FR3015780A3 - SYSTEM FOR HOLDING A BATTERY TEMPERATURE. - Google Patents

Abstract

System for regulating the temperature of a motor vehicle battery comprising at least two accumulators, comprising: at least one layer of phase change material (3) thermally coupled with the accumulator, at least one fluidic channel (5) in thermal coupling with the layer of phase-change material (3) and in which a coolant is able to circulate for cooling or heating the phase-change material, a means for controlling the circulation of the coolant in the fluidic channel (5), so that the coolant circulates only in the channel during charging phase of the battery, and means for controlling the temperature of the heat transfer fluid intended to flow in the fluidic channel (5) as a function of the battery temperature and / or outside temperature.

Description

System for maintaining the temperature of a battery. The technical field of the invention is electric accumulators, and more particularly the management of the temperature of such accumulators. Accumulators used to assemble a module or a battery (set of modules) give off heat when electrically solicited. Whether in discharge mode (discharging the battery to provide a current) or in charging mode (recharging the battery by an electric current), the temperature of the accumulators increases during their use. A temperature of the accumulators judged to be too high has repercussions on their lifetime and thus generates premature aging. The change or replacement of some accumulators, or even a module or a complete pack is very expensive and the cost is charged either to the consumer or to the car manufacturer in the case of a pack rental for example for an application to a motor vehicle.

The control of the temperature of a battery is therefore a key point requiring either temperature maintenance technologies (cooling in hot weather or heating in cold weather), or thermal management strategies. The problem is very different depending on the field of use of a battery. For a stationary application, cooling, heating or maintaining temperature is less problematic than for a mobile application for reasons of space, weight, availability and temperature of thermal sources (cold or hot) and availability of the power grid. For a mobile application, the available space is very limited and therefore compactness is a key factor to consider. In the same way, any mass embarked on board must be justified since it reduces the autonomy of the vehicle. In the end, in a very competitive environment, the cost generated either by additional components or by the associated energy consumption must be justified by notions of profitability or addition of comfort. A state transition refers to the transition from one physical state to another of a body by the supply or withdrawal of energy, including calories. It is called melting temperature for a passage from a solid state to liquid for example. This state transition is characterized by its phase change enthalpy, that is, the energy per unit of mass to be supplied or removed to effect the change of state. A phase change material (PCM) is characterized by the fact that this transformation takes place at a constant temperature. In theory, as long as the transformation is not complete, the body remains at a constant temperature, typically at its melting temperature for a solid / liquid transition and to use the example given above.

The phase change materials are numerous and are distinguished mainly from each other by their phase change enthalpy and their melting temperature. The high phase change enthalpy of the MCP absorbs the heat generated by the operation of the accumulators once they have reached the melting temperature of the MCPs. It is thus possible to freeze the temperature of the accumulators to a value close to the melting point of the MCP. In other words, when contacting accumulators and a MCP, the thermal power dissipated by the accumulators will be transmitted to the MCP which will gradually melt. In theory, as long as the MCP is not fully melted, it remains at almost constant temperature. Due to the equilibrium of the system, the accumulator also remains at an almost constant temperature. At the end of the complete melting of the MCP, we end up with a liquid material whose temperature will increase if the accumulator continues to communicate heat. It is therefore advantageous to choose a MCP having a melting temperature close to the desired temperature value for the accumulators and the greater capacity to absorb the thermal power, that is to say the highest enthalpy. From the state of the prior art, the following documents are known.

Documents US2010273041 and DE102010015743 describe the use of two MCPs, respectively dedicated to cold and hot ambient temperatures, for the purpose of exchanging calories between the MCPs and a battery. CN101546843 also discloses the use of MCP to extend the life of a battery and improve its performance in terms of power through the homogenization of the temperature of one battery to another. The document describes the use of an outer envelope containing the accumulators and filled with MCP. The seal is provided by an insulating tape.

The envelope is provided with ventilation holes that can allow the evacuation of power to the outside. JP2010073406 discloses the use of an alternation of accumulators and layers of MCP to prevent the propagation of heat from a faulty accumulator to another accumulator in normal operation. The melting temperature of the MCP is chosen to be greater than the conventional operating temperature and lower than a cell break temperature. Orifices are present in the MCP for refrigerant circulation.

Document US2009169983 discloses the use of MCP as a means of controlling the temperature of battery packs comprising a plurality of electrically interconnected cells, at least one MCP tank, at least one cold plate and at least one heating element.

Document US 2012/0171523 discloses elements of a battery comprising the use of compressible insulation, typically metal foams impregnated with MCP. Channels in direct contact with the accumulator allow circulation of cooling fluid or heating so as to provide or extract power. US 7147071 discloses a thermal management system for a hybrid vehicle. The entire battery temperature management system is described for different operating cases, in particular depending on the outside temperatures, typically either to heat or to cool the accumulators. A heat exchanger, common to both operations and containing MCP, ensures a storage of potentially reusable energy thereafter. The various embodiments of the storage exchanger have as a common feature a circulation of two separate heat transfer fluids and the use of a PCM as a means of heat exchange between the two fluids.

It thus appears that the various documents of the state of the prior art are intended to limit the heating of the accumulators to avoid reaching a temperature of damage. It is thus described that it is normal and acceptable for the temperature of an accumulator to change between 0 and 40 ° C., the accumulators constantly undergoing temperature cycles as they are used. However, the temperature variation of an accumulator within a normal operating range accelerates aging. There is therefore a need for a system capable of maintaining a constant temperature of a battery, especially in mobile applications such as the battery of a motor vehicle. The subject of the invention is a system for managing the temperature of a battery comprising at least one accumulator. The system comprises at least one layer of phase-change material in thermal coupling with the accumulator, at least one fluidic channel in thermal coupling with the layer of phase-change material and in which a coolant is able to circulate to cool. or heating the phase change material, a means for controlling the circulation of the heat transfer fluid in the fluidic channel, so that the coolant circulates only in the channel during the charging phase of the battery, and a control means the temperature of the coolant intended to circulate in the fluidic channel as a function of the temperature of the battery and / or the outside temperature. By thermal coupling between two elements is meant a direct or indirect contact between two elements allowing heat exchange between the two elements and can achieve a thermal equilibrium between the two. The phase change material may be a material having a melting temperature of between 25 ° C and 35 ° C to ± 2 ° C. The phase-change material may be a eutectic material, especially compounds based on salt hydrates such as LiNO 3 · 2H 2 O or Na 2 SO 4 · 10H 2 O or a paraffin, in particular paraffins having a number of carbons varying between 15 and 20. The phase change material may be included in a base envelope, which is impermeable and permeable to heat exchange, in particular with the accumulator. The base shell comprising the phase change material can be removable and replaceable. The heat transfer fluid may be liquid, especially water or glycol water, or gaseous, including air or a refrigerant. The traffic control means may be a compressor or a fan, when the coolant is gaseous, or a pump, when the heat transfer fluid is liquid. At least one thermally conductive fin may be disposed in contact with or inserted into each layer of phase change material to facilitate the transport of thermal energy to and from the phase change material. The fins may be in contact with the fluidic channel.

The means for controlling the temperature of the coolant may be a heat exchanger adapted to cool or heat said heat transfer fluid before entering the fluid channel. The heat exchanger may also be thermally connected to a heat pump on board a vehicle and connected to an air conditioning system blown into the passenger compartment of said vehicle. The battery is a battery for a motor vehicle and the means for controlling the setting in motion of the coolant and the means for controlling the temperature of the heat transfer fluid can be arranged outside the vehicle, forming a terminal intended to be fixed to the ground, the terminal being adapted to be temporarily connected to the fluidic channel disposed on board the vehicle. A thermal insulator may be disposed around the battery when the phase change material is to be cooled by the coolant. The subject of the invention is also a method for implementing a system for managing the temperature of a battery comprising a step of circulating the heat transfer fluid at a controlled temperature in the fluidic channel during the charging phase of the battery. battery. The invention has the advantage of alternating much more often MCP phase changes to maintain a battery temperature almost constant.

The invention also has the advantage of being a passive thermal management solution during the running of the vehicle, that is to say without energy consumption to maintain the temperature of the battery and which does not require use a cooling fluid during the rolling phase. The system is activated only during the charging phase of the battery (excluding driving), so as to readjust or regulate the temperature of the battery and the MCP to the desired temperature.

The invention has the advantage of making the MCP much more active, that is to say, to alternate much more often the phase changes of the MCP. Other objects, features and advantages of the invention will become apparent on reading the following description, given solely by way of nonlimiting example and with reference to the appended drawings in which: FIG. 1 illustrates a simplified diagram of FIG. a module of a battery without temperature management, - Figure 2 illustrates a simplified diagram of a module of a battery with a phase change material, - Figure 3 illustrates a base envelope containing a layer. of phase change material, and - Figures 4a to 4c illustrate different embodiments of fluidic channels disposed in a layer of phase change material, and - Figure 5 schematically illustrates the connection of the battery to a system. of air conditioning of a vehicle. The melting temperature of the MCP is a parameter to be taken into account in the battery temperature management system, since the temperature of the accumulator will be almost identical to this melting temperature when the MCP is in a state of transition. between the liquid state and the solid state. By heating, the accumulator transmits its heat to the MCP which itself heats up. As long as the MCP melting temperature is not reached, the temperature of the MCP and accumulator increases. As the melting temperature of the MCP is reached, the temperature of the MCP stabilizes and remains theoretically constant, as long as the MCP is not fully in the liquid state. The goal is to use this energy storage at constant temperature to keep the accumulators at a constant temperature. As the MCP is fully melted, the temperatures of the MCP and the accumulator increase again.

To avoid this rise in temperature at the end of melting, it is possible either to increase the mass of MCP so as to obtain more energy necessary to liquefy all the MCP, or to extract the energy stored in the MCP.

The increase in the mass of MCP implies an increase in the embedded mass and the size of a battery. In addition, because of the poor thermal conductivity of MCP, the increase in mass does not increase the amount of energy stored in the PCM. Increasing the mass of MCP is therefore not an acceptable solution. On the other hand, extracting part of the energy stored in the MCP at a suitable moment makes it possible to limit the onboard weight of MCP while smoothing the temperature variations of the accumulator. Figure 1 illustrates a simplified diagram of a module of a battery without temperature management. As can be seen the battery 1 comprises accumulators 2 juxtaposed with each other. Figure 2 illustrates the same battery with MCP. As can be seen, the battery 1 comprises layers of MCP referenced 3, interposed between two accumulators 2, leading to alternations of a layer of MCP 3 and a battery 2. For an application on board a motor vehicle , the battery is usually requested daily. The amount of energy to be managed is determined according to the use of the vehicle. An example of use consists of a taxi in the morning and an evening and a weekend outing. Each run involves a heating of the accumulators followed by a cooling phase. These phases of heating and cooling are repeated with breaks longer or shorter depending on use. In addition, when charging accumulators, usually at night, the batteries will heat up again. A battery has a large mass coupled with significant thermal inertia. A battery thus requires a time of several hours to cool in the open air, that is to say without ventilation action or fluid circulation.

It should be noted that the outside temperature is a very influential parameter for cooling in the open air. On the one hand, the temperature of a battery can only reach a temperature equal to the ambient temperature. On the other hand, the cooling will be even faster than the temperature difference between the temperature of a battery and the ambient temperature is important. If we consider a cooling in the open air, it is then possible to determine the evolution of the temperatures of the accumulators during the accumulation of the rollings of the week. For this, one chooses a rolling for a vehicle, and paraffin-type MCP having three different melting temperatures, 28 ° C, 32 ° C and 36 ° C. For the rest of the description, it will be considered that the temperature of damage to the accumulators is 40 ° C. This temperature thus constitutes a limit temperature not to be exceeded.

For use of the vehicle in hot periods, more conducive to increasing the temperature of the batteries, it is considered that the average outside temperature oscillates between 18 and 35 ° C. Simulations show that MCP with melting temperatures of 32 ° C and 36 ° C never melt, whereas MCP with a melting point of 28 ° C melts at least partially. It also appears that the use of a MCP reaching an at least partially melted state can greatly attenuate the amplitude of the temperature oscillations perceived in the battery.

In addition, there is also a temperature divergence during the cycles showing that the MCP reaches a fully molten state after a few days, thus canceling the attenuation effect of the temperature oscillations. According to these simulations, it is proposed to avoid this divergence in temperature and to maintain a smoothing of the temperature oscillations experienced by the accumulators by using a system for managing or regulating the temperature of the battery, activated only during charging. drums.

The system comprises a set of pipes connected to a heat exchanger, for example to the heat exchanger of the air conditioning system of a vehicle, to different fluidic channels arranged in contact with or passing through the layers of MCP arranged between the accumulators of the battery, and a means for controlling the circulation of the coolant in the fluid channel only during the charging phase of the battery. Due to the structure of the fluidic channels and the small volume of the pipe assembly, there is no risk of leakage of the heat transfer fluid into the battery. In addition, since the volume of the fluidic channels is small, the traffic control means may have a size and characteristics of low flow, limiting the size and weight of the system. When the fluidic channels are in simple contact with the MCP layers, thermal energy diffuses from the contact zone to the MCP or from the MCP to the contact zone. The coolant may be liquid such as water or brine or gaseous water such as air, or a refrigerant. When the coolant is liquid, the traffic control means is a pump. When the coolant is gaseous, the traffic control means is a compressor or a fan. The control system may also comprise, alternatively or in combination with the first embodiment, a set of thermally conductive fins in contact with the MCP and protruding from the base envelope so that thermal energy thermal transport with the MCP is possible. These fins may be in contact with fluidic channels so as to ensure the transfer of thermal energy between the heat transfer fluid included in the fluidic channels and the MCP. It is chosen to circulate the heat transfer fluid at a certain temperature, only during periods of charging the battery, phases during which the vehicle is connected to a power supply network. Since the vehicle is powered by the electrical network, its autonomy is not affected by the circulation and maintenance of the heat transfer fluid. According to an alternative embodiment, it is possible to have the traffic control means, the heat exchanger and a portion of the pipes outside the vehicle in order to pool the costs between several vehicles, to reduce the weight embedded in the vehicle. the vehicle and increase the efficiency of the heat exchanger by using a static system more important than an embedded system.

The coolant circulates between the charging station and the vehicle through a set of flexible pipes connected and disconnected on demand when the vehicle starts or finishes its load. The connection can be made for example with a quick coupling for liquids or gases. In such a case, the coolant circulates in open circuit from the point of view of the vehicle. Thus, as soon as the charge is complete, the coolant is substantially completely removed from the vehicle, limiting the risk of damage by leakage, and limiting the weight on board. The fluidic channels arranged in the MCP layers will be described in more detail in the light of FIGS. 3, 4a, 4b and 4c. In FIG. 3, a base envelope containing a layer of MCP phase change material 3 can be seen. FIGS. 4a to 4c show fluidic channels 5 arranged in the MCP and allowing fluid to circulate. coolant, especially liquid, for example water. The base envelope is arranged between two accumulators 2 so that a layer of MCP phase change material 3 is arranged between two accumulators 2, in a manner similar to that illustrated in FIG. acceptable between the increase in mass due to the addition of MCP layers and the maximization of the exchange surface between the accumulators and the MCP layers. Figures 4a, 4b and 4c illustrate various embodiments in which fluidic channels 5 are formed in a rigid structure 4 to hold them in place when the MCP phase change material 3 goes into the liquid state. MCP is a compound chosen from paraffins and eutectics, more specifically compounds based on salt hydrates such as LiNO 3 · 2H 2 O or Na 2 SO 4 · 10H 2 O or paraffins having a carbon number varying between 15 and 20. has the advantage of a lower melting temperature than those usually used, especially a melting temperature of between 25 ° C and 35 ° C to ± 2 ° C.

The base envelope can be made of a material allowing a suitable heat exchange between the accumulators and the MCP. It can be rigid or flexible, for example metal such as aluminum or stainless steel or a polymer material compatible with the PCM used.

The fluidic channels may be made of the same material as the base envelope, or aluminum. Aluminum has a weight / heat capacity ratio that is particularly advantageous for the application presented in particular. The first embodiment, illustrated in FIG. 4a, comprises medium-sized fluidic channels integrated in a rigid structure that holds them in place when the MCP is in a liquid state. The second embodiment, illustrated in Figure 4b, comprises small fluid channels, typically a few millimeters to limit the protrusions relative to the rigid structure keeps them in place when the MCP is in a liquid state. The third embodiment, illustrated in FIG. 4c, comprises fluidic channels making it possible to facilitate the flow of the coolant. In addition, the baffle structure of the rigid structure makes it possible to increase the exchange surface between a fluidic channel and the MCP. The heat exchange efficiency is thus increased despite the poor heat conduction ability of the PCM.

In all three embodiments, the size of the channels is limited by the thickness of the base envelope, which may be, for example, 2 cm. Figure 5 schematically illustrates the connection of the battery to an air conditioning system of a vehicle. As can be seen, the vehicle comprises a heat exchanger, or air conditioning exchanger referenced 6, which is connected to an air conditioning system according to the state of the prior art. This circuit comprises a means for controlling the flow of heat transfer fluid, reference 8, and a second heat exchanger adapted to change the temperature of the passenger compartment of the vehicle referenced 7. These various elements are connected by non-referenced pipes. Unlike an air conditioning system according to the state of the prior art, the system illustrated in Figure 5 comprises a bypass to include the battery 1 through the fluid channels not shown in the air conditioning system . It is thus possible to circulate the heat transfer fluid of the air conditioning system in the fluidic channels arranged in the layers of MCP. Different valves referenced 9, 10 and 11 are arranged in the circuit in order to isolate the fluidic channels of the battery 1, the exchanger 6 or the cabin heat exchanger 7 of the rest of the circuit. An example of use of the temperature maintenance system will now be described. The battery is discharged without active cooling during which the battery and the MCP heat up. The discharge is then followed by a charge with active cooling during which the accumulator is again subjected to heating. However, during this load, the control system makes it possible to evacuate part of the thermal energy accumulated in the MCP, thanks to the circulation of the heat transfer fluid in the fluidic channels. The thermal energy accumulated in the MCP can be generated during the charge or discharge phase of the battery.

In such an example, a discharge of 2C passes the accumulator an average temperature of 26.85 ° C before discharge at an average temperature of 29.55 ° C after the discharge, ie a reduced temperature increase due to the presence of MCP. Such a case is comparable to the situation of a user who after making a trip, corresponding to the discharge of 2C, wants to recharge the battery immediately after shutdown. The charge is thus launched with an accumulator temperature equal to that of end of discharge and a melted MCP. A charge is injected at 2C and at the same time a cooling fluid is circulated in some channels embedded in the MCP. With this example of operation, it is shown that at the end of charge at 2C, the average temperature of the accumulator can even be lower than that imposed at the beginning of discharge (at t = 0s, 26.85 ° C) since reaches a temperature of 24 ° C and a completely solid MCP with a water inlet temperature of 20 ° C. It is then possible to chain a new path without active cooling of the MCP.

The device shown above can also be used to warm the battery when the vehicle is used with particularly cold weather conditions. Indeed, below a certain temperature, the energy and the extractable power of the battery decreases when the temperature decreases.

The device used is identical to that used to cool the battery. In the present embodiment, the temperature of the heat transfer fluid is higher than the liquefaction temperature of the MCP, which causes the melting of said MCP. The battery is then heated during the charging phase through the MCP layers via the coolant. Once charging is complete, the MCP maintains the battery at a temperature corresponding to the phase change temperature of the MCP until enough heat energy is dissipated for the MCP to return to the solid state. However, the sizing of the MCP layers makes it possible to maintain an optimal temperature of the battery pack for several hours. An exemplary embodiment will now be described. The battery comprises a structure similar to that illustrated by one of FIGS. 4a to 4c. However, the battery is also equipped with thermal insulation to prevent a drop in temperature below 0 ° C when parking the vehicle despite the warming generated by daily driving. The addition of a thermal insulation around the battery also limits the amplitude of the temperature difference between the batteries and the battery between day and night. The MCP used is identical to that used for cooling the battery during operation in hot weather. Specifically, MCP is a paraffin, whose melting point is 28 ° C for an enthalpy of 150 to 300 kJ / kg. We also consider the same periods of driving and recharging as for the previous example in hot weather. In the winter period with external conditions of -20 ° C, the worst case that can be considered corresponds to a constant temperature of -20 ° C over the entire period considered. A constant external temperature of -20 ° C is therefore considered. When recharging the battery, the MCP is brought to a completely melted state thanks to the energy supplied by the temperature maintenance system. After stopping the charge of the battery, the temperature maintenance system no longer provides energy to the MCP, which begins to lose energy, including natural convection. However, the MCP inserted into a battery pack with thermal insulation keeps the battery warm for up to 12 hours. At the end of this period, the MCP is solid again and the temperature of the battery starts to fall again. However, it can be considered that the duration of 12 hours is greater than the time between two runs or the time between the last ride and loading the vehicle. It can then be considered that the battery does not perceive low temperature in the use profile of the vehicle considered. It will be obvious to those skilled in the art that the temperature and enthalpy parameters of the MCP, sizing of the MCP layers and insulation can be adapted according to the outside temperature considered so that one maintains an optimal temperature of the battery. It should be noted that under the same extreme outside temperature conditions, a lower MCP melting temperature than that considered above, for example 15 ° C., for example for a C16 type paraffin, makes it possible to reduce the difference in temperature. temperature between the pack and the outside. This has the effect of limiting heat loss and reducing the temperature oscillations of the battery. The electrical power consumed on the network to ensure the heating of the battery and the melting of the MCP is also reduced, which reduces the cost.

Claims (14)

REVENDICATIONS1. Battery temperature management system comprising at least one accumulator (2), characterized in that it comprises: at least one layer of phase change material (3) in thermal coupling with the accumulator (2) ), at least one fluidic channel (5) in thermal coupling with the layer of phase change material (3) and in which a heat transfer fluid is circulating to cool or heat the phase change material, a control means the circulation of the coolant in the fluidic channel (5), so that the coolant circulates only in the channel during the charging phase of the battery, and a means for controlling the temperature of the coolant intended to circulate in the the fluidic channel (5) as a function of the temperature of the battery and / or the outside temperature. The system of claim 1, wherein the phase change material (3) is a material having a melting temperature of between 25 ° C and 35 ° C to ± 2 ° C. 3. System according to claim 2, characterized in that the phase change material (3) is a eutectic material, including compounds based on salt hydrates such as LiNO3,2H20 or Na2SO4,10H20 or paraffin. , especially paraffins having a carbon number varying between 15 and 20. 4. System according to any one of claims 1 to 3, wherein the phase change material (3) is included in a base envelope, sealed and permeable to heat exchange, in particular with the accumulator (2). The system of claim 4, wherein the base shell comprising the phase change material (3) is removable and replaceable. 6. System according to any one of the preceding claims, wherein the heat transfer fluid is liquid, especiallywater or brine, or gaseous, including air or a refrigerant. 7. System according to claim 6, wherein the means for controlling the circulation is a compressor or a fan, when the coolant is gaseous, and a pump, when the heat transfer fluid is liquid. 8. System according to any one of the preceding claims, wherein at least one thermally conductive fin is disposed in contact with or inserted into each layer of phase change material (3) so as to facilitate the transport of thermal energy from and to the phase change material (3). 9. System according to claim 8, wherein the fins are in contact with the fluidic channel (5). 10. System according to any one of the preceding claims, wherein the means for controlling the temperature of the heat transfer liquid is a heat exchanger adapted to cool or heat said heat transfer fluid before entering the fluid channel. 11. System according to claim 10, wherein the heat exchanger is also thermally connected to a heat pump on board a vehicle and connected to a conditioned air system blown into the passenger compartment of said vehicle. 12. System according to any one of the preceding claims, wherein the battery is a battery for a motor vehicle and the means for controlling the setting in motion of the heat transfer fluid and the control means for controlling the temperature of the coolant are arranged outside the vehicle, forming a terminal intended to be fixed to the ground, the terminal being adapted to be temporarily connected to the fluidic channel (5) disposed on board the vehicle. 13. The system of claim 11, wherein a thermal insulator is disposed around the battery, when the phase-change material (3) is intended to be cooled by the coolant. 14. A method of implementing a battery temperature management system according to any one of claims 1 to 13, characterized in that it comprises a step of circulating the heat transfer fluid at a temperature. controlled in the fluidic channel during the charging phase of the battery.