Method for adjusting an exhaust gas recirculation parameter of an internal combustion engine and control unit for an internal combustion engine

Abstract

Method for adjusting an exhaust gas recirculation parameter of an internal combustion engine (1) at a steady load point comprising the following steps: - Control of the exhaust gas recirculation quantity given in an exhaust gas recirculation path (5) on the basis of a first functional relationship (9) between a recirculated exhaust gas mass and a first selection (11) of quantities measured at the internal combustion engine (1), and - Rules of the recirculated exhaust mass by comparing a first exhaust mass (13) calculated on the basis of the first functional relationship (9) with a second exhaust mass (39), wherein the second exhaust mass (39) is calculated on the basis of a second functional relationship (37) between the recirculated exhaust mass and a second selection (41) of quantities measured on the internal combustion engine (1), and wherein the first functional relationship (9) is adjusted on the basis of the comparison of the first exhaust mass (13) with the second exhaust mass (39).

Description

[0001] The invention relates to a method for adjusting an exhaust gas recirculation parameter of an internal combustion engine according to claims 1, 2 and 3, and a control unit for an internal combustion engine according to claim 12.

[0002] Exhaust gas recirculation (EGR) is typically used in internal combustion engines to reduce nitrogen oxide (NOx) emissions. Exhaust gas from the engine is recirculated into a combustion chamber, primarily to increase the proportion of inert gas in the combustion chamber and to influence the combustion temperature. Fast and precise control of the EGR, especially depending on the engine's load point, is desirable because, on the one hand, no potential for NOx reduction should be wasted, and on the other hand, misfires caused by an overdose of recirculated inert exhaust gas in the combustion chamber should be avoided. However, it has been shown that known approaches for controlling an EGR parameter, particularly the recirculated exhaust gas mass or the EGR rate (i.e., the ratio of the recirculated exhaust gas mass to the engine's intake mass), are very sluggish.This is due, firstly, to the lack of precise feedforward control and, secondly, to the use of slow control variables, such as a lambda sensor reading. However, to react quickly and flexibly, especially to load changes in the internal combustion engine, it is desirable to be able to adjust the exhaust gas recirculation (EGR) value within the actuation speed of an EGR valve. This can significantly improve emissions and combustion stability in the internal combustion engine. This is particularly desirable for sensitive and difficult-to-control combustion processes, such as the combustion process used in a HCCI (homogeneous charge compression ignition) engine. It is fundamentally possible to control the EGR value, especially using a model-based approach. This allows the EGR value to be adjusted within the actuation speed of the EGR valve.Pressure losses in an exhaust gas recirculation (EGR) system of an internal combustion engine increase with its service life, for example, because the EGR system becomes increasingly clogged with deposits, thus increasing its flow resistance. Such long-term effects cannot be captured by control systems alone.

[0003] German patent application DE 10 2007 007 945 A1 discloses a method for adjusting the exhaust gas recirculation rate of an internal combustion engine, whereby the adjustment is achieved by means of a control system with a superimposed control loop or a feedforward control system. A feedforward signal is generated based on data contained in characteristic curves or maps, which are based on the laws of fluid dynamics and, in particular, take into account a driving pressure differential underlying the exhaust gas recirculation. In this respect, the exhaust gas recirculation rate is controlled along the exhaust gas recirculation path based on a functional relationship between the recirculated exhaust gas and quantities measured at the internal combustion engine. The feedforward control is fast.Its precision is increased by the inclusion of a learning function, in which the pure feedforward signal is compared with the total control signal, i.e., the feedforward signal superimposed with a controller signal. The result of the control superimposed on the feedforward signal is fed back into a learning map. This learning function also allows for the consideration of long-term drifts, for example, due to contamination of the exhaust gas recirculation (EGR) system. However, this solution is comparatively complex and elaborate, particularly because it comprises feedforward control, superimposed control, and an additional learning function based on a comparison of the total control signal (composed of the feedforward signal and the controller signal) with the feedforward signal. A method for setting an EGR rate is also described in EP 1 870 584 A2.

[0004] The invention aims to create a method that does not have the aforementioned disadvantages. In particular, the method should make it possible to quickly and precisely adjust the exhaust gas recirculation parameter of an internal combustion engine, while simultaneously enabling compensation for long-term drifts. The invention further aims to provide a control unit for an internal combustion engine with which the method can be implemented.

[0005] The problem is solved by creating a method with the features of claim 1, a method with the features of claim 2 and a method with the features of claim 3.

[0006] In this process, an exhaust gas recirculation parameter, preferably an exhaust gas recirculation mass or an exhaust gas recirculation rate, is controlled in an exhaust gas recirculation system based on a first functional relationship between a recirculated exhaust gas mass and a first selection of parameters measured at the internal combustion engine. The recirculated exhaust gas mass is controlled by comparing a first exhaust gas mass, calculated based on the first functional relationship, with a second exhaust gas mass, calculated based on a second functional relationship between the recirculated exhaust gas mass and a second selection of parameters measured at the internal combustion engine. The first functional relationship is then adjusted based on the comparison of the first and second exhaust gas masses.Because the exhaust gas recirculation (EGR) quantity is controlled based on the first functional relationship, very rapid adjustment of the EGR valve's actuation speed is possible. This control is model-based, with the first functional relationship representing a model of the recirculated exhaust gas mass, particularly as a function of the EGR valve position. Simultaneously, the control is precise and stable with regard to long-term drift because it is corrected by continuously adjusting the first functional relationship to regulate the recirculated exhaust gas mass. This allows for the rapid and precise adjustment of the EGR rate or EGR mass within suitable limits throughout the entire service life of the internal combustion engine.This prevents an excessively low exhaust gas recirculation rate, which would otherwise lead to high combustion speeds, premature combustion, and consequently, loud and component-damaging combustion, along with increased nitrogen oxide emissions. Likewise, it avoids an excessively low exhaust gas recirculation rate that could cause combustion to extinguish or result in increased soot emissions and exhaust gas temperatures. Using this method, it is always possible to adjust the exhaust gas recirculation rate to the precise ratio required within the physical response times. The control of the recirculated exhaust gas mass incorporates a learning function that compensates for long-term drifts in the exhaust gas recirculation system, such as those caused by fouling.The method is both simple and precise because, within the framework of the control system, the exhaust gas mass calculated according to the first functional relationship is essentially compared with the exhaust gas mass calculated according to the second functional relationship. In particular, this does not require a complex combination of feedforward structure, superimposed control loop, and additional learning function. In a first embodiment according to the invention, the exhaust gas recirculation parameter is set at a steady-state load point.

[0007] In this context, an exhaust gas recirculation quantity generally refers to either the exhaust gas recirculation mass or the exhaust gas recirculation rate. Both quantities are readily convertible into one another. The exhaust gas recirculation rate is the quotient of the exhaust gas recirculation mass divided by the mass flow of the internal combustion engine.

[0008] A preferred method is characterized by the fact that the first and second functional relationships are chosen such that the first functional relationship can be calculated more quickly than the second and is defined across the entire operating range of the internal combustion engine. However, it is less precise than the second functional relationship, which is slower to calculate. Preferably, the second functional relationship is chosen such that it is only valid at steady-state load points of the internal combustion engine. This allows a very precise functional relationship to be selected as the second functional relationship, so that the first functional relationship is always adjusted based on a very precise, independent calculation of the recirculated exhaust gas mass. This increases the accuracy of the method.In contrast, the first functional relationship can be quickly calculated even during load changes of the internal combustion engine, thus enabling rapid control within the physical response times. It is defined across the entire operating map of the internal combustion engine, meaning it can be calculated independently of any specific load point, allowing control at all times and in all load points. In load points or operating map regions where the second functional relationship is not defined, preferably no adjustment or correction of the first functional relationship is made. Instead, it is used unchanged for control until the internal combustion engine returns to a steady-state load point, at which point the second functional relationship can again be used to adjust the first.Since the second functional relationship within the control system primarily serves to compensate for long-term drifts, the precision and accuracy of the exhaust gas recirculation (EGR) parameter setting is not significantly affected. In particular, no abrupt changes due to aging or fouling of the EGR system are expected, ensuring that the first functional relationship between two steady-state load points of the internal combustion engine always provides sufficient accuracy for controlling the EGR parameter.

[0009] In a second embodiment of the invention, the first functional relationship is based on a pressure gradient underlying and driving the exhaust gas recirculation. This first functional relationship is thus based on the laws of fluid dynamics, in particular on the fact that the recirculated exhaust gas is returned by a pressure gradient from an exhaust gas section downstream of the combustion chamber to a charge air section upstream of the combustion chamber. The method is particularly suitable for implementation in an internal combustion engine with high-pressure exhaust gas recirculation, in which pressurized exhaust gas is extracted upstream of an exhaust gas turbocharger turbine and returned to a pressurized charge air line downstream of a charge air compressor.A pressure gradient exists between the exhaust gas pressure upstream of the exhaust gas turbocharger turbine and the charge air downstream of the charge air compressor, which is driven by the exhaust gas turbocharger turbine. The pressure upstream of the turbine is higher than the pressure downstream of the compressor, causing the exhaust gas to flow along this pressure gradient from the exhaust gas area to the charge air area. The first functional relationship involves a pressure loss coefficient, which essentially describes the flow resistance of the exhaust gas recirculation (EGR) system. Within the control system, an EGR valve position is calculated based on the pressure loss coefficient and a target value for the EGR system, as defined by the first functional relationship. This target value includes a setpoint for the EGR quantity, i.e., an EGR mass or an EGR rate. The pressure loss coefficient is then corrected within the control system.The second functional relationship is preferably independent of the pressure loss coefficient. Thus, while the first exhaust gas mass is calculated based on the first functional relationship as a function of the pressure loss coefficient, the second exhaust gas mass is calculated based on the second functional relationship independently of the pressure loss coefficient. It is then possible to correct the pressure loss coefficient by comparing the first and second exhaust gas masses, thereby aligning the less accurately calculated first exhaust gas mass with the more accurately calculated second exhaust gas mass. In this way, the pressure loss coefficient, as an element of the first functional relationship, is continuously adjusted within the control system, ensuring sufficient accuracy and precision for controlling the exhaust gas recirculation variable.

[0010] In this context, according to a first alternative of the second embodiment of the invention, a first function of the pressure loss coefficient is calculated within the control system based on the first functional relationship. Simultaneously, a predetermined number of second functions of the pressure loss coefficient are calculated depending on a predetermined number of exhaust gas recirculation (EGR) valve positions and the pressure loss coefficient read from a characteristic map. Preferably, the first function of the pressure loss coefficient is calculated based on a target value for the recirculated exhaust gas mass and further on the basis of parameters measured at the internal combustion engine. The second functions, on the other hand, are calculated by reading the pressure loss coefficient from a characteristic map and by assuming a first EGR valve position, in particular by guessing or by taking it from a previous calculation.Starting with the first exhaust gas recirculation (EGR) valve position, values ​​for a predetermined number of EGR valve positions are defined at predetermined intervals, for example, from at least 0.9 multiplied by the first EGR valve position to at most 1.1 multiplied by the first EGR valve position. These values, together with the pressure loss coefficient read from the characteristic map, result in a predetermined number of second functions, which depend functionally on the pressure loss coefficient and parametrically on the different EGR valve positions. The deviation between the first function and the second functions is then minimized such that the second function with the smallest deviation from the first is determined.This minimum corresponds to a specific exhaust gas recirculation (EGR) flap position, which is determined accordingly. The EGR flap position determined in this way is then applied to the EGR flap, or the EGR flap is positioned in the determined position.

[0011] An exhaust gas recirculation flap position preferably addresses an angle of the exhaust gas recirculation flap which describes its pivoting between an open position and a closed position.

[0012] The exhaust gas recirculation (EGR) flap position determined in the described manner is used in a recalculation of the predetermined number of secondary functions, thus serving as the starting point for re-determining the interval of possible EGR flap positions. In this way, the actual EGR flap position is gradually approximated to a value at which the pressure loss coefficient of the EGR system corresponds to the pressure loss coefficient assumed according to the first functional relationship. Overall, this enables control of the EGR flap position and, ultimately, the EGR volume.

[0013] A preferred method involves continuously correcting the pressure loss coefficient values ​​stored in the characteristic map by the control system. This ensures that the primary functional relationship is always adjusted, thereby correcting or compensating for long-term trends or drifts in the exhaust gas recirculation system.

[0014] The pressure loss coefficient is preferably stored in the characteristic map as a function of a charge air pressure, an exhaust gas pressure or a function of these values, as well as as a function of the exhaust gas recirculation flap position.

[0015] According to a second alternative of the second embodiment of the invention, a basic map is provided which includes basic values ​​of the pressure loss coefficient as a function of the charge air pressure, the exhaust gas pressure or a function of these values, as well as as a function of the exhaust gas recirculation flap position. This basic map preferably remains unchanged over the lifetime of the internal combustion engine. The correction of the pressure loss coefficient is effected by storing correction values ​​for it in a correction map. The correction map is continuously updated by the control system. The correction values ​​are preferably also stored in the correction map as a function of the charge air pressure, the exhaust gas pressure or a function of these values, as well as as a function of the exhaust gas recirculation flap position.The correction values ​​can be summands or factors that are added to or multiplied by the base value of the pressure loss coefficient read from the base characteristic map in order to adjust the corrected pressure loss coefficient ultimately used within the first functional relationship. The corrected pressure loss coefficient is therefore preferably given by the sum or the product of the base value taken from the base characteristic map and the correction value.

[0016] A preferred method is characterized by the fact that the first functional relationship is given by the equation: mAGR=Aξ2pA|pA−pL|RLTA.

[0017] Here, A is a fixed, predetermined cross-sectional area of ​​the exhaust gas recirculation (EGR) section, which limits the EGR. The flow resistance of the EGR section is described by the cross-sectional area A and the pressure loss coefficient ξ, which preferably consists of a base value ξ0 and a correction value ξ according to the following equation (2). Korr results in: ξ=ξ0ξCorr.

[0018] Preferably, the pressure loss coefficient ξ has a value range of at least 0 to at most 1, where it particularly describes a cross-sectional narrowing of the exhaust gas recirculation path, for example due to contamination. The base value ξ0 is preferably taken from an invariant characteristic map in which it varies depending on the charge air pressure p. A , the exhaust pressure p L or a function of these values, in particular the absolute difference | PA -p LThe correction value ξ is stored based on the current exhaust gas recirculation (EGR) flap position, in particular the angle of the EGR flap. Korr is preferably dependent on the same parameters stored in a correction map, whereby the correction map is continuously re-updated based on the control described here. The correction of the first functional relationship according to equation (1) is thus achieved by adjusting the correction values ​​ξ Korr carried out.

[0019] To calculate the recirculated exhaust gas mass m AGR Based on a fluid dynamics model, the exhaust gas pressure – preferably upstream of the turbine – p is further determined. A , as well as the pressure difference of the same to the charge air pressure - preferably behind a compressor - p L The calculation then incorporates the temperature of the exhaust gas – preferably before the turbine – T. A one. R L is the gas constant in the area of ​​the charge air.

[0020] Accordingly, the first selection of quantities measured on the internal combustion engine includes the exhaust pressure p. A , the charge air pressure p L , and the exhaust gas temperature T A Therefore, to determine these values, a first pressure sensor in the charge air area, a second pressure sensor in the exhaust gas area - preferably upstream of the exhaust gas turbocharger turbine - and a temperature sensor in the exhaust gas area are required.

[0021] A preferred method involves the second functional relationship being given by the following equation: mAGR=mS−λLStmB.

[0022] This is m S The intake mass of the internal combustion engine, that is, the total mixture mass supplied to the internal combustion engine, which consists of the recirculated exhaust gas mass and the charge air mass. The intake mass can be calculated using the following equation: mS=pLVHλaRLTL.

[0023] where p L again the pressure in the charge air area, V H is the displacement volume of the internal combustion engine, λ a R is the air consumption of the internal combustion engine, thus the ratio of the intake mass to a mixture mass that can theoretically be supplied to the internal combustion engine. L is in turn the gas constant in the area of ​​the charge air, and T L is the temperature measured in the charge air area – preferably downstream of the compressor. The factor by which the air requirement λ is determined according to equation (4) a When multiplied, this represents the theoretically available mixture mass for the internal combustion engine. To calculate the intake mass m S This therefore requires a pressure sensor in the charge air area - preferably downstream of the compressor.

[0024] In equation (3), λ is a ratio between a fresh air mass and a fuel mass m, determined by a lambda sensor in the exhaust system. B based on a stoichiometric ratio of these masses, which is given in equation (3) with L St is specified. From the product of the stoichiometric ratio L St and the fuel mass m B This results in the stoichiometric fresh air mass, where the fresh air mass actually supplied to the internal combustion engine is multiplied by the ratio λ measured by the lambda sensor, resulting in a total product λL St m B is obtained. Consequently, the recirculated exhaust gas mass m is calculated. AGR as difference of swallowing mass m S and the actual mass of fresh air supplied. The mass of fuel supplied m BThis is typically known from a control unit of the internal combustion engine, because it is used for load control of the same, in particular for controlling injectors.

[0025] The recirculated exhaust gas mass m AGR is very precisely determinable according to equation (3). However, the measured value λ of the lambda sensor varies only very slowly with changing operating conditions of the internal combustion engine, so that equation (3) is only applicable or valid at steady-state load points and, moreover, not across the entire operating map of the internal combustion engine. The fluid-mechanical relationship between the recirculated exhaust gas mass m, given by equation (1), AGRThe quantities listed there, on the other hand, are valid across the entire operating map of the internal combustion engine, whereby the quantities included in equation (1) can also be measured quickly, precisely, and, in particular, with sufficient accuracy even during load changes. However, the thus obtained recirculated exhaust gas mass m AGR The result calculated according to equation (1) is less accurate than the result calculated according to equation (3). Therefore, equation (1) is preferably used for control, while equation (3) is used in connection with regulation and the correction of the pressure loss coefficient ξ.

[0026] Overall, a preferred embodiment of the method comprises the following procedure: The control of the exhaust gas recirculation quantity by adjusting the exhaust gas recirculation flap position is carried out as follows: The functional relationship according to equation (1) is solved for (Aξ) 2, where this function of ξ is derived from the measured quantities included in equation (1) and a target value for the recirculated exhaust gas mass m AGRThe target value is calculated. This is preferably determined by a control unit, particularly depending on a load point of the internal combustion engine. Simultaneously, a corresponding second function of the pressure loss coefficient ξ is calculated by assuming a first exhaust gas recirculation flap position, in particular an exhaust gas recirculation flap angle, or by taking this value as the result from a previous calculation. Based on this first value, a number of further values, preferably twenty, are calculated, ranging from at least 0.9 times the first value to at most 1.1 times the first value.For each of these multiple exhaust gas recirculation flap positions, as well as the measured values ​​for exhaust gas pressure and charge air pressure or the function calculated therefrom, a value for the pressure loss factor is read from the corresponding map, and the corresponding second function is calculated from the fixed cross-section A and the pressure loss coefficient ξ read from the map and preferably corrected with the correction value.

[0027] The first function, calculated based on equation (1), is now compared stepwise with the second functions, with the aim of finding a minimum in the form of the second function that deviates least from the first. The exhaust gas recirculation (EGR) valve position corresponding to this second function is then determined. The EGR valve is actuated using the EGR valve position assigned to this function. This EGR valve position is also fed back into the process and serves as the starting value for recalculating the EGR valve position according to the described procedure.In this way, the exhaust gas recirculation flap position is gradually adjusted until the value of the pressure loss coefficient read from the map, particularly as a function of the exhaust gas recirculation flap position, finally corresponds as closely as possible to the value that results according to the functional relationship according to equation (1) on the basis of the target specification for the recirculated exhaust gas mass m. AGR results.

[0028] This control can be implemented very quickly. However, it is obvious that it relies heavily on the values ​​given for the pressure loss coefficient ξ and the correction value ξ. Korr are stored in the corresponding characteristic fields.

[0029] Therefore, within the framework of the regulation, a learning algorithm is applied to these quantities, which derives its information independently of the pressure loss coefficient ξ, namely from a calculation of the recirculated exhaust gas mass m. AGR according to equation (3).

[0030] The procedure is as follows: First, according to equation (1), a first exhaust gas mass is calculated based on the measured values ​​and the pressure loss coefficient ξ read from the associated characteristic map(s). Simultaneously, according to equation (3), a second exhaust gas mass is calculated based on the measured values ​​received there, in particular the flow rate m. S and the ratio λ determined by the lambda sensor. The first exhaust gas mass and the second exhaust gas mass are fed to a controller, which calculates the pressure loss coefficient ξ or, preferably, the correction value ξ. Korr It adjusts in such a way that the first exhaust gas mass and the second exhaust gas mass are equalized. In particular, the first exhaust gas mass is regulated as a target value to the second exhaust gas mass by adjusting the pressure loss coefficient ξ or the correction value ξ. Korr will be adjusted accordingly.

[0031] The controller is preferably designed as an integral controller, a proportional / integral (PI) controller or a proportional-integral-differential (PID) controller.

[0032] In this way, the first functional relationship is continuously adjusted – at least at steady-state load points of the internal combustion engine – using the very precise calculation of the recirculated exhaust gas mass according to equation (3), which allows, in particular, long-term drifts of the exhaust gas recirculation system, including an exhaust gas recirculation cooler, to be detected. Either the characteristic map for the pressure loss coefficient ξ or, preferably, the characteristic map for the correction values ​​ξ is used. KorrThe correction is continuously recalculated at steady-state load points of the internal combustion engine. If no steady-state load point of the internal combustion engine exists, the correction or control is preferably suspended, whereby the values ​​of the pressure loss coefficient ξ or the correction factor ξ stored in the corresponding characteristic map are used. Korr The load is kept constant until a steady-state load point is reached and a meaningful correction or control is possible.

[0033] The control is carried out in the manner described above, always based on the current values ​​for the pressure loss coefficient ξ.

[0034] This method is particularly suitable for adjusting exhaust gas recirculation in internal combustion engines that employ sensitive combustion processes, such as HCCI (high-pressure combustion) or PCCI (premixed charge compression ignition). In these cases, the highly complex combustion control necessitates both rapid and precise regulation of the exhaust gas recirculation. The method is also especially well-suited for internal combustion engines that can run on different fuels, such as gasoline and diesel, particularly in dual-fuel operation.

[0035] This process can be used in an internal combustion engine to power a land, water, or air vehicle, particularly heavy agricultural machinery, open-pit mining vehicles, defense vehicles such as tanks, or trains. For example, the internal combustion engine can be used in a railcar or locomotive. It can also be used in an aircraft or ship. Furthermore, the internal combustion engine can be used for stationary applications, such as driving a generator for emergency power, continuous load operation, or peak load operation. Especially when the internal combustion engine is gas-powered, it can be used in a combined heat and power plant.Furthermore, it is possible that the internal combustion engine is used in a stationary environment to drive auxiliary and / or secondary units, for example fire pumps on an oil rig.

[0036] The problem is ultimately solved by creating a control unit for an internal combustion engine with the features of claim 12. The control unit is characterized in that it is configured to carry out a method according to one of the previously described embodiments. It is possible that the corresponding method is permanently implemented in a hardware structure of the control unit. Alternatively, it is provided that a computer program is loaded into the control unit, which includes instructions according to which a method according to one of the previously described embodiments is carried out when the computer program is running on the control unit. In this case, the advantages described in connection with the method are realized.

[0037] The invention is explained in more detail below with reference to the drawing. The single figure shows a schematic representation of an embodiment of the method in the form of a block diagram.

[0038] The figure shows a schematic representation of a preferred embodiment of the method in a block diagram. The method serves to adjust an exhaust gas recirculation parameter, in particular an exhaust gas recirculation rate, of an internal combustion engine 1, and is preferably implemented by a control unit 3 which is encompassed by the internal combustion engine 1. This is particularly preferably the engine control unit of the internal combustion engine 1, which also controls or regulates its other functions. The internal combustion engine 1 comprises an exhaust gas recirculation section 5, schematically indicated in the figure, the flow resistance of which can be adjusted by means of an exhaust gas recirculation flap 7, also schematically indicated here, thereby allowing the recirculated exhaust gas mass or the exhaust gas recirculation rate to be adjusted.

[0039] A first functional relationship 9 is shown schematically, which is based on equation (1) and to which a first selection 11 of quantities is fed as input variables, wherein the first selection 11 is preferably the charge air pressure p. L , the exhaust pressure p A and the exhaust gas temperature T A This includes the charge air pressure p. L preferably measured downstream of a charge air compressor. The exhaust gas pressure p A and the exhaust gas temperature T A are preferably measured upstream of a turbine of an exhaust gas turbocharger. The cross-sectional area A and the gas constant R also appear as fixed parameters in the first functional relationship 9. L a.

[0040] To calculate a first exhaust gas mass 13 – preferably according to equation (1) – a pressure loss coefficient 15 is further incorporated into the first functional relationship 9. This coefficient is determined by reading a base value 23 for the pressure loss coefficient from a characteristic map 17 as a function of the charge air pressure and the exhaust gas pressure, preferably as a function 19 of these quantities, in particular as a function of the magnitude of the difference between the exhaust gas pressure and the charge air pressure, and as a function of a position 21 of the exhaust gas recirculation flap 7. This base value 23 is then applied in a calculation element 25 with a correction value 27. The calculation element 25 is preferably configured as an addition element or as a multiplication element, with the correction value 27 preferably being defined either as a summand or as a multiplier.By offsetting the base value 23 with the correction value 27 in the offsetting element 25, the pressure loss coefficient 15, which ultimately enters into the first functional relationship 9, is calculated.

[0041] Also based on the first functional relationship 9, a first function 29 of the pressure loss coefficient 15 - preferably as (Aξ) 2 calculated from the correspondingly solved equation (1). This is incorporated into a determining element 31, which ultimately determines the position 21 of the exhaust gas recirculation flap 7. Further quantities are incorporated into the determining element 31, in particular a target value 33 for the exhaust gas recirculation parameter, preferably the exhaust gas recirculation rate. Depending on whether the exhaust gas rate or the exhaust gas mass is used as the basis for the control, the intake mass m is also incorporated into the determining element 31. Sthe internal combustion engine 1. Furthermore, the current position 21 of the exhaust gas recirculation flap 7 is preferably also included in the determination, whereby a plurality of second functions are calculated from this, which are compared with the first function 29, whereby a new value for the position 21 of the exhaust gas recirculation flap 7 is found by minimization.

[0042] The correction value 27 is calculated by a controller 35. For this purpose, a second exhaust gas mass 39 is calculated according to a schematically represented second functional relationship 37, preferably according to equation (3). A second selection 41 of quantities measured at the internal combustion engine 1 is included in the second functional relationship 37. The second selection 41 preferably includes, in particular, the measured value λ of a lambda sensor and the intake mass m. S of the internal combustion engine 1 or corresponding measured quantities from which the mass flow m can be determined. Sis calculable. Furthermore, the second functional relationship 37 preferably includes the fuel mass m supplied to the internal combustion engine 1. B and preferably also a stoichiometric ratio L St a fresh air mass to the fuel mass m B supplied.

[0043] The first exhaust gas mass 13 and the second exhaust gas mass 39 are compared in a comparison element 43, with a comparison result 45 being supplied to the controller 35. Based on the comparison result 45, the controller calculates the correction value 27, which is preferably stored in a correction map 47 depending on the function 19 and the position 21 of the exhaust gas recirculation flap 7. During operation of the internal combustion engine 1, the correction map 47 is continuously updated, at least at steady-state load points, so that currently adapted correction values ​​27 are always available for control via the first functional relationship 9. Thus, it is particularly possible to compensate for long-term drift of the exhaust gas recirculation path 5, for example due to fouling, using the controller 35.

[0044] Overall, it is shown that the method makes it possible to quickly and precisely adjust an exhaust gas recirculation parameter, in particular an exhaust gas recirculation rate of an internal combustion engine 1, while at the same time compensating for long-term drifts of an exhaust gas recirculation path 5 in a simple way.

Claims

[1] Method for adjusting an exhaust gas recirculation parameter of an internal combustion engine (1) at a steady load point comprising the following steps: - Control of the exhaust gas recirculation quantity given in an exhaust gas recirculation path (5) on the basis of a first functional relationship (9) between a recirculated exhaust gas mass and a first selection (11) of quantities measured at the internal combustion engine (1), and - Rules of the recirculated exhaust mass by comparing a first exhaust mass (13) calculated on the basis of the first functional relationship (9) with a second exhaust mass (39), wherein the second exhaust mass (39) is calculated on the basis of a second functional relationship (37) between the recirculated exhaust mass and a second selection (41) of quantities measured on the internal combustion engine (1), and wherein the first functional relationship (9) is adjusted on the basis of the comparison of the first exhaust mass (13) with the second exhaust mass (39). [2] Method for adjusting an exhaust gas recirculation parameter of an internal combustion engine (1) comprising the following steps: - Control of the exhaust gas recirculation quantity given in an exhaust gas recirculation path (5) on the basis of a first functional relationship (9) between a recirculated exhaust gas mass and a first selection (11) of quantities measured at the internal combustion engine (1), and - Rules of the recirculated exhaust gas mass by comparing a first exhaust gas mass (13) calculated on the basis of the first functional relationship (9) with a second exhaust gas mass (39), wherein the second exhaust gas mass (39) is calculated on the basis of a second functional relationship (37) between the recirculated exhaust gas mass and a second selection (41) of quantities measured at the internal combustion engine (1), and wherein the first functional relationship (9) is adjusted on the basis of the comparison of the first exhaust gas mass (13) with the second exhaust gas mass (39), wherein the first functional relationship (9) is based on one of the pressure gradients underlying and driving the exhaust gas recirculation, comprising a pressure loss coefficient (15) that describes a flow resistance of the exhaust gas recirculation path (5),wherein, within the framework of the control, an exhaust gas recirculation flap position (21) is calculated on the basis of the pressure loss coefficient (15) and a target value (33) for the exhaust gas recirculation path (5) according to the first functional relationship (9), wherein, within the framework of the regulation, the pressure loss coefficient (15) is corrected, and wherein, within the framework of the control, a first function (29) of the pressure loss coefficient (15) is calculated on the basis of the first functional relationship (9), wherein a predetermined number of second functions of the pressure loss coefficient (15) are calculated depending on a predetermined number of exhaust gas recirculation flap positions (21) and the pressure loss coefficient (15) read from a characteristic map (17, 47), wherein a deviation between the first function (29) and the second functions is minimized and the exhaust gas recirculation flap position (21) associated with the minimum is determined. [3] Method for adjusting an exhaust gas recirculation parameter of an internal combustion engine (1) comprising the following steps: - Control of the exhaust gas recirculation quantity given in an exhaust gas recirculation path (5) on the basis of a first functional relationship (9) between a recirculated exhaust gas mass and a first selection (11) of quantities measured at the internal combustion engine (1), and - Rules of the recirculated exhaust gas mass by comparing a first exhaust gas mass (13) calculated on the basis of the first functional relationship (9) with a second exhaust gas mass (39), wherein the second exhaust gas mass (39) is calculated on the basis of a second functional relationship (37) between the recirculated exhaust gas mass and a second selection (41) of quantities measured at the internal combustion engine (1), and wherein the first functional relationship (9) is adjusted on the basis of the comparison of the first exhaust gas mass (13) with the second exhaust gas mass (39), wherein the first functional relationship (9) is based on one of the pressure gradients underlying and driving the exhaust gas recirculation, comprising a pressure loss coefficient (15) that describes a flow resistance of the exhaust gas recirculation path (5),wherein, within the framework of the control, an exhaust gas recirculation flap position (21) is calculated on the basis of the pressure loss coefficient (15) and a target value (33) for the exhaust gas recirculation path (5) according to the first functional relationship (9), wherein, within the framework of the control, the pressure loss coefficient (15) is corrected, and wherein a basic map (17) is provided which includes basic values ​​(23) of the pressure loss coefficient (15) as a function of a charge air pressure, an exhaust gas pressure or a function of these values, as well as as a function of the exhaust gas recirculation flap position (21), wherein correction values ​​(27) for the pressure loss coefficient (15) are stored in a correction map (47), wherein the correction map (47) is continuously re-updated by the control. [4] Method according to any one of the preceding claims, characterized by, that the first functional relationship (9) and the second functional relationship (37) are chosen such that the first functional relationship (9) can be calculated more quickly and is defined in an entire characteristic map of the internal combustion engine (1), but is less accurate than the second functional relationship (37), which is slower to calculate. [5] Method according to claim 1, characterized by , that the first functional relationship (9) is based on one of the pressure gradients underlying and driving the exhaust gas recirculation, comprising a pressure loss coefficient (15) that describes a flow resistance of the exhaust gas recirculation path (5), wherein, within the framework of the control, an exhaust gas recirculation flap position (21) is calculated on the basis of the pressure loss coefficient (15) and a setpoint (33) for the exhaust gas recirculation path (5) according to the first functional relationship (9), and wherein, within the framework of the regulation, the pressure loss coefficient (15) is corrected. [6] Method according to any one of claims 2 to 5, characterized by , that the second functional relationship (37) is independent of the pressure loss coefficient (15). [7] Method according to one of claims 3 or 5, characterized by , that within the framework of the control a first function (29) of the pressure loss coefficient (15) is calculated on the basis of the first functional relationship (9), wherein a predetermined number of second functions of the pressure loss coefficient (15) are calculated depending on a predetermined number of exhaust gas recirculation flap positions (21) and the pressure loss coefficient (15) read from a characteristic map (17,47), wherein a deviation between the first function (29) and the second functions is minimized and the exhaust gas recirculation flap position (21) associated with the minimum is determined. [8] Method according to any one of claims 2, 3, 4, 6 or 7, characterized by, that the values ​​of the pressure loss coefficient (15) stored in the characteristic map (17,47) are continuously corrected by the control system. [9] Method according to any one of claims 1, 2, 4, 5, 6, 7 or 8, characterized by , that a basic map (17) is provided which includes basic values ​​(23) of the pressure loss coefficient (15) depending on a charge air pressure, an exhaust gas pressure or a function of these values, as well as depending on the exhaust gas recirculation flap position (21), wherein correction values ​​(27) for the pressure loss coefficient (15) are stored in a correction map (47), wherein the correction map (47) is continuously re-updated by the control system. [10] Method according to any one of the preceding claims, characterized by , that the first functional relationship (9) is given by the equation: mAGR=Aξ2pA|pA−pL|RLTA. [11] Method according to any one of the preceding claims, characterized by, that the second functional relationship (37) is given by the equation: mAGR=mS−λLStmB. [12] Control unit (3) for an internal combustion engine (1), characterized by , that the control unit (3) is configured to execute a method according to one of claims 1 to 11.

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