FR2849897A1 - Internal combustion engine operating method, involves determining curve of counter pressure of exhaust gas based on average pressure on exhaust valve for engine cycle, and average downstream pressure of friction charge unit - Google Patents

Abstract

The method involves determining a counter pressure of an exhaust gas from an exhaust gas pipe (10) of an engine (1). A curve of the counter pressure of the exhaust gas or average value of the counter pressure is determined based on an average pressure on a level of an exhaust valve (15) for the engine operating cycle, average downstream pressure of a friction charge unit (5) for the cycle, and an engine speed.

Description

Field of the invention

  The present invention relates to a method of operating an internal combustion engine having at least one pressure drop element in the exhaust gas line of the engine, according to which the exhaust gas back pressure is determined.

  State of the art Document DE 199 48 136 AI describes a method for determining the back pressure by the exhaust gases in the turbine of an exhaust gas turbocharger installed in the exhaust gas channel 10 an internal combustion engine. Using the measured or calculated exhaust gas temperature upstream of the turbine, a calculated mass flow of the exhaust gas, the measured or calculated pressure downstream of the turbine and the working ratio d 'A load regulating member calculates the back pressure of the exhaust gases at the turbine.

  Disclosure and advantages of the invention The present invention relates to a method of the type defined above, characterized in that for a predetermined angular range of the crankshaft, the curve of the exhaust gas back pressure or of its value is determined average as a function of an average pressure at the exhaust valve for an engine cycle, the average pressure downstream of at least one pressure drop element for an engine cycle and the engine speed.

  The method according to the invention has the advantage of allowing a particularly precise determination of the exhaust gas back pressure in the interesting angular range of the crankshaft. Knowledge of the exhaust gas back pressure curve is particularly important in an angular range of the crankshaft in which, due to the overlapping of the valves, both an intake valve and an exhaust valve of the engine are open.

  This is particularly advantageous, because the average value of the exhaust gas backpressure in the predetermined angular range of the crankshaft makes it possible to calculate more simply certain quantities derived in the engine control than if the precise evolution of exhaust gas back pressure.

  It is advantageous to determine the curve of the exhaust gas back pressure or its average value in the predetermined angular range of the crankshaft further depending on the position of a bypass valve in the bypass which bypasses at least one element of pressure drop. This makes it possible to determine in an even more precise manner the evolution or the average value of the exhaust gas back pressure within the predetermined angular range of the crankshaft quin.

  It is more advantageous to determine the curve of the exhaust gas back pressure or of its average value in the predetermined angular range of the crankshaft by using at least one characteristic field and / or at least one characteristic curve. 1o This allows the evolution of the exhaust gas back pressure or its average value within the predetermined angular range of the crankshaft to be determined simply and economically.

  It is also advantageous to make an approximation of the evolution of the exhaust gas back pressure by an exponential function i5. This makes it possible to obtain a good approximation of the effective development of the exhaust gas back pressure at least in part of the possible angular range of the crankshaft and this in a simple manner.

  It is moreover advantageous to determine the time constant of the exponential function as a function of the position of the bypass valve. This makes it possible to have a particularly good approximation of the exponential function in the angular range of interest for the effective evolution of the back pressure of the exhaust gases.

  It is also advantageous to determine a limit value 25 of the exponential function according to the average pressure downstream of at least one pressure drop element, which makes it possible to adapt the exponential function particularly well to the effective development of the back pressure. exhaust gases in the interesting angular range.

  It is also of interest to determine the instant at which the curve of the exhaust gas backpressure cuts the average pressure at the exhaust valve. This allows a particularly good adaptation of the exponential function to the actual evolution of the exhaust gas back pressure in the interesting angular range of the crankshaft.

  It is also interesting to evaluate the time constant of the exponential function, which allows the economy of the means to determine the exponential function.

  It is also advantageous to determine the curve of the exhaust gas back pressure or its average value in the predefined angular range at the exhaust valve, which makes it possible to reliably determine the influence of the exhaust gas back pressure on the combustion process in the combustion chamber of the internal combustion engine.

  Drawings The present invention will be described below in more detail with the aid of an exemplary embodiment shown in the appended drawings in which: - Figure 1 is a schematic view of an internal combustion engine, - the FIG. 2 is a functional diagram for the description of the process of the invention, FIG. 3 shows an example of an exhaust gas back pressure curve as a function of the angle of the crankshaft.

Description of the embodiment

  According to Figure 1, the reference 1 designates a heat engine, for example that of a motor vehicle which in this example is a gasoline engine. The dull internal combustion engine or combustion engine 1 comprises one or more cylinders 5 each with a piston and a combustion chamber 50. Fresh air supplies the combustion chamber 50 via the intake suction pipe 35. The mass flow of air is regulated by the throttle flap 30 fitted to the suction line 35. The fresh air arrives in the combustion chamber 50 through 25 to an intake valve 40. The fuel injection takes place done by an injector 75 directly in the combustion chamber 50. The injection can also be carried out as a variant in the suction line 35. In the latter case, the fuel / air mixture is formed in the suction line 35 to arriving in the combustion chamber 50 by passing over the inlet valve 40.

  The air / fuel mixture of the combustion chamber 50 is ignited by a spark plug 45. The exhaust gases developed by the combustion of the air / fuel mixture in the combustion chamber 50 are discharged to the exhaust gas line 10 in passing through the exhaust valve 15. By the combustion of the air / fuel mixture in the combustion chamber 50, the piston 70 is driven which itself drives the crankshaft. A rotational speed sensor 60 measures the rotational speed (speed) of the internal combustion engine 1 using the rotations of the crankshaft. A pressure drop element 5 is installed in the exhaust gas pipe 10. This element can be optionally bypassed as shown in FIG. 1 by a bypass 25 provided with a bypass valve 20. There is also provided a motor control 55 receiving the measurement signal from the speed sensor 60.

  The intake valve 40 is controlled at opening and closing by an intake camshaft not shown in FIG. 1. The exhaust valve 15 is controlled at opening and closing by a shaft exhaust cam not shown in Figure 1. Position 10 of the intake camshaft and that of the exhaust camshaft are also provided to engine control 55. This is indicated in FIG. 1 by an arrow between the intake valve 40 and the engine control 55 as well as by an arrow between the exhaust valve 15 and the engine control 55. The engine control 55 also receives the position of the valve bypass 20 which can also be supplied as a model from other sizes. In the latter case there is no sensor determining the position of the bypass valve 20. The engine control 55 acts on the throttle flap 30, on the injector 75 and on the spark plug 45 as well as on the bypass 20 to achieve, for example, the required engine torque.

  The pressure drop element 5 may for example be the turbine of an exhaust gas turbocharger. In this case, the charge pressure supplied by the exhaust gas turbocharger on the suction side of the internal combustion engine 1 is regulated or regulated using the bypass valve 20. The pressure drop element 5 can also be a catalyst. In this case there is no provision for bypass 25. It is also possible to have several pressure drop elements in the exhaust gas pipe 10. The pressure drop element 5 can also consist of several pressure drop elements . Thus, the turbine of the exhaust gas turbocharger and the catalyst can be considered each time as a pressure drop element or a partial pressure drop element grouped into a single pressure drop element. It is also possible to have other pressure drop elements in the exhaust gas line 10, for example an exhaust pipe. It is established in the internal combustion engine 1 and its exhaust gas line 10 equipped with components such as catalysts, exhaust pipes and / or the turbine of an exhaust gas turbocharger, a counter -exhaust gas pressure upstream of these components. This back pressure is higher than the ambient pressure. This is due to the fact that the components represent pressure losses for the flow of exhaust gas between the exhaust valve 15 and the exhaust outlet. If we go up against the current in the exhaust gas line 10, the average pressure increases at the level of each pressure drop element. At the outlet of the exhaust, the ambient pressure prevails and at the exhaust valve 15 the highest pressure is encountered. The pressure in the exhaust gas line 10 is called the exhaust gas back pressure. If applicable, this expression covers the difference between the pressure in the exhaust gas line 10 and the ambient pressure. The engine control 55 needs for various reasons to know the back pressure of the exhaust gases. This information is necessary inter alia for the following reasons: - to calculate the internal residual gases. This is the quantity of gas which returns to the combustion chamber 50 of the cylinder 65 during the simultaneous opening of the intake valve 40 and the exhaust valve 15, that is to say during the overlapping of the valves, returning from the exhaust gas line 10, - to correct the signal from the pressure sensors of the exhaust gas line 10, sensors not shown in FIG. 1, - to calculate the quantity of air in the case of direct fuel injection or the air / fuel mixture in the case of injection into the suction line; this quantity passes during the overlapping of the valves of the suction line 35 through the combustion chamber 50 directly in the exhaust gas line 10 without participating in the combustion. This phenomenon is encountered only if the pressure in the suction line 35 during the overlapping of the valves is higher than the pressure in the exhaust gas line 10. In general, this situation exists only in engines with internal combustion with supercharging, for example engines fitted with an exhaust gas turbocharger or more simply a compressor.

  For reasons of economy, it is generally avoided to mount a pressure sensor in the exhaust gas line 10. The exhaust gas back pressure is preferably determined from quantities modeled using the quantities available. in motor control 55. These are either quantities supplied by sensors or resulting from other modeled calculations such as, for example, ambient pressure, mass flow of exhaust gases and temperature of exhaust gases . Modeling is generally done by proceeding in the direction opposite to that of the gas circulation, starting from the ambient pressure and then successively calculating the pressure difference on either side of each element with a pressure drop. In engines fitted with an exhaust gas turbocharger and the turbine of which is generally mounted directly downstream of the intake valve 15, the pressure difference on both sides must also be modeled in the last step. of this component. The average values of the pressure in an engine cycle, that is to say a complete cycle of a cylinder 65, are modeled according to the operating point of the internal combustion engine 1. The range of valve overlap mentioned in the first and the third of the above examples is an invariable constructive characteristic of an internal combustion engine 1, the camshafts of which are not adjustable. Nowadays, more and more internal combustion engines 1 are used, fitted with adjustable camshafts. However, depending on the type of construction, the intake camshaft or the exhaust camshaft or both may be adjustable. The overlap range then depends on the adjustment angle of the camshaft (s). By way of example, an internal combustion engine 1 can be envisaged having a fixed exhaust camshaft and a continuously adjustable intake camshaft; the angle of the crankshaft for closing the exhaust valve 15 will be fixed invariably 25 to a crankshaft angle of 3650 downstream from the top ignition dead center while for the opening of the intake valve 40 , there is, depending on the setting, a crankshaft angle between 325 and 3600 downstream of the top ignition center. The valve overlap range thus has an amplitude between 50 and 400 of crankshaft angle.

  In the internal combustion engine 1 equipped with a pressure drop element 5 which is provided for example the turbine of an exhaust gas turbocharger, it is to model according to the invention the curve of the back pressure of the exhaust gas in the exhaust gas line 10, in particular at the exhaust valve 15 for a predetermined angular range of the crankshaft.

  Compared to known methods in which only the average exhaust gas back pressure is modeled over a complete engine cycle, this method offers advantages for the functions mentioned above consisting in calculating the internal residual gases and the mixtures air or air / air fuel passing during the overlapping of the valves as well as to correct the pressure sensitive sensor signal installed in the exhaust gas line 10.

  It appears that for the calculation of the internal residual gases and of the amount of air or of air / fuel mixture which passes, the back pressure of the exhaust gases, in particular at the level of the exhaust valve 15 during the overlapping of the valves , is an important quantity. Measurements have shown that pressure pulses can be formed at the exhaust valves, so that the average exhaust gas back pressure over a full engine cycle provides only insufficient information about the conditions. pressure prevailing during valve overlap.

  The input quantities for modeling the evolution 15 (or curve) of the exhaust gas backpressure as a function of the angle of the crankshaft at the exhaust valve 15 or generally at the level of the exhaust valves of the internal combustion engine 1, upstream of the turbine 5, are the following: the average back pressure of the exhaust gases at the level of the exhaust valve 15 or generally of the exhaust valves , the average exhaust gas back pressure downstream of the turbine 5 and the engine speed. In this example, only one cylinder of the internal combustion engine 1 will be considered to describe below the curve of the exhaust gas back pressure at the exhaust valve 15 according to FIG. 1, depending on the angle of the crankshaft.

  However, this description transposes to the other exhaust valves of the internal combustion engine 1 and corresponds to the pressure of the exhaust gases upstream of the turbine 5.

  As an additional input quantity for modeling, the position of the bypass valve 20 can be used. This position is either that measured by a sensor or that modeled. The bypass valve 20 in this example constitutes an exhaust door. The position of the bypass valve 20 can be modeled, for example, in a known manner from the working ratio of the control of the exhaust valve 20 on the side of the engine control 55, starting from the ambient pressure. and supply pressure in the suction line 35, this pressure being supplied by the exhaust gas turbocharger.

  It does not matter for the process of the invention that the average exhaust gas backpressures at the exhaust valve 15 or downstream of the turbine 5 are each measured by a pressure sensor or are obtained from A model. In general, the average back pressure of the exhaust gases and the position of the bypass valve 20 are determined by modeling in order to save on measurement devices.

  The average exhaust gas back pressure downstream of the turbine 5 can be modeled, for example, by using the ambient pressure, the mass flow rate of the exhaust gases and the temperature of the exhaust gases in the catalysts; the exhaust gas temperatures in this case also come from a model. The average exhaust gas back pressure at the exhaust valve 15 can be modeled from the average exhaust gas back pressure, itself modeled, downstream of the turbine 5, of the mass flow rate of the exhaust gases in the turbine 5 and pressures in the suction line upstream and downstream of the turbocharger.

  The engine speed is provided by the rotation speed sensor 60.

  The modeling of the exhaust gas back pressure curve, as a function of the angle of the crankshaft, is done in this example for the area of the exhaust valve 15 and can be executed in the engine control 55. Measurements have shown that the exhaust gas back pressure at the exhaust valves reaches a maximum during and immediately after the opening of an exhaust valve; then the back pressure decreases until the exhaust valve is opened again. This development is plausible because there prevails in the combustion chamber 50 and before the opening of an exhaust valve 15, a higher overpressure resulting from combustion after the opening of the exhaust valve 15 during the outlet of the burned air / fuel mixture. We can achieve a good approximation of the attenuation curve by an exponential function. It suffices to exclude only the angular range of the crankshaft, the narrowest, around the instant of opening of the exhaust valve 15, that is to say the increase in the back pressure of the gases. exhaust to the maximum pressure and then a few degrees of crankshaft angle after the maximum. This range cannot be defined by approximation using an exponential function. On the other hand, the approximation by the exponential function is very precise, in the zone of overlapping of the valves.

  Figure 3 shows this situation in the form of a diagram. 5 In this diagram, the pressure is measured in bars as a function of the angle of the crankshaft represented in degrees. This angle is taken after the top dead center of ignition. It is assumed that the exhaust valve 15 opens for a crankshaft angle of between 1300 and 1400 after the top dead center of ignition. Curve 200 in FIG. 3 gives the ef10 fectively measured evolution of the exhaust gas back pressure. The maximum is reached for a crankshaft angle of around 1,700 after the top dead center of ignition. From a crankshaft angle of around 1900 after top dead center of ignition, the evolution of the exhaust gas back pressure can be represented by an exponential function of 105. The evolution of the exponential function 205 is shown in broken lines for the crankshaft angles less than 190. From the crankshaft angle of 190 following the top ignition center point to a crankshaft angle of around 2300 after the top ignition point there is the exponential function 205 which practically coincides with l measured evolution 200 of the exhaust gas back pressure. For crankshaft angles greater than 230, the exponential function 205 is slightly above the measured curve 200 of the exhaust gas back pressure. However, it still represents a good approximation of the exhaust gas back pressure curve. This is particularly the case for the range of valve overlap taken by way of example above. This range is between a crankshaft angle of 3250 and 3650 after the top ignition center. The range of valve overlap between 3250 and 3650 of crankshaft angle, maximum according to the example above, after the top dead center bears the reference 210 in FIG. 3.

  The exponential function of the evolution of the exhaust gas back pressure at the exhaust valve 15 is defined by a time constant, a limit value and a pressure value for each point corresponding to a crankshaft angle. 35 The measurements show that these parameters can be correlated with a good approximation to the quantities supplied by the motor control 55. The constant of the exponential function depends mainly on the position of the bypass valve 20. It can be deduced from the position or degree of opening of the bypass valve 20 using a characteristic curve obtained for example on a test bench. The crankshaft angle after the top ignition center point at which the curve of the exhaust gas back pressure 5 at the exhaust valve 15 cuts the average value of the exhaust gas back pressure at the exhaust valve 15 depends mainly on the engine speed. One can also use by way of example a characteristic curve obtained on a test bench giving the crankshaft angle after the top dead center i0 of ignition depending on the engine speed, angle at which the exhaust gas back pressure at level of the exhaust valve 15 is equal to the average value of the exhaust gas back pressure at the level of this exhaust valve 15.

  The average value of the exponential function is equal to 15 the average back pressure of the exhaust gases downstream of the turbine 5.

  The exponential function is represented by the following equation: pmod (t) = phT + (p.AV-p.hT) * exp {- (t-tS) /,} (1) In this equation, pmod (t) represents the curve of the exhaust gas back pressure as a function of time t, modeled by the exponential function; p.AV represents the average back pressure of the exhaust gases at the level of the exhaust valve 15; phT represents the average back pressure of the exhaust gases downstream of the turbine 5; US represents the time after the instant of top ignition dead point at which the curve of the exhaust gas back pressure at the exhaust valve 15 cuts the va30 their average of the gas back pressure d exhaust at the exhaust valve 15 and X is the time constant of the exponential function.

  In FIG. 3 is shown the average back pressure of the exhaust gases pAV at the level of the exhaust valve 15 as well as the average back pressure of the exhaust gases phT downstream of the turbine 5; the average exhaust gas back pressure phT downstream of the turbine 5 is less than the average exhaust gas back pressure pAV at the exhaust valve 15. The point of intersection of the curve the exhaust gas back pressure at the exhaust valve 15, represented by approximation by the exponential function 205 and the average exhaust gas back pressure p.AV at the exhaust valve 15, is indicated by the reference 215 in FIG. 3.

  For a given engine speed nm (rotation per minute) [1 / min] the relation between the crankshaft angle KWV is represented in degrees after the top dead center of ignition and the instant t in seconds s after the top dead center ignition is given by the following relation: 10 t [s] = 1 / (60 * nm [1 / minl) * KWT ['] (2) This allows to calculate the evolution over time of the back pressure exhaust gases according to equation (1) in the predetermined angular range of the crankshaft, which is of interest, particularly during valve overlap using the exponential function of equation (1).

  If instead of the precise curve of the exhaust gas back pressure one only wants to calculate the average exhaust gas back pressure in the predetermined crankshaft angular range, this is possible simply by using the equation (1) as well as the instants tstart, t-end after the top dead center of ignition. These instants define the beginning and the end of the predetermined angular range of the crankshaft. For the average exhaust gas back pressure 25 pmodjMW in the predetermined angular range of the crankshaft, the following formula is applied: pmod -MW = phT + (p.AV-phT) * tau ...

  * (exp {- (t_début-tS) / t} - exp {((tfin-tUS) / X} / (tfin-tdébut) (3) 30 The evolution of the calculation of the exponential function according to the equation (1 ) is shown schematically in Figure 2. Figure 2 shows a functional diagram executed for example in the motor control 55 in the form of a wired circuit and / or a program. A module 80 determines the position of the camshaft from the signals diagrammatically showing the intake valve 40 and the exhaust valve 15, signals supplied by the engine control 55 for the adjustment angle w_N of the intake camshaft; this quantity the adjustment angle w_N is supplied to a module 95 to calculate the predetermined angular range of the crankshaft, in this example this angular range is that of the overlapping of the valves. In engines fitted with intake camshaft and exhaust, both adjustable, the module 80 5 would determine the adjustment angle wNE and wNA of the camshaft d intake and exhaust camshaft to supply them to module 95. Module 95 then calculates the initial crankshaft angle w_start and the end crankshaft angle wfin; these angles define the predetermined angular range of the crankshaft. These angles wstart and wfin 10 are supplied to the module 100 which calculates a time curve, normalized pn (t) of the exhaust gas back pressure at the exhaust valve 15 for the predetermined angular range of the crankshaft, range between the initial crankshaft angle wstart and the end crankshaft angle wfin. The normalized pressure pn is given by the following relation: pn (t) = exp 1- [t-tS) / t]} (4) A module 85 is also provided for determining the position of the bypass valve 20 or its degree of openness. This position has the reference dw. This signal is also supplied to module 100. The degree of opening dw is modeled, for example, as described on the basis of the working report of the control of the bypass valve 20, the ambient pressure and the boost pressure. The mo25 dule 100 also receives the engine speed nm supplied by the speed sensor 60. A module 90 is also provided which determines the average exhaust gas back pressure at the exhaust valve 15 as well as the average back pressure of the exhaust gases downstream of the turbine 5; this quantity is obtained as described above, for example by modeling from the respective input quantities, namely, on the one hand, the average back pressure of the exhaust gases pAV at the level of the pressure valve. exhaust 15, and, on the other hand, the average back pressure of the exhaust gas p.hT downstream of the turbine 5.

  From the degree of opening dw, the module 100 calculates the time constant T as described from the engine speed nm, the module 100 determines the time tS after the top dead center instant from ignition, at which the curve of the exhaust gas back pressure at the exhaust valve 15 cuts the average value of the exhaust gas back pressure at the exhaust valve 15. From from the time constant t and from the time tS the normalized curve pn (t) of the exhaust gas back pressure 5 at the exhaust valve 15 is determined according to equation 3; it suffices to determine this curve only for the predetermined angular range of the crankshaft between the start angle wstart and the end angle wfin.

  This corresponds for example to wstart equal to 3250 and wfin 10 equal to 3650 of crankshaft angle after top dead center of ignition. The normalized pressure pn is applied to a multiplier element 110 which also receives the difference A = p.AV-phT formed by a subtractor element 105; this difference A is that between the average exhaust gas back pressure at the exhaust valve 15 and the average exhaust gas back pressure downstream of the turbine 5. At the outlet of the multiplier element 110 we obtain the product A * pn. This product is supplied to an adder element 1 15 to be added to the average exhaust gas back pressure p-hT downstream of the turbine 5. At the outlet of the adder element 115 there is the curve in function. the time pmod (t) of the exhaust gas back pressure at the exhaust valve 15 within the predetermined angular range of the crankshaft. With the exception of the pressure sensor 60, the other components of the functional diagram of FIG. 2 can be implemented by program and / or wired circuits of the motor control 55.

  If you want to calculate not the precise curve of the exhaust gas back pressure but only the average value of the exhaust gas back pressure in the predetermined angular range of the crankshaft, you just have to modify the calculation sequence of FIG. 2 by calculating in module 95 the mean value pn -MW of the normalized pressure pn in the predetermined angular range of the crankshaft, namely: pn_MWV = t * (exp {- (tdebut-tS) /,} - exp {- (tfin-tS) / t}) / (t end-tdébut) (5) The described process can be transposed to internal combustion engines not equipped with exhaust gas turbocharger.

  The pressure drop element 5 in this case does not represent a turbine but for example the catalyst or the exhaust. As in this case it is no longer necessary to provide a bypass 25 and that moreover this must not exist, the input quantity corresponding to the degree of opening dw of the bypass valve of FIG. 2 disappears . The same applies to the module 85 which determines the degree of opening dw of the bypass valve 20. For internal combustion engines equipped with an exhaust gas turbocharger, it is possible to consider eliminating the input quantity dw of the opening degree of the bypass valve 20. In the absence of the input quantity dw of the opening degree of the bypass valve 20 it is necessary to evaluate the time constant X of the exponential function pmod with slightly less precise modeling; this evaluation is done for example by measuring the change over time or as a function of the crankshaft angle of the exhaust gas back pressure at the exhaust valve 15 by a pressure sensor installed in the 15 exhaust gas line 10 at the exhaust valve 15 during an application phase (bench test). It is also possible to measure several curves of exhaust gas back pressure on the exhaust valve 15 and determine the resulting time constants for the attenuation of the exhaust gas back pressure 20 and to form a value. evaluated from the time constant for the exponential function pmod.

  Alternatively, for reasons of available resource, it is possible not to calculate the exponential function pmod in the engine control 55 but to calculate the evolution of the exhaust gas back pressure depending on the angle of the crankshaft, so modeled, to the exhaust valve 15 within a predetermined angular range of the crankshaft using a field of characteristics and / or at least one characteristic curve and applying to it the above input variables which determine the parameters mentioned above of the exponential function pmod. As described, these variables are the adjustment angle of the camshaft w_N or the adjustment angles wNE and wNA of the intake camshaft and the exhaust camshaft if these two shafts are cams are adjustable as well as the engine speed nm, the average exhaust gas back pressure p.AV at the exhaust valve 15, the average exhaust gas back pressure p-hT downstream of the turbine or of the pressure drop element 5 and, where appropriate, the degree of opening dw of the bypass valve 20.

Claims (9)

RESELL I CATI ONS   10) Method of operating an internal combustion engine (1) having at least one pressure drop element (5) in the exhaust gas line (10) of the engine (1), according to which the counter5 is determined exhaust gas pressure, characterized in that for a predetermined angular range of the crankshaft, the curve of the exhaust gas back pressure or of its average value is determined as a function of an average pressure at the level of the valve 10 exhaust (15) for an engine cycle, the average downstream pressure of at least one pressure drop element (5) for an engine cycle and engine speed.   2) Method according to claim 1, characterized in that the curve of the exhaust gas back pressure or its average value is further determined as a function of the position of a bypass valve (20) installed in a branch (25) which bypasses at least one pressure drop element (5). 30 30) Method according to claim 1, characterized in that one determines the curve of the exhaust gas back pressure or its average value for the predetermined angular range of crankshaft 25 using at least one field of characteristics and / or at least one characteristic curve.   40) Method according to claims 1 and 2,   characterized in that the exhaust gas backpressure curve is approximated to an exponential function.   50) Method according to claim 4 combined with claim 2, characterized in that the time constant of the exponential function is determined according to the position of the bypass valve (20).   6) Method according to claims 4 or 5,   characterized in that a limit value of the exponential function is determined according to the average pressure downstream of at least one pressure drop element (5).   70) Method according to claims 4, 5, 6,   characterized in that the instant at which the curve of the exhaust gas back pressure cuts the average pressure at the exhaust valve (15) is determined.   80) Method according to claim 4, characterized in that the time constant of the exponential function is evaluated.   9) Method according to claim 1, characterized in that the pressure drop element (5) is the turbine of an exhaust gas turbocharger or / and a catalyst.   10) Method according to claim 1, characterized in that one determines the curve of the exhaust gas back pressure or its average value at the exhaust valve (15).