EP0489628A1 - Evaporative cooling method for an internal combustion engine and device for carrying out this method - Google Patents

Abstract

Method for cooling an internal combustion engine, in which the cooling is obtained by the evaporation of a cooling fluid and the vapour is subsequently returned to the liquid state by drawing off heat in a cooling device, characterised in that it involves, on the one hand, circulating the cooling fluid in a forced manner through a flow circuit (C1, C2) containing the water chamber (20) of the engine and, on the other hand, adjusting the flow rate of the cooling fluid and the pressure prevailing in the flow circuit (C1, C2) as a function of one or more operating parameters of the engine and/or of the physical characteristics of the cooling fluid. <IMAGE>

Description

The invention relates to a cooling method for an internal combustion engine and in particular to a method ensuring the cooling of an automobile engine by evaporation of a coolant.

The invention also relates to a cooling circuit and its components for implementing the method.

The role of cooling systems is essential for the proper functioning of internal combustion engines. The efficiency of these engines, that is to say the ratio between the energy provided by combustion is low: around 30% for spark-ignition engines. Most of the energy provided by combustion is therefore dissipated in the form of heat.

About half of this heat is carried away by the exhaust gases. The other half must be evacuated through the walls of the combustion chambers, otherwise serious malfunctions will occur: tightening of the pistons in the cylinders (due to the difference in expansion coefficients), deformation of the cylinder head and leaks at the level of the seal, cracks in the combustion chamber, etc.

Evacuation of calories by a cooling system is therefore necessary.

The cooling of an internal combustion engine is generally ensured by forced convection: a cooling fluid: water, air, oil ... sweeps the walls of the combustion chambers.

Conventionally, cooling systems use a forced circulation of water (mixed with rust inhibitors and antifreeze) in a closed loop circuit. The water driven by a pump absorbs heat from the hot parts of the engine mainly in a water chamber surrounding the cylinders, then is cooled in turn in a radiator, where ambient air circulates, before returning to the engine. We improves this operation by means ensuring temperature regulation, by degassing means, by means of pressurizing the water circuit to avoid cavitation of the pump or also by means of rapid rise in temperature during cold engine starts.

However, such cooling systems have a number of drawbacks.

The quantity of liquid introduced into the cooling circuit is large.

avec µ : viscosité dynamique, Cp : chaleur spécifique à pression constante et k : coefficient de conductivité) ; il est nécessaire d'utiliser une assez grande quantité d'eau pour assurer un refroidissement correct du moteur à pleine charge.Indeed, given the low value of the number of Prandtl water $$\text{Pr = µ.}\frac{\text{Cp}}{\text{k}}$$

with µ: dynamic viscosity, Cp: specific heat at constant pressure and k: conductivity coefficient); it is necessary to use a sufficient quantity of water to ensure correct cooling of the engine at full load.

This quantity of water is penalizing: in terms of weight: it weighs down the engine and in terms of temperature rise during cold starts: it slows down this rise, resulting in unburnt and pollutant emissions.

In addition, at certain points in the water chamber, particularly in areas with high heat flux, the temperatures of the walls reach values high enough to cause an uncontrolled local boiling. It then creates pockets of steam which separate the wall and the liquid and cause a sudden drop in the heat transfer coefficient. Therefore hot spots appear locally. These hot spots accentuate the production of certain NO and HC pollutants in particular and can cause cracking of the walls.

For these reasons, other cooling systems have been developed, and in particular two-phase cooling systems of the water-vapor type. One can quote on this subject among the most recent publications the patents US 4,572. 115, US 4,570,579 and US 4,367,699.

The principle of these systems is simple: use the evaporation of water to absorb large quantities of engine heat thanks to the latent heat phenomenon of water vaporization.

In a typical evaporative (or boiling) cooling system, for an internal combustion engine, the coolant evaporates inside the water chamber. Via the sampling system, in the upper part of the water chamber, the steam passes through tubular pipes and for example liquid-vapor phase separators, up to the radiator, where the steam is condensed by fan cooling. The condensate is returned, from the condensate collector, to the engine water chamber in an appropriate way at a low point, either under the action of the force of gravity (in so far as the condenser is placed above of the water chamber) or by means of a small lifting pump.

• la quantité de liquide nécessaire est réduite,
• les points chauds sont limités, peu ou pas de gradients de température car l'ébullition se fait à température constante pour une pression donnée.

Many advantages of two-phase cooling systems have been shown:

• the amount of liquid required is reduced,
• hot spots are limited, little or no temperature gradients because the boiling is done at constant temperature for a given pressure.

However, some problems remain:

A significant production of steam, especially during high load operations, causes a strong pressurization of the circuit which can damage the engine. To avoid excessive pressure levels, safety valves must be provided. These discharges of vapors to the outside leads to a progressive consumption of the liquid which compromises the autonomy of the vehicle and requires regular maintenance.

Pressurization of the circuit can also occur if the evacuation of the steam at the engine outlet is not well arranged. In this case a Reverse flow can occur and cause the areas at the top of the engine to dry out.

Most boiling cooling systems are implemented leaving a free surface for the liquid. That is, the engine is cooled by stagnant boiling. The amount of vaporized liquid is then systematically renewed.

For this, level sensors are installed to allow the starting of a pump when necessary.

The development of these sensors poses enormous problems; the free surface of a boiling liquid is not clearly defined.

Stagnant boiling is also ill-suited to slope cooling.

The object of the present invention is to overcome these drawbacks by proposing a method and a cooling circuit by evaporation of a liquid which ensure efficient cooling whatever the conditions of use of the engine and this in a fairly simple manner.

The method for cooling an internal combustion engine, in which the cooling is obtained by evaporation of a cooling liquid and the vapor is then brought back to the liquid state by drawing off heat in a cooling device, is characterized in that '' it consists on the one hand, to circulate the coolant in a forced manner following a flow circuit comprising the engine water chamber and on the other hand, to adapt the flow of coolant and the prevailing pressure in the flow circuit as a function of one or more engine operating parameters.

Thanks to this process the cooling takes place by circulating boiling unlike the classic stagnant boiling process, which eliminates the problem of level sensors and allows efficient cooling whatever the inclination of the engine while retaining the advantage of a reduced amount of liquid. The adaptation of the physical characteristics of the circulating boiling: flow and pressure, allows an adequacy of the means of cooling and the cooling requirements of the engine. Thanks to the invention, excessive or insufficient cooling is greatly limited, which penalizes the operation of the engine in terms in particular of emissions of polluting products.

According to a variant of the method according to the invention, the flow rate of the coolant and the pressure prevailing in the flow circuit change with the power developed by the engine.

According to another variant of the method according to the invention, as long as the engine power is less than a predetermined value, the flow rate of the coolant and the pressure prevailing in the flow circuit are kept constant at predetermined values Q₁ and P₁ and when the engine power exceeds said predetermined value, said flow rate and said pressure are brought to new predetermined values Q₂ and P₂ with Q₂> Q₁ and P₂ <P₁.

The invention also relates to a cooling device for implementing the method, characterized in that it comprises means for ensuring the forced circulation of the coolant in the engine water chamber and means for adjusting the flow rate. and coolant pressure with engine operation.

According to one embodiment of the cooling device, the means for ensuring the forced circulation of the liquid comprise a primary circuit and as a bypass a secondary circuit for the treatment of the vapor.

According to a characteristic of the invention, the primary circuit for circulating the coolant consists of the engine water chamber, a manifold, a phase separator and a return line to the chamber. with a hydraulic pump.

According to a characteristic of the invention, the secondary bypass circuit comprises a heat exchanger cooled by a fan and connected to the phase serarator by a supply line, a liquid storage tank and a return line to the primary circuit.

According to another characteristic, the means for adapting the flow rate and the pressure of the coolant with the operation of the engine include an electronic computer which, depending on the power supplied by the engine, the temperature of the liquid in the separator and / or the rate vacuum at the motor outlet controls the fan, the valve and the pump.

• la figure 1 est une vue schématique, en coupe partielle du dispositif de refroidissement ;
• la figure 2 est une vue en coupe partielle précisant un mode de réalisation du séparateur de phase schématisé à la figure 1 ;
• les figures 3a et 3b sont des vues détaillant la vanne antivapeur schématisée à la figure 2 ;
• la figure 4 est une vue en coupe partielle du condenseur représenté à la figure 1 ;
• la figure 5 est une vue en coupe des moyens de mesure du taux de vide utilisés pour le pilotage du dispositif de refroidissement ;
• la figure 6 précise la réalisation des moyens de mesure de la figure 5.
• la figure 7 est une vue schématique en coupe partielle d'une variante du dispositif de refroidissement ;

Other characteristics and advantages of the invention will be highlighted in the following description given by way of nonlimiting example of several embodiments of the invention with reference to the appended drawings in which:

• Figure 1 is a schematic view, in partial section of the cooling device;
• Figure 2 is a partial sectional view showing an embodiment of the phase separator shown diagrammatically in Figure 1;
• Figures 3a and 3b are views detailing the anti-vapor valve shown schematically in Figure 2;
• Figure 4 is a partial sectional view of the condenser shown in Figure 1;
• Figure 5 is a sectional view of the means for measuring the vacuum rate used for controlling the cooling device;
• FIG. 6 specifies the embodiment of the measurement means of FIG. 5.
• Figure 7 is a schematic view in partial section of a variant of the cooling device;

According to Figure 1, the cooling device comprises a primary circuit for circulating the cooling fluid C₁. This primary circuit comprises the "water chamber" 20 of the internal combustion engine 1. This water chamber 20 consists of an enclosure surrounding the walls of the combustion chambers, defined in the cylinder block and is extending into the cylinder head. The upper part of the water chamber 20 communicates by a collector 2, with a phase separator 3. The primary circuit C₁ then continues with a pipe 5 which connects the lower part of the phase separator 3, where the liquid is collected , to a feed pump 4 and pump 4 to the water chamber. The primary circuit C₁ therefore constitutes a circulation loop for the coolant.

This primary circuit C₁ admits a secondary circuit C₂ bypass for the treatment of the vapor phase. This second circuit C₂ comprises a line 12 connecting the upper part of the phase separator 3 where the steam circulates, to an exchanger 6, where the condensate is collected, in which communicates with a tank 11 via the line 13. This tank 11 is provided a valve 10 for adjusting the pressure therein. The bypass generated by the second circuit ends in line 15 connecting the tank 11 to the pump 4, line 15 is equipped with a valve 8 controlled by the level of liquid in the tank 11 by means of a float device 9.

The implementation of the pump 4, the fan 7 and the valve 10 is controlled by an electronic computer 17 according to different parameters: the temperature of the liquid in the phase separator (probe 18), the power of the motor, the temperature at the walls of the combustion chambers, or the vacuum rate at the outlet of the water chamber (conductimetric probe 19).

The operation of the device which has just been described is as follows:

Before starting the engine 1, the cooling fluid is in liquid form and is only present in the primary circuit C₁ except for a small amount retained in the tank 11, the valve 8 is in the closed position, preventing the passage of the liquid from the primary circuit C₁ to the tank 11 and the exchanger 6. When starting the computer 17 generates a setpoint P₁ for the pressure prevailing in the tank 11 and therefore in the entire cooling device via the exchanger 6 and line 12. This pressure is generated by the operation of the valve 10. The computer 17 also determines a flow rate value Q₁ for the pump 4. The cooling fluid circulates according to the primary circuit C₁ until the liquid begins to boil in the water chamber 20 at contact of the hot walls of the combustion chambers. From then on, the collector 2 discharges a liquid-vapor mixture. The phases are separated in the separator 3. The liquid continues to circulate in a closed loop in the primary circuit C₁. The vapor imprints on the second circuit C₂, said branch circuit, and passes through the exchanger 6, expelling the air which is there and compressing it in the reservoir 11.

The condensate feeds the reservoir 11 and thus raises the level of the liquid. When a level threshold is exceeded, the float device 9 forming a level sensor opens the valve 8 which allows to recirculate in the primary circuit or loop C₁ a certain amount of liquid. The float device 9 closes the valve 8 as soon as the level has dropped sufficiently.

If the pressure increases in the circuit, the computer 17 controls the operation of the fan in order to accelerate the condensation at the level of the radiator 6 and if the condensation is not sufficient, operate the valve 10 so as to escape the compressed air beforehand stored in the reservoir 11. The pressure prevailing in the circuit is monitored by the temperature sensor 18 placed in the lower part of the phase separator 3 in contact with the liquid phase.

This regulation therefore makes it possible to maintain an almost constant pressure and therefore a fixed vaporization temperature, which does not require frequent opening of the regulation valve.

When, during operation, the engine power exceeds a predetermined threshold, the computer 17 then generates a second setpoint P₂ for the pressure prevailing in the cooling circuit with P₂ <P₁, by controlling the fan 7 and the valve 10.

Similarly, the flow rate of pump 4 is modified and brought to a value Q une with Q₂> Q₁.

By lowering the boiling point and increasing the flow of coolant, the system is able to meet increased cooling needs by using the same device and the same amount of coolant.

When the engine stops, the vacuum created in the radiator 6 and the phase separator 3 causes the reserve 11 to be emptied.

Figure 2 specifies a preferred embodiment of the phase separator 3 and the collector 2 described above.

A phase separator requires a large volume so as to slow down the liquid vapor mixture upon its entry and thus reduce the effect of the drag force of the two phases. The two phases are then separated by their gravitational force: the vapor exits from the top of the separator, while the liquid collected at the bottom of the container exits from the bottom.

As for the steam collector, its role is to facilitate the evacuation of steam from the engine to the condenser. With its vertical pipes located to the right of the cylinder head of the engine it reduces the risk of a boiling crisis by homogenizing the vacuum rate and the temperature of the two-phase flow.

Furthermore, to facilitate the passage of steam from the collector to the separator, it is necessary to connect these two elements with a pipe of large diameter.

As a result, a collector-separator assembly usually occupies a large volume that is hardly compatible with the requirements of today's vehicles.

According to the embodiment of FIG. 2, the separator and the collector have been combined into a single assembly 23. This assembly comprises a plurality of vertical pipes 232, a cylindrical chamber 234, a steam outlet 233 and a water outlet 231 fitted with an anti-steam valve.

The vertical conduits 232 protrude inside the chamber 234 up to about a third of the height of the latter. Thus, the liquid vapor vapor mixture discharged directly from the engine can freely emerge from the conduits 232 into the chamber 234. The vapor exits from the top of the separator towards the condenser via the conduit 12, while the liquid falls to the bottom of the collector where it is then evacuated down through line 5 after passing through the anti-vapor valve.

This anti-vapor valve is specified in accordance with Figures 3a and 3b. The role of this valve is to prohibit any passage of vapor in the circuit 5 for returning the liquid to the engine, a passage which could cause harmful depressions.

The valve is housed in a cavity 235 at the bottom of which the water outlet orifice 231 is formed. This orifice is provided with a seat 236 which can be closed off by the lower end of a float 237 forming a needle. The float 237 is held above the seat, housed in a cylindrical guide tube 238 closed in its upper part and perforated in its lower part for the passages of the liquid.

When liquid is evacuated through the vertical conduits 232 it fills the cavity 235 and the float 237 rises in the guide tube 238 freeing the orifice 231. When there is no more liquid the float 237 drops, the needle in pressing against the seat 236 closes the orifice 231 and prevents any passage of vapor.

According to Figure 4 the condenser 6 described above is of the two pass type. It is formed by a radiator 46 comprising two vertical distribution boxes: a first box 460 and a second box 461, these boxes communicate with each other by bundles 462 of tubes of small diameter extending substantially horizontally. The first box 460 where the steam supply line 12 opens out is split into two half-boxes by a horizontal partition wall.

The steam enters the upper half-box and crosses the bundles of horizontal tubes 462 to reach the second box 461. Part of the steam condenses during this passage and flows to the bottom of the second box 461.

The remaining steam crosses the horizontal tubes in the opposite direction to reach the lower half-box. A new part of the vapor condenses during this second pass and is collected at the bottom of the lower half-box.

The residual steam is sucked up and reintroduced into the upper half-box using a suction system actuated by a turbine 463. Due to the low pressure drop between the inlet and the outlet of this type of condenser , the turbine requires only a small driving power.

The lower half-box and the second box are provided at the bottom with a condensate discharge orifice. To prevent steam from escaping from the condenser without having been condensed, each of these orifices is provided with a vapor valve 464 similar to that described above.

FIG. 5 shows more precisely a sectional view of the conductimetric probe 19 of the means for measuring the vacuum rate. It essentially consists of two annular electrodes 191 - 192 inserted coaxially at a certain distance from each other in an insulating and heat resistant cylinder 190. This assembly thus produced forms an outlet of the cooling circuit connecting the outlet of the engine water chamber to the separator.

FIG. 6 represents the electrical circuit connected to the output of the electrodes and allowing the measurement of the average vacuum rate. It consists of a conductivity meter C associated with an integrator I. The conductivity meter comprises: a voltage source U _o connected to one of the electrodes of the conductimetric probe, a resistor R₁ connected between earth and the second electrode of the probe. The integrator conventionally comprises an operational amplifier T₁ and a capacitor C₁.

The probe having a conductance G constitutes with the resistor R₁ a dividing bridge on which the measurement of the vacuum rate can be preveled by measuring the voltage U _r across the resistor R₁.

Ohm's law allows to write: $${\text{U}}_{\text{r}}\text{=}\frac{\text{R₁}}{\frac{\text{1}}{\text{G}}\text{+ R ₁}}{\text{x U}}_{\text{o}}$$

R₁ is chosen such that 1 / G is much greater than R₁
hence U _r = R₁ x G x U _o
from where $$\text{G =}\frac{\text{1}}{\text{R₁}}\text{x}\frac{{\text{U}}_{\text{r}}}{{\text{U}}_{\text{o}}}$$

The conductance being directly linked to the void rate, this is known.

or U_s est la tension de sortie du système.Integration conventionally allows an estimate of the average void rate by estimating the average conductance over time t _o : $$\text{<G> =}\frac{\text{- R₂C}}{{\text{R₁u}}_{\text{o}}}\text{x}\frac{{\text{U}}_{\text{s}}}{{\text{t}}_{\text{o}}}$$

or U _s is the system output voltage.

Figure 7 shows an alternative embodiment of the cooling circuit in which the vent valve 10 is removed. It appears in fact that if such a purge system is simple to implement, it nevertheless has certain drawbacks, among which may be mentioned the loss of coolant and the acceleration of the aging of the latter by oxygenation.

To avoid these drawbacks, it is proposed to keep the circuit completely closed as in a conventional single-phase cooling circuit, by using a variable volume tank compensating for the expansion of the volume.

Such a system allows adjustment of the circuit pressure in a way that is simple, safe and stable: a simple pressure on the bellows increases the pressure of the circuit unlike a purge system which requires a longer time to adjust the pressures.

Similar to the circuit described in FIG. 1, the present circuit comprises a primary circuit for circulation of the cooling fluid V₁. The primary circuit V₁ comprises the "water chamber" of the engine 1, a vapor separator-collector 23, a pipe 5 equipped with a non-return valve 55 which makes it possible to connect the lower part of the separator collecting the liquid to a feed pump 4 and which continues from the pump to the inlet of the water chamber.

The vapor phase is treated in a secondary circuit V₂ bypass to the circuit V₁ where a pipe 12 connects the steam outlet of the separator 23 to the inlet of the condenser 46, a precision sensor equips this pipe.

A turbine 122 is inserted before the inlet of the condenser, in order to facilitate the extraction of the engine outlet steam if it was problematic.

At the outlet of the exchanger, the condensate is collected in a pipe 13 equipped with a non-return valve 131. This pipe communicates with a variable volume tank 51 and extends to a valve 8 controlled by the computer.

The V₂ branch ends with a line connecting the valve 8 to the pump 4.

This circuit being completely closed, there is no vent valve as in the device described above, it is necessary to place a safety valve 47 in the upper part of the condenser 46. This has for aim to avoid any increase in pressure that could not be controlled. The origin of this overpressure can be a pump failure or blockage of a valve for example.

• puissance du moteur
• température au niveau des parois des chambres de combustion
• pression dans la branche vapeur
• taux de vide, etc...

The implementation of the pump 4, the fan 7, the valve 81, the tank 51 and possibly the turbine 122 is controlled by a electronic computer 171 according to different parameters:

• engine power
• temperature at the walls of the combustion chambers
• pressure in the steam branch
• vacuum rate, etc ...

The operation of the device which has just been described is as follows. When cold, before the engine 1 starts, the entire circuit (V₁ and V₂) is filled with the coolant in the liquid state. The variable volume tank 51 is then in the minimum position.

When starting the computer 171 orders the valve 8 to be closed, thus preventing the circulation of the fluid in the bypass V₂, and determines a flow rate Q for the pump 4, as well as an operating pressure P. The adjustment of the variable volume tank 51 from the data of the sensor 121 allows an almost instantaneous adaptation of the pressure. The heating of the liquid in the loop V₁, causes expansion of the fluid which is compensated by the expansion of the variable volume tank 51.

When the boiling is initiated in the water chamber of the engine 1, the two-phase liquid-vapor mixture is separated in the collector-separator 23. The liquid continues to circulate in the loop V₁. The vapor imprints the line 12 of the circuit V₂ and enters the condenser 46.

The occupation of a certain volume, in the pipe 123 and the exchanger 46, by the steam causes the evacuation of a corresponding volume of liquid towards the variable-volume tank 51. The computer 171 receiving information from the pressure 121 authorizes a progressive displacement of the bellows forming the reservoir 51 so as to maintain the pressure substantially constant.

When the tank is full or when the liquid level in the condenser reaches a limit value, the computer 17 starts the fan 7 and opens the valve 81.

The computer 171 then controls the pressure and the cooling of the fluid by more or less condensing the vapor in the exchanger. It simultaneously controls the variable volume reservoir so as to attenuate the pressure fluctuations which are too great, by varying the volume of the bellows as required.

The computer 171 varies the setpoint of the actuators (pump, fan, bellows) so as to adapt P and Q to the desired operating regime.

During a system malfunction (uncontrolled increase in pressure) the safety valve will release a certain amount of vapor. The computer 17 then immediately compensates for this loss of fluid, by reducing the volume of the bellows 51 to reinject the liquid into the circuit.

Thus an increase in pressure due to a malfunction does not cause an immediate shutdown of the system.

The purpose of the non-return valves 51 and 131 is to prevent any liquid rising through the lines 5 and 12 when the volume of the bellows is reduced.

When the engine 1 stops, the condensation of the vapor remaining in the circuit is terminated and the volume of the bellows is gradually reduced, so as to be in the initial configuration, that is to say V₁ and V₂ full of water. During this time the pump 4 continues to provide a flow rate in order to mix the fluids of the circuits V₁ and V₂.

It is obvious that the invention is not limited to the embodiments described and that other variant embodiments can be made to it.

Thus it is possible to have an adaptation of the pressure and of the N-modal flow N> 2 and not only bimodal by breaking down the domain of evolution of the engine power into N segments.

Thus it is possible to have an adaptation of the pressure and the flow which takes into account the power of the engine but also the temperature at the level of the walls of the combustion chambers.

Claims (16)

Method for cooling an internal combustion engine, in which the cooling is obtained by evaporation of a cooling liquid and the vapor is then brought back to the liquid state by drawing off heat in a cooling device, characterized in that it consists on the one hand, in circulating the liquid of (C₁, C₂) comprising the water chamber (20) of the engine and on the other hand in adapting the flow rate of the coolant and the pressure prevailing in the circuit flow (C₁, C₂) as a function of one or more engine operating parameters and / or of the physical characteristics of the cooling fluid. Method for cooling an engine according to claim 1, characterized in that the flow rate of the coolant and the pressure prevailing in the flow circuit (C₁, C₂) change with the power developed by the engine. Method for cooling an engine according to claim 2, characterized in that as long as the engine power is less than a predetermined value, the flow rate of the coolant and the pressure prevailing in the flow circuit (C₁, C₂) are maintained constants at predetermined values Q₁ and P respectivement respectively and in that when the engine power exceeds said predetermined value, said flow rate and said pressure are brought to new predetermined values Q₂ and P₂ with Q₂> Q₁ and P₂ <P₁. Cooling device for implementing the method according to any one of claims 1 to 3, characterized in that it comprises means (C₁, C₂) for ensuring the forced circulation of the coolant and means (17) to adapt the flow in the engine's water chamber (20) and the coolant pressure with the engine running. Cooling device according to claim 4, characterized in that the means for ensuring the forced circulation of the coolant comprise a primary circuit (C₁) and in bypass a secondary circuit (C₂) for the treatment of steam. Cooling device according to claim 5, characterized in that the primary circuit (C₁) for circulation of the coolant consists of the engine water chamber of a manifold (2, 23), of a phase separator (3, 23) and a return line (5) to the water chamber provided with a hydraulic pump (4). Cooling device according to claim 6, characterized in that said collector and said phase separator are combined in a single assembly (23). Cooling device according to any one of claims 6 to 7, characterized in that the mouth (231) of the return line (5) is provided with a float valve (237) preventing the passage of steam. Cooling device according to any one of claims 5 to 8, characterized in that the secondary branch circuit (C₂) comprises a heat exchanger (6, 46) cooled by a fan (7) and connected to the phase separator by a supply line (12), a storage tank (11, 511) for the liquid and a return line (15) to the primary circuit. Cooling device according to claim 9, characterized in that said heat exchanger is formed by a two-pass radiator (46) comprising two vertically arranged collecting water boxes (460, 461) said water boxes being connected by bundles of horizontal tubes (462), the condensate discharge orifices arranged in the bottom of said water boxes are provided with anti-vapor valves (464), a turbine (463) ensuring a circulation of the residual vapor until its total condensation . Cooling device according to any one of Claims 9 to 10, characterized in that the said liquid storage tank consists of a tank with viable volume (511). Cooling device according to claim 11, characterized in that the reservoir is formed by a bellows enclosure (512) whose volume is controlled by control means. Cooling device according to claim 9, characterized in that said return line (15) is provided with shutter means (8, 9) controlled by the level of liquid in said tank. Cooling device according to any one of Claims 7 to 8, characterized in that the storage tank (11) is provided with a valve (10) making it possible to adjust the pressure in the tank and in all of the circuits primary and secondary (C₁, C₂). Cooling device according to any one of Claims 5 to 13, characterized in that the means for adapting the flow rate and the pressure of the coolant with the operation of the engine include an electronic computer (17) which, depending on the power supplied by the motor and the temperature of the liquid in the separator (3) and where the vacuum rate controls the fan (7), the valve (10) or the bellows (512), and the pump (4). Cooling device according to claim 15, characterized in that the means for measuring the vacuum rate comprise a conductimetric probe (19) with two electrodes arranged at the outlet of the water chamber.

Images