Cooling device for an electric energy storage system with gravity heat pipes, electric energy storage system and motor vehicle

Description

[0001] The invention relates to a cooling device for an electrical energy storage device for cooling the energy storage cells of the electrical energy storage device, wherein the cooling device comprises gravitational heat pipes with a working medium for absorbing waste heat from the energy storage cells. The invention also relates to an electrical energy storage device and a motor vehicle.

[0002] The present case focuses on electrical energy storage devices, which can be used, for example, as traction batteries for electrified motor vehicles, i.e., electric or hybrid vehicles. Such electrical energy storage devices typically comprise at least one cell array consisting of several energy storage cells. Cooling devices are used to cool the energy storage cells during operation. Such cooling devices can, for example, include gravitational heat pipes, as disclosed in WO 2020 / 207 718 A1. Cooling devices with heat pipes are known from DE 10 2015 106 948 A1 and DE 10 2017 218 248 A1.

[0003] The object of the present invention is to provide a solution for how gravitational heat pipes can be easily integrated into an electrical energy storage device.

[0004] This problem is solved according to the invention by a cooling device, an electrical energy storage device, and a motor vehicle with the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description, and the figures.

[0005] A cooling device according to the invention for an electrical energy storage device serves to cool the energy storage cells of the electrical energy storage device. The cooling device comprises gravitational heat tubes with a working medium for absorbing waste heat from the energy storage cells. Furthermore, the cooling device has a frame with walls for forming recesses for the energy storage cells, wherein the gravitational heat tubes are integrated into the walls.

[0006] The invention also includes an electrical energy storage device with at least one cell assembly of energy storage cells and a cooling device according to the invention, wherein the energy storage cells are arranged in the frame's receptacles, and with a storage housing in which the cell assembly is arranged. The electrical energy storage device can, for example, be a high-voltage energy storage device used as a rechargeable traction battery or traction accumulator for an electrically powered motor vehicle. The electrical energy storage device has the at least one cell assembly comprising several energy storage cells. The energy storage cells can, for example, be designed as prismatic energy storage cells or pouch cells. Preferably, the energy storage cells are designed as cylindrical cells. The energy storage cells have cell terminals or...Cell poles are located in the area of ​​a cell housing cover of the energy storage cells. The cell housing also has cell housing side walls and a cell housing base.

[0007] The storage housing can comprise housing components in the form of a housing cover or upper section and a housing base or lower section, which are joined together to form an interior housing space. At least one cell assembly is arranged within this interior housing space. To cool the energy storage cells, the at least one cell assembly also includes a cooling device. This cooling device comprises gravitational heat pipes. Gravitational heat pipes, or two-phase thermosiphons, are heat exchangers that transfer waste heat via the latent heat of vaporization. For this purpose, the gravitational heat pipes have an elongated sleeve that extends vertically along the direction of gravity. A working fluid is arranged within this sleeve, which remains in a liquid state as long as the temperature of the energy storage cells caused by the waste heat falls below the boiling point of the liquid working fluid.As soon as the temperature exceeds the boiling point, the working fluid evaporates. In other words, the working fluid changes from a liquid to a gaseous state. The working fluid rises as vapor against the direction of gravity, condenses there on a heat sink of the cooling unit coupled to the gravitational heat pipe, and thus releases the transported waste heat to the heat sink. The working fluid then changes back from the gaseous state to the liquid state and falls back down as liquid droplets due to gravity. The return transport of the condensed working fluid is therefore carried out by gravity. The heat sink is formed in particular by a housing component of the storage unit, specifically the upper housing section.

[0008] These gravitational heat pipes are integrated into the frame designed to hold the energy storage cells. The frame has walls that form the recesses for the energy storage cells. For cylindrical energy storage cells, these recesses can be cavities with a round or honeycomb cross-section. The energy storage cells are inserted into these recesses, so that the walls extend vertically along the cell housing sidewalls. The gravitational heat pipes are integrated into these walls. Thus, the gravitational heat pipes are located adjacent to the energy storage cells and extend between them along the cell housing sidewalls. The frame is made of a highly thermally conductive material, such as aluminum or magnesium. For example, the frame can be manufactured using die casting.To electrically insulate the energy storage cells from the frame, an insulating element, for example in the form of a plastic heat-shrink tube, can be placed between the cell casings of the energy storage cells and the walls of the frame. The energy storage cells can then transfer the waste heat via their highly thermally conductive walls to the gravity heat pipes, from where it is transported to the heat sink.

[0009] By integrating the gravity heat pipes into the frame, the gravity heat pipes can be integrated into the electrical energy storage system in a particularly simple and space-saving manner.

[0010] Preferably, the frame is also designed to absorb impact forces. The frame thus protects the energy storage cells from the effects of such forces. The frame can also incorporate crash structures. These crash structures can be located on a section facing the front of the vehicle, on a section facing the rear of the vehicle, or on lateral sections of the frame extending along a longitudinal axis of the vehicle. The crash structures can, for example, be designed as shear panels and / or honeycomb structures.

[0011] The walls feature tubular cavities which are filled with the working fluid to form the gravitational heat pipes. The gravitational heat pipes are thus formed by the frame itself, with the cavities being incorporated into the walls as elongated channels and filled with the working fluid. The cavities can be open at one end, for example, on the top of the frame. The top of the frame can be sealed to the upper part of the housing, so that the gravitational heat pipes are thermally connected to the upper part of the housing.

[0012] In an advantageous further development of the electrical energy storage device, it comprises a carrier and a cell contacting system for interconnecting the energy storage cells, with the cell contacting system and the frame being integrated into the carrier. The cell contacting system is specifically designed as a die-cut comb with a conductor track pattern, enabling a predetermined interconnection of the energy storage cells. This die-cut comb is manufactured by first structuring a conductor material, for example, a sheet metal sheet, and cutting out recesses from the conductor material. In a second step, the structured conductor material and the frame are joined to the carrier. Joining the conductor material and the frame to the carrier can be achieved, for example, by forming. For this purpose, the structured conductor material and the frame are overmolded with an insulating material and / or potted.During overmolding or potting, certain areas of the conductor material can be left exposed to complete the die-cut comb in a third step. Additional recesses can be cut out of the conductor material to create a predetermined conductor pattern.

[0013] The invention also includes a motor vehicle with at least one electrical energy storage device according to the invention. The motor vehicle is, in particular, an electrified motor vehicle and has the electrical energy storage device in the form of a traction battery. Specifically, the frame of the electrical energy storage device is connected to the body of the motor vehicle by forming a supporting structure.

[0014] The embodiments and advantages presented with reference to the cooling device according to the invention apply accordingly to the electrical energy storage device according to the invention and to the motor vehicle according to the invention.

[0015] Further features of the invention will become apparent from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown in the figures alone, are not only usable in the combinations specified, but also in other combinations or on their own.

[0016] The invention will now be explained in more detail with reference to a preferred embodiment and the drawings. The drawings show: Fig. 1 a schematic representation of an electrical energy storage device; Fig. 2 a schematic sectional view of a first embodiment of an electrical energy storage device in a first plane; Fig. 3 a schematic sectional view of the first embodiment of an electrical energy storage device in the second plane; Fig. 4 a schematic sectional view of a second embodiment of an electrical energy storage device in the first plane; Fig. 5 a schematic sectional view of the second embodiment of an electrical energy storage device in the second plane; and Fig. 6 a schematic sectional view of an embodiment of an electrical energy storage device in a third plane.

[0017] In the figures, identical or functionally equivalent elements are provided with the same reference symbols.

[0018] Fig. 1 Figure 1 shows an electrical energy storage device (EES) comprising a storage housing 1 with a first housing part 2a in the form of a lower housing part and a second housing part 2b in the form of a housing upper part. The electrical energy storage device (EES) can be used, for example, as a traction battery for an electrically powered vehicle and can be designed as a high-voltage energy storage device. The housing upper part 2b can be double-walled and contain a space 3 for a flowing cooling fluid. The space 3 can be connected to an external cooling circuit via terminals. A cell array 4 is arranged in the storage housing 1 between the lower housing part 2a and the housing upper part 2b.

[0019] The cell assembly 4 exhibits, as in the exemplary embodiment of the electrical energy storage system EES according to Fig. 2 bis Fig. 5 shown, a frame 5 and energy storage cells 6. The electrical energy storage system EES according to Fig. 2 bis Fig. 5 The diagram is presented as a cross-sectional view in a zx-plane (B) and in a section (A) angled 30° relative to x. The x-direction corresponds, for example, to a (vehicle) transverse direction, and the z-plane corresponds, for example, to a (vehicle) vertical direction. Fig. 6 Figure 1 shows a cross-sectional view of an electrical energy storage device (EES) in an xy-plane. The y-direction corresponds, for example, to a (vehicle) longitudinal direction. The embodiments of the electrical energy storage device (EES) according to Figure 1 are shown. Fig. 2 and Fig. 4 correspond to a cut along the in Fig. 6 Section line A shown. The same embodiments of the electrical energy storage system EES according to Fig. 3 and Fig. 5 correspond to a cut along the in Fig. 6 shown section line B.

[0020] The energy storage cells 6 each have a cell housing 7, which includes a cell housing base 7a, cell housing side walls 7b, and a cell housing cover 7c. The energy storage cells 6 can, for example, be cylindrical cells, such that the cell housing covers 7c and the cell housing bases 7a are circular and the cell housing side walls 7b are cylindrical. The cell housing side walls 7b extend in the vertical direction z. The cell housing covers 7c can have cell terminals 8a, 8b, or cell poles, which are electrically connected by means of a cell contacting system 9 for interconnecting the energy storage cells 6. The energy storage cells 6 can also have degassing openings 10 for releasing hot gas in the event of a fault, for example, an internal short circuit.In an exemplary embodiment, to form a cooling chamber for hot gas, the lower part 2a of the storage housing 2 is arranged at a distance from the degassing openings 10 or is designed as an expandable heat shield.

[0021] The frame 5 has walls 11 which form recesses for the energy storage cells 6 and which extend along the vertical direction z at least partially over the height of the cell housing side walls 7b. The walls 11 can absorb the waste heat emitted by the energy storage cells 6 and conduct it towards the upper housing part 2b. The heat transfer from the energy storage cells 6 towards the upper housing part 2b is facilitated by gravitational heat tubes 12, which, due to the section line A encompassing the gravitational heat tubes 12, are only visible in the representations according to Fig. 2 and Fig. 3 The gravity heat pipes 12 are shown and supported. They are monolithically integrated into the frame 5 or joined to the frame 5 as separate components. The gravity heat pipes 12 also extend vertically z along the cell housing side walls 7b and are arranged between the energy storage cells 6. The frame 5 is thermally connected to the housing top 2b, e.g., by gluing, screwing, riveting, clinching, soldering, or welding. The gravity heat pipes 12 contain a working medium, for example, a liquid, which evaporates due to the waste heat from the energy storage cells 6 and thereby transports the waste heat upwards in the vertical direction z against gravity. The gravity heat pipes 12 are thermally coupled to the housing top 2b, which forms a heat sink or condenser. The gravity heat pipes 12 can be open at the top and directly connected to the housing top 2b.The gravitational heat tubes 12 are sealed at the bottom by the walls 11 of the frame 5. The vaporized working medium condenses on the upper part of the housing 2b, releasing waste heat to the upper part of the housing 2b, and falls downwards again due to gravity in the opposite direction z, where it can evaporate again to absorb waste heat.

[0022] The operating range of the gravitational heat tubes 12 is adapted to the permissible temperature range of the energy storage cells 6 by the type of filling, the filling pressure, a variation in shape and dimensions along their length, and the control of the heat flow. In a particularly advantageous configuration, the gravitational heat tubes 12 contribute significantly to heat transport in the intended operating range of the electrical energy storage system (EES) and dry out in the event of thermal overload in order to shield the area surrounding a degassing energy storage cell 6 from the heat load of the degassing energy storage cell 6.

[0023] The energy storage cells 6 are electrically insulated from the lower housing part 2a, the upper housing part 2b, and the frame 5. In an exemplary embodiment, the energy storage cells 6 have electrical insulation 13 from the frame 5, e.g., in the form of a shrink-fitted plastic tube. The energy storage cells 6 are each sealed in the frame 5, at least in the area of ​​the cell contacting system 9, and are fixed, for example, by snap-in elements 14 of the frame 5. Contact surfaces of the cell contacting system 9 are metallurgically or by pressure connected to the associated cell terminals 8a, 8b of the energy storage cells 6. Fig. 2 and Fig. 3 The upper housing part 2b has at least one anvil-shaped protrusion 25 on an inner surface 24 facing the cell assembly 4, which presses the contact surfaces of the cell contacting system 9 against the cell terminals 8a, 8b. The upper housing part 2b is thus integrated into the force-fit connection of the pressure contact system of the cell contacting system 9. An insulating layer 26 is arranged between the inner surface 24 of the upper housing part 2b and the cell terminals 8a, 8b, at least in the area of ​​the protrusion 25. This embodiment enables additional contact-side cooling of the energy storage cells 6.

[0024] In an advantageous embodiment, the frame 5 has, as in Fig. 1 The figure shows a lateral boundary 15 of the electrical energy storage system (EES) and a space 16 for a hydraulically compensating filling 17 under external forces. The frame also comprises 5 elements for mechanical integration into a motor vehicle and can be used as a load-bearing structural component of the vehicle body, for example, as a floor assembly. Properties such as manufacturability, assembly, thermal conductivity, load-bearing capacity, and weight can be optimized through material selection, cutouts, and adjustments to wall thicknesses and rib structures.

[0025] For example, the frame 5 is manufactured using a casting process or as a 3D print from aluminum or magnesium. A frame 5 manufactured from magnesium is particularly easy to cast, has especially favorable draft angles, and is particularly lightweight. The cell contacting system 9 is designed, for example, as a leadframe or die-cut comb. The frame 5 and the cell contacting system 9 are joined together by a joining process, such as potting. The frame 5 can also be integrated into a monolithic component within a single casting manufacturing step for an electrically insulating carrier 18 of the cell contacting system 9, or the monolithic component can be produced as a 3D print.

[0026] To protect the energy storage cells 6 against hot gas, as described in Fig. 2 bis Fig. 5 As shown, an additional and optionally additionally sealing cell cover 19 is attached to the frame 5 on the bottom side of the cell housing. This cover detaches from the frame 5 in the event of overpressure, opening the path for the hot gas and / or containing a bursting element 20 for the passage of the hot gas. In the event of servicing, the following can be done: Fig. 2 and Fig.3 In the arrangement shown, direct access to the cell contacting system 9 is not required, and servicing is performed solely by removing the lower housing part 2a, the cell cover 19, and the energy storage cell 6. A particular advantage is that servicing can be carried out with high specificity and direct accessibility from the underbody of the vehicle. Alternatively, or additionally, the cell housing bottoms 7a can also be coated with a fire-retardant lacquer instead of the cell cover 19.

[0027] In one embodiment of the electrical energy storage device according to Fig. 4 and Fig. 5 The upper housing part 2b in the area of ​​the energy storage cells 6 can be interrupted by means of recesses 21 to ensure metallurgical contact of the energy storage cells 6 and the insertion of a potting compound 22. The recesses 21 are then fitted with a contact cover 23. In the event of servicing, the contact cover 23 can be removed, at least locally, and then sealed with a patch.

Claims

1. Cooling device for an electrical energy store (EES) for cooling energy storage cells (6) of the electrical energy store (EES), wherein the cooling device comprises gravity heat pipes (12) with a working medium for taking up waste heat from the energy storage cells (6), characterized in that the cooling device has a frame (5) with walls (11) for forming receptacles for the energy storage cells (6), wherein the gravity heat pipes (12) are integrated in the walls (11) and the walls (12) for this have cavities which are vertically tubular along the direction of gravity and are filled with the working medium to form the gravity heat pipes (12).

2. Cooling device according to Claim 1, characterized in that the frame (5) is additionally designed to take up forces caused by an accident.

3. Cooling device according to either of the preceding claims, characterized in that the cooling device has a heat sink, on which the evaporated working medium transporting the exhaust heat condenses to discharge the exhaust heat.

4. Cooling device according to Claim 3, characterized in that the heat sink is formed by a housing part (2b) of a store housing (1) of the electrical energy store (EES).

5. Cooling device according to one of the preceding claims, characterized in that the frame (5) is manufactured, in particular from aluminium or magnesium, by die casting.

6. Electrical energy store (EES) having at least one cell assembly (4) having energy storage cells (6) and a cooling device according to one of the preceding claims, wherein the energy storage cells (6) are disposed in the receptacles in the frame (5), and having a store housing (1), in which the at least one cell assembly (4) is disposed.

7. Electrical energy store (EES) according to Claim 6, characterized in that the electrical energy store (EES) comprises a support (18) and a cell contact-connection system (9) for interconnecting the energy storage cells (6), wherein the cell contact-connection system (9) and the frame (5) are integrated in the support (18).

8. Motor vehicle having at least one electrical energy store (EES) according to Claim 6 or 7.

9. Motor vehicle according to Claim 8, characterized in that the frame (5) is connected to a bodywork of the motor vehicle with formation of a support structure.