DE10344709B4 - Method for determining an exhaust gas recirculation quantity - Google Patents

Abstract

Method for determining an external exhaust gas recirculation quantity for an internal combustion engine,
which is determined from an exhaust gas temperature (T ₃ ), a fresh gas temperature (T ₂ ), a fresh gas quantity (m _L ) and an internal exhaust gas recirculation _quantity (m _Ri , m _Ri0 ),
wherein the internal exhaust gas recirculation _amount (m _Ri , m _Ri0 ) takes into account a first _{quantity of} combustion gas (m _RiOT ) remaining in a cylinder (3) of the internal combustion engine during a top dead center charge cycle,
and an ideal inner exhaust gas recirculation _amount (m _Ri0 ) is used for the determination of the outer exhaust gas recirculation _amount , which is from the inner exhaust gas recirculation amount (m _Ri ) taking into account the ratio of exhaust gas temperature (T ₃ ) to a cylinder temperature (T _2Z ) before admixing the internal exhaust gas recirculation amount (m _Ri ) results.

Description

The The invention relates to a method for determining an exhaust gas recirculation amount for one Internal combustion engine, in particular an internal combustion engine for a motor vehicle. The use of exhaust gas recirculation offers Benefits in terms of fuel consumption and exhaust emissions.

From the publication DE 199 34 508 A1 A method of exhaust gas recirculation control is known in which a target exhaust gas recirculation amount is detected based on engine load, engine torque and air pressure, an actual exhaust gas recirculation amount and the opening and closing movement of a throttle are sensed and an exhaust gas recirculation control valve is dependent on the difference between actual and the target exhaust gas recirculation amount and a throttle opening signal and a throttle valve closing signal and the respective associated air pressure is actuated. The sensory detection of the exhaust gas recirculation amount is carried out by differential pressure measurement at a throttle opening, which is provided in an associated exhaust gas recirculation line.

From the DE 198 19 937 C1 is a method for operating an electronic engine control is known in which a proportion of exhaust gas in the combustion chamber is determined before a subsequent combustion exclusively from a conventionally measurable fuel / air mass ratio in the exhaust gases and from an adjusted by means of an engine control fuel / air mass ratio in the fresh gas , A first signal value correlating to the fuel / air mass ratio in the exhaust gas is preferably determined from a measurement of the oxygen content in the exhaust gas by means of a λ-probe. The first signal value is combined with a second signal value, which correlates with the fuel / air ratio in the fresh gas and the engine control is already known. From the two signal values, a third signal value correlating with the exhaust gas portion in the combustion chamber is subsequently determined in the control unit.

From the DE 32 20 832 C2 a method for determining an exhaust gas recirculation rate in diesel engines is known in which a temperature difference is determined from a measured fresh gas temperature and a measured exhaust gas temperature. Furthermore, for carrying out the method, a proportion of the fresh air at the total amount of air supplied to the internal combustion engine and an engine speed are determined. In a characteristic field, values for a desired temperature difference are stored as a function of the measured proportion of the fresh air and of the engine speed for optimum exhaust gas recirculation rates. During operation of the internal combustion engine, the measured temperature difference is compared with a desired temperature difference determined from the characteristic field. Via an exhaust gas recirculation valve, the amount of recirculated exhaust gas is varied and adjusted in this way, the temperature difference.

Often - especially in diesel engines - particle filter provided in the exhaust system of a motor vehicle to the exhaust emissions to keep low. The exhaust back pressure is from the load of the particulate filter dependent and it may change significantly depending on the particulate filter loading the back pressure of the exhaust come as disturbances to the control affect the outer exhaust gas recirculation amount and degrade the accuracy of the control.

Of the The invention is based on the object, a method for determining to provide the exhaust gas recirculation amount, by the exhaust gas recirculation amount at various engine operating conditions, especially during use a particulate filter, accurately and reliably determine.

Of the The term "quantity" is present for the sake of simplicity, comprehensively designates any quantitative indicator physical sizes used, like for example the mass or the mass or mass rate of recirculated exhaust gas or in the engine fed gas mixture.

The Invention solves the task by providing a method of determination the exhaust gas recirculation amount with the features of claim 1. In the method according to the invention becomes the exhaust gas recirculation amount from an exhaust gas temperature, a fresh gas temperature and so on called inner exhaust gas recirculation amount (also exhaust gas retention called) determined. The internal exhaust gas recirculation amount describes the amount of combustion gas, the while the charge or gas exchange at top dead center according to the Compression volume remains in a cylinder of the internal combustion engine and mixed with the sucked fresh gas.

In an embodiment of the invention, the inner exhaust gas recirculation amount additionally takes into account a possible backflow of combustion gas into the intake pipe, which takes place when there is a pressure gradient between the exhaust gas and intake sides during a valve overlap, so that exhaust gas flows back into the intake pipe. Under certain boundary conditions, for example in the case of external charging, the pressure gradient can also reverse, which leads to a flushing of the combustion chamber with fresh air. A valve overlap is understood to mean the area in which intake and exhaust valves are open at the same time.

The internal exhaust gas recirculation quantity is essentially due to the internal combustion engine underlying Concept and the parameters of the charge change influenced. At a fast-running, supercharged diesel engine for a passenger car is the internal exhaust gas recirculation amount usually low. This is touching on the one hand, therefore, that the compression volume is typically small is and thus little combustion gas during the charge change in top dead center remains in the cylinder. This leads to a low internal Exhaust gas recirculation, which over the Runtime usually is largely constant. Furthermore, the valve overlap typically very short, resulting in a low backflow or flush leads.

One essential operating parameter, the internal exhaust gas recirculation amount affects, is the exhaust back pressure. Does this change significantly, z. B. by the use of a particulate filter, it changes the inner exhaust gas recirculation amount also significant.

at Control / control method, which the internal exhaust gas recirculation amount not explicitly determine and consider, expresses itself For example, an increase in the internal exhaust gas recirculation amount (eg by an elevated Abgasgegendruck) in an operating point without external exhaust gas recirculation in a drop of the measured value of the amount of fresh gas. This is called an increase in the outer exhaust gas recirculation amount interpreted. Since this is based on the regulatory / control procedure lying concept or model only on an external exhaust gas recirculation between Exhaust tract and intake manifold based, which usually takes place via a cooler, stays the much higher Temperature at which the mixing of the fresh gas with the inner EGR amount takes place in the cylinder, disregarded in this type of control / control. The significantly higher Temperature of the exhaust gas recirculation amount leads mixing with the amount of gas sucked in to cause the gas mass in the cylinder sinks. For a control without consideration the internal exhaust gas recirculation and their temperature is thus the total actual exhaust gas recirculation amount too high, what if you want to adjust to a desired Setpoint value too low or too low Exhaust gas recirculation rate leads.

Around the accuracy in determining the exhaust gas recirculation amount can increase the for the determination needed measured amount of fresh gas and / or change in air effort by comparison between the measured size and the from pressure, temperature and filling behavior of the internal combustion engine (so-called air consumption) determined amount of fresh gas be updated or adapted during operation. The amount of fresh gas becomes common measured by means of a so-called hot-film air mass meter (HFM). A correction of the measured amount of fresh gas may be necessary for example, to compensate for drift of the sensor. hereby not only the accuracy in determining the exhaust gas recirculation amount elevated, but of course as well the accuracy of all other functions / calculations / investigations, the indirect or direct from the measured amount of fresh gas depend. Since the adaptation method is a deactivated exhaust gas recirculation or at least one constant in each adaptation point, low exhaust gas recirculation amount presupposes leads a disregarded, not negligible internal exhaust gas recirculation too erroneous measured variables or to incorrect updating or adaptation.

at the method according to the invention Both the inner and the outer exhaust gas recirculation amount are considered. This leads to, That is, the EGR amount calculated by the method is high in accuracy under stationary, unsteady and different environmental conditions. It can be one high control accuracy can be achieved. Furthermore, the sucked Amount of fresh gas with higher Accuracy determined and if necessary by comparison with calculated Values are corrected.

The inventive method is preferably implemented in a control unit associated with the internal combustion engine.

Further advantageous embodiments of the invention will become apparent from the dependent claims and the embodiments illustrated below with reference to the drawing. Hereby show:

1 1 is a schematic representation of an exemplary cylinder of an internal combustion engine with a suction pipe and an exhaust pipe,

2 a schematic representation of the intake gas quantity and the internal exhaust gas recirculation amount and

3 a block diagram of a model for determining the internal exhaust gas recirculation amount.

In the same reference numerals designate functionally the same Components or sizes.

3 shows a schematic representation of an exemplary cylinder 3 an internal combustion engine with a suction pipe 1 and an exhaust pipe 2 in which the inventive method for controlling / controlling the exhaust gas recirculation amount can be used. It is an exhaust gas recirculation 7 provided, which the exhaust pipe 2 with the suction pipe 1 connects and exhaust from the exhaust pipe 2 in the suction pipe 1 passes. In the exhaust gas recirculation 7 are preferably an unillustrated radiator and an unillustrated actuator, preferably a throttle provided. The cylinder 3 are a piston 4 , an inlet valve 5 and an exhaust valve 6 assigned.

About the suction pipe 1 the cylinder is supplied with a sucked gas amount m _2S , which is composed of a fresh gas amount m _L and a recirculated exhaust gas amount m _R. The amount of fresh gas m _L is determined for the inventive method by means of a corresponding sensor, not shown, for example, a hot-film air mass meter. In the exhaust pipe 2 prevail an exhaust back pressure p ₃ , which is preferably measured by a corresponding sensor, not shown, and an exhaust gas temperature T _3rd The exhaust gas temperature T ₃ is preferably via a corresponding map or simulation model from the cylinder 3 or the amount of fuel supplied to the internal combustion engine and the rotational speed of the internal combustion engine determined. In the intake manifold 1 prevails upstream of the exhaust gas recirculation 7 a boost pressure p ₂ and a temperature T ₂ , which are preferably determined by corresponding sensors, not shown. Immediately after mixing the exhaust gas recirculation amount m _R is in the intake manifold 1 the temperature T _2S before, which can be determined by measurement and / or calculation. In the cylinder 3 prevails before admixture or without consideration of the internal exhaust gas recirculation amount, the temperature T _2Z . After admixing or taking into account the internal exhaust gas recirculation amount is in the cylinder 3 the temperature T _Z before.

wobei R die universelle Gaskonstante und V_C das Kompressionsvolumen ist.The internal exhaust gas recirculation amount takes into account the amount of combustion gas m _{RiOT remaining} during a charge change at top dead center in a cylinder of the internal combustion engine. Assuming that during a charge change at top dead center, the compression volume is filled with residual gas having at least approximately the exhaust gas temperature T ₃ and whose pressure corresponds to the exhaust back pressure p ₃ , the combustion _{gas amount} m _RiOT remaining in the cylinder can be described as follows via the thermal equation of state become:

where R is the universal gas constant and V _{C is} the compression volume.

wobei n die Drehzahl, A der momentan effektive Ventilquerschnitt bzw. empirisch ermittelte Ventilüberschneidung hinsichtlich Zeit und Querschnitt und κ der Isentropenexponent ist. Inwieweit die Rückströmung m_RiR berücksichtigt werden sollte, hängt von der Anwendung bzw. dem zu Grunde liegenden System ab. Ist die Ventilüberschneidung, wie beispielsweise bei aufgeladenen Dieselmotoren mit hoher Verdichtung bzw. Aufladung, sehr kurz, so kann die Rückströmung m_RiR insbesondere bei hohen Drehzahlen vernachlässigt werden.In addition, in the internal exhaust gas recirculation amount, a possible backflow of combustion gas into the intake manifold when opening the intake valve can be taken into account when the pressure p ₃ in the exhaust pipe exceeds the pressure p ₂ in the intake manifold. This backflow m _RiR can be described as _follows , based on the so-called Saint-Venant flow equation:

where n is the speed, A is the currently effective valve cross section or empirically determined valve overlap in terms of time and cross section and κ isentropic exponent. The extent to which the backflow m _RiR should be taken into account depends on the application or the underlying system. If the valve overlap, as for example in supercharged diesel engines with high compression or supercharging, is very short, the backflow m _RiR can be neglected, especially at high speeds.

The entire internal exhaust gas recirculation m _Ri is derived from the change in the charge in the upper dead center in the cylinder remaining combusted gas amount m _RiOT and flowing back into the intake amount of combustion gas _RiR m according to the following equation: m Ri = m RiR + m RiOT , (3)

Neglecting the backflow m _RiR simplifies equation (3) to: m Ri = m RiOT , (4)

The Internal exhaust gas recirculation leads in the cylinder to a heating of the entire cylinder charge. This leads to a Decrease of the total gas mass in the cylinder with increasing internal EGR amount. Around this drop in the cylinder mass due to the higher temperature of the exhaust gas recirculation in regulations / controls, adaptations and / or modeling / simulations to take into account is preferably an idealized internal exhaust gas recirculation amount formed on the assumption of constant temperature conditions and hereinafter referred to as "apparent" internal exhaust gas recirculation amount referred to as.

2 shows a schematic representation of the proportions in the cylinder combustion chamber. The bar A represents the ideal conditions without consideration of the internal exhaust gas recirculation. In this case, the cylinder quantity m _Z corresponds to the intake gas quantity m _2S0 . The bar B shows the real conditions with consideration of the internal exhaust gas recirculation, in which the gas amount in the cylinder of the intake gas amount m _2S , which consists of the intake fresh gas amount and the exhaust gas amount of the external exhaust gas recirculation, and the internal exhaust gas recirculation amount m _Ri composed. The amount difference .DELTA.m corresponds to the reduction of the cylinder amount m _Z because of the heating by the exhaust gas stirring m _Ri . The bar C shows the conditions under the assumption that an internal exhaust gas recirculation takes place, but a heating of the cylinder charge does not take place. The total amount of gas in the cylinder thus corresponds to the amount of gas in the case of the bar A and it is composed of the intake gas amount m _2S and an apparent internal exhaust gas recirculation _amount m _Ri0 , which would in addition to the intake gas amount m _2S fit into the cylinder, if by the increased exhaust gas temperature justified heating of the cylinder charge would not take place. The apparent internal exhaust gas recirculation _quantity m _Ri0 results from the summation of the actual internal exhaust gas recirculation quantity m _Ri and the quantity difference Δm. The apparent, sucked gas quantity m _2S0 results from the sum of the actually sucked gas quantity m _2S and the apparent inner exhaust gas recirculation _amount m _Ri0 .

wobei der Druck p_2Z dem Druck entsprechen soll, der im unteren Totpunkt, das heißt beim Ende des Saugtaktes, im Zylinder vorliegt. Die Variable V_C kennzeichnet das Kompressionsvolumen und die Variable V_H kennzeichnet das Hubvolumen. Die im Zylinder befindliche Gasmenge m_Z entspricht in diesem Fall der angesaugte Gasmenge m_2S, welche ohne innere Abgasrückführung der scheinbaren angesaugten Gasmenge m_2S0 entspricht.Assuming that the amount of gas sucked increases when flowing into the cylinder from the temperature T _2S in the intake manifold to the temperature T _2Z in the cylinder and this increase is known, can be for the case without internal exhaust gas recirculation, ie the apparent amount of sucked gas m _2S0 corresponds to the actually sucked gas quantity m _2S , the thermal equation of state at bottom dead center is formulated as follows:

wherein the pressure p _{2Z is} to correspond to the pressure which is present in the cylinder at bottom dead center, that is to say at the end of the suction cycle. The variable V _C denotes the compression volume and the variable V _H indicates the stroke volume. The gas quantity m _Z in the cylinder corresponds in this case to the intake gas quantity m _2S , which corresponds to the apparent intake gas quantity m _2S0 without internal exhaust gas recirculation.

wobei m_2S0 = m_Ri0 + m_2S ist, wie oben beschrieben.Considering the internal exhaust gas recirculation and assuming that the intake gas quantity m _2S is heated to the temperature T _2Z by the inflow and not by mixing with the internal exhaust gas recirculation amount and that the exhaust gas recirculation amount m _{Ri is} admixed with the temperature T ₃ , then With the help of the mixture equation the thermal equation of state can be formulated as follows:

where m is _2S0 = m _Ri0 + m _2S , as described above.

From the equation (6), the apparent exhaust gas recirculation _amount m _{Ri0 now} becomes:

The temperature T _2Z present in the cylinder can be determined by measurement by means of a corresponding sensor. Should a corresponding sensor not be provided, for example from cost and / or space considerations, the temperature T _{2Z can be determined} from an already known state variable by means of an observer and / or via a suitable characteristic diagram or model.

Preferably, the temperature T _2Z on the measured and / or calculated temperature T _2S , which is present in the intake manifold after admixing the outer exhaust gas recirculation, determined, preferably an additive correction depending on the rotational speed n and the injection quantity q. The temperature in the cylinder then results in: T 2Z = T 2S + f (n, q), (8) where f (n, q) is a function of the rotational speed n and the injection quantity q, which is empirically determined, for example, by corresponding tests or tests and / or by physical modeling and / or system identification (eg by means of the least squares method) can be.

In the method according to the invention, an external exhaust gas recirculation quantity is determined on the basis of the exhaust gas temperature T ₃ , the fresh gas temperature T ₂ , the intake fresh gas quantity m _L and the internal exhaust gas recirculation quantity m _Ri , wherein preferably the determination is based on the apparent internal exhaust gas recirculation _quantity m _Ri0 , as defined above. based. This has the advantage that the temperature difference between the intake gas quantity and the internal exhaust gas recirculation quantity can be taken into account in the determination and thus in the regulation / control of the external exhaust gas recirculation quantity. The - preferably apparent - internal exhaust gas recirculation _amount m _Ri or m _Ri0 is preferably taken into account in the determination of the outer exhaust gas recirculation amount to the preferably measured by intake, sucked fresh gas amount m _L to form a so-called apparent sucked fresh gas amount m _L0 as follows is added: m L0 = m Ri0 + m L (9)

For a regulation / control the outer exhaust gas recirculation amount becomes the calculated outer exhaust gas recirculation amount the calculated internal exhaust gas recirculation amount added.

Furthermore, in particular for increasing the accuracy of the calculation of the external exhaust gas recirculation quantity or, in particular, for the correction of the measured fresh gas quantity, an adaptive function or a learning function is used which updates or corrects the intake fresh gas quantity or the air expenditure during the running process / system, Thus, the internal exhaust gas recirculation amount is preferably taken into account also in this update. The correction / updating of the amount of fresh gas or the air consumption is thus preferably not only based on the measured amount of fresh gas m _L , but on the apparent amount of fresh gas m _L0 , where m _L0 calculated according to equation (9).

Based on the equations (1) to (8), the calculation of the actual inner exhaust gas recirculation amount and the apparent inner exhaust gas recirculation amount is preferably performed as in FIG 3 shown schematically in the form of a block diagram. For the sake of simplicity, the backflow into the intake manifold (see equation 2) is neglected in the calculation. That is, the internal exhaust gas recirculation results according to equation (4). Of course, the backflow can be taken into account via a corresponding characteristic map or model which represents the calculation of equation (2).

Preferably, the calculation of the internal exhaust gas recirculation amount or the apparent internal exhaust gas recirculation amount is carried out relatively. That is, the change of the inner exhaust gas recirculation amount or the apparent inner exhaust gas recirculation amount is calculated with changing exhaust back pressure p ₃ . The change of the inner exhaust gas recirculation _amount is _hereinafter referred to as the relative inner exhaust gas recirculation _amount m _Rirel . The change in the apparent internal exhaust gas recirculation _amount is referred to as the relative apparent internal exhaust gas recirculation _amount m _Ri0rel . In the case of small changes in the exhaust gas counterpressure, in particular for the operating case without particle filter, in this way a simple, little computationally demanding application / application is possible.

In the 3 represents the function block 8th a map or a model, which calculates an absolute internal exhaust gas recirculation amount m _Ri according to the equation (1) from the input variables instantaneous exhaust back pressure p ₃ and current exhaust gas temperature T ₃ . From the current speed n and the current injection quantity q is by means of the function block 9 , which is a map or a corresponding model, a base value m _{Ribas formed} for the inner exhaust gas recirculation amount. This base value m _Ribas preferably corresponds to an internal exhaust gas recirculation amount, as in an application without Parti Kefilter or with not or slightly polluted / loaded particulate filter occurs. At a connection point 10 the basic value m _Ribas for the inner exhaust gas recirculation _{amount is} subtracted from the absolute inner exhaust gas recirculation _amount m _Ri , forming the relative inner exhaust gas recirculation _amount m _Rirel .

According to equations (7) and (8), the relative apparent internal exhaust gas recirculation _amount m _{Ri0rel is} formed. By means of the function block 11 , which is a map or a corresponding model, is calculated from the current speed n and the instantaneous injection quantity q, the value f (n, q), which in a node 12 is added to form the present in the cylinder temperature T _2Z to the prevailing in the intake manifold temperature T _2S . The present in the intake manifold temperature T _2S can be determined by measurement and / or calculation. The relative internal exhaust gas recirculation _amount m _Rirel becomes a _node 13 multiplied by the exhaust gas temperature T ₃ and in a node 14 divided by the cylinder _temperature T _2Z to form the relative apparent internal exhaust gas recirculation _amount m _Ri0rel .

If the return flow m _{RiR is} to be taken into account in the calculation, this can be done via the function _block 8th corresponding function block based on equation (2), whose output is additive and with respect to the signal flow before the node 10 is additionally taken into account in the formation of the relative internal exhaust gas recirculation. The function block 9 should be adjusted accordingly if necessary.

That in the 3 Of course, the block diagram shown may be simplified to calculate absolute rather than relative values. For this purpose, the subtraction of the underlying m _Ribas would have to be dispensed with.

The in the 3 shown structure for calculating the internal exhaust gas recirculation amount or the apparent internal exhaust gas recirculation amount is preferably implemented by software in a control unit associated with the internal combustion engine.

Claims (3)

Method for determining an external exhaust gas recirculation quantity for an internal combustion engine, which is determined from an exhaust gas temperature (T ₃ ), a fresh gas temperature (T ₂ ), a fresh gas quantity (m _L ) and an internal exhaust gas recirculation _quantity (m _Ri , m _Ri0 ), wherein the internal exhaust gas recirculation _quantity (m _Ri , m _Ri0 ) takes into account a first _{quantity of} combustion gas (m _RiOT ), which during a charge change at top dead center in a cylinder ( 3 ) remains of the internal combustion engine, and an idealized internal exhaust gas recirculation _amount (m _Ri0 ) is used for the determination of the external exhaust gas recirculation _amount , which is determined from the internal exhaust gas recirculation amount (m _Ri ) taking into account the ratio of exhaust gas temperature (T ₃ ) to a cylinder temperature ( T _2Z ) before adding the internal exhaust gas recirculation quantity (m _Ri ). A method according to claim 1, characterized in that the cylinder temperature (T _2Z ) before admixing the internal exhaust gas recirculation amount (m _Ri ) as a function of speed (n) and injection quantity (q) from a temperature (T _2S ) in the intake manifold ( 1 ) is determined after admixing the outer exhaust gas recirculation amount. Method according to Claim 1 or 2, characterized in that the internal exhaust gas recirculation quantity (mRi, mRi0) additionally takes into account a second quantity of combustion gas (mRiR) which, when the valve overlaps into the intake manifold ( 1 ) flows back.