FR2953561A3 - Method for correcting measurement of air flow admitted in internal combustion engine of vehicle, involves determining correction function according to variation between treated value and estimated value of air flow admitted in engine - Google Patents

Abstract

The method involves carrying out treatment on a measurement signal of air flow admitted in an internal combustion engine. Recirculation of gases is completed. Another treatment on the measurement signal of air flow admitted in the internal combustion engine with a model based on closing of gases recirculation circuits is carried out. The air flow admitted in the engine is estimated. The correction function is determined according to the variation between the treated value and the estimated value of air flow admitted in the engine. An independent claim is also included for a system for correction of measurement of air flow admitted in an internal combustion engine, comprising gas recirculation circuits.

Description

B09 / 4134EN / GBO PJ-09-0299 / YK / CL Société par Actions Simplifiée known as: RENAULT sas Process and system for correcting a measurement of air flow admitted into an internal combustion engine Invention of: ROBERT Kevin Process and correction system for an air flow measurement admitted in an internal combustion engine

The present invention relates to a method and a system for correcting the drifts and dispersions of the measurement of the flow of fresh air entering an internal combustion engine equipped with a high pressure and low pressure recirculation circuit. The amount of nitrogen oxides produced by an engine, especially diesel, is strongly related to the composition of the reactive mixture in the engine cylinders air and fuel, and the presence of inert gases. The inert gases do not participate in the combustion, and come from one or more circuits deriving a portion of the exhaust gas to the air intake circuit of the combustion engine. Such a circuit thus allows the recirculation of gas (circuit called "EGR" for Exhaust Gas Recirculation). The recirculation of the gases is ensured by placing the exhaust circuit and the intake circuit in communication via a passage section the size of which is regulated by an EGR valve. There are two types of recirculation circuit: a high pressure circuit (HP EGR) and a low pressure circuit (EGR BP). The gas recirculation circuits in particular make it possible to reduce the emissions of nitrogen oxides (NOx) by controlling the oxygen content of the gases admitted to the engine, to reduce the hydrocarbon and carbon monoxide emissions by the checking the temperature of the gases admitted to the engine and checking the auto-ignition time of the fuel. On the other hand, the gases sucked by an engine, such as the injected fuel, can increase the amount of fumes emitted by the engine, if the quantities of EGR are not correctly regulated and controlled. However, the total amount of gas sucked by a motor is equal to the amount of fresh air admitted plus the amount of gas from each recirculation circuit.

The amount of recirculated gas is currently controlled by an electronic computer (ECU) depending in particular on the amount of fresh air admitted to the engine and the temperature of the collector. To measure this amount of fresh air, a flow meter is commonly used. Problems are generally encountered when using the flow meters because of the dispersions of measures inherent to their design and use, and present from their manufacture. Moreover this dispersion of the results can evolve over time in the form of a drift between real air flow and measured, in particular because of the aging and the fouling of the flowmeter. Similarly, the actual flow into the engine, or engine intake capacity, has a dispersion from manufacture. The control strategies of the engine operation must therefore not only take into account the measured flow rates but also the dispersions of these measured flow rates. To reduce the drift and dispersion of the admitted fresh air flow measurements, the solutions generally relate to the component itself via, for example, technological improvements or changes in manufacturing processes. For substantial gains, these solutions are often expensive. To circumvent these problems, systems and methods for controlling the operation of the engine have been developed so as to use calculation means to correct the dispersions of the measurement results.

In an internal combustion engine, the raw signals acquired by the flow meter are processed by an electronic control unit to condition the signals and filter them to provide reliable information for control strategies of the internal combustion engine.

An air flow measurement by a flow meter is based on a measurement of the local air speed multiplied by the section of the flow meter. This method is sensitive to the air velocity profile in the flowmeter section as well as the flow pulsations resulting from the cyclic operation of the motor.

The speed and the load of the internal combustion engine appear as the main variables of the engine, influencing the shape of the flow pulsation. When the admission configurations are independent or directly related to these two parameters, it is possible to correct the air flow information with mapping according to these two parameters. The configuration of the air intake, however, does not depend solely on these two parameters. It is necessary to take into account each air intake configuration, such as the activation of the high-pressure exhaust gas recirculation circuit, the activation of the low-pressure exhaust gas recirculation circuit, the activation of the air shutter, the activation of swirling devices (denoted swirl in English) variable, and all types of operating mode of the engine.

In view of the foregoing, the present invention relates to a method and a system for accurately compensating, and for each engine, the dispersion and drift of the means for measuring the flow of fresh air admitted into a motor. internal combustion. In one aspect, there is provided a method of correcting an intake air flow measurement in an internal combustion engine, the internal combustion engine comprising one or more gas recirculation circuits. According to the method, the flow of air admitted into the internal combustion engine is measured, a first treatment is carried out on the flow measurement signal of the air admitted into the internal combustion engine, and a correction function is applied. to the treated value of the air flow admitted to the engine. The method also comprises a step of learning the correction function during which, during a learning phase: - the gas recirculation circuit (s) are closed, - a second treatment is carried out on the measurement signal of air flow admitted into the internal combustion engine with a model taking into account the closure of the recirculation circuit (s), - the intake air flow in the engine is estimated, and - the correction function is determined depending on the difference between the processed value and the estimated value of the air flow admitted to the engine. Thus, the acquisition of the flow meter is modified as a function of the operation of the engine, in particular as a function of the activation of the gas recirculation circuit or circuits, so as to obtain a correction which does not depend on the operating state of the or recirculating gas circuits. The correction function applies to both operating modes of the combustion engine: with recirculation of gases and without gas recirculation. Preferably, the internal combustion engine comprises a low pressure gas recirculation circuit and a high pressure gas recirculation circuit. The first treatment can be carried out on the flow measurement signal of the air admitted into the internal combustion engine, with a model depending on the opening of the gas recirculation circuit (s). The first treatment and the second treatment can be performed by linearizing the measurement values and then applying a correction corresponding to the aero-acoustic effects. In this case, during the second signal processing, the measurement values are linearized taking into account the closure of the gas recirculation circuit (s). According to another aspect, there is provided a system for correcting an intake air flow measurement in an internal combustion engine, the internal combustion engine comprising: one or more gas recirculation circuits; measurement of the air flow admitted into the internal combustion engine, - first processing means able to process the measured value of the flow rate of the air admitted into the internal combustion engine, with an operating model of the measuring means, and correction means able to apply a correction function to the value processed by the processing means.

In particular, the internal combustion engine also comprises means for learning, during a learning phase, the correction function comprising: - closing means of the gas recirculation circuit (s), - second means for processing the measured value of the flow rate of the air admitted into the internal combustion engine, with a model taking into account the closure of the gas recirculation circuit (s), - means for estimating the air flow admitted into the the engine, and - means for determining the correction function as a function of the difference between the processed value and the estimated value of the air flow admitted into the engine. Preferably, the internal combustion engine comprises a high pressure gas recirculation circuit and a low pressure gas recirculation circuit. The first processing means may be able to process the measured value of the flow rate of the air admitted into the internal combustion engine, with an operating model of the measuring means depending on the opening of the gas recirculation circuit (s). The first and second processing means may comprise means for linearizing the measured value. The first and second processing means may comprise means for correcting the aero-acoustic effects on the linearized value. In this case, the linearization means of the second processing means may be able to linearize the measured value with a model taking into account the closure of the gas recirculation circuit (s). Other advantages and characteristics of the invention will appear on examining the detailed description of an embodiment of the invention, which is in no way limitative, and the attached drawings, in which: FIG. 1 represents, schematically, an internal combustion engine with its air intake system and exhaust gas system; FIG. 2 schematically illustrates a system for correcting a measurement of air flow admitted into an internal combustion engine associated with a measurement processing system; and FIG. 3 is a block diagram of a method for learning the correction function of a measurement of the air flow rate admitted into an internal combustion engine. FIG. 1 schematically represents an internal combustion engine 1 with its air intake system 2 and its exhaust gas system 3. The internal combustion engine 1 can be chosen from any type of engine equipped with a flowmeter for measuring the flow of fresh air and low pressure and high pressure gas recirculation circuits. Thus, the engine can be a diesel engine, gasoline, hybrid, gas, etc. It is considered in the following description that the engine 1 is a diesel engine. The air intake system 2 comprises an air filter 4, at the inlet of the air intake system 2, the output of which is coupled to a mass flow meter of fresh air for measuring the flow rate. of fresh air admitted into the air intake system 2. The air leaving the mass flowmeter 5 of fresh air is then injected into the compressor 6a of a turbocharger 6 which increases the inlet air pressure. of the engine 1 and therefore the amount of air injected into the internal combustion engine 1. A charge air cooler 7 is coupled at the outlet of the compressor 6a of the turbocharger 6 so as to cool the air heated by the compression of the turbocharger 6. An inlet air flap 30 coupled to the outlet of the charge air cooler 7 makes it possible to regulate the admission of air into the internal combustion engine 1. A variable swirling device 9, denoted swirl in English, is coupled as input to an eligibility collector the internal combustion engine 1, after the air intake flap 8. This device 10 makes it possible to inject the air with a swirling trajectory and thus to increase the quantity of air injected into the internal combustion engine. The exhaust system 3 of the internal combustion engine 1 comprises an exhaust manifold 11 of the gases, comprising an exhaust aftertreatment system 12 which thus makes it possible to filter and treat the exhaust gases in a purpose of depollution, and whose output is coupled to the turbine 6b of the turbocharger 6.

The exhaust aftertreatment system 12 may for example be a particulate filter. The particulate filter reduces the amount of particles released into the environment. It consists of a set of microchannels in which a large part of the particles are trapped. Once the filter is full, it must be emptied by burning the particles during a so-called "regeneration" phase. The regeneration can be obtained either by a heating device or by specific engine settings. The particulate filter 12 is placed in the exhaust line downstream of the turbo compressor.

An internal combustion engine 1 may also comprise a low pressure gas recirculation circuit 13 comprising a low pressure valve 14, and coupled between the air intake system 2 before the compressor 6a turbocharger 6 and the exhaust system. gas 3 after the turbine 6b of the turbocharger 6, and in particular downstream of the particulate filter 12. The low pressure EGR BP communicates the exhaust circuit, downstream of the turbine and in particular downstream of the particulate filter, and the intake circuit, upstream of the compressor, via a passage section the size of which is regulated by a valve. An exhaust flap placed downstream in the exhaust line makes it possible to increase the pressure difference across the BP EGR circuit and thus to increase the BP EGR level. This type of recirculation circuit is called "low pressure" because it is external to the supercharging circuit, that is to say that the inlet is downstream of the turbine and the outlet is upstream of the compressor. The internal combustion engine 1 may also comprise a high-pressure exhaust gas recirculation circuit 15 coupled between the air intake system 2 and the gas exhaust system 4 between the internal combustion engine 1 and the turbocharger 6. The high pressure exhaust gas recirculation circuit 15 comprises a high pressure valve 16, exhaust gas cooling means 17 and a bypass system of the cooler 18. HP high pressure EGR circuit communicates the exhaust circuit, upstream of the turbine, and the intake circuit, downstream of the compressor, via a passage section whose size is adjusted by a valve. An intake flap placed upstream of the valve makes it possible to increase the pressure difference across the HP EGR circuit and thus to increase the HP EGR rate. This type of recirculation circuit is called "high pressure" because it is internal to the supercharging circuit, that is to say that the inlet is upstream of the turbine and the outlet is downstream of the compressor.

Finally, the exhaust system 3 of the internal combustion engine 1 may also comprise a second exhaust after-treatment system 19, mounted downstream of the low-pressure gas recirculation circuit 13, and which also makes it possible to filter and / or treat the exhaust.

An electronic control unit 20 controls the various elements of the internal combustion engine 1 from data collected by sensors such as the flow meter 5. The electronic control unit 20 thus retrieves the data from the different sensors in order to process them to control the different elements of the internal combustion engine 1. The method and system described relate to engine control. The control of the operation of the engine is managed by a set of sensors and actuators according to a set of control laws, called "software strategies", and characterization parameters or engine calibrations. All these laws and parameters are stored in the electronic control unit or ECU. The electronic control unit 20 thus comprises a system for correcting an air flow measurement admitted into an internal combustion engine 1. This correction system is presented schematically in FIG. 2. The system and the method described allows to reduce the drifts and dispersions of the flowmeter 5 measuring the flow of fresh air, based on a comparison between the air flow rate measured by the flow meter 5 (called flow measured Qair mes) on the one hand and the estimator of flow of gas entering the engine (called estimated flow Qmot is) on the other hand, in the absence of recirculation of exhaust gas (EGR valves 14 and 16 closed). Indeed, in certain modes of operation of the engine, especially in the absence of EGR, it is possible to estimate the fresh air flow admitted into the engine sometimes more accurately than the measurement of this same flow by the flowmeter 5. It is then a matter of learning at different points in the life of the vehicle, a correction based on the ratio or the difference between the measured air flow rate and the estimated air flow rate. This correction depends on parameters chosen from those influencing the drift and the measurement dispersion of the flowmeter, for example the very value of the measured air flow rate. The system for correcting an air flow measurement measured by an air flow measurement means comprises correction means 22 able to apply a correction function to the air flow values Qair mes measured by the flow meter 5, and learning means 23 of the correction function. The correction function can be a function to compensate the measurement error of the flow meter, according to the air flow measured by it.

The number of airflow values for which a correction is determined is previously chosen by calibration: it is then determined airflow values. This number is chosen large enough so that the entire range of airflow values measured by the flowmeter is taken into account.

However, before being corrected, the signal supplied by the flowmeter is, in a conventional manner, processed so as to obtain a Qair tri signal exploitable and representative of the measured quantity. Indeed, the flow meter delivers a raw signal Qair mes in the form of voltage or analog frequency image of the air flow passing through the intake line 2 of the combustion engine 1. This raw signal is discretized and then converted into air flow discreet by means of a linearization curve of the flowmeter. This linearization curve represents the actual air flow through the flow meter as a function of the raw signal delivered by the latter when the engine is operating with the gas recirculation circuits. In addition, after the average calculation phase and filtering, the average air flow can also be corrected by a correction of the aero-acoustic effects as a function of engine speed and load. These treatments are carried out by the first processing means 21, in order to deliver the processed Qair sort values to the correction means 22. The learning means 23 require the absence of recirculation of the gases. Thus, during a learning phase, the circuits 13 and 15 are closed, then a correction function is determined as a function of the air flow rate measured during the learning phase. It is this same correction function that is applied by the means 22 during normal operation of the combustion engine 1, that is to say when the recirculation circuits of the gases are open.

However, the correction determined by the means 23 may also be due to the change in operation of the combustion engine 1, in this case may also be due to the shutdown of the gas recirculation circuits. However, such a correction must not apply when the recirculation circuits of the gases are open, as is the case during normal operation of the engine, in which case the correction function would introduce an error in the values Qair corn that would correspond to the error introduced by the stopping of the gas recirculation circuits during the learning phase.

Such an error is due to the processing of the signal supplied by the flowmeter 5. In fact, the treatments carried out by the first processing means 21, and in particular the linearization of the signal, are designed for operation of the motor with the recirculation circuits. gas. To prevent this error from being corrected during engine operating modes during which it does not occur (i.e., when the recirculation circuits are open), the correction function learning means 23 The training means 23 are based on the distinction of the linearization curves of the flow meter between the conditions with EGR and the conditions without EGR (learning phase). Thus, each operating mode of the motor is assigned a linearization curve of the Qair mes flowmeter values. The means 23 comprise closing means 24 able to close the EGR circuits 13, 15. This step makes it possible to obtain sufficient precision on the difference between the measured air flow rate and the estimated air flow, thanks to the absence of exhaust gas recirculation. The learning phase is then started. The learning means 23 comprise second processing means 25. The second processing means 25 perform a linearization and a correction of the aeroacoustic effects on the signal Qair mes. However, the linearization model, and possibly the aero-acoustic effects correction model, used by the second processing means 25 are chosen so as to take into account the operation of the internal combustion engine 1 without EGR. In this way, errors specific to the operating mode without EGR of the motor are corrected by the second processing means 25 and are no longer taken into account when determining the correction function. The learning means 23 also comprise means 26 for estimating the flow rate of the air admitted into the internal combustion engine 1. The means 26 for estimating the flow calculate and send a value Qmot to means for determining the the correction function 27, which also receive the measured values Qair tr2 of the air flow treated by the means 25 and the output signal of the closure means 24 indicating that the EGR circuits are closed and that the correction function can be determined . When receiving a learning trigger signal from the closing means 24, the determining means 27 calculates the correction function. For this, they can for example start by estimating the standard deviation of the measurement of the air flow and the standard deviation of the estimation of the flow rate of the gases admitted to the engine. For purposes of simplification, it is considered here that the standard deviation of Qair airflow measurement tr2 is equal to the standard deviation of Qair mes airflow measurement. The standard deviation of the measurement of the air flow can be given for example from the known information on the flow meter. The standard deviation of the estimate can be provided at the same time as the estimation model. The means 27 then compare the values of the standard deviation of the intake air flow rate and the flow rate of the gases admitted to the engine, to a calibration value (8) and calculates the estimated optimum flow rate Qmot_est_opti of the gases entering the engine. . The determining means 27 then calculate the measured air flow rate correction function, based on the air flow rate supplied by the means 25, and the estimated optimum flow rate of the gases entering the previously calculated engine. Finally, the correction function calculated by the learning means 23 is supplied to the correction means 22 in parallel with the Qair values sorted by the first means 21, which then calculate the fresh air flow admitted corrects Qair corn. The estimated optimum flow rate of the gases admitted to the engine is calculated by comparing the standard deviations of the dispersions of the measured air flow (6Qair mes) and the flow rate of the gases admitted into the estimated engine (6Qmot est). For this, we use the function: zz Qair mes + GQmot_est 2 ≤ 6 g Qmot is where: Qmot is 6Qair mes: standard deviation of the dispersion of the gas flow admitted to the estimated engine, standard deviation of the dispersion of the measured air flow, calibration variable In the case where this inequality is satisfied, the estimated optimum flow rate of the gases admitted into the Qmot engine is opti is equal to the arithmetic mean of Qmot is and Qair tr2. Otherwise the estimated optimum flow rate of the gases admitted into the engine is equal to Qmot is. The corrective values on fresh air flow measurement can be interpreted mathematically, either as multiplicative factors or as additive factors. This means that, for a given operating point (i) of the motor, the corrective value can be represented either with the ratio of the estimated optimum flow rate of the gases admitted into the engine Qmot is opti (i) on the air flow Qair treated tr2 (i) (multiplicative factor), or with the difference between these two same flow rates (additive ratio). The determining means 27 stores the measured air flow and corrective value couples for each learning point. The average of several fresh air flow measurements and several gas flow calculations allowed in the estimated engine can be averaged prior to storing the values. The values thus obtained are stored in a non-volatile memory making it possible to ensure the durability of the correctives learned, when stopping the engine 1. The corrective values are then interpolated so as to obtain a function covering all the operating points of the engine. , then the correction function k is determined from this function covering the operating points of the motor.

In the case of a multiplicative error, the airflow corrected for a given operating point (j) is calculated as follows: Qair corr (i) where k X Qair tri ~ J) with k multiplicative correction function resulting from the values corrective. In the case of an additive error, the airflow corrected for a given operating point (j) is calculated as follows: Qair corr ~ J) ù k + Qair sort ~ J) with k additive correction function resulting from the values This correction is valid regardless of the operating conditions of the engine 1, including exhaust gas recirculation. The corrected air flow thus obtained is provided to the different strategies for controlling the operation of the engine via the unit 20. In addition, the corrective values are determined at different moments of the life of the vehicle, for example at predetermined mileage intervals. transparently for the driver of the vehicle.

The learning automatically detects the driving conditions that are favorable for the learning phases. Thus, thanks to the system described above, it is possible to avoid the generation of an error during the linearization of Qair mes values during the learning phase, and thus to avoid shifting the Qair corn values during the correction. By the means 22, the correction of the drifts and dispersions of the air flow meter is improved, during an acquisition of the raw signals with linearization and correction of the aero-acoustic effects. The correction function applied by the means 22 makes it possible to compensate for the drifts and dispersions of the Qair mes signal and not for errors occurring solely during operation of the engine without EGR. FIG. 3 is a block diagram of a method for learning the function of correcting an air flow measurement admitted in an internal combustion engine 1, during a learning phase. In a first step 31, the gas recirculation circuits 13 and 15 are closed, then, after a duration greater than or equal to the closing time of the EGRs and a period of aeraulic stabilization, the second treatment of the measured value is carried out with a model taking into account the closing of the gas recirculation circuits. The flow of air admitted into the internal combustion engine 1 is then estimated in a step 33. Finally, in a step 34, the correction function to be applied to the measurement of the air flow admitted into the engine is determined. internal combustion 1, depending on the estimated flow rate and the measured airflow. This correction function is valid regardless of the operating conditions of the engine 1, including with exhaust gas recirculation. The corrected air flow thus obtained is provided to the various strategies for controlling the operation of the engine via the unit 20. The method and the system therefore make it possible to reduce the drifts and dispersions of the flowmeter taking into account the recirculation circuits of the gases. to control the flow of fresh air entering the internal combustion engine equipped with an HP EGR circuit and a BP EGR circuit. Pollutant emissions can be reduced when there is recirculation of gases, as well as smoke emissions.

Claims (9)

REVENDICATIONS1. A method of correcting an intake air flow measurement in an internal combustion engine (1), the internal combustion engine comprising one or more gas recirculation circuits, characterized in that: - the flow rate of air intake (Qair mes) in the internal combustion engine, - a first treatment is carried out on the flow measurement signal of the air admitted into the internal combustion engine, and - a correction function is applied to the value treated. (Qair sorting) of the air flow admitted into the engine, the method also comprising a step (30) of learning the correction function during which, during a learning phase,: - the one or more recirculation circuits for the gases (31), - a second treatment is carried out on the flow measurement signal of the air admitted into the internal combustion engine with a model taking into account the closure of the recirculation circuit (s) ( 32), - the air flow is estimated admitted in the motor (33), and - the correction function is determined as a function of the difference between the processed value (Qair tr2) and the estimated value (Qmot is) of the air flow admitted into the engine (34) . 2. The method of claim 1 wherein the internal combustion engine comprises a low pressure gas recirculation circuit and a high pressure gas recirculation circuit. 3. Method according to claim 1 or 2 wherein the first treatment is carried out on the flow measurement signal of the air admitted into the internal combustion engine, with a model depending on the opening of the recirculation circuit (s). gas. 4. Method according to one of claims 1 to 3 wherein performs the first treatment and the second treatment by linearizing the measurement values. 5. Method according to claim 4 wherein the first treatment and the second treatment are carried out by applying also a correction corresponding to the aero-acoustic effects. 6. The method of claim 4 or 5 wherein, during the second signal processing (32), the measurement values are linearized taking into account the closure of the recirculation circuit (s). 7. A system for correcting an intake air flow measurement in an internal combustion engine (1), characterized in that the internal combustion engine comprises: one or more gas recirculation circuits; measurement (5) of the air flow admitted into the internal combustion engine; - first processing means (21) able to process the measured value of the flow rate of the air admitted into the internal combustion engine, with a model of operation of the measuring means, and correction means (22) capable of applying a correction function to the value processed by the processing means, the internal combustion engine (1) also comprising learning means (23). during a learning phase, the correction function comprising: - means for closing the gas recirculation circuit (s) (24), - second processing means (25) for the measured flow rate value. the air admitted into the combustion engine internal, with a model taking into account the closure of the recirculation circuit (s), - means for estimating (26) the air flow admitted into the engine, and- means for determining (27) the function correction as a function of the difference between the value processed and the estimated value of the air flow admitted into the engine. The system of claim 7 wherein the internal combustion engine comprises a high pressure gas recirculation circuit (15) and a low pressure gas recirculation circuit (13). 9. System according to claim 7 or 8 wherein the first processing means (21) are able to process the measured value of the flow rate of the air admitted into the internal combustion engine, with a model of operation of the measuring means depending the opening of the recirculation circuit (s).