Method for controlling the flow rate in a partial exhaust gas recirculation duct at the intake of an engine and associated device

Abstract

This method for controlling the flow rate of gas circulating in a partial exhaust gas recirculation duct (10) at the intake of an internal combustion engine (1), the duct (10) comprising an inlet (10a), an outlet (10b) and a recirculated gas control valve (16) disposed between the inlet (10a) and the outlet (10b), the gas upstream of the valve (16) being at an upstream pressure and the gas downstream of the valve being at a downstream pressure, includes a step of increasing the upstream pressure and maintaining the downstream pressure to increase the pressure differential between the inlet (10a) and the outlet (10b) of the duct (10). Figure for the abbreviation: Fig 1

Description

Title of the invention: Method for controlling the flow rate in a partial exhaust gas recirculation duct at the intake of an engine and associated device technical field

[0001] The invention relates, in general, to a device and a method for controlling the flow of gas circulating in a partial exhaust gas recirculation circuit at the intake of an internal combustion engine, in particular intended to be incorporated in a motor vehicle. Previous techniques

[0002] The benefits of exhaust gas recirculation (EGR) in a combustion engine are well known, whether in diesel engines to reduce nitrogen oxide (NOx) emissions in the combustion gases or in gasoline engines to slow down combustion and reduce susceptibility to knocking, thus allowing for increased ignition timing. Exhaust gas recirculation also reduces engine pumping losses by increasing the pressure in the intake manifold connected to the engine cylinders, thanks to an increased gas flow rate in the engine for a given intake air flow rate.

[0003] New standards such as Euro 6D-Full, Euro7, etc. require more precise control of exhaust gas recirculation.

[0004] The flow rate of a gas circulating in a recirculation duct equipped with a valve is determined from an application of the Barré-Saint-Venant equation at the valve terminals, from the relation:

[0005] x BSV(^ H1)

[0006] in which: Q is the mass flow rate of the gas, r is the ideal gas constant, is the effective section of the conduit dependent on the opening of the valve, Pt,„t is the pressure upstream of the valve, Psort is the pressure downstream of the valve, and BSV is a coefficient called the Saint Venant Barré coefficient depending on the ratio of valve pressure between the upstream pressure Pent and the downstream pressure P.wri.

[0007] It is known from the prior art of methods for controlling the flow of gases circulating in the partial recirculation duct in which the flow is controlled by playing on the opening of the recirculated gas control valve disposed in the partial recirculation duct, more or less effectively, using flow estimation methods such as the Barré Saint Venant formula.

[0008] However, when the pressure ratio of the recirculated gas regulating valve approaches 1, that is, when the upstream pressure Pent and the downstream pressure Psort become substantially equal, the Saint Venant Barré coefficient BSV becomes extremely sensitive to the value of the pressure ratio, which introduces a large margin of error in the calculation of the partial recirculation flow rate and / or effective section, which can have consequences in the calculation of flow setpoints for example and cause a malfunction of the motor.

[0009] On the other hand, a pressure ratio of the recirculating gas control valve close to 1 generally indicates saturation of the recirculating gas control valve, which has reached its operating limit, meaning it is in a substantially maximum open position without achieving the desired recirculation flow rate. The recirculation duct is then no longer functioning at capacity, meaning it cannot reach the desired flow rate.

[0010] In view of the foregoing, the present invention aims to provide a method for controlling the flow of gas circulating in a partial exhaust gas recirculation duct at the intake of an engine, allowing an increase in the partial recirculation flow when the opening of the recirculated gas control valve is no longer sufficient, and allowing this increased flow to be obtained with a reduced uncertainty in the calculation of the value of the partial recirculation flow.

[0011] The invention therefore relates to a method for controlling the flow of gas circulating in a partial exhaust gas recirculation duct at the intake of an internal combustion engine, the duct comprising an inlet, an outlet and a recirculated gas control valve disposed between the inlet and the outlet, the gas upstream of the valve being at an upstream pressure and the gas downstream of the valve being at a downstream pressure.

[0012] The process includes a step of increasing the upstream pressure and maintaining the downstream pressure to increase the pressure differential between the inlet and outlet of the conduit.

[0013] Thus, the pressure differential between the inlet and outlet of the recirculation duct is increased, which makes it possible to achieve higher flow rates in the recirculation duct and improved accuracy in determining these flow rates.

[0014] Advantageously, the step of increasing upstream pressure and maintaining downstream pressure is implemented when the recycled gas control valve is in the substantially maximum open position.

[0015] Thus, it is possible to achieve higher flow rates in the recirculation duct even when the recycled gas control valve is at its operating limit, i.e. fully open without allowing a flow rate setpoint to be reached.

[0016] Preferably, the upstream pressure corresponds to the inlet pressure of a turbine of a turbocharger of the engine, and the downstream pressure corresponds to the pressure in an engine intake manifold.

[0017] Advantageously, the step of increasing the upstream pressure and maintaining the downstream pressure comprises the following sub-steps: - Determination of a minimum upstream pressure increase term. - Application of the minimum increase term to the upstream pressure. - Maintaining downstream pressure at a manifold pressure setpoint constant admission.

[0018] Preferably, the application of the minimum increase term to the upstream pressure is carried out via the turbine, and the maintenance of the downstream pressure is carried out via a flow control valve for the engine's air intake gases.

[0019] Advantageously, the minimum upstream pressure increase term is determined as a function of a minimum increase term relating to the accuracy of engine condition data sensors used and a minimum increase term relating to the permeability of the partial recirculation duct.

[0020] Preferably, the minimum increase term relating to the permeability of the partial recirculation duct depends on the type and fouling of the recirculated gas control valve.

[0021] Advantageously, the minimum upstream pressure increase term is applied by imposing a turbine expansion ratio such that:

[0022] =£^,where:

[0023] is the turbine expansion ratio, PavtmM is the pressure at the turbine inlet increased by the minimum increase term and Papt is the pressure at the turbine outlet.

[0024] Advantageously, maintaining the downstream pressure involves applying a pressure ratio through the air intake gas flow control valve such that, where: P^ cmim PuM*

[0025] is the pressure ratio of the intake gas flow control valve Air pressure, Pca]ls / , is the pressure setpoint in the engine's intake manifold, at the outlet of the intake air flow control valve. Papcrttini is the inlet pressure of the intake air flow control valve, or boost pressure, which is obtained after applying the turbine expansion ratio. is a compressor compression ratio of the turbocharger dependent on the turbine expansion ratio and Pavc is the compressor inlet pressure.

[0026] The invention also relates to a device for controlling the flow rate of gas circulating in a partial exhaust gas recirculation duct at the intake of a internal combustion engine capable of implementing a process as defined above. Brief description of the drawings

[0027] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0028] [Fig-1] schematically illustrates an internal combustion engine according to one aspect of the invention;

[0029] [Fig.2] schematically illustrates a recirculation flow regulation device partial according to the invention;

[0030] [Fig.3] schematically illustrates a module for developing a re-device regulation according to the invention;

[0031] [Fig.4] schematically illustrates a term determination block of minimal increase in upstream pressure; and

[0032] [Fig.5] schematically illustrates a method according to the invention; Detailed description of at least one embodiment

[0033] With reference to [Fig. 1], a portion of an internal combustion engine 1 is schematically represented according to one aspect of the present invention. The internal combustion engine 1 is a turbocharged engine intended for incorporation into a motor vehicle. However, without departing from the scope of the invention, it is possible to incorporate the internal combustion engine 1 into another type of device, in particular a transport device with a turbocharged engine, for example in the naval or railway sectors.

[0034] The engine 1 includes a low-pressure intake duct 2 and a high-pressure intake duct 3. The engine 1 is supercharged by a turbocharger which includes a compressor 4 located between the low-pressure intake ducts 2 and the high-pressure intake ducts 3.

[0035] The engine 1 comprises a cylinder block 5, here with four cylinders 5a, 5b, 5c and 5d. The cylinders are supplied with fuel by fuel injectors connected to an intake manifold 6.

[0036] The engine 1 includes a high-pressure exhaust duct 7 and a low-pressure exhaust duct 8 located downstream of the high-pressure exhaust duct 7. The turbocharger includes a turbine 9 disposed between the high-pressure ducts 7 and the low-pressure ducts 8.

[0037] The engine 2 includes an exhaust gas recirculation duct 10, also known by its Anglo-Saxon name "Exhaust Gas Recirculation", or by the corresponding acronym "EGR". The duct 10 connects the duct

[0038]

[0039]

[0040]

[0041]

[0042]

[0043] high-pressure exhaust duct 7 and high-pressure intake duct 3. More specifically, the recirculation duct 10 includes an inlet located at a point 10a of the high-pressure exhaust duct 7 upstream of the turbine 9, and an outlet located at a point 10b of the high-pressure intake duct 3 downstream of the compressor 4. In other words, the duct 10 is a high-pressure EGR duct. In addition, the engine 1 may also include a low-pressure EGR duct (not shown in [Fig. 1]). Engine 1 includes an air filter 11 and an intake valve 12 located on duct 2. The intake valve 12 regulates the air flow rate admitted into engine 1. Duct 2 includes a flow meter 13 for measuring the mass flow rate of air Q admitted through valve 12, a pressure sensor PI, and a temperature sensor Tl located downstream of valve 12. The PI pressure in the illustrated example corresponds to the compressor inlet pressure denoted Pavc and commonly referred to as "pressure before compressor". Engine 2 in this example includes a supercharged intake gas cooler 14. It includes means for determining the value of the boost pressure Pape, that is, the pressure downstream of the compressor. For example, pressure values ​​measured by a pressure sensor mounted downstream of the supercharged intake gas cooler 14 are used, and the boost pressure is approximated by the value measured by the sensor, or alternatively, the boost pressure value is deduced by adding to said measured value the value of the pressure drop in the cooler, which can be modeled from the gas flow rate through said cooler. The engine includes an intake gas flow control valve 15, generally called a throttle body 15 in the case of a gasoline engine. The intake gas flow control valve 15 and the cooler 14 are located on duct 3. The valve 15 is located downstream of the cooler 14. The outlet point 10b of the high-pressure EGR duct 10 is located downstream of the valve 15. Duct 3 includes a sensor for an intake manifold pressure P2 at the outlet of the valve 15 and a temperature sensor T2. The pressure P2, and the temperature T2, respectively, at the outlet of the valve 15 correspond to the pressure Pcoïi, and the temperature Tcou, respectively, in the engine's intake manifold 6. The valve 15 defines an effective area SeMlm by its opening and a pressure ratio 11^ such that: n _ P2_ „ (2) iteer — P — P r apc jt apc Where Pape corresponds to the pressure of the fluid flow at the inlet of valve 15 and corresponds to the pressure after compressor 4, or boost pressure, measured by a pressure sensor mounted at the outlet of the cooler (see above).

[0044] The engine 2 includes a recirculated gas control valve 16, also known by its Anglo-Saxon name EGR valve, or partial recirculation valve, which defines an effective area Se^r by its opening. The engine 2 also includes a recirculated gas cooler 17. The recirculated gas cooler 17 and the recirculated gas control valve 16 are mounted on the recirculation duct 10, the valve 16 being located upstream of the cooler 17.

[0045] The turbine 9 shown in [Fig. 1] has a plurality of blades 9a and is therefore a variable geometry turbine. The blades 9a form a variable angle with an axial direction (not referenced) of the turbocharger. The turbocharger includes an actuator 18 capable of modifying this angle.

[0046] Alternatively, the turbine 9 is a fixed geometry turbine and the actuator 18 is capable of modifying an associated discharge valve, also called by the Anglo-Saxon term "waste gate".

[0047] The motor 2 includes means for determining the pressure at the outlet of the turbine 9, for example a sensor for an outlet pressure Papt of the turbine 9 or a calculation model. An inlet pressure of the turbine 9 is denoted Pavt-

[0048] The engine 2 includes an electronic control unit 19 comprising a regulating device 20 whose function is to control the flow in the high-pressure EGR duct 10. More specifically, the regulating device 20 has the function of increasing the pressure differential between the inlet 10a and the outlet 10b of the duct 10 when the EGR valve 16 is at the end of its operation, i.e., when the EGR valve 16 is substantially at its maximum opening and the pressure differential between the inlet 10a and the outlet 10b of the duct 10 is no longer sufficient for the exhaust gases to flow up the EGR duct 10 to the high-pressure intake duct 3.

[0049] Unless otherwise specified, the term "upstream pressure" refers to the pressure of the fluid located upstream of the EGR valve 16. Similarly, unless otherwise specified, the term "downstream pressure" refers to the pressure of the fluid located downstream of the EGR valve 16. In the illustrated example, the downstream pressure is denoted Pdwn and the upstream pressure is denoted Pup. In the illustrated example, the downstream pressure Pdwn corresponds to the pressure in the intake manifold 6 measured by the pressure sensor P2, denoted Pcon.

[0050] In addition, the upstream pressure Pup is measured by a pressure sensor P3 disposed in the high-pressure exhaust duct 7. The measured pressure P3 also corresponds to the inlet pressure of the turbine Pavt in the illustrated example.

[0051] More specifically, the regulating device 20 increases the pressure differential between the inlet 10a and the outlet 10b by increasing the upstream pressure Pup and maintaining the downstream pressure Pdwn substantially constant. Indeed, it is necessary to maintain the pressure PC <M dans le collecteur 6 sensiblement constante afin d’assurer un The airflow required for the desired torque production by engine 1 and / or to prevent smoke generation in the case of a diesel engine. The downstream pressure Pjwn, corresponding to the pressure Pcou of the fluid in the intake manifold 6, must also be approximately constant.

[0052] In the illustrated example, the inlet pressure Pavt of the turbine 9 is identical to the upstream pressure Pup.

[0053] With reference to figure 2, the device 20 includes a processing module 21. The processing module 21a has the function of processing a turbine expansion ratio 77 and a pressure ratio 77 of the valve 15 regulating the flow rate of the air intake gases.

[0054] The device 20 comprises a first actuation means 22 and a second actuation means 23. The first actuation means 22 is capable of applying the expansion ratio of the turbine 77 determined by the module 21 and the second actuation means 23 is capable of applying the pressure ratio 77 of the valve 15 regulating the flow rate of the air intake gases.

[0055] In particular, the first actuation means 22 may include the actuator 18 and the second actuation means 23 may include an actuator 24 capable of modifying the opening and therefore the effective Seadm section of the valve 15.

[0056] In [Fig.3], the processing module 21 of the control device 20 of [Fig.2] has been schematically represented.

[0057] The processing module 21 includes a receiving block 25 capable of receiving a plurality of input data. In this case, the receiving block 25 communicates information with a module 26 for determining a setpoint Pc,,ns for the intake manifold pressure at the outlet of the valve 15 and with a module 26' for determining a corrected maximum cross-section Se„mXœr. The receiving block 25 also receives the pressure at the outlet of the turbine Papt.

[0058] Module 26 is in communication with the electronic control unit 19, so as to be able to receive an air flow setpoint Qair and a partial recirculation rate setpoint also called EGR rate, the air flow setpoint Qair and the partial recirculation rate setpoint 7esrv depending on a torque setpoint requested from the engine 1.

[0059] Module 26 also receives the values ​​of pressure Pcoii and temperature Tcou in the intake manifold 6 measured by sensors P2 and T2.

[0060] More specifically, module 26 determines the pressure setpoint in the intake manifold PCollsp according to the equation:

[0061] DJ r \ (3) Pcoik,, = 'f\filling]

[0062] Where the function f(filling) is a function describing a known filling model depending on the engine speed 1, the pressure Pcon and the temperature Tcou at the intake manifold.

[0063] Furthermore, module 26' is in communication with the electronic control unit 19, so as to receive measurements taken by status data sensors. More specifically, module 26' receives the readings of the effective area of ​​the EGR valve 16 and determines the corrected maximum area SemaXa„, such that:

[0064] — Semax " (4)

[0065] Where Se is a nominal maximum section of the EGR valve 16 determined on LJ cmax test bench with a reference engine, is a first calibration of the maximum nominal section depending on the supplier of the valve used as EGR valve 16 and allowing to reduce the impact of engine to engine dispersions, and Se^^is a second calibration of the maximum nominal section depending on the fouling of the EGR valve 16 and the cooler 17.

[0066] More precisely, this second calibration Seof,^ is adaptive and evolves over the lifetime of the valve 16 and the cooler 17. For example, this second calibration is learned when the EGR valve 16 is at its maximum operating range for a predetermined duration, and simultaneously a target cross-sectional area is not reached. The target cross-sectional area is compared with a measurement of the cross-sectional area Seesr, and the difference constitutes the second calibration A for the current driving conditions.

[0067] Modules 26 and 26' can be part of the regulation device 20.

[0068] The processing module 21 includes a block 27 for determining a minimum upstream pressure increase term defined as:

[0069] n _ p^Ki (5) 11 egr . — ~p---

[0070] Where P is the upstream pressure increased by the application of the minimum increase term

[0071] The minimum upstream pressure increase term Tregr^n is therefore a pressure ratio between the upstream and downstream of the EGR duct 10.

[0072] Block 27 is illustrated more precisely with reference to [Fig.4].

[0073] Block 27 includes a sub-block 28 for determining a minimum increase term relating to the accuracy of sensors and a sub-block 29 for determining a minimum increase term relating to the permeability of the partial recirculation duct 10.

[0074] Subblock 28 determines a minimum increase term relating to the accuracy of state data sensors ^caPt€ur\ùm. More precisely, the term ^caPteursmni allows the impact of the accuracy of the upstream pressure measurement Pup and

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082] downstream Pjwn due to the quality of the P3 and P2 sensors used for these pressures. Subblock 28 determines the term ^(:aPteursmini of minimum increase relative to the accuracy of sensors such that: TT „ (g) 11 sensors. —-------------â Where ôsensors is a calibration based on the accuracy of state data sensors such as pressure sensors P3 and P2 measuring Pup and downstream Pdwn pressures, and / or sensors measuring state data to measure the effective area of ​​the partial recirculation valve 16. Subblock 29 determines a minimum increase term related to the permeability of the partial recirculation duct 10, TlpermmM. More precisely, the term nPcrm„,i„i allows for a reduction in the impact of the type of valve used as the EGR valve 16. More precisely, subblock 29 determines the term such that: \ (7) TTperm — DP V [ T---' —5-- mon 1 aemaxm “up / Where Qegt. is an air flow setpoint in duct 10, r is the ideal gas constant, Tup is the temperature upstream of the EGR valve 16 measured by a temperature sensor T3 disposed in the high-pressure exhaust duct 7, and SemaXmr is the maximum corrected and supplied inlet section of block 27 and subblock 29 by the receiving block 25. Thus, the determination of the minimum increase term relating to the permeability of the duct 10 of partial recirculation trr p / -1 uses the inverse bijection of the function for calculating the Saint-Venant Barré coefficient. Block 27 further includes a selection block 30 configured to select the maximum value between the minimum increase term relating to the accuracy of state data sensors 7r <xlPteursmini déterminé par le sous-bloc 28 et le terme 77ferm,,,1,,1 d’augmentation minimale relatif à la perméabilité du conduit 10 de recirculation partielle déterminé par le sous-bloc 29. En résultat, le bloc de sélection 30 délivre le terme d’augmentation minimale de la pression amont The processing module 21 includes a block 31 for calculating a minimum upstream pressure increase PuP„,im as a function of the determined minimum increase term. The pressure P2 at the outlet of valve 15 corresponds in the illustrated example to the downstream pressure Pdwn, and this pressure P2 must remain constant because it is identical to the pressure Pcon in the manifold 6, which must also remain constant. The setpoint Pœ!lsl, the pressure in the intake manifold 6 at the outlet of valve 15, is a downstream pressure setpoint Pdwn,p. It is thus possible to determine the minimum upstream pressure Pla, the downstream pressure Pdwn being fixed at the value of the setpoint Patllsp for the intake manifold 6 pressure. The calculation block 31 therefore determines the increased upstream pressure minimum PuPmu„ such that:

[0083] PuPmM ~ Pdwnsp ' ^egrmi„-, = PCollsp ' ïïegrmiai (8)

[0084] The processing module 21 further includes a block 32 for determining the minimum expansion ratio of the turbine 9 as a function of a minimum inlet pressure Pavtmltl,àe of the turbine. Since the upstream pressure Pup measured by sensor P3 is identical in the illustrated example to the pressure Pavt at the inlet of the turbine 9, the minimum inlet pressure of the turbine Pavtmini is identical to the minimum upstream pressure PupmM. Block 32 therefore determines the ratio such that:

[0085] (9)

[0086] Where the pressure at the outlet of the Papt turbine is supplied at the inlet of block 32 by the receiving block 25. This pressure at the outlet of the Papt turbine is constant, the flow rates not being required to change.

[0087] Block 32 sends the undetermined minimum expansion ratio on the one hand to the output of the processing module 21 and on the other hand to a block 33 for determining a minimum compression ratio

[0088] Block 33 determines the minimum compression ratio defined as the ratio between a minimum outlet pressure of the compressor Papcniim, i.e. the minimum boost pressure, and the inlet pressure of the compressor Pavc, which in the illustrated example corresponds to the pressure PL. Using the principle of conservation of power, according to which the power developed by the turbine 9 is equal to the power developed by the compressor 4, the turbine 9 being driven by a common shaft with the compressor 4, block 33 determines the minimum compression ratio, for example, by the following formula: t0089! _ / 1 . . ^ / r. \ \ (1°) 7Tr. . — -ô---- — | 1 4 ■-----7—7:------ ' ( 1 - TT t ' ■ " II rîPlTll P ave \ x / J

[0090] Where Tavt is the temperature at the inlet of turbine 9, is the efficiency of turbine 9, is the efficiency of compressor 4, Tavc is the temperature at the inlet of compressor 4 corresponding to temperature Tl, ^turb is the gas flow rate through turbine 9, incmp is the gas flow rate through compressor 4, is the adiabatic coefficient (Laplace coefficient) of the gases in turbine 9, padm is the adiabatic coefficient (Laplace coefficient) of the gases in compressor 4, Cp h is the specific heat capacity of the gases in turbine 9 and Cp is the specific heat capacity of the gases in compressor 4.

[0091] The processing module 21 finally includes a block 34 for determining the pressure ratio of the air intake gas flow control valve 15, defined as the ratio between a minimum inlet pressure of the valve 15, which corresponds to the minimum outlet pressure Papc.^ of the compressor 4 (boost pressure minimum) and the desired outlet pressure P2 of valve 15, which corresponds to the pressure setpoint in the intake manifold Pcou. Block 34 therefore determines the pressure ratio of valve 15 such that:

[0092] = P^ Pave Peoll,., Cmîni PaM„

[0093] The processing module 21 sends to output the pressure ratios of the valve 15 regulating the flow rate of the inlet gases and the minimum expansion w of the turbine 9, which are applied by the device 20 through the actuation means 22 and 23.

[0094] Thus, the upstream pressure Pup is increased by a minimum term and the downstream pressure is maintained constant at the intake manifold pressure setpoint PCoUsp by means of an action on the turbine 9 and on the valve 15 in addition to the EGR valve 16. The pressure differential between the inlet 10a and the outlet 10b of the exhaust gas recirculation duct 10 is thus increased, in the case where the EGR valve 16 is at the end of its operation.

[0095] The device 20 is thus able to implement a method of controlling the flow of gas circulating in the recirculation duct 10 defined below and illustrated in [Fig.5].

[0096] In a first stage El, the motor is in conventional operation from a torque demand.

[0097] In a second step E2, the corrected maximum section term Se maxM is determined. This term is determined as described previously by the module 26' of the device 20.

[0098] In a third step E3, a comparison is made between the corrected maximum area term Semax™ and a measurement of the effective area Seegr of the EGR valve 16. More specifically, if the effective area Se^r of the EGR valve 16 is greater than or equal to the corrected maximum area term Semaxm™, then the process proceeds to a step E4 because the EGR valve 16 is considered to be at its operating limit, i.e., in a substantially maximum opening state. It is then necessary to increase the pressure differential between the inlet 10a and the outlet 10b of the partial exhaust gas recirculation duct 10. Otherwise, the process is not implemented, and the engine continues its conventional operation in which the pressure differential in the duct 10 is managed solely by means of the effective area of ​​the EGR valve 16 and / or the turbine 9.

[0099] In step E4, the upstream pressure Pup is increased and the downstream pressure Pdwn is maintained. More specifically, the pressure difference between the inlet 10a and the outlet 10b of the recirculation duct 10 is increased without hindering the torque production of the engine 1, the pressure PCoii in the intake manifold 6 corresponding to the downstream pressure Pdwn remaining constant.

[0100] More specifically, step E4 comprises the following substeps.

[0101] In a first substep E5, a minimum increase term of the The upstream pressure Pup is determined as described previously.

[0102] In a second substep E6, the minimum increase term is applied to the upstream pressure Pup. More specifically, the first actuation means 22 modifies the opening of the turbine 9 blades via the actuator 18 in order to apply the minimum increase term, i.e. to obtain an upstream pressure value Pup equal to the minimum increased upstream pressure P“P,™- More specifically, the first actuation means 22 imposes the minimum expansion ratio on the turbine 9.

[0103] Thus, the upstream pressure Pup at the inlet of valve 16 is indeed increased. However, since the expansion ratio of turbine 9 is modified, the power developed by turbine 9 is also modified, which in turn modifies the power developed by compressor 4, as turbine 9 and compressor 4 form a turbocharger connected by the same shaft. Consequently, the pressure at the outlet of compressor Pape, or boost pressure, which corresponds to the pressure at the inlet of valve 15, is modified, which could lead to operating problems in engine 1.

[0104] It is then necessary to determine a boost pressure maintenance term in a third sub-step E7 in order to maintain the downstream pressure Pdwn constant at the value of the intake manifold pressure setpoint Pcou at the outlet of valve 15 determined by block 26.

[0105] More specifically, the intake manifold pressure holding term is the pressure ratio of the intake air gas flow control valve 15, and it is determined as described previously.

[0106] In a fourth step E8, the downstream pressure Pdwn is maintained constant at the setpoint value PColl, the intake manifold pressure at the outlet of valve 15, by applying the holding term

[0107] More specifically, the second actuation means 23 modifies the opening of the valve 15 and therefore its effective area via the actuator 24 in order to apply the holding term, i.e., to obtain a downstream pressure value Pdwn equal to the setpoint value Pcoiisp of the intake manifold pressure at the outlet of the valve 15. Thus, the change in power developed by the compressor 4 due to the expansion ratio imposed on the turbine 9 is compensated, and the intake manifold pressure remains unchanged. The torque produced by the engine is therefore not affected, the pressure P,011 in the intake manifold 6 remaining constant throughout the process, and the pressure differential increased by the opening of the turbine blades 9a at step E6 is maintained.

[0108] Steps E6 and E8 can be substantially simultaneous in order to gain efficiency in flow control.

[0109] Thus, by using not only the turbine 9 but also the valve 15, the recirculation conduit 10 is again capacitive even in the event of saturation of the valve 15, and higher recirculation flow rates can be achieved compared to the flow rates obtained using known prior art methods.

Claims

Demands

1. A method for controlling the flow rate of gas circulating in a partial exhaust gas recirculation duct (10) at the intake of an internal combustion engine (1), the duct (10) comprising an inlet (10a), an outlet (10b), and a recirculated gas control valve (16) disposed between the inlet (10a) and the outlet (10b), the gas upstream of the valve (16) being at an upstream pressure (Pup) and the gas downstream of the valve being at a downstream pressure (Pdwn), characterized in that the method comprises a step (E4) of increasing the upstream pressure (Pup) and maintaining the downstream pressure (PwH) to increase the pressure differential between the inlet (10a) and the outlet (10b) of the duct (10), and wherein the step (E4) of increasing the upstream pressure (Pup) and maintaining the downstream pressure (Pdwn) comprises the substeps following: - Determination (E5) of a minimum increase term ( of upstream pressure.- Application (E6) of the minimum increase term (77^.^) to the upstream pressure (Pup). - Maintenance (E8) of the downstream pressure (Pdwn) at a constant intake manifold pressure setpoint (Pmllv)-.

2. A method according to claim 1, wherein the step (E4) of increasing upstream pressure (Pup) and maintaining downstream pressure (Pdwn) is implemented when the recycled gas control valve (16) is in the substantially maximum open position.

3. A method according to claim 1 or 2, wherein the upstream pressure (Pup) corresponds to the inlet pressure (Pavt) of a turbine (9) of a turbocharger of the engine (1), and the downstream pressure (Pdwn) corresponds to the pressure in an intake manifold (Pcoii) of the engine (1).

4. A method according to claim 1, wherein the application of the minimum increase term (nè„r) to the upstream pressure (Pup) is carried out via the turbine (9), and the maintenance of the downstream pressure (Pdwn) is carried out via a valve (15) regulating the flow rate of the engine's (1) air intake gases.

5. A method according to any one of claims 1 or 4, wherein the minimum increase term ') of the upstream pressure is determined as a function of a minimum increase term relating to the accuracy of engine state data sensors used ^caPteur!imini) and a minimum increase term relating to the permeability of the partial recirculation duct (77^^^).

6. A method according to claim 5, wherein the minimum increase term relating to the permeability of the partial recirculation duct (10) depends on the type and fouling of the recirculated gas control valve (16).

7. A method according to any one of claims 5 or 6, wherein the minimum upstream pressure increase term (^5™,) is applied by imposing a pressure expansion ratio on the turbine (9) such that: _ WHERE ' 7Tf = ~ô--- ' 'mira is the pressure expansion ratio of the turbine, Pa^,„hü is the pressure at the inlet of the turbine (9) increased by the minimum increase term and Papt is the pressure at the outlet of the turbine.

8. A method according to claim 7, wherein the maintenance of the downstream pressure (Pdwn) is achieved by applying a pressure ratio (P) by the intake air flow control valve (15) such that Pdwn is the pressure of the intake air flow control valve (15), Pdwn is the pressure setpoint in the intake manifold (6) at the outlet of the intake air flow control valve (15), Papcnil is the boost pressure at the inlet of the intake air flow control valve (15), which is obtained after applying the turbine expansion ratio, Pmim is a compressor (4) compression ratio of the turbocharger depending on the turbine expansion ratio (pdwn), and Pavc is the compressor inlet pressure. (4).

9. A device for controlling the flow of gas circulating in a partial recirculation duct (10) of exhaust gases at the intake of an internal combustion engine (1) capable of implementing a method according to any one of claims 1 to 8.

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