EP0820559B1 - Process for finding the mass of air entering the cylinders of an internal combustion engine with the aid of a model - Google Patents

Description

The invention relates to a method for model-based determination the flowing into the cylinders of an internal combustion engine Air mass according to the preamble of claim 1.

Engine control systems for internal combustion engines that work with fuel injection require the air mass m _{cyl drawn in} by the engine as a measure of the engine load. This parameter forms the basis for realizing a required air-fuel ratio. Growing demands on engine control systems, such as the reduction of pollutant emissions from motor vehicles, mean that the load size for stationary and transient processes must be determined with low permissible errors. In addition to the above-mentioned operating cases, the precise load detection during the warm-up phase of the internal combustion engine offers considerable potential for reducing pollutants.

In air-mass-controlled engine control systems, it is in non-stationary operation that as the load signal of the internal combustion engine serving signal of the air mass meter, the upstream of the Intake pipe is arranged, no measure of the actual filling the cylinder because the volume of the intake manifold is downstream the throttle valve acts as an air reservoir that fills and must be emptied. The decisive air mass for the Injection time calculation is the air mass that comes from out of the intake manifold and into the respective cylinder.

In intake manifold pressure-guided engine control systems there are the output signal of the pressure sensor the actual pressure conditions in the intake manifold again, but the parameters are there i.a. only relatively due to the necessary averaging of the measured variable available late.

With the introduction of variable intake systems and variable valve controls are created for empirically derived models Obtaining the load size from measurement signals a very large variety of influencing variables, the corresponding model parameters influence.

Model-based calculation methods based on physical approaches represent a good starting point for the exact determination of the air mass in _cyl .

DE 39 19 488 C2 describes a device for regulating and for the predetermination of the intake air quantity of an intake manifold pressure-guided Internal combustion engine is known in which the throttle valve opening degree and the engine speed as the basis for Calculation of the current value in the combustion chamber of the Machine sucked air can be used. This calculated, current intake air volume is then used as a basis to calculate the predetermined value for the intake air quantity, which in the combustion chamber of the machine at a certain Time from the point at which the calculation is performed was sucked in, used. The pressure signal that downstream of the throttle valve is measured using corrected by theoretical relationships, making an improvement reached the determination of the intake air mass and so that a more precise calculation of the injection time is possible.

However, it is in the transient operation of the internal combustion engine desirable to determine the inflow into the cylinder Perform air mass even more precisely.

The invention has for its object to provide a method with which the actually in the cylinder of the internal combustion engine inflowing air mass with high accuracy can be determined. In addition, system-related dead times, that due to the fuel storage and the computing time can occur when calculating the injection time, be compensated.

This object is achieved according to the features of patent claim 1 solved.

Advantageous further developments can be found in the subclaims.

Based on a known approach, a model description results, that on a nonlinear differential equation based. The following is an approximation of this presented nonlinear equation. As a result of this The system behavior can be approximated using a bilinear Describe the equation that the quick fix of Relationship in the engine control unit of the motor vehicle under real-time conditions allowed. The chosen model approach includes thereby the modeling of variable suction systems and systems with variable valve controls. The through this arrangement and by dynamic reloading, i.e. through reflections effects caused by pressure waves in the intake manifold exclusively through the selection of stationary determinable parameters of the model are taken into account very well. All model parameters are physically interpretable on the one hand and on the other hand exclusively from stationary measurements win.

Most algorithms for discrete-time solving of the differential equation, the behavior of the model used here describes, especially with a low pressure drop above the throttle valve, i.e. a very small calculation step at full load, to work numerically stable. The consequence would be an unacceptable computing effort in determining the Load size. Since load detection systems usually work in segment synchronization, i.e. for 4-cylinder engines, a measurement value is taken every 180 ° KW sampled, the model equation must also be segment synchronous be solved. The following is an absolute stable difference scheme for solving differential equations used the numerical stability at any Guaranteed increment.

The model-based calculation method according to the invention also offers the possibility of predicting the load signal by a selectable number of sampling steps, i.e. a Prediction of the load signal with a variable prediction horizon. If the prediction horizon at constant speed proportional prediction time not too long, so get a predicted load signal of high accuracy.

Such a prediction is necessary because there is a dead time between the acquisition of relevant measured values and the calculation of the load size. Furthermore, for reasons of mixture preparation, the fuel mass must be measured as precisely as possible via the injection valves before the actual start of the intake phase of the respective cylinder, which is in the desired ratio to the air mass m _cyl in the course of the upcoming intake phase. A variable prediction horizon improves the quality of the fuel metering in transient engine operation. Since the segment time decreases as the speed increases, the injection process must start a larger number of segments earlier than is the case at a lower speed. In order to be able to determine the fuel mass to be metered as precisely as possible, the prediction of the load size by the number of segments by which the fuel is stored is necessary in order to maintain the required air-fuel ratio in this case too. The prediction of the load size thus contributes from a substantial improvement in compliance with the required fuel-air ratio in the transient engine operation. This system for model-based load detection is used in the known engine control systems, i.e. in the case of engine control systems controlled by air mass or intake manifold pressure, a correction algorithm in the form of a model control loop is formulated below, which allows permanent accuracy improvement, i.e. a model comparison in stationary and transient operation, in the event of inaccuracies in model parameters.

Figur 1

eine Prinzipskizze zum Saugsystem einer Otto-Brennkraftmaschine einschließlich der entsprechenden Modell- und Meßgrößen,

Figur 2

die Durchflußfunktion und die dazugehörige Polygonzugapproximation,

Figur 3

eine Prinzipdarstellung zum Modellregelkreis für luftmassengeführte Motorsteuerungssysteme und

Figur 4

eine Prinzipdarstellung zum Modellregelkreis für saugrohrdruckgeführte Motorsteuerungssysteme.

An embodiment of the method according to the invention is described with reference to the following schematic drawings. Show:

Figure 1

a schematic diagram of the intake system of an Otto engine, including the corresponding model and measurement variables,

Figure 2

the flow function and the associated polygon approximation,

Figure 3

a schematic diagram of the model control loop for air mass-guided engine control systems and

Figure 4

a schematic diagram of the model control loop for intake manifold pressure-guided engine control systems.

In the model-based calculation of the load size m and _cyl , the basic arrangement shown in FIG. 1 is assumed. For reasons of clarity, only one cylinder of the internal combustion engine is shown. Reference number 10 denotes an intake manifold of an internal combustion engine, in which a throttle valve 11 is arranged. The throttle valve 11 is connected to a throttle valve position sensor 14 which determines the degree of opening of the throttle valve. An air mass meter 12 is arranged upstream of the throttle valve 11 in an air mass-guided engine control system, while an intake manifold pressure sensor 13 is arranged in the intake manifold in an intake manifold pressure-guided engine control system. Depending on the type of load detection, only one of the two components 12, 13 is therefore present. The outputs of the air mass meter 12, the throttle valve position sensor 14 and the intake manifold pressure sensor 13, which is available as an alternative to the air mass meter 12, are connected to inputs of an electronic control device of the internal combustion engine, which is not shown and is known per se. In addition, an inlet valve 15, an outlet valve 16 and a piston 18 movable in a cylinder 17 are shown schematically in FIG.

In addition, selected variables or parameters are shown in FIG of the suction system. The roof symbol means "^" over a size that it is a model size, while sizes without a roof symbol "^" represent measured values. In particular:

P _U ambient pressure, P _S intake manifold pressure, T _S temperature of the air in the intake manifold, V _S the volume of the intake manifold.

Sizes with a dot symbol indicate the first time derivative of the corresponding sizes. m ˙ _DK is the air mass flow at the throttle valve and m ˙ _cyl is the air mass flow that actually flows into the cylinder of the internal combustion engine.

die sich unter der Voraussetzung konstanter Temperatur der Luft im Saugrohr T_S aus der Zustandsgleichung idealer Gase herleiten läßt.The basic task in the model-based calculation of the engine load condition now consists in solving the differential equation for the intake manifold pressure

which can be derived from the equation of state of ideal gases under the condition of constant air temperature in the intake manifold T _S.

R _L denotes the general gas constant.

bestimmt. Die durch (2.1) beschriebenen Verhältnisse sind auf Mehrzylinder-Brennkraftmaschinen mit Schwingrohr- (Schaltsaugrohr-) und/oder Resonanzsaugsysteme ohne strukturelle Änderungen anwendbar.The load size m and _cyl is created by integration from the cylinder mass flow

certainly. The relationships described by (2.1) can be applied to multi-cylinder internal combustion engines with vibrating tube (switching intake manifold) and / or resonance intake systems without structural changes.

bei Multi-Point-Einspritzung entsprechend

For systems with multi-point injections, in which the fuel is metered by several injectors, equation (2.1) gives the situation more accurately than for single-point injections, that is to say in injections in which the fuel is metered by means of a single fuel injector will, is the case. With the first-mentioned type of fuel metering, almost the entire intake system is filled with air. There is a fuel-air mixture only in a small area in front of the intake valves. In contrast, in single-point injection systems, the entire intake manifold from the throttle valve to the intake valve is filled with a fuel-air mixture, since the injection valve is arranged in front of the throttle valve. In this case, the assumption of an ideal gas is a closer approximation than is the case with multi-point injection. With single-point injection, the fuel is metered accordingly

with multi-point injection accordingly

The following is the calculation of mass flows and described in more detail.

mit

für überkritische Druckverhältnisse bzw. ψ = const. für kritische Druckverhältnisse bestimmt.

:

Modellgröße des Luftmassenstromes an der Drosselklappe

Â_RED ^:

reduzierter Strömungsquerschnitt

κ:

Adiabatenexponent

R_L:

allgemeine Gaskonstante

T_S:

Temperatur der Luft im Saugrohr

P and_U :

Modellgröße des Umgebungsdruckes

P and_S :

Modellgröße des Saugrohrdruckes

ψ:

Durchflußfunktion.

The model size of the air mass flow at the throttle valve is described by the flow equation of ideal gases through throttling points. Flow losses occurring at the throttle point are taken into account by the reduced flow cross section  _RED . The air mass flow is therefore through the relationship

With

for supercritical pressure conditions or ψ = const. for critical pressure conditions certainly.

:

Model size of the air mass flow at the throttle valve

 _RED ^:

reduced flow cross-section

κ:

Adiabatic exponent

R _L :

general gas constant

T _S :

Air temperature in the intake manifold

P and _U :

Model size of the ambient pressure

P and _S :

Model size of the intake manifold pressure

ψ:

Flow function.

At the throttle point, that is to say flow losses occurring at the throttle valve, are taken into account by the suitable choice of  _RED . From stationary measurements, at known pressures upstream and downstream of the throttle point and known mass flow through the throttle point, an association between the throttle valve angle determined by throttle valve position sensor 14 and the corresponding reduced cross section  _{RED can be} specified.

The air mass flow described by the relationship (2.2) on the throttle valve, a complex algorithm arises for the numerically correct solution of the differential equation (2.1). To reduce the computational effort, the flow function ψ is approximated by a polygon.

für i = (1...k)
approximiert werden.Figure 2 shows the course of the flow function ψ and the approximation principle applied to it. Within a section i (i = 1 ... k) the flow function ψ is represented by a straight line. With a reasonable number of straight line sections, a good approximation can be achieved. With such an approach, equation (2.2) can be used to calculate the mass flow at the throttle valve through the relationship

for i = (1 ... k)
be approximated.

In this form, m _{i describes} the slope and n _i the absolute term of the respective line segment. The values for the slope and for the absolute member are stored in tables as a function of the ratio of intake manifold pressure to ambient pressure P and _S / P and _U.

The pressure ratio P and _S / P and _U is plotted on the abscissa of FIG. 2 and the function value (0-0.3) of the flow function ψ is plotted on the ordinate.

For pressure conditions P S P U ≤ κ κ-1 2nd κ + 1 is ψ = constant, which means that the flow at the restriction is only dependent on the cross-section and no longer on the pressure conditions. The air mass flowing into the respective cylinders of the internal combustion engine is difficult to determine analytically, since it depends strongly on the gas exchange. The filling of the cylinders is largely determined by the intake manifold pressure, the speed and the valve timing.

For the most accurate calculation of the mass flow in the respective cylinder it is therefore necessary on the one hand to describe the conditions in the intake tract of the internal combustion engine by means of partial differential equations and on the other hand to calculate the mass flow at the inlet valve according to the flow equation as a necessary boundary condition. Only this complicated approach allows dynamic reloading effects to be taken into account, which are significantly influenced by the speed, the intake manifold geometry, the number of cylinders and the valve timing.

ausgegangen werden.Since a calculation based on the above-mentioned approach cannot be implemented in the electronic control device of the internal combustion engine, a possible approximation is based on a simple relationship between intake manifold pressure P and _S and cylinder mass flow out. For a wide range of useful valve timing, it can be approximated by a linear approach to the shape

be assumed.

The slope γ ₁ and the absolute member γ _{0 of} the relationship (2.4) are functions of the speed, the intake manifold geometry, the number of cylinders, the valve timing and the temperature of the air in the intake manifold T _S , taking into account all essential influencing factors. The dependency of the values of γ ₁ and γ ₀ on the influencing variables speed, intake manifold geometry, number of cylinders and the valve timing and valve lift curves can be determined using stationary measurements. The influence of vibrating tube and / or resonance suction systems on the air mass sucked in by the internal combustion engine is also well reproduced via this value determination. The values of γ ₁ and γ ₀ are stored in maps of the electronic engine control device.

The intake manifold pressure P _{S is} selected as the determining variable for determining the engine load. With the help of the model differential equation, this quantity should be estimated as precisely and quickly as possible. The estimation of P and _S requires the solution of equation (2.1).

approximiert werden. Betrachtet man, entsprechend den Voraussetzungen zur Herleitung von Gleichung (2.1), die Temperatur der Luft im Saugrohr T_S als eine langsam veränderliche Meßgröße sowie Â_RED als Eingangsgröße, so läßt sich die nichtlineare Form der Differentialgleichung (2.1) durch die bilineare Gleichung (2.5) approximieren.With the simplifications introduced using formulas (2.2) and (2.3), (2.1) can be determined by the relationship

be approximated. If, in accordance with the requirements for the derivation of equation (2.1), the temperature of the air in the intake manifold T _{S is} regarded as a slowly changing measured variable and  _RED as an input variable, the nonlinear form of the differential equation (2.1) can be determined by the bilinear equation (2.5 ) approximate.

To solve equation (2.5), this relationship is broken down into a suitable equation of difference transferred.

1. Das Differenzenschema muß auch unter extremen dynamischen Anforderungen konservativ sein, d.h. die Lösung der Differenzengleichnung muß der Lösung der Differentialgleichung entsprechen,

2. die numerische Stabilität muß zu Abtastzeiten, die den maximal möglichen Segmentzeiten entsprechen, im gesamten Arbeitsbereich das Saugrohrdruckes garantiert sein.

The following basic requirements for the solution properties of the difference equation to be formed can be formulated as a criterion for selecting the suitable difference scheme:

1. The difference scheme must be conservative even under extreme dynamic requirements, ie the solution of the difference equation must correspond to the solution of the differential equation,

2. The numerical stability must be guaranteed in the entire working area of the intake manifold pressure at sampling times that correspond to the maximum possible segment times.

Claim 1 can be met by an implicit calculation algorithm. Because of the approximation of the nonlinear differential equation (2.1) by a bilinear equation emerging implicit solution scheme without using iterative Method solvable, since the difference equation is explicit Form can be transferred.

Due to the conditioning of the differential equation (2.1) and its approximation (2.5), the second requirement can only be met by a calculation rule for the formation of the difference equation, which works absolutely stable. These methods are also known as A-stable methods. Characteristic of this A stability is the property of the algorithm to be numerically stable in the case of a stable output problem for any values of the sampling time, ie segment time T _A. A possible calculation rule for the numerical solution of differential equations that meets both requirements is the trapezoidal rule.

definiert. The difference equation resulting from the application of the trapezoid rule is in the present case

Are defined.

zur Berechnung des Saugrohrdruckes P and_S [N] als Maß für die Motorlast.If this rule is applied to (2.5), the relationship results

to calculate the intake manifold pressure P and _S [ N ] as a measure of the engine load.

[N] means the current segment or the current calculation step, [ N +1] the next following segment or the next calculation step.

The following is the calculation of the current and predicted Load signals described.

The air mass flow can be calculated from the calculated intake manifold pressure P and _S which flows into the cylinders can be determined using the relationship (2.4). If a simple integration algorithm is used, the relationship is obtained for the air mass sucked in by the internal combustion engine during an intake stroke

geschrieben werden.It is assumed that the initial value of the load size is zero. For segment-synchronous load detection, the segment time decreases with increasing speed, while the number of segments by which the fuel is stored must increase. For this reason, it is necessary to design the prediction of the load signal for a variable prediction horizon H, ie for a specific, primarily speed-dependent number H of segments. Taking into account this variable prediction horizon H, equation (2.8) can be in the form

to be written.

an.For the further considerations it is assumed that the segment time T _A and the parameters γ ₁ and γ _{0 of} the relationship (2.4), which are used to determine the mass flow from the intake manifold pressure P and _{S are} required, do not change over the prediction time. Under this condition, the prediction of a value for [ N + H ] achieved by predicting the corresponding pressure value P and _S [ N + H ]. As a result, equation (2.9) takes the form

on.

Since the change in the intake manifold pressure P and _S with time is present in an analytical form in the described method, the prediction of the pressure value P and _S [ N + H ] is achieved in the following by applying the trapezoidal rule H times. In this case you get the relationship

angegeben werden.If one determines the pressure P and _S [ N + H -1] in an analog manner, then the equation can be used for the predicted load signal

can be specified.

One chooses values in the order of magnitude for the prediction horizon H of 1 ... 3 segments, with the formula (2.12) a well-predicted load signal can be obtained.

In the following, the principle of model matching for air mass and intake manifold pressure-guided engine control systems explained.

Due to the use of engines with variable valve control and / or variable intake manifold geometry, manufacturing tolerances and signs of aging, as well as temperature influences, the values of γ ₁ and γ _{0 are associated} with a certain degree of uncertainty. As described above, the parameters of the equation for determining the mass flow in the cylinders are functions of various influencing variables, of which only the most important ones can be recorded.

When calculating the mass flow at the throttle valve measurement errors affect the detection of the throttle valve angle and approximation errors in the polygon approximation the flow function ψ on the model sizes. Especially at small throttle valve angles the system sensitivity is especially against the first mentioned errors high. It follows that there are small changes in the throttle valve position a serious impact on mass flow or intake manifold pressure. To see the effect of these influences reduce, a method is proposed below which allows certain sizes to influence the model calculation have to correct so that an accuracy-enhancing Model adaptation for stationary and transient Engine operation can be performed.

The adjustment of essential parameters are the model for determining the load variable of the internal combustion engine by correcting the determined from the measured throttle valve angle reduced cross-section  _RED by the correction quantity Δ Â _RED.

The input variable for the corrected intake manifold pressure calculation  _RED is thus given by the relationship  REDKORR =  RED + Δ RED described.

In the equation (2.2) and the formulas below,  _{RED is} replaced by  _REDKORR . In order to improve the subsequent behavior of the control loop, the reduced throttle valve cross section  _RED derived from the measured value of the throttle valve angle is included in the model calculation. The correction quantity Δ _RED is formed by implementing a model control loop.

For air mass- _guided engine control systems, the air mass flow m ˙ _{DK_LMM} measured by means of the air mass meter on the throttle valve is the _reference variable of this control loop, while the intake manifold pressure P _S measured is used as the reference variable for intake manifold pressure-guided systems. The value of ΔÂ _RED is determined via a follow-up control so that the control deviation between the reference variable and the corresponding control variable is minimized.

To improve accuracy even in dynamic operation To achieve this method, the measured value must be recorded be reproduced as closely as possible to the reference variable. In the most cases are the dynamic behavior of the sensor, i.e. either the air mass meter or the intake manifold pressure sensor and a subsequent averaging to consider.

In a first approximation, the dynamic behavior of the respective sensor can be modeled as a system of the first order with any delay times T ₁ that may be dependent on the operating point. In the case of an air mass-guided system, one possible equation is to describe the sensor behavior

A quantity that has a significant influence on the maximum possible mass flow in the chosen approach the ambient pressure is P and _U. For this reason, a constant value of this size cannot be assumed, but an adjustment is made in the manner described below.

The value of the ambient pressure P and _U is changed if the amount of the correction variable ΔA _RED exceeds a certain threshold or if the pressure ratio P and _S / P and _{U is} greater than a selectable constant. This ensures that an ambient pressure adjustment can take place both in the partial and in the full-load range.

The following is a model comparison for air mass guided Engine control systems explained. For this system, the in Figure 3 shown model structure can be specified.

. Wird als Regler in diesem Modellregelkreis ein PI-Regler eingesetzt, so ist die bleibende Regelabweichung null, d.h. Modellgröße und Meßgröße des Luftmassenstromes an der Drosselklappe sind identisch. Die Pulsationserscheinungen des Luftmassenstromes an der Drosselklappe, die vor allem bei 4-Zylindermotoren zu beobachten sind, führen bei betragsbildenden Luftmassenmessern zu erheblichen positiven Meßfehlern und somit zu einer stark fehlerbehafteten Führungsgröße. Durch eine Abschaltung des Reglers, d.h. einer Verkleinerung der Reglerparameter kann zum gesteuerten modellgestützten Betrieb übergegangen werden. Bereiche, in denen die genannten Pulsationen auftreten, können somit mit dem selben Verfahren unter Berücksichtigung dynamischer Zusammenhänge behandelt werden, wie diejenigen Bereiche, in denen eine nahezu ungestörte Führungsgröße vorliegt. Im Gegensatz zu Verfahren, die relevante Meßwerte nur in stationären Betriebspunkten berücksichtigen, bleibt das beschriebene System nahezu uneingeschränkt arbeitsfähig. Bei Ausfall des Luftmassensignals oder des Signals des Drosselklappenstellungsfühlers ist das vorgestellte System in der Lage, ein entsprechendes Ersatzsignal zu bilden. Bei Ausfall der Führungsgröße muß der gesteuerte Betrieb realisiert werden, während im anderen Fall der geregelte Betrieb die kaum beeinträchtigte Funktionsfähigkeit des Systems garantiert.The throttle valve position sensor 14 (FIG. 1) supplies a signal corresponding to the degree of opening of the throttle valve 11, for example a throttle valve opening angle. Values associated with various values of this throttle valve opening angle for the reduced cross section of the throttle valve _{RED RED are} stored in a map of the electronic engine control device. This assignment is represented by the block "static model" in FIG. 3 and in FIG. 4. The “intake manifold model” subsystem in FIGS. 3 and 4 represents the behavior described by (2.7). The reference variable of this model control loop is the measured value of the air mass flow at the throttle valve, averaged over a segment

. If a PI controller is used as the controller in this model control loop, the remaining control deviation is zero, ie the model size and measured variable of the air mass flow at the throttle valve are identical. The pulsation phenomena of the air mass flow at the throttle valve, which can be observed especially in 4-cylinder engines, lead to considerable positive measurement errors in the case of air mass meters that form the amount, and thus to a command variable with a lot of errors. By switching off the controller, ie reducing the controller parameters, it is possible to switch to controlled model-based operation. Areas in which the pulsations mentioned can thus be treated with the same method, taking dynamic relationships into account, as those areas in which there is an almost undisturbed reference variable. In contrast to methods that only take relevant measured values into account at stationary operating points, the system described remains operational almost without restrictions. If the air mass signal or the signal from the throttle valve position sensor fails, the system presented is able to generate a corresponding substitute signal. If the command variable fails, the controlled operation must be implemented, while in the other case the regulated operation guarantees the hardly impaired functionality of the system.

und die Größe . Nach der Modellierung des Sensorübertragungsverhaltens d.h. des Übertragungsverhaltens des Luftmassenmessers und der Abtastung wird die Modellgröße

einer Mittelung unterzogen, so daß die gemittelte Größe

und der vom Luftmassenmesser gemessene durchschnittliche Luftmassenstrom

einem Vergleicher zugeführt werden können. Die Differenz beider Signale bewirkt eine Änderung Δ _RED des reduzierten Strömungsquer-schnittes  _RED , so daß stationär und instationär ein Mo-dellabgleich erfolgen kann.The "intake manifold model" block represents the relationships as described using equation (2.7) and therefore has the model size P and _S and the time derivative as an output variable

and the size . After modeling the sensor transmission behavior, ie the transmission behavior of the air mass meter and the sampling, the model size becomes

averaged so that the averaged size

and the average air mass flow measured by the air mass meter

can be fed to a comparator. The difference between the two signals causes a change Δ _{RED RED of} the reduced flow cross section _{RED RED} , so that a model comparison can be carried out in a stationary and non-stationary manner.

identisch. Wie oben beschrieben, bleibt auch das vorliegende System nahezu uneingeschränkt arbeitsfähig, da bei Ausfall des Saugrohrdrucksignales oder des Meßwertes für den Drosselklappenwinkel ein entsprechendes Ersatzsignal gebildet werden kann.The model structure shown in FIG. 4 is given for intake manifold pressure-guided engine control systems, the same blocks as in FIG. 3 being given the same designations. As with the air mass-guided engine control system, the "intake manifold model" subsystem represents the behavior described by the difference equation (2.7). The reference variable of this model control loop is the measured value of the intake manifold pressure averaged over a segment P _{s_s} . If a PI controller is also used, as in FIG. 3, the measured value of the pressure in the intake manifold is in the stationary case P _{s_s} with the model size

identical. As described above, the present system also remains almost fully functional, since if the intake manifold pressure signal or the measured value for the throttle valve angle fails, a corresponding substitute signal can be generated.

The model sizes P and _S obtained from the intake manifold model, are fed to a block "prediction". Since the models also calculate the pressure changes in the intake manifold, these pressure changes can be used to estimate the future pressure curve in the intake manifold and thus the cylinder air mass for the next [ N +1] or for the next segments [ N + H]. The size m and _cyl or the size m and _cyl [ N +1] then serve for the exact calculation of the injection time during which fuel is injected.

Claims (11)

1. Method for determining the air mass flowing into the cylinder or cylinders of an internal combustion engine with

   an induction system which comprises an induction manifold (10) and a throttle valve (11) arranged within it as well as a throttle valve position sensor (14) which detects the degree of opening of the throttle valve (19),

   a sensor (12; 13) which produces a load signal (

   

   ; P _{S_S} ) of the internal combustion engine,

   an electrical control device, which calculates a basic injection time on the basis of the measured load signal ( ; P _{S_S} ) and the speed of the internal combustion engine, whereby

   the conditions in the induction system are simulated by an induction manifold charging model, wherein parameters representing the degree of opening of the throttle valve (11), the ambient pressure (P_U ) and the valve position are used as input variables of the model,

   a model variable for the air mass flow (

   

   ) at the throttle valve (11) is described by means of the flow-through equation of ideal gases through throttling points,

   a model variable for the air mass flow (

   

   ) into the cylinder or cylinders (17) is described as a linear function of the induction manifold pressure (P and_S ) by a mass balance of the air mass flows ( , ),

   these model variables are linked by a differential equation, the induction manifold pressure (P and_S ) being calculated therefrom as a defining variable for determining the actual load of the internal combustion engine, and

   the air mass ( ) flowing into the cylinder or cylinders (17) is obtained from the linear relationship between calculated induction manifold pressure (P and_S ) and the model variable for the air mass flow (m and_Zyl ) in the cylinder or cylinders (17) by integration.
2. Method in accordance with claim 1, characterized in that the load signal (

   

   ; P _{S_S} ) measured by the load sensor (12; 13) is used to correct and therefore to adjust the model variables ( ) in a closed control circuit, the load signal ( ; P _{S_S} ) serving as reference variable of the control circuit.
3. Method in accordance with claim 2, characterized in that the adjustment is made in the steady-state and/or transient mode of the internal combustion engine, allowing for the transmission behaviour of the load sensor (12; 13).
4. Method in accordance with claim 2, characterized in that a value of a reduced cross-section of the throttle valve (Â _RED) is allocated to each measured variable of the degree of opening of the throttle valve and the model variables are adjusted by correcting the reduced cross-section (Â _RED) by a correction variable (ΔÂ _RED) such that the deviation between reference variable and corresponding model variable is minimized.
5. Method in accordance with claim 4, characterized in that the reduced cross-section (Â _RED) is determined from steady-state measurements on the engine test stand and is entered into a map in a memory in the electric control device.
6. Method in accordance with claim 1, characterized in that, when portraying the model variable for the air mass flow ( ) at the throttle valve (11), a flow-through function (ψ) present in the flow-through equation (equation 2.2) is divided into individual sections (i = 1...k) and these sections are approximated by straight line sections, the respective straight line sections being determined as a function of the ratio of induction manifold pressure (P and_S ) to ambient pressure (P and_U ) for the gradient (m_i) and for the absolute term (n_i) and being entered into a map.
7. Method in accordance with claim 1, characterized in that the gradient (γ₁) and the absolute term (γ₀) of the linear function for the model variable for the air mass flow into the cylinder or cylinders ( ) are established as a function of at least one of the parameters of speed of the internal combustion engine, number of cylinders, induction manifold geometry, temperature of the air (T_S) in the induction manifold (10) and valve control symbol.
8. Method in accordance with claim 7, characterized in that the parameters are determined by steady-state measurements on the engine test stand and are entered into maps.
9. Method in accordance with claim 1, characterized in that the air mass (m and_Zyl ) flowing into the cylinders is calculated by the equation

   

   where

   T_A

   is the sampling interval or segment time

   [N]

   is the model variable of the air mass flow during the current sampling step or segment

   [N-1]

   is the model variable of the air mass flow during the previous sampling step or segment.

10. Method in accordance with claim 1, characterized in that the air mass (m and_Zyl ) flowing into the cylinder or cylinders is estimated for a defined prediction horizon (H) located in the future with respect to the current load detection at the moment of sampling [N] by estimating the corresponding pressure value in accordance with the following equation:

    

    where

    T_A:

    sampling interval or segment time

    H:

    prediction horizon, number of sampling steps located in the future

    γ₁ :

    gradient of the linear equation

    γ₀:

    absolute term for determining

    N:

    current sampling step

11. Method in accordance with claim 10, characterized in that the number (H) of segments for which the load signal is to be estimated for the future is established as a function of the speed.

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