can still be calculated correctly.

According to a further aspect, an engine control unit for controlling an internal combustion engine is provided, which is designed to carry out the above method.

According to a further aspect, a computer program is provided which contains a program code which, when it is executed on a data processing unit, executes the above method.

Figure list

• 1 eine schematische Darstellung eines Motorsystems mit einem Verbrennungsmotor mit Abgasrückführung;
• 2 ein Funktionsblockdiagramm zur Veranschaulichung der Funktion zur Bestimmung der Luftfüllung und der Restgasrate; und
• 3 eine detailliertere Darstellung des Kennfeldblocks des Funktionsblockdiagramms der 2.

Preferred embodiments are explained in more detail below with reference to the accompanying drawings. Show it:

• 1 a schematic representation of an engine system with an internal combustion engine with exhaust gas recirculation;
• 2 a function block diagram to illustrate the function for determining the air filling and the residual gas rate; and
• 3 a more detailed representation of the map block of the functional block diagram of FIG 2 .

Description of embodiments

1 shows schematically an engine system 1 with an internal combustion engine 2 with four cylinders as an example 3 . The internal combustion engine 2 is air through a suction pipe 4th an air supply system supplied. In the suction pipe 4th is via an injection valve 5 Fuel in the intake manifold 4th injected to there an air-fuel mixture for admission into the cylinder 3 of the internal combustion engine 2 to build. Fresh air is the intake manifold 4th controlled by a throttle valve 11 fed.

Combustion gases from the cylinders are released through an exhaust system 6th discharged. Between the exhaust system 6th and the suction pipe 4th is an exhaust gas recirculation system 7th provided that an exhaust gas recirculation cooler 8th and an exhaust gas recirculation valve 9 and exhaust gas from the exhaust system 6th into the suction pipe 4th can guide. The exhaust gas recirculation arrangement 7th ends at a discharge point 10 into the suction pipe 4th .

It's an engine control unit 12th provided, the position of the throttle valve 11 , the position of the exhaust gas recirculation valve 9 , the operation of the fuel injector 5 and the ignition of the air-fuel mixture in the cylinders 3 by specifying ignition timing of spark plugs 13th for each of the cylinders 3 controls. To carry out the control of this component, it is necessary that the engine control unit 12th the current air filling in the cylinders 3 as well as the residual gas rate even in dynamic operation of the engine system 1 precisely determined.

In particular, the engine control unit must 12th the amount of fuel to be injected based on the current air charge in the cylinders 3 to adjust. Depending on the residual gas rate, the ignition angle, that is to say the ignition time, has to be adapted accordingly as a function of the position of the crankshaft angle. Furthermore, it may be necessary to also adjust the position of the throttle valve in order to maintain the engine torque 11 must be adjusted accordingly. This is done with the aid of engine control and regulation methods known from the prior art, which will not be discussed in more detail here.

A function in the engine control unit is used to determine the actual cylinder charge rlfgsb and the actual residual gas rate rragrzw 12th executed in 2 is shown schematically. An input variable for this function is an unfiltered cylinder charge rlroh calculated from the air mass flow. The air mass flow is determined with the aid of a not shown in front of the throttle valve 11 arranged hot film air mass sensor measured. Another input variable arises from the return into the intake manifold 4th directed exhaust gas recirculation mass flow (EGR mass flow) resulting unfiltered EGR filling fraction rfrexroh. The EGR mass flow can be determined from the pressure difference between the pressure in the exhaust system 6th and the pressure in the intake manifold 4th and from the position of the exhaust gas recirculation valve 9 can be determined according to a model.

The unfiltered cylinder charge is fed to a first summing element 21 fed. Furthermore, the unfiltered EGR charge fraction rfrexroh is transferred to the first summing element 21 fed. The output of the first summing element 21 supplies the sum of the unfiltered cylinder charge rlroh and the unfiltered EGR charge proportion rfrexroh and corresponds to an unfiltered total charge rges. The unfiltered total filling rges is sent to a non-inverting input of a differential element 22nd created. To an inverting input of the differential element 22nd an indication of an entire cylinder charge rfrges is created.

The difference between the unfiltered total filling rges and the normalized filling rfrges is calculated via a first multiplication element 23 to an integration link 24 created. The first multiplication term 23 multiplies the filling difference at the output of the differential element 22nd is applied, with a first dynamic correction factor fvisrm, which represents a first time constant for the dynamic behavior of the intake manifold. The integration link 22nd integrates the differential filling. In other words, since the process is carried out cyclically, the integration element adds up 22nd the difference fills. A demodulated intake manifold pressure ps is thus made available at the output of the integration element. The modulated intake manifold pressure ps is assigned to a map block 25th supplied, in which, taking into account other parameters such as the engine speed nmot, a height factor fho and a combustion chamber temperature factor ftbr and a map, the entire cylinder charge rfrges is determined. The entire cylinder charge rfrges, which is also applied to the inverting input of the differential element 22nd provided.

In 3 is the map block 25th again shown in more detail. It can be seen that the normalized intake manifold pressure ps is first divided by the altitude factor fho, which results from the ambient pressure divided by 1013 hPa, before the result is fed to the map together with the engine speed nmot. The map models the relationship between pressure and charge depending on the speed. This makes it possible to calculate the actual intake manifold pressure. Addressing the map is necessary because the non-linear relationship between pressure and charge does not depend on the absolute intake manifold pressure. The intake manifold pressure normalized to ambient pressure is decisive for this. For this reason, the normalized intake manifold pressure is divided by the altitude factor fho.

In order to adapt it to the actual ambient pressure conditions, the result from the map is now multiplied again by the altitude factor fho in a multiplier and then multiplied by a combustion chamber temperature factor ftbr in a further multiplier in order to obtain the entire cylinder charge rfrges. The combustion chamber temperature factor ftbr results from a modeled gas temperature evtmod in the combustion chamber from the formula ftbr = 273 K / (273 K + evtmod).

The total cylinder charge rfrges indicates the total amount of gas flowing through the cylinder. The entire cylinder charge rfrges is assigned to a second multiplier 26th supplied, in which the entire cylinder charge rfrges is multiplied by the residual gas rate rragrzw, which is determined separately, in order to obtain a residual gas charge rfragr.

The result of the multiplication is then sent to a second differential term 27 fed. In the second differential term 27 the difference between the normalized charge rfrges and the total cylinder charge rfrges multiplied by the residual gas rate rragrzw is subtracted to obtain the current air charge rlfgsb as the result of the subtraction at the output of the second differential element 27 to obtain.

• Die ungefilterte AGR-Füllung rfrexroh wird einem nicht invertierenden Eingang eines dritten Differenzgliedes 30 zugeführt. Die Restgas-Füllung rfragr wird dem invertierenden Eingang des dritten Differenzgliedes 30 zugeführt. Die in dem dritten Differenzglied 30 gebildete AGR-Füllungsdifferenz als Differenz der ungefilterten AGR-Füllung rfrexroh und der Restgas-Füllung rfragr wird in einem dritten Multiplikationsglied 31 mit einem zweiten Dynamikkorrekturfaktor fvisragr multipliziert und das Multiplikationsergebnis einem zweiten Integrationsglied 32 zugeführt.

The residual gas rate rragrzw is determined as follows:

• The unfiltered EGR filling rfrexroh is a non-inverting input of a third differential element 30th fed. The residual gas filling rfragr is the inverting input of the third differential element 30th fed. The one in the third differential term 30th The EGR filling difference formed as the difference between the unfiltered EGR filling rfrexroh and the residual gas filling rfragr is calculated in a third multiplication element 31 multiplied by a second dynamic correction factor fvisragr and the multiplication result to a second integration element 32 fed.

At the output of the second integration element 32 the result is a partial pressure with respect to the EGR charge proportion as EGR partial pressure, which is obtained by integrating the EGR charge difference multiplied by the second dynamic correction factor fvisragr. The second dynamic correction factor fvisragr represents a second time constant which describes the effect of the intake manifold with regard to the recirculated exhaust gas. The EGR partial pressure psrext is divided by the modeled intake manifold pressure ps in order to obtain the residual gas rate rragrzw as the pressure ratio.

The functional representation of the 2 dissolves from the approach followed in the prior art of adding the modeled partial pressures. Instead, rlroh and rfrexroh are added from the partial fills provided on the input side and in the first differentiator, which is determined by the first difference unit 22nd , the first multiplier 23 , the first integration link 24 and the map block 25th is formed (upper feedback loop), a total cylinder charge rfrges is calculated. A first time constant is used as a basis, which is specified by the first dynamic correction factor fvisrm.

The use of the first differential term 22nd enables a simple construction of the first differentiating block, in which the sum of the partial fillings rlroh and rfrexroh are subtracted from the total cylinder fill rfrges. In this way, an intake manifold pressure model can be implemented which, as before, assumes and models the low-pass filter effect based on the volume of the intake manifold with a specific time constant.

In the lower part (lower feedback loop) of the functional representation of the 2 the dynamic behavior of the intake manifold with respect to the EGR charge ratio rfrexroh is modeled, a second differentiating element being formed by the elements, the third difference element 30th , third multiplication term 31 , second integration link 32 , Division member 33 and second multiplier 26th . By the third multiplication term 31 a second time constant is implemented by multiplying with the second dynamic correction factor fvisragr. This makes it possible to model the faster dynamic behavior of the EGR volume in the intake manifold. The determined partial pressure psrext is used to determine the residual gas rate rragrzw by dividing the two values with the modeled intake manifold pressure ps.

wobei Vh dem Hubvolumen eines Zylinders, Vagr näherungsweise dem Volumen der im Saugrohr 4 vorhandenen Abgaswolke und tagrisr einer modellierten AGR-Gastemperatur entsprechen.The second dynamic correction factor fvisragr can be calculated using the following formula: $$\text{fviasragr}=\left(\text{Vh}/\left(\text{Vagr}+\text{Vh}\right)\right)\cdot \left(\left(\text{tagrisr}+273\text{K}\right)/273\text{K}\right)\cdot 10.13\text{hPa}/\%,$$

where Vh is the displacement of a cylinder, Vagr is approximately the volume in the intake manifold 4th existing exhaust gas cloud and tagrisr correspond to a modeled EGR gas temperature.

When forming the volume ratio, the lower EGR mixing volume is used instead of the intake manifold volume. This is determined during the application. A dependence of the volume ratio on the operating point of the engine (intake manifold pressure, EGR mass flow, engine speed) is conceivable and could be implemented by a suitable map.

The functional diagram shows that with the present method, the two dynamic correction factors, i.e. the two time constants for the differentiating elements, can be set separately from one another, so that the calculation of the residual gas rate rragrzw can be modeled in a dynamic behavior independent of the intake manifold time constant.

In this structure it is possible to calculate a dynamically correct air charge and residual gas rate in order to take into account different points of introduction of the exhaust gas recirculation line into the intake manifold. The correct air fillings and residual gas rates determined with the above procedure allow the intake manifold 4th correctly set the amount of fuel to be injected and specify the correct ignition angle.

Claims (7)

Method for determining an entire cylinder charge (rfrges) in cylinders of an internal combustion engine (2) with exhaust gas recirculation, with exhaust gas being recirculated at an inlet point (10) into an intake manifold (4) for feeding a gas mixture into the cylinders (3), with the entire cylinder charge (rfrges) indicates an instantaneous total amount of gas in the cylinders (3), the total cylinder charge (rfrges) depending on a sum of the gas mass flows fed to the intake manifold (4) and depending on a first dynamic correction factor (fvisrm), which determines the dynamic behavior of the Describes the intake manifold (4) with regard to the intake manifold pressure that is established there, the entire cylinder charge (rfrges) being determined as a function of a current intake manifold pressure (ps), the current intake manifold pressure (ps) being determined by integrating the with the first dynamic correction factor (fvisrm) acted upon difference between an unfiltered cylinder filling, which indicates the filling, which is through di e would adjust the gas mass flows fed to the intake manifold (4), and the total cylinder charge (rfrges) is determined, the total cylinder charge (rfrges) as a function depending on the current intake manifold pressure (ps), depending on a current engine speed (nmot) and depending on Correction factors, in particular an altitude factor (fho) for adapting to an ambient pressure and a combustion chamber temperature factor (ftbr) for taking into account the gas temperature in the cylinders (3), is determined, with exhaust gas at an inlet point (10) in an intake manifold (4) for feeding a Gas mixture is fed back into the cylinder (3), the residual gas rate (rragrzw) indicating the current proportion of exhaust gas in the cylinder (3) total gas, with the following steps: - Determination of the residual gas rate (rragrzw) depending on an exhaust gas partial pressure ( psrext) and depending on the current intake manifold pressure (ps), the exhaust gas partial pressure depending on the intake manifold supplied exhaust gas mass flow, depending on a second dynamic correction factor, which describes the dynamic behavior of the intake manifold (4) taking into account the introduction point (10) with regard to the resulting exhaust gas partial pressure (psrext), and is determined depending on a current exhaust gas cylinder charge. Procedure according to Claim 1 , whereby the current exhaust gas cylinder filling is determined depending on the residual gas rate (rragrzw) and the total cylinder filling (rfrges). Procedure according to Claim 1 or 2 , the exhaust gas partial pressure (psrext) by integrating the difference, to which the second dynamic correction factor is applied, between the AG R filling proportion, which indicates a filling of exhaust gas in the cylinder (3), which is set due to the exhaust gas mass flow currently supplied to the intake manifold (3) and the exhaust gas cylinder charge is determined. Method for determining a current air charge (rlfgsb) in cylinders (3) of an internal combustion engine (2) with exhaust gas recirculation, with exhaust gas being recirculated at an inlet point (10) into an intake pipe (4) for feeding a gas mixture into the cylinder (3) following steps: - Determine the total cylinder charge (rfrges) according to the method according to Claim 1 ; - Providing a residual gas rate (rragrzw) or determining the residual gas rate (rragrzw) according to a method according to one of the Claims 1 until 3 ; - Determination of the current air charge (rlfgsb) depending on the total cylinder charge (rfrges) and the residual gas rate (rragrzw). Method for controlling an internal combustion engine (2), comprising the following steps: determining the instantaneous air charge according to the method Claim 4 ; - Control of a position of a throttle valve (11) of the internal combustion engine (2) and / or an injection quantity of fuel into an intake manifold (4) of the internal combustion engine (2) and / or an ignition angle for igniting an air / fuel mixture depending on the current air charge ( rlfgsb). An engine control unit for controlling an internal combustion engine, which is designed, a method according to one of the Claims 1 until 5 perform. Computer program which contains a program code which, when it is executed on a data processing unit, a method according to one of the Claims 1 until 5 executes.

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