Method for controlling the fuel mixture richness of an internal combustion engine in a motor vehicle

Abstract

This method for controlling the air-fuel ratio of a fuel mixture in an internal combustion engine (10) of a motor vehicle equipped with a variable valve timing system (50) comprises the steps of: detecting a change in the engine operating point; calculating at least one setpoint for the position of said system; measuring a current position of said system; predictively calculating a position of said system; estimating the airflow from said predictive calculation; calculating, from the airflow estimation, the quantity of fuel to be injected for engine operation at air-fuel ratio 1; and opening the engine's fuel injectors to inject said quantity of fuel. The predictive calculation of the position of the variable valve timing system (50) corresponds to the position of said system at the moment the fuel injectors open. Figure 1

Description

Title of the invention: Method for controlling the fuel mixture richness of an internal combustion engine of a motor vehicle technical field

[0001] The present invention relates to the control of an internal combustion engine and more particularly of a spark-ignition engine, during a transient operating phase of the engine. Previous techniques

[0002] During a change in the operating point of an internal combustion engine, such as a change in rotational speed or a change in torque setpoint, it is observed that the actual air-fuel ratio deviates from the setpoint. The air-fuel ratio is evaluated relative to a ratio of 1, which corresponds to fuel combustion under stoichiometric conditions.

[0003] This difference in fuel mixture is due to a poor estimation of the airflow entering the engine and can lead to an increase in pollutant emissions, an increase in engine noise and / or a problem with driving comfort due to jerking.

[0004] Typically, for an engine mounted on a motor vehicle, the driver determines the vehicle's acceleration by pressing the accelerator pedal. Based on this acceleration command and the engine speed, a computer defines the engine torque required to achieve this acceleration command.

[0005] In the case of a spark-ignition engine (running in particular on gasoline), the torque setpoint is translated into a mass air flow setpoint Qair, into an ignition advance value AA which is preferably chosen to optimize combustion efficiency, and into a richness setpoint generally equal to 1, which corresponds to the fuel flow rate which must be burned in stoichiometric proportions to obtain the torque while operating a three-way catalyst of the engine in its catalytic operating range in which it is able to treat unburned hydrocarbons, carbon monoxide and nitrogen oxides.

[0006] It should be noted that in the case of a hybrid drive system consisting of a thermal engine and at least one electric machine, the torque variations required from the thermal engine are not necessarily correlated solely with the accelerator pedal, because the torque is distributed over all available drive sources.

[0007] Furthermore, when the vehicle is equipped with a partial exhaust gas recirculation system From exhaust to engine intake, a mass flow rate target for recirculated gases Qegr is also defined, which corresponds to the recirculation rate to be applied to meet the target fuel consumption.

[0008] The sum of the air flow rate Qair and the recirculated gas flow rate Qegr represents the total gas mass flow rate Qmot entering the engine, which is generally set by adjusting the position of a throttle body in the engine air intake circuit, so as to obtain a pressure value Pcol in the engine intake manifold corresponding to the desired total gas flow rate, the recirculated gas flow rate Qegr being obtained by adjusting the position of a valve in the partial recirculation circuit, the desired air flow rate Qair being obtained indirectly as the difference between the total gas flow rate Qmot and the recirculated gas flow rate Qegr.

[0009] An engine computer uses an air filling model, which makes it possible to determine the value of the minimum pressure of the intake manifold to meet the engine torque setpoint.

[0010] This filling pattern follows the following equation:

[0011] (1) rdvl nx Cylinder capacity x

[0012] In which:

[0013] ^rdvl designates the volumetric yield or "filling", dimensionless;

[0014] Qmot denotes the actual total incoming mass flow rate, in kg / s;

[0015] N designates the regime, in revolutions / min;

[0016] Cylinder capacity refers to the engine's cylinder capacity, in m3;

[0017] Pcol denotes the pressure in the intake manifold, in Pa;

[0018] Tcol denotes the temperature in the intake manifold, in K; and

[0019] R denotes the ideal gas constant for air, equal to approximately 287.058 J / kgxK •

[0020] The term "filling" is defined as being equal to the ratio between the mass of air actually aspirated and the mass of air that could have entered by considering only the total volume of the cylinders.

[0021] In all cases, the value of the efficiency ^rdvl depends at least on the engine speed N and the pressure in the intake manifold Pcol.

[0022] However, if the engine is also equipped with a variable valve timing system (also called a VVT system, from the English acronym for: Variable Valve Timing), particularly at the intake, which is the case for many modern engines, the efficiency ^rdvl also depends on the position of this VVT system at the intake, which determines the opening and closing times of the intake valves in the engine's combustion cycle.

[0023] It should also be noted that in the case where the engine is also equipped with a VVT system In the exhaust, efficiency also depends on the position of this VVT system in the exhaust, which determines the opening and closing times of the exhaust valves, although the sensitivity of the efficiency value to the position of the VVT ​​system in the exhaust is significantly less than in the case of a VVT system in the intake.

[0024] The volumetric efficiency is mapped by preliminary bench tests as a function of these parameters: engine speed; torque; and the position of the VVT ​​system at the intake, and the map is stored in the engine control unit's memory. For example, the position of the VVT ​​system at the exhaust can be disregarded if the engine is equipped with such a system.

[0025] Thus, according to the prior art, during vehicle operation, the control unit determines a current value for the engine speed N, the intake manifold pressure Pcol, and the position of the VVT ​​system at the intake. It then uses the mapping to calculate the volumetric efficiency. The control unit also determines a current value for the exhaust manifold temperature Tcol. It then uses the filling model to calculate a value for the total gas flow rate Qmot, and subsequently a value for the air flow rate Qair by subtracting the recirculated gas flow rate Qegr from the total gas flow rate Qmot. The recirculated gas flow rate Qegr can, for example, be determined in a manner known per se from a Saint-Venant equation at the terminals of the recirculation circuit valve.

[0026] The fuel mixture adjustment is generally carried out in a closed loop using a setpoint value. The system measures, for example, the actual richness of the combustion gases exiting the engine using a proportional oxygen sensor located upstream of a three-way catalytic converter in the engine.

[0027] The value of the difference in richness between the measured value and the setpoint value is sent as input to a controller, for example of the PID (proportional, integral, derivative) type, whose output value is a fuel flow correction value which is added to a fuel flow value calculated for open-loop control, to correspond to the theoretical fuel flow allowing combustion in stoichiometric proportions.

[0028] The fuel mixture is adjusted by adjusting the amount of fuel injected by imposing the duration of the opening of the engine's fuel injectors.

[0029] For example, the quantity of fuel is the sum of a first quantity of fuel calculated in open loop from the current air flow rate at a ratio of one gram of fuel to 14.7 grams of air, to correspond to the stoichiometric proportions, and a correction term used for closed-loop control. The values ​​of the correction term are smaller the more accurate the first calculated quantity.

[0030] The tidal airflow rate used in the calculation of the tidal airflow rate estimate is obtained from the filling model of equation 1, which depends in particular on the pressure in the intake manifold and the position of the VVT ​​system at the intake. However, due to the rapid dynamics of the processes involved, by the time the order to open the injectors is given by an engine control unit, the pressure Pcol in the intake manifold and the position of the VVT ​​system at the intake generally no longer correspond to the measured values ​​used to calculate the volumetric efficiency, then the total gas flow rate Qmot and the airflow rate Qair.

[0031] Thus, the estimation of the current airflow is distorted, and the quantity of fuel to be injected, determined by open-loop calculation from the airflow, no longer corresponds to the pressure measured in the intake manifold or to the measured position of the VVT ​​system at the intake and the corresponding opening and closing times of the intake valves. It is then observed that the controller, which controls the fuel mixture value based on a setpoint (generally equal to 1), must use higher fuel quantity correction terms to compensate for the error in calculating the airflow.

[0032] However, it can be estimated that the pressure variations in the intake manifold Pcol are significantly less dynamic than the variations in the position of the VVT ​​system at the intake, and therefore than the corresponding variations in the opening and closing times of the intake valves, and thus have less influence on the mixture setting. This lesser influence is particularly true for engines operating on asymmetrical Atkinson or Miller cycles, in which the throttle body tends to be left wide open in order to increase the pressure in the intake manifold and reduce pumping losses. In both cases, the mass of air admitted into the combustion chamber is adjusted by controlling the intake valves, with intake valve closing delay (RFA) values ​​significantly offset from bottom dead center (BDC).The main actuator controlling the engine's air load is then the variable intake valve timing system in both scenarios, instead of the throttle body in traditional engines that do not use one of these cycles. Description of the invention

[0033] In view of the foregoing, the object of the invention is to improve the control of the fuel mixture richness during the transient phases of engine operation during which the position of a variable valve timing system, and more particularly of a variable intake valve timing system, changes between the the beginning and end of the transitional phases.

[0034] The invention relates to a method for controlling the richness of a fuel mixture for an internal combustion engine of a motor vehicle equipped with a variable valve timing system for the engine's intake valves.

[0035] This process comprises the following steps: - detection of a change in the engine's operating point; - calculation of at least one position setpoint of said variable calibration system (50), corresponding to the new operating point setpoint; - measurement of a current position of said variable adjustment system; - predictive calculation of a position of said variable calibration system (50); - estimation of airflow from said predictive calculation; - calculation, based on the estimated air flow, of the quantity of fuel to be injected for engine operation at a fuel-air ratio of 1, and opening of the engine's fuel injectors to inject said quantity of fuel

[0036] characterized in that the predictive calculation of the position of the variable timing system corresponds to the position of said system at the time of the start of opening of the fuel injectors.

[0037] The fuel mixture control method is configured to improve the accuracy of calculating the amount of fuel to be injected during transient phases of engine operation.

[0038] Advantageously, the predictive calculation of the position of the variable intake valve timing system at the time of the start of the opening of the fuel injectors uses a model of response to a setpoint of the valves.

[0039] For example, the response model of the variable valve timing system is characterized by a dead time parameter and a maximum system displacement speed.

[0040] Advantageously, the response model of the variable valve timing system takes into account an anticipation to obtain an actual position anticipated relative to the measured position.

[0041] For example, the anticipation is between 30 ms and 70 ms, and is preferably equal to 50 ms.

[0042] According to another feature, the engine includes at least one partial exhaust gas recirculation circuit at the intake.

[0043] Advantageously, the fresh air flow estimation anticipates the variation in EGR flow, by calculating the position of the EGR valve from the EGR flow setpoint and the response time in order to obtain an anticipated EGR flow compared to the EGR flow calculated from the measurement of the EGR valve position.

[0044] According to another aspect, the invention relates to a fuel mixture control system for an internal combustion engine of a motor vehicle equipped with a variable valve timing system, in particular a variable intake valve timing system.

[0045] The fuel mixture control system includes means for detecting a change in the engine operating point, means for calculating at least one variable valve timing system position setpoint, means for predictive calculation of a variable valve timing system position, means for estimating the air flow rate and means for calculating the quantity of fuel to be injected for engine operation at richness 1. Brief description of the drawings

[0046] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0047] [Fig.1] illustrates, in a very schematic way, an example of the structure of an internal combustion engine of a motor vehicle equipped with a fuel mixture control system according to the invention;

[0048] [Fig.2] illustrates a flowchart of the wealth control process according to a mode implementation of the invention;

[0049] [Fig.3] illustrates an example of position setpoint, actual position and position actual anticipated of a variable intake valve timing system of the engine of the [Fig.1] according to the invention;

[0050] [Fig.4] illustrates a diagram for constructing an anticipated trajectory of a position of the variable intake valve timing system according to the invention; and

[0051] [Fig. 5] illustrates the application according to the invention of a reduced dead time during the Changes in the direction of the variable intake valve timing system. Detailed description of at least one embodiment.

[0052] In the example illustrated in [Fig. 1], the internal combustion engine 10 is of the spark-ignition (gasoline) type and comprises, but is not limited to, three inline cylinders 12, a fresh air intake manifold 14, an exhaust manifold 16, a turbocharger or turbocharger 18, a variable valve timing system 50 for the engine's intake valves 51, and optionally, a variable valve timing system 52 for the engine's exhaust valves 53. The variable valve timing system 50 for the intake valves is equipped with a sensor 54 that allows its angular position to be known at any given moment, corresponding to specific times of opening and closing of the intake valves 51 in the engine's combustion cycle (these moments being generally measured in degrees of crankshaft relative to a top dead center position). The variable timing system 52 of the exhaust valves, if present, is also equipped with a sensor 55 which allows its angular position to be known at any instant, which also corresponds to determined instants of opening and closing of the exhaust valves 53 in the combustion cycle of the engine.

[0053] The cylinders 12 are supplied with air via the intake manifold 14, or distributor, itself supplied by a pipe 20 equipped with an air filter 22 and a compressor 18a of the turbocharger 18 of the engine 10.

[0054] The turbocharger 18 essentially comprises a turbine 18b driven by the exhaust gases and the compressor 18a mounted on the same shaft as the turbine 18b and ensuring compression of the air distributed by the air filter 22 or air box, in order to increase the quantity (mass flow) of air admitted into the cylinders 12 of the engine 10 for an identical volumetric flow rate.

[0055] The internal combustion engine 10 includes an intake circuit Ca and an exhaust circuit Ce.

[0056] The intake circuit Ca comprises, from upstream to downstream in the direction of airflow:

[0057] - the air filter 22;

[0058] - a flow meter 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;

[0059] - an air intake valve 28;

[0060] - the compressor 18a of the turbocharger 18;

[0061] - a throttle body 30 or a gas intake valve in the engine;

[0062] - a heat exchanger 32 configured to cool the intake gases cor responding to a mixture of fresh air and recirculated gases after their compression in compressor 18a;

[0063] -pressure and temperature sensors 33 for measuring the pressure and temperature in the intake manifold 14; and

[0064] - the intake manifold 14.

[0065] The compressor is associated with a bypass circuit equipped with an inlet relief valve 56 which opens in the event of sudden closure of the throttle body 30, to prevent the compressed air, located between the compressor 18a and the throttle body 30, from passing through the compressor 18a and degrading it, when for example, the driver of the vehicle suddenly lifts his foot off the accelerator pedal.

[0066] The exhaust circuit Ce comprises, from upstream to downstream in the direction of flow of the burnt gases:

[0067] - the exhaust manifold 16;

[0068] - the turbine 18b of the turbocharger 18; and

[0069] - an engine combustion gas pollution control system (not shown), including a three-way catalytic converter.

[0070] As regards the exhaust manifold 16, it recovers the exhaust gases from the combustion and expels them to the outside, via an exhaust gas duct 34 opening at the inlet of the turbine 18b of the turbocharger 18 and via an exhaust line 36 mounted downstream of the turbine 18b.

[0071] The engine 10 further includes a partial recirculation circuit 38 of the exhaust gases to the intake, called the “EGR” circuit (“exhaust gas recirculation” in Anglo-Saxon terms).

[0072] The engine 10 may not be equipped with an EGR circuit, without this falling outside the scope of the invention.

[0073] This circuit 38 is herein, without limitation, a low-pressure exhaust gas recirculation circuit. It is connected to the exhaust line 36, downstream of said turbine 18b, and in particular downstream of the exhaust gas aftertreatment system, and returns the exhaust gases to the fresh air supply line 20, upstream of the compressor 18a of the turbocharger 18, in particular downstream of the flow meter 26. The flow meter 26 measures only the fresh air flow rate.

[0074] As illustrated, this recirculation circuit 38 comprises, in the direction of recirculated gas flow, a cooler 38a, a filter 38b, and a valve 38c configured to regulate the flow of low-pressure exhaust gases. The valve 38c is located downstream of the cooler 38a and the filter 38b and upstream of the compressor 18a.

[0075] The engine is associated with a fuel circuit comprising, for example, fuel injectors (not referenced) injecting gasoline directly into each cylinder from a fuel tank (not shown).

[0076] Furthermore, the engine includes an electronic control unit 70 configured to control the various elements of the internal combustion engine from data collected by sensors at different locations in the engine.

[0077] The electronic control unit 70 comprises a calculation module 72, a measurement module 73 and a control module 74.

[0078] We will now describe with reference to [Fig.2] a method 60 for controlling the richness in the transient phase of operation of the engine 10.

[0079] Such a process is implemented in particular by the computer 70 from the measurements delivered by the various sensors of the engine and by controlling the various elements of the engine.

[0080] The method 60 includes a preliminary step 61 of detecting a change in the operating point of the engine 10, or operating point setpoint, in which the computer 70 detects a new operating point corresponding to A change in the operating point of engine 10. An operating point of engine 10 is characterized by a rotational speed, an engine load 10, and an operating temperature, generally corresponding to the temperature of the engine coolant 10. Thus, a change in the operating point corresponds to a variation in at least one of these parameters, for example, but not limited to, a relative value of 5%. For example, a change in the operating point can result from a sufficient change in the vehicle's accelerator pedal depressor, which alters the torque setting.

[0081] During the following step 62, the computer 70 calculates, based on the new operating point setpoint detected in step 61, an optimal position setpoint for the variable timing system 50 of the intake valves 51, and possibly also for the variable timing system 52 of the exhaust valves 53.

[0082] This position setpoint of the variable timing system 50 of the intake valves corresponds to the value that the position of the variable timing system 50 of the intake valves will take on this new operating point in stabilized operation, but this position is not reached instantaneously because there is a time required for the variable timing system of the intake valves to move from their old position to their new setpoint value.

[0083] Now, as already mentioned above and in particular with reference to equation (1) of the filling model, the actual or current position of the variable timing system 50 of the intake valves 51 (and to a lesser extent, that of the variable timing system 52 of the exhaust valves 53) has a first order influence on the air filling of the engine 10 because it determines the times of opening and closing of the intake valves, which allow the introduction of air into the engine cylinders.

[0084] In order to operate at richness 1, the quantity of fuel to be injected depends on the quantity of air actually admitted into the cylinders 12, therefore predominantly on the moment of opening of the intake valves 51 corresponding to the position of the variable timing system 50 of the intake valves 51.

[0085] During a change in the operating point of the engine 10, the variation in air flow must be estimated as accurately as possible so that the quantity of fuel injected corresponds to the mass of air enclosed in the cylinders 12 at each engine revolution.

[0086] However, the greater the air flow gradients, the more the calculation of the air flow is misled when the calculations use information provided by sensors which themselves have intrinsic response times.

[0087] Since a non-zero duration necessarily elapses, generally between 30 and 70 milliseconds, for example on the order of 50 milliseconds, between the instant when the The position of the variable timing system 50 of the intake valves is measured and the moment when the computer activates the fuel injectors and begins to open them in order to inject the fuel flow, after calculating the air flow and then the said fuel flow to be injected in open loop, it is understood that the fuel flow actually injected may no longer correspond to the flow that should be injected, because the actual air flow no longer corresponds to the air flow corresponding to the measured position of the variable timing system.

[0088] To improve the accuracy of calculating the air and fuel flow rates to be injected during transient phases, the control unit 70 does not, according to the invention, use the position of the variable valve timing system 50 of the intake valves 51 measured by the sensor 54, but in the following step 64, it performs a predictive calculation of the position that the variable valve timing system 50 of the intake valves 51 will have at the moment the fuel injectors begin to open, as determined by the engine control unit. Optionally, this step may also include a predictive calculation of the position that a variable valve timing system 52 of the exhaust valves 53 will have when the injectors are activated.

[0089] At this stage, the computer 70 uses maps constituting a model 63 of response to a position command of the variable timing system 50 of the intake valves 51 (respectively of the variable timing system 52 of the exhaust valves), pre-programmed and contained in its memory, which allow it to estimate trajectories of the positions of the variable timing system 50.

[0090] The estimates of the trajectories of the positions of the variable timing system 50 of the intake valves 51 (and possibly also of the variable timing system 52 of the exhaust valves 53) are made over a time horizon which corresponds to the duration between the instant when the position of the variable timing system 50 of the intake valves is measured and the instant when the fuel flow begins to be injected (i.e.: the instant of the start of opening of the fuel injectors).

[0091] The response model to a command of variable timing system 50 of the intake valves 51 (and possibly of the variable timing system 52 of the exhaust valves) can be characterized by two parameters, namely a dead time and a maximum speed of movement of said timing system.

[0092] Dead time accounts for the period of time during which a variable timing system 50,52 remains in position, and therefore the opening and closing times of the valves are not yet modified, after the establishment of a new position setpoint for this valve by the computer 70.

[0093] The maximum speed of movement corresponds to the maximum angular position variation that a variable valve timing system can follow.

[0094] Figure 3 illustrates the actual trajectory 82 of a variable pitch control system valves, in particular intake valves, subject to a position setpoint 80, and an anticipated trajectory 81 used to estimate the amount of air admitted into the combustion chamber and the amount of fuel at the time of opening the fuel injectors.

[0095] Figure 4 illustrates a diagram of the construction of an anticipated trajectory of a position of a variable valve timing system.

[0096] When the position setpoint 83 changes value, it is possible to estimate an anticipated real position 84 of the variable positioning system in anticipation 85 with respect to the real position 86.

[0097] The dead time 87 between the setpoint 83 and the actual position 86 is reduced by the anticipation 85 to the reduced dead time 88 which corresponds to the dead time between the setpoint 83 and the anticipated actual position 84.

[0098] After taking into account in advance 85 the reduced dead time 88, the response model 63 uses for the anticipated actual position 84 the same position gradient as that of the setpoint 83, and this until the value of the setpoint 83 is reached. However, in the case where the position gradient of the setpoint 83 is greater than the maximum speed of movement of the variable valve timing system, the gradient of the anticipated actual position 84 is limited to this maximum speed.

[0099] As illustrated in [Fig.5], the reduced dead time 88 can also be applied during changes of direction of the variable valve timing system (i.e.: changing from a clockwise to a counterclockwise direction or vice versa) without there having been stabilization of the position.

[0100] In the next step 65, the computer 70 estimates the required airflow from the results obtained in step 64 of predictive calculation of the position of the variable timing system 50 of the intake valves (and possibly also of the variable timing system 52 of the exhaust valves).

[0101] This air flow rate is estimated from the following relationship:

[0102] ^xl2° (1) rdvl nx Cylinder capacity x 1 coi* n

[0103] In which:

[0104] ^rdvl designates the volumetric yield or "filling", dimensionless;

[0105] Qmot denotes the actual total incoming mass flow rate, in kg / s;

[0106] N denotes the regime, in revolutions / min;

[0107] Cylinder capacity refers to the engine's cylinder capacity, in m3;

[0108] Pcol denotes the pressure in the intake manifold, in Pa;

[0109] Tcol denotes the temperature in the intake manifold, in K; and

[0110] R denotes the ideal gas constant for air, equal to approximately 287.058 J / kg·K■

[0111] The process 60 continues in step 66 by calculating the quantity Q of fuel to be injected into the cylinders 12, for an engine 10 operating at a richness equal to 1, and by opening the fuel injectors by the computer in order to inject the calculated fuel flow.

[0112] The quantity Q of fuel to be injected is calculated from the estimated air flow rate, and in particular, in the case where the richness setpoint is equal to 1, the fuel flow rate is calculated in proportion to 1 g of fuel for 14.7 g of air.

[0113] For engines with at least one EGR circuit, it is still possible to anticipate the variation in EGR flow rate Qegr which enters into the calculation of the fresh air flow rate Qair, by calculating the position of the EGR valve 38c from the EGR flow rate setpoint and the response time in order to obtain an anticipated EGR flow rate compared to the EGR flow rate calculated from the position of the EGR valve 38c.

Claims

Demands

1. A method for controlling the richness of a fuel mixture for an internal combustion engine of a motor vehicle equipped with a variable valve timing system (50) for the intake valves (51) of the engine, characterized in that it comprises the following steps: - detection of a change in the operating point of the engine (10); - calculation of at least one position setpoint for said variable valve timing system (50) corresponding to the new operating point setpoint; - measurement of a current position of said variable valve timing system; - predictive calculation of a position of said variable valve timing system (50); - estimation of the air flow rate from said predictive calculation; - calculation, from the air flow rate estimation, of the quantity of fuel to be injected for engine (10) operation at a richness level of 1, and opening of the engine fuel injectors for the injection of said quantity of fuel;said position calculated by predictive calculation corresponding to the position of said system at the moment of the start of the opening of the fuel injectors.;

2. A method according to claim 1, wherein the predictive calculation of the position of the variable timing system (50) of the intake valves (51) uses a model of response to a position setpoint of the system.

3. Method according to claim 2, wherein the response model of the variable valve timing system is characterized by a dead time parameter and a maximum system displacement speed.

4. Method according to claim 3, wherein the response model of the variable valve timing system takes into account an anticipation to obtain an actual position anticipated relative to a measured position.

5. A method according to claim 4, wherein the anticipation is between 30 and 70 milliseconds, and is preferably equal to 50ms.

6. Method according to claim 1, wherein the engine includes at least one partial recirculation circuit (38) of the exhaust gases to the intake.

7. A method according to claim 6, wherein the fresh air flow estimation anticipates the variation in EGR flow, by calculating the position of the EGR valve (38c) from the EGR flow setpoint and response time in order to obtain an anticipated EGR flow compared to the EGR flow calculated from the measurement of the position of the EGR valve (38c).

8. Fuel mixture control system for an internal combustion engine of a motor vehicle equipped with a variable valve timing system, characterized in that it comprises means for detecting a change in the operating point of the engine (10), means for calculating at least one position setpoint of the variable valve timing system, means for predictive calculation of the position of the variable valve timing system, means for estimating the air flow and means for calculating the quantity of fuel to be injected for engine operation (10) at a richness 1, said position calculated by the predictive calculation corresponding to the position of said system at the time of the start of opening of the fuel injectors.

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