Method for controlling pressure of dielectric liquid circulating in a cooling system - Patents.com

Abstract

The present invention relates to a method for controlling the pressure of a dielectric liquid circulating in a cooling system of at least one battery cell of an at least partially electrically propelled vehicle, the cooling system comprising a circuit through which the dielectric liquid circulates, the battery cell being immersed in the dielectric liquid, the cooling system comprising means for pressurizing the dielectric liquid in the circuit.

Description

[Technical field]

[0001] The present invention relates to the field of cooling battery modules for hybrid or fully electric vehicles, and more particularly to a pressure control method adapted to keep a cooling system under proper operating conditions.

[0002] Automotive manufacturers are looking to improve the performance and range of batteries in electric vehicles. They also want to reduce the time required to charge the batteries in such vehicles. These improvements may impose new constraints on the batteries, for example: -Significant cooling is required to allow for faster battery charging To improve the service life and performance of the battery cells, and to improve the safety of the user, it is necessary to constantly apply significant pressure to the battery cells. The volumetric variations of the battery cells need to be managed during continuous charge and discharge operation and / or as the battery cells age.

[0003] The prior art includes certain cooling systems designed to manage the pressure and temperature on the battery cells. However, such systems are not utilized in the best conditions and have a negative impact on the service life and performance of the batteries of electric vehicles. The charging and discharging processes are not predicted and the pressures in these systems are not properly managed to obtain the best service life and performance for the batteries.

[0004] In particular, German patent application DE102018215477 describes the use of a piston system, a pump and a pressure sensor in a battery module, in which the electrochemical cells are partially immersed, to control the pressure of a cooling fluid. Since the fluid circuit comprises an expansion vessel, it is at substantially atmospheric pressure. This fluid is therefore pressurized by the pump, since the piston is only present to compensate for the volumetric variations of the cells. The pump must constantly generate a very high pressure (equal to the pressure at which the cells must be compressed), which is increased by the hydraulic head losses in the circuit, which is for example about 3 bar at full pressure. If such a pump even exists, it would be heavy, bulky and expensive.

[0005] The invention provides a pressure control method for adapting the pressure in the cooling circuit according to the operating mode, in particular the charging or discharging phase, which makes it possible to better take into account the various steps of the life cycle of the electrochemical cells used to drive the vehicle.

[0006] The main object of the present invention is therefore to provide a method for controlling the pressure of a dielectric liquid circulating in a cooling system for cooling at least one cell of a battery of an at least partially electric vehicle, comprising: the cooling system comprises a circuit completely filled with a dielectric liquid and through which the dielectric liquid circulates; The battery cells are immersed in a dielectric liquid; The cooling system includes a pressurizing means for pressurizing a dielectric liquid in the circuit, and a detection member for detecting the pressure of the dielectric liquid in the circuit; The control method includes at least the following steps: a first step of preparing the cells of the battery for charging, in which a dielectric liquid pressurizing means increases or decreases the pressure in the circuit to a first pressure, a second step of charging the cells of the battery, the second step being performed by the pressure means to maintain the first pressure in the circuit; a third step of preparing the cells of the battery for discharging, in which the dielectric liquid pressurizing means increases or decreases the pressure in the circuit to a second pressure, A fourth step of discharging the cells of the battery, the pressurizing means maintaining the second pressure in the circuit. Includes.

[0007] The cooling system includes a circuit through which a dielectric fluid circulates, and the cells of the battery are immersed in the dielectric liquid.

[0008] A dielectric liquid is a liquid designed to make contact with various electrical components without causing a short circuit.

[0009] The cooling system comprises pressurizing means for pressurizing the dielectric liquid in the circuit, which may be an electrically controlled piston. Such a system makes it possible to generate a pressure of, for example, 4 bar, which allows the cells to function in optimal conditions in terms of performance, durability and safety when subjected to charge and discharge cycles.

[0010] The pressure applied during the first warm-up step establishes the necessary pressure in the circuit to reduce the time required to charge the cell and to maximize the useful life of the cell.

[0011] In a second step, the pressurizing means maintains the first pressure in the circuit by appropriately positioning an electric actuator acting on a piston of the pressurizing means.

[0012] In a third step (corresponding to a step of preparing the battery cells for discharge), the dielectric liquid pressurizing means reduces the pressure of the liquid in the circuit, for example to a second pressure (corresponding to the pressure required in the circuit to optimize the cell discharge and to maximize the service life of the battery cells).

[0013] In a fourth step (corresponding to the step of discharging the cells of the battery), the pressure means maintain the second pressure in the circuit, in particular by appropriately positioning said electric actuator.

[0014] Advantageously, the pressure control method uses at least two pressure thresholds, a first pressure threshold designed for charging, whereas a second threshold pressure is designed for discharging. The setting of such a control method makes it possible to retard the aging of the battery cells, to optimize their performance and / or to limit heat loss from the battery cells.

[0015] According to one characteristic, the cooling system comprises at least one circulation means for circulating said dielectric liquid in a circuit. According to the invention, the circulation means (especially if in the form of a pump) and the dielectric liquid pressurization means (especially if in the form of a cylinder) cooperate with each other to establish a pressure (for example the first pressure or the second pressure) in the circuit.

[0016] According to another feature of the invention, the first step, the second step, the third step, and the fourth step form a cycle that is repeated multiple times.

[0017] According to another feature of the invention, the pressurizing means comprises at least one piston, which is in contact with the dielectric liquid and is moved by an electric actuator, and by moving the piston the first pressure is maintained during the second step or the second pressure is maintained during the fourth step.

[0018] In the first scenario, the movement exerted by the piston may be an axial translational movement to maintain pressure by moving the piston forwards or backwards along its coaxial axis.

[0019] In a second scenario, the movement performed by the piston may be a rotational movement, and the shape of the piston and the chamber filled with the dielectric liquid are configured to compress the dielectric liquid in the cooling system and to relieve pressure on the dielectric liquid in the cooling system.

[0020] According to another feature of the invention, the first pressure is maintained during the second step by retracting the piston, i.e. by releasing the force exerted on the dielectric liquid by the piston. The first pressure is maintained during the second step by the piston relieving the pressure on the dielectric liquid as the cell is charged and increases in volume.

[0021] According to another feature of the invention, the second pressure is maintained during the fourth step by moving the piston forward, i.e., by increasing the force exerted by the piston on the dielectric liquid. The second pressure is maintained during the fourth step by the piston compressing the dielectric liquid as the cell discharges and reduces its volume.

[0022] It should be noted that in this example, the first pressure is higher than the second pressure.

[0023] According to another feature of the invention, the movement of the pressure means is effected in response to a pressure sensed by a sensing member.

[0024] The pressure sensing member may be the same as a pressure sensor, and pressure information in a circuit is sent to a computer which controls the change in piston position to control pressure in response to charging or discharging the cell.

[0025] According to another feature of the invention, any of the first to fourth steps is preceded by a step of applying a vacuum to the circuit.

[0026] A vacuum is applied to minimize the presence of gas in the circuit.

[0027] According to another characteristic of the invention, the circuit is completely filled with dielectric liquid, which is understood to mean that during normal operation, none of the parts of the circuit are in contact with any fluid other than the dielectric liquid.

[0028] According to another feature of the invention, prior to the first step, a pressurizing means brings the dielectric liquid from atmospheric pressure to a pressure appropriate for the state of charge of the battery cells, such as a first pressure, a second pressure, or another pressure.

[0029] When the cooling system is first started or when any work is performed on the cooling system, the circuit is filled with dielectric liquid and sealed at atmospheric pressure, followed by a first movement of the pressurizing means to bring the dielectric liquid to the pressure required for the charge level of the battery.

[0030] According to another feature of the invention, the cooling system comprises at least one heat exchanger configured to release the thermal energy present in the dielectric liquid to the external environment.

[0031] The circulation means may be the same as the pump for circulating the dielectric liquid in the circuit, which by means of said circulation overcomes the fluid head losses in the cooling system and helps to maintain the system at a constant pressure. The fluid head losses in the system are approximately 0.5 bar. The pressurizing means raises the static pressure in the circuit to a value of approximately 3.5 bar. These pressure values ​​are exemplary but illustrate ratios. The pump can thus be reduced in size and weight and also in consumption compared to prior art systems, thus improving the electric range of the electric vehicle.

[0032] The heat exchanger forms part of the circuit and makes it possible to release the thermal energy stored in the dielectric liquid due to the heating of the battery cells to the external environment.

[0033] The invention also relates to a cooling system for cooling at least one cell of a battery of an at least partially electric motor vehicle, the cooling system comprising a circuit completely filled with a dielectric liquid, the circuit through which the dielectric liquid circulates, The battery cells are immersed in a dielectric liquid; The cooling system is at least one pressurizing means for pressurizing the dielectric liquid present in the circuit; a circulating means for circulating the dielectric liquid in the circuit; a sensing member for sensing the pressure of the dielectric liquid in the circuit; and At least one heat exchanger configured to release the thermal energy present in the dielectric liquid to the external environment. Equipped with The pressurizing means maintains the dielectric liquid at a pressure higher than atmospheric pressure, while the circulation means circulates the dielectric liquid in the circuit.

[0034] In this document, the term "cell" is used to refer to both a single cell and a set of cells that form a battery, and multiple batteries assembled in close proximity to one another are referred to as a battery pack or battery module.

[0035] Other characteristics, details and advantages of the invention will become more clearly apparent from reading the following description on the one hand and with reference to the attached drawings, in which: [Brief description of the drawings]

[0036] [Figure 1] 1 illustrates a schematic of a cooling system for cooling a battery pack. [Diagram 2] 2 shows a pressure control method according to the present invention applied to the cooling system of FIG.

[0037] The features, variations, and different embodiments of the invention may be combined with each other in various combinations, unless they are mutually incompatible or mutually exclusive. In particular, variations of the invention having only a selection of features described below may be envisioned in isolation from the other features described, so long as the selection of features is sufficient to provide a technical advantage and / or to differentiate the invention from the prior art.

[0038] FIG. 1 shows a cooling system 1 for cooling a battery pack 2.

[0039] The battery 4 is an electrical storage element intended to supply electrical energy at least to an engine for driving a vehicle equipped with a cooling system.

[0040] 1 comprises a number of batteries 4 in which a dielectric fluid circulates. The cooling system also comprises a circuit 6 serving to direct the flow of the dielectric liquid between the various elements of the cooling system 1.

[0041] The cooling system 1 further comprises a heat exchanger 8 and a dielectric liquid circulation means 10, said circuit, the heat exchanger 8, the circulation means 10 and the battery 4 forming a closed loop, inside which the dielectric fluid circulates.

[0042] The cooling system 1 further comprises pressurizing means 12 for pressurizing the dielectric liquid within the circuit and a sensing member 14 for sensing the pressure of the dielectric liquid within the circuit 6 .

[0043] 1 comprises, for example, six batteries 4, each housing a number of cells 16. The batteries 4 comprise a chamber 17 defining a volume 18 filled with a dielectric liquid, inside which the cells 16 are completely immersed, i.e. totally submerged, in the dielectric liquid, so that there is no air in the circuit 6.

[0044] The dielectric liquid circuit 6 connects each of the six batteries 4 and comprises pipes 20, shown in dashed lines, forming an inlet for cooled dielectric fluid for each battery 4. The dielectric liquid circulating along the cells 16 in the battery 4 collects the thermal energy dissipated by each cell 16 and this heated dielectric liquid is sent through pipes 22 to the heat exchanger 8 (see solid lines in FIG. 1).

[0045] The circuit 6 thus consists of a supply section 20 (starting at the outlet of the heat exchanger 8 and ending at the inlet of at least one battery 4) and a collection section 22 (starting at the outlet of at least one battery 4 and ending at the inlet of the heat exchanger 8).

[0046] The heat exchanger 8 is a component intended to release the thermal energy present in the dielectric liquid to the outside environment, which may for example be an air flow through the heat exchanger 8 or another heat exchange liquid. The heat exchanger 8 is placed immediately downstream of the battery 4 and in the direction of circulation of the dielectric liquid in the circuit 6, to allow a rapid discharge of the thermal energy recovered in the cells 16.

[0047] Circulation means 10 are arranged in the circuit 6 immediately downstream of the heat exchanger 8. According to one exemplary embodiment, the circulation means 10 are a pump actuated by an electric motor, the role of which is to circulate the dielectric liquid inside the circuit 6, inside the battery 4 and inside the heat exchanger 8, forming a closed circuit.

[0048] The pressurizing means 12 is connected to the circuit 6 by an arm 24 external to the circuit 6 (which arm is connected to the circuit 6), for example between the outlet of the circulation means 10 and the inlet of at least one battery 4, or at any other point connecting the circuit within the scope of the present invention.

[0049] The pressurizing means 12 comprises an electric actuator 26 constituted by an electric motor 27 and a mechanical system 28 for converting the rotation of the electric motor 27 into a translational movement. This translational movement makes it possible to move a pin 30 of a piston 32 and thus to move the piston 32 into a body 34. The piston 32 is in contact with the dielectric liquid. The body 34, the piston 32 and the pin 30 form a cylinder 31.

[0050] The role of the pressurizing means 12 is to maintain homogeneous and continuous pressure conditions throughout the circuit 6, according to the charge or discharge phase of the cycle. The dielectric liquid is by nature not very compressible, so the movement of the piston 32 is reduced in order to bring the circuit 6 to the pressure required for its proper functioning.

[0051] According to the invention, the pressurizing means 12 provides the static pressure in the circuit 6, whereas the circulation means 10 provides the dynamic pressure required to circulate the dielectric liquid in the circuit. Such a design is advantageous since it allows the use of simpler and cheaper circulation means and also allows the invention to reduce the electrical consumption, thereby increasing the electric range of the vehicle.

[0052] 2 shows a method for controlling the pressure in the cooling system, which makes it possible to adapt the pressure in the circuit 6 for a better service life and better performance of the battery pack 2.

[0053] The pressure control method shown in FIG. 2 is illustrated in three graphs 36, 38, and 40, each of which has the same time axis.

[0054] A first graph 36 shows on the vertical axis the position of the piston 32 in the body 34 of the cylinder 31 and on the horizontal axis the time. A second graph 38 shows on the vertical axis the charge level of the cell (%) and on the horizontal axis the time. The last graph 40 of Figure 2 shows on the vertical axis the pressure in the circuit 6 (bar) and on the horizontal axis the time.

[0055] The three graphs 36, 38, 40 in Figure 2 are chronologically linked to each other in the sense that their horizontal axes represent time on the same scale and starting from the same instant in time.

[0056] The curves of these three graphs 36, 38, 40 vary over time with the position of the piston 32 and with the pressure in the circuit 6, depending on the charging or discharging of the battery 2. The dashed lines in the three graphs 36, 38, 40 indicate a change in pressure, a change in the level or cycle of charge, or a change in the position of the pressurizing means 12, or an intermediate waiting step between two active steps (for example between E and F).

[0057] The pressure control method includes a step of preparing the battery pack 2 for discharge between F and G. This preparation is characterized by the movement of the piston 32, which allows the pressure in the circuit 6 to be relieved to a second pressure (corresponding to the pressure established before the cell discharge step).

[0058] From the third graph 40, it can be seen that according to an exemplary embodiment, the second pressure (also referred to as the discharge pressure 42 of the battery pack 2) is lower than the first pressure (also referred to as the charge pressure 44).

[0059] Between points G and H, the battery pack 2 is discharged, in particular due to the fact that the battery pack supplies electrical energy to the engine for driving the vehicle. Here, it is understood that the electric vehicle is in the driving phase.

[0060] During this discharge phase or process, the volume of the cell 16 decreases. This volume decrease is manifested as a pressure decrease of the dielectric liquid in the circuit 6. This pressure decrease is then detected by the pressure sensing element 14, which, by means of a control module implementing the control system, commands the pressurizing means to keep the second pressure constant in the circuit 6. According to one example, the piston 32 moves forward, maintaining a force on the dielectric liquid that is continuous and proportional to the discharge occurring in the battery cell. In this way, it is guaranteed that the pressure on the cell is constant throughout the discharge phase.

[0061] The pressure control method includes priming the cells 16 of the battery pack 2 for charging between points I and J. This priming is characterized by the movement of the piston 32, which increases the force the piston exerts on the dielectric liquid, thereby compressing the circuit 6 and allowing it to reach charging pressure 44.

[0062] From the third graph 40, it can be seen that the charging pressure 44 of the battery pack 2 is higher than the discharging pressure 42 according to an exemplary embodiment.

[0063] The preparation steps, referred to as the first and third steps, are intended both to provide the dielectric fluid with a pressure appropriate for the steps that follow and to anticipate the charge or discharge phase that will follow immediately after the preparation step.

[0064] Between points J and K, the cells of the battery pack 2 are charged. Here, it is understood that, for example, an electric vehicle is in a parked state connected to a charging terminal.

[0065] Now, while being charged, the volume of the cells 16 of the battery 4 increases. This volume increase causes an increase in pressure in the circuit 6, which is picked up by the pressure sensing member 14. The pressurizing means moves to maintain a constant first pressure in the circuit 6. The piston 32 thus retracts, thereby reducing the load it exerts on the dielectric liquid in order to maintain a constant pressure in the circuit 6 during the charging process.

[0066] Steps FG, GH, IJ and JK form a cycle that is repeated throughout the useful life of the battery pack 2. This cycle includes two pressure thresholds in the circuit 6, a first pressure threshold corresponding to the charge pressure 44 of the cells, and a second pressure threshold corresponding to the discharge pressure of the cells for the battery or batteries of the battery pack.

[0067] Between points A and B, the battery 4 is filled with a dielectric fluid at atmospheric pressure. A vacuum is pre-applied to the circuit 6 to avoid the presence of air in the circuit.

[0068] The third graph 40 of Fig. 2 shows that the circuit 6 is brought to a first pressure when going from point B to point C. The circuit 6 is set to a charging pressure 44, since in this particular case, as shown here, the battery pack 2 is 30% charged. The next phase would therefore be the charging process of the battery pack 2. The change from atmospheric pressure to the first pressure (corresponding to the transition from point B to C) is achieved by a pressurizing means which increases the force applied to the dielectric fluid.

[0069] In another use case, the battery pack 2 may be charged and the circuit 6 will first be brought to a second pressure (ie, the discharge pressure 42).

[0070] Steps AB and BC are performed when the cooling system according to the present invention is first started up and / or during maintenance procedures on the battery pack 2.

[0071] Once the battery pack 2 is 100% charged, charging stops, so the piston 32 stops moving and the pressure in the circuit 6 remains constant.

[0072] The phases between points C and D, between points E and F and between points H and I are waiting phases before a charging or discharging process.

[0073] The invention as just described achieves indeed the above mentioned objectives and makes it possible to provide a cooling system for cooling a battery pack, in which the pressure of the dielectric liquid is kept constant during the two essential phases for the battery, namely the charging phase and the discharging phase of the battery. According to the invention, the management of the pressure is predicted by pressure means. This cooling system is particularly attractive in that it makes it possible to use circulation means that are simple, cheap and energy efficient, since the pump overcomes only the hydraulic head losses in the circuit and not the additional head losses (forming the static pressure of the circuit) with respect to the set pressure. Variations not described here can be carried out without departing from the context of the invention, as long as they carry out the control method according to the invention.

Claims

1. 1. A method for controlling the pressure of a dielectric liquid circulating in a cooling system (1) for cooling at least one cell (16) of a battery (4) of an at least partially electric vehicle, comprising: The cooling system (1) comprises a circuit (6) completely filled with the dielectric liquid and through which the dielectric liquid circulates, The cells (16) of the battery (4) are immersed in the dielectric liquid; The cooling system (1) comprises a pressurizing means (12) for pressurizing the dielectric liquid in the circuit (6), and a detecting element (14) for detecting the pressure of the dielectric liquid in the circuit (6), The method comprises at least the following steps: a first step of preparing the cells (16) of the battery (4) for charging, in which a dielectric liquid pressurizing means (12) brings the pressure in the circuit (6) to a first pressure (44); a second step of charging the cells (16) of the battery (4), in which the pressure means (12) maintains the first pressure (44) in the circuit (6); a third step of preparing the cells (16) of the battery (4) for discharging, in which the dielectric liquid pressurizing means (12) brings the pressure in the circuit (6) to a second pressure (42); a fourth step of discharging the cells (16) of the battery (4), in which the pressure means (12) maintains the second pressure (42) in the circuit (6); wherein the first pressure (44) is higher than the second pressure (42).

2. 2. A control method according to claim 1, wherein the cooling system comprises at least one circulation means (10) for circulating the dielectric liquid in the circuit (6).

3. The method of claim 1 , wherein the first step, the second step, the third step, and the fourth step form a cycle that is repeated multiple times.

4. 2. The control method of claim 1, wherein the pressurizing means (12) comprises at least one piston (32), which is in contact with the dielectric liquid and is moved by an electric actuator (26), and by moving the piston (32), the first pressure (44) is maintained during the second step or the second pressure (42) is maintained during the fourth step.

5. 5. The method of claim 4, wherein the first pressure (44) is maintained by retracting the piston (32) during the second step.

6. 5. The method of claim 4, wherein the second pressure (42) is maintained by moving the piston (32) forward during the fourth step.

7. 2. The control method according to claim 1, wherein the movement of the pressure means (12) is performed in response to the pressure detected by the detection member (14).

8. 2. The control method according to claim 1, further comprising the step of applying a vacuum to the circuit (6) before any of the first to fourth steps.

9. 8. The method of claim 7, wherein, before the first step, the pressurizing means (12) brings the dielectric liquid from atmospheric pressure to a pressure appropriate for the state of charge of the cells (16) of the battery (4).

10. 2. The method of claim 1, wherein the cooling system comprises at least one heat exchanger (8) configured to release the thermal energy present in the dielectric liquid to the external environment.

11. A cooling system (1) for cooling at least one cell (16) of a battery (4) of an at least partially electric motor vehicle, said cooling system (1) comprising a circuit (6) completely filled with a dielectric liquid and through which said dielectric liquid circulates, The cells (16) of the battery (4) are immersed in the dielectric liquid; The cooling system (1) comprises: at least one pressurizing means (12) for pressurizing the dielectric liquid present in the circuit (6); a circulation means (10) for circulating the dielectric liquid in the circuit (6); a sensing element (14) for sensing the pressure of the dielectric liquid in the circuit (6); and At least one heat exchanger (8) configured to release the thermal energy present in the dielectric liquid to the external environment. Equipped with In a cooling system, the pressurizing means (12) maintains the dielectric liquid at a pressure higher than atmospheric pressure, while the circulation means (10) circulates the dielectric liquid in the circuit (6), the pressure applying means (12) is an electric actuator (26) composed of an electric motor (27) and a mechanical system (28), the electric actuator (26) being for converting rotation of the electric motor (27) into translational movement; A cooling system comprising:

Images