FR3145779A1 - Method and system for controlling a supercharged internal combustion engine configured to manage the storage and desorption of liquid water in a charge air cooler - Google Patents

Abstract

Method (100) for controlling a supercharged internal combustion engine (10) in which: - the mass (M_water) of liquid water stored in real time on internal walls of an exchanger (30) receiving a mixture of fresh air and recycled burnt gases is estimated; - a difference in water masses (ΔM_water) between said mass of water (M_water) and a predetermined critical mass (MC) of liquid water is determined; and- the maximum mass of water that can be stored by the exchanger (30) is managed when the absolute value of said difference (abs(ΔM_water)) is less than a threshold value (S) by reducing an EGR rate (Tx_EGR) by controlling an EGR control valve (38c) and/or by reducing the flow rate of a cooling fluid (Q_WCAC) flowing through the exchanger (30) by controlling a pump configured to circulate the cooling fluid in the exchanger (30) and/or by increasing the temperature (T_WCAC) of the cooling fluid of the exchanger (30). Figure for abstract: Fig 3

Description

Method and system for controlling a supercharged internal combustion engine configured to manage the storage and desorption of liquid water in a charge air cooler

The present invention relates to the field of internal combustion engines, and more particularly supercharged internal combustion engines, gasoline or Diesel.

More particularly, the invention relates to the reduction of condensation in a charge air cooler.

Typically, a supercharged internal combustion engine includes a charge air cooler and a low-pressure circuit for partial recirculation of exhaust gases at the intake, called the "EGR" circuit ("exhaust gas recirculation" in Anglo-Saxon terms). The low-pressure EGR circuit allows burnt gases from combustion to be re-injected into the intake and reintroduced upstream of the supercharger.

These inert gases make it possible in particular to increase the total mass of gas admitted into the combustion chamber in a gasoline engine, which reduces the need to lower the pressure of the intake manifold to manage the air load. This limits pumping losses and improves combustion. On the other hand, mainly in Diesel engines, the partial readmission of burnt gases makes it possible to cool the combustion temperature and intrinsically reduce nitrogen oxide emissions.

However, using a low-pressure EGR circuit leads to problems with water condensation in the engine intake circuit. This water generally comes from the humidity in the fresh air arriving from the fresh air intake and/or from the water vapor contained in the exhaust gases recirculated by the low-pressure EGR circuit.

This condensed water can then lead to:

- the projection of liquid water droplets upstream of the compressor and generating premature wear of the wheel of said compressor;

- water storage in low points of the intake circuit causing corrosion problems, for example the charge air cooler or the EGR cooler.

- the formation of ice in the intake circuit in extreme ambient conditions, either during the driving phase or when the engine is cooling down when stationary. Slow progressive storage concomitant with freezing can then lead to ice build-up. When the ambient temperature rises above 0°C, this ice turns into liquid, which in turn can cause corrosion or premature wear of the compressor wheel. This water can also be sucked into the engine, particularly during the engine start-up phase, and damage it.

Furthermore, during operating phases that promote water condensation, for example due to environmental conditions, such as high ambient humidity and/or low ambient temperature, or due to engine operation, the water vapour contained in the fresh air and EGR gas mixture is likely to condense in the intake circuit and in particular on the surface of the charge air cooler.

This water is stored in the cooler and can be desorbed, which can disrupt the combustion of the engine or even shut it down.

Document US 20200182204 is known, which proposes a method for controlling the EGR circuit valve using a humidity sensor in order to prevent condensation in the intake circuit. According to this method, the humidity of the intake air is measured, a molar fraction of water vapor included in the intake air is determined, the water vapor pressure in the EGR circuit is determined and an EGR valve is opened so that the EGR gases flow when the water vapor in the EGR circuit is lower than the saturated water vapor pressure in the EGR circuit. This document proposes a variant in which the flow rate of a coolant in the EGR cooler is increased before opening the EGR valve.

Also known is document US 20140102428 which proposes a method for increasing the flow rate of exhaust gas recirculation EGR when the estimated amount of condensate accumulated in an EGR cooler exceeds a threshold. Said estimated amount of accumulated condensate is estimated based on an amount of condensate evaporated using a condensation model. This document proposes a variant in which the flow rate of a coolant in the EGR cooler is increased.

However, these solutions have the effect of limiting the flow of liquid water entering the engine resulting from stabilized conditions, or even the flow of water stored in the EGR cooler. None of these solutions concern unstabilized, i.e. transient, operation of the engine.

These solutions therefore do not effectively address the problem of water storage in the charge air cooler which may be followed by a sudden release phenomenon, particularly during a sharp increase in the flow rate of the EGR air and gas mixture drawn in by the engine, for example, following a request for full load when the driver presses the accelerator pedal. This sudden release of liquid water into the combustion chamber can lead to combustion extinction, i.e. the absence of torque production or combustion misfires, known as "misfire" in English terms, which can ultimately damage the engine or some of its associated components such as a pollution control catalyst.

There is a need to improve the management of liquid water storage and desorption in the intake circuit, and more particularly in the charge air cooler of a supercharged air internal combustion engine.

The object of the present invention is therefore to provide a method and an engine control system configured to manage the storage and desorption of liquid water in the charge air cooler.

The present invention relates to a method for controlling an internal combustion engine comprising at least one cylinder, a fresh air intake manifold supplied with fresh air by a pipe provided with a flow meter, a compressor, a turbocharger and a heat exchanger or charge air cooler downstream of said compressor and upstream of the intake manifold.

The engine further comprises an exhaust circuit comprising, from upstream to downstream in the direction of circulation of the burnt gases, an exhaust manifold, a turbocharger turbine and a system for depolluting the combustion gases of the engine, and a circuit for partial recirculation of the exhaust gases to the intake originating at a point in the exhaust circuit, downstream of said turbine, and in particular downstream of the system or part of the gas depolluting system and opening into the fresh air supply line, upstream of the compressor of the turbocharger, said partial EGR recirculation circuit comprising an EGR adjustment valve.

During the method, the mass of liquid water stored in real time on internal walls of the exchanger is estimated; a difference in water masses between the mass of water and a predetermined critical mass of liquid water is determined; and the maximum mass of water that can be stored by the exchanger is managed when the absolute value of said difference is less than a threshold value by reducing an EGR rate by controlling the EGR adjustment valve and/or by reducing the flow rate of a cooling fluid passing through the exchanger by controlling a pump configured to circulate the cooling fluid in the exchanger and/or by increasing the temperature of the cooling fluid of the exchanger.

Thus, the process solves the problem of progressive condensation of liquid water in the charge air cooler in order to avoid any risk of rapid desorption and extinction of the engine combustion.

Generally, the control method of a supercharged internal combustion engine is configured to manage the storage and desorption of liquid water in a charge air cooler.

Liquid water can be stored temporarily in the charge air cooler without risk to the engine, provided there is a balance between:

- condensation of the fresh air and EGR gas mixture on the internal walls of the charge air cooler;

- evaporation of liquid water deposited on the internal walls of the charge air cooler; and

- the flow rate of the fresh air and EGR gas mixture passing through the charge air cooler.

The method according to the invention makes it possible to create a balance between these different points.

The water mass estimation step makes it possible to determine the mass of water that the exchanger is capable of temporarily storing without desorption towards the combustion chambers.

Reducing the flow rate of a cooling fluid passing through the exchanger has the effect of increasing the temperature of the internal walls of the exchanger and therefore of promoting the evaporation of the water stored on said walls and of increasing the temperature of the mixture of air and EGR gas passing through said exchanger, which increases the speed of evaporation of the water stored in the exchanger.

Increasing the temperature of the coolant flowing through the exchanger can be achieved, in particular using a controlled thermostat allowing the liquid to circulate or not in a radiator, in order to increase the temperature of the walls of the exchanger.

Advantageously, the step of estimating the mass of liquid water stored in real time on the internal walls of the exchanger includes:
- a step of estimating the mass flow rate of water vapour contained in the fresh air admitted as a function of the temperature of the fresh air admitted, the air flow rate and an estimate of the ambient relative humidity, for example either via a hygrometry rate sensor placed in the intake circuit, for example in the flow meter, or outside the vehicle, or by a meteorological service, in particular if the vehicle is a so-called "connected"vehicle;
- a step of estimating the mass flow rate of water vapor contained in the exhaust gases as a function of the flow rate of fresh air, a flow rate of injected fuel, an average composition of said fuel and a combustion richness;
- a step of estimating the mass flow rate of water vapor in the partial recirculation EGR conduit as a function of the mass flow rate of water vapor contained in the exhaust gases and the EGR rate;
- a step of estimating the mass flow rate of water vapor contained in the mixture of fresh air and EGR burnt gases upstream of the air compressor, as equal to the sum of the mass flow rate of water vapor contained in the fresh air admitted and the mass flow rate of water vapor in the EGR duct;
- a step of estimating the mass flow rate of liquid water condensing on the internal walls of the exchanger as a function of the mass flow rate of water vapor contained in the mixture of fresh air and burnt gases EGR upstream of the air compressor, of the temperature of said internal walls, for example through a measurement of the temperature of the coolant flowing through said exchanger, via one or more sensors arranged upstream and/or downstream of said exchanger, and of a value of the supercharging pressure; and
- a step of estimating the mass of liquid water stored on the surface of the internal walls of the exchanger as a function of the difference in mass flow rates between the mass flow rate of liquid water condensing on the internal walls of the exchanger and a mass flow rate of water evaporated in the exchanger which is determined as a function of the temperature of the gases passing through the exchanger and the mass flow rate of the engine.

For example, engine mass flow is dependent on air flow, fuel flow, and EGR rate.

For example, the liquid water mass estimation step receives a time integral of the difference in mass flow rates between the mass flow rate of liquid water condensing on the internal walls of the exchanger and the mass flow rate of water evaporating in the exchanger.

Said time integral of the difference in mass flow rates is permanently saturated by a predetermined maximum limit corresponding to the maximum mass of liquid water storable in the exchanger taking into account the current volume flow rate of the gases passing through said exchanger.

Indeed, depending on the geometry of the exchanger, its inclination, the material constituting its exchange surface on the gas side, each value of current volume flow, i.e. instantaneous, of gas passing through it determines a maximum limit, i.e. a maximum mass of liquid water storable in the exchanger, which is characterizable.

For example, in order to determine the maximum limit, the dry exchanger is weighed; the volume usually covered by the flow of air and EGR gas mixture passing through the exchanger is completely filled with water; and, the said exchanger is installed on a test bench and a constant air flow is blown through it until the mechanical evacuation of the water it contains, without waiting for the water to evaporate. The exchanger is then weighed to estimate the mass of water it has retained.

Advantageously, the step of estimating the mass of liquid water stored in real time comprises a step of estimating a volume flow rate of the engine as a function of the temperature of the gases passing through the exchanger, the maximum limit being determined as a function of said volume flow rate.

Advantageously, during the step of determining the difference in water masses between the water mass and the critical liquid water mass, the critical water mass is determined, which is defined as the minimum water mass that would lead to the extinction of the combustion if it reached the combustion chambers, and the subtraction between the water mass and said critical water mass is carried out.

The critical water mass corresponds to the mass of water which poses the risk of combustion extinction if a desorption phenomenon were to occur, for example in the event of a sharp increase in the air flow admitted by the engine, following an acceleration request, for example, which reduces the maximum limit, i.e. the maximum mass of liquid water storable in the exchanger.

The critical water mass can be estimated by testing on a stationary engine test bench, by injecting an increasing mass of liquid water into the cylinder intake and measuring the internal combustion pressure. Then, the maximum permissible liquid water mass per individual combustion cycle and per cylinder, and the maximum permissible liquid water mass for the engine, taking into account its dynamics, are deduced.

For example, the EGR rate setpoint reduction is continuous, i.e. applied throughout the use of the engine as a maximum limit not to be exceeded or applied punctually for a specific duration in order to punctually reduce the mass of liquid water stored in real time on the internal walls of the exchanger.

For example, the reduction in the flow rate of the coolant flowing through the exchanger is continuous, i.e. applied throughout the use of the engine as a maximum limit not to be exceeded or applied punctually for a specific duration in order to punctually reduce the mass of liquid water stored in real time on the internal walls of the exchanger.

For example, the increase in the temperature of the flow of coolant passing through the exchanger is continuous, i.e. applied throughout the use of the engine as a maximum limit not to be exceeded, or applied punctually for a specific duration in order to punctually reduce the mass of liquid water stored in real time on the walls of the exchanger.

According to an embodiment in which the motor vehicle is a hybrid vehicle comprising a heat engine and at least one electric motor, the step of managing the maximum mass of water storable by the exchanger comprises a step of controlling the speed and torque of the electric motor to increase the flow rate sucked in by the heat engine so as to punctually evacuate the film of water stored on the walls of the exchanger.

According to a second aspect, the invention relates to an electronic control unit for an internal combustion engine comprising at least one cylinder, a fresh air intake manifold supplied with fresh air by a pipe provided with a flow meter, a compressor, a turbocharger and a heat exchanger downstream of said compressor and upstream of the intake manifold.

The engine further comprises an exhaust circuit comprising, from upstream to downstream in the direction of circulation of the burnt gases, an exhaust manifold, a turbocharger turbine and a system for depolluting the combustion gases of the engine, and a circuit for partial recirculation of the exhaust gases to the intake originating at a point in the exhaust circuit, downstream of said turbine, and in particular downstream of the system or part of the gas depolluting system, and opening into the fresh air supply line, upstream of the turbocharger compressor, said partial EGR recirculation circuit comprising an EGR adjustment valve.

The electronic control unit includes an engine control system comprising:
- a module for estimating the mass of liquid water stored in real time on the internal walls of the exchanger;
- a module for determining a water mass difference between the water mass and a predetermined critical liquid water mass; and
- a module for managing the maximum water mass storable by the exchanger configured to reduce an EGR rate by controlling the EGR adjustment valve and/or reduce the flow rate of a cooling fluid passing through the exchanger by controlling a pump configured to circulate the cooling fluid in the exchanger and/or increase the temperature of the cooling fluid of the exchanger, when the absolute value of the difference in water masses is less than a threshold value.

Typically, the control system of a supercharged internal combustion engine is configured to manage the storage and desorption of liquid water in a charge air cooler.

Advantageously, the module for estimating the mass of liquid water stored in real time on the internal walls of the exchanger is configured to estimate the mass flow rate of water vapor contained in the fresh air admitted as a function of the temperature of the fresh air admitted, the air flow rate obtained by the flow meter, and an estimate of the ambient relative humidity, either through a hygrometry rate sensor arranged in the intake circuit, for example in the flow meter, or outside the vehicle, or by a meteorological service, in particular if the vehicle is a so-called “connected” vehicle.

Advantageously, the module for estimating the mass of stored liquid water is also configured to estimate the flow rate of water vapor contained in the exhaust gases as a function of the flow rate of fresh air, the flow rate of injected fuel, the average composition of said fuel and the combustion richness, and to deduce therefrom the mass flow rate of water vapor in the EGR conduit as a function of said flow rate of water vapor contained in the exhaust gases and the EGR rate.

Advantageously, the module for estimating the mass of stored liquid water is also configured to estimate the mass flow rate of water vapor contained in the mixture of fresh air and EGR burnt gases upstream of the air compressor by summing the mass flow rate of water vapor contained in the fresh air admitted and the mass flow rate of water vapor in the EGR conduit.

Advantageously, the module for estimating the mass of stored liquid water is also configured to estimate the mass flow rate of liquid water condensing on the internal walls of the exchanger as a function of said mass flow rate of water vapor contained in the mixture of fresh air and burnt gases upstream of the air compressor, of the temperature of said internal walls, for example through a measurement of the temperature of the coolant flowing through said exchanger, via one or more sensors arranged upstream and/or downstream of said exchanger, and of a boost pressure value.

Advantageously, the module for estimating the mass of stored liquid water is also configured to estimate the mass flow rate of the engine as a function of the air flow rate, the fuel flow rate and the EGR rate and to deduce therefrom an estimate of the mass of water evaporated in the exchanger and an estimate of the volume flow rate of the engine as a function of the temperature of the gases passing through the exchanger.

For example, the stored liquid water mass estimation module is also configured to estimate the mass of liquid water stored on the surface of the internal walls of the exchanger as the integral of the difference between the mass flow rate of liquid water condensing on the internal walls of the exchanger and the mass flow rate of water evaporated in the exchanger.

Advantageously, the integral is permanently saturated by a maximum limit corresponding to the maximum capacity of water storable in the exchanger taking into account the current volume flow rate of the gases passing through the exchanger.

The water mass estimation module allows to determine the mass of liquid water that the exchanger is capable of temporarily storing without desorption towards the combustion chambers.

This mass of stored liquid water is all the more critical when the ambient humidity is high, the EGR rate is high, the boost pressure is high, the temperature of the coolant flowing through the exchanger is low and the flow rate of the mixture of air and EGR gas passing through said exchanger and entering the combustion chambers is low.

Advantageously, the management module is configured to control the various actuators of the internal combustion engine when the absolute value of said water mass difference is less than a threshold value, i.e. when the stored liquid water mass is too close to the critical water mass and runs the risk of combustion extinction if a desorption phenomenon were to occur, for example in the event of a sharp increase in the air flow admitted by the engine, following an acceleration request, for example.

According to another aspect, the invention relates to a motor vehicle comprising an electronic control unit as described above.

Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely as a non-limiting example, and made with reference to the appended drawings in which:

represents, in a very schematic manner, an example of the structure of an internal combustion engine of a motor vehicle comprising a control unit comprising a control system according to the invention;

represents a curve illustrating the evolution of the maximum mass of liquid water storable in the exchanger as a function of the volume flow rate of the engine;

represents the synopsis of a control method according to the invention implemented by the control system of the ; And

illustrates in detail the mass estimation step of the process of the .

On the , the general structure of an internal combustion engine 10, in particular of the spark-ignition type running on gasoline, of a motor vehicle is shown schematically. Alternatively, it may be a Diesel type engine.

These architectures are given as examples and do not limit the invention to the sole configuration to which the motor control according to the invention can be applied.

In the illustrated example, the internal combustion engine 10 comprises, in a non-limiting manner, three in-line cylinders 12, a fresh air intake manifold 14, an exhaust manifold 16 and a turbo-compression system 18.

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.

Each cylinder 12 is supplied with fuel, for example gasoline.

In a known manner, the turbocharger 18 essentially comprises a turbine 18a driven by the exhaust gases and a compressor 18b mounted on the same axis or 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 rate) of air admitted into the cylinders 12 of the engine 10. The turbine 18a may be of the “variable geometry” type, that is to say that the turbine wheel is equipped with blades with variable inclination in order to modulate the quantity of energy taken from the exhaust gases, and thus the boost pressure.

A heat exchanger 30 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 thus comprises an intake circuit Ca, an exhaust circuit Ce and a fuel injection circuit (not shown).

The intake circuit Ca includes, from upstream to downstream in the direction of air circulation:

- air filter 22 or air box;

- a flow meter 24 arranged in the intake duct 20 downstream of the air filter 22; the flow meter 24 being configured to measure the actual value of the air flow entering the engine 10. The flow meter 26 only measures the flow of fresh air alone;

- an air intake valve 26, comprising, for example, a position sensor (not shown);

- the compressor 18b of the turbocharger 18 configured to compress the air taken from the outside atmosphere and, where appropriate, recycled exhaust gases at low pressure, as will be described later;

- a 28 butterfly housing or a gas intake valve in the engine;

- the heat exchanger 30 configured to cool the intake gases corresponding to a mixture of fresh air and recycled gases, after their compression in compressor 18b; and

- the intake manifold 14.

The heat exchanger 30 is a cooler of the so-called “supercharged” intake gases, corresponding, here, to an air-water exchanger, called “water charged air cooler” in Anglo-Saxon terms. The terms “heat exchanger 30” and “supercharge air cooler 30” designate, subsequently, the same element. Alternatively, it may be an air-air cooler.

The exhaust circuit This includes, from upstream to downstream in the direction of flow of burnt gases:

- the exhaust manifold 16;

- the turbine 18a of the turbocharger 18 configured to draw energy from the exhaust gases passing through it, said expansion energy being transmitted to the compressor 18b via the common shaft, for the compression of the intake gases;

- a 40 system for depolluting the engine combustion gases.

With regard to the exhaust manifold 16, the latter recovers the exhaust gases resulting from the combustion and evacuates them to the outside, via a gas exhaust duct 30 opening onto the turbine 18a of the turbocharger 18 and via an exhaust line 36 mounted downstream of said turbine 18a.

By way of non-limiting example, the system 40 for depolluting the combustion gases of the engine comprises a first device 42 comprising a three-way catalyst 42a associated with a first oxygen sensor 43a, of the proportional type, mounted upstream of the first depollution device 42, that is to say upstream of said catalyst 42a.

In a manner known per se, the first upstream oxygen sensor 43a is generally used to regulate in a closed loop the value of the richness of the air-fuel mixture in the engine around a set value, for example the value 1 corresponding to an air-fuel mixture in stoichiometric proportions. By “richness” is meant the ratio between the mass flow rate of fuel and the mass flow rate of air, divided by the ratio between the mass flow rate of fuel and the air flow rate in stoichiometric proportions.

Furthermore, a second oxygen sensor 43b, for example of the binary or proportional type, is most frequently mounted downstream of the first pollution control device 42 so as to be able to correct said setpoint value of the aforementioned richness regulation loop, in particular for the purpose of adjusting the quantity of oxygen stored inside the first pollution control device 42. However, the presence of this second downstream sensor is not essential to the implementation of the invention.

The gas depollution system 40 further comprises a second device 44 which is here a fine particle filter, and an exhaust pipe 45 mounted at the outlet of the second depollution device 44 and opening outwards. The gas depollution system 40 may also comprise a third oxygen probe 43c, for example of the binary type, mounted downstream of the second device 44, for example for diagnostic purposes.

As illustrated, the engine 10 includes a partial recirculation circuit 38 of the exhaust gases at the intake, called the “EGR” circuit (“exhaust gas recirculation” in Anglo-Saxon terms).

This circuit 38, here a low-pressure exhaust gas recirculation circuit, called “EGR BP”, originates at a point on the exhaust line 36, here, in the exhaust pipe 45, downstream of said turbine 18a, and in particular, in the case of the , downstream of the gas depollution system 40 and returns the exhaust gases to a point in the fresh air supply line 20, upstream of the compressor 18b of the turbocharger 18, in particular downstream of the intake valve 26.

In a variant not shown, the low-pressure exhaust gas recirculation circuit could originate at the outlet of the turbine 18a, or downstream of only part of the gas depollution system 40, for example between the first and second depollution devices 42, 44.

As illustrated, this recirculation circuit 38 comprises, in the direction of circulation of the recycled gases, a cooler 38a of the EGR gases, a filter 38b, and a “V EGR BP” adjustment valve 38c configured to regulate the flow rate of the low-pressure exhaust gases. The “V EGR BP” valve 38c is arranged downstream of the cooler 38a and upstream of the compressor 18b.

By way of non-limiting example, 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 50.

The engine may also comprise, in a non-limiting manner, a fuel vapor purge circuit 60 comprising a canister 62 or fuel vapor reservoir 62 receiving fuel vapors from the fuel tank 50, an active pump 64 connected downstream of the canister 62 and a purge solenoid valve 66 connected downstream of the pump 64. The purge solenoid valve 66 is connected to the engine intake, downstream of the flow meter 24.

The engine comprises an electronic control unit ECU comprising a control system 70 configured to control the various elements of the internal combustion engine and in particular the EGR rate Tx_EGR, the flow rate of the coolant Q_WCAC passing through the exchanger 30 (water, in the case of an air-water exchanger) and the temperature T_WCAC of the coolant of the exchanger 30.

The control system 70 receives data collected by sensors at different locations of the engine or estimated.

The control system 70 could receive other data, such as temperatures at different locations in the engine, or other pressures.

The control system 70 comprises a module 72 for estimating the mass M_eau of liquid water stored in real time on the internal walls of the exchanger 30.

The module 72 for estimating the mass M_water of liquid water stored in real time on the internal walls of the exchanger 30 is configured to estimate the mass flow rate Q_M_vapor_A of water vapor contained in the fresh air admitted as a function of the air temperature T_fresh air admitted, of the air flow rate Qair obtained by the flow meter 24, and of an estimate of the ambient relative humidity H, either through a hygrometry rate sensor arranged in the intake circuit Ca, for example in the flow meter 24, or outside the vehicle, or by a meteorological service, in particular if the vehicle is a so-called “connected” vehicle.

The module 72 is also configured to estimate the mass flow rate Q_M_vapor_E of water vapor contained in the exhaust gases, more precisely in the entire flow rate of combustion gases emitted by the engine before a portion is taken to be recycled to the intake, as a function of the fresh air flow rate Qair, the injected fuel flow rate Qcarb, the average composition of said fuel carb and the combustion richness, and it is configured to deduce therefrom the mass flow rate Q_M_vapor_EGR of water vapor in the EGR duct 38 as a function of said mass flow rate Q_M_vapor_E of water vapor contained in the exhaust gases and the EGR rate Tx_EGR.

The module 72 is also configured to estimate the mass flow rate Q_M_vapor_Ca of steam contained in the mixture of fresh air and EGR burnt gases upstream of the air compressor 18b, as equal to the sum ΣQ_M of the mass flow rate Q_M_vapor_A of water vapor contained in the fresh air admitted and the mass flow rate Q_M_vapor_EGR of water vapor in the EGR conduit 38.

The module 72 is also configured to estimate the mass flow rate Q_M_WCAC of liquid water condensing on the internal walls of the exchanger 30 as a function of the mass flow rate Q_M_vapor_Ca of vapor contained in the mixture of fresh air and burnt gases EGR upstream of the air compressor 18b, of the temperature T_WCAC of said internal walls, for example through a measurement of the temperature of the coolant flowing through said exchanger 30, via one or more sensors arranged upstream and/or downstream of said exchanger 30, and of a boost pressure value Psuralim.

The module 72 is also configured to estimate the mass flow rate Q_M of the engine as a function of the air flow rate Qair, the fuel flow rate Qcarb and the EGR rate Tx_EGR, and to deduce therefrom an estimate of the mass flow rate Q_M_eau_evap of water evaporated in the exchanger 30 and an estimate of the volume flow rate Q_V of the engine as a function of the temperature T_gaz_WCAC of the gases passing through the exchanger 30.

The module 72 is also configured to estimate the mass M_eau of liquid water stored on the surface of the internal walls of the exchanger 30 as being equal to the time integral ∫ΔQ_M of the difference between the mass flow rate Q_M_WCAC of liquid water condensing on the internal walls of the exchanger 30 and the mass flow rate Q_M_eau_evap of water evaporated in the exchanger 30.

The time integral ∫ΔQ_M is permanently saturated by a maximum limit M_eau_max corresponding to the maximum mass of liquid water storable in the exchanger 30 taking into account the volume flow rate of the gases (air and EGR gas) passing through the exchanger 30.

Indeed, depending on the geometry of the exchanger 30, its inclination, the material constituting its exchange surface on the gas side, it is possible to characterize the maximum mass of liquid water storable by said exchanger 30 as a curve which is a decreasing function of the volume flow rate of gas passing through it. In the usual case where the entire volume flow rate of compressed intake gas in the compressor 18b is then cooled, this through volume flow rate coincides with the volume flow rate Q_V of the engine.

In order to determine the maximum mass M_eau_max of liquid water that can be stored in the exchanger, the exchanger 30 is weighed in the dry state, the volume usually traveled by the mixture of air and EGR gas is completely filled with water, said exchanger 30 is installed on a test bench and a constant air flow is blown through it until the mechanical evacuation of the water it contains, without waiting for the water to evaporate. The exchanger 38 is then weighed to estimate the mass of water that it has retained. This mass corresponds to the maximum mass M_eau_max of liquid water that can be stored, for the constant air flow considered.

We can deduce a curve which looks like that of the , on which the abscissa represents the volume flow rate passing through the exchanger Q_V and the ordinate represents the maximum mass M_eau_max of liquid water storable in the exchanger.

Note that, since this is a strictly decreasing curve, each time the volume flow rate Q_V crossing increases, for example by going from a value Q_V (A) corresponding to the abscissa of a point A on the , for which the mass of water M_liquid water stored is not necessarily already saturated by the maximum mass M_water_max of storable liquid water, up to a value Q_V (B) corresponding to the abscissa of a point B on the , a mass of water corresponding to the difference between the mass of water M_liquid water stored in real time corresponding to point A and the maximum mass M_water_max (B) of liquid water corresponding to the volume flow rate of point B is released downstream of the exchanger. In particular, in the case where the flow rate increases abruptly to the maximum value of the engine flow rate Q_V (Pmax) which is that of the full load point at the maximum power of the engine, represented by point Pmax on the , the maximum mass M_liquid water stored in the exchanger decreases very sharply up to the maximum mass M_water_max (Pmax) of storable liquid water of the maximum power point Pmax. And, this release of liquid water becomes dangerous in the case where the quantity released is greater than the critical mass of liquid water likely to extinguish the combustion, or too close to it.

The module 72 for estimating the mass M_eau of liquid water makes it possible to determine the mass of water that the exchanger 30 is capable of temporarily storing without desorption towards the combustion chambers.

This mass of stored liquid water is all the more critical as the ambient humidity is high, the EGR rate is high, the boost pressure is high, the temperature of the coolant flowing through the exchanger 30 is low and the flow rate of the mixture of air and EGR gas passing through said exchanger 30 and entering the combustion chambers is low.

Indeed, the mass of liquid water stored on the internal walls of the exchanger 30 is not problematic as long as it remains stored, but becomes problematic following a strong and rapid increase in the flow rate of the mixture of air and EGR gas passing through the exchanger 30, for example linked to a high load demand, associated with a downshift leading to an increase in torque and speed, with pressing the accelerator pedal, etc. The stored liquid water will then suddenly be desorbed from the walls of the exchanger 30 and introduced into the combustion chambers of the engine.

The control system 70 further comprises a module 74 for determining a difference in water masses ΔM_water between the liquid water mass M_water and a critical liquid water mass MC, corresponding to the minimum water mass which would lead to the extinction of the combustion if it reached the combustion chambers quickly.

The critical water mass MC corresponds to the mass of water which poses a risk of combustion extinction if a desorption phenomenon were to occur, for example in the event of a sharp increase in the air flow admitted by the engine, following an acceleration request, for example.

The critical water mass MC can be estimated by testing, on a stationary engine test bench, by injecting an increasing mass of liquid water into the cylinder intake and by measuring the internal combustion pressure which allows the indicated torque produced to be estimated. Then, the maximum admissible liquid water mass per combustion cycle and per cylinder, corresponding to a combustion defect, is deduced.

The critical water mass MC for the engine can then be deduced by knowing the dynamics of the engine, i.e. the duration, and therefore the number of combustion cycles which are necessary to reach the maximum power point.

The control system 70 further comprises a module 76 for managing the maximum mass of liquid water that can be stored by the exchanger 30. The management module 76 is configured to control the various actuators of the internal combustion engine when the absolute value abs(ΔM_water) of the difference ΔM_water is less than a calibratable threshold value S. This corresponds to the fact that the mass of liquid water that can be released, corresponding to the difference between the mass M_water of liquid water stored in real time and the maximum mass M_water_max (Pmax) of liquid water that can be stored at the maximum power point becomes equal to, or, taking into account a safety margin, becomes too close to the critical mass of water MC and runs the risk of extinction of the combustion if a desorption phenomenon were to occur, for example in the event of a sharp increase in the air flow admitted by the engine, following a request for acceleration to the maximum power of the engine, for example.

The management module 76 is notably configured to control the various actuators of the internal combustion engine in order to limit the mass of water stored in the exchanger 30.

Thus, the management module 76 is configured in particular to reduce the EGR rate setpoint Tx_EGR in order to bring less humidity, and therefore liquid water, to the intake in the exchanger 38. This reduction in the EGR rate setpoint can be continuous, that is to say applied throughout the use of the engine as a maximum limit not to be exceeded or applied punctually for a determined duration in order to punctually reduce the mass M_water of liquid water stored in real time on the internal walls of the exchanger 30.

The management module 76 is also configured to reduce the flow rate of the cooling fluid passing through the exchanger 30 by controlling a pump supplying said cooling fluid. This has the effect of increasing the temperature T_WCAC of the internal walls of the exchanger 30 and therefore promoting the evaporation of the water stored on said walls and increasing the temperature T_gaz_WCAC of the mixture of air and EGR gas passing through said exchanger 30, which increases the speed of evaporation of the water stored in the exchanger 30.

This reduction in the flow rate of the coolant flowing through the exchanger 30 may be continuous, i.e. applied throughout the use of the engine as a maximum limit not to be exceeded, or applied punctually for a determined duration in order to punctually reduce the mass M_eau of liquid water stored in real time on the internal walls of the exchanger 30.

Finally, the management module 76 is also configured to increase the temperature of the cooling fluid flowing through the exchanger 30, in particular using a controlled thermostat allowing the liquid to circulate or not in a radiator, in order to increase the temperature T_WCAC of the walls of the exchanger 30.

In the case where the motor vehicle is a hybrid vehicle comprising a thermal engine and at least one electric motor, the management module 76 is configured to control the speed N and the torque C of the electric motor to increase the flow rate sucked in by the thermal engine so as to punctually evacuate the film of water stored on the walls of the exchanger 30.

The management module 76 is therefore configured to choose, depending on the conditions and the operating point of the engine, one of the solutions making it possible to limit the mass of water stored in the exchanger 30.

Thus, if the need for intervention to contain the mass of water stored in real time appears at low load, and in the absence of a need to contain the intake temperature to limit knocking, or promote performance, we could for example prioritize increasing the temperature of the coolant flowing through the exchanger 30. At high load on the contrary, and to contain the intake temperature to limit knocking, or promote performance, we would prefer to reduce the EGR rate Tx_EGR setpoint. At low ambient temperature, and in the absence of risk on the cooling circuit, we would for example favor increasing the temperature of the coolant flowing through the exchanger 30, while at hot ambient temperature (or engine temperature) we would exclude this solution. It should be noted that the use of each of these solutions is possible individually or simultaneously.

The 100 motor control process, illustrated in detail on the , includes a step 102 of initializing the mass of water stored in the exchanger 30.

The engine control method 100 further comprises a step 110 of estimating the mass M_water of liquid water stored in real time on the internal walls of the exchanger 30, a step 125 of determining a difference in water masses ΔM_water between the water mass M_water and a critical liquid water mass MC corresponding to the minimum water mass that would lead to the combustion being extinguished if it reached the combustion chambers quickly, and a step 130 of managing the maximum water mass that can be stored by the exchanger 30 when the absolute value abs(ΔM_water) of the difference ΔM_water is less than a threshold value S. During the step 130 of managing the maximum water mass that can be stored by the exchanger 30, the various actuators of the internal combustion engine are controlled in order to limit the water mass stored in the exchanger 30, as will be described later.

Step 110 of estimating the mass M_water is detailed on the .

Step 110 of estimating the mass M_water of liquid water stored in real time on the internal walls of the exchanger 30 comprises a step 111 of estimating the mass flow rate Q_M_vapor_A of water vapor contained in the fresh air admitted as a function of the air temperature T_fresh air admitted, of the air flow rate Qair obtained by the flow meter 24, and of an estimation of the ambient relative humidity H, either through a hygrometry rate sensor arranged in the intake circuit Ca, for example in the flow meter 24, or outside the vehicle, or by a meteorological service, in particular if the vehicle is a so-called “connected” vehicle.

The step 110 of estimating the mass M_water further comprises a step 112 of estimating the mass flow rate Q_M_vapor_E of water vapor contained in the exhaust gases, considering the entire flow rate of combustion gases leaving the engine, as a function of the flow rate of fresh air Qair, the flow rate of injected fuel Qcarb, the average composition of said fuel carb and the combustion richness, and a step 113 of estimating the mass flow rate Q_M_vapor_EGR of water vapor in the EGR conduit 38 as a function of the mass flow rate Q_M_vapor_E of water vapor contained in the exhaust gases and the EGR rate Tx_EGR.

Step 110 of estimating the mass M_water further comprises a step 114 of estimating the mass flow rate Q_M_vapor_Ca of the mixture of fresh air and burnt gases EGR upstream of the air compressor 18b, as equal to the sum ΣQ_M, calculated in step 115, of the mass flow rate Q_M_vapor_A of water vapor contained in the fresh air admitted and of the mass flow rate Q_M_vapor_EGR of water vapor in the EGR conduit 38.

The step 110 of estimating the mass M_water further comprises a step 116 of estimating the mass flow rate Q_M_WCAC of liquid water condensing on the internal walls of the exchanger 30 as a function of said mass flow rate Q_M_vapor_Ca of the mixture of fresh air and burnt gases EGR upstream of the air compressor 18b, of the temperature T_WCAC of said internal walls, for example through a measurement of the temperature of the coolant flowing through said exchanger 30, via one or more sensors arranged upstream and/or downstream of said exchanger 30, and of a value of the boost pressure Psuralim.

The step 110 of estimating the mass M_water further comprises a step 117 of estimating the mass flow rate Q_M of the engine as a function of the air flow rate Qair, the fuel flow rate Qcarb and the EGR rate Tx_EGR, a step 118 of estimating the mass flow rate Q_M_water_evap of water evaporated in the exchanger 30 as a function of said mass flow rate Q_M of the engine and the temperature T_gas_WCAC of the gases passing through the exchanger 30, and a step 119 of estimating the volume flow rate Q_V of the engine as a function of said mass flow rate Q_M of the engine and the temperature T_gas_WCAC of the gases passing through the exchanger 30.

Step 110 of estimating the mass M_eau further comprises a step 120 of estimating the mass M_eau of liquid water stored on the surface of the internal walls of the exchanger 30 as being the time integral ∫ΔQ_M of the difference ΔQ_M between the mass flow rate Q_M_WCAC of liquid water condensing on the internal walls of the exchanger 30 and the mass flow rate Q_M_eau_evap of water evaporated in the exchanger 30. Said difference ΔQ_M is calculated in step 121.

The time integral ∫ΔQ_M is saturated by a maximum limit M_eau_max, calculated in step 122. The maximum limit M_eau_Max corresponds to the maximum mass of liquid water storable in the exchanger 30 taking into account the volume flow rate Q_V of the gases passing through the exchanger 30.

Indeed, depending on the geometry of the exchanger 30, its inclination, the material constituting its exchange surface on the gas side, it is possible to characterize the mass of water storable by said exchanger 30 as a curve depending on the gas flow rate Q_V passing through it.

The determination of the maximum limit M_eau_Max is described above and will not be repeated in the rest of the description.

Step 110 of estimating the mass M_eau of current liquid water makes it possible to determine the mass of water that the exchanger 30 is capable of temporarily storing without desorption towards the combustion chambers.

Step 125 of determining a difference ΔM_water between the mass of water M_water and a mass MC of critical liquid water comprises a step 126 of determining the critical mass of water MC corresponding to the minimum mass of water which would lead to the extinction of the combustion if it reached the combustion chambers quickly.

The critical water mass MC corresponds to the mass of water which poses a risk of combustion extinction if a desorption phenomenon were to occur, for example in the event of a sharp increase in the air flow admitted by the engine, following an acceleration request, for example, which suddenly causes the volume flow Q_V of the engine to change to the volume flow value of the full load point at maximum engine power.

The determination of critical water mass MC is described above.

Step 125 of determining a difference ΔM_water includes a step 127 of subtraction between the mass of water M_water and the mass MC of critical liquid water.

Step 130 of managing the maximum mass of water storable by the exchanger 30 comprises a step 131 of determining, as a function of the conditions and the operating point of the engine, one of the following choices making it possible to limit the mass of water stored in the exchanger 30.

Thus, if the need for intervention to contain the mass of water stored in real time appears at low load, and in the absence of a need to contain the intake temperature to limit knocking, or promote performance, we could for example prioritize increasing the temperature of the coolant flowing through the exchanger 30. At high load on the contrary, and to contain the intake temperature to limit knocking, or promote performance, we would prefer to reduce the EGR rate Tx_EGR setpoint. At low ambient temperature, and in the absence of risk on the cooling circuit, we would for example favor increasing the temperature of the coolant flowing through the exchanger 30, while at hot ambient temperature (or engine temperature) we would exclude this solution. Note that the use of each of these solutions is possible individually or simultaneously.

Step 130 of managing the maximum mass of water that can be stored by the exchanger 30 comprises a step 132 of reducing the EGR rate setpoint Tx_EGR in order to bring less humidity, and therefore liquid water, to the intake into the exchanger 38. This reduction in the EGR rate setpoint can be continuous, i.e. applied throughout the use of the engine as a maximum limit not to be exceeded, or applied punctually for a determined duration in order to punctually reduce the mass M_water of liquid water stored in real time on the internal walls of the exchanger 30.

Step 130 of managing the maximum mass of water that can be stored by the exchanger 30 comprises a step 133 of reducing the flow rate of the cooling fluid passing through the exchanger 30 by controlling a pump supplying said cooling fluid. This has the effect of increasing the temperature T_WCAC of the internal walls of the exchanger 30 and therefore promoting the evaporation of the water stored on said walls and increasing the temperature T_gaz_WCAC of the mixture of air and EGR gas passing through said exchanger 30, which increases the speed of evaporation of the water stored in the exchanger 30.

This reduction in the flow rate of the coolant flowing through the exchanger 30 may be continuous, i.e. applied throughout the use of the engine as a maximum limit not to be exceeded, or applied punctually for a determined duration in order to punctually reduce the mass M_eau of liquid water stored in real time on the internal walls of the exchanger 30.

Finally, step 130 of managing the maximum mass of water storable by the exchanger 30 comprises a step 134 of increasing the temperature of the cooling fluid flowing through the exchanger 30, in particular using a controlled thermostat allowing the liquid to be circulated or not in a radiator, in order to increase the temperature T_WCAC of the walls of the exchanger 30.

In the case where the motor vehicle is a hybrid vehicle comprising a heat engine and at least one electric motor, the step 130 of managing the maximum mass of water storable by the exchanger 30 comprises a step 135 of controlling the speed N and the torque C of the electric motor to increase the flow rate sucked in by the heat engine so as to punctually evacuate the film of water stored on the walls of the exchanger 30.

Steps 132, 133 and 134 can be activated separately or at the same time.

During step 130 of managing the maximum mass of water storable by the exchanger 30, it is possible to control the EGR rate Tx_EGR and/or the flow rate of the cooling fluid Q_WCAC passing through the exchanger 30 and/or the temperature T_WCAC of the cooling fluid of the exchanger 30 and/or in the case of a hybrid vehicle, control the speed N and the torque C of the electric motor, these actions being cumulative.

Thanks to the invention, it is possible to solve the problem of progressive condensation of liquid water in the charge air cooler in order to avoid any risk of rapid desorption and extinction of the engine combustion.

Claims (11)

Method (100) for controlling an internal combustion engine (10) comprising at least one cylinder (12), a fresh air intake manifold (14) supplied with fresh air by a pipe (20) provided with a flow meter (24), a compressor (18b), a turbocharger (18) and a heat exchanger (30) downstream of said compressor (18b) and upstream of the intake manifold (14), the engine further comprising an exhaust circuit (Ce) comprising, from upstream to downstream in the direction of circulation of the burnt gases, an exhaust manifold (16), a turbine (18a) of the turbocharger (18) and a system (40) for depolluting the combustion gases of the engine, and a partial recirculation circuit (38) of the exhaust gases at the intake originating at a point in the exhaust circuit (Ce), downstream of said turbine (18a), and opening into the pipe (20) for supplying fresh air, upstream of the compressor (18b) of the turbocharger (18), said partial EGR recirculation circuit (38) comprising an EGR adjustment valve (38c), in which:
- the mass (M_water) of liquid water stored in real time on the internal walls of the exchanger (30) is estimated;
- a water mass difference (ΔM_water) is determined between the water mass (M_water) and a predetermined critical liquid water mass (MC); and
- the maximum mass of water that can be stored by the exchanger (30) is managed when the absolute value of said difference (abs(ΔM_water)) is less than a threshold value (S) by reducing an EGR rate (Tx_EGR) by controlling the EGR adjustment valve (38c) and/or by reducing the flow rate of a cooling fluid (Q_WCAC) passing through the exchanger (30) by controlling a pump configured to circulate the cooling fluid in the exchanger (30) and/or by increasing the temperature (T_WCAC) of the cooling fluid of the exchanger (30). Method according to claim 1, in which the step (110) of estimating the mass (M_water) of liquid water stored in real time on the internal walls of the exchanger (30) comprises:
- a step (111) of estimating the mass flow rate (Q_M_vapor_A) of water vapor contained in the fresh air admitted as a function of the fresh air temperature (T_air) admitted, the air flow rate (Qair) and an estimate of the ambient relative humidity (H);
- a step (112) of estimating the mass flow rate (Q_M_vapor_E) of water vapor contained in the exhaust gases as a function of the fresh air flow rate (Qair), a flow rate of injected fuel (Qcarb), an average composition of said fuel (carb) and a combustion richness;
- a step (113) of estimating the mass flow rate (Q_M_vapor_EGR) of water vapor in the partial recirculation EGR conduit (38) as a function of the flow rate (Q_M_vapor_E) of water vapor contained in the exhaust gases and the EGR rate (Tx_EGR);
- a step (114) of estimating the mass flow rate (Q_M_vapeur_Ca) of water vapor contained in the mixture of fresh air and EGR burnt gases upstream of the air compressor (18b) as equal to the sum (ΣQ_M) of the mass flow rate (Q_M_vapeur_A) of water vapor contained in the fresh air admitted and the mass flow rate (Q_M_vapeur_EGR) of water vapor in the EGR conduit (38);
- a step (116) of estimating the mass flow rate (Q_M_WCAC) of liquid water condensing on the internal walls of the exchanger (30) as a function of the mass flow rate (Q_M_vapeur_Ca) of water vapor contained in the mixture of fresh air and burnt gases EGR upstream of the air compressor (18b), of the temperature (T_WCAC) of said internal walls, and of a boost pressure value (Psuralim); and
- a step (120) of estimating the mass (M_eau) of liquid water stored on the surface of the internal walls of the exchanger (30) as a function of the difference in mass flow rates (ΔQ_M) between the mass flow rate (Q_M_WCAC) of liquid water condensing on the internal walls of the exchanger (30) and a mass flow rate (Q_M_eau_evap) of water evaporated in the exchanger (30) which is determined as a function of the temperature (T_gaz_WCAC) of the gases passing through the exchanger (30) and the mass flow rate (Q_M) of the engine. Method according to claim 2, in which the step (120) of estimating the mass (M_eau) of liquid water receives a time integral (∫ΔQ_M) of the difference in mass flow rates (ΔQ_M) between the mass flow rate (Q_M_WCAC) of liquid water condensing on the internal walls of the exchanger (30) and the mass flow rate (Q_M_eau_evap) of water evaporated in the exchanger (30). Method according to claim 3, in which the time integral (∫ΔQ_M) of the difference in mass flow rates (ΔQ_M) is permanently saturated by a predetermined maximum limit (M_eau_max) corresponding to the maximum mass of liquid water storable in the exchanger (30) taking into account the current volume flow rate of the gases passing through said exchanger (30). Method according to claim 4, in which the step (110) of estimating the mass (M_eau) of liquid water stored in real time comprises a step (119) of estimating a volume flow rate (Q_V) of the engine as a function of the temperature (T_gaz_WCAC) of the gases passing through the exchanger (30) and in which the maximum limit (M_eau_max) is determined as a function of said volume flow rate (Q_V). Method according to any one of the preceding claims, in which during the step (125) of determining the difference in water masses (ΔM_water) between the water mass (M_water) and the critical liquid water mass (MC), the critical water mass (MC) corresponding to the minimum liquid water mass which would lead to the extinction of the combustion if it reached the combustion chambers is determined in step (126), and the subtraction between the water mass (M_water) and said critical water mass (MC) is carried out. Method according to any one of the preceding claims, in which the reduction of the EGR rate setpoint (Tx_EGR) is continuous or applied punctually for a determined duration. Method according to any one of the preceding claims, in which the reduction in the flow rate of the cooling fluid passing through the exchanger (30) is continuous or applied punctually for a determined duration. Method according to any one of the preceding claims, in which the motor vehicle is a hybrid vehicle comprising a heat engine and at least one electric motor, and in which the step (130) of managing the maximum mass of water storable by the exchanger (30) comprises a step (135) of controlling the speed (N) and the torque (C) of the electric motor to increase the flow rate sucked in by the heat engine. Electronic control unit (ECU) of an internal combustion engine (10) comprising at least one cylinder (12), a fresh air intake manifold (14) supplied with fresh air by a pipe (20) provided with a flow meter (24), a compressor (18b), a turbocharger (18) and a heat exchanger (30) downstream of said compressor (18b) and upstream of the intake manifold (14), the engine further comprising an exhaust circuit (Ce) comprising, from upstream to downstream in the direction of circulation of the burnt gases, an exhaust manifold (16), a turbine (18a) of the turbocharger (18) and a system (40) for depolluting the combustion gases of the engine, and a partial recirculation circuit (38) of the exhaust gases at the intake originating at a point in the exhaust circuit (Ce), downstream of said turbine (18a), and opening into the pipe (20) for supplying fresh air, upstream of the compressor (18b) of the turbocharger (18), said partial EGR recirculation circuit (38) comprising an EGR adjustment valve (38c), the electronic control unit (ECU) comprising an engine control system (70) comprising:
- a module (72) for estimating the mass (M_water) of liquid water stored in real time on internal walls of the exchanger (30);
- a module (74) for determining a water mass difference (ΔM_water) between the water mass (M_water) and a predetermined critical liquid water mass (MC); and
- a module (76) for managing the maximum mass of water that can be stored by the exchanger (30) configured to reduce an EGR rate (Tx_EGR) by controlling the EGR adjustment valve (38c) and/or reduce the flow rate of a cooling fluid (Q_WCAC) passing through the exchanger (30) by controlling a pump configured to circulate the cooling fluid in the exchanger (30) and/or increase the temperature (T_WCAC) of the cooling fluid of the exchanger (30), when the absolute value of said difference (abs(ΔM_water)) is less than a threshold value (S). Motor vehicle comprising an electronic control unit according to claim 10.