FR2853693A1 - Exhaust gas pressure estimating method for internal combustion engine e.g. diesel engine, turbine, involves estimating ratio of exhaust gas pressure in upstream and downstream of turbine, based on calculated exhaust gas weight - Google Patents

Abstract

The method involves determining exhaust gas temperature in an upstream of a turbine. Exhaust gas flow coming out of an engine is calculated, based on air and fuel flows entering into the engine. Weight of exhaust gas in the turbine upstream is calculated based on calculated gas flow. A ratio of exhaust gas pressure in the upstream and downstream of the turbine is estimated, based on calculated weight of the exhaust gas. An independent claim is also included for a device for controlling functions of an internal combustion engine.

Description

Method for estimating the gas pressure upstream of a

  The present invention relates to a method for estimating the pressure of the exhaust gas upstream of a turbine in an internal combustion engine equipped with '' a turbocharger supercharger assembly comprising a compressor and a variable geometry turbine. The invention also relates to a device for controlling the operation of a supercharged internal combustion engine, in particular of such an engine comprising two turbocharger assemblies with an inlet and an exhaust common to all the engine cylinders.

  The control of the operation of an internal combustion engine consists in managing the engine from a set of sensors and actuators. The set of control laws in the form of software strategy and characterization parameters in the form of engine calibration are generally stored in a computer in the form of an electronic control unit (ECU).

  A turbocharger assembly includes a turbine and a compressor intended to increase the amount of air admitted into the engine cylinders. In the case of an engine supercharged by two turbochargers, for example when the architecture of the engine is of the V-twin-turbo type, two turbines are placed at the outlet of the engine exhaust gas collectors so as to be driven by the exhaust gases from the two engine cylinder banks. The outputs of the two cylinder banks are connected downstream of the two turbines. The power supplied by the exhaust gases to the turbines can be modulated by installing relief valves or by providing turbines with blades with variable orientation so as to constitute a variable geometry turbocharger (TGV).

  Each compressor is mounted on a mechanical axis also receiving the turbine so that the two compressors compress the air which enters the intake manifold.

  A heat exchanger can be placed between the compressors 5 and the intake manifold common to the two cylinder banks in order to cool the compressed air at the outlet of the compressors.

  Actuators are used to control the opening and closing of the relief valves or the orientation of the blades of the turbines so as to modify the geometry of said turbines. The 10 control signals for these actuators are provided by the electronic control unit (ECU) and allow in particular to control the pressure prevailing in the intake manifold.

  In the particular case of a twin-turbo V engine architecture where the two compressors compress the air in an inlet 15 common to all the cylinders, it is important to control the balancing of the two turbochargers. Indeed, in the transient phase, the two compressors must participate in the development of the boost specification without interaction of one on the other. In stabilized operation, the two compressors must rotate at the same speed to provide the same operating conditions on the two cylinder banks.

  In the case of a diesel engine, the quantity of nitrogen oxides produced is mainly linked to the composition of the reactive mixture in the engine cylinders, a mixture which contains air, fuel and inert gases . These inert gases do not participate in combustion and come from a circuit diverting part of the exhaust gases to the intake circuit in order to reduce the amount of nitrogen oxides in the exhaust gases. This bypass circuit allowing the recirculation of part of the exhaust gases, known as the "EGR circuit" comprises a valve which makes it possible to modulate the quantity of exhaust gases recycled in the intake manifold.

  Still in the case of a diesel engine and in order to reduce the quantity of particles discharged into the exhaust gases, provision may be made for the installation of a particle filter in the exhaust pipe. Such a filter comprises a set of microchannels 5 in which a large part of the particles is trapped.

  When the filter is saturated with particles, it should be emptied by burning the particles during a regeneration phase which can be implemented by means of a heating device or by a specific adjustment of the engine.

  The introduction of such a particulate filter into the exhaust line downstream of the turbines of the turbocharger assemblies, causes an increase in the exhaust back pressure all the more significant as the filter is gradually loaded with particles.

  Such back pressure results in turbochargers by a reduction in the expansion rate represented by the ratio of the exhaust gas pressure upstream of the turbine to the exhaust gas pressure downstream of the turbine. It also results in a reduction in the power supplied by the exhaust gases to the turbines and a reduction in engine performance.

  To combat this reduction in power and maintain the same level of performance, the expansion rate should be maintained by increasing the pressure prevailing in the exhaust gases upstream of the turbine or turbines. Such an increase in pressure is obtained by closing the relief valves or by an appropriate orientation of the fins modifying the geometry of the turbine (s).

  Such regulation of the supercharging of a heat engine is therefore usually done by servo-control of the pressure in the exhaust manifold on a pressure setpoint 30 stored in the electronic control unit UCE. The pressure setpoint can for example result from a map as a function of the engine rotation speed and of the fuel flow injected, a map which is stored in the electronic control unit.

  A regulating device, for example of the PID type (proportional, integral, derivative) can then regulate the pressure of the manifold from the set value, by acting on the orientation of the fins so as to modify the geometry of the turbines.

  In the case of a twin-turbo engine comprising two turbochargers, the regulation must also ensure balancing of the two turbochargers in order to maintain them at the same speed of rotation.

  In all cases, the regulation compensates for the reduction in the expansion rate of the turbines by increasing the pressure prevailing in the exhaust gases upstream of the turbines. Such regulation is satisfactory although there is no control over the absolute value of the pressure prevailing in the exhaust gases upstream of the turbines.

  However, the value of such a pressure must be controlled in order to avoid deterioration of the turbochargers. If, in fact, the expansion rate is kept constant by increasing the pressure upstream of the turbine, the temperature of the exhaust gases upstream of the turbine will also increase, thus causing a risk of deterioration of the turbocharger (s) and of the engine.

  It is therefore necessary to limit the absolute value of the pressure prevailing upstream of the turbine as well as the resulting temperature from a measurement of the pressure of the exhaust gases upstream of the turbine.

  For such an exhaust gas pressure measurement upstream of the turbine, it is possible to use a pressure sensor device supplying an electrical quantity supplied to the injection computer via the electronic control unit. But mounting the pressure sensor on the engine presents great difficulties. In fact, the temperature of the exhaust gases is greater than 800 ° C., that is to say much greater than the normal operating temperature of such a sensor which is generally limited to approximately 130 ° C. It is therefore necessary to offset the sensor via a portion of pipe. The presence of soot in the exhaust gases, in particular in the case of a diesel engine, tends to clog the pipe and to distort the pressure measurement. In addition, the stitching of a pressure measurement pipe in the exhaust manifold generates an additional cost and can cause problems of thermomechanical behavior of the parts. The reliability of the engine is called into question by the mounting of such a pressure sensor.

  US Pat. No. 6,067,800 describes the mounting of such a pressure sensor upstream of the turbine of a turbocharger in the case of a diesel engine with a variable geometry turbocharger and comprising a partial gas recirculation valve. exhaust (EGR) to reduce nitrogen oxide emissions. The pressure measured by the sensor is used in a closed-loop regulating device for the orientation of the blades of the variable geometry turbine and the flow rate of the turbine.

  Japanese patent application JP 2000-356 162 describes a device for regulating the operation of a variable geometry turbocharger provided with an exhaust gas recirculation (EGR) valve in which an attempt is made to estimate the outlet pressure using the air flow admitted into the engine, the engine load, the cross-section of the turbocharger and the temperature of the exhaust gases upstream of the turbine. Such a device is not entirely satisfactory in view of the input data used and also does not allow it to function properly when a particulate filter is integrated in the exhaust line.

  The object of the present invention is to solve the difficulties encountered with known devices and to enable the exhaust gas pressure upstream of the turbine to be determined, in particular in the case of a twin-turbo engine with a single manifold. intake and turbine inputs connected together.

  The invention also relates to such a device which is able to eliminate the difficulties usually encountered when mounting a pressure sensor on the exhaust pipe upstream of the turbine or turbines.

  The present invention also relates to a method and a device allowing a precise determination of the pressure prevailing in the exhaust gases upstream of the turbine in the case of a diesel engine provided with a particulate filter inserted in the line. exhaust.

  The method according to the invention makes it possible to estimate the pressure of the exhaust gases upstream of a turbine in an internal combustion engine equipped with a turbocharger supercharging assembly comprising a compressor and a variable geometry turbine, the compressor supplying the engine with air at a pressure greater than atmospheric pressure and the turbine being traversed by the exhaust gases from the engine.

  According to the invention, the procedure is as follows: the temperature of the exhaust gases upstream of the turbine (Tavt) is determined, the flow rate of the gases leaving the engine is calculated from a measurement of the flow rate of air entering the engine and the fuel flow rate, the mass of the exhaust gases upstream of the turbine (Mavt) is calculated as a function of the turbine flow rate, the turbine flow rate is calculated taking into account its variable geometry as a function of a first estimate of the ratio of the exhaust gas pressures upstream and downstream of the turbine, an estimated value of the pressure of the exhaust gases upstream of the turbine is deduced therefrom (Pavt) and repeats the above operations iteratively.

  The value of the exhaust gas pressure upstream of the turbine thus obtained by estimation can be used for regulating the supercharging by the turbocharger assembly, under the same conditions as a measured value. The reliability of the engine is increased by the fact that no sensor must be mounted on the exhaust gas collector, risking affecting its thermomechanical behavior.

  The determination of the temperature of the exhaust gases upstream of the turbine (Tat) can be made by means of a suitably placed temperature sensor or, preferably, by an estimate made using a mapping in dependent on engine speed and fuel flow to the engine.

  Advantageously, the flow rate of the turbine is determined by interpolation on a map of the operation of the turbine as a function of the ratio of the pressures upstream and downstream of the turbine (Pavt / Papt) and of the instantaneous geometry of the turbine, the result of this interpolation then being reduced to the actual conditions of use of the engine taking into account the pressure of the exhaust gases upstream of the turbine (Pav,) and the temperature of the exhaust gases upstream of the turbine ( Tavt) The method according to the invention is preferably applied to an internal combustion engine comprising two identical turbocharger assemblies supplying the engine with compressed air by a single intake manifold, the steps of the method being carried out simultaneously for the two turbines. In this case, the inputs and outputs of the two turbines are generally connected together.

  The method is particularly useful when the engine is a diesel engine, the exhaust pipe being provided with a particle filter.

  A device according to the invention is suitable for controlling the operation of an internal combustion engine of a motor vehicle equipped with a turbocharger boost assembly comprising a compressor and a variable geometry turbine, the compressor supplying the engine with air at a pressure above atmospheric pressure and the turbine being traversed by the exhaust gases from the engine.

  The device includes an electronic control unit (ECU) capable of carrying out calculations from stored data and measured values and sensors for measuring in particular the air flow entering the engine, the flow of fuel supplying the engine and the instantaneous geometry of the turbine. The electronic control unit (ECU) comprises means for iterating an estimated value of the pressure of the exhaust gases upstream of the turbine (Pavt) t The internal combustion engine preferably comprises two identical turbocharger assemblies supplying the engine in compressed air by a single intake manifold.

  The device is particularly suitable for a diesel engine, the exhaust pipe of which is fitted with a particle filter.

  The invention will be better understood on studying a particular embodiment described by way of nonlimiting example and illustrated by the appended drawings, in which: - Figure 1 schematically illustrates the main elements of a device control of the operation of an internal combustion engine equipped with a device according to the invention; - Figure 2 schematically illustrates the different signal processing blocks for estimating the pressure upstream of the turbine; and - Figure 3 is a flowchart of iterative calculations used in the context of the estimation method of the invention.

  To proceed according to the invention to the estimation of the pressure of the exhaust gases upstream of a turbine in an internal combustion engine equipped with a turbocharger, it is necessary to have the following input data - the flow of fresh air entering the engine, - in the case of a diesel engine comprising a partial exhaust gas recirculation (EGR) valve, the flow of these recycled gases Qegr - the flow of fuel injected into the engine (Qcarb) - atmospheric pressure (Patmo), - the pressure prevailing in the exhaust gases downstream of the turbine (Papt), - the position of the fins of the turbine (s), in the case of a twin engine -turbo: Pos0 and Pos2 '- the temperature of the exhaust gases upstream of the turbine (Tavt).

  Each of these quantities can be measured by means of a sensor or be the subject of an estimate. This is how the air flow (in the case of a Qairi and Qai, 2 twin-turbo engine) is generally measured by one or more flow meters placed at the outlet of the air filter (s).

  The flow rate of Qerg recirculated exhaust gases can advantageously be estimated and reference may be made in this regard to French patent application FR 2 789 731 which describes a method for determining the flow rate of air entering an internal combustion engine equipped with an exhaust gas recirculation circuit.

  The atmospheric pressure is determined by means of a sensor which can be located in the electronic control unit.

  The temperatures upstream and downstream of the turbine or turbines are advantageously estimated as will be seen below. The pressure prevailing in the exhaust gases downstream of the turbine (s) can easily be estimated if no particulate filter is fitted in the exhaust line. Otherwise, provision may be made to measure it by means of a pressure sensor mounted downstream of the turbine or turbines.

  FIG. 1 shows by way of example the application of the invention to the case of a diesel engine having a twin-turbo V architecture. The engine 1 is associated with two identical turbochargers 2a, 2b. Air is admitted into the two cylinder banks 3a, 3b via an intake duct 4 common to the two banks 3a, 3b. The fresh air entering through the inlets 4a, 4b first passes through the air filters 5a, 5b before being brought through the lines 6a, 6b to each of the compressors, 7a, 7b of the respective turbocharger assemblies 2a, 2b 5 . In FIG. 1, the circulation of air before compression is shown diagrammatically by the arrows 8 and the circulation of the compressed air downstream of the compressors 7a, 7b by the arrows 9. Part of the calories of the compressed air 9 is recovered by cooling in a heat exchanger 10, the cooled compressed air then entering 10 the common intake duct 4. At the outlet of the engine 1, the exhaust gases, the circulation of which is shown diagrammatically in FIG. 1 by the arrows 11, circulates in the exhaust manifolds 12a, 12b.

  Part of these exhaust gases is taken up in a recirculation pipe 13 to be reintroduced into the intake duct 4 15 in an amount regulated by an EGR valve referenced 14. The exhaust gases from the exhaust manifolds 12a , 12b drive the turbines 15a, 15b with variable geometry of the respective turbocharger assemblies 2a, 2b. The energy of the exhaust gases which expand in the turbines 15a, 15b allows the driving of the compressors 7a, 7b mounted on the same mechanical axis 16a, 16b as the turbines 15a, 15b. The outputs of the turbines 15a, 15b are connected by a line 17 common to the two turbines 15a, 15b and communicating with the exhaust pipe 18 along which are mounted a particle filter 19 and a silent device 20.

  An electronic control unit UCE 21 is shown diagrammatically in FIG. 1 with some of its functional elements. In the example illustrated, the electronic control unit 21 comprises a device 22 for balancing the two turbochargers 2a, 2b, a device 23 for regulating the boost pressure, a device 24 for limiting the setpoint value of the boost pressure, and a device 25 for calculating the set value of the boost pressure. Finally, the electronic control unit 21 also incorporates a device 26 for estimating the pressure upstream of the turbines according to the invention. An atmospheric pressure sensor 27 supplies a signal to the device 25 for calculating the boost charge pressure and to the device 26 5 for estimating the pressure upstream of the turbines. Two air temperature sensors 28a and 28b determine the air temperature in the fresh air supply lines 6a, 6b. The signal is brought by the connections 29a, 29b to the device 24 for limiting the boost setting.

  Two flow meters 30a, 30b mounted in the air supply lines 6a, 6b provide a signal transmitted by connections 31a, 31b both to the device 24 for limiting the boost setting and to the device 26 for estimating the pressure upstream of the turbines. A pressure sensor 32 mounted in the intake duct 4 provides a signal transmitted by the connection 33 to the device 23 for regulating the boost pressure. A sensor 34 mounted in the exhaust pipe 17 downstream of the turbines l5a, l5b measures the temperature of the exhaust gases downstream of the two turbines l5a, l5b and provides by the connection 35 a signal 20 which is transmitted to the device 26 d estimate of the pressure upstream of the turbines.

  Reference will now be made to FIG. 2, which schematically shows the main elements allowing the determination of the pressure of the exhaust gases upstream of the turbine according to the method of the invention. The process takes place schematically according to the flow chart illustrated in FIG. 3 which represents a calculation cycle. The calculation values of a cycle are assigned the index n, and for the previous cycle the index n-1.

  The first step of the method consists in a step 36 30 (FIG. 3) in estimating the temperature of the exhaust gases upstream of the turbine or turbines (Tavt). In the example illustrated in FIG. 2, this estimate is made from a map stored in block 37 as a function of the rotation speed of the engine Nmot and of the flow of injected fuel (Qcarb). The signal from block 37 is filtered in block 38, which, in the example illustrated, is a first order filter with pure delay, so as to delay the estimate of 1.5 turns of the motor 5 in order to take into account counts the four-stroke cycle of the engine. Filtering simulates the thermal inertia of the exhaust manifold.

  The second step of the calculation cycle, referenced 39 in FIG. 3, consists in calculating the flow rate of exhaust gas leaving the engine (Qmot) This gas flow rate is the algebraic sum of the flow rate of fresh air entering the engine by the respective inputs 4a and 4b visible in FIG. 1 (Q1ai, and Qair2), of the flow of recycled exhaust gas passing through the EGR14 valve (Qegr) and of the flow of fuel injected into the engine (Qcarb) The flow of fresh air entering the engine is measured by flowmeters 30a and 30b (Figure 1). The measurement result can advantageously be filtered by means of a filter not shown in the figures in order to take into account the volume of the intake circuit during the transient phases of the engine in order to improve the desired estimate. The filtered value taken into account 20 is noted (Qairl + Qai, 2) f. The result of the algebraic sum carried out by the adder 40 of FIG. 2 is subjected to a pure delay in the delay block 41 corresponding for example to 1.5 engine revolutions, that is to say to three passages in top dead center of the engine (3 pmh). The output signal of the delay block 41 is the estimated value of the flow rate of gas leaving the engine (Qmot).

  The third step of a calculation cycle, referenced 42 in FIG. 3, performs the calculation of the mass of the exhaust gases in the exhaust manifold (Mavt). This value is the integral of the algebraic sum of the flows entering the collector and leaving the collector. The adder 43 shown in FIG. 2 receives on its positive input the value of the flow rate of gas leaving the engine (Qmot) coming from the preceding block 41. The adder 43 also receives on three negative inputs, the flow rate of exhaust gas recycled by the EGR valve (Qeg,) and the flow rates from the two turbines l5a, l5b visible in FIG. 1 both affected by the negative sign. The flow rate of the first turbine 15a is noted Qturbl while the flow rate of the second turbine 15b is noted Qturb2 The signal resulting from this algebraic sum, coming from the summing block 43, is brought to the input of the integrator 44 whose output signal is the mass of the gases in the exhaust manifold (Mavt).

  The flow rates of the turbines are obtained in the example illustrated 10 by interpolation in a map in the operating field of each of the turbines as a function of the expansion rate and of the position of the fins of the turbine considered. Experience shows that it is possible to simplify an operating field of a turbine in order to make it independent of the speed of rotation of the turbine. We can then define a normalized flow from a turbine operating field, written after simplification Qmbfrbch fI | Pos I (1) o Pavt is the pressure prevailing upstream of the turbine, Pap, is the pressure prevailing downstream, the ratio of these two pressures being the expansion rate td of the turbine and POS being the position of the fins defining the turbine geometry.

  To estimate the flow rate of the turbine, it is then necessary to divide the normalized flow rate coming from the operating field of the turbine by the estimated value of the pressure upstream of the turbine (Pavt) then to multiply by the square root of the temperature in upstream of the turbine (Tavt) in the form Qturb p QturbCh (2) avt A more precise determination of the flow rate of the turbines can be carried out if desired, either by direct measurement or by an estimate which also takes account of the speed turbine rotation.

  In the example illustrated, one proceeds by simplified estimation as indicated above for each of the two turbines 15a, 15b. The calculation cycle continues for each of the two turbines 10a5a, 15b in the respective step 45a, 45b which is carried out in the example of FIG. 2 by means of the blocks 47a, 47b which comprise in stored form the operating field respective turbines 15a, 15b. The blocks 47a, 47b allow the determination by interpolation of the reduced turbine flow rates QturbChl and QtuTbch2 according to formula (1) above, as a function of the position of the fins of each of two turbines referenced P. ,, and Pos2 and of the pressure upstream of the Pavt turbine which is the subject of the final estimate as will be seen below.

  The interpolated values of the flow rates of the reduced turbines (QturbChl and QturbCh2) are then divided by the estimated value of the pressure prevailing upstream of the turbines (Pavt) resulting from the preceding calculation cycle, in the dividing blocks 48a, 48b. It will be noted that for this calculation, the estimated value of the pressure upstream of the turbine resulting from the previous calculation cycle (Pavtni-) is used for each calculation cycle n. The expansion rate td = Pavt / Papt is calculated in the same conditions by the divider block 46 which receives on one of its inputs the value of the pressure upstream of the turbine, previously estimated (Pavt) and on its other input the value also estimated of the pressure downstream of the turbine ( Papt) from the previous calculation cycle nl.

  The value of the pressure downstream of the turbine (Papt) can be calculated from the temperature downstream of the turbine which can be measured by the sensor 34 (Figure 1), according to the formula = C. - .c Qrb + a- ptn * pn-1 RT o - C is the pressure drop after turbine - R is the ideal gas line; - Patmo is the atmospheric pressure measured by the sensor 10 27.

  The temperature of the exhaust gases upstream of the Tavt turbine which was previously estimated and appears at the outlet of the filter block 38 is brought to the inlet of a block 49 which extracts the square root therefrom, this square root then being brought to the respective inputs 15 of two multiplier blocks 50a, 50b. The latter receive on their other input the output signal from the dividers 48a and 48b. The result of this calculation is a signal appearing at the output of the respective blocks 50a and 50b and which represents the calculated value of the flow rates of the two turbines 15a, 15b, these flow rates being denoted Qturbl and Qturb2- These are the values which are brought by the connections 51, 52 visible in FIG. 2 to the negative inputs of the adder 43 as previously indicated. The calculations carried out in blocks 50a and 50b are carried out in steps 53a, 53b illustrated in FIG. 3.

  The value of the pressure upstream of the turbines (Pat) is estimated in step 54 of the calculation process illustrated in FIG. 3, step which follows on from step 42. This pressure value is estimated by applying the relation perfect gases: PxV = MxRxT where P is the gas pressure, V its volume, M the mass of the gas, R the gas constant (for exhaust gases 287 Joules / kg /! K) and T is the temperature some gas.

  The multiplier block 54 illustrated in FIG. 2 therefore receives 5 at its three inputs, respectively the mass of the exhaust gases upstream of the Mavt turbine coming from the integrator block 44, the constant R of the exhaust gases and the estimated value of the temperature of the gases upstream of the Tat turbine coming from the filter block 38. The result of the calculation coming from the multiplier block 54 is applied to a dividing block 55 which also receives the value Vavt of the volume of the gases between the engine outlet and the inlet of the turbines 15a, 15b which is determined as a function of the structure of the engine and of the pipes. The output of the divider block 55 provides the sought signal representing the estimated value of the pressure upstream of the turbines Pa ,,. 15

Claims (10)

  1. Method for estimating the pressure of the exhaust gases upstream of a turbine in an internal combustion engine equipped with a turbocharger boost assembly comprising a compressor 5 and a variable geometry turbine, the compressor supplying the engine in air at a pressure higher than atmospheric pressure and the turbine being traversed by the exhaust gases from the engine, characterized in that the temperature of the exhaust gases upstream of the turbine (Tavt) is determined, the flow rate of gases leaving the engine is calculated from a measurement of the air flow entering the engine and of the fuel flow, the mass of the exhaust gases upstream of the turbine (Mavt) is calculated as a function of the turbine flow rate, the turbine flow rate is calculated taking into account its variable geometry, as a function of a first estimate of the ratio of the exhaust gas pressures upstream and downstream of the turbine, deduces therefrom an estimated value of the exhaust gas pressure upstream of the turbine (Pavt) and the above operations are repeated iteratively.   2. Method according to claim 1 characterized in that the value of the pressure of the exhaust gases downstream of the turbine (Papt) is further calculated as a function of the flow rate of the turbine and the temperature of the gases d exhaust downstream of the turbine (Tapt).   3. Method according to one of claims 1 or 2 characterized in that the temperature of the exhaust gases upstream of the turbine (Tavt) is determined by an estimate made using a function mapping engine speed and fuel flow to the engine.   4. Method according to any one of the preceding claims, characterized in that the turbine flow rate is determined by interpolation on a map of the operation of the turbine as a function of the pressure ratio upstream and downstream of the turbine (Pavt / Papt) and the instantaneous geometry of the turbine, the result of this interpolation then being brought back to the actual conditions of use of the engine taking into account the pressure of the exhaust gases upstream of the turbine (Pavt) and the exhaust gas temperature upstream of the turbine (Tavt).   5. Method according to any one of the preceding claims, characterized in that it is applied to an internal combustion engine comprising two identical turbocharger assemblies supplying the engine with compressed air by a single intake manifold, the steps of the method being performed simultaneously for both turbines.   6. Method according to claim 5 characterized in that the inputs and outputs of the two turbines are connected together, the calculation of the temperature of the exhaust gases downstream of the turbine (Tapt) and optionally the value of the pressure exhaust gas downstream of the turbine (Papt), being made for the joint outlet of the two turbines.   7. Method according to claim 6 characterized in that the engine is a diesel engine, the exhaust pipe being provided with a particulate filter.   8. Device for controlling the operation of an internal combustion engine of a motor vehicle equipped with a supercharging turbocharger assembly comprising a compressor and a variable geometry turbine, the compressor supplying the engine with air at a pressure greater than the pressure atmospheric and the turbine being traversed by the exhaust gases from the engine, the device comprising an electronic control unit (ECU) capable of carrying out calculations from stored data and measured values, sensors for measuring the flow rate of air entering the engine, the flow of fuel supplying the engine and the instantaneous geometry of the turbine, characterized in that the electronic control unit (ECU) comprises means for calculating by iteration an estimated value of the pressure 30 exhaust gas upstream of the turbine (Pavt).   9. Device according to claim 8 characterized in that the internal combustion engine comprises two identical turbocharger assemblies supplying the engine with compressed air by a single intake manifold.   10. Device according to claims 8 or 9 characterized in that the engine is a diesel engine, the exhaust pipe being provided with a filter.