DE102008042819A1 - Method and device for determining an entire cylinder filling and / or the current residual gas rate in an internal combustion engine with exhaust gas recirculation - Google Patents

Abstract

The invention relates to a method for determining an overall cylinder charge (rfrges) in cylinders of an internal combustion engine (2) with exhaust gas recirculation, wherein exhaust gas is recirculated at a discharge point (10) in a suction pipe (4) for supplying a gas mixture in the cylinder (3), wherein the total cylinder charge (rfrges) indicates an instantaneous total amount of gas in the cylinders (3), the total cylinder charge (rfrges) being dependent on a sum of the gas mass flows supplied to the intake manifold (4) and a first dynamic correction factor (fvisrm) describes the dynamic behavior of the suction pipe (4) with respect to the there adjusting Saugrohrdrucks, is determined. Further, a current residual gas rate (rragrzw) indicative of the instantaneous amount of exhaust gas in the total gas in the intake manifold (4) may be determined depending on an exhaust partial pressure (psrext) and depending on the instantaneous intake manifold pressure (ps) the exhaust gas partial pressure, depending on a exhaust gas mass flow supplied to the intake manifold, depending on a second dynamic correction factor, which describes the dynamic behavior of the intake manifold (4) taking into account the discharge point (10) with respect to the resulting exhaust partial pressure (psrext), and depending on a current exhaust cylinder filling is determined. Furthermore, the instantaneous air charge (rlfgsb) can depend on the total cylinder charge (rfrges) and on the residual gas rate ...

Description

Technical area

The The invention relates to an internal combustion engine with exhaust gas recirculation, the is controlled by a motor control unit, wherein in the engine control unit, the current air filling dependent is determined by the residual gas rate.

State of the art

In increasing Exhaust gas recirculations are provided in internal combustion engines to the Reduce fuel consumption and, where appropriate, the exhaust emissions to optimize. In this case, exhaust gas is taken from the exhaust system and via a Exhaust gas recirculation line with an exhaust gas recirculation valve doses the fresh air of a suction pipe of an air supply system added.

The Exhaust gas recirculation valve is from the engine control unit controlled, so that a certain residual gas rate (exhaust gas recirculation rate) can be adjusted. The admixed exhaust gas displaces the fresh air, without participating in the combustion. That is, to the engine torque constant must keep, with increasing residual gas content in certain operating points the throttle valve continues to open become. The desired Effect is an increase the intake manifold pressure, without the engine torque increases. Thereby can reduce the pumping losses of the internal combustion engine, increase the efficiency and thereby reduce fuel consumption.

Farther can by admixing of exhaust gas to the fresh air in the intake manifold the Combustion temperature are lowered, resulting in reduced formation the harmful Nitrogen oxides in the exhaust gas leads.

Around To keep the engine torque constant, it is therefore necessary that the engine control unit knows the current air charge of the cylinders to based on the current air filling the corresponding position of the throttle or the corresponding Injection quantity and the ignition angle to be able to determine so that the required engine torque can be kept constant. Contexts between the engine speed, the throttle position, the intake manifold pressure, the cylinder total filling and the cylinder air filling is used with the previously implemented functions under steady state conditions correctly described. Also can considered dynamic processes become.

Next the influence on the air supply system are mentioned above, at an exhaust gas recirculation too Corrections in the ignition system required. By dilution of the fuel-air mixture in the combustion chamber by recirculated exhaust gas The combustion speed is lowered, which are compensated by a previous ignition got to. Therefor is the knowledge of the relationship from residual gas mass to total gas mass in the combustion chamber, the so-called Exhaust gas recirculation rate, decisive.

at the consideration the dynamic processes So far, it is generally assumed that the initiated Distribute exhaust gas in the intake manifold homogeneously, since so far usually the Exhaust intake point is located close behind the throttle. However, have Measurements showed that in an internal combustion engine in which The Abgaseinleitstelle the exhaust gas recirculation very close to the inlet valves is located, the exhaust gas is not distributed homogeneously in the intake manifold, but on their short way from the point of discharge to the inlet valve of the cylinder occupy only a very small volume, which rises much faster and degraded as the entire intake manifold pressure. Thus, the momentum of the air system the recirculated exhaust gas of dynamics of the air system the fresh air different.

There the engine manufacturer the discharge point for exhaust gas recirculation in choose the rule, is the resulting different dynamics with respect to the recirculated exhaust gas and regarding the supplied Fresh air unknown. In particular, this difference becomes all the more more serious, the more the discharge point of the recirculated exhaust gas at the intake valves lies. The previous model, both for the recirculated exhaust gas and for the supplied fresh air using the same dynamic model, both of them Underlying intake manifold, so the current filling and the current residual gas rate is insufficient in dynamic operation determine exactly.

According to the conventional Methods for determining the current air charge can therefore be for the recirculated exhaust gas and for the supplied fresh air two partial pressures From their addition, the resulting measurable intake manifold pressure results. The intake manifold dynamics are taken into account with a common dynamic correction factor, the temporal behavior of the residual gas rate and the intake manifold pressure sets. However, this is due to the above observed behavior only correct from the case where the discharge point of exhaust gas recirculation at or close to the throttle.

It is an object of the present invention to provide a method and a device with which in an internal combustion engine with the exhaust gas recirculation the current air filling and / or the residual gas rate in cylinders of the internal combustion engine can be determined more accurately independently of the point of introduction of the exhaust gas into the intake manifold.

Disclosure of the invention

These Task is performed by the method of determining the total cylinder filling air filling in an exhaust gas recirculation internal combustion engine according to claim 1, the method for determining an actual residual gas rate, the method for determining a momentary air filling as well as by the engine system according to the siblings claims solved.

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

According to one The first aspect is a method for determining an entire cylinder fill in Cylinders of an internal combustion engine with exhaust gas recirculation provided with exhaust gas at a discharge point in a suction pipe for supplying a gas mixture in the cylinder is recycled, the entire cylinder filling dependent from a sum of the suction pipe supplied gas mass flows and dependent from a first dynamic correction factor, which is the dynamic behavior of the suction pipe with respect describes the there adjusting Saugrohrdrucks determined becomes.

The above method allows a dynamically correct detection of the entire cylinder filling as basis for the correct determination of the momentary air filling in the cylinders or the residual gas rate under consideration the discharge point of recirculated exhaust gas in the suction pipe.

While in the Prior art partial pressures modeled in sum, the resulting measurable intake manifold pressure in the above method, the sum is suggested the partial fillings or the partial mass flows from flowing into the suction pipe Use gas to determine the total cylinder filling.

According to one embodiment can the entire cylinder filling dependent be determined from the current intake manifold pressure, wherein the instantaneous Intake manifold pressure by integrating the with the first dynamic correction factor acted difference between an unfiltered, the suction pipe supplied Gas mass flow and the total gas mass flow supplied to the cylinder is determined.

Farther can the entire cylinder fill as Function dependent from the current intake manifold pressure, depending on a current engine speed and dependent correction factors, in particular a height factor for adaptation to an ambient pressure and a combustion chamber temperature factor for consideration the gas temperature in the cylinder can be determined.

• – 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 Verhaken 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 exhaust gas recirculation internal combustion engine is provided, wherein exhaust gas is recirculated at a point of introduction into a suction pipe for feeding a gas mixture into the cylinders, the residual gas rate being the instantaneous fraction of exhaust gas in the exhaust gas Cylinder located total gas indicates. The method comprises the following steps:

• Performing the above method to determine the current intake manifold pressure;
• Determining the residual gas rate as a function of an exhaust gas partial pressure and depending on the instantaneous intake manifold pressure, wherein the exhaust gas partial pressure depends on a suction pipe supplied exhaust gas mass flow, depending on a second dynamic correction factor, the dynamic entanglement of the intake manifold taking into account the discharge with respect to adjusting themselves Exhaust gas partial pressure describes, and is determined depending on a current exhaust gas cylinder filling.

While in the Prior art partial pressures modeled in sum, the resulting measurable intake manifold pressure In the above method, the dynamic behavior is suggested the entire cylinder filling and the exhaust gas fraction (indicated by the residual gas rate) with different To consider time constants.

Farther can the current exhaust cylinder filling depending on the residual gas rate and the entire cylinder filling be determined.

Farther can be provided that the exhaust gas partial pressure by integrating the difference applied to the second dynamic correction factor between the EGR filling fraction, the one filling indicates exhaust gas in the cylinder, which is due to the intake manifold currently fed Set exhaust gas mass flow, 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 for determining a current air charge in cylinders of an internal combustion engine with exhaust gas recirculation is provided, wherein exhaust gas is recirculated at a point of introduction into a suction pipe for supplying a gas mixture in the cylinder. The method comprises the following steps:

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

In another aspect, a method for controlling an internal combustion engine is provided. The method comprises the following steps:

• Determining the current air charge 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 a suction pipe of the internal combustion engine and / or a firing angle for igniting an air / fuel mixture depending on the current air filling.

By the dynamically correct filling detection can be the adjustment of the fuel path for a correction of the fuel metering improved in a dynamic operating case (transition compensation) become. This achieves better exhaust emissions and improved performance Drivability. Due to the dynamically correct determination of the residual gas rate can continue the ignition angle calculated correctly.

According to one Another aspect is an engine control unit for controlling an internal combustion engine provided that is configured to perform the above method.

According to one Another aspect is a computer program is provided, the program code contains which, when executed on a data processing unit, performs the above method.

Brief description of the drawings

preferred embodiments will be explained in more detail with reference to the accompanying drawings. It demonstrate:

1 a schematic representation of an engine system with an internal combustion engine with exhaust gas recirculation;

2 a functional block diagram illustrating the function for determining the air charge and the residual gas rate; and

3 a more detailed representation of the map block of the function block diagram of 2 ,

Description of embodiments

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

Combustion gases from the cylinders are via an exhaust system 6 dissipated. Between the exhaust system 6 and the suction tube 4 is an exhaust gas recirculation arrangement 7 provided, which is an exhaust gas recirculation cooler 8th and an exhaust gas recirculation valve 9 and exhaust from the exhaust system 6 in the suction pipe 4 can guide. The exhaust gas recirculation arrangement 7 ends at a discharge point 10 in the suction pipe 4 ,

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

In particular, the engine control unit must 12 the amount of fuel to be injected to the momentary air filling in the cylinders 3 to adjust. Depending on the residual gas rate, the ignition angle, that is to say the ignition time, must furthermore be adapted accordingly as a function of the position of the crankshaft angle. Furthermore, it may be necessary that for maintaining the engine torque and the position of the throttle 11 must be adjusted accordingly. This is done by means of known from the prior art engine control and regulation method, which will not be discussed here in detail.

To determine the actual cylinder filling rlfgsb and the actual residual gas rate rragrzw becomes a function in the engine control unit 12 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 by means of a throttle flap, not shown 11 arranged hot film air mass sensor measured. Another input sets itself from the recirculated, in the intake manifold 4 Guided exhaust gas recirculation mass flow (EGR mass flow) resulting unfiltered EGR filling fraction rfrexroh dar. The EGR mass flow can from the pressure difference between the pressure in the exhaust system 6 and the pressure in the intake manifold 4 and from the position of the exhaust gas recirculation valve 9 be determined according to a model.

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

The difference between the unfiltered total charge rges and the normalized charge rfrges is via a first multiplier 23 to an integrator 24 created. The first multiplier 23 multiplies the filling difference at the output of the difference element 22 is present, with a first dynamic correction factor fvisrm, which represents a first time constant for the dynamic behavior of the intake manifold. The integration element 22 integrates the difference filling. Ie. since the procedure is cyclic, the integrator sums 22 the difference fillings. At the output of the integration member thus a demodulated intake manifold pressure ps is provided. The modulated intake manifold pressure ps becomes a map block 25 in which, taking into account further parameters, such as the engine speed nmot, an altitude factor fho and a combustion chamber temperature factor ftbr and a characteristic map, the total cylinder charge rfrges is determined. The entire cylinder filling rfrges, which is also at the inverting input of the differential element 22 provided.

In 3 is the map block 25 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 filling as a function of the speed. This makes it possible to calculate the actual intake manifold pressure. The addressing of the map is necessary because the non-linear relationship of pressure to filling does not depend on the absolute intake manifold pressure. For this purpose, the normalized to ambient pressure intake manifold pressure is crucial. For this reason, the standardized intake manifold pressure is divided by the height factor fho.

The Result from the map will be to get it to the actual Adjust ambient pressure conditions, again with the altitude factor fho multiplied in a multiplier and then in another multiplier with a combustion chamber temperature factor ftbr multiplied to obtain the total cylinder charge rfrges. Of 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 is the total amount of gas flowing through the cylinders. The entire cylinder charge rfrges becomes a second multiplier 26 fed, in which the total cylinder charge rfrges multiplied by the Restgasra rragrrzw, which is determined separately, to obtain a residual gas filling rfragr.

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

The residual gas rate rragrzw is determined as follows:
The unfiltered EGR filling rfrexroh becomes a non-inverting input of a third differential element 30 fed. The residual gas filling rfragr is the inverting input of the third differential element 30 fed. The in the third differential element 30 formed EGR filling difference as the difference of the unfiltered EGR filling rfrexroh and the residual gas filling rfragr is in a third multiplier 31 multiplied by a second dynamic correction factor fvisragr and multiplication result by a second integrator 32 fed.

At the output of the second integration element 32 A partial pressure with respect to the EGR filling fraction results as the EGR partial pressure resulting from integration of the EGR filling difference multiplied by the second dynamic correction factor f avragr. The second dynamic correction factor fvisragr represents a second time constant which describes the effect of the intake manifold with respect 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 a pressure ratio.

The functional representation of the 2 removes the approach taken 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, by the first difference unit 22 , the first multiplier 23 , the first integrator 24 and the map block 25 is formed (upper feedback loop), an entire cylinder charge rfrges calculated. Since a first time constant is used, which is given by the first dynamic correction factor fvisrm.

The use of the first differential element 22 allows a simple construction of the first differentiation block, in which the sum of the partial fills rlroh and rfrexroh are subtracted from the total cylinder filling rfrges. In this way, an intake manifold pressure model can be implemented which, as before, adopts and models the low-pass filter effect due to the volume of the intake manifold with a given time constant.

In the lower part (lower feedback loop) of the functional representation of the 2 For example, the dynamic behavior of the intake manifold with respect to the EGR charge fraction is rfrexroh modeled, wherein a second differentiator is formed by the elements, third differential element 30 , third multiplier 31 , second integrator 32 , Divisional member 33 and second multiplier 26 , By the third multiplier 31 a second time constant is realized by multiplication 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 both values with the modeled intake manifold pressure ps.

The second dynamic correction factor fvisragr can be calculated by the following formula: fviasragr = (Vh / (Vagr + Vh)) · ((tagrisr + 273 K) / 273 K) · 10.13 hPa /%, where Vh is the stroke volume of a cylinder, Vagr approximately the volume of the intake manifold 4 existing exhaust cloud and tagrisr a modeled EGR gas temperature.

at the formation of the volume ratio becomes instead of the intake manifold volume now the lower EGR mixing volume used. This is determined during the application. A dependency the volume ratio from 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 representation shows that in the present process the two dynamics correction factors, d. H. the two time constants for the differentiating links, can be set separately from each other, so that the calculation the residual gas rate rragrzw in one of the Saugrohrzeitkonstanten independent dynamic behavior is modelable.

In this structure, it is possible to calculate a dynamically correct air charge and residual gas rate, so as 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 by the above method make it possible to feed into the intake manifold 4 Correctly adjust the amount of fuel to be injected and indicate the correct ignition angle.

Claims (10)

Method for determining an overall cylinder charge (rfrges) in cylinders of an internal combustion engine ( 2 ) with exhaust gas recirculation, wherein exhaust gas at a discharge point ( 10 ) in a suction tube ( 4 ) for feeding a gas mixture into the cylinders ( 3 ), where the total cylinder charge (rfrges) is an instantaneous total amount of gas in the cylinders ( 3 ), wherein the total cylinder charge (rfrges) depends on a sum of the intake manifold ( 4 ) and depending on a first dynamic correction factor (fvisrm), the dynamic behavior of the intake manifold ( 4 ) with respect to the there adjusting intake manifold pressure is determined. The method of claim 1, wherein the total cylinder charge (rfrges) is determined in response to a current intake manifold pressure (ps), the instantaneous intake manifold pressure (ps) being calculated by integrating the difference between an unfiltered cylinder charge applied to the first dynamic correction factor (fvisrm) and the charge indicating that the suction tube ( 4 ), and the total cylinder charge (rfrges) is determined. The method of claim 2, wherein the total cylinder charge (rfrges) as a function of the instantaneous intake manifold pressure (ps), depending on a current engine speed (nmot) and depending on correction factors, in particular an altitude factor (fho) to adapt to an ambient pressure and a combustion chamber temperature factor (ftbr) to take into account the gas temperature in the cylinders ( 3 ), is determined. Method for determining a current residual gas rate (rragrzw) in cylinders ( 3 ) of an internal combustion engine ( 2 ) with exhaust gas recirculation, wherein exhaust gas at a discharge point ( 10 ) in a suction tube ( 4 ) for feeding a gas mixture into the cylinders ( 3 ), wherein the residual gas rate (rragrzw) the current proportion of exhaust gas in the in the cylinder ( 3 ) indicates total gas, with follow the steps: - performing the method of claim 2 or 3 to determine the instantaneous intake manifold pressure (ps); - Determining the residual gas rate (rragrzw) depending on a partial pressure of exhaust gas (psrext) and dependent on the instantaneous intake manifold pressure (ps), the exhaust gas partial pressure depending on a suction pipe supplied exhaust gas mass flow, depending on a second dynamic correction factor, the dynamic behavior of the Suction tube ( 4 ) taking into account the discharge point ( 10 ) with respect to the adjusting exhaust partial pressure (psrext), and is determined as a function of a current exhaust cylinder filling. The method of claim 4, wherein the current exhaust cylinder filling depends on the residual gas rate (rragrzw) and the total cylinder charge (rfrges) is determined. The method of claim 4 or 5, wherein the partial pressure of exhaust gas (psrext) by integrating the difference between the EGR filling fraction applied to the second dynamic correction factor, which is a filling of exhaust gas in the cylinder ( 3 ), which due to the suction tube ( 3 ) would currently set supplied exhaust gas mass flow, and the exhaust cylinder filling is determined. Method for determining a momentary air charge (rlfgsb) in cylinders ( 3 ) of an internal combustion engine ( 2 ) with exhaust gas recirculation, wherein exhaust gas at a discharge point ( 10 ) in a suction tube ( 4 ) for feeding a gas mixture into the cylinders ( 3 ), comprising the steps of: - determining the total cylinder charge (rfrges) according to the method of any one of claims 1 to 3; - Providing a residual gas rate (rragrzw) or determining the residual gas rate (rragrzw) by a method according to any one of claims 4 to 6; Determining the instantaneous air charge (rlfgsb) depending on the total cylinder charge (rfrges) and on the residual gas rate (rragrzw). Method for controlling an internal combustion engine ( 2 ), comprising the steps of: - determining the instantaneous air charge according to the method of claim 7; - driving a position of a throttle valve ( 11 ) of the internal combustion engine ( 2 ) and / or an injection quantity of fuel into a suction pipe ( 4 ) of the combustion engine ( 2 ) and / or an ignition angle for igniting an air / fuel mixture depending on the instantaneous air charge (rlfgsb). Engine control unit for controlling an internal combustion engine ( 2 ) configured to perform a method according to any one of claims 1 to 8. Computer program containing a program code which, when running on a computing device, a method according to a the claims 1 to 8 executes.