EP2310648B1 - Method for controlling the flow of a cooling liquid - Google Patents

Description

The invention relates to the field of control of water pumps in a combustion engine of a motor vehicle. The invention particularly relates to a method for controlling the flow of coolant circulated by a water pump in a combustion engine of a motor vehicle.

Such a motor vehicle comprises a water pump that can be mechanical or electrical.

A water pump has the role of converting velocity energy into pressure energy. Thanks to the evolutionary section of a volute at a turbine, the speed of the fluid decreases and the pressure increases.

A mechanical water pump comprises, as illustrated in the figure 1 , a body M8 housed in a housing M9 of a motor, an axis M2 on which is coaxially mounted a turbine M1 and a pulley M3, a dynamic seal M4 and M5 bearings.

The motor body M8 defines on three sides an M6 tank. The last side is delimited by the M5 bearings.

Along the axis M2 are successively arranged the pulley M3, the bearings M5, the seal M4 and finally the turbine M1. The pulley M3, the bearings M5 and part of the seal M4 are arranged in a first so-called dry portion. The turbine M1 and another part of the seal M4 are arranged in a second part in contact with the coolant.

The pulley M3 is rotated by the motor. The rotational movement is transmitted to the turbine M1 via the axis M2. M5 bearings provide rotational movement with good guidance and low wear. The seal M4 seals between the dry portion and the portion in contact with the coolant. This M4 seal has two rings. A first ring is fixed and linked to the body M8. A second ring rotates and is linked to the M2 axis.

To limit the temperature of the M4 seal, a low coolant leak is admitted through the M4 seal. This leak is collected in the tank M6 where the liquid solidifies in contact with the air.

In an engine equipped with a mechanical water pump, the coolant is circulated by the engine. Thus, as soon as the engine is running, the coolant circulates and cools the engine.

However, in certain cases, especially during start-up and / or when the ambient temperature is low, it is desirable for the water pump to be deactivated. Indeed, as the engine temperature does not exceed a given critical temperature, beyond which the operation of the engine may be abnormal, there is no need to cool.

Also, the higher the temperature of the engine, and the lower the viscosity of the oil, which reduces the friction and therefore the engine consumption.

An electric water pump includes, as illustrated on the figure 2 , a body E8, an axis E2 on which are mounted, coaxially and integrally, a turbine E1, two bearings E4 and a magnet E6. In the body E8 is housed a fixed coil E5 facing the magnet E6.

The bearings are arranged on either side of the magnet E6. The turbine E1 and outside the body E8.

The rotational movement is not transmitted, in the case of an electric water pump, by the engine but by an electric motor. When the winding is powered, the magnetic field thus generated rotates the axis E2 through the magnet E6.

The seal between a dry portion and a portion in contact with the coolant is provided by a set of static seal E3.

The M5 bearings of the mechanical water pump are replaced in the electric water pump by the two bearings E4 usually carbon which are immersed in the coolant and are therefore naturally cooled. There is no leak.

The document JP2005-256642 describes a method comprising the following steps: a thw temperature of coolant is detected; at from the detected coolant temperature is determined a corresponding base output Pb using a correspondence table thw / Pb; a temperature of the engine Tm is estimated; a difference (Ts = Tm - Tf) between the engine temperature and the coolant temperature is calculated; a correction coefficient V is determined using a correspondence table Ts / V; this corrective coefficient V finally makes it possible to correct the value of the basic output Pb to be injected into the electric water pump.

The document JP2000-303841 discloses a method for controlling an electric water pump by: comparing a coolant temperature in an engine water jacket and a first threshold; comparisons between a coolant temperature in an engine heat sink and a second, third and fourth threshold.

These two proposed solutions use temperature sensors which must be robust since they are used in a hot environment (water temperature of the order of 100 ° C), otherwise the detection of the temperature may be erroneous. These solutions are therefore expensive.

However, it would be advantageous to take advantage of the facilities already present in many models of combustion engines available today.

Such solutions have already been proposed.

The document US 2003/0113213 describes a method in which either a temperature of the coolant present in the engine is determined and compared to a set temperature, or a quantity of fuel injected into the engine since startup is compared to a quantity of fuel oil. These comparisons make it possible to control the circulation of cooling fluid by the electric water pump.

However, using the amount of fuel injected to determine the activation times of the electric water pump is not a reliable solution. Indeed, the amount of fuel is not directly related to a temperature of the hottest point in an engine (this temperature to know when the electric water pump must be started), since the temperature of this point depends on several parameters including the efficiency of the engine, the combustion air mixture, the quality of the fuel, etc.

The document DE 102 48 552 discloses a method in which the starting of the electric water pump is controlled when at least one of the following values exceeds a respective threshold: the temperature of the coolant; the temperature of the intake air; the heating power; and a running time.

Also, the electric water pump is started if an engine speed exceeds a threshold speed at the same time as the vehicle speed exceeds a threshold speed.

However, one of the disadvantages of this method is that the water pump is turned on after a determined operating time. That is to say that whatever the ambient temperature, the coolant is circulated beyond this operating time, even though under certain conditions, it would be more economical not to proceed with cooling the engine since this one is still cold.

An object of the invention is to provide a coolant flow control method using the equipment already present in most combustion engines.

For this purpose, the invention proposes a method for controlling the flow rate of a cooling liquid in a combustion engine comprising a housing and a water pump, characterized in that an estimate of a material temperature, corresponding to the point the hottest of the casing, is made from a calculation of a stored energy calculated by an integral of a power output corresponding to a power returned to the coolant if the coolant was set in motion.

An advantage of the method according to the invention is that it allows a more accurate estimation of the temperature of the combustion engine and thus make the operation of the water pump more economical.

• le procédé comprend les étapes consistant à déterminer la puissance restituée à partir d'un régime moteur et d'une puissance du moteur ;
• le procédé comprend les étapes consistant à déterminer une décision sur le débit du liquide de refroidissement à partir de la puissance restituée et d'un état du moteur ;
• l'étape consistant à déterminer une décision sur le débit du liquide de refroidissement comprend les sous-étapes suivantes : initialisation d'une première énergie seuil quand l'état du moteur correspond à un démarrage du moteur ; calcul de l'énergie emmagasinée de manière itérative tant que l'énergie emmagasinée est en deçà de la première énergie seuil à partir de la puissance emmagasinée ; et arrêt du calcul de l'énergie emmagasinée dès que l'énergie emmagasinée atteint ou dépasse la première énergie seuil ;
• la décision sur le débit du liquide de refroidissement est telle que : le liquide de refroidissement n'est pas mis en circulation tant que l'énergie emmagasinée est en deçà de la première énergie seuil ; et le liquide de refroidissement est mis en circulation dès que l'énergie emmagasinée atteint ou dépasse la première énergie seuil ;
• l'étape consistant à déterminer une décision sur le débit du liquide de refroidissement comprend, en outre, la sous-étape d'initialisation d'une deuxième énergie seuil intermédiaire inférieure à la première énergie seuil quand l'état du moteur correspond à un démarrage du moteur ;
• la décision sur le débit du liquide de refroidissement est telle que : le liquide de refroidissement n'est pas mis en circulation tant que l'énergie emmagasinée est en deçà de la deuxième énergie seuil intermédiaire ; le liquide de refroidissement est mis en circulation à un premier débit dès que l'énergie emmagasinée atteint ou dépasse la deuxième énergie seuil intermédiaire et tant qu'elle est en deçà de la première énergie seuil ; et le liquide de refroidissement est mis en circulation à un deuxième débit supérieur au premier débit dès que l'énergie emmagasinée atteint ou dépasse la première énergie seuil ;
• le procédé comprend un premier mode sécurité consistant à mettre en circulation le liquide de refroidissement au moins à un troisième débit prédéterminé dès qu'une température de liquide correspondant à la température du liquide de refroidissement dans le moteur atteint ou dépasse une température seuil ;
• le procédé comprend un deuxième mode sécurité consistant à mettre en circulation le liquide de refroidissement au moins à un quatrième débit prédéterminé au bout d'un temps prédéterminé depuis le démarrage du moteur ;
• l'initialisation de la première énergie seuil et, le cas échéant, de la deuxième énergie seuil intermédiaire est réalisée en fonction d'une température du liquide de refroidissement dans le moteur au moment du démarrage de celui-ci ; et
• l'estimation de la température matière à partir de l'énergie emmagasinée est effectuée grâce à une table de correspondance énergie emmagasinée/température matière ; et en ce que cette table énergie emmagasinée/température matière est obtenue par apprentissage en régime de rotation déterminée et quand la puissance emmagasinée est stable.

Other non-limiting and optional features are:

• the method comprises the steps of determining the power output from engine speed and engine power;
• the method comprises the steps of determining a decision on coolant flow from the returned power and a condition of the engine;
• the step of determining a decision on the coolant flow includes the following substeps: initializing a first threshold energy when the engine state corresponds to a starting of the engine; calculating the stored energy iteratively as long as the energy stored is below the first threshold energy from the stored power; and stopping the calculation of the stored energy as soon as the stored energy reaches or exceeds the first threshold energy;
• the decision on the coolant flow rate is such that: the coolant is not circulated as long as the energy stored is below the first threshold energy; and the coolant is circulated as soon as the stored energy reaches or exceeds the first threshold energy;
• the step of determining a decision on the coolant flow further comprises the substep of initializing a second intermediate threshold energy lower than the first threshold energy when the engine state corresponds to a start of the motor ;
• the decision on the flow rate of the coolant is such that: the coolant is not circulated as long as the stored energy is below the second intermediate threshold energy; the coolant is circulated at a first rate as soon as the stored energy reaches or exceeds the second intermediate threshold energy and as long as it is below the first threshold energy; and the coolant is circulated at a second rate higher than the first rate as soon as the stored energy reaches or exceeds the first threshold energy;
• the method comprises a first safety mode of circulating the coolant at least at a third flow rate predetermined when a liquid temperature corresponding to the temperature of the coolant in the engine reaches or exceeds a threshold temperature;
• the method comprises a second safety mode of circulating the coolant at least at a fourth predetermined rate after a predetermined time since starting the engine;
• the initialization of the first threshold energy and, if appropriate, of the second intermediate threshold energy is performed as a function of a temperature of the coolant in the engine at the start of the latter; and
• the estimation of the material temperature from the stored energy is performed by means of a stored energy / material temperature correspondence table; and in that this stored energy / material temperature table is obtained by learning in determined rotational mode and when the stored power is stable.

• un capteur de température du carter ;
• une unité de détermination de la puissance emmagasinée à partir d'un régime moteur et d'un couple moteur ; et
• une unité de décision déterminant le débit du liquide de refroidissement en fonction de l'énergie emmagasinée.

The invention also proposes a system for controlling the flow rate of coolant, implementing the method according to any one of the preceding claims, characterized in that the system comprises:

• a crankcase temperature sensor;
• a unit for determining the power stored from an engine speed and a driving torque; and
• a decision unit determining the flow rate of the coolant as a function of the energy stored.

• la figure 1 est une représentation schématique d'une pompe à eau mécanique ;
• la figure 2 est une représentation schématique d'une pompe à eau électrique ;
• la figure 3 est une représentation schématique d'une unité de détermination de la puissance emmagasinée ;
• la figure 4 est un logigramme représentant un premier mode de réalisation d'une unité de décision selon l'invention ;
• la figure 5 est un logigramme représentant un deuxième mode de réalisation d'une unité de décision selon l'invention ;
• la figure 6 est une représentation schématique d'une unité de surveillance de la température du liquide de refroidissement ; et
• la figure 7 est une représentation schématique d'un exemple de réalisation du procédé selon l'invention.

Other features, objects and advantages of the present invention will appear on reading the detailed description which follows, with reference to the appended drawings, given as non-limiting examples and in which:

• the figure 1 is a schematic representation of a mechanical water pump;
• the figure 2 is a schematic representation of an electric water pump;
• the figure 3 is a schematic representation of a unit of determination of the stored power;
• the figure 4 is a logic diagram representing a first embodiment of a decision unit according to the invention;
• the figure 5 is a logic diagram representing a second embodiment of a decision unit according to the invention;
• the figure 6 is a schematic representation of a coolant temperature monitoring unit; and
• the figure 7 is a schematic representation of an exemplary embodiment of the method according to the invention.

As previously stated, the warmer the material, which is a motor, is, the lower the viscosity of the engine oil. This leads to a decrease in friction and therefore a decrease in consumption.

The motor material, however, must not exceed a critical temperature. Beyond this critical temperature, the engine is no longer reliable and severe engine damage can occur.

However, depending on the ambient temperature, a temperature of the engine material (hereafter referred to as the material temperature) may, before starting, be below the critical temperature.

For a period from start up until the material temperature exceeds the critical temperature, it is therefore advantageous not to cool the engine.

Therefore, in some cases of use, it is advantageous to delay a circulation of a coolant in a cooling circuit of the engine equipped with an electric water pump.

In order to know when the coolant needs to be circulated, it is necessary to determine the material temperature of the engine. The engine material temperature taken into consideration must be a temperature T _max of a point of the engine which is the hottest point P1.

Preferably, this point P1 is located at an inter-valve gate exhaust / exhaust.

The acquisition of this temperature T _max is however not advantageous for reasons of cost and reliability. This temperature T _max is then, according to the invention, determined from an amount of energy stored in the engine.

When the electric water pump is running, this amount of stored energy is returned to the coolant. In the absence of a circulation of the coolant, this quantity of energy is then transmitted to the engine material, which causes its heating.

This amount of stored energy is therefore a true image of the material temperature taking into account the material temperature during startup. And an estimate of this temperature is made thanks to a table of correspondence energy stored / temperature matter.

avec t₀ l'instant du début du cycle et t₁ l'instant auquel l'énergie emmagasinée est considérée ; P_eau une puissance restituée au liquide de refroidissement quand celui-ci est en circulation et à la matière du moteur sinon ; N(t) un régime moteur à l'instant t ; et PME(t) une puissance moteur efficace à l'instant t.This amount of energy stored is expressed by: $$E\square \underset{t_0}{\overset{t_1}{\int }}{P}_{\mathit{water}}\left(\mathrm{NOT}\left(t\right),\mathit{SMEs}\left(t\right)\right)\mathrm{.}\mathit{dt};$$

with t ₀ the moment of the beginning of the cycle and t ₁ the moment at which the energy stored is considered; P _water power returned to the coolant when it is circulating and to the engine material otherwise; N ( t ) an engine speed at time t ; and PME ( t ) an effective engine power at time t.

This amount of energy is determined by a stored energy determination unit whose operation is as follows.

The _water power P is determined from a calorie / water correspondence table expressed in the form of a two-input table (engine speed and effective engine power).

This table is predetermined by a test for which the power P _water is measured for each pair ( N ( t ); PME ( t )) of the table.

The energy E is then compared with a threshold _threshold energy E which depends on the material temperature at startup which is taken as equal to the liquid temperature of the coolant in the engine.

This threshold energy E _threshold is determined during a steady-state test on a steady-state point and a constant engine power. Under zero coolant flow, an acquisition from the start of operation of the engine until the critical temperature is reached allows, with a calculation of the integral (giving E and simplified because of the established regime), the determination of the threshold energy E _threshold .

A decision unit determines a mode of operation of the water pump.

As long as the energy E is lower than the threshold _threshold energy E, the electric water pump is not put into operation.

Thus the electric water pump has at least two modes of operation.

In the first mode of operation, when E < E _threshold , the water pump is not actuated, so there is no circulation of coolant.

In the second mode of operation corresponding to E > Eseuil, the pump is actuated and its rotational speed is related to the conditions of use of the engine.

In another embodiment of the invention, an intermediate operating mode is added and a second energy threshold E _int lower than the threshold _threshold energy E. Thus the pump has three modes of operation.

In a variant, the second threshold is an intermediate threshold energy corresponding to a critical temperature of use of a member of the cooling circuit.

In another variant, the second threshold is added in order to allow a circulation of the cooling liquid actuated by the water pump not related to the conditions of use of the engine. For example, this is sought to mitigate a delay of information on the liquid temperature delivered by a sensor due to the non-circulation of coolant.

The intermediate operating mode corresponds to a coolant flow rate lower than or equal to that of the second mode of operation.

As a variant of the first and second embodiments, a time threshold, corresponding to a duration of use beyond which the coolant is circulated, is added. This is determined by a coolant temperature monitoring unit.

As a further variant of the first and second embodiments, a threshold on the temperature of the coolant may be added. If the temperature of the coolant, included in the engine but not circulating, exceeds this threshold, the coolant is circulated.

In another variant, the time threshold and the threshold on the temperature may both be added to the first and / or second embodiments.

With reference to Figures 3 to 6 are described below particular embodiments, given by way of example, each of the units.

The stored power P _water ( t ) is calculated by the unit 3 for determining the energy stored from a measurement of the engine speed N ( t ), and a measurement of the engine torque CMI ( t ). A multiplier 32 multiplies the values of these measurements and gives to its output the power of the efficient engine PME ( t ) , according to the formula: $$\mathit{SMEs}\left(t\right)=\frac{2\cdot \pi }{60}\cdot \mathit{CMI}\left(t\right)\cdot \mathrm{NOT}\left(t\right)\mathrm{.}$$

The power of the efficient engine PME ( t ) and the engine speed N ( t ) are then sent to the input of the calorie / water correspondence table 31 which outputs the stored power.

The figure 4 is a flowchart illustrating the coolant flow rate control method according to the first two mode embodiment of the decision unit 4.

In the first step S1, the values of the stored power, the threshold energy are initialized. The initial stored power is zero and that of the threshold energy depends on the initial temperature of the coolant, i.e., at start-up. This threshold energy is determined from an input variable array (initial coolant temperature).

As long as there is no engine start, we stay at the first step. If the engine is started, a calculation module calculates the stored energy E ( t ) in step S2. This calculation is repeated at regular intervals dt . Thus the energy stored at time t is: $$E\left(t\right)=E\left(t-\mathit{dt}\right)+P_{\mathit{water}}\left(t\right)\mathrm{.}\mathit{dt}\mathrm{.}$$

Before each reiteration of the calculation, a comparison module compares the value of the energy stored with the threshold energy determined during step S1 (Q1).

If the energy stored is less than the threshold energy, then the calculation is repeated.

If the stored energy is greater than the threshold energy, then the calculation is not reiterated and the water pump is activated in step S3.

The figure 5 is a logic diagram illustrating the second embodiment of the method of three modes of operation of the 4 'decision unit.

In a first step S1 ', the stored power P _water , the first threshold _threshold energy E and the second intermediate threshold energy E _int are initialized. As long as there is no start of the engine, the method remains in the first step S1 '.

After starting, the calculation module calculates the stored energy in a second step S2 'identical to step S2.

An intermediate level comparison module compares the stored energy E ( t ) with the second intermediate threshold energy E _int (Q2 ').

If the stored energy E ( t ) is less than the second intermediate threshold energy E _int , the calculation is reiterated in step S2 '. Otherwise, a comparison module compares the stored energy E ( t ) with the first threshold energy E _threshold (Q1 ').

If the stored energy E ( t ) is lower than the first threshold _threshold energy E then the intermediate operating mode is activated in step S4 '.

If the stored energy E ( t ) is greater than the first threshold _threshold energy E then the second intermediate operating mode is activated and the calculation of the stored energy E ( t ) is stopped, in step S3 ' .

Finally, convective losses in the coolant help to increase the coolant temperature and, depending on the arrangement of the circuit, to create a thermosiphon. It is therefore possible to use a threshold on the temperature of the liquid T _{threshold in} order to take into account this increase in the temperature of the coolant.

Another threshold on the time spent since startup is also possible.

The thresholds on the liquid temperature and on the time spent since startup are alternatively safety thresholds, that is to say whatever the decision taken by the unit 4, 4 'of decision, if the threshold the temperature of the coolant and / or the threshold on the time spent since starting is / are reached and / or exceeded then the coolant is circulated.

The figure 6 is a diagram illustrating the operation of the unit 6 monitoring the temperature of the coolant to take into account the increase in the liquid temperature due to convection losses. This module comprises a comparator 61 comparing the temperature of liquid T _water threshold T _threshold . The liquid temperature is measured by a conventional temperature sensor for this type of use. The output of the comparator is connected to a switch 62 making it possible to switch from a nominal control mode M _n to a security mode M _s , giving the output of the monitoring unit 6 a safety instruction S _p determining the operating mode. the pump must operate in safety mode.

The nominal driving mode corresponds to the operating mode determined by the decision unit 4, 4 '. The security mode corresponds to a predetermined fixed operating mode.

For example, to the safety mode, lump operation mode associated therewith corresponds to a _threshold W threshold rotational speed, for example 85% of the maximum possible throughput. The failover condition in safety mode is T _water ≥ T _threshold ·

With reference to the figure 7 is hereinafter described an illustrative and nonlimiting example of an embodiment implementing the three units described above.

• la température de liquide T_eau ;
• le régime de rotation du moteur N(t) ;
• le couple du moteur CMI(t) ; et
• l'état du moteur marche/arrêt Et_m .

In this embodiment, the input data is:

• the temperature of liquid T _water ;
• the rotation speed of the motor N ( t );
• the torque of the engine CMI ( t ); and
• the state of the motor on / off And _m .

The output data is a coolant flow control setpoint, expressed here in the form of pulse width modulation PWM (or PWM, Pulse Width Modulation in English). That is, the time spent in the high state, during a period of the generated square wave signal, determines the flow rate of the coolant.

The unit 3 for determining the stored energy receives as input the rotational speed of the engine N ( t ) and the torque of the engine CMI ( t ) and returns the power P _water ( t ).

The decision unit 4, 4 'receives, as input, the power P _water ( t ) as well as the state of the engine Et _m (start-up or not) and returns a decision on the flow rate of the coolant to be put in place. in the engine De.

The unit 6 for monitoring the liquid temperature receives as input the measurement of the liquid temperature. It sends back a decision on the flow of the coolant which is either that determined by the decision unit 4, 4 'or a security flow corresponding to the security mode.

The outputs of the units 4 (or 4 ') and 6 are sent to the input of a flow rate determination unit 7 which determines the flow rate of _the cooling liquid Q ₁ to be put in place according to this information and according to the engine speed. N ( t ).

Alternatively, a unit 8 for monitoring the time spent since the start can be added comprising a timing device and returns the time elapsed since the start Δ t. Its output is sent to the unit 7 for determining the flow rate.

The method according to the invention is not limited to a use for the control of the flow of coolant in a motor equipped with an electric water pump; it can advantageously be used for determining an activation threshold of an electromagnetic, pneumatic, friction roller or valve-associated water pump.

An advantage of this method is not to use other sensors than those already existing in most engines with a mechanical water pump.

Another advantage of this method is to be able to have the necessary information for the implementation of the method on a network of the engine computer (torque regime, temperature).

Claims (13)

1. Method for controlling the rate of flow of a liquid coolant in a combustion engine comprising a crank case and a water pump, characterized in that an estimate of a material temperature, corresponding to the hottest point of the crank case, is made on the basis of a calculation of stored energy (E) calculated as an integral of a restored power (P_water(t)) corresponding to a power restored to the liquid coolant if the liquid coolant was set in motion.
2. Method according to the preceding claim, characterized in that it comprises the steps consisting in:

   - determining the restored power (P_water(t)) on the basis of an engine speed (N(t)) and of an engine power (PME(t)).
3. Method according to either one of the preceding claims, characterized in that it further comprises the steps consisting in:

   - determining a decision (De) regarding the rate of flow of liquid coolant on the basis of the restored power (P_water(t)) and of an engine status (Et_m).
4. Method according to the preceding claim, characterized in that the step consisting in determining a decision (De) regarding the rate of flow of liquid coolant comprises the following substeps:

   - initializing a first threshold energy (E_thresh) when the engine status (Et_m) corresponds to a starting of the engine;

   - calculating the stored energy (E) iteratively as long as the stored energy is below the first threshold energy (E_thresh), on the basis of the stored power; and

   - stopping the calculation of stored energy (E) as soon as the stored energy (E) reaches or exceeds the first threshold energy (E_thresh).
5. Method according to the preceding claim, characterized in that the decision (De) regarding the rate of flow of liquid coolant is such that:

   - the liquid coolant is not circulated as long as the stored energy (E) is below the first threshold energy (E_thresh); and

   - the liquid coolant is circulated as soon as the stored energy (E) reaches or exceeds the first threshold energy (E_thresh).
6. Method according to Claim 3, characterized in that the step consisting in determining a decision (DE) regarding the rate of flow of liquid coolant further comprises the following substep:

   - initializing a second intermediate threshold energy (E_int) lower than the first threshold energy (E_thresh) when the engine status (Et_m) corresponds to a starting of the engine.
7. Method according to the preceding claim, characterized in that the decision (De) regarding the rate of flow of liquid coolant is such that:

   - the liquid coolant is not circulated as long as the stored energy (E) is below the second intermediate threshold energy (E_int) ;

   - the liquid coolant is circulated as a first flow rate as soon as the stored energy (E) reaches or exceeds the second intermediate threshold energy (E_int) and as long as it is below the first threshold energy (E_hresh); and

   - the liquid coolant is circulated as a second flow rate higher than the first flow rate as soon as the stored energy (E) reaches or exceeds the first threshold energy (E_thresh).
8. Method according to any one of Claims 3 to 7, characterized in that it further comprises a first safety mode that consists in circulating the liquid coolant at least at a predetermined third flow rate as soon as a coolant temperature (T_water) corresponding to the temperature of the liquid coolant in the engine reaches or exceeds a threshold temperature (T_thresh).
9. Method according to any one of Claims 3 to 8, characterized in that it further comprises a second safety mode that consists in circulating the liquid coolant at least at a predetermined fourth flow rate after a predetermined time has elapsed since the engine was started.
10. Method according to any one of Claims 3 to 9, characterized in that the first threshold energy (E_thresh) and, where appropriate, the second intermediate threshold energy (E_int) is/are initialized as a function of a temperature of the liquid coolant in the engine at the time of starting of the engine.
11. Method according to any one of the preceding claims, characterized in that the estimate of the material temperature on the basis of the stored energy is made using a stored energy/material temperature look-up table; and in that this stored energy/material temperature table is obtained during a learning phase at a determined rotational speed and when the stored power is stable.
12. System for controlling the rate of flow of liquid coolant, the system comprising:

    - a crank case temperature sensor;

    - a determining unit (3) for determining the stored power on the basis of an engine speed (N(t)) and of an engine torque (CMI(t)); and

    - a decision unit (4, 4') that determines the rate of flow of liquid coolant as a function of the stored energy (E),

    characterized in that the system implements the method according to any one of the preceding claims.
13. Motor vehicle characterized in that it comprises the system according to Claim 12.

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