System for heat treatment of an electrical energy storage device

Abstract

The present invention relates to a system (100) for heat treatment of an electrical energy storage device including electrical energy storage members (22), the heat treatment system (100) including the electrical energy storage device and a dielectric liquid circuit including: - at least one channel (24) for the dielectric liquid to circulate between at least a portion of the electrical energy storage members (22) of the storage device; - a dielectric liquid circulation pump (3); - a heat exchanger (5) configured for heat treatment of the dielectric liquid, the heat treatment system (100) being characterised in that the dielectric liquid circuit includes an expansion tank (1) and in that the heat treatment system (100) includes a variable-volume tank (14) connected to the expansion tank (1).

Description

[0001] Thermal treatment system for an electrical energy storage device

[0002] The present invention relates to the fields of thermodynamics and electricity, and more specifically concerns a cooling and / or heating system for an energy storage device such as a battery, finding particular application in the automotive industry.

[0003] Electric and hybrid vehicles carry high-voltage batteries, which are necessary to power the electric motors connected to the wheels of these vehicles, to ensure their traction or propulsion. In order to ensure sufficient mileage range for such a vehicle while not impacting the available volume in this vehicle, the trend is towards increasing the power density of these batteries, which often use lithium-based technology.

[0004] However, such batteries, with a maximum no-load voltage of around 200 to 800V, require an efficient cooling system. Indeed, their energy storage cells tend to heat up, particularly during rapid charging or discharging. Their temperature must be maintained within a temperature range that does not allow them to combust in the event of high heat and peak electrical consumption by the vehicle.

[0005] Available cooling solutions use cooling plates, for example, with glycol water flowing through them, or phase change materials. The cooling plates can only be brought into contact with insulated walls of the battery, and therefore have a small exchange surface with the storage cells, which makes this type of cooling device relatively inefficient. Phase change materials can be brought into direct contact with the storage cells, but this solution is complex and expensive, especially when the battery has several modules, each grouping several cells. This solution requires a closed circuit per module, so as not to generate imbalances in the state of the phase change material from one module to another.Another cooling solution consists of bathing the battery's energy storage cells in a dielectric liquid, itself cooled by an exchanger in which glycolated water circulates, for example. However, this solution requires a large volume of dielectric, around 20 liters, and a very large and pressure-resistant battery case to maintain its seal during variations in the volume of the dielectric liquid. Indeed, the storage cells increase in volume when they are charged and / or age, and the dielectric liquid itself increases in volume when it is hot. The case must therefore have a large expansion tank to compensate for this variation in volume. And even with a large tank, the pressure inside the tank varies and can reach 2.5 bars absolute when hot and when the battery is charged.

[0006] There is therefore a need for an efficient cooling system for a battery of energy storage cells, which is simple and compact.

[0007] The present invention aims to remedy at least in part the aforementioned drawbacks by providing a system for heat treatment of an electrical energy storage device and a method for filling a dielectric circuit of such a heat treatment system with dielectric liquid, which make it possible to circulate a dielectric liquid in contact with the energy storage members of the storage device, without generating a pressure variation in the housing of the storage device during the life cycle thereof.

[0008] To this end, the invention proposes a system for heat treatment of an electrical energy storage device comprising electrical energy storage members, the heat treatment system comprising the electrical energy storage device, and a dielectric liquid circuit comprising:

[0009] - at least one channel for circulation of the dielectric liquid between at least part of the electrical energy storage members of the storage device,

[0010] - a dielectric liquid circulation pump,

[0011] - a heat exchanger configured to thermally treat the dielectric liquid, the heat treatment system being characterized in that the dielectric liquid circuit comprises an expansion tank and in that the heat treatment system comprises a variable volume reservoir connected to the expansion tank.

[0012] The energy storage device is, for example, a high-voltage battery of an electric or hybrid vehicle, the thermal treatment system according to the invention making it possible to cool or heat the high-voltage battery depending on the context of use of the vehicle.

[0013] The electrical energy storage organs of the storage device are, for example, energy accumulator cells, for example cylindrical Lithium-ion cells, or prismatic Lithium cells, or even pocket-shaped cells also called "pouch cells" in English.

[0014] The dielectric liquid circulates in the heat treatment system according to the invention between these members, the circulation channel being able to be formed by the entire housing of the storage device, provided with an inlet and an outlet for dielectric liquid. Preferably, however, several circulation channels are provided in the storage device to better channel the dielectric liquid, which is for example oil or any other dielectric liquid capable of cooling the members of the storage device.

[0015] The thermal treatment system is configured to keep the dielectric liquid in the liquid state, i.e. there is no vapor or solid phase of the dielectric liquid in the dielectric liquid circuit during operation. In particular, a suitable choice of the dielectric liquid makes it possible to keep it liquid over the operating temperature range of the storage device.

[0016] The heat treatment system according to the invention can of course contain more elements, in particular several heat exchangers, several expansion vessels or variable volume tanks, but this complicates the system without additional advantage.

[0017] Although preferably the housing of the storage device is hermetic, the oil bathing the storage members being in direct contact with the housing, alternatively the oil is confined in one or more hermetic containers containing the storage members, and the housing has spaces between these containers and its walls to house other elements of the heat treatment system such as the expansion tank, the variable volume tank, the heat exchanger and the pump.

[0018] In this variant, the dielectric liquid circuit is entirely confined in the housing of the storage device, which may nevertheless have an outlet and an inlet for heat transfer liquid or refrigerant, passing through the heat exchanger. For example, the heat exchanger is traversed by glycol water, which circulates in one or more cooling circuit loops making it possible to cool, in addition to the storage device, power electronic modules.

[0019] Thanks to the expansion tank and the variable volume reservoir, the invention makes it possible not to oversize the volume of the storage device housing compared to a storage device cooled with a cooling plate for example, and to maintain the pressure within the storage device at a pressure close to atmospheric pressure, therefore approximately one bar apart from the pressure drop in the pipes. Indeed, the variable volume reservoir makes it possible to absorb a volume variation of the order of 3 liters, without increasing the pressure in the jar, and thus limits the pressure inside the storage device housing. The invention is also suitable for filling the heat treatment system with dielectric liquid, carried out under vacuum in the assembly line. Indeed, since absolute vacuum is not ensured, there always remains a volume of air present in the heat treatment system after assembly thereof.

[0020] Preferably, the expansion tank is made of rigid material and the variable volume tank of flexible material. For example, they are made of PVC (polyvinyl chloride), but other types of material are of course usable. The expansion tank can be made of several materials but capable of containing in a fixed volume dielectric liquid and air, the expansion tank allowing degassing of the dielectric liquid present in the dielectric liquid circuit. The tank can also be made of several materials, capable of allowing the volume of the tank to decrease or increase. The variable volume tank takes for example the form of a flexible pocket easily accommodated in the underbody of a vehicle integrating the storage device, or in the storage device itself. Such an embodiment makes the shape of the variable volume tank, even when it is filled, adaptable to constrained spaces and of varied shapes.

[0021] In addition, the expansion tank allows the dielectric liquid circulating between the storage members to discharge into air bubbles in the expansion tank which is filled partly with dielectric liquid and partly with air, and therefore to maintain an efficient heat exchange between the dielectric liquid and the storage members of the storage device.

[0022] In one embodiment of the invention, in the heat treatment system according to the invention, the electrical energy storage members of the storage device are grouped into modules, each of the modules comprises at least one dielectric liquid circulation channel, the dielectric liquid circuit comprises a dielectric liquid inlet collector connecting together inlets of the modules and a dielectric liquid outlet collector connecting together outlets of the modules, and the expansion tank is connected on the one hand to the outlet collector and on the other hand to a point of the dielectric liquid circuit located downstream of the outlet collector and upstream of the circulation pump.

[0023] In this application, the terms “upstream” and “downstream” of course refer to the direction of circulation of the dielectric liquid.

[0024] In this embodiment of the invention, the expansion tank therefore receives a portion of the flow of dielectric liquid from the outlet manifold, and the dielectric liquid leaving the expansion tank joins a main circulation of dielectric liquid upstream of the circulation pump. A branch of the dielectric liquid circuit therefore connects the expansion tank to the outlet manifold, and another branch of the dielectric liquid circuit connects the expansion tank to an inlet of the circulation pump or to yet another branch of the dielectric liquid circuit connecting the outlet manifold to an inlet of the circulation pump.In another embodiment of the invention, in the heat treatment system according to the invention, the electrical energy storage members of the storage device are grouped into modules, each of the modules comprises at least one dielectric liquid circulation channel, the dielectric liquid circuit comprises a dielectric liquid inlet collector connecting together inlets of the modules, a first dielectric liquid outlet collector connecting together outlets located in the upper part of the modules and a second dielectric liquid outlet collector connecting together outlets located in the lower part of the modules, the expansion tank being connected on the one hand to the first outlet collector and on the other hand to the second outlet collector.

[0025] In this other embodiment of the invention, the upper part of each module is higher than the lower part of the module. In other words, the first outlet manifold is located higher than the second outlet manifold, the terms "high" and "low" here referring to the vertical direction in which the heat treatment system is intended to be positioned in operation. The first manifold has a much smaller section than that of the second manifold because its function is to capture air bubbles at the top of each module, and its flow rate is much lower than that of the second manifold.

[0026] The first and second outlet collectors are further positioned to receive dielectric liquid from the circulation channels, i.e. the lightest dielectric liquid, therefore charged with air bubbles, circulating in the circulation channels, exits the modules through the first outlet collector, while the heaviest dielectric liquid, therefore discharged with air, circulating in the circulation channels, exits the modules through the second outlet collector.

[0027] The expansion tank therefore receives bubble-laden dielectric liquid from the first outlet manifold, and the dielectric liquid leaves the expansion tank discharged with air to enter the second outlet manifold and then enter the circulation pump. A branch of the dielectric liquid circuit optionally connects the first outlet manifold and the second outlet manifold, in order to let the dielectric liquid not charged with air descend by gravity into the second outlet manifold.

[0028] In these embodiments of the invention, the modules are for example compartments of the housing of the storage device, each comprising several energy accumulator cells immersed in the dielectric liquid in each of these compartments.

[0029] Preferably in the invention, the variable volume tank is directly connected to the expansion tank. A pipe therefore connects the expansion tank to the variable volume tank, which has no other connection to the dielectric liquid circuit.

[0030] If the expansion tank is located outside the battery box (i.e., the storage device), and if it is located vertically at a level above the battery box, the connection to the expansion tank of the line connecting the outlet manifold and the inlet of the expansion tank can be located vertically at any level of the expansion tank. On the other hand, if the jar is integrated into the battery box, or if it is below the battery box, the line must be connected to a lower portion of the expansion tank where there is always liquid. This prevents air from the expansion tank from rising to the outlet manifold.

[0031] When the inlet of the expansion tank is located in the lower portion of the expansion tank, an obstacle to the fluid flow is optionally arranged in the expansion tank between this inlet and the outlets of the expansion tank, one being connected to the variable volume tank and the other to another outlet manifold or to the circulation pump depending on the embodiment of the invention. This prevents suction of air bubbles arriving through the inlet of the expansion tank, towards the outlets of the expansion tank.

[0032] The expansion tank may be housed in an empty volume of the battery housing, or integrated into one of the battery modules. Furthermore, according to an optional and advantageous feature of the invention, the expansion tank comprises a filling cap. This cap makes it possible to fill the circuit with dielectric liquid or to drain it.

[0033] According to another optional and advantageous feature of the invention, the dielectric liquid circuit comprises a safety valve. This is for example connected to an outlet manifold of the dielectric liquid circuit, or arranged on the filling cap of the expansion tank.

[0034] For example, the expansion tank is capable of holding 0.5 to 2 liters of dielectric liquid, and the variable volume reservoir is capable of holding 2 to 8 liters of dielectric liquid. Preferably, the expansion tank is capable of holding 1 to 1.5 liters of dielectric liquid, and the variable volume reservoir is capable of holding 3 to 6 liters of dielectric liquid.

[0035] The invention also relates to a method for filling the dielectric liquid circuit of a heat treatment system according to the invention with dielectric liquid, comprising steps of:

[0036] - evacuation of air present in the dielectric liquid circuit,

[0037] - introduction of a predetermined quantity of dielectric liquid into the dielectric liquid circuit,

[0038] - activation of the circulation pump,

[0039] - comparison of a first quantity of dielectric liquid present in the variable volume tank with a first predetermined quantity, and comparison of a second quantity of dielectric liquid present in the expansion tank with a second predetermined quantity, and, if the first and second quantities of dielectric liquid correspond respectively to the first and second predetermined quantities,

[0040] - watertight closure of the dielectric liquid circuit by fitting the filler cap to the expansion tank. This filling process is carried out, for example, when installing the storage device in the vehicle, or when draining the dielectric liquid circuit to renew it.

[0041] The evacuation of air from the dielectric liquid circuit is, for example, a vacuum using an ejector or a vacuum pump connected to the opening of the dielectric liquid circuit formed by a prior opening of the filler cap. In addition, the activation of the circulation pump makes it possible to degas the dielectric liquid and therefore to be able to control quantities of dielectric liquid in the expansion tank and in the variable volume reservoir which are representative of the quantities present in these containers during operation of the vehicle.

[0042] The first and second quantities of dielectric liquid correspond to the first and second predetermined quantities when the first quantity of dielectric liquid is equal to the first predetermined quantity to within a tolerance of the order of 0.1 liters, and when the second quantity of dielectric liquid is equal to the second predetermined quantity to within a tolerance of the order of 0.1 liters.

[0043] When this correspondence is not achieved, if the first and second quantities of dielectric liquid are less than the first and second predetermined quantities, more dielectric liquid is introduced in small quantities into the dielectric liquid circuit until these first and second predetermined quantities are reached after a new step of activating the circulation pump. On the contrary, if the first and second quantities of dielectric liquid are greater than the first and second predetermined quantities, dielectric liquid is extracted in small quantities from the dielectric liquid circuit until these first and second predetermined quantities are reached after a new step of activating the circulation pump.

[0044] For example, the first predetermined quantity is between 1 and 3 liters at an ambient temperature of 20°C (degrees Celsius).

[0045] The invention also relates to an electric or hybrid vehicle comprising a heat treatment system according to the invention for an electrical energy storage device. The vehicle and the method according to the invention have advantages similar to those of the heat treatment system according to the invention.

[0046] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which:

[0047] [fig 1] illustrates a thermal treatment system according to the invention of an electrical energy storage device, in a first embodiment of the invention,

[0048] [fig 2] illustrates a thermal treatment system according to the invention of an electrical energy storage device, in a second embodiment of the invention,

[0049] [fig 3] is a sectional view of a thermal treatment system according to the invention of an electrical energy storage device, in an alternative embodiment of the first embodiment of the invention, at the start of the life of the electrical energy storage device, the latter being discharged with electricity, at a temperature of the order of 20°C,

[0050] [fig 4] is a sectional view of the heat treatment system of figure 3, at the end of life of the energy storage device, at the end of an electrical charge, and at a relatively high temperature,

[0051] [fig 5] is a sectional view of the heat treatment system of figure 3, at the start of the life of the energy storage device, the latter being lightly charged with electricity and the ambient temperature being -30°C, and

[0052] [fig 6] represents steps of a filling method according to the invention of a thermal treatment system according to the invention of an electrical energy storage device, in one embodiment of the invention.

[0053] According to a first embodiment of the invention shown in Figure 1, a heat treatment system 100 according to the invention comprises an electrical energy storage device, which is here a high voltage battery of an electric or hybrid vehicle. The storage device comprises a sealed housing 9, for example made of aluminum.

[0054] The housing 9 of the storage device is compartmentalized into four modules 2 each comprising several electrical energy storage members 22, here prismatic type energy accumulator cells, which may be in a variant embodiment "pouch" cells, or else cylindrical cells. In Figure 1, not all the members 22 are shown so as not to overload the figure, but each module 2 comprises more than two members, for example ten members. Similarly, the storage device in Figure 1 only comprises four modules to make the different elements of the heat treatment system 100 more easily visible, but it is understood that the invention applies to storage devices which may contain many more than four modules.

[0055] The members 22 are immersed in a dielectric liquid, for example oil, in each module 2, the dielectric liquid completely filling the volume available in each module around the members 22.

[0056] The heat treatment system 100 also comprises a dielectric liquid circuit circulating the dielectric liquid in particular within the modules 2, which form circulation channels for the dielectric liquid. In each module 2, the dielectric liquid circulates between the members 22 and the walls of the module 2 but also between the members 22. The members 22 being here of oblong and parallelepipedal shape, a natural circulation channel 24 is in particular formed between two adjacent members 22 of the same module 2.

[0057] The modules 2 each comprise, in this first embodiment of the invention, an inlet 62 for dielectric liquid, proximal to one end of a circulation channel 24 of the module 2 in question, and two outlets 42, 82 for dielectric liquid proximal to the other end of the circulation channel 24.

[0058] The arrows not referenced in Figures 1 and 2 show the direction of circulation of the dielectric liquid. A first outlet 82 of the two outlets is located in the upper part of the module 2, and a second outlet 42 of the two outlets is located in the lower part of the module 2, that is to say that the first outlet 82 is arranged in height relative to the second outlet 42 when the heat treatment system 100 is integrated in the vehicle and operating normally.

[0059] The dielectric liquid circuit comprises an inlet manifold 6 which takes the form of a pipe running along a first wall 92 of the housing 9, transverse to the modules 2, the pipe comprising four fluid connections to the four dielectric liquid inlets 62 of the modules 2 on the first transverse wall 92 of the housing 9.

[0060] The dielectric liquid circuit also comprises a first outlet collector 8, arranged at the top of a second wall 94 of the housing 9, transverse to the modules 2, the second wall 94 being opposite the first wall 92 relative to the housing 9. The first outlet collector 8 similarly takes the form of a pipe running along the second wall 94, and which comprises four fluid connections to the four dielectric liquid outlets 82 located in the upper part of the modules 2.

[0061] The dielectric liquid circuit also comprises a second outlet collector 4, arranged at the bottom of the second wall 94 of the housing 9. The second outlet collector 4 takes the form of a pipe running along the second wall 94, and comprises four fluid connections to the four dielectric liquid outlets 42 located in the lower part of the modules 2.

[0062] The first outlet collector 8 is therefore arranged in height relative to the second outlet collector 4. It makes it possible to collect a portion of the dielectric liquid charged with air bubbles at the outlet of the modules 2, while the second outlet collector 4 makes it possible to collect a portion of the dielectric liquid devoid of air at the outlet of the modules 2, this portion devoid of air being heavier than the portion charged with air bubbles.

[0063] The dielectric liquid circuit further comprises a circulation pump 3 and a heat exchanger 5, crossed on the one hand by the dielectric liquid and on the other hand by a heat transfer liquid 55 such as glycolated water or by a refrigerant fluid, making it possible to cool or heat the dielectric liquid depending on the operating mode of the heat treatment system 100. The glycolated water or the refrigerant fluid circulates inside another circuit, not shown.

[0064] The heat exchanger 5 has a dielectric liquid outlet connected by a branch 65 of the dielectric liquid circuit to the inlet of the inlet manifold 6, arranged at one end of its pipe shape. The circulation pump 3 has a dielectric liquid outlet connected by a branch 53 of the dielectric liquid circuit to the dielectric liquid inlet of the heat exchanger 5, and a dielectric liquid inlet connected by a branch 34 of the dielectric liquid circuit to the outlet of the second outlet manifold 4 located at one end of its pipe shape.

[0065] The terms "connected" or "connection" in this application of course refer to a fluid connection, the branches of the dielectric liquid circuit being sealed pipes.

[0066] The dielectric liquid circuit further comprises an expansion vessel 1, rigid, for example made of high-density polyethylene (HDPE), fitted with a filling cap 16.

[0067] The expansion tank 1 has an inlet located in a lower portion of the expansion tank 1, so as to always open into dielectric liquid present in the expansion tank 1 under the nominal operating conditions of the heat treatment system 100. This inlet is connected by a branch 18 of the dielectric liquid circuit to the first outlet manifold 8, which allows it to receive air bubbles in its upper part. The expansion tank 1 also has an outlet located in its lower part, connected by a branch 41 of the dielectric liquid circuit to the second outlet manifold 4.Thus, the expansion tank 1 being filled in its lower part with dielectric liquid and in its upper part with air, the dielectric liquid present in the expansion tank 1 can flow towards the second outlet collector 4, without encountering a significant air pocket between these two elements of the dielectric liquid circuit.

[0068] Finally, the dielectric liquid circuit comprises a variable volume reservoir 14, in the form of a pocket made of flexible synthetic material, for example PVC. The variable volume reservoir 14 is connected by a pipe 10 to another opening of the expansion tank 1, located in the lower part thereof. It can advantageously be arranged in an available empty space close to the modules 2, this space being able to be of any shape as long as it comprises the maximum volume taken by the variable volume reservoir 14, provided during operation of the heat treatment system 100.

[0069] Thus, when the circulation pump 3 is started, the dielectric liquid at its outlet reaches the heat exchanger 5, then enters the inlet manifold 6, which brings the dielectric liquid into each of the modules 2 via the inlets 62 thereof. The dielectric liquid passes through each of the modules 2, a portion of the dielectric liquid charged with air leaving via the outlets 82 located in the upper part of the modules 2 to enter the first outlet manifold 8, and a portion of the dielectric liquid devoid of air leaving via the outlets 42 located in the lower part of the modules 2 to enter the second outlet manifold 4. The dielectric liquid present in the second outlet manifold 4 reaches the inlet of the circulation pump 3, while the dielectric liquid present in the first outlet manifold 8 is brought via the branch 18 of the dielectric liquid circuit into the expansion tank 1 to be degassed there.The dielectric liquid, once degassed in the expansion tank 1, is drawn, by the suction of the circulation pump 3, into the branch 41 of the dielectric liquid circuit.

[0070] The expansion vessel 1 has a degassing function and, to a lesser extent, a limitation of the pressure rise in the dielectric liquid circuit when this circuit is hot and the dielectric liquid expands.

[0071] The variable volume reservoir 14 absorbs the variations in volume of the dielectric liquid and of the members 22, due to variations in temperature and / or the charged or discharged state of the members 22, and therefore makes it possible to keep the pressure in the expansion tank 1 close to atmospheric pressure.

[0072] In this first embodiment of the invention, a safety valve 30 is nevertheless arranged on the first outlet manifold 8. Alternatively, this safety valve is arranged elsewhere on the cooling circuit, for example it is arranged in the filler cap 16.

[0073] For information purposes, the volume occupied by the members 22 is approximately 130 liters at the start of the storage device's life, the members 22 being discharged, this volume being increased by two liters at the end of the storage device's life, the members 22 being charged. The volume of the dielectric liquid is approximately twenty liters in the housing 9 of the storage device. The expansion tank 1 has a capacity of 1 to 1.5 liters and the variable volume reservoir 14 has a capacity of 3 to 6 liters.

[0074] We will now describe in connection with Figure 2, a heat treatment system 102 of an electrical energy storage device, in a second embodiment of the invention. This second embodiment of the invention comprises many elements common to the first embodiment of the invention, which are referenced in the same way. In particular, the storage device comprises a housing 9 compartmentalized into four modules 2 each comprising a set of energy storage members 22, which are immersed in dielectric liquid, here oil, in each module 2.

[0075] The heat treatment system 102 comprises an inlet manifold 6 arranged on a first wall 92 of the housing 9, bringing the dielectric liquid into each of the modules 2, but comprises a single outlet manifold 8, arranged on a second wall 94 of the housing 9, opposite the first wall 92 of the housing 9 with respect thereto. As in the first embodiment of the invention, the outlet manifold 8 is arranged against an upper part of the module 2 so as to receive the dielectric liquid charged with air bubbles, and to be able to degas it into a rigid expansion tank 1, identical to that of the first embodiment of the invention. The outlet manifold 8 is further provided with a safety valve 30.

[0076] A variable volume reservoir 14 makes it possible to absorb variations in the volume of the dielectric liquid during the life of the storage device.

[0077] The heat treatment system 102 also comprises a heat exchanger 5 and a circulation pump 3. The dielectric liquid outlet of the heat exchanger 5 is connected by a branch 65 of the dielectric liquid circuit to the inlet of the inlet manifold 6. The outlet of the circulation pump 3 is connected by a branch 53 of the dielectric liquid circuit to the dielectric liquid inlet of the heat exchanger 5, and the inlet of the circulation pump 3 is connected by a branch 38 of the dielectric liquid circuit to an outlet of the outlet manifold 8.

[0078] The expansion tank 1 has an inlet located in a lower portion of the expansion tank 1, so as to open into dielectric liquid present in the expansion tank 1. This inlet is connected by a branch 18 of the dielectric liquid circuit to the outlet manifold 8, which allows it to receive air bubbles in its upper part. The expansion tank 1 also has an outlet located in its lower part, connected by a branch 31 to the branch 38 of the dielectric liquid circuit. An obstacle (not shown in Figure 2) of 2 to 5 times the diameter of the branch 18 is possibly arranged just opposite the outlet thereof, to prevent the air bubbles from being sucked directly towards the two outlets of the expansion tank 1 connected to the pipe 10 and to the branch 31.The expansion vessel 1 being filled in its lower part with dielectric liquid and in its upper part with air, the dielectric liquid present in the expansion vessel 1 can flow towards the circulation pump 3, without encountering a significant air pocket between these two elements of the dielectric liquid circuit.

[0079] The variable volume tank 14, identical to that of the first embodiment, is connected by the pipe 10 to another opening of the expansion tank 1, located in the lower part of the latter.

[0080] Thus, when the circulation pump 3 is started, the dielectric liquid at its outlet reaches the heat exchanger 5, then enters the inlet manifold 6, which brings the dielectric liquid into each of the modules 2 via the inlets 62 thereof. The dielectric liquid passes through each of the modules 2, then enters, loaded with air (during a degassing phase after draining and then filling with dielectric liquid during after-sales service or on the vehicle assembly line), the outlet manifold 8. A portion of the dielectric liquid then passes into the branch 18 towards the expansion tank 1 where it is degassed, then returns to the circulation pump 3 via the branches 31 and 38 of the dielectric liquid circuit, while another portion of the dielectric liquid arrives directly from the outlet manifold 8 in the circulation pump 3 via the branch 38 of the dielectric liquid circuit.

[0081] Figures 3 to 5 illustrate an alternative embodiment of the first embodiment, in which the elements identical to the first embodiment are referenced in the same way. This alternative differs from the first embodiment mainly in the arrangement of the variable volume reservoir 14, which is here a flexible plastic bag arranged on the modules 2 of the storage device, and in that a housing 90 of the storage device is separate from the walls of the modules 2. The housing 90 in fact integrates, in this alternative embodiment, all the elements of the dielectric liquid circuit. The housing nevertheless comprises in one wall, an inlet and an outlet for heat transfer liquid or refrigerant fluid allowing it to circulate in the exchanger 5. For the visibility of Figures 3 to 5, only the lower wall of the housing 90 is shown.

[0082] Figure 3 illustrates the state of the heat treatment system according to the invention, where the bag 14 is placed on top of the modules. In this embodiment variant, at an ambient temperature of 20°C and at the start of the life of the storage device, i.e. the energy storage members 22, not yet charged with electricity. In this state, the dielectric circuit has been filled with 22.4 liters of dielectric liquid. The variable volume reservoir 14 contains 2 liters of dielectric liquid, while the expansion tank 1 contains 0.7 liters of dielectric liquid and 0.3 liters of air. This filling at the start of the life of the storage device makes it possible to avoid a depression in the dielectric liquid circuit when the temperature in this circuit drops to a very low temperature, for example to -30°C. At this temperature, in fact, the volume of the dielectric liquid shrinks a lot.

[0083] It should be noted that the use of the variable volume reservoir 14 brings many advantages. Indeed, this use makes it possible to avoid an increase in pressure in the dielectric liquid circuit, which would be very significant with a conventional expansion tank of the same capacity. In particular, a variable volume reservoir 14 with a capacity of 4 to 6 liters can absorb an increase in total volume in the dielectric liquid circuit, of the order of 3 liters. Its location on the modules 2 also does not create a significant static pressure difference, the housing 90 having a height generally of the order of ten centimeters. In the proposed embodiment variant, the pressure in the variable volume reservoir 14 and the expansion tank 1 remains close to atmospheric pressure.

[0084] Figure 4 illustrates the state of the thermal treatment system according to the invention, in this embodiment variant, at a temperature of the storage members 22 and of the dielectric liquid well above 20°C, for example at 60°C at the end of rapid recharging, and at the end of life of the storage device, that is to say that the energy storage members 22 have undergone a very large number of recharges and discharges. Furthermore, in this figure 4, the energy storage members 22 are charged with electricity. Under these conditions, the volume of the dielectric liquid contained in the modules is minimum, and the variable volume reservoir receives the maximum amount of dielectric liquid.

[0085] Due to the aging of the energy storage members 22, and the recharging of the storage device causing thermal expansion, the volume of the storage members 22 is increased by two liters compared to the state of the thermal treatment system of Figure 3. The volume occupied by the dielectric liquid in the storage device is therefore reduced by two liters, which are expelled towards the expansion tank 1 and the variable volume reservoir 14. The dielectric liquid itself being expanded by approximately one liter, the modules 2 are filled with 20 liters of dielectric liquid, the variable volume reservoir 14 contains approximately 5 liters of dielectric liquid and the volume of air in the expansion tank is expanded from 0.3 liters to 0.34 liters.

[0086] Figure 5 illustrates the state of the heat treatment system according to the invention, in this embodiment variant, where the volume of the dielectric liquid contained in the modules is maximum, where a temperature of the storage members 22 and of the dielectric liquid is at -30°C, and at the start of the life of the storage device, the energy storage members 22 being electrically discharged. Due to this very low temperature, the volume of the energy storage members 22 shrinks as well as the casings of the modules 2. The volume occupied by the dielectric liquid in the modules 2 increases if the reduction in the volume of members 22 is greater than the reduction in the casings of the modules 2. The modules 2 therefore suck up the dielectric liquid present in the variable volume tank 14, which initially contained a volume of dielectric liquid of 2 liters. The dielectric liquid itself also shrinks.The air in expansion tank 1 also shrinks from a volume of 0.3 liters to 0.22 liters, which means that expansion tank 1 also draws dielectric liquid from variable volume tank 14. The volume of dielectric liquid in expansion tank 1 therefore increases to 0.78 liters, that in variable volume tank 14 is close to 0 liters.

[0087] During the cooling of the heat treatment system, thanks to the flexible bag, the pressure in the expansion tank 1 remains at atmospheric pressure, but with a rigid container, it would be the liquid in the container that would be sucked in, there would be a depression created in the container, this depression can be significant if the volume of air is not sufficient, the safety valve could open to let air in to limit this depression, which could create a mechanical problem and a problem of sealing the circuit.

[0088] We will now describe in relation to Figure 6, a method 200 for filling the dielectric liquid circuit of one of the heat treatment systems 100 or 102 described above. This filling with dielectric liquid takes place, in the example of use described here, at a temperature of 20°C and at the start of the life of the storage device, the energy storage members 22 not being charged with electricity. In other words, this filling is carried out in the factory before mounting the storage device in an electric or hybrid vehicle.

[0089] A first step 202 of the filling method 200 is the opening of the dielectric liquid circuit by unscrewing the filling cap 16 of the expansion tank 1. This first step is of course optional if the heat treatment system is supplied for filling with the expansion tank already open. A second step 204 of the filling method 200 is a vacuum drawing through the opening of the expansion tank 1, for example by connecting a vacuum pump to this opening, so as to evacuate the air from the dielectric liquid circuit.

[0090] A third step 206 of the filling method 200 is the introduction of a predetermined quantity of dielectric liquid into the dielectric liquid circuit, here 22.4 liters.

[0091] A fourth step 208 of the filling method 200 is the activation of the circulation pump 3 in order to degas the dielectric liquid in the dielectric liquid circuit, the air escaping through the opening of the expansion tank 1.

[0092] In a fifth step 210 of the filling method 200, it is verified that the volume of dielectric liquid present in the variable volume reservoir 14 is approximately 2 liters and that the volume of dielectric liquid present in the expansion tank 1 is approximately 0.7 liters, to within plus or minus 0.1 liters.

[0093] If during this fifth step 210, the conditions on the volumes of dielectric liquid present in the variable volume tank and the expansion tank 1 are met, then (branch Y) we move on to the sixth step 212 of the method, which is the watertight closure of the dielectric liquid circuit by screwing the filling cap 16 back onto the expansion tank 1.

[0094] If, on the contrary, during this fifth step 210, the conditions on the volumes of dielectric liquid present in the variable volume reservoir and the expansion tank 1 are not met, we move on (branch N) to a step 211 where it is a question of adding or extracting dielectric liquid so that the volumes of dielectric liquid present in the variable volume reservoir 14 and in the expansion tank 1 are within the expected ranges. By noting the quantity introduced and its complement, we can determine the total quantity necessary, and its dispersion. We can thus inject the total quantity necessary from step 206 to avoid the correction of step 211, during a new execution of the method on another identical vehicle.

[0095] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention. In particular, the characteristics of the different embodiments or variants of the invention envisaged in this application can be combined to achieve the invention, insofar as these embodiments or variants are not incompatible with each other.

Claims

CLAIMS 1- Heat treatment system (100, 102) of an electrical energy storage device comprising electrical energy storage members (22), the heat treatment system (100, 102) comprising the electrical energy storage device, and a dielectric liquid circuit comprising: - at least one circulation channel (24) for the dielectric liquid between at least part of the electrical energy storage members (22) of the storage device, - a circulation pump (3) for dielectric liquid, - a heat exchanger (5) configured to thermally treat the dielectric liquid, the heat treatment system (100, 102) being characterized in that the dielectric liquid circuit comprises an expansion tank (1) and in that the heat treatment system (100, 102) comprises a variable volume reservoir (14) connected to the expansion tank (1). 2- Thermal treatment system (102) of an electrical energy storage device according to claim 1, in which the electrical energy storage members (22) of the storage device are grouped into modules (2), each of the modules (2) comprising at least one circulation channel (24) of dielectric liquid, the dielectric liquid circuit comprises a dielectric liquid inlet collector (6) connecting together inlets (62) of the modules and a dielectric liquid outlet collector (8) connecting together outlets (82) of the modules, the expansion tank (1) being connected on the one hand to the outlet collector (8) and on the other hand to a point of the dielectric liquid circuit located downstream of the outlet collector (8) and upstream of the circulation pump (3). 3- Thermal treatment system (100) of an electrical energy storage device according to claim 1, in which the electrical energy storage members (22) of the storage device are grouped into modules (2), each of the modules (2) comprising at least one circulation channel (24) of dielectric liquid, the dielectric liquid circuit comprises a dielectric liquid inlet collector (6). connecting together inlets (62) of the modules, a first outlet collector (8) of dielectric liquid connecting together outlets (82) located in the upper part of the modules and a second outlet collector (4) of dielectric liquid connecting together outlets (42) located in the lower part of the modules, the expansion tank (1) being connected on the one hand to the first outlet collector (8) and on the other hand to the second outlet collector (4). 4- Thermal treatment system (100, 102) of an electrical energy storage device according to any one of claims 1 to 3, in which the variable volume tank is directly connected to the expansion tank. 5- Heat treatment system (100, 102) of an electrical energy storage device according to any one of claims 1 to 4, in which the expansion tank (1) comprises a filling cap (16). 6- Thermal treatment system (100, 102) of an electrical energy storage device according to any one of claims 1 to 5, in which the dielectric liquid circuit comprises a safety valve (30). 7- Thermal treatment system (100, 102) of an electrical energy storage device according to any one of claims 1 to 6, in which the expansion tank (1) is capable of containing 0.5 to 2 liters of dielectric liquid, and the variable volume reservoir (14) is capable of containing 2 to 8 liters of dielectric liquid. 8- Thermal treatment system (100, 102) of an electrical energy storage device according to any one of claims 1 to 7, in which the expansion tank is made of rigid material and the variable volume tank is made of flexible material. 9- Method for filling (200) with dielectric liquid, the dielectric liquid circuit of a heat treatment system (100, 102) according to any one of claims 1 to 8 taken in the dependency of claim 5, comprising steps of: - evacuation (204) of the air present in the dielectric liquid circuit, - introduction (206) of a predetermined quantity of dielectric liquid into the circuit of dielectric liquid, - activation (208) of the circulation pump (3), - comparison (210) of a first quantity of dielectric liquid present in the variable volume tank (14) with a first predetermined quantity, and comparison of a second quantity of dielectric liquid present in the expansion tank (1) with a second predetermined quantity, and, if the first and second quantities of dielectric liquid correspond respectively to the first and second predetermined quantities, - watertight closure (212) of the dielectric liquid circuit by mounting the filler cap (16) on the expansion tank (1). 10- Electric or hybrid vehicle comprising a thermal treatment system (100, 102) according to any one of claims 1 to 8 of an electrical energy storage device.

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