DE10213138B4 - Method, computer program, control and / or regulating device for operating an internal combustion engine - Google Patents

Abstract

Method for operating an internal combustion engine (10), in which, when determining a pressure (ps) in a region (20) situated upstream of an inlet valve (22), a fresh air charge (rl) of a combustion chamber (16) or during the determination of the fresh air charge ( rl) of the combustion chamber (16) the pressure (ps) in the upstream of the inlet valve (22) located region (20) is taken into account, wherein in the determination also takes into account a speed (nmot) of a crankshaft (18) of the internal combustion engine (10) is, wherein the fresh air filling (rl) or the pressure (ps) by means of thermodynamic equations and / or by flow equations to at least one discrete time (72) during a cycle of the internal combustion engine (10) is calculated (66), wherein in the calculation After closing the inlet valve (22) in the combustion chamber (16) existing residual gas (m_rg) is taken into account, characterized in that the temperature (T_bres) of bef in the combustion chamber (16) bef indium gas mixture is determined on the basis of the mixture formula taking into account the mass fractions (m_rgreasp, m_fg) of the reaspirative residual gas and the fresh air and the respective temperatures (T_rgreasp, T_fg).

Description

State of the art

The invention relates firstly to a method for operating an internal combustion engine in which, when determining a pressure in a region located upstream of an inlet valve, a fresh air filling of a combustion chamber or in the determination of the fresh air filling of the combustion chamber the pressure in the region located upstream of the inlet valve is taken into account , Wherein a speed of a crankshaft of the internal combustion engine is taken into account in the determination.

Such a method is known from the market. It is used for example in internal combustion engines with intake manifold injection. In such internal combustion engines, either an air mass sensor in the vicinity of a throttle or a Saugrohrdrucksensor is installed in a suction pipe. For the control of the internal combustion engine, however, both the intake manifold pressure and the fresh air charge are usually required. This means that the variable not detected by a sensor in each case has to be simulated by means of a model. The corresponding model is called a "charge-exchange model".

On the basis of this charge exchange model, the fresh air mass drawn in by the internal combustion engine is calculated, for example, from the input variable "intake manifold pressure". The calculation is made by means of a linear equation comprising a linear slope factor multiplied by the difference between the intake manifold pressure and a partial pressure of an internal residual gas.

By taking into account this internal residual gas, the fact is taken into account that the cylinder charge of internal combustion engines always includes a certain amount of residual gas from the last combustion. In an internal exhaust gas recirculation by valve overlap also passes a certain proportion of the exhaust gas from the exhaust pipe back into the combustion chamber. This can be z. B. be achieved in that the exhaust valve closes only after exceeding the top dead center of the piston of the internal combustion engine. Thus, a period may arise in which the exhaust valve and the intake valve of a combustion chamber are open at the same time. Based on a camshaft revolution, this period is referred to as the overlap angle.

From the marketplace, functions for calculating the internal partial pressure of the residual gas in the combustion chamber and the linear gradient factor are known with the help of maps. In the maps, for example, the speed of the crankshaft of the internal combustion engine, the overlap angle of the camshaft and optionally the overlap center of gravity of the camshafts are fed. However, such maps have a relatively large memory requirement. In addition, there is a need in today's internal combustion engines to be able to calculate the fresh air filling or intake manifold pressure with even greater precision.

From the market simulation programs are also known with which the thermal and dynamic conditions within the internal combustion engine can be simulated very fine-step. The actual processes during the charge cycle can be simulated quite well with such simulation programs. Even during operation occurring pulsations in the intake manifold and in the exhaust system of the internal combustion engine can be modeled. Due to the high computational complexity, however, an invoice in real time, for example, in a control unit of the internal combustion engine with such simulation programs is not possible.

The EP 1 104 844 A2 describes a control method for varying the valve timing of intake and exhaust valves of an internal combustion engine, wherein an intake valve closing point is controlled so as to achieve a desired intake air amount and a desired amount of internal exhaust gas recirculation for a cylinder charge.

From the publication DE 198 44 637 C1 a method for determining the exhaust gas recirculation mass flow of an internal combustion engine with exhaust gas recirculation is known, wherein an exhaust gas recirculation arranged in the exhaust gas recirculation valve is modeled using a physically based model for a throttle point to determine based on the model exhaust gas recirculation mass flow through the exhaust gas recirculation. In particular, the EGR mass flow is determined as a function of the exhaust back pressure, the exhaust gas temperature, the effective cross-sectional area of the exhaust gas recirculation valve, a flow characteristic and a gas constant.

The present invention therefore has the object of developing a method of the type mentioned so that with him with little computational effort, but at the same time with high precision, the desired size can be determined. This object is achieved by a method for operating an internal combustion engine having the features mentioned in the independent claims. In addition, a computer program and a control device for carrying out the method are specified.

Advantages of the invention

By using thermodynamic equations and / or flow equations, the actual thermal and dynamic conditions in the combustion chamber and in the combustion chamber near areas of the internal combustion engine can be determined with very high precision. In this case, in contrast to the use of empirical equations and / or maps, the complex thermal and dynamic behavior of modern internal combustion engines can be modeled very precisely. The computational load of a control unit, with the functions of the internal combustion engine are controlled or regulated, is very low:
The formula or resulting formulas resulting from the thermodynamic equations and / or flow equations for calculating the fresh air charge or the pressure must in fact only be calculated once during a working cycle of the internal combustion engine. A continuous fine-step calculation of the current thermal and dynamic state in the internal combustion engine, as is required in conventional simulation programs using large computer systems, is not required in the method according to the invention. Furthermore, the influence of the actual temperature of the supplied fresh gas and the temperature of the exhaust gas can be simulated physically in a simple manner, which also benefits the precision of the calculation result.

IEs it is proposed that the calculation is taken into account after the closing of an intake valve in the combustion chamber residual gas. Such residual gas is to a small extent almost always present, but in particular present when the internal combustion engine has an internal or external exhaust gas recirculation. In such an internal exhaust gas recirculation, the opening timing of the intake valve and / or the closing time of an exhaust valve is set so that the combustion chamber is filled at the beginning of a new cycle not only with fresh air, but also with residual exhaust gas originating from a previous combustion. By residual gas, the flame temperature can be reduced in the combustion chamber and thus the nitrogen oxide formation can be reduced. The consideration of this residual gas present in the combustion chamber is very well possible with the method according to the invention.

Furthermore, it is proposed that during the calculation, a residual residual gas present after closing the inlet valve in the combustion chamber and / or a residual purge gas present in the combustion chamber after closing the inlet valve be taken into account. This further improves the accuracy in the calculation of the fresh air charge or the pressure in the region upstream of the intake valve. As used herein, the term "upstream" always refers to that region which is located between the inlet valve and the start of the intake manifold, regardless of whether the flow actually flows from the intake manifold into the combustion chamber or from the combustion chamber into the intake manifold.

Residual residual gas is understood as meaning the residual gas enclosed in the combustion chamber volume with combustion chamber temperature and under exhaust backpressure at the time of closing the exhaust valve of the internal combustion engine. The reaspirative residual gas is understood to mean the residual gas flowing during the valve overlap (ie simultaneously opened inlet and outlet valves) from a region located downstream of the outlet valve through the combustion chamber into the region located upstream of the inlet valve. It overlaps with the residual residual gas.

The sum of residual and reaspirative residual gas forms the entire internal residual gas of the internal combustion engine. By dividing the residual gas into a residual and a reaspirative fraction, comparatively simple thermodynamic and / or flow equations can be used to calculate the respective proportions. In addition, the influences on the various residual gas components, such as the switching timing of the intake and exhaust valve and the valve overlap can be considered even better.

unter Berücksichtigung der Massenanteile des residualen Restgases und/oder des reaspirativen Restgases und der Frischluft und der jeweiligen Temperaturen bestimmt werden. Diese Formel kann im Steuergerät leicht berechnet werden und bietet gute Ergebnisse.In this case, the temperature of the gas mixture in the combustion chamber based on the mixture formula

be determined taking into account the mass fractions of the residual residual gas and / or the reaspirative residual gas and the fresh air and the respective temperatures. This formula can be easily calculated in the controller and gives good results.

It is also particularly preferred if, in order to calculate the amount of the refractory residual gas present in the combustion chamber, it is assumed that in certain operating states of the internal combustion engine gas can flow from an area located downstream of an outlet valve via an equivalent throttle into the area located upstream of the inlet valve Amount of the return gas from a supercritical mass flow is calculated from at least one of the opening angle of the intake valve with the closing angle of the exhaust valve, a temperature of the gas in the downstream of the exhaust valve, a pressure of the gas in the downstream of the exhaust valve, and / or a ratio of the pressure of the gas in the downstream of the exhaust valve region to the pressure of the gas in the upstream of the intake valve region is dependent.

First of all, it should be pointed out that the term "downstream" is always used to denote that region which is located between the outlet valve and the end of the exhaust pipe, irrespective of whether the flow is actually from the combustion chamber into the exhaust pipe or from the exhaust pipe into the combustion chamber flows. So he refers to the direction of the "mainstream".

The above-mentioned model assumption corresponds very well to the actual conditions of the internal combustion engine. The flow of the exhaust gas through the opening of the exhaust valve, through the combustion chamber, and through the opening of the intake valve can be expressed very well by a flow of a gas through an equivalent throttle. Such a flow through a throttle can be calculated with high precision by the known thermodynamic and aerodynamic equations. The properties of the equivalent throttle can be determined in experiments.

The supercritical mass flow may also depend on the position of the center of gravity of the intersection of the two valve curves. If the closing speed of the exhaust valve is equal to the opening speed of the intake valve, the center of gravity is just below the top of the approximately triangular section. At a closing speed different from the opening speed, the center of gravity, and thus the time at which the said values are detected, correspondingly shifts.

It is also advantageous if the supercritical mass flow is multiplied by the output value of a characteristic curve in which the ratio of the pressure in a region downstream of the outlet valve to the pressure in the combustion chamber or in an area upstream of the inlet valve is fed. Such a characteristic is also referred to as "characteristic outflow". This is an equation known from fluid mechanics, which describes the flow through a diaphragm. With it, the flow behavior is expressed in a simple manner as a function of the pressure difference on both sides of the panel.

It is assumed that the gas flowing back during the valve overlap has exhaust gas temperature and exhaust back pressure. However, when pulsations of the pressure downstream of the exhaust valve and upstream of the intake valve occur depending on the rotational speed of the crankshaft of the internal combustion engine, during the intersection of the pressure quotient may assume a value different from its mean value.

In order to take this into account in the calculation, it is also proposed that the ratio of the pressure of the gas in the region upstream of the inlet valve to the pressure of the gas in the region downstream of the outlet valve be multiplied by a correction factor which depends on the speed of the crankshaft the internal combustion engine depends.

In another development, it is proposed that, in the calculation, the measured or modeled pressure of the gas in the region located downstream of the exhaust valve be corrected as a function of the rotational speed of the crankshaft of the internal combustion engine and / or as a function of the closing angle of the exhaust valve. This accounts for the fact that the pressure in the region downstream of the exhaust valve may pulsate at certain speed ranges and / or when the exhaust valve closes at some point in the engine's working cycle. These pressure pulsations are taken into account by the correction proposed according to the invention.

In the simplest case, the correction can be carried out by multiplying the measured pressure with the output of a map into which the rotational speed of the crankshaft of the internal combustion engine and the closing angle of the exhaust valve are fed. This correction can also take into account that when the exhaust valve closes well before the top dead center or significantly after the top dead center of the piston associated with the combustion chamber, and at higher speeds of the crankshaft of the internal combustion engine, a pressure compensation no longer takes place. Closes the exhaust valve before the top dead center of the piston, the pressure of the residual residual gas is higher, on the other hand closes the exhaust valve after the top dead center of the piston, the pressure of the residual residual gas in the combustion chamber is lower.

Similarly, in the calculation, the measured or modeled pressure of the gas may be in the upstream of the intake valve Range can be corrected depending on the speed of the crankshaft of the internal combustion engine and / or depending on the opening angle of the intake valve.

It is further provided that the mass of the residual residual gas is determined by means of the combustion chamber volume, which is present at the closing time of the exhaust valve or approximately in the middle of the valve overlap. It would also be possible to use that combustion chamber volume in the calculation, which is present when both valves have the same valve lift. In all these cases, the mass of the residual residual gas can be calculated precisely.

The thermodynamic calculations are particularly preferably based on the equation of state for ideal gases. This allows significant simplifications in the calculation, without affecting the result.

It can also be assumed according to the invention that the heat capacity and / or the isentropic exponent of the residual gas or the proportions of the residual gas have the same values as those of fresh air. This assumption is possible, since in both gases predominantly nitrogen is present.

A further approximation, which contributes to the simpler implementation of the method according to the invention, is that the equation of state is used for ideal gases for adiabatic conditions. In the thermodynamic relationships so heat transfer to the valves, on the walls of the combustion chamber and other components in the combustion chamber and in the combustion chamber near areas are neglected. This is possible without degrading the accuracy of the calculation too much.

However, for example, the influence of heat transfers to a sensed or modeled temperature in the region upstream of the inlet valve may be taken into account by means of a correction function. Thus, on the one hand adiabatically calculated, which allows considerable simplification in the derivation of the equations, on the other hand, the influence of heat transfer is not completely unconsidered. The calculation is thus simple yet precise.

The invention also relates to a computer program suitable for carrying out the above method when executed on a computer. It is preferred if the computer program is stored on a memory, in particular on a flash memory.

Furthermore, the invention relates to a control and / or regulating device for operating an internal combustion engine. In such a control and / or regulating device is proposed that it comprises a memory on which a computer program of the above type is stored.

drawing

Hereinafter, a particularly preferred embodiment of the present invention will be explained in detail with reference to the accompanying drawings. In the drawing show:

1 a schematic representation of an internal combustion engine;

2 : a diagram showing the procedure for the determination of a standardized fresh air filling in the operation of the internal combustion engine of 1 shows;

3 a diagram in which the stroke of a piston is plotted against the angle of a crankshaft;

4 a diagram in which the valve position of an intake and exhaust valve of the internal combustion engine of 1 is shown over the angle of a camshaft;

5 a graph showing the derivation of a thermodynamic equation for calculating the fresh air charge of a combustion chamber of the internal combustion engine of 1 shows; and

6 : a representation similar 5 in which the derivation is further detailed.

Description of the embodiment

In 1 an internal combustion engine carries the reference numeral 10 , It includes several cylinders, of which in 1 only those with the reference number 12 is visible. There is a piston in it 14 Slidably guided, which a combustion chamber 16 limited. About a connecting rod (without reference numeral) is the piston 14 with a symbolic crankshaft 18 connected.

Fresh air is the combustion chamber 16 via a suction pipe 20 and an inlet valve 22 fed. In the intake manifold 20 is an injector 24 present, which with a fuel system 26 connected is. Upstream of the injector 24 is a throttle 28 arranged, which by a servomotor 30 can be moved to a desired position. Between the injector 24 and the throttle 28 be the temperature the supplied fresh air from a sensor 32 and the pressure of the supplied fresh air from a sensor 34 tapped.

The hot combustion gases are removed from the combustion chamber 16 via an exhaust valve 36 and an exhaust pipe or exhaust manifold 38 dissipated. A catalyst 40 cleans the exhaust gases. Between the exhaust valve 36 and the catalyst 40 The temperature of the exhaust gas is measured by a temperature sensor 42 and the pressure of the exhaust gas from a pressure sensor 44 tapped.

The internal combustion engine 10 has a double continuous camshaft control. This means that the closing or opening times of the intake valve 22 or the exhaust valve 36 can be adjusted continuously. For this purpose, the inlet valve 22 from an intake camshaft 46 and the exhaust valve 36 from an exhaust camshaft 48 actuated. About actuators 50 and 52 can the camshafts 46 and 48 be adjusted during operation so that the desired closing or opening times are present.

That in the combustion chamber 16 the internal combustion engine 10 existing air-fuel mixture is from a spark plug 54 ignited, which in turn from an ignition system 56 is controlled.

The operation of the internal combustion engine 10 is from a control and regulating device 58 controlled or regulated. The control and regulating device 58 is on the input side with the temperature sensor 32 and the pressure sensor 34 in the intake manifold 20 connected. It also receives signals from the temperature sensor 42 and from the pressure sensor 44 in the exhaust pipe 38 , A giver 60 also provides signals that make up the speed of the crankshaft 18 and their angular position can be obtained. Analogous to this are sensors 62 and 64 provided, which is the angular position of the intake camshaft 46 or the exhaust camshaft 48 to capture. The output side is the control and regulating device 58 with the injector 24 , the servomotor 30 the throttle 28 , the actors 50 and 52 the intake camshaft 46 or the exhaust camshaft 48 and with the ignition system 56 connected.

In order to determine the amount of fuel that the user of the internal combustion engine 10 desired torque and at the desired mixture composition in the combustion chamber 16 is achieved, it is necessary to reduce the amount of fuel into the combustion chamber 16 to determine at a working cycle fresh air. Although a sensor could be used for this purpose, this is not used for cost reasons, if, as in the present case, in the intake manifold 20 a pressure sensor 34 is available. In an embodiment not shown, an air mass sensor is installed in the intake manifold instead of the pressure sensor. In this case, to determine the air filling of the combustion chamber from the detected signals, the pressure in the intake manifold would have to be determined.

The determination of the fresh air filling rl (this is a fresh air filling normalized to standard conditions) is determined by the in 1 illustrated internal combustion engine 10 on the in 2 shown manner performed. The corresponding method is a computer program on a memory in the control unit 58 stored.

From the sensors of the internal combustion engine 10 Various readings are provided. The temperature sensor 32 in the intake manifold 20 measures the temperature T_fg of the intake air in the intake manifold 20 , The pressure sensor 34 measures the pressure ps of the intake air in the intake manifold 20 , The temperature sensor 42 measures the temperature T_abg of the exhaust gas in the exhaust pipe 38 , and analogously detects the pressure sensor 44 the pressure p_abnav of the exhaust gas in the exhaust pipe 38 , The giver 60 provides information about the current speed nmot of the crankshaft 18 as well as the angular position wk of the crankshaft 18 , The encoders deliver this analogously 62 and 64 Information about the angular positions wne or wna of the intake camshaft 62 or the exhaust camshaft 64 ,

These measured values are put into a processing block 66 fed. It uses thermodynamic equations and flow equations to calculate the measured values after the end of a suction stroke of the piston 14 in the cylinder 12 present normalized fresh air filling rl calculated (reference numeral 68 in 2 ). To simplify the calculation, certain physical assumptions are made. For example, it is assumed that in the combustion chamber 16 and in the combustion chamber near areas in the intake manifold 20 and in the exhaust pipe 38 Adiabatic conditions are present.

Heat transfers from the components present in these areas to the flowing gas are thus initially not taken into account. Nevertheless, in order to achieve as precise a calculation result as possible, they are in the processing block 66 also correction functions 70 filed by the simplifications in the flow equations and thermodynamic equations 68 caused inaccuracies again at least partially compensate. The temperature of the intake air is thus modified accordingly by the correction functions.

The calculation of the standardized fresh air filling rl is not continuous. Instead, it becomes in the present embodiment once during a working cycle of the cylinder 12 (under A work cycle is understood in a four-stroke internal combustion engine passing through all four cycles) at a discrete time, in this case in the region of top dead center of the piston 14 , performed before the beginning of a suction stroke (reference numeral 72 in 3 ). The calculation of the fresh air filling rl thus takes place in one to the crankshaft 18 angle synchronous time grid.

The calculations in the processing block 66 are formulaic in the 5 and 6 shown. In equation (1) in 5 the standardization of the fresh air filling is given. In this case, the mass m_fg of the fresh air supplied is related to a standard mass m0. The mass m0 again results from the ideal gas equation (2) at a standard pressure p0 of 1013.25 hPa, a standard temperature T0 of 273 Kelvin and the stroke volume Vh of the piston 14 the internal combustion engine 10 , The factor Zylza is the number of cylinders of the internal combustion engine 10 ,

The fresh air mass m_fg in equation (1) results from the equations (3) to (6) in 5 , Equation (4) is the general gas mixture formula with which the temperature in the combustion chamber 16 at a time when the inlet valve 22 closes, is calculated. At this time is located in the combustion chamber 16 a residual gas mass m_rg with a temperature T_rg and a fresh gas mass m_fg with a temperature T_fg.

As can be seen from equation (5), the total mass m_ges of the combustion chamber is set 16 existing gas from the fresh air mass m_fg and the residual gas mass m_rg together. It is again derived from the ideal gas equation at a pressure p_bres in the combustion chamber 16 at the time when the inlet valve 22 closes. The residual gas mass m_rg will be discussed in detail below.

Depending on the speed nmot of the crankshaft 18 the internal combustion engine 10 and angle wnwe intake camshaft 46 in which the inlet valve 22 it can open in the intake manifold 20 come to pressure pulsations. Therefore, the pressure p_bres does not always correspond to that of the pressure sensor 34 detected intake manifold pressure ps. This is therefore in accordance with equation (6) by a map FPESKORR depending on the speed nmot and depending on the opening angle wnwe of the intake valve 22 corrected.

The residual gas mass m_rg is the following:
To reduce the nitrogen oxides in the exhaust gas of the internal combustion engine 10 has the in 1 illustrated internal combustion engine 10 via a so-called "internal exhaust gas recirculation". This is understood to mean that part of the exhaust gases from the exhaust pipe 38 back in the combustion chamber 16 get back or the combustion chamber 16 does not leave at all. That proportion of exhaust gas, which in the combustion chamber 16 remains, is "residual residual gas", that proportion of exhaust gas, which enters the combustion chamber 16 is sucked back, becomes "reaspirative residual gas" (see equation (8) in 6 ).

The mass m_rgres of the residual residual gas and m_rgreasp of the residual residual gas is determined by the closing angle wnwa of the outlet valve 36 and the opening angle wnwe of the intake valve 22 and the resulting valve overlap wnwvue determined (see. 4 ).

Are the equations (2) to (6) in the equation (1) in 5 used, the equation (7) results in 6 , Using equations (8) to (13) in 6 below the equation (7), the residual gas mass m_rg can be determined. The mass m_rgres of the residual residual gas is determined by means of the ideal gas equation (9). It is assumed that the pressure of the residual residual gas is normally shortly before the exhaust valve closes 36 equal to the pressure of the exhaust gas in the exhaust pipe 38 is which of the pressure sensor 44 is detected.

Close the exhaust valve 36 however, before the top dead center or clearly after the top dead center, this assumption is no longer correct. The same applies at high speeds of the crankshaft 18 , For this reason, the measured value p_abnav of the pressure sensor becomes 44 multiplied by the output of a map FPABNAVRESKOR, in which on the one hand the speed nmot of the crankshaft 18 and on the other hand, the closing angle wnwa of the exhaust valve 36 is fed (see equation (10)).

In determining the volume V_brrgres used in the equation (9), a case distinction is made:
When the exhaust valve 36 closes before the inlet valve 22 opens (so if there is no valve overlap), the volume V_brrgres is equal to the volume of the combustion chamber 16 at the time when the exhaust valve 36 closes. Opens the inlet valve 22 however, before the exhaust valve 36 closes (this case is in 4 represented by the valve overlap wnwvue), for the volume V_brrgres that volume of the combustion chamber 16 taken at a middle time between the opening timing of the intake valve 22 and the closing time of the exhaust valve 36 is present. It would also be possible to use that volume which is present at a time when the strokes of the two valves are the same. The temperature T_brrgres used in equation (9) is that of the temperature sensor 42 detected temperature at the already mentioned in connection with the volume V_brrgres times.

The determination of the mass m_rgreasp of the reaspirative residual gas takes place in equation (12) in 6 , When determining the mass of the reaspirative residual gas, the simplifying assumption is made that the flow from the exhaust pipe 38 through the outlet valve 36 over the combustion chamber 16 and the inlet valve 22 in the suction pipe 20 corresponds to a flow through an equivalent throttle or through an equivalent aperture. This mass flow lies during the overlap period wnwvue, ie between wnwe and wnwa ( 4 ) in front.

The opening released during the intersection is transformed into an equivalent opening throughout the cycle. The corresponding constant mean mass flow has the normalized supercritical value MSNREASP. In the present case, the mass flow MSNREASP thus depends only on the overlap angle wnwvue. Conceivable. However, it is also a function of the center of gravity of the overlap area (dashed area in 4 ). With regard to the temperature of the residual gas flowing back, it is assumed that this is that of the temperature sensor 42 detected exhaust gas temperature T_abg corresponds.

The supercritical mass flow MSNREASP is multiplied in equation (12) by the output of a so-called "characteristic outflow" (abbreviated "KLAF"). This describes the flow through a diaphragm or a throttle point as a function of the pressure difference in front of / behind the diaphragm or throttle point. It is further assumed that the exhaust gas flowing back during the valve overlap wnwvue has the exhaust back pressure p_abnavk.

Since it is in operation of the internal combustion engine 10 to pressure pulsations in the exhaust pipe 38 and in the intake manifold 20 can come, and especially at high speeds, the pressure ratio ps / p_abnav multiplied by the output of a characteristic FPABGKOR, in which the speed nmot is fed from the encoder 60 is detected. The size umsrlm is a conversion factor with which a mass flow [kg / h] can be converted into a percentage of the combustion chamber filling under standard conditions. This is in turn derived from equation (13). KUMSRL is a constant dependent on the stroke volume.

The temperature T_rg of the residual gas is calculated by means of the formulas which in 6 are given above the equation (7). Equation (14) again corresponds to the mixture equation known from thermodynamics, in which the temperature T_rgreasp of the reaspirative residual gas was determined by the Poisson equation (15). The equations (9) to (13), which are also used to determine the temperature T_rg, have already been explained above. They will not be discussed again in detail here.

As based on the 5 and 6 can be seen, with the measured values T_fg, p_abnav, ps, nmot, T_abg, wk (to determine the different volumes V_x), as well as wnwe and wnwa (from which in turn can be derived wnwvue) ultimately the relative fresh air filling rl can be determined by calculation. To simplify the thermodynamic equations, adiabatic ratios are assumed and it is assumed that the heat capacity and the isentropic exponent (κ) of the exhaust gas and the fresh air are the same. This assumption is correct, since both gases consist equally of approximately 80% nitrogen.

To simplify the calculation of the backflow of the exhaust gas into the intake manifold 20 the equations of a flow through an aperture are used. Again, this assumption is correct, since ultimately the column of the exhaust valve 36 and the intake valve 22 can be considered as an equivalent orifice. The inaccuracies resulting from the assumption of adiabatic ratios are substantially compensated by the different correction functions. The calculations of formulas (1) to (15) can be done in the control unit 58 be done very quickly. In the present exemplary embodiment, they are performed once within a working cycle, namely shortly before the beginning of a time haul. The corresponding period is in 3 with the reference number 72 Mistake. In an embodiment, not shown, of a conventional angle synchronous calculation grid, this point in time is opposite to the representation in FIG 3 shifted by about 70 ° to the front.

Claims (17)

Method for operating an internal combustion engine ( 10 ), in which when determining a pressure (ps) in an upstream of an inlet valve ( 22 ) ( 20 ) a fresh air charge (rl) of a combustion chamber ( 16 ) or in the determination of the fresh air charge (rl) of the combustion chamber ( 16 ) the pressure (ps) in the upstream of the inlet valve ( 22 ) ( 20 ), wherein in the determination also a rotational speed (nmot) of a crankshaft ( 18 ) of the internal combustion engine ( 10 ), wherein the fresh air charge (rl) or the pressure (ps) by means of thermodynamic equations and / or by means of flow equations to at least one discrete time ( 72 ) during a working cycle of the internal combustion engine ( 10 ) is calculated ( 66 ), wherein in the calculation after closing the inlet valve ( 22 ) in the combustion chamber ( 16 ) existing residual gas (m_rg) is taken into account, characterized in that the temperature (T_bres) of the in the combustion chamber ( 16 ) gas mixture based on the mixture formula

is determined taking into account the mass fractions (m_rgreasp, m_fg) of the reaspirative residual gas and the fresh air and the respective temperatures (T_rgreasp, T_fg). A method according to claim 1, characterized in that in the calculation after closing of the inlet valve ( 22 ) in the combustion chamber ( 16 ) residual residual gas (m_rgres) and / or after closing the inlet valve ( 22 ) in the combustion chamber ( 16 ) existing reaspirative residual gas (m_rgreasp) is / will be considered. A method according to claim 1 or 2, characterized in that the temperature (T_bres) of the in the combustion chamber ( 16 ) gas mixture based on the mixture formula

is determined taking into account the mass fractions (m_rgres, m_rgreasp, m_fg) of the residual residual gas and the reaspirative residual gas and the fresh air and the respective temperatures (T_rgres, T_rgreasp, T_fg). Method according to one of the preceding claims, characterized in that for calculating the amount (m_rgreasp) of the in the combustion chamber ( 16 ) assumed reaspirative residual gas, that in certain operating conditions of the internal combustion engine ( 10 ) Gas from a downstream of an exhaust valve ( 36 ) ( 38 ) via an equivalent throttle in the upstream of the inlet valve ( 22 ) ( 20 ), wherein the amount (m_rgreasp) of the recirculating gas is calculated from a supercritical mass flow (MSREASP) flowing through that restrictor, and wherein the supercritical mass flow (MSREASP) is from an overlap (wnwvue) of the opening angle (wnwe) of the inlet valve ( 22 ) with the closing angle (wnwa) of the exhaust valve ( 36 ), a temperature of the gas in the downstream of the exhaust valve, a pressure of the gas in the downstream of the exhaust valve and / or a ratio of the pressure (p_abnav) of the gas in the downstream of the exhaust valve ( 36 ) ( 38 ) to the pressure (ps) of the gas in the upstream of the inlet valve ( 22 ) ( 20 ) depends. A method according to claim 4, characterized in that the supercritical mass flow also depends on the position of the center of gravity of the intersection of the two valve curves. Method according to one of claims 4 or 5, characterized in that the supercritical mass flow (MSREASP) is multiplied by the output value of a characteristic curve (KLAF), in which the ratio of the pressure (p_abnav) in a downstream of the outlet valve ( 36 ) ( 38 ) to the pressure (ps) in the combustion chamber or in an upstream of the inlet valve ( 22 ) ( 20 ) is fed. Method according to claim 6, characterized in that the ratio of the pressure (ps) of the gas in the upstream of the inlet valve ( 22 ) ( 20 ) to the pressure (p_abnav) of the gas in the downstream of the exhaust valve ( 36 ) ( 38 ) is multiplied by a correction factor (FPABGKOR) which depends on the rotational speed (nmot) of the crankshaft ( 18 ) of the internal combustion engine ( 10 ) depends. Method according to one of claims 1 to 7, characterized in that in the calculation of the measured or modeled pressure (p_abnav) of the gas in the downstream of the exhaust valve ( 36 ) ( 38 ) depending on the speed (nmot) of the crankshaft ( 18 ) of the internal combustion engine ( 18 ) and / or depending on the closing angle (wnwa) of the exhaust valve ( 36 ) is corrected. Method according to one of the preceding claims, characterized in that in the calculation of the measured or modeled pressure (ps) of the gas in the upstream of the inlet valve ( 22 ) ( 20 ) depending on the speed (nmot) of the crankshaft ( 18 ) of the internal combustion engine ( 10 ) and / or depending on the opening angle (wnwe) of the inlet valve ( 22 ) is corrected. Method according to one of claims 1 to 9, characterized in that the mass (m_rgres) of the residual residual gas is determined by means of the combustion chamber volume (V_es), which is present at the closing time of the exhaust valve or approximately in the middle of the valve overlap (wnwvue). Method according to one of the preceding claims, characterized in that in the thermodynamic calculations of the equation of state for ideal gases is assumed. A method according to claim 11, characterized in that it is assumed in the calculation that the heat capacity and / or the isentropic exponent of the residual gas or the proportions of the residual gas have the same values as those of fresh air. Method according to one of claims 11 or 12, that the equation of state is used for ideal gases for adiabatic conditions. Method according to one of claims 11 to 13, characterized in that the influence of heat transfer to a detected or modeled temperature in the region upstream of the inlet valve by means of a correction function is taken into account. Computer program, characterized in that it is suitable for carrying out the method according to one of the preceding claims, when it is executed on a computer. Computer program according to claim 15, characterized in that it is stored on a memory, in particular on a flash memory. Control and / or regulating device ( 58 ) for operating an internal combustion engine ( 10 ), characterized in that it comprises a memory on which a computer program according to one of claims 15 or 16 is stored.

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