WO2012101384A1 - Cooling device for an electronic power system in a vehicle - Google Patents

Abstract

The invention relates to a device which, in order to cool a component of an electronic power system in a vehicle, includes: a tank (11) containing a fluid in a state of equilibrium between the liquid and vapour phases thereof; an evaporator (12) arranged so as to pump the fluid in the liquid phase from the tank (11) by capillary action and convert the fluid into the vapour phase by absorbing a heat load (2) generated by the component (20); a condenser (16) connected to the output of the evaporator (12) so as to receive the fluid in the vapour phase, to a cold source for converting the fluid from the vapour phase into the liquid phase, and to the input of the tank (11) in order to return the fluid in liquid phase to the tank.

Description

 "Cooling device for electronic power system in a vehicle"

The invention relates to a cooling device for an electronic power system in a vehicle, particularly in a motor vehicle.

 An electronic power system is particularly useful in a hybrid or all-electric vehicle to provide power and recovery in electrical energy used to drive and slow the vehicle. Such a system generally comprises many components among which may be mentioned for illustrative and not exhaustive, a battery, super capacitors, thyristors or power transistors.

 The known cooling devices are unsatisfactory.

 The finned panels or radiators are poorly adapted to the new components, the dissipated power of which results in a considerable bulk resulting from the necessary exchange surface.

 Mono-phase coolers of cylindrical type or water plates, pose a problem of integration for large powers to dissipate.

 The two-phase diphasic cooling of the components is based on a boiling phenomenon which involves implementation and maintenance constraints that are too high for its application in the automotive industry.

 Two-phase gravity devices, such as for example thermosiphons, can only operate vertically, which causes integration difficulties. Their transfer capacities remain limited compared to other two-phase technologies.

 Known cooling devices

(fins, air loop, fluid loop ...) have another disadvantage, that of not absorbing peaks of power in severe stresses with the consequence of making difficult the thermal regulation of the power electronics. However, a sudden rise in temperature can cause irreversible damage to electrical components. To avoid this, conventional cooling devices are generally oversized, which implies additional constraints of space and weight.

 To remedy the problems posed by the prior art, the subject of the invention is a device for cooling at least one electronic power system component in a vehicle comprising:

 a reservoir containing a fluid at steady state under both its liquid and vapor phases;

 an evaporator arranged to pump the fluid in the liquid phase from the reservoir by capillarity and to bring the fluid into the vapor phase by absorbing a thermal load generated by the component;

 a condenser connected at the outlet of the evaporator for receiving the fluid in the vapor phase, at a cold source for bringing the fluid from the vapor phase to the liquid phase and at the inlet of the reservoir for returning the fluid to the liquid phase.

 In particular, the evaporator comprises a porous medium so as to pump the fluid by capillarity.

 Advantageously, the reservoir comprises a heating element to bring the temperature of the fluid to the liquid-vapor equilibrium.

 Preferably, the device comprises a regulation module for acting on the heating element so as to homogenize a temperature of the evaporator to a saturation temperature which corresponds to a reference pressure for the device.

This amounts to setting the reference pressure in the device to the saturation pressure at the liquid-vapor equilibrium. The pressure, and thus the saturation temperature, in the other elements of the device, in particular the evaporator, is thus fixed by means of the various pressure drops in the circuit.

 The invention also relates to a motor vehicle comprising at least one power electronics component, characterized in that it comprises a device according to the invention.

 The following explanatory description refers to the accompanying schematic drawings given solely by way of example, illustrating several embodiments of the invention and in which:

 Figure 1 is a block diagram of the device;

 FIG. 2 shows in more detail an evaporator of the device.

 With reference to FIG. 1, the device according to the invention uses a diphasic fluid loop with thermo-capillary pumping (BFDPT) contiguous to the power electronics housings present in large quantities on hybrid and electric vehicles.

 Among the main elements of the device, there are one or more evaporators 12 for absorbing a thermal load 2 generated by electronic power components (not shown), a condenser 16 for discharging the heat load in the form of a flow of heat 6 to a cold source and a reservoir 11 fed by a fluid in the form of a liquid 1.

 The evaporator 12 is arranged to pump the fluid in liquid form by capillary action from the reservoir 11 by means of capillary tubes or preferably of a porous medium such as that explained hereinafter with reference to FIG. 2.

Under the effect of the heat load 2 applied to the porous medium included in the evaporator 12, the liquid 1 vaporizes and vapor 5 escapes into a manifold 14.

Border 3 schematically shows, in the form of meniscus, the limit at which the fluid pumped by capillarity in the evaporator 12 in the liquid phase 1 reaches the saturation temperature (liquid-vapor equilibrium state) T _s from which he evaporates.

Considering a mass flow rate M _F of liquid 1 with a specific heat capacity C _p i which enters evaporator 12 at a temperature Tu at the outlet of the reservoir 11, the heat flux absorbed by sensible heat Φ ₁ -3 is given by a formula of type:

i) 0 ₁ _ ₃ = M _F x C _pl (T _s -T ₁₁ )

Considering the mass flow rate M _F of the evaporative mass enthalpy fluid H _iv that evaporates in the evaporator 12 at the temperature T _s , the latent heat absorbed heat flux Φ3 is given by a formula of the type:

Considering that the thermal load 2 generates a thermal flow Φ2 towards the evaporator 12, the device is dimensioned so as to obtain a mass flow M _F of optimal fluid which satisfies the relation:

iii) Φ ₂ = Φ, _ ₃ + Φ _3.4 = M _F x [C _p (T _s -T _n ) + H _lv ] The capillarity and the evaporation allow the fluid to move in a completely passive manner, so that the mass flow M _F is obtained without the need to involve any mechanical pump to ensure the circulation of the fluid. This results in a considerable maintenance gain compared to conventional cooling circuits.

The collector 14 of the evaporator is connected to the condenser 16 via a pipe 15 in which the fluid in the vapor phase 5 flows at a vapor temperature T ₅ close to the saturation temperature T _s . The pipe 15 extends in the form of a bent tube 17 in the condenser until it opens into a second pipe 18 which connects the condenser 16 to the tank 11.

The condenser 16 is in contact with a cold source 6 at a temperature Ίζ less than the saturation temperature T _s so that the vapor 5 condenses in the tube 17 between two points 7 and 8 of temperature T _s .

Considering the mass flow M _F of two-phase fluid of condensing mass enthalpy H _vi which liquefies in the condenser 16 at the temperature T _s , the exhumed thermal flux Φ7-8 is given by a formula of the type:

iv) Φ ₇ _ ₈ = Μ _Ρ χΗ _ν1

The liquefied fluid continues to cool beyond the point 8 to the outlet of the tube 17 so that the liquid 1 is obtained at the outlet of the condenser 16 at a sub-cooling temperature ΊΊ between the saturation temperature T _s and the cold source temperature Ίζ. Considering the mass flow rate M _F of liquid 1 of specific heat capacity C _p i which enters steady state in the tank 11 at the temperature ΊΊ at the outlet of the condenser 16, the exhumed heat flow Φδ-ι ι is given by a formula of the type :

 Finally, the cold source 6 resorbs a heat flow Φβ of the condenser 16, according to the relation:

vi) Φ ₆ = Φ _7.8 + Φ _{8 1} = M _F x [H _VL + C _PL (T _S - T _T )]

It can be seen that the thermal flux Φς is discharged at the level of the cold source, independently of the temperature T ₂ of the heat load 2 which stabilizes at a value close to the saturation temperature T _s and the temperature T ₆ of the cold source 6. The expression of the heat flux Φς, as a function of the difference in temperature (T ₂ - T ₆ ) and of a thermal conductance K _t hr is of the form:

vil) Φ ₆ = Κ _Λ (Τ ₆ - Τ ₂ )

This observation amounts to considering the thermal conductance K _t h as a variable conductance that adapts naturally at the difference of temperature to convey the thermal flow. This phenomenon is explained by the length of condensation between the points 7 and 8 which naturally increases when the temperature T2 or the thermal flow <I> 6 increases and vice versa.

 In summary, the steam generated in the evaporator 12 by the heat load 2, then flows to the condenser 16 where the power of the heat load is dissipated. The subcooled liquid then exits the condenser 16 to return to the evaporator 12 and ensure the cycle. The adaptation of the length of condensation allows the device to have a variable conductance so that the cold source temperature has little influence on the maintenance of the temperature level at one evaporator in contact with the electronic power components, provided that of course, the cold source temperature is below the saturation temperature.

 The evaporator 12 is shown in more detail in FIG. 2 where a body 19 of the evaporator is in contact with an electronic power component 20. The evaporator contains a porous medium which draws the liquid 1 by capillarity.

 The upper face of the porous medium 13 of the evaporator 12 is in contact with either a solid part of the body 19 which transmits the heat load 2 generated by the electronic power component 20 to the porous medium by thermal conduction, or of an opening in the body 19 arranged to constitute the collector 14 which discharges the steam 5 towards the outlet of the evaporator 12.

 The tank 11 is positioned above the evaporator.

In the tank 11, a heating element 21 such as an electrical resistance, a thermo element or the like, is connected to an electronic unit 22 which regulates the operating temperature of the device so as to maintain homogeneous temperature T2 at an optimum value at the interface of the control unit. Moreover, the naturally variable conductance K _th of the device makes it possible to maintain this temperature whatever the power dissipated, of course insofar as the device is sufficiently sized.

The regulation is parameterized to provide a power given by the relation viii) so as to obtain the desired saturation temperature T _s in the tank:

viii) P _2l = M _p xC _≠ ( _s -T _l )

The following table makes it possible to compare the evaporation enthalpy H _iv and the specific heat capacity C _p i in the liquid state of various fluids selected during debugging tests of the device:

It is noted that the amount of heat absorbed by the evaporation enthalpy is 150 to 1 hexane to 250 ammonia times higher than the amount of heat absorbed by heat capacity to raise the temperature of the liquid by 1 Kelvin.

 Several variants of the device are possible.

 In a CPL type architecture ("Capillary

Pumped Loop "), the tank 11 is decoupled from the pipe 18 while in an LHP type architecture (" Loop Heat Pipe "), the reservoir is attached to 1 'evaporator. The regulation of the tank must therefore be adapted accordingly.

 The design of the tank 11 may also vary in terms of shapes and volumes. Different designs of the evaporator are possible. Other fluids than those mentioned above can also be used in the device, in particular depending on the operating temperature that is to be achieved.

Among the many advantages of using a device pumped two-phase fluid loop thermo ^¬ capillary, in particular with thermal regulation of the reservoir for the cooling of power electronics include a maintenance gain related to the absence mechanical pump, a high transfer capacity (up to 10kW per 1m of pipe) related to the latent heat of the fluid used, a maintenance and a regulation of the temperature of the electronics for different powers to be dissipated, in particular thanks to the conductance variable, a possibility of regulating the temperature of the power electronics through the tank and ease of integration resulting from an absence of stress on the position of the cold source relative to the dissipation zone.

Claims

A device for cooling at least one electronic power system component (20) in a vehicle comprising:  a reservoir (11) containing a fluid at equilibrium state under its two liquid and vapor phases;  an evaporator (12) arranged to pump the fluid in the liquid phase coming from the reservoir (11) by capillarity and to bring the fluid into the vapor phase by absorbing a heat load (2) generated by the component (20);  a condenser (16) connected at the outlet of the evaporator (12) for receiving the vapor phase fluid, at a cold source for supplying the fluid from the vapor phase to the liquid phase and at the inlet of the reservoir (11) to make it return the fluid to the liquid phase. 2. Device according to claim 1, characterized in that the evaporator (12) comprises a porous medium so as to pump the fluid by capillarity. 3. Device according to one of the preceding claims, characterized in that the reservoir (11) comprises a heating element (21) for bringing the fluid temperature to the equilibrium liquid-vapor state. 4. Device according to claim 3, characterized in that it comprises a regulation module (22) for acting on the heating element (21) to homogenize a temperature of the evaporator (12) to a saturation temperature which corresponds to a reference pressure for the device. Motor vehicle comprising at least one power electronics component (20), characterized in that it comprises a device according to one of claims 1 to 4 for cooling said component (20).