Hybrid cooling system

Abstract

The invention relates to a cooling system (1) comprising a housing (2), at least one electronic device (3), at least one liquid-cooled heat sink (4), a coolant (5), and at least one circulating device (13), in which system the at least one liquid-cooled heat sink (4) is either directly or indirectly thermally coupled to the coolant (5); and the at least one electronic device (3) and the coolant (5) are positioned in the housing (2), the at least one electronic device (3) being immersed in the coolant (5); and the at least one circulating device (13) allows the coolant (5) to be circulated inside the housing (2); the at least one electronic device (3) being chosen from an energy storage device and power electronics.

Description

[0001] DESCRIPTION

[0002] TITLE: HYBRID COOLING SYSTEM

[0003] TECHNICAL FIELD OF THE INVENTION

[0004] The present invention relates to the field of cooling systems for electronic devices, in particular cooling systems for battery cells.

[0005] STATE OF THE ART

[0006] Cooling systems are commonly implemented with electrical and / or electronic devices, particularly in the context of battery cells, in order to ensure that these devices are maintained at temperature levels that ensure optimal operation and an extension of their lifespan.

[0007] Among the various cooling systems used with electronic devices, it is known from the state of the art to use cooling systems implementing immersion cooling (also known as "immersion cooling"). In this type of system, the electronic device is placed in a case containing a cooling fluid, such as oil or demineralized water. In this way, the residual heat generated by the electronic device is captured by the cooling liquid inside the case. The heat is then conveyed to a heat exchanger through a cooling circuit. Then, the cooling fluid is cooled by a secondary air-liquid or liquid-liquid heat exchanger, before being dissipated or reused.Thus, the coolant circulates inside the case but also outside of it thanks to the cooling circuit.

[0008] It is also known from the prior art to use cooling systems implementing cooling by liquid-cooled heat sinks. In this type of system, the liquid-cooled heat sink comprises an internal cooling circuit in which a cooling fluid circulates. On the other hand, the liquid-cooled heat sink comprises a semiconductor material allowing thermal transfer of heat between the components. In this case, the liquid-cooled heat sink is directly attached to the electronic device. In this way, the residual heat generated by the electronic device is captured by the external wall of the liquid-cooled heat sink, which is cooled by the internal cooling circuit of the heat sink thanks to the principle of thermal convection.The cooling systems mentioned above often prove to be expensive, complex, of limited effectiveness in terms of heat dissipation or temperature homogeneity of the electronic device, and sometimes insufficient to prevent the spread of thermal runaway to neighboring electronic devices.

[0009] It is therefore an object of the present invention to propose a new, simple-to-implement system for cooling electronic devices aimed at improving the evacuation of heat from electronic devices and preventing the propagation of thermal runaway from a faulty electronic device.

[0010] SUMMARY OF THE INVENTION

[0011] According to a first aspect, the invention relates to a cooling system comprising a housing, at least one electronic device, at least one liquid-cooled heat sink, a cooling fluid, and at least one circulation device, wherein: said at least one liquid-cooled heat sink is thermally coupled directly or indirectly to the cooling fluid; and said at least one electronic device and the cooling fluid are positioned in the housing, the at least one electronic device being immersed in the cooling fluid; and said at least one circulation device makes it possible to circulate the cooling fluid inside the housing; said at least one electronic device being chosen from an energy storage device and power electronics.

[0012] By "housing", it is understood and within the scope of the present invention, an enclosure capable of receiving a cooling fluid and at least one electronic device. The housing may be sealed in itself or, if it is not, the arrangement of the liquid-cooled heat sink and the housing may be such that this arrangement is sealed.

[0013] By "cooling fluid", it is understood and within the scope of the present invention, a heat transfer fluid capable of cooling the at least one electronic device. It is a fluid capable of absorbing the thermal energy produced by the at least one electronic device.

[0014] By "thermally coupled", it is understood and within the scope of the present invention, a mechanical or exothermic connection mode allowing thermal conduction with the housing.

[0015] By "circulation device", it is understood and within the meaning of the invention, any type of device internal or external to the housing allowing the cooling fluid to be circulated inside the housing, such as a circulation device comprising channels and at least one pump and / or at least one accelerator. When it is external to the housing, the circulation device can be connected to heat exchangers of the electric vehicle (outside the cooling system of the invention).

[0016] A cooling system according to the first aspect of the invention makes it possible to optimize the evacuation of heat emanating from the at least one electronic device. Indeed, the presence of at least one liquid-cooled heat sink and a cooling fluid according to the first aspect of the invention makes it possible to improve the temperature uniformity of the at least one electronic device in that they avoid the creation of hot spots in the cooling fluid.

[0017] In a cooling system according to the first aspect, the cooling of the at least one electronic device is ensured by the cooling fluid which is cooled by the at least one heat sink thanks to a thermal conduction phenomenon.

[0018] A cooling system according to the first aspect of the invention makes it possible to limit the risks of propagation of thermal runaway of at least one electronic device.

[0019] The cooling fluid is circulated in the housing of the cooling system thanks to the circulation device creating a phenomenon of thermal convection, also referred to as "forced thermal convection", which is opposed to the phenomenon of "natural thermal convection" which is carried out in the absence of a circulation device. This circulation of the fluid coupled with the heat sink (for example cold plate) makes it possible to surprisingly improve the cooling of said at least one electronic device.

[0020] A cooling system according to the first aspect of the invention is particularly suitable for energy storage devices or power electronics. Indeed, energy storage devices or power electronics are subject to particular operations, sometimes causing sudden temperature increases. The cooling system according to a first aspect therefore allows particularly efficient cooling for these types of devices and / or electronics.

[0021] In one embodiment, the housing of the cooling system is a rectangular parallelepiped, a cube, or a cylinder.

[0022] According to one embodiment, the housing comprises 5 walls and the cooling system is made watertight by the arrangement of the liquid-cooled heat sink. In one embodiment, the housing of the cooling system comprises a means allowing a gas to escape, in particular during thermal runaway of at least one electronic device.

[0023] By "means allowing a gas to escape", it is understood and within the meaning of the invention, any type of vent allowing the gas to escape either automatically, for example by means of a valve, or in a controlled manner, for example by means of a valve.

[0024] This embodiment allows the extraction of excess gas produced by the at least one electronic device, particularly during thermal runaway. This makes it possible, in particular, to avoid excess pressure in the housing.

[0025] According to one embodiment, the means allowing a gas to escape is positioned in an upper part of the housing in the direction of gravity, when the at least one electronic device is in the operating position.

[0026] This embodiment simplifies the extraction of gases present in the housing. In fact, the gases will be positioned above the cooling fluid, in the upper part of the housing along the vertical axis, that is to say in the direction of gravity.

[0027] By "electronic device in operating position" is meant and within the meaning of the invention, the position in which the at least one electronic device will be used, for example when it is connected to the electric vehicle. In such a position, it is then possible to determine a top and a bottom of the electronic device.

[0028] In one embodiment, the housing is made of at least one thermally conductive material, such as aluminum, copper, stainless steel, or a combination of at least two materials from this list of materials.

[0029] This embodiment makes it possible to improve the thermal conductivity of the housing and to optimize the evacuation of heat emanating from at least one electronic device.

[0030] In one embodiment, the housing of the cooling system includes at least one opening for replacing and / or adding coolant.

[0031] This embodiment makes it easier to maintain the cooling system.

[0032] In one embodiment, said at least one liquid-cooled heat sink is indirectly thermally coupled to the cooling fluid. According to this embodiment, at least one wall of the housing is located between said liquid-cooled heat sink and said cooling fluid. According to this embodiment, the at least one liquid-cooled heat sink may be coupled to at least a portion of the outer surface of at least one of the walls of the housing. Advantageously, according to this embodiment, the liquid-cooled heat sink is in contact with the outer surface of at least one of the walls of the housing, preferably with the entire outer surface of a wall of the housing, preferably the bottom or top wall of the housing.

[0033] In one embodiment, the at least one liquid-cooled heat sink is thermally coupled directly to the cooling fluid, i.e., the liquid-cooled heat sink is in direct contact with the cooling fluid. According to this embodiment, the at least one liquid-cooled heat sink may be coupled to at least a portion of the inner surface of the housing.

[0034] By "direct contact" it is understood and within the meaning of the invention, that the cooling fluid is in contact with the at least one liquid-cooled heat sink without intermediary, for example, without the intermediary of the housing wall. There is therefore nothing between the cooling fluid and the liquid-cooled heat sink.

[0035] This embodiment allows for increased heat exchange between the cooling fluid, the housing and / or the at least one liquid-cooled heat sink. In addition, the cooling of the at least one electronic device is improved and the temperature uniformity of the at least one electronic device is improved.

[0036] According to one embodiment, the cooling system comprises a single liquid-cooled heat sink.

[0037] This embodiment makes it possible to limit the size of the cooling system and to reduce the manufacturing costs of such a system.

[0038] The liquid-cooled heat sink may be positioned in any position at any wall of the enclosure. Preferably, the liquid-cooled heat sink is positioned at the top or bottom wall of the enclosure in the direction of gravity when the at least one electronic device is in the operating position. In a particular embodiment, the at least one liquid-cooled heat sink is positioned at the bottom wall of the enclosure in the direction of gravity when the at least one electronic device is in the operating position.

[0039] By "at the wall" is meant in the immediate vicinity of said wall, or even in contact with said wall. In other words, "at the wall" means that the dissipator is in contact with the wall or that there is only fluid between the dissipator and the wall.

[0040] Advantageously, the liquid-cooled heat sink is thermally coupled to an internal or external surface of a wall of the housing. By "lower wall" is meant and within the meaning of the invention, the part located at the bottom in the direction of gravity, when the at least one electronic device is in the operating position. This terminology is opposed to the term "upper wall" which refers to the part located at the top in the direction of gravity, when the at least one electronic device is in the operating position. The lower wall is located at a lower altitude than the upper wall.

[0041] Typically, within the scope of the invention, the liquid-cooled heat sink is not in direct contact with the electronic device(s).

[0042] In one embodiment, the liquid-cooled heat sink is fully enclosed within the cooling system housing.

[0043] This embodiment makes it easier to arrange the cooling system.

[0044] According to one embodiment, the at least one liquid-cooled heat sink is configured to cover at least 20% of the surface (internal or external) of a wall of the housing, preferably at least 50% of the surface of a wall of the housing, and more preferably at least 75% of the surface of a wall of the housing, even more preferably to cover 100% of the surface of a wall of the housing, the housing being able for example to have a thermal conductivity of at least 15 W / (mK).

[0045] This embodiment makes it possible to optimize the evacuation of heat emanating from at least one electronic device. Indeed, the presence of at least one liquid-cooled heat sink covering at least 20% of the surface of a wall of the housing makes it possible to improve the temperature homogeneity of the at least one electronic device. When the liquid-cooled heat sink covers 100% of the surface of a wall of the housing, the synergy effect with the cooling fluid is improved.

[0046] For example, the liquid in the liquid-cooled heat sink will have a temperature ranging from -40°C to 70°C.

[0047] According to one embodiment, the energy storage device is a battery cell, such as a battery cell of an electric or hybrid vehicle.

[0048] By "battery cell" is meant and within the meaning of the invention, a homogeneous assembly transforming chemical energy into electrical energy at a given voltage.

[0049] The circulation device may be internal or external to the housing, preferably internal to the housing. According to one embodiment, said at least one circulation device comprises at least one pump. Preferably, said at least one pump is located outside the housing.

[0050] This embodiment ensures the circulation of the fluid inside the housing.

[0051] The inventors discovered that the coolant and the heat sink cooperated to synergistically improve the cooling of electronic devices when the coolant was circulated inside the case.

[0052] In a preferred embodiment, said pump is configured to deliver said cooling fluid at a flow rate greater than or equal to 8 L / min, preferably greater than or equal to 10 L / min, preferably greater than or equal to 12 L / min, and even more preferably greater than or equal to 15 L / min. Advantageously, the flow rate of the cooling fluid will be from 8 to 30 L / min, preferably from 10 to 20 L / min.

[0053] Circulation with these flow rates surprisingly makes it possible to significantly increase the cooling of said at least one electronic device by the cooling system of the invention comprising both a liquid-cooled heat sink and a cooling fluid. This embodiment is particularly advantageous in the case where the electronic device(s) are completely immersed in the cooling fluid.

[0054] This embodiment makes it possible to improve the temperature homogeneity of the at least one electronic device. More specifically, in the case where the housing comprises a multitude of electronic devices, for example several battery cells, the cooling system of the invention with forced convection of the cooling fluid as defined in the invention makes it possible to significantly reduce the temperature difference between the average of the temperatures of each electronic device and the temperature of the electronic device having the lowest temperature within the housing.

[0055] This embodiment also makes it possible to maintain the coolant at a relatively constant temperature, in other words, the temperature difference between two points of the coolant is relatively small.

[0056] For example, the cooling fluid is at a temperature ranging from -40 to 70°C when it is implemented during the installation of the cooling system, before starting up the electronic device. In one embodiment, the circulation device is positioned in an upper part of the housing in the direction of gravity, when the at least one electronic device is in the operating position.

[0057] This embodiment makes it possible to optimize the useful space of said cooling system.

[0058] In one embodiment, the liquid-cooled heat sink is a cooling plate, particularly a cold plate.

[0059] This embodiment makes it possible to optimize the evacuation of heat emanating from at least one electronic device, and to improve the cooling capacity of the cooling fluid.

[0060] According to one embodiment, the cold plate has a thickness of between 1 mm and 50 mm, preferably between 5 mm and 30 mm.

[0061] This embodiment makes it possible to improve the overall compactness of the cooling system.

[0062] According to one embodiment, the at least one electronic device is completely immersed in the cooling fluid.

[0063] This embodiment makes it possible to optimize the evacuation of heat emanating from the at least one electronic device, to improve the uniformity of the temperature of the at least one electronic device, and to limit the presence of hot spots at the level of the at least one electronic device.

[0064] According to one embodiment, the cooling system comprises a plurality of electronic devices arranged separated from each other, preferably equidistantly.

[0065] This embodiment ensures uniform cooling of each electronic device.

[0066] In case the case has several electronic devices, preferably the cooling fluid is in contact with all the electronic devices.

[0067] According to one embodiment, the cooling fluid according to the invention comprises one or more base oils, preferably in a total content of at least 70% by weight, preferably ranging from 70 to 100% by weight, more preferably from 80 to 98% by weight, preferentially from 85 to 95% by weight, relative to the total weight of the cooling fluid. These base oils may be chosen from base oils conventionally used in the field of lubricating oils, such as mineral, synthetic or natural, animal or vegetable oils or mixtures thereof. It may be a mixture of several base oils, for example a mixture of two, three, or four base oils.

[0068] The base oils of the coolant considered according to the invention may in particular be oils of mineral or synthetic origin belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATI EL classification) and presented in table 1 below or their mixtures. The coolant may consist of 100% base oil of mineral, synthetic, biosourced or recycled origin.

[0069] [Table 1]

[0070] Mineral base oils include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, de-alphatting, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing.

[0071] Blends of synthetic and mineral oils, which can be bio-sourced, can also be used.

[0072] For example, the cooling fluid used according to the invention may comprise at least 80% by weight or at least 90% by weight or 100% by weight of an isoparaffinic bio-sourced hydrocarbon cut, said isoparaffinic bio-sourced hydrocarbon cut comprising a weight content of isoparaffins ranging from 90 to 100%, a weight content of normal paraffins ranging from 0 to 10% and a content of carbon of biological origin greater than or equal to 90% by weight relative to the total weight of carbon atoms in the bio-sourced hydrocarbon cut. The isoparaffinic bio-sourced hydrocarbon cut may be prepared according to the method described in document WO2018078024. The content of carbon of biological origin may be measured according to the ASTM D6866 standard.

[0073] Thus, according to an advantageous embodiment, the cooling fluid used according to the invention has a biodegradability at 28 days of at least 60%, preferably at least 70%, preferentially at least 75% and even more preferentially at least 80% measured according to the OECD 301 B standard.

[0074] The coolant may be derived in whole or in part from the recycling of one or more lubricating oils. In particular, the coolant may be a recycled or re-refined oil or may comprise at least one recycled or re-refined oil. For example, the recycled or re-refined oil may be an oil that has been subjected to one or more prior steps selected from the steps of dehydration, distillation, filtration, hydrogenation, liquid / liquid extraction, decantation and / or passage of the used lubricant over an adsorbent material.

[0075] There is generally no limitation on the use of different base oils to produce the cooling fluids used according to the invention, except that they must have properties, in particular in terms of viscosity, viscosity index, or resistance to oxidation, suitable for use in propulsion systems of an electric or hybrid vehicle.

[0076] The base oils of the cooling fluids according to the invention can also be chosen from synthetic oils, such as certain esters of carboxylic acids and alcohols, polyalphaolefins (PAO), and polyalkylene glycols (PAG) obtained by polymerization or copolymerization of alkylene oxides comprising from 2 to 8 carbon atoms, in particular from 2 to 4 carbon atoms.

[0077] PAOs used as base oils are, for example, obtained from monomers comprising 4 to 32 carbon atoms, for example from octene or decene. The weight-average molecular mass of the PAO can vary quite widely. Preferably, the weight-average molecular mass of the PAO is less than 600 Da. The weight-average molecular mass of the PAO can also range from 100 to 600 Da, from 150 to 600 Da, or from 200 to 600 Da.

[0078] According to a preferred embodiment, the base oil or oils of the cooling fluid used according to the invention are chosen from biosourced isoparaffinic hydrocarbon cuts, recycled or re-refined oils, polyalphaolefins (PAO), polyalkylene glycol (PAG) and esters of carboxylic acids and alcohols, silicone, ether.

[0079] Additional additives may be implemented in the coolant of the invention. Among these additives, antioxidants, anti-corrosion additives, anti-foam additives and pour point depressants may be mentioned.

[0080] According to a particularly preferred embodiment, the cooling fluid according to the invention comprises at least one antioxidant additive.

[0081] The antioxidant additive generally helps to delay the degradation of the fluid in service. This degradation can notably result in the formation of deposits, the presence of sludge or an increase in the viscosity of the fluid.

[0082] Antioxidant additives act in particular as radical inhibitors or hydroperoxide destroyers. Among the commonly used antioxidant additives, mention may be made of phenolic antioxidant additives, amine antioxidant additives, and phosphosulfur antioxidant additives. Some of these antioxidant additives, for example phosphosulfur antioxidant additives, may be ash-generating. Phenolic antioxidant additives may be ash-free or in the form of neutral or basic metal salts. The antioxidant additives may in particular be chosen from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted by at least one C1-C12 alkyl group, N, N'-dialkyl-aryl-diamines and mixtures thereof.

[0083] Preferably according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol group of which at least one vicinal carbon of the carbon carrying the alcohol function is substituted by at least one C1-C10 alkyl group, preferably a C1-C6 alkyl group, preferably a C4 alkyl group, preferably by the tert-butyl group.

[0084] Amino compounds are another class of antioxidant additives that can be used, optionally in combination with phenolic antioxidant additives. Examples of amine compounds are aromatic amines, for example aromatic amines of the formula NR4R5R6 in which R4 represents an aliphatic group or an aromatic group, optionally substituted, R5 represents an aromatic group, optionally substituted, R6 represents a hydrogen atom, an alkyl group, an aryl group or a group of the formula R7S(O)zR8 in which R7 represents an alkylene group or an alkenylene group, R8 represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2. Sulphurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

[0085] Another class of antioxidant additives is copper compounds, e.g. copper thio- or dithio-phosphates, copper salts of carboxylic acids, dithiocarbamates, sulphonates, phenates, copper acetylacetonates. Copper I and II salts, succinic acid or anhydride salts can also be used.

[0086] The cooling fluid according to the invention may contain all types of antioxidant additives known to those skilled in the art.

[0087] The cooling fluid according to the invention may comprise from 0.1 to 2% by weight of at least one antioxidant additive, relative to the total weight of the cooling fluid.

[0088] According to a particular embodiment, the cooling fluid according to the invention is free of antioxidant additive of aromatic amine type or sterically hindered phenol type.

[0089] The cooling fluid according to the invention may comprise at least one anti-corrosion additive.

[0090] The anti-corrosion additive advantageously helps to delay or prevent corrosion of the metal parts of the battery.

[0091] A cooling fluid according to the invention may comprise from 0.01 to 2% by weight or from 0.01 to 5% by weight, preferably from 0.1 to 1.5% by weight or from 0.1 to 2% by weight of anti-corrosion agent, relative to the total weight of the fluid.

[0092] The cooling fluid according to the invention may further comprise at least one antifoaming agent.

[0093] The antifoam agent can be chosen from polyacrylates or waxes.

[0094] The cooling fluid according to the invention may comprise from 0.01 to 2% by weight or from 0.01 to 5% by weight, preferably from 0.1 to 1.5% by weight or from 0.1 to 2% by weight of antifoaming agent, relative to the total weight of the fluid.

[0095] The cooling fluid according to the invention may also comprise at least one pour point lowering additive (also known as “PPD” agents for “Pour Point Depressant” in English).

[0096] By slowing the formation of paraffin crystals, pour point depressants generally improve the cold behavior of the fluid. Examples of pour point depressants include polyalkyl methacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, and alkylated polystyrenes.

[0097] The cooling fluid may also be a dielectric fluid. According to a second aspect, the invention relates to a cooling method implemented in the cooling system according to the invention, the method comprising: a step of circulating the cooling fluid inside the housing; a step of heat exchange between the liquid-cooled heat sink and the cooling fluid; and a step of heat exchange between the cooling fluid and said at least one electronic device.

[0098] During the cooling process, the electronic device is put into operation. It is this operation that will likely create heat and generate thermal exchanges.

[0099] The invention also relates to the use of the cooling system for cooling at least one battery cell of an electric or hybrid vehicle, such as a motor vehicle or an air vehicle, preferably an electric vehicle.

[0100] According to a third aspect, the invention relates to an electric or hybrid vehicle battery, preferably electric, comprising at least one cooling system according to the first aspect of the invention.

[0101] According to an embodiment of the first aspect, the cooling system according to the invention comprises a housing, at least one electronic device, at least one liquid-cooled heat sink, a cooling fluid, and at least one circulation device, wherein: said at least one liquid-cooled heat sink is thermally coupled directly or indirectly to the cooling fluid; and said at least one electronic device and the cooling fluid are positioned in the housing, the at least one electronic device being immersed in the cooling fluid; and said at least one circulation device makes it possible to circulate the cooling fluid inside the housing; said at least one electronic device being chosen from an energy storage device and power electronics;wherein wherein said at least one circulation device is located at least partially outside the housing, said circulation device comprising at least one pump and at least two channels; and wherein said pump is configured to deliver said cooling fluid at a flow rate greater than or equal to 8 L / min.;

[0102] According to an embodiment of the first aspect, the cooling system according to the invention comprises a housing, at least one electronic device, at least one liquid-cooled heat sink, a cooling fluid, and at least one circulation device, wherein: said at least one liquid-cooled heat sink is thermally coupled directly or indirectly to the cooling fluid; and said at least one electronic device and the cooling fluid are positioned in the housing, the at least one electronic device being immersed in the cooling fluid; and said at least one circulation device makes it possible to circulate the cooling fluid inside the housing; said at least one electronic device being chosen from an energy storage device and power electronics;wherein said at least one liquid-cooled heat sink is indirectly thermally coupled to the cooling fluid, at least one wall of the housing being located between said liquid-cooled heat sink and said cooling fluid; wherein wherein said at least one circulation device is located at least partially outside the housing, said circulation device comprising at least one pump and at least two channels; and wherein said pump is configured to deliver said cooling fluid at a flow rate greater than or equal to 8 L / min.;

[0103] BRIEF DESCRIPTION OF THE FIGURES

[0104] Other characteristics and advantages of the invention will appear on reading the following detailed description, by way of non-limiting example, and the appended figures, among which:

[0105] [Fig. 1] represents a sectional side view of a cooling system according to one embodiment;

[0106] [Fig. 2] represents a sectional side view of a cooling system according to one embodiment; [Fig. 3] represents in three dimensions and in section a cooling system according to one embodiment;

[0107] [Fig. 4] shows a sectional side view of an electric vehicle battery according to one embodiment.

[0108] DETAILED DESCRIPTION OF THE INVENTION

[0109] A cooling system according to embodiments is described with reference to Figure 1.

[0110] The cooling system 1 shown in this figure comprises a housing 2, a plurality of electronic devices 3, a cold plate 4, a circulation device 13, and a cooling liquid 5. The cooling system 1 allows the cooling of at least one electronic device 3 during the operation of at least one of the latter.

[0111] In this embodiment, the housing 2 is rectangular in shape. In another embodiment not shown, the housing 2 is cubic or cylindrical in shape.

[0112] In Figure 1 shown, the housing 2 comprises four side walls 8, an upper wall 9, a lower wall 10, said walls having a thickness e. Thus, the housing 2 comprises an external surface 6 and an internal surface 7. The upper wall 9 and the lower wall 10 being defined according to the direction of gravity, when the electronic devices 3 are in the operating position.

[0113] Preferably, the housing 2 is made of a material having good thermal conductivity, typically a thermal conductivity of at least 15 W / (mK). For example, the housing 2 may be made of aluminum, copper, stainless steel, or a combination of at least two materials from this list of materials. In a non-illustrated embodiment, the housing includes means for allowing gas trapped in the housing 2 to escape, for example, a valve that opens when the pressure reaches a certain level inside the housing.

[0114] Typically, inside the housing 2, the cooling system 1 comprises a cooling fluid 5 and a plurality of electronic devices 3.

[0115] The electronic devices 3 are, for example, power electronics or energy storage devices, such as battery cells.

[0116] The electronic devices 3 may be held together by a support not shown, for example a perforated plate into which the electronic devices 3 are inserted. The perforated plate may be fixed to the internal surface of the housing 7 by any known fixing means. As shown in Figure 3, the electronic devices 3 may be arranged equidistant from each other, in other words, the distance separating several consecutive electronic devices may be identical. The electronic devices 3 are shown in the form of rectangular electronic devices, but any shape is possible provided that the circulation of the cooling fluid 5 between the electronic devices 3 is allowed. For example, the electronic devices are cylindrical, cubic, or prismatic in shape.

[0117] When the electronic devices 3 are energy storage devices, such as battery cells, each of the latter has an anode and a cathode, as well as an electrolyte, these elements are not shown. The energy storage devices can be battery cells of the lithium-ion family, that is to say, whose electrolyte is composed of lithium.

[0118] As shown in Figure 1, the electronic devices 3 are completely immersed in the cooling fluid 5, in other words, the cooling fluid completely envelops the electronic devices 3.

[0119] In one embodiment, the coolant 5 may comprise one or more base oils and optionally one or more additives. The coolant 5 may comprise one or more compounds such that the coefficient of variation of density as a function of the temperature of the coolant is greater than or equal to 0.6 kg / m3 / K or even greater than or equal to 0.7 kg / m3 / K. This coefficient defines the variation in density and / or volume that the fluid undergoes during a variation in temperature. In one embodiment, the composition of the coolant is chosen so as to have a high coefficient of variation of density as a function of the temperature of the coolant 5, i.e. a fluid whose volume increases sharply with the increase in temperature or a fluid whose density reduces sharply with the increase in temperature.Such a cooling fluid undergoes more intense natural thermal convection.

[0120] Similarly, the intensity of natural thermal convection depends on the kinematic viscosity of the coolant 5, the thermal conductivity of the coolant 5 and / or the specific heat capacity of the coolant 5. Thus, the components of the coolant will be chosen so as to have:

[0121] - a kinematic viscosity of the fluid lower than a maximum kinematic viscosity threshold; and / or

[0122] - a thermal conductivity of the fluid lower than a maximum thermal conductivity threshold; and / or

[0123] - a specific heat capacity of the fluid lower than a maximum specific heat capacity threshold.

[0124] For example, the kinematic viscosity threshold at 25°C according to ASTM D445 can be 100 cSt or 15 cSt. The thermal conductivity threshold at 25°C can be 180 mW / (mK), or 160 mW / (mK) or 140 mW / (mK). The specific heat capacity threshold can be 2500 J / (kg.K), or 2200 J / (kg.K), or 2000 J / (kg.K).

[0125] A coolant 5 with such a temperature-dependent density variation coefficient, such a kinematic viscosity, such a thermal conductivity and such a specific heat capacity makes it possible to produce intense natural thermal convection within the coolant, in particular when the temperature of an electronic device increases sharply during thermal runaway.

[0126] As shown in the embodiment of Figure 1, the cold plate 4 is positioned at the bottom wall 10 of the housing 2 and is in contact with the latter. The cold plate 4 is thermally coupled to the external surface of the housing 6. According to this embodiment, the bottom wall 10 of the housing is made of a material having good conductivity, typically a thermal conductivity of at least 15W / (mK).

[0127] In an embodiment not shown, the cold plate 4 is positioned at one of the side walls 8, or the upper wall 9. According to this latter embodiment, the cold plate 4 is thermally coupled to the external surface 6 of the wall at which the cold plate 4 is positioned.

[0128] Typically, the cold plate 4 comprises a plurality of channels within which a cooling fluid circulates (not shown).

[0129] According to one embodiment, the cold plate covers the entire lower wall of the housing 2. Thus, in the embodiment shown in FIG. 1, the cold plate 4 covers the entire lower wall 10, in other words, the surface of the cold plate 4 in contact with the lower wall 10 and the external surface 6 of the lower wall 10 are of the same dimensions. This embodiment makes it possible to improve the cooling of the electronic devices 3 by guaranteeing an increased heat exchange surface between the cold plate 4 and the cooling fluid 5.

[0130] In an embodiment not illustrated, the cold plate 4 covers at least 20% of the external surface 6 of the lower wall 10, preferably at least 50%, and even more preferably at least 75% of the external surface 6 of the lower wall 10. This embodiment makes it possible to guarantee sufficient heat exchange between the cooling fluid 5 and the cold plate 4. According to one embodiment, the cold plate covers 100% of the external surface 6 of the lower wall 10 of the housing 2. This is the embodiment illustrated in FIG. 1.

[0131] The cold plate 4 may be metallic, or made of any other material having good thermal conductivity. For example, the cold plate 4 is made of a material similar to the housing 2 or of a material chosen from the list of materials that can be considered for the housing 2 mentioned above. According to one embodiment, the cold plate 4 has a thickness of between 1 mm and 50 mm, and more particularly between 5 mm and 30 mm, this makes it possible to improve the overall compactness of the cooling system 1.

[0132] In an embodiment not shown, the cold plate 4 has a thickness similar to the thickness of the housing 2.

[0133] The coolant circulating inside the channels of the cold plate may be water or a coolant similar to coolant 5.

[0134] In the embodiment where a cold plate 4 is used, the latter is connected to a cooling circuit external to the cooling system 1. The external cooling circuit typically comprises channels connected to a pump and to an air-liquid or liquid-liquid heat exchanger. During operation of the cold plate, the coolant circulating inside the latter is circulated by the pump of the external cooling circuit. The coolant of the cold plate will then circulate through the different channels and the air-liquid or liquid-liquid heat exchanger. Thus, thanks to this heat exchanger, the heat accumulated by the coolant of the cold plate is evacuated.

[0135] As shown in the embodiment of Figure 1, the circulation device 13 comprises a pump 14, an inlet channel 15 and an outlet channel 16. According to the embodiment shown, the pump 14 is located outside the housing 2.

[0136] In an embodiment not shown, the circulation device 13 is positioned in the upper part of the housing in the direction of gravity, when the electronic devices are in the operating position. According to this embodiment, the circulation device 13 can be held in the upper part by fixing means not shown.

[0137] According to the embodiment shown, the pump 14 of the circulation device 13 is configured to deliver the cooling fluid at a given flow rate, preferably a flow rate greater than or equal to 8 L / min, preferably at a flow rate greater than or equal to 12 L / min, and even more preferably at a flow rate greater than or equal to 15 L / min. Such a pump coupled to these flow rates makes it possible to dispense with the use of a heat exchanger to cool the cooling fluid. Indeed, the pump 14 makes it possible to maintain the temperature of the fluid at a relatively constant temperature.

[0138] The operation of the cooling system 1 shown in Figure 1 will now be explained.

[0139] During operation of the electronic devices 3, the temperature of the latter will increase, thus generating residual heat (also known by the terminology "thermal energy"). The generated residual heat will be captured by the cooling fluid 5 contained inside the housing 2. The cooling fluid 5 in contact with the surface of the electronic devices 3 or in the area close to the electronic devices 3 quickly rises to a high temperature.

[0140] The circulation device 13 makes it possible to circulate the cooling fluid 5 inside the housing 2. The circulation device 13 can be located at least partially outside the housing 2. During operation of said circulation device 13, the cooling fluid 5 will be sucked into the inlet channel 15 by means of the pump 14. Then said cooling fluid 5 will be evacuated via the outlet channel 16. This embodiment shown in FIG. 1 makes it possible to accentuate the cooling of the electronic devices 3 thanks to a phenomenon of forced thermal convection.

[0141] According to the embodiment illustrated in Figure 1, the pump 14 is located outside the housing 2 and the channels 15 and 16 respectively allow the cooling fluid 5 to be introduced into the housing and the cooling fluid 5 to be extracted from the housing.

[0142] By circulating the cooling fluid 5 inside the housing 2, the cooling fluid 5 which is in contact or in the proximity zone of the electronic devices 3 is evacuated away from them, thus transferring the thermal energy transmitted by the electronic devices 3 away from them.

[0143] The thermal energy is then distributed in a larger volume of cooling fluid 5 and over a larger number of electronic devices 3, ensuring that the cooling fluid 5 and the electronic devices 3 in operation remain at a relatively low temperature. In addition, the thermal energy accumulated by the cooling fluid 5 can be transferred to the housing 2 to be discharged to the outside, discharge to the outside which is here improved by the cold plate 4. Thus, the cooling system 1 makes it possible to cool the electronic devices 3 in a homogeneous and efficient manner, even when using a device for managing the cooling fluid which is simplified.

[0144] The cooling of the electronic devices 3 is therefore ensured by the cooperation of the cooling fluid 5, circulated by the circulation device 13, and the cold plate 4 within the cooling system 1 itself. The cooling system of the invention thus makes it possible to do without an external heat exchanger to cool the cooling fluid.

[0145] Figure 2 represents the same cooling system 1 as that described in figure 1, but in an embodiment where the housing 2 comprises four side walls 8, and a top wall 9. According to this embodiment, the walls of the housing 2 could have low thermal conductivity.

[0146] According to the embodiment of Figure 2, in the absence of lower wall 10, the cold plate 4 replaces the latter, in other words, the cold plate 4 is positioned in place of the lower wall 10.

[0147] The cold plate 4 thus arranged is thermally coupled to the internal surface 7 of the housing 2, in direct contact with the cooling fluid 5.

[0148] The mechanical coupling between the cold plate 4 and the housing 2 guarantees the sealing of the housing 2.

[0149] The cold plate 4 has a thickness between 1 mm and 50 mm, more particularly between 5 mm and 30 mm.

[0150] In an embodiment not shown, the cold plate 4 has a thickness similar to the thickness of the walls of the housing 2.

[0151] In the embodiment shown in Figure 2, the cold plate 4 is completely included in the housing 2, in other words, the cold plate 4 does not protrude from the housing 2. This embodiment makes it easier to arrange the cooling system 1.

[0152] In an embodiment not shown, the cold plate 4 projects from the housing 2. This embodiment makes it possible to increase the volume available inside the housing 2.

[0153] The embodiment shown in Figure 2 allows an increased exchange of heat between the different elements of the cooling system 1, i.e. between the cooling fluid 5 and the electronic devices 3, and between the cooling fluid 5 and the cold plate 4.

[0154] Figure 3 represents the same cooling system 1 as that described in Figure 2, but in an embodiment where the housing 2 comprises an inlet channel 15 allowing the circulation of the cooling fluid 5.

[0155] According to the embodiment shown, the inlet channel 15 is positioned on one of the side walls of the housing 2.

[0156] According to an embodiment not illustrated, the outlet channel 16 is positioned on one of the side walls of the housing 2.

[0157] Figure 4 shows an electric vehicle battery 12 comprising a plurality of cooling systems 1 as described in Figure 1.

[0158] According to a non-illustrated embodiment, the electric vehicle battery 12 comprises a plurality of cooling systems 1 comprising a circulation device 13 common to several cooling systems 1. In other words, the circulation device 13 can make it possible to circulate the cooling fluid 5 in several housings 2. Thus, the circulation device 13 makes it possible to circulate the cooling fluid 5 inside each of the housings 2 of the plurality of cooling systems 1.

[0159] This embodiment makes it possible in particular to simplify the manufacturing and reduce the associated costs of such a battery, and of the cooling systems 1.

[0160] Of course, various other modifications may be made to the invention within the scope of the appended claims.

[0161] EXAMPLES

[0162] The cooling of an electric vehicle battery pack module was simulated using the simulation software: COMSOL MULTI PHYSICS® 6.0, based on the finite element method.

[0163] The modeled battery module comprises 8 cells, each identical and in the shape of a non-deformable rectangular parallelepiped with dimensions:

[0164] - Length L (dimension x) = 148mm,

[0165] - width I (dimension z) = 91mm and

[0166] - thickness e (dimension y) = 26.7mm.

[0167] The properties of thermal grease are as follows:

[0168] - Density: rho = 1700 kg / m 3 ;

[0169] - Specific heat capacity: Cp = 1000 J / (kg.K);

[0170] - Isotropic thermal conductivity: kxx = kyy = kzz = 0.7 W / (mK).

[0171] Each heating cartridge delivers a constant heating power of 4.25W, or a power per cell of 12.75W. The initial temperature of the system is 20°C.

[0172] The temperature of the cold plate is 15°C.

[0173] The cooling fluid is an isoparaffinic fluid comprising at least 90% by weight of isoparaffins having from 15 to 18 carbon atoms, relative to the total weight of the isoparaffinic fluid.

[0174] A slight heat exchange between the casing (housing) and the ambient air has been set: 5W / (m 2 .K) with an outside temperature of 21°C.

[0175] A simulation was carried out in the presence of a cold plate (i) without fluid, (ii) with a static fluid and (iii) with a circulating fluid. [Table 2]

[0176] In Table 2: the average temperature corresponds to the average of the temperatures within a cell. the maximum temperature corresponds to the maximum temperature within the same cell. the minimum temperature corresponds to the minimum temperature within the same cell.

[0177] Table 2 illustrates this simulation, and highlights the temperature differences in cell volume for the case of a cold plate alone, in the case of a cold plate and a static fluid (static fluid + cold plate) and for the case of the invention (fluid + cold plate + circulation device) at different flow rates.

[0178] It has been observed that the circulation of the coolant coupled with a cold plate allows a decrease in the temperature of the cells, whether at the level of average, maximum or minimum temperatures. On the other hand, as illustrated in Table 2, the higher the flow rate of the coolant, the more the temperature of the cells decreases, which reflects an improvement in the cooling of said cells.

[0179] Thus, the cooling system of the invention makes it possible to reduce thermal gradients within the cells thanks to a more homogeneous distribution of heat exchanges. Consequently, the cooling system of the invention may have an extended lifespan.

Claims

CLAIMS 1. Cooling system (1) comprising a housing (2), at least one electronic device (3), at least one liquid-cooled heat sink (4), a cooling fluid (5), and at least one circulation device (13), wherein: said at least one liquid-cooled heat sink (4) is thermally coupled directly or indirectly to the cooling fluid (5); and said at least one electronic device (3) and said cooling fluid (5) are positioned in the housing (2), said at least one electronic device (3) being immersed in the cooling fluid (5); and said at least one circulation device (13) allows the cooling fluid (5) to be circulated inside the housing (2); said at least one electronic device (3) being selected from an energy storage device and power electronics.

2. Cooling system (1) according to claim 1, wherein the liquid-cooled heat sink (4) is in contact with the external surface (6) of at least one of the walls of the housing (2).

3. Cooling system (1) according to claim 1 or 2, wherein said at least one liquid-cooled heat sink (4) is indirectly thermally coupled to the cooling fluid (5), at least one wall of the housing (2) being located between said liquid-cooled heat sink (4) and said cooling fluid (5).

4. Cooling system (1) according to any one of claims 1 to 3, wherein the liquid-cooled heat sink (4) is configured to cover at least 20% of the surface area of ​​one of the walls of the housing (2), preferably at least 50% of the surface area of ​​one of the walls of the housing (2), more preferably at least 75% of the surface area of ​​one of the walls of the housing (2), even more preferably 100% of the surface area of ​​one of the walls of the housing (2).

5. Cooling system (1) according to any one of claims 1 to 4, wherein said at least one circulation device (13) is located at least partially outside the housing (2), said circulation device (13) comprising at least one pump (14) and at least two channels (15, 16).

6. Cooling system (1) according to claim 5, wherein said pump (14) is configured to deliver said cooling fluid (5) at a flow rate greater than or equal to 8 L / min, preferably greater than or equal to 10 L / min, preferentially greater than or equal to 12 L / min, and even more preferentially greater than or equal to 15 L / min.

7. Cooling system (1) according to any one of claims 1 to 6, wherein the housing comprises at least one opening allowing cooling fluid (5) to be replaced and / or added.

8. Cooling system (1) according to any one of claims 1 to 7, wherein the energy storage device is a battery cell, such as a battery cell of an electric or hybrid vehicle.

9. Cooling system (1) according to any one of claims 1 to 8, wherein the liquid-cooled heat sink (4) is a cooling plate, in particular a cold plate.

10. Cooling system (1) according to claim 9, wherein the cold plate has a thickness of between 1 mm and 50 mm, preferably between 5 mm and 30 mm.

11. Cooling system according to any one of claims 1 to 10, wherein said at least one electronic device (3) is completely immersed in the cooling fluid (5).

12. Cooling system (1) according to any one of claims 1 to 11, comprising a plurality of electronic devices (3) arranged separated from each other, preferably equidistantly.

13. Cooling system (1) according to any one of claims 1 to 12, wherein the cooling fluid (5) comprises at least 70% by weight of base oil(s), relative to the total weight of the cooling fluid (5).

14. Use of the cooling system (1) according to any one of claims 1 to 13 for cooling at least one battery cell of an electric or hybrid vehicle, such as a motor vehicle or an aircraft.

15. Electric vehicle battery comprising at least one cooling system (1) according to any one of claims 1 to 13.

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