FR2728622A1 - IC-engine evaporation cooler - Google Patents

Abstract

The cooler consists of a radiator (4) which acts as a condenser, a variable-volume tank (7) and a pump (9) for circulating a given flow of coolant. It also has a controlled three-way valve (6) which is able to direct the fluid flow from the engine through the radiator-condenser and/or a duct (36) which by-passes the radiator-condenser, with the pump maintaining a constant fluid flow regardless of the engine's operating mode. The size of the fluid flow is determined by the motor's heat exchange requirements, and is between 500 and 1500 litres per hour. The three-way valve (6) is controlled according to the coolant temperature, and the volume of the tank is adjusted to give a balancing pressure of 1.2-3 bars, and preferably 2-2.5 bars.

Description

DB COOLING DEVICE
EVAPORATION FOR MOTIOR TO INTERNAL COKBU8TIO
The present invention relates to a cooling device for an internal combustion engine intended to equip noted a motor vehicle. The invention relates more particularly to a cooling device operating in two-phase mode characterized by the evaporation and condensation in a closed circuit of a cooling liquid.

 I1 has long been known to use the boiling phenomenon of a liquid such as water, to remove heat from an internal combustion engine. Such evaporative cooling devices for internal combustion engines are described in particular in US Patents 4,572,115 and US 4,570,579.

 In these typical evaporative (or boiling) cooling devices, the coolant is maintained at a substantially constant level, leaving a free surface for the fluid inside the engine's water chamber surrounding the cylinders. Via a suitable withdrawal system, the steam produced is discharged into a phase separator and then into a radiator where the steam is condensed, the condensate then being returned to the engine's water chamber.

 Such two-phase cooling devices have significant advantages the amount of liquid required is reduced, little or no temperature gradients because the boiling is done at constant temperature for a given pressure. These so-called "stagnant boiling" devices do, however, present certain production difficulties which hamper their industrialization.

 Indeed, stagnant boiling devices require the use of level sensors which control the operation of the water pump when necessary, but the development of these sensors poses a problem because the free surface of a liquid boiling is not clearly defined. Furthermore, these devices cause a strong release of vapor, noted during operations at full loads, which results in a significant pressurization of the device and a rise in temperature capable of damaging the engine. Safety valves must therefore be provided, leading to the release of vapors outside the device, resulting in a progressive consumption of the liquid compromising the autonomy of the vehicle and requiring regular maintenance.

To remedy these drawbacks, the
Applicant has developed a new evaporative cooling device which was the subject of European patent application EP-A-489,628.

 This new device is characterized by a forced circulation of the coolant inside the engine's water chamber and by the use of a variable volume expansion tank (membrane vessel or bellows) to compensate automatically increase the volume of fluids in circulation while avoiding the release of vapors to the atmosphere.

 Thanks to such a device, the cooling is effected by circulating boiling unlike the conventional stagnant boiling process, which eliminates the need for level sensors and allows efficient cooling whatever the inclination of the engine.

 Although the production of steam generated by a circulating boiling cooling device is significantly less than that of a stagnant boiling device, it is however necessary to be able to control any risk of significant pressurization of the device at critical operating points. of the engine, pressurization which would prevent effective cooling of the latter and would lead to its destruction.

 To prevent this risk, the aforementioned device offers two solutions: either increase the dimensions of the variable volume tank as well as those of the condenser but this then poses problems of space in the engine compartment, or even adjust the flow liquid through the engine according to the operation of the latter, which however complicates the cooling device and therefore increases the cost.

 The object of the present invention is therefore to remedy these latter drawbacks by proposing an evaporative cooling device for an internal combustion engine of the type with circulating boiling of a liquid which is particularly simple to produce and which provides efficient cooling whatever whatever the operating conditions of the engine.

 The evaporative cooling device of an internal combustion engine equipping in particular a motor vehicle, object of the invention is of the type comprising a radiator forming a condenser, a variable volume tank and a centralization pump for circulating a flow given coolant.

 According to the invention, the evaporative cooling device is characterized in that it comprises a piloted three-way valve able to direct the flow of fluid leaving the engine selectively through the radiator-condenser and / or a bypass line allowing bypass said radiator-condenser and in that the pump maintains the flow of fluid substantially constant whatever the operating conditions of the engine.

 According to another characteristic of the evaporative cooling device which is the subject of the invention, the value of the fluid flow rate is determined according to the heat exchange requirements of the engine and is between 500 and 1500 liters / hour.

 According to another characteristic of the evaporative cooling device which is the subject of the invention, the latter comprises an air heater intended for heating the passenger compartment of the motor vehicle, this air heater being arranged downstream of the variable volume tank in the direction of flow. fluid.

 According to another characteristic of the evaporative cooling device which is the subject of the invention, the three-way valve is controlled as a function of the temperature of the cooling fluid so as to direct all of the fluid in circulation through the bypass pipe as long as the fluid temperature has not reached a predetermined value.

 According to another characteristic of the evaporative cooling device which is the subject of the invention, the volume V of the variable-volume tank is adjusted so as to obtain an equilibrium pressure, obtained once the tank is completely filled, which is between 1, 2 and 3 bars.

 According to another characteristic of the evaporative cooling device which is the subject of the invention, the volume V of the variable scroll tank is adjusted so as to obtain an equilibrium pressure of between 2 and 2.5 bars.

The aims, aspects and advantages of the present invention will be better understood from the description given below of an embodiment of the invention applied to an internal combustion engine, this embodiment being given by way of non-limiting example, with reference to the appended drawing, in which
- Figure 1 schematically shows an evaporative cooling device according to the invention.

 According to FIG. 1, the evaporative cooling device for a heat transfer liquid, such as water mixed with an antifreeze and a corrosion inhibitor (for example a 35% water-ethylene-glycol mixture), is more particularly intended to cool an internal combustion engine 1 of the multicylinder type intended in particular to equip a motor vehicle. Only the elements of the device necessary for understanding the invention have been shown.

 The device conventionally comprises passages arranged in the engine, also called water chambers, surrounding the walls of the combustion chambers. The coolant driven by an electric water pump 9 at a predetermined constant flow rate Q depending on the engine considered, enters the engine 1 through an inlet 10 and exits through one or more outlets 11 in the form of a liquid two-phase mixture- steam.

 A collecting pipe 12 then brings this liquid-vapor mixture from the outlet 11 of the engine to the inlet of a heat exchanger system 2, of the water / air type, used for heating the intake air of the engine 1. A pipe 23 then connects the outlet of the exchanger 2 to a T-shaped pipe element 3 at the bottom of which is connected a bypass pipe 36.

 The fluid is then brought through a pipe 34, from the pipe element 3 to the inlet 40 of a radiator-condenser 4 forming a heat exchanger where the condensation of the vapor phase of the cooling fluid takes place.

 A fan 5 intended to produce a forced air current is arranged in front of the radiator-condenser 4. The fan can be driven in rotation by an electric motor controlled notably according to the temperature of the coolant from the information delivered by a thermoswitch placed in the device (see the control device shown in dotted lines in the figure).

 The condensate is discharged from the radiator-condenser 4 by an outlet 41. A pipe 47 then brings the liquid into a variable-volume reservoir 7, such as a bellows vessel, the predetermined dimensions of which and in particular the maximum volume V are characterized below. after. Such a system allows the pressure of the cooling device to be adjusted quickly and easily. A line 78 then connects the outlet of the variable volume tank 7 to an air heater 8 for heating the passenger compartment of the motor vehicle.

 The variable volume reservoir 7 being more or less filled with coolant depending on the temperature reached and the vapor produced, the two pipes 47 and 78 open into the reservoir 7 below the minimum level of liquid therein. This arrangement allows any residual vapor bubbles to be trapped in the tank.

 A pipe 89 provides the connection between the air heater 8 and the circulation pump 9 and finally, a pipe 91 brings the liquid from the pump 9 to the inlet 10 of the engine 1.

 The bypass pipe 36, opening into the lower part of the pipe element 3, joins at its other end the pipe 47 by means of a piloted three-way thermostatic valve 6 which also controls the circulation between the radiator-condenser 4 and the reservoir 7. This three-way valve 6, controlled as a function of the temperature of the coolant, makes it possible to selectively authorize the circulation of the liquid-vapor mixture leaving the engine 1, through the bypass line 36 and / or the radiator. -condenser 4.

 The operation of the cooling device which has just been described is therefore as follows.

 When the engine is running, the pump 9 circulates through the cooling device a constant flow rate Q of coolant.

 During the so-called engine start-up phase, the three-way thermostatic valve 6 closes the outlet of the radiator-condenser 4, all of the coolant which is circulated under the action of the pump 9 then passes through line 36. This configuration in restricted circulation avoids the passage of the coolant through the radiator-condenser 4, which allows a rapid rise in the temperature of the coolant.

 When the liquid temperature reaches the set value of the three-way thermostatic valve 6, the outlet of the radiator-condenser 4 then begins to open, a part of the liquid leaving the engine can then pass through the pipe 34 and the radiator condenser 4 which slows the rise in temperature of the liquid. This trigger threshold of the thermostat 6 is determined as a function of the characteristics of the device and in particular of the cavitation threshold of the pump 9.

 Then, when the temperature of the coolant continuing to rise reaches a second threshold value, close to the saturation temperature of the vapor, the thermostat 6 then closes the bypass line 36 so as to force the entire flow of liquid through the radiator-condenser 4. In this way, the whole of the vapor phase which forms with the rise in temperature in the circuit, is directed directly through the radiator-condenser 4.

 As the temperature rises through the device, the reservoir 7 fills with liquid so as to automatically compensate for the increase in the volume of the fluids (by expansion and by vaporization), which makes it possible to maintain the constant pressure until the tank is completely filled 7.

 Once the tank is completely filled, if the steam production remains above the rate of condensation, the mass of steam continues to increase, as well as the pressure and the temperature, while the difference between the thermal power given to the water by the engine and the thermal power evacuated by the radiator-condenser 4, it decreases. This process therefore continues until an equilibrium between the exchanges takes place, thus resulting in the stability of the pressure and the temperature. This equilibrium point is controlled by the choice of the volume V of the reservoir 7 and the flow rate Q to optimize the operation of the device.

 The performance of the two-phase cooling device which has just been described is, in fact, essentially determined by the pressure and temperature values, respectively Pr and T, at the equilibrium point defined above when the power evacuated by the radiator -condenser 4 is equal to the thermal power transmitted to the water by the motor 1. However, it turns out that these values of pressure and temperature at the equilibrium point result essentially from the values of the parameters flow rate Q of the fluid through the closed circuit defined by the device and maximum volume V of the variable volume reservoir 7 and that in particular the values of the pressure and the equilibrium temperature depend directly on the volume V of the reservoir 7 for a given flow rate Q.

 I1 follows that if the tank 7 is undersized, the pressure and the equilibrium temperature are then too high, which entails a risk of insufficient cooling of the engine and therefore a risk of destruction of the latter and that if the tank 7 is oversized, the equilibrium pressure and temperature are then too low, which degrades the performance of the radiator-condenser 4 with the risk of not being able to condense all of the steam produced and therefore entraining the cavitation of the pump. 9 unless this in turn oversize this radiator-condenser 4, but then the device is of a significant cost and size.

 It is therefore essential to best adjust the volume V of the reservoir 7 in order to limit its size and to produce an equilibrium pressure value Pr which makes it possible to ensure a high efficiency of the radiator-condenser 4, without requiring to resort to complex means of adaptation of the flow rate as in the prior art cited above. The Applicant has been able to establish that this pressure value should be between 1.2 and 3 bars and preferably between 2 and 2.5 bars for internal combustion engines fitted to motor vehicles, the maximum thermal powers of which are transferred to the water. are less than 100 kW.

 With regard to the water flow rate Q inside the circuit defined by the device according to the invention, this must be relatively low to cause a satisfactory boiling in the water chambers of the engine 1, but sufficiently large to meet the heat exchange needs of the latter (air heater 8, heating of the intake manifold 2, or water / oil exchanger not shown, etc.) and to limit the temperature of the water at the engine inlet so as to prevent any cavitation of the pump 9. Preferably, this flow rate is chosen between 500 and 1500 liters / hour with regard to the aforementioned motors.

 The value of the flow rate Q having been chosen directly as a function of the characteristics of the engine concerned, the corresponding optimal volume V of the reservoir 7 is then established in order to obtain an equilibrium pressure Pr within the aforementioned range under the critical operating conditions of the engine (strong engine load, low vehicle speed and air temperature of 350C).

 To do this, a programmable dimensioning method is used which is simple to implement and which makes it possible to determine for a given value of the volume V the corresponding equilibrium pressure Pr and thus to deduce therefrom by scanning of successive values, the adequate volume corresponding to a desired pressure value Pr.

 The dimensioning process adopted makes it possible to obtain in a simple manner from the values of the flow rate Q chosen and the volume V considered, the equilibrium pressure Pr resulting therefrom, by successive iterations over time t from a certain number d 'equations representative of the operation of the device according to the invention.

The characteristic equations are as follows. First, the volume Vl (t) occupied by the liquid in the reservoir 7 at time t, is determined by the following formula
V1 = Vdila + Vvmot + Vvrad + Vvtub (1)
where Vdila, Vvmot, Vvrad, Vvtub are respectively the increase in the volume of liquid in the whole of the circuit by its expansion, the volumes of vapor in the engine 1, the radiator-condenser 4, and the part of circuit connecting this last to the engine 1.These different volumes considered at time t, each express themselves in the following form
Vdila = s Vi / (rl (Ti) - rl (To)) (2)
Vvmot = Vmot * A * B / Pmot (3)
Vvrad = Vrad * A * B / Prad (4)
A = Q * L * rl / (rl - rg)
B = (X - C) * ln (l + X / C)
C = rg / (rl - rg)
Vvtub = Vtub * Tv (5)
with: Vi volume of liquid in component i (motor, pump, tubes, etc.);
To initial temperature of the circuit;
Ti temperature of the liquid in component i at time t;
Viot volume of engine water chambers;
Vrad interior volume of the radiator-condenser;
Vtub volume of the circuit connecting the engine to the radiator-condenser;
rl density of the liquid (function of the temperature);
rg vapor density (a function of temperature and pressure)
Pmot power transferred to the coolant by the engine (depends on the engine operating point);
Prad power evacuated by the radiator-condenser (depends on the design of the radiator-condenser, the flow rate of the fluid, the pressure prevailing in the circuit and also the rate of vapor at the inlet of the radiator-condenser);
Q mass flow of the mixture;
Latent heat of steam (function of pressure)
Tv steam volume rate (ratio of steam flow to total liquid and steam flow);
X vapor title.

The vapor titer X is a function of time t and of the component considered (motor and condenser) considered in the circuit. We can thus write Xmot (t) = (hs.mot (t) - hsat.mot (Pr)) / L (Pr) (6)
Xrad (t) = (he.rad (t) - hsat.rad (Pr)) / L (Pr) (7)
and mi * dhs.i / dt = (Q * (hs.i - he.i)) + Qi (8)
with: hs.i mass enthalpy of the liquid leaving component i;
hsat. i mass enthalpy of the liquid in saturation in the component i;
he.i mass enthalpy of the liquid entering component i;
Pr pressure of the two-phase mixture;
mid total mass of the liquid vapor mixture in component i;
Qi power exchanged with the wall in component i.

As long as the tank 7 is not filled (i.e. V1 less than V the volume of the tank 7) the pressure inside the tank is equal to atmospheric pressure, and when the tank is completely filled we have then
Pr = R * T * s Mvi (t) / s Vvi (t) (9)
ii
with: R gas constant (pure vapor);
T steam temperature;
Mvi mass of vapor in component i
Vvi volume of vapor in component i;
By iteration over time and on equations (1) to (9) above, we therefore deduce the values of the pressure Pr, the temperature T at different points of the device as well as the power transferred to the Prad radiator . By operating with different values of tank volume 7, it is then possible to determine with precision the dimensions of the latter in order to obtain the desired values of pressure Pr and of temperature at the motor input.

 Of course, the invention is in no way limited to the embodiment described and illustrated, which has been given only by way of example.

 On the contrary, the invention includes all the technical equivalents of the means described and their combinations if these are carried out according to the spirit.

Claims (6)

 (1) Evaporative cooling device for an internal combustion engine (1) equipping in particular a motor vehicle, of the type comprising a radiator (4) forming a condenser, a variable volume tank (7) and a drive pump ( 9) for circulating a given flow rate of cooling fluid, characterized in that it comprises a piloted three-way valve (6), said valve (6) being capable of directing the flow of fluid leaving the engine selectively through the radiator-condenser (4) and / or a bypass line (36) allowing to bypass said radiator-condenser (4) and in that said pump (9) maintains the flow of fluid substantially constant whatever the operating conditions of the motor (1). [2] Evaporative cooling device of an internal combustion engine according to claim 1, characterized in that the value of said fluid flow is determined according to the heat exchange requirements of the engine (1) and is between 500 and 1500 liters / hour.  (3] Evaporative cooling device for an internal combustion engine according to any one of claims 1 to 2, characterized in that it comprises an air heater (8) intended for heating the passenger compartment of the motor vehicle, said air heater (8) being located downstream of the variable volume tank (7) in the direction of fluid flow.  [4] Evaporative cooling device of an internal combustion engine according to any one of claims 1 to 3, characterized in that said three-way valve (6) is controlled as a function of the temperature of the cooling fluid so directing all of the fluid in circulation through the bypass line (36) until the temperature of the fluid has reached a predetermined value. [5] Evaporative cooling device of an internal combustion engine according to any one of claims 1 to 4, characterized in that the volume V of said variable volume tank (7) is adjusted so as to obtain a pressure d balance between 1.2 and 3 bars. V of said variable volume reservoir (7) is adjusted so as to obtain an equilibrium pressure of between 2 and 2.5 bars.  (6] Evaporative cooling device of an internal combustion engine according to claim 5, characterized in that the volume