WO2023083681A1 - Method for low-frequency estimation of a recirculated exhaust gas flow rate at the intake of an internal combustion engine - Google Patents

Method for low-frequency estimation of a recirculated exhaust gas flow rate at the intake of an internal combustion engine Download PDF

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Publication number
WO2023083681A1
WO2023083681A1 PCT/EP2022/080646 EP2022080646W WO2023083681A1 WO 2023083681 A1 WO2023083681 A1 WO 2023083681A1 EP 2022080646 W EP2022080646 W EP 2022080646W WO 2023083681 A1 WO2023083681 A1 WO 2023083681A1
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rate
πmoy
expansion
exhaust gas
venant
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PCT/EP2022/080646
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French (fr)
Inventor
Hugo DAMANCE
Vivien SMIS-Michel
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Renault S.A.S.
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Publication of WO2023083681A1 publication Critical patent/WO2023083681A1/en

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/0065—Specific aspects of external EGR control
    • F02D41/0072—Estimating, calculating or determining the EGR rate, amount or flow
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/45—Sensors specially adapted for EGR systems
    • F02M26/46—Sensors specially adapted for EGR systems for determining the characteristics of gases, e.g. composition
    • F02M26/47—Sensors specially adapted for EGR systems for determining the characteristics of gases, e.g. composition the characteristics being temperatures, pressures or flow rates

Definitions

  • TITLE Method for low frequency estimation of a flow rate of recycled exhaust gases at the intake of an internal combustion engine
  • the present invention relates to motor vehicle internal combustion engines of the spark ignition type (gasoline) or of the compression ignition type (diesel), and relates in particular to a partial exhaust gas recirculation circuit at the exhaust of such an engine, called a circuit EGR, for "ExhaustGaz Recirculation” in Anglo-Saxon terms or “Recirculation des Gaz d'Echappement” in French.
  • a circuit EGR for "ExhaustGaz Recirculation” in Anglo-Saxon terms or “Recirculation des Gaz d'Echappement” in French.
  • EGR flow a method and a system for low-frequency calculation of the flow of the exhaust gases recycled in such an EGR circuit, also called EGR flow.
  • the recirculation of exhaust gases is a process making it possible to limit the production of nitrogen oxides (NOx) in the combustion gases of a diesel engine, or to reduce the fuel consumption of gasoline engines.
  • This EGR process consists of taking gases from the exhaust and sending them to the intake, for example downstream of an engine air flow control valve.
  • NOx nitrogen oxides
  • This EGR process consists of taking gases from the exhaust and sending them to the intake, for example downstream of an engine air flow control valve.
  • the action on the formation of NOx can go up to 50% of global reduction and is interpreted by a reduction in the temperatures of combustion gases due to the dilution and a consequent slowing down of the kinetics of formation of the pollutant.
  • the reduction in fuel consumption is due to the engine being less sensitive to knocking, which makes it possible to increase the ignition advance and to the reduction in losses by engine pumping, the supply of recycled gases making it possible to increase the pressure in the engine intake manifold for the same air flow value necessary for torque production.
  • the quantity of recycled gas is estimated using a differential pressure sensor at the level of a valve regulating the flow of the EGR circuit, called the EGR valve. This sensor makes it possible to estimate the flow which has just passed through the level of the valve, called the EGR flow.
  • EGR rate that is to say, the ratio between the exhaust gas flow at the intake and the total flow of gases admitted into the engine ( air and recycled gases), which affects the level of NOx pollutants or fuel consumption.
  • Poor control of the EGR flow rate can lead to undesired effects that can compromise the operation of the vehicle. drastic in terms of degraded reliability or non-compliance with regulatory pollution control standards.
  • the difficulty in estimating the EGR flow is due to the fact that a flow sensor is not used at the EGR valve itself, which would be expensive and inaccurate. Instead of such a flowmeter, a differential pressure sensor is employed which measures the difference between the pressure downstream and upstream of the valve. The flow rate passing through the valve is estimated based on a model which uses the measured differential pressure and the opening level of the valve. Even if this model can provide very precise results, the differential pressure information invariably has a disturbed and very dynamic character because it presents high frequency oscillations, which are difficult to follow using electronic control units with limited calculation capacities. Thus, it is not possible in practice to make calculations with the information from the differential pressure sensor captured at high frequency, i.e. with a periodicity of 1 millisecond.
  • the invention consists in developing a low-frequency calculation method for estimating an EGR flow rate, ie with a periodicity of about 20 milliseconds, while maintaining a level of precision equivalent to a high-frequency calculation.
  • a low-frequency calculation method for estimating an EGR flow rate ie with a periodicity of about 20 milliseconds, while maintaining a level of precision equivalent to a high-frequency calculation.
  • the first method consists in making a model of the total flow of the engine intake gases, on the one hand, and in determining the only air flow, on the other hand.
  • the total flow can be determined by a filling model, from the pressure and the temperature in the engine intake manifold, and from a filling efficiency value which is itself a function of a set of parameters comprising at least minus the speed, the pressure in the intake manifold, and possibly other parameters such as the timing position of the intake and exhaust valves.
  • the fresh air flow is determined by a flow meter. of EGR is then equal to the total inlet gas flow from which the fresh air flow is subtracted. This approach is described in particular in document US 2016/0069285, or in document FR 2938016.
  • the estimate is based on knowing the total intake gas flow, which is conventionally a volumetric pump model, and the fresh air flow, which is directly measured by the sensor.
  • the available accuracy of this information is d 'approximately +/- 5% for the sensor measurement and approximately +/- 3% for the total flow, which may generate inconsistent results, particularly on low EGR flow values and values in transient state.
  • a second method consists in using a valve cross-section model, which generally uses the Barré de Saint-Venant equation or the “Throttle Equation” in Anglo-Saxon equivalent.
  • the equation gives very precise results, if one controls the position of the valve and the pressure difference which exists at its terminals. On the other hand, it is extremely sensitive to the pressure values at the valve terminals and to the angular position of the valve, when the pressure difference is low or when the valve is close to closing.
  • This cross section method is used for example in the document EP 1 416 138 with the addition of a correction map taking into account the upstream pressure, the downstream pressure and the cross section of the valve, or in the document EP 3 434 888, with the addition of a dynamic correction map depending on the positions of the valve.
  • the cross section method has the disadvantage of being strongly non-linear in the very closed or very open positions of the valve.
  • the pressure variations are very fast dynamic phenomena, of the order of a millisecond, which are generally filtered for use in the management of the EGR system, whose order of magnitude of the constant of time is around 10 to 20 milliseconds.
  • significant errors are introduced by using filtered pressure values.
  • the object of the invention is to improve the accuracy of the estimation of an EGR flow rate, in particular for use in the management of the low-frequency EGR system.
  • the object of the invention is a method for calculating the flow rate of recirculation of exhaust gases at the intake of an internal combustion engine allowing the control of said engine.
  • the minimum ⁇ min and maximum ⁇ max values of an expansion rate ⁇ are measured, defined as the ratio between the pressure measured in upstream and the pressure measured downstream of the exhaust gas recirculation valve,
  • the method for calculating the EGR flow rate thus makes it possible to calculate the EGR flow rate precisely using the Barré de Saint-Venant function and the second derivative of this function, applied to the average value of the expansion rate ⁇ moy .
  • the second derivative of the Barré de Saint-Venant function applied to the average value of the expansion rate ⁇ moy is calculated using three terms obtained by applying the Barré de Saint-Venant function to the envelope values ⁇ min and ⁇ max and the average value ⁇ avg.
  • the exhaust gas recirculation rate is calculated by summing a first term directly proportional to the Barré de Saint-Venant function applied to the average value of the expansion rate ⁇ moy, and a second term directly proportional to the second derivative of the Barré de Saint-Venant function applied to the mean value of the rate of expansion ⁇ moy .
  • the minimum ⁇ min and maximum ⁇ max values can be measured at high frequency.
  • the minimum ⁇ min and maximum ⁇ max values can be measured at low frequency.
  • the mean value ⁇ moy can be measured at low frequency.
  • the internal combustion engine is equipped with at least one high pressure partial recirculation circuit of the exhaust gases and at least one partial low pressure recirculation circuit of the exhaust gases.
  • Another object of the invention is a system for calculating the flow rate of exhaust gas recirculation at the inlet of an internal combustion engine allowing the control of said engine.
  • the flow rate calculation system comprises means for measuring the minimum ⁇ min and maximum ⁇ max values of an expansion rate ⁇ , defined as the ratio between the pressure measured upstream and the pressure measured downstream of the recirculation valve of the exhaust gas, means for measuring the average value of the expansion rate ⁇ avg, means for calculating the Barré de Saint-Venant function applied to the average value of the expansion rate ⁇ avg, means for calculating the second derivative of the Barré de Saint-Venant function applied to the mean value of the rate of expansion ⁇ moy, , and of the means for calculating the flow rate of recirculation of the exhaust gases.
  • FIG 1 schematically illustrates the structure of an internal combustion engine of a motor vehicle equipped with a high pressure partial recirculation circuit of the exhaust gases, a partial low pressure recirculation circuit exhaust gas pressure and an EGR flow calculation system according to the invention
  • FIG 2 illustrates a flowchart of the method for calculating the EGR flow rate, implemented by the calculation system, according to one mode of implementation of the invention
  • FIG 3 schematically illustrates the information accessible at the EGR valves.
  • FIG 4 is a flowchart used for the classic estimation of the EGR flow rate.
  • FIG 5 is a flowchart used in the invention for estimating the EGR flow rate.
  • the internal combustion engine 10 comprises, in a non-limiting manner, four cylinders 12 in line, a fresh air intake manifold 14, an exhaust manifold 16, a turbo-compression 18, a high pressure partial exhaust gas recirculation circuit (“high pressure EGR circuit”) and a low pressure partial exhaust gas recirculation circuit (“low pressure EGR circuit”) .
  • high pressure EGR circuit high pressure partial exhaust gas recirculation circuit
  • low pressure EGR circuit low pressure partial exhaust gas recirculation circuit
  • the cylinders 12 are supplied with air via the intake manifold 14, or intake distributor, itself supplied by a pipe 20 provided with an air filter 22 and the compressor 18b of the turbocharger 18 of the engine 10 .
  • the turbocharger 18 essentially comprises a turbine 18a driven by the exhaust gases and a compressor 18b mounted on the same shaft as the turbine 18a and providing compression of the air distributed by the air filter 22, with the aim of increasing the quantity (mass flow) of air admitted into the cylinders 12 of the engine 10.
  • a heat exchanger 24 is placed after the outlet of the compressor 18b equipping the supply line 14a of the intake manifold 14 with fresh air.
  • the internal combustion engine 10 comprises an intake circuit Ca and an exhaust circuit Ce.
  • the intake circuit Ca comprises, from upstream to downstream in the direction of air circulation:
  • a flowmeter 26 disposed in the intake duct 20 downstream of the air filter 22 to measure the actual value of the air flow entering the engine 10;
  • the compressor is associated with a bypass circuit with an intake relief valve 55 which opens in the event of sudden closure of the throttle body 30, to prevent the compressed air, located between the compressor 18b and the housing butterfly 30, does not cross the compressor 18b and does not degrade it, when for example, the driver of the vehicle suddenly lifts his foot from the accelerator pedal.
  • the exhaust circuit Ce comprises, from upstream to downstream in the direction of circulation of the burnt gases:
  • the latter collects the exhaust gases resulting from combustion and evacuates them to the outside, via a gas exhaust duct 34 leading to the turbine 18a of the turbocharger 18 and by an exhaust line 36 mounted downstream of said turbine 18a.
  • the engine 10 here comprises two partial exhaust gas recirculation circuits at the intake, called “EGR” circuits (“exhaust gas recirculation” in Anglo-Saxon terms), namely a high-pressure EGR circuit 15 and a circuit Low pressure EGR 38.
  • EGR exhaust gas recirculation circuits
  • Circuit 38 here a low-pressure exhaust gas recirculation circuit, called “EGR BP”, originates at a point on exhaust line 36, downstream of said turbine 18a, and in particular downstream of the system. 40 for gas pollution control and returns the exhaust gases to a point in the fresh air supply pipe 20, upstream of the compressor 18b of the turbocharger 18, in particular downstream of the flowmeter 26.
  • the flowmeter 26 only measures the flow of fresh air alone.
  • this recirculation circuit 38 comprises, in the direction of circulation of the recycled gases, a cooler 38a, a filter 38b, and a valve 38c intended to regulate the flow of low-pressure exhaust gases.
  • the valve 38c is arranged downstream of the cooler 38a and upstream of the compressor 18b.
  • the air intake valve 28 can also be used to force the circulation of a low pressure exhaust gas flow in the EGR circuit BP in the case where the depression between the exhaust circuit and the intake circuit would be insufficient. In this case, closing the valve 28 makes it possible to create a depression downstream thereof, able to suck in gases from the EGR circuit BP.
  • the high pressure EGR circuit 15, called “EGR HP”, originates at a point in the exhaust circuit Ce, upstream of said turbine 18a and returns the exhaust gases to a point in the admission circuit Ca, downstream of the heat exchanger 32.
  • this recirculation circuit 15 includes a valve 15a configured to regulate the flow of high pressure exhaust gases.
  • the engine is associated with a fuel circuit comprising, for example, fuel inj ectors (not referenced) injecting gasoline directly into each cylinder from a fuel tank (not shown).
  • the engine comprises an electronic control unit 70 configured to control the various elements of the internal combustion engine from data collected by sensors at various locations of the engine.
  • the electronic control unit 70 comprises a calculation module 72, a measurement module 73 and a control module 74.
  • the gas pressure downstream of the EGR valve called Paval is measured using a relative pressure sensor.
  • Pressure differential ⁇ P is measured using a differential pressure sensor.
  • the opening angle of the Oegr valve is measured using a position sensor placed on the electric motor which drives the valve.
  • Tamont the temperature upstream of the valve, in K Pamont, the pressure upstream of the valve, expressed in Pa.
  • the Barré de Saint-Venant function is expressed when the flow is non-sonic, i.e. for all the calculations that interest us, by the following expression:
  • ⁇ the rate of expansion, i.e. the ratio between Pamont and Pavai, dimensionless ⁇ , the adiabatic index of gases, dimensionless r, the ratio between the perfect gas constant divided by the molar mass of the gas in question, expressed in J kg -1 K -1
  • pressure information is extremely dynamic due to the acyclic behavior of an internal combustion engine. This acyclism creates strong volatilities of the differential pressure signal and by that implies strong variations on the rate of expansion ⁇ .
  • the present invention corresponds to a method which consists in using the following terms of the Taylor expansion in order to complete the information available without excessively increasing the computational load.
  • Figure 4 illustrates the procedure used in the conventional estimate, in order to better appreciate the contribution of the invention, the procedure of which is presented in Figure 5.
  • the information of the expansion rate is captured at high frequency, either every millisecond.
  • the information is filtered by taking the mean ⁇ moy at low frequency, ie every 10 milliseconds.
  • the function B SV2 is then applied to the mean value ⁇ moy and the coefficient ⁇ is multiplied to obtain the estimate of the EGR flow rate.
  • the information is captured at high frequency, ie every millisecond.
  • the maximum ⁇ max , minimum ⁇ min and average ⁇ average values at low frequency, ie every 10 milliseconds, are then recovered.
  • the function B SV2 is then applied to these three maximum values ⁇ max , minimum ⁇ min and mean ⁇ moy with a weighting of 1 ⁇ 4 for the maximum value, 1 ⁇ 2 for the mean value and 1 ⁇ 4 for the minimum value and a multiplication is carried out by the coefficient ⁇ to obtain the estimate of the EGR flow rate.
  • the flowchart represented in FIG. 2 illustrates the method for calculating the EGR flow rate, implemented by the calculation system 70.
  • a first step 61 the maximum and minimum values of the rate of expansion are measured, then, during the following step 62, the average value of the rate of expansion is measured.
  • the method 60 further comprises a step 63 for calculating the function B SV2 applied to the average expansion rate, according to equations (2) and (4), and a step 64 for calculating the second derivative of the function B SV2 applied to the mean expansion rate, according to equation (16).
  • the method 60 continues with a step 65 of calculating the average flow, according to equation (17).
  • the method 60 finally comprises a step 66 of engine control, through an EGR flow setpoint Q.
  • the invention proposes a method for estimating the flow of EGR used for engine control, requiring little computing resources and which can use the pressure values filtered at low frequency, with sufficient accuracy of the results.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
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Abstract

The invention relates to a method for calculating the exhaust gas recirculation flow rate at the intake of an internal combustion engine, which comprises: measuring the minimum value Πmin and maximum value Πmax of an expansion ratio Π; measuring the average value Πmoy of the expansion ratio; calculating the Saint-Venant's function applied to the average value of the expansion ratio; calculating the second derivative of the Saint-Venant's function; and calculating the exhaust gas recirculation flow rate.

Description

DESCRIPTION DESCRIPTION
TITRE :Procédé d’estimation à basse fréquence d’un débitde gaz d’échappement recyclésà l’admission d’un moteur à combustion interne TITLE: Method for low frequency estimation of a flow rate of recycled exhaust gases at the intake of an internal combustion engine
Domaine technique Technical area
La présenteinvention concernelesmoteursàcombustion interne de véhicule automobile de type à allumage commandé (essence) ou de type à allumage parcompression (diesel),etse rapporte en particulierà un circuit de recirculation partielle des gaz d’échappement à l’échappementd’un tel moteur,appelé circuit EGR,pour« ExhaustGaz Recirculation » en termes anglo-saxons ou « Recirculation des Gaz d’Echappement» en français. The present invention relates to motor vehicle internal combustion engines of the spark ignition type (gasoline) or of the compression ignition type (diesel), and relates in particular to a partial exhaust gas recirculation circuit at the exhaust of such an engine, called a circuit EGR, for "ExhaustGaz Recirculation" in Anglo-Saxon terms or "Recirculation des Gaz d'Echappement" in French.
Elle concerne plusparticulièrementun procédé et un système de calculà basse fréquence du débitdesgaz d’échappementrecyclésdans un tel circuit EGR,ditaussidébitd’EGR. It relates more particularly to a method and a system for low-frequency calculation of the flow of the exhaust gases recycled in such an EGR circuit, also called EGR flow.
Techniquesantérieures Previous techniques
Classiquement, la recirculation des gaz d’échappement est un procédé permettant de limiter la production d’oxydes d’azote (NOx) dans les gaz de combustion d’un moteur diesel, ou de diminuer la consommation de carburant des moteurs à essence. Ce procédé EGR consiste à prélever des gaz à l’échappement et à les envoyer à l’admission,par exemple en aval d’une vanne de régulation du débit d’air du moteur.Sur les moteurs diesel,l’action sur la formation des NOx peutallerjusqu’à 50% de réduction globale ets’interprète parune diminution destempératuresdesgaz de combustion due à la dilution et un ralentissementconséquentde la cinétique de formation du polluant. Sur les moteurs à essence, la diminution de la consommation de carburant estdue à une moindre sensibilité du moteur au cliquetis qui permetd’augmenterl’avance à l’allumage età la diminution despertes par pompage du moteur, l’apport de gaz recyclés permettant d’augmenterla pression dansle collecteurd’admission du moteurpour une même valeurde débitd’airnécessaire à la production du couple. Généralement la quantité de gaz recyclés est estimée à l’aide d’un capteur de pression différentielle au niveau d’une vanne de régulation du débitdu circuit EGR,dite vanne EGR.Ce capteurpermet d’estimerledébitquivientdepasserau niveau delavanne,appelédébit d’EGR. La bonne maîtrise du débit d’EGR est essentielle car il détermine le taux d’EGR,c’est-à-dire,le rapportentre le débitde gaz d’échappement à l’admission et le débit total des gaz admis dans le moteur(airetgaz recyclés),quiinflue surle niveau despolluantsNOx ou la consommation de carburant. Une mauvaise maîtrise du débit d’EGR peutconduire à effetsnon désirés pouvantremettre en cause le fonctionnementdu véhicule.Parexemple,une estimation trop élevée du débitd’EGR peutaboutir à des émissions de NOx plusimportantes sur lesmoteursdieselou à desphénomènesde cliquetisdanslesmoteurs à allumage commandé.Cela peut entraîner des conséquences drastiques en termes de fiabilité dégradée ou de non-respect de normes de dépollution réglementaires. Conventionally, the recirculation of exhaust gases is a process making it possible to limit the production of nitrogen oxides (NOx) in the combustion gases of a diesel engine, or to reduce the fuel consumption of gasoline engines. This EGR process consists of taking gases from the exhaust and sending them to the intake, for example downstream of an engine air flow control valve. On diesel engines, the action on the formation of NOx can go up to 50% of global reduction and is interpreted by a reduction in the temperatures of combustion gases due to the dilution and a consequent slowing down of the kinetics of formation of the pollutant. On gasoline engines, the reduction in fuel consumption is due to the engine being less sensitive to knocking, which makes it possible to increase the ignition advance and to the reduction in losses by engine pumping, the supply of recycled gases making it possible to increase the pressure in the engine intake manifold for the same air flow value necessary for torque production. Generally the quantity of recycled gas is estimated using a differential pressure sensor at the level of a valve regulating the flow of the EGR circuit, called the EGR valve. This sensor makes it possible to estimate the flow which has just passed through the level of the valve, called the EGR flow. Good control of the EGR flow is essential because it determines the EGR rate, that is to say, the ratio between the exhaust gas flow at the intake and the total flow of gases admitted into the engine ( air and recycled gases), which affects the level of NOx pollutants or fuel consumption. Poor control of the EGR flow rate can lead to undesired effects that can compromise the operation of the vehicle. drastic in terms of degraded reliability or non-compliance with regulatory pollution control standards.
La difficulté liée à l’estimation du débit d’EGR estdue au fait que l’on n’utilise pas de capteur de débit au niveau de la vanne EGR elle-même, ce qui serait coûteux et peu précis. A la place d’un tel débitmètre,on emploie un capteurde pression différentielle quimesure l’écartentre la pression en avaleten amontde la vanne.On estime le débit qui passe par la vanne sur la base d’un modèle qui utilise la pression différentielle mesurée et le niveau d’ouverture de la vanne. Même sice modèle peutfournir desrésultatstrèsprécis,l’information de pression différentielle a invariablement un caractère perturbé et très dynamique car présentantdes oscillations à haute fréquence,difficiles à suivre à l’aide d’unitésde contrôle électronique dontlescapacitésde calculsontlimitées. Ainsi, il n’ est pas envisageable en pratique de faire des calculs avec les informations du capteur de pression différentielle capturéesàhautefréquence,soitavecune périodicitéde 1milliseconde. The difficulty in estimating the EGR flow is due to the fact that a flow sensor is not used at the EGR valve itself, which would be expensive and inaccurate. Instead of such a flowmeter, a differential pressure sensor is employed which measures the difference between the pressure downstream and upstream of the valve. The flow rate passing through the valve is estimated based on a model which uses the measured differential pressure and the opening level of the valve. Even if this model can provide very precise results, the differential pressure information invariably has a disturbed and very dynamic character because it presents high frequency oscillations, which are difficult to follow using electronic control units with limited calculation capacities. Thus, it is not possible in practice to make calculations with the information from the differential pressure sensor captured at high frequency, i.e. with a periodicity of 1 millisecond.
L’invention consiste à développerun procédé de calculà basse fréquence de l’estimation d’un débit d’EGR,soit avec une périodicité d’environ 20 millisecondes,touten conservantun niveau de précision équivalentà un calculen haute fréquence. Ilexiste, dansl’étatde la technique,différentes méthodes pour l’estimation d’un débitd’EGR. The invention consists in developing a low-frequency calculation method for estimating an EGR flow rate, ie with a periodicity of about 20 milliseconds, while maintaining a level of precision equivalent to a high-frequency calculation. There are, in the state of the art, various methods for estimating an EGR flow rate.
La première méthode consiste à réaliserun modèle de débit total desgaz d’admission du moteur,d’une part,età déterminerle seuldébit d’air,d’autre part. Pour cela, le débittotalpeutêtre déterminé parun modèle de remplissage,à partirde la pression etde la température dans le collecteur d’admission du moteur,et d’une valeur de rendement de remplissage qui est elle-même fonction d’un ensemble de paramètres comprenant au moins le régime, la pression dans le collecteur d’admission,etéventuellement d’autres paramètres comme la position de calage des soupapes d’admission et d’échappement.Le débit d’air frais est quant à lui déterminé par un débitmètre.Le débit d’EGR est alorségalau débittotaldesgaz d’admission auquelon soustraitle débit d’airfrais.Cette approche estdécrite notammentdans le documentUS 2016/0069285,ou dansle documentFR 2938016. The first method consists in making a model of the total flow of the engine intake gases, on the one hand, and in determining the only air flow, on the other hand. For this, the total flow can be determined by a filling model, from the pressure and the temperature in the engine intake manifold, and from a filling efficiency value which is itself a function of a set of parameters comprising at least minus the speed, the pressure in the intake manifold, and possibly other parameters such as the timing position of the intake and exhaust valves. The fresh air flow is determined by a flow meter. of EGR is then equal to the total inlet gas flow from which the fresh air flow is subtracted. This approach is described in particular in document US 2016/0069285, or in document FR 2938016.
Ces approches sont simples, mais comportent plusieurs désavantages. These approaches are simple, but have several disadvantages.
Par exemple, pour les moteurs qui disposent de deux circuits EGR, notamment un circuitEGR à basse pression etun circuitEGR à haute pression, elles ne permettent pas de distinguer entre les taux d’EGR à basse ou à haute pression. , seul le taux d’EGR global pouvant être estimé à l’aide de cette méthode. For example, for engines that have two EGR circuits, namely a low pressure EGR circuit and a high pressure EGR circuit, they cannot distinguish between low pressure and high pressure EGR rates. , only the overall EGR rate can be estimated using this method.
Ensuite,l’estimation repose sur la connaissance du débit total des gaz d’admission, qui est classiquement un modèle de pompe volumétrique, et du débit d’air frais, qui est directement mesuré par capteur.La précision disponible de ces informations est d’environ +/- 5% pourla mesure parcapteuretd’environ +/-3% pourle débittotal,ce quipeutgénérerdesrésultatsincohérentsnotammentsurlesvaleursde faiblesdébitd’EGR etlesvaleursen régime transitoire. Then, the estimate is based on knowing the total intake gas flow, which is conventionally a volumetric pump model, and the fresh air flow, which is directly measured by the sensor. The available accuracy of this information is d 'approximately +/- 5% for the sensor measurement and approximately +/- 3% for the total flow, which may generate inconsistent results, particularly on low EGR flow values and values in transient state.
Une deuxième méthode consiste à utiliserun modèle de section efficacedevanne,quiutilisegénéralementl’équation deBarréde Saint- Venantou « Throttle Equation » en équivalentanglo-saxon. L’ équation donne des résultatstrès précis,sil’on maîtrise la position de la vanne etla différence de pression quiexiste à sesbornes. En revanche, elle est extrêmement sensible aux valeurs de pression aux bornes de la vanne et de position angulaire de la vanne, lorsque la différence de pression est faible ou lorsque la vanne est proche de sa fermeture. A second method consists in using a valve cross-section model, which generally uses the Barré de Saint-Venant equation or the “Throttle Equation” in Anglo-Saxon equivalent. The equation gives very precise results, if one controls the position of the valve and the pressure difference which exists at its terminals. On the other hand, it is extremely sensitive to the pressure values at the valve terminals and to the angular position of the valve, when the pressure difference is low or when the valve is close to closing.
Afin d’ améliorer sa précision, il est courant d’ aj outer des termes correctifs prenant en compte les dispersions, voire de lui préférer la première méthode citée précédemment sur les points de fonctionnement problématiques. Cette méthode de section efficace est utilisée par exemple dans le document EP 1 416 138 avec l ’ajouo d’une cartographie de correction prenant en compte la pression amont, la pression aval et la section efficace de la vanne, ou dans le document EP 3 434 888, avec l ’ aj out d’une cartographie dynamique de correction en fonction des positions de la vanne. In order to improve its accuracy, it is common to add corrective terms taking into account the dispersions, or even to prefer the first method cited above on the problematic operating points. This cross section method is used for example in the document EP 1 416 138 with the addition of a correction map taking into account the upstream pressure, the downstream pressure and the cross section of the valve, or in the document EP 3 434 888, with the addition of a dynamic correction map depending on the positions of the valve.
La méthode de section efficace a le désavantage d’ être fortement non-linéaire dans les positions très fermées ou très ouvertes de la vanne. D’ autre part, les variations de pression sont des phénomènes dynamiques très rapides, de l ’ ordre de la milliseconde, que l ’ on filtre généralement pour une utilisation dans la gestion du système EGR, dont l ’ ordre de grandeur de la constante de temps est aux alentours de 10 à 20 millisecondes. Toutefois, étant donné le caractère fortement non linéaire de l ’ équation sur certaines positions, on introduit des erreurs importantes en utilisant des valeurs de pression filtrées. The cross section method has the disadvantage of being strongly non-linear in the very closed or very open positions of the valve. On the other hand, the pressure variations are very fast dynamic phenomena, of the order of a millisecond, which are generally filtered for use in the management of the EGR system, whose order of magnitude of the constant of time is around 10 to 20 milliseconds. However, given the strongly nonlinear character of the equation on certain positions, significant errors are introduced by using filtered pressure values.
Exposé de l’ invention Disclosure of the invention
Au vu de ce qui précède, le but de l ’ invention est d’ améliorer la précision de l ’ estimation d’un débit d’EGR, notamment pour une utilisation dans la gestion du système EGR à basse fréquence. In view of the foregoing, the object of the invention is to improve the accuracy of the estimation of an EGR flow rate, in particular for use in the management of the low-frequency EGR system.
L’invention a pour obj et un procédé de calcul du débit de recirculation des gaz d’ échappement à l ’ admission d’un moteur à combustion interne permettant le contrôle dudit moteur. The object of the invention is a method for calculating the flow rate of recirculation of exhaust gases at the intake of an internal combustion engine allowing the control of said engine.
Selon le procédé : According to the process:
- On mesure les valeurs minimale Π min et maximale Π max d’un taux de détente Π , défini comme le rapport entre la pression mesurée en amont et la pression mesurée en aval de la vanne de recirculation des gaz d’ échappement, - The minimum Π min and maximum Π max values of an expansion rate Π are measured, defined as the ratio between the pressure measured in upstream and the pressure measured downstream of the exhaust gas recirculation valve,
- On mesure la valeur moyenne du taux de détente Πmoy,- We measure the average value of the rate of expansion Πmoy,
- On calcule la fonction de Barré de Saint-Venant appliquée à la valeur moyenne du taux de détente Πmoy, - On calcule la dérivée seconde de la fonction de Barré de Saint-Venant appliquée à la valeur moyenne du taux de détente Πmoy, , - On calcule le débit de recirculation des gaz d’ échappement.- Calculate the Barré de Saint-Venant function applied to the average value of the expansion rate Πmoy, - Calculate the second derivative of the Barré de Saint-Venant function applied to the average value of the expansion rate Πmoy, , - The exhaust gas recirculation rate is calculated.
Le procédé de calcul du débit d’EGR permet ainsi de calculer de manière précise le débit d’EGR en utilisant la fonction de Barré de Saint-Venant et la dérivée seconde de cette fonction, appliquées à la valeur moyenne du taux de détente Πmoy . The method for calculating the EGR flow rate thus makes it possible to calculate the EGR flow rate precisely using the Barré de Saint-Venant function and the second derivative of this function, applied to the average value of the expansion rate Πmoy .
Avantageusement, la dérivée seconde de la fonction de Barré de Saint-Venant appliquée à la valeur moyenne du taux de détente Πmoy est calculée à l ’ aide de trois termes obtenus en appliquant la fonction de Barré de Saint-Venant aux valeurs enveloppes Π min et Π max et à la valeur moyenne Πmoy. Advantageously, the second derivative of the Barré de Saint-Venant function applied to the average value of the expansion rate Πmoy is calculated using three terms obtained by applying the Barré de Saint-Venant function to the envelope values Π min and Π max and the average value Πavg.
Avantageusement, le débit de recirculation des gaz d’ échappement est calculé en faisant la somme d’un premier terme directement proportionnel à la fonction de Barré de Saint-Venant appliquée à la valeur moyenne du taux de détente Πmoy, et d’un second terme directement proportionnel à la dérivée seconde de la fonction de Barré de Saint-Venant appliquée à la valeur moyenne du taux de détente Πmoy . Advantageously, the exhaust gas recirculation rate is calculated by summing a first term directly proportional to the Barré de Saint-Venant function applied to the average value of the expansion rate Πmoy, and a second term directly proportional to the second derivative of the Barré de Saint-Venant function applied to the mean value of the rate of expansion Πmoy .
Par exemple, on peut mesurer à haute fréquence les valeurs minimale Π min et maximale Π max. For example, the minimum Π min and maximum Π max values can be measured at high frequency.
Par exemple, on peut mesurer à basse fréquence les valeurs minimale Π min et maximale Π max. For example, the minimum Π min and maximum Π max values can be measured at low frequency.
Par exemple, on peut mesurer à basse fréquence la valeur moyenne Πmoy. For example, the mean value Πmoy can be measured at low frequency.
Avantageusement, le moteur à combustion interne est équipé d’ au moins un circuit de recirculation partielle à haute pression des gaz d’ échappement et d’ au moins un circuit de recirculation partielle à basse pression des gaz d’ échappement. L’invention a également pour obj et un système de calcul du débit de recirculation des gaz d’ échappement à l ’ admission d’un moteur à combustion interne permettant le contrôle dudit moteur. Advantageously, the internal combustion engine is equipped with at least one high pressure partial recirculation circuit of the exhaust gases and at least one partial low pressure recirculation circuit of the exhaust gases. Another object of the invention is a system for calculating the flow rate of exhaust gas recirculation at the inlet of an internal combustion engine allowing the control of said engine.
Le système de calcul du débit comprend des moyens de mesure des valeurs minimale Π min et maximale Π max d’un taux de détente Π , défini comme le rapport entre la pression mesurée en amont et la pression mesurée en aval de la vanne de recirculation des gaz d’ échappement, des moyens de mesure de la valeur moyenne du taux de détente Π moy, des moyens de calcul de la fonction de Barré de Saint- Venant appliquée à la valeur moyenne du taux de détente Πmoy,, des moyens de calcul de la dérivée seconde de la fonction de Barré de Saint- Venant appliquée à la valeur moyenne du taux de détente Πmoy, , et des moyens de calcul du débit de recirculation des gaz d’ échappement. The flow rate calculation system comprises means for measuring the minimum Π min and maximum Π max values of an expansion rate Π , defined as the ratio between the pressure measured upstream and the pressure measured downstream of the recirculation valve of the exhaust gas, means for measuring the average value of the expansion rate Π avg, means for calculating the Barré de Saint-Venant function applied to the average value of the expansion rate Π avg, means for calculating the the second derivative of the Barré de Saint-Venant function applied to the mean value of the rate of expansion Πmoy, , and of the means for calculating the flow rate of recirculation of the exhaust gases.
Brève description des dessins Brief description of the drawings
D’ autres buts, caractéristiques et avantages de l ’ invention apparaîtront à lecture de la description suivante, donnée uniquement à titre d’ exemple non limitatif, et faite en référence aux dessins annexés sur lesquels : Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:
[Fig 1 ] illustre, de manière schématique, la structure d’un moteur à combustion interne d’un véhicule automobile équipé d’un circuit de recirculation partielle à haute pression des gaz d’ échappement, d’un circuit de recirculation partielle à basse pression des gaz d’ échappement et d’un système de calcul du débit d’EGR selon l ’ invention ; [Fig 1] schematically illustrates the structure of an internal combustion engine of a motor vehicle equipped with a high pressure partial recirculation circuit of the exhaust gases, a partial low pressure recirculation circuit exhaust gas pressure and an EGR flow calculation system according to the invention;
[Fig 2] illustre un diagramme de flux du procédé de calcul du débit d’EGR, mis en œuvre par le système de calcul, selon un mode de mise en œuvre de l ’ invention ; [Fig 2] illustrates a flowchart of the method for calculating the EGR flow rate, implemented by the calculation system, according to one mode of implementation of the invention;
[Fig 3 ] illustre de manière schématique, les informations accessibles au niveau des vannes EGR. [Fig 3] schematically illustrates the information accessible at the EGR valves.
[Fig 4] est un logigramme utili sé pour l ’ estimation classique du débit d’EGR. [Fig 5] est un logigramme utilisé dans l ’ invention pour l ’ estimation du débit d’EGR. [Fig 4] is a flowchart used for the classic estimation of the EGR flow rate. [Fig 5] is a flowchart used in the invention for estimating the EGR flow rate.
Exposé détaillé d’au moins un mode de réalisation Detailed description of at least one embodiment
Dans l ’ exemple illustré dans la figure 1 , le moteur à combustion interne 10 comprend, de manière non limitative, quatre cylindres 12 en ligne, un collecteur d’ admission d’ air frais 14, un collecteur d’ échappement 16, un système de turbo-compression 18, un circuit de recirculation partielle à haute pression des gaz d’ échappement (« circuit EGR à haute pression ») et un circuit de recirculation partielle à basse pression des gaz d’ échappement (« circuit EGR à basse pression »). In the example illustrated in Figure 1, the internal combustion engine 10 comprises, in a non-limiting manner, four cylinders 12 in line, a fresh air intake manifold 14, an exhaust manifold 16, a turbo-compression 18, a high pressure partial exhaust gas recirculation circuit (“high pressure EGR circuit”) and a low pressure partial exhaust gas recirculation circuit (“low pressure EGR circuit”) .
Les cylindres 12 sont alimentés en air par l ’ intermédiaire du collecteur d’ admission 14, ou répartiteur d’ admission, lui-même alimenté par une conduite 20 pourvue d’un filtre à air 22 et du compresseur 18b du turbocompresseur 18 du moteur 10. The cylinders 12 are supplied with air via the intake manifold 14, or intake distributor, itself supplied by a pipe 20 provided with an air filter 22 and the compressor 18b of the turbocharger 18 of the engine 10 .
Le turbocompresseur 18 comporte essentiellement une turbine 18a entraînée par les gaz d’ échappement et un compresseur 18b monté sur le même arbre que la turbine 18a et assurant une compression de l ’ air distribué par le filtre à air 22, dans le but d’ augmenter la quantité (débit massique) d’ air admise dans les cylindres 12 du moteur 10. The turbocharger 18 essentially comprises a turbine 18a driven by the exhaust gases and a compressor 18b mounted on the same shaft as the turbine 18a and providing compression of the air distributed by the air filter 22, with the aim of increasing the quantity (mass flow) of air admitted into the cylinders 12 of the engine 10.
Un échangeur thermique 24 est placé après la sortie du compresseur 18b équipant la conduite d’ alimentation 14a du collecteur d’ admi ssion 14 en air frais. A heat exchanger 24 is placed after the outlet of the compressor 18b equipping the supply line 14a of the intake manifold 14 with fresh air.
Le moteur à combustion interne 10 comprend un circuit d’ admission Ca et un circuit d’ échappement Ce. The internal combustion engine 10 comprises an intake circuit Ca and an exhaust circuit Ce.
Le circuit d’ admission Ca comprend, d’ amont en aval dans le sens de circulation de l ’ air : The intake circuit Ca comprises, from upstream to downstream in the direction of air circulation:
- le filtre à air 22 ou boîte à air ; - the air filter 22 or air box;
- un débitmètre 26 disposé dans la conduite d’ admission 20 en aval du filtre à air 22 pour mesurer la valeur réelle du débit d’ air entrant dans le moteur 10 ; - A flowmeter 26 disposed in the intake duct 20 downstream of the air filter 22 to measure the actual value of the air flow entering the engine 10;
- une vanne d’ admission d’ air 28 ; - an air inlet valve 28;
- le compresseur 18b du turbocompresseur 18; - un boîtier papillon 30 ou une vanne d’ admission des gaz dans le moteur ; - the compressor 18b of the turbocharger 18; - A butterfly housing 30 or a gas inlet valve in the engine;
- un échangeur thermique 32 pour refroidir les gaz d’ admi ssion correspondant à un mélange d’ air frais et de gaz d’ échappement recirculés après leur compression dans le compresseur 18b ; et - A heat exchanger 32 for cooling the admission gases corresponding to a mixture of fresh air and recirculated exhaust gases after their compression in the compressor 18b; And
- le collecteur d’ admission 14. - the intake manifold 14.
Le compresseur est associé à un circuit de contournement avec une vanne de décharge à l ’ admission 55 qui s’ ouvre en cas de fermeture brutale du boîtier papillon 30, pour éviter que l ’ air comprimé, se trouvant entre le compresseur 18b et le boîtier papillon 30, ne traverse le compresseur 18b et ne le dégrade, lorsque par exemple, le conducteur du véhicule lève brutalement le pied de la pédale d’ accélération. The compressor is associated with a bypass circuit with an intake relief valve 55 which opens in the event of sudden closure of the throttle body 30, to prevent the compressed air, located between the compressor 18b and the housing butterfly 30, does not cross the compressor 18b and does not degrade it, when for example, the driver of the vehicle suddenly lifts his foot from the accelerator pedal.
Le circuit d’ échappement Ce comprend, d’ amont en aval dans le sens de circulation des gaz brûlés : The exhaust circuit Ce comprises, from upstream to downstream in the direction of circulation of the burnt gases:
- le collecteur d’ échappement 16 ; - the exhaust manifold 16;
- la turbine 18a du turbocompresseur 18 ; et - The turbine 18a of the turbocharger 18; And
- un système 40 de dépollution des gaz de combustion du moteur.- A system 40 for depolluting the engine combustion gases.
En ce qui concerne le collecteur d’ échappement 16, celui-ci récupère les gaz d’ échappement issus de la combustion et évacue ces derniers vers l ’ extérieur, par l ’ intermédiaire d’un conduit d’ échappement des gaz 34 débouchant sur la turbine 18a du turbocompresseur 18 et par une ligne d’ échappement 36 montée en aval de ladite turbine 18a. As regards the exhaust manifold 16, the latter collects the exhaust gases resulting from combustion and evacuates them to the outside, via a gas exhaust duct 34 leading to the turbine 18a of the turbocharger 18 and by an exhaust line 36 mounted downstream of said turbine 18a.
Le moteur 10 comprend ici deux circuits de recirculation partielle des gaz d’ échappement à l ’ admission, dit circuits « EGR » (« exhaust gas recirculation » en termes anglo-saxons), à savoir un circuit EGR à haute pression 15 et un circuit EGR à basse pression 38. The engine 10 here comprises two partial exhaust gas recirculation circuits at the intake, called “EGR” circuits (“exhaust gas recirculation” in Anglo-Saxon terms), namely a high-pressure EGR circuit 15 and a circuit Low pressure EGR 38.
Le circuit 38, ici un circuit de recirculation des gaz d’ échappement à basse pression, dit « EGR BP », prend naissance en un point de la ligne d’ échappement 36, en aval de ladite turbine 18a, et notamment en aval du système 40 de dépollution des gaz et renvoie les gaz d’ échappement en un point de la conduite 20 d’ alimentation en air frais, en amont du compresseur 18b du turbocompresseur 18, notamment en aval du débitmètre 26. Le débitmètre 26 ne mesure que le débit d’ air frais seul . Circuit 38, here a low-pressure exhaust gas recirculation circuit, called “EGR BP”, originates at a point on exhaust line 36, downstream of said turbine 18a, and in particular downstream of the system. 40 for gas pollution control and returns the exhaust gases to a point in the fresh air supply pipe 20, upstream of the compressor 18b of the turbocharger 18, in particular downstream of the flowmeter 26. The flowmeter 26 only measures the flow of fresh air alone.
Tel qu’ illustré, ce circuit 38 de recirculation comprend, dans le sens de circulation des gaz recyclés, un refroidisseur 38a, un filtre 38b, et une vanne 38c destinée à réguler le débit des gaz d’ échappement à basse pression. La vanne 38c est disposée en aval du refroidisseur 38a et en amont du compresseur 18b . As illustrated, this recirculation circuit 38 comprises, in the direction of circulation of the recycled gases, a cooler 38a, a filter 38b, and a valve 38c intended to regulate the flow of low-pressure exhaust gases. The valve 38c is arranged downstream of the cooler 38a and upstream of the compressor 18b.
On notera que la vanne d’ admission d’ air 28 peut aussi servir à forcer la circulation d’un débit des gaz d’ échappement à basse pression dans le circuit EGR BP dans le cas où la dépression entre le circuit d’ échappement et le circuit d’ admission serait insuffisante. Dans ce cas, une fermeture de la vanne 28 permet de créer une dépression à son aval, apte à aspirer des gaz du circuit EGR BP. It will be noted that the air intake valve 28 can also be used to force the circulation of a low pressure exhaust gas flow in the EGR circuit BP in the case where the depression between the exhaust circuit and the intake circuit would be insufficient. In this case, closing the valve 28 makes it possible to create a depression downstream thereof, able to suck in gases from the EGR circuit BP.
Le circuit EGR haute pression 15, dit « EGR HP », prend naissance en un point du circuit d’ échappement Ce, en amont de ladite turbine 18a et renvoie les gaz d’ échappement en un point du circuit d’admisssion Ca, en aval de l ’ échangeur thermique 32. The high pressure EGR circuit 15, called "EGR HP", originates at a point in the exhaust circuit Ce, upstream of said turbine 18a and returns the exhaust gases to a point in the admission circuit Ca, downstream of the heat exchanger 32.
Tel qu’ illustré, ce circuit 15 de recirculation comprend une vanne 15 a configurée pour réguler le débit des gaz d’ échappement à haute pression. As illustrated, this recirculation circuit 15 includes a valve 15a configured to regulate the flow of high pressure exhaust gases.
Le moteur est associé à un circuit de carburant comprenant, par exemple, des inj ecteurs de carburant (non référencés) inj ectant de l ’ essence directement dans chaque cylindre à partir d’un réservoir à carburant (non représenté). The engine is associated with a fuel circuit comprising, for example, fuel inj ectors (not referenced) injecting gasoline directly into each cylinder from a fuel tank (not shown).
Le moteur comprend une unité électronique de commande 70 configurée pour commander les différents éléments du moteur à combustion interne à partir de données recueillies par des capteurs à différents endroits du moteur. The engine comprises an electronic control unit 70 configured to control the various elements of the internal combustion engine from data collected by sensors at various locations of the engine.
L’unité électronique de commande 70 comporte un module de calcul 72, un module de mesure 73 et un module de commande 74. The electronic control unit 70 comprises a calculation module 72, a measurement module 73 and a control module 74.
Tel qu’ illustré dans la figure 3 , plusieurs informations sont accessibles au niveau des vannes EGR 15a et 38c. As illustrated in figure 3 , several pieces of information are accessible at the level of the EGR valves 15a and 38c.
Par exemple, la pression des gaz en aval de la vanne EGR appelée Paval est mesurée à l’ aide d’un capteur de pression relative. La pression différentielle ΔP est mesurée grâce à un capteur de pression différentielle. L’angle d’ouverture de la vanne Oegr est mesuré à l’aide d’un capteur de position placée sur le moteur électrique qui entraine la vanne. For example, the gas pressure downstream of the EGR valve called Paval is measured using a relative pressure sensor. Pressure differential ΔP is measured using a differential pressure sensor. The opening angle of the Oegr valve is measured using a position sensor placed on the electric motor which drives the valve.
Il est généralement admis que le débit traversant la vanne Qegr peut être décrit suivant l’équation suivante :
Figure imgf000011_0001
It is generally accepted that the flow through the Q egr valve can be described according to the following equation:
Figure imgf000011_0001
Avec : With :
Qegr, débit massique, en kg/s Q egr , mass flow, in kg/s
Se, la section efficace de la vanne, en mm2 S e , the effective section of the valve, in mm 2
BSV, la fonction de Barré de Saint-Venant calculée selon l 'équation (2), ci-après et exprimée en
Figure imgf000011_0002
BSV, the Barré de Saint-Venant function calculated according to equation (2), below and expressed as
Figure imgf000011_0002
Tamont, la température à l’amont de la vanne, en K Pamont, la pression en amont de la vanne, exprimée en Pa. Tamont, the temperature upstream of the valve, in K Pamont, the pressure upstream of the valve, expressed in Pa.
La fonction de Barré de Saint-Venant s’exprime lorsque l’écoulement est non sonique, soit pour l’intégralité des calculs qui nous intéressent, par l’expression suivante :
Figure imgf000011_0003
The Barré de Saint-Venant function is expressed when the flow is non-sonic, i.e. for all the calculations that interest us, by the following expression:
Figure imgf000011_0003
Avec : With :
Π , le taux de détente soit le rapport entre Pamont et Pavai, adimensionnel γ, l’indice adiabatique des gaz, adimensionnel r, le rapport entre la constante des gaz parfait divisée par la masse molaire du gaz en question, exprimée en J ·kg-1 ·K-1 Π, the rate of expansion, i.e. the ratio between Pamont and Pavai, dimensionless γ, the adiabatic index of gases, dimensionless r, the ratio between the perfect gas constant divided by the molar mass of the gas in question, expressed in J kg -1 K -1
En multipliant de chaque côté l’équation (1) par Π , on obtient l’équation suivante :
Figure imgf000011_0004
By multiplying equation (1) on each side by Π , we obtain the following equation:
Figure imgf000011_0004
Figure imgf000012_0001
Figure imgf000012_0001
Comme indiqué précédemment, les informations de pression sont extrêmement dynamiques du fait de l ’ acyclisme du comportement d’un moteur à combustion interne. Cet acyclisme crée de fortes volatilités du signal de pression différentielle et par cela implique des variations fortes sur le taux de détente Π . As stated earlier, pressure information is extremely dynamic due to the acyclic behavior of an internal combustion engine. This acyclism creates strong volatilities of the differential pressure signal and by that implies strong variations on the rate of expansion Π.
Afin de limiter le bruit sur le débit total, il est nécessaire de filtrer cette information. Or, filtrer l ’ information de pression a un impact direct sur la précision du débit recalculé par l ’ équation ( 1 ) ou (3). En effet, ces équations utilisent la fonction de Barré de Saint- Venant (B SV) qui est non linéaire. In order to limit the noise on the total bit rate, it is necessary to filter this information. However, filtering the pressure information has a direct impact on the accuracy of the flow rate recalculated by equation (1) or (3). Indeed, these equations use the Barré de Saint-Venant (B SV) function which is non-linear.
Il n’ est donc pas équivalent de calculer la moyenne de la fonction sur toutes les pressions rencontrées, ce qui correspond à une véritable moyenne du débit, que de calculer la moyenne des pressions et de lui appliquer la fonction de Barré de Saint-Venant. L’ écart entre ces deux calculs peut être assez important, parfois supérieur à 20% selon certains calculs, ce qui risque d’ entraîner une surestimation du débit interprété par le reste du contrôle moteur. It is therefore not equivalent to calculate the average of the function on all the pressures encountered, which corresponds to a real average of the flow, than to calculate the average of the pressures and to apply the Barré de Saint-Venant function to it. The difference between these two calculations can be quite significant, sometimes greater than 20% according to certain calculations, which risks leading to an overestimation of the flow rate interpreted by the rest of the motor control.
Il est ainsi proposé de se rapprocher au maximum de la valeur réelle du débit d’EGR tout en effectuant l ’ ensemble des calculs à plus basse fréquence, soit toutes les 10 millisecondes par exemple. It is thus proposed to get as close as possible to the actual value of the EGR flow rate while performing all the calculations at the lowest frequency, i.e. every 10 milliseconds for example.
Pour y parvenir, les variations du taux de détente Π présenté plus haut sont assimilées à une sinusoïde qui s’ aj oute à un signal moyen variable en fonction du temps, la sinusoïde ayant une amplitude inconnue A et une pulsation inconnue ω comme décrit dans l ’ équation suivante :
Figure imgf000012_0002
To achieve this, the variations in the rate of expansion Π presented above are assimilated to a sinusoid which is added to a mean signal varying as a function of time, the sinusoid having an unknown amplitude A and an unknown pulsation ω as described in l following equation:
Figure imgf000012_0002
Pour calculer le débit EGR à partir de l ’ équation (3), il est nécessaire d’ estimer correctement la fonction BSV2 (Π(t)) suivante : To calculate the EGR flow from equation (3), it is necessary to correctly estimate the following BSV 2 (Π(t)) function:
BSV2 (Π(t)) = BSV2 (Πmoy + Α .sin(ωt)) (6) A cette fin, on utilise les développements de Taylor sous leurs formes approchées à savoir :
Figure imgf000013_0001
BSV 2 (Π(t)) = BSV 2 (Π avg + Α .sin(ωt)) (6) To this end, we use the Taylor expansions in their approximate forms, namely:
Figure imgf000013_0001
Que l ’ on applique ici avec a = Πmoy et h = Α. sin(ωt). That we apply here with a = Π mean and h = Α. sin(ωt).
On obtient alors au deuxième ordre l ’ approximation suivante :
Figure imgf000013_0002
We then obtain at second order the following approximation:
Figure imgf000013_0002
La méthode classique d’ estimation, qui consiste, comme expliqué plus haut, d’ abord à filtrer ou moyenner le taux de détente et ensuite à appliquer la fonction de Barré de Saint-Venant conduirait au résultat sous la forme suivante :
Figure imgf000013_0003
The classic estimation method, which consists, as explained above, of first filtering or averaging the rate of expansion and then applying the Barré de Saint-Venant function would lead to the result in the following form:
Figure imgf000013_0003
Ce qui correspond uniquement au premier terme de l ’ approximation (8). Which corresponds only to the first term of the approximation (8).
La présente invention correspond à un procédé qui consiste à utiliser les termes suivants du développement de Taylor afin de compléter l ’ information disponible sans augmentation excessive de la charge de calcul . The present invention corresponds to a method which consists in using the following terms of the Taylor expansion in order to complete the information available without excessively increasing the computational load.
Pour calculer le débit moyen sur une période T donnée on intègre l ’ équation (3) sur cette période :
Figure imgf000013_0004
To calculate the average flow over a given period T, we integrate equation (3) over this period:
Figure imgf000013_0004
Si l ’ on considère que la période de calcul est assez courte, par exemple de l ’ ordre d’une oscillation de pression, on peut admettre que la position de la vanne θegr et Tamont est une constante. On peut également admettre que la pression Paval reste constante et que l ’ essentiel des oscillations se manifeste sur Pamont. If we consider that the calculation period is quite short, for example of the order of a pressure oscillation, we can assume that the position of the valve θ egr and T upstream is a constant. It can also be assumed that the pressure P downstream remains constant and that most of the oscillations occur on P upstream .
On peut poser :
Figure imgf000013_0005
We can ask:
Figure imgf000013_0005
Et réécrire l ’ équation ( 10) ainsi :
Figure imgf000013_0006
And rewrite equation (10) as:
Figure imgf000013_0006
En utilisant les équations ( 12) et (8) on obtient alors :
Figure imgf000014_0001
By using equations (12) and (8) we then obtain:
Figure imgf000014_0001
Que l ’ on peut réécrire comme :
Figure imgf000014_0002
Which can be rewritten as:
Figure imgf000014_0002
Sur une période T grande par rapport à la pulsation ω, on obtient
Figure imgf000014_0003
Over a period T large compared to the pulsation ω, we obtain
Figure imgf000014_0003
En choisissant un filtre avec une constante de temps adéquate on obtient alors :
Figure imgf000014_0005
By choosing a filter with an adequate time constant, we then obtain:
Figure imgf000014_0005
Pour calculer la valeur du débit moyen d’EGR il faut calculer la dérivée seconde de la fonction B SV2. To calculate the value of the average EGR flow, it is necessary to calculate the second derivative of the function B SV 2 .
A l ’ aide d’un schéma numérique de type différences centrées, on peut ensuite évaluer la dérivée seconde de la fonction B SV2 comme suit :
Figure imgf000014_0006
Using a numerical scheme of the centered differences type, we can then evaluate the second derivative of the function B SV 2 as follows:
Figure imgf000014_0006
On obtient alors l ’ expression du débit moyen d’EGR suivante :
Figure imgf000014_0004
We then obtain the following expression for the average EGR flow rate:
Figure imgf000014_0004
Cela revient à considérer l ’ estimation classique a BSV2 (Πmoy) à laquelle on raj oute un correctif lié aux estimations de débit maximum et de débit minimum. On remarque que le correctif est peu gourmand en ressources de calcul parce qu’ il consiste à effectuer des pondérations pour les trois informations suivantes seulement : ¼ pour le débit maximum, ½ pour le débit moyen et ¼ pour le débit minimal . This amounts to considering the conventional estimate a BSV 2 (Π moy ) to which a correction linked to the maximum bit rate and minimum bit rate estimates is added. It is noted that the corrective is not very greedy in calculation resources because it consists in carrying out weightings for the three following information items only: ¼ for the maximum bit rate, ½ for the average bit rate and ¼ for the minimum bit rate.
On peut remarquer également que toutes les dérivées impaires des fonctions sinus entraînent une moyenne de débit nulle car , pour tout k naturel. L’ expression ( 17) est ainsi une
Figure imgf000014_0007
approximation du troisième ordre, ce qui assure une précision acceptable même lorsque les écarts entre Πmin et Π max deviennent importants. We can also notice that all the odd derivatives of the sine functions lead to a zero throughput mean because , for all natural k. The expression (17) is thus a
Figure imgf000014_0007
third-order approximation, which ensures acceptable precision even when the differences between Π min and Π max become large.
La figure 4 illustre la procédure utili sée dans l ’ estimation classique, afin de mieux apprécier l ’ apport de l ’ invention dont la procédure est présentée à la figure 5. Classiquement, les informations du taux de détente sont captées à haute fréquence, soit toutes les millisecondes. On procède à un filtrage des informations en prenant la moyenne Πmoy à basse fréquence, soit toutes les 10 millisecondes. On applique ensuite la fonction B SV2 sur la valeur moyenne Πmoy et on multiplie par le coefficient α pour obtenir l ’ estimation du débit d’EGR. Figure 4 illustrates the procedure used in the conventional estimate, in order to better appreciate the contribution of the invention, the procedure of which is presented in Figure 5. Conventionally, the information of the expansion rate is captured at high frequency, either every millisecond. The information is filtered by taking the mean Π moy at low frequency, ie every 10 milliseconds. The function B SV2 is then applied to the mean value Π moy and the coefficient α is multiplied to obtain the estimate of the EGR flow rate.
En référence à la figure 5, les informations sont captées à haute fréquence, soit toutes les millisecondes. On récupère ensuite les valeurs maximale Πmax, minimale Πmin et moyenne Πmoy à basse fréquence, soit toutes les 10 millisecondes. On applique ensuite la fonction B SV2 sur ces trois valeurs maximale Π max , minimale Πmin et moyenne Πmoy avec une pondération de ¼ pour la valeur maximale, ½ pour la valeur moyenne et ¼ pour la valeur minimale et l ’ on effectue une multiplication par le coefficient α pour obtenir l ’ estimation du débit d’EGR. Referring to Figure 5, the information is captured at high frequency, ie every millisecond. The maximum Π max , minimum Π min and average Π average values at low frequency, ie every 10 milliseconds, are then recovered. The function B SV2 is then applied to these three maximum values Π max , minimum Π min and mean Π moy with a weighting of ¼ for the maximum value, ½ for the mean value and ¼ for the minimum value and a multiplication is carried out by the coefficient α to obtain the estimate of the EGR flow rate.
L’ organigramme représenté dans la figure 2, illustre le procédé de calcul du débit d’EGR, mis en œuvre par le système de calcul 70. The flowchart represented in FIG. 2 illustrates the method for calculating the EGR flow rate, implemented by the calculation system 70.
Lors d’une première étape 61 on mesure les valeurs maximales et minimales du taux de détente pui s, lors de l ’ étape 62 suivante, on mesure la valeur moyenne du taux de détente. During a first step 61, the maximum and minimum values of the rate of expansion are measured, then, during the following step 62, the average value of the rate of expansion is measured.
Le procédé 60 comprend en outre une étape 63 calcul de la fonction B SV2 appliquée au taux de détente moyen, selon les équations (2) et (4), et une étape 64 de calcul de la dérivée seconde de la fonction B SV2 appliquée au taux de détente moyen, selon l ’ équation ( 16). The method 60 further comprises a step 63 for calculating the function B SV2 applied to the average expansion rate, according to equations (2) and (4), and a step 64 for calculating the second derivative of the function B SV2 applied to the mean expansion rate, according to equation (16).
Le procédé 60 se poursuit par une étape 65 de calcul du débit moyen, selon l ’ équation ( 17). The method 60 continues with a step 65 of calculating the average flow, according to equation (17).
Le procédé 60 comprend enfin une étape 66 de contrôle moteur, à travers une consigne de débit EGR Q. Ainsi l ’ invention propose un procédé d’ estimation du débit d’EGR utilisée pour le contrôle moteur, peu gourmand en ressources de calcul et qui peut utiliser les valeurs de pression filtrées à basse fréquence, avec une précision suffisante des résultats. The method 60 finally comprises a step 66 of engine control, through an EGR flow setpoint Q. Thus, the invention proposes a method for estimating the flow of EGR used for engine control, requiring little computing resources and which can use the pressure values filtered at low frequency, with sufficient accuracy of the results.

Claims

REVENDICATIONS
1. Procédé de calcul du débit de recirculation des gaz d’ échappement à l ’ admission d’un moteur à combustion interne ( 10) permettant le contrôle dudit moteur ( 10), caractérisé en ce que : a) On mesure les valeurs minimale ( Πmin) et maximale ( Πmax) d’un taux de détente Π , défini comme le rapport entre la pression mesurée en amont et la pression mesurée en aval de la vanne de recirculation des gaz d’ échappement ( 15a et/ou 38c), b) On mesure la valeur moyenne du taux de détente ( Πmoy), c) On calcule la fonction de Barré de Saint-Venant appliquée à la valeur moyenne du taux de détente ( Πmoy), d) On calcule la dérivée seconde de la fonction de Barré de Saint-Venant appliquée à la valeur moyenne du taux de détente ( Πmoy), e) On calcule le débit de recirculation des gaz d’ échappement (Q) 1. Method for calculating the flow rate of recirculation of exhaust gases at the intake of an internal combustion engine (10) allowing the control of said engine (10), characterized in that: a) the minimum values ( Πmin) and maximum (Πmax) of an expansion rate Π, defined as the ratio between the pressure measured upstream and the pressure measured downstream of the exhaust gas recirculation valve (15a and/or 38c), b ) We measure the average value of the rate of expansion (Πmoy), c) We calculate the Barré de Saint-Venant function applied to the average value of the rate of expansion (Πmoy), d) We calculate the second derivative of the function of Barré de Saint-Venant applied to the average value of the expansion rate (Πmoy), e) The exhaust gas recirculation flow rate (Q) is calculated
2. Procédé selon la revendication 1 , dans lequel la dérivée seconde de la fonction de Barré de Saint-Venant appliquée à la valeur moyenne du taux de détente ( Πmoy) est calculée à l ’ aide de trois termes obtenus en appliquant la fonction de Barré de Saint-Venant aux valeurs enveloppes ( Πmin) et ( Πmax) et à la valeur moyenne ( Πmoy). 2. Method according to claim 1, in which the second derivative of the Barré de Saint-Venant function applied to the mean value of the rate of expansion (Πmoy) is calculated using three terms obtained by applying the Barré function of Saint-Venant to the envelope values ( Πmin) and ( Πmax) and to the mean value ( Πmoy).
3. Procédé selon la revendication 1 , dans lequel le débit de recirculation des gaz d’ échappement est calculé en faisant la somme d’un premier terme directement proportionnel à la fonction de Barré de Saint-Venant appliquée à la valeur moyenne du taux de détente ( Πmoy) et d’un second terme directement proportionnel à la dérivée seconde de la fonction de Barré de Saint-Venant appliquée à la valeur moyenne du taux de détente ( Πmoy). 3. Method according to claim 1, in which the exhaust gas recirculation flow rate is calculated by summing a first term directly proportional to the Barré de Saint-Venant function applied to the average value of the expansion rate. ( Πmoy) and a second term directly proportional to the second derivative of the Barré de Saint-Venant function applied to the mean value of the rate of expansion ( Πmoy).
4. Procédé selon l ’une quelconque des revendications 1 , 2 ou 3 , dans lequel on mesure à haute fréquence les valeurs minimale ( Πmin) et maximale ( Πmax). 4. Method according to any one of claims 1, 2 or 3, in which the minimum (Πmin) and maximum (Πmax) values are measured at high frequency.
5. Procédé selon l ’une quelconque des revendications 1 , 2 ou 3 , dans lequel on mesure à basse fréquence les valeurs minimale ( Πmin) et maximale ( Πmax). 5. Method according to any one of claims 1, 2 or 3, in which the minimum (Πmin) and maximum (Πmax) values are measured at low frequency.
6. Procédé selon l ’une quelconque des revendications 1 , 2 ou 3 , dans lequel on mesure à basse fréquence la valeur moyenne ( Πmoy). 6. Method according to any one of claims 1, 2 or 3, in which the mean value (Πmoy) is measured at low frequency.
7. Procédé selon l ’une quelconque des revendications précédentes, dans lequel le moteur à combustion interne ( 10) est équipé d’ au moins un circuit haute pression de recirculation des gaz d’ échappement ( 15) et d’ au moins un circuit basse pression de recirculation des gaz d’ échappement (38). 7. Method according to any one of the preceding claims, in which the internal combustion engine (10) is equipped with at least one high-pressure exhaust gas recirculation circuit (15) and at least one low-pressure circuit. exhaust gas recirculation pressure (38).
8. Système de calcul du débit de recirculation des gaz d’ échappement à l ’ admission d’un moteur à combustion interne ( 10) permettant le contrôle dudit moteur ( 10), caractérisé en ce qu’ il comporte des : a) Moyens de mesure des valeurs minimale ( Πmin) et maximale ( Πmax) d’un taux de détente Π , défini comme le rapport entre la pression mesurée en amont et la pression mesurée en aval de la vanne de recirculation des gaz d’ échappement ( 15a et/ou 38c), b) Moyens de mesure de la valeur moyenne du taux de détente ( Πmoy), c) Moyens de calcul de la fonction de Barré de Saint- Venant appliquée à la valeur moyenne du taux de détente ( Πmoy), d) Moyens de calcul de la dérivée seconde de la fonction de Barré de Saint-Venant appliquée à la valeur moyenne du taux de détente ( Πmoy), e) Moyens de calcul du débit de recirculation des gaz d’ échappement (Q) 8. System for calculating the flow rate of recirculation of exhaust gases at the intake of an internal combustion engine (10) allowing the control of said engine (10), characterized in that it comprises: a) Means of measurement of the minimum (Πmin) and maximum (Πmax) values of an expansion rate Π, defined as the ratio between the pressure measured upstream and the pressure measured downstream of the exhaust gas recirculation valve ( 15a and/ or 38c), b) Means for measuring the average value of the rate of expansion (Πmoy), c) Means for calculating the Barré de Saint-Venant function applied to the mean value of the rate of expansion (Πmoy), d) Means for calculating the second derivative of the Barré de Saint-Venant function applied to the average value of the expansion rate (Πmoy), e) Means for calculating the exhaust gas recirculation flow rate (Q)
PCT/EP2022/080646 2021-11-09 2022-11-03 Method for low-frequency estimation of a recirculated exhaust gas flow rate at the intake of an internal combustion engine WO2023083681A1 (en)

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EP1630387A1 (en) * 2004-06-24 2006-03-01 Renault s.a.s. Method for controlling the amount of recirculated exhaust gas in an internal combusiton engine of a vehicle
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Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1416138A2 (en) 2002-11-01 2004-05-06 Toyota Jidosha Kabushiki Kaisha EGR-gas flow rate estimation apparatus for internal combustion engine
EP1630387A1 (en) * 2004-06-24 2006-03-01 Renault s.a.s. Method for controlling the amount of recirculated exhaust gas in an internal combusiton engine of a vehicle
US8844505B2 (en) * 2008-07-22 2014-09-30 Valeo Systemes De Controle Moteur Method for managing the exhaust gas circulation circuit of a petrol thermal engine and corresponding recirculation system
FR2938016A1 (en) 2008-10-30 2010-05-07 Renault Sas DYNAMIC ESTIMATING METHOD OF FRESH AIR FLOW SUPPLYING MOTOR WITH HIGH AND LOW PRESSURE EGR CIRCUITS
FR2939475A1 (en) * 2008-12-09 2010-06-11 Renault Sas Method for anti-pollution treatment of exhaust gas from drive train of motor vehicle, involves deducing correction of aeraulic curve of exhaust gas recirculation valve based on difference between measured and estimated operating quantities
FR2979389A1 (en) * 2011-08-29 2013-03-01 Renault Sa SYSTEM AND METHOD FOR CONTROLLING AN EXHAUST GAS RECIRCULATION INTERNAL COMBUSTION ENGINE FOR A MOTOR VEHICLE IN TRANSIENT OPERATION
US20160069285A1 (en) 2014-09-10 2016-03-10 Mitsubishi Electric Corporation Internal combustion engine egr flow rate estimation apparatus and internal combustion engine control apparatus
EP3434888A1 (en) 2016-03-25 2019-01-30 Honda Motor Co., Ltd. Egr control device and egr control method for internal combustion engine

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