GB2593187A

GB2593187A - Battery module clamping arrangement

Info

Publication number: GB2593187A
Application number: GB2003901.2A
Authority: GB
Inventors: Alexander Newnham Ian; Piersa Michal; N Lewis Alan; Rojas Oscar; Ali Mirhadizadeh Seyed; Babu Jalli Spurgeon; C Stewart Martin; Junaidi Haroon
Original assignee: Cummins Inc
Current assignee: Cummins Inc
Priority date: 2020-03-18
Filing date: 2020-03-18
Publication date: 2021-09-22
Also published as: CN214706144U; CN214706037U; GB202003901D0

Abstract

A battery module clamping arrangement is disclosed for clamping a battery module 12 in a battery pack (10, fig 1), the battery pack comprising a cooling system 14. The clamping arrangement comprises means 52 for applying a clamping force to the battery module such that the battery module maintains thermal contact with the cooling system, and may also include means 58 for applying a counter force to the cooling system. Support means 56 are provided for supporting the battery module. The support means comprise a compression stop, preferably in the form of a compression pin (fig 9A). This can allow the battery module to maintain thermal contact with the cooling system while ensuring that any additional forces are transferred through the support means rather than through the cooling system. The clamping arrangement is preferably arranged such that the battery module contacts the compression stop when the clamping force is above a predetermined value, which could lead to deformation of the cooling system. A thermally conductive pad 54 for providing thermal contact between the battery module and the cooling system is also disclosed.

Description

BATTERY MODULE CLAMPING ARRANGEMENT

The present invention relates to clamping arrangements for a battery module, and in particular a battery module for use with a battery pack comprising a plurality of battery modules. The present invention has particular, but not exclusive, application in battery packs for use in mobile applications such as electric or hybrid electric vehicles, construction equipment, and so forth.

Electric vehicles and hybrid electric vehicles, such as cars, buses, vans and trucks, typically use battery packs that are designed with a high ampere-hour capacity in order to give power over sustained periods of time. A battery pack typically comprises a large number of individual electrochemical cells connected in series and parallel to achieve the total voltage and current requirements. To assist in manufacturing and assembly, the cells in a battery pack may be grouped into modules. The battery modules may include a support structure and a battery management unit to manage cell charge and discharge. The battery modules and other components of the battery pack may be housed within a housing, which may include a frame and housing panels. Cross members may be provided inside the frame, between rows of battery modules.

In order to help with packing efficiency, some known battery modules use pouch cells. Typically, a number of pouch cells are stacked together inside a support structure to form a battery module. The cells in the module are connected in series and parallel to achieve the target voltage. Pouch cells provide energy dense electrical storage in the form of a relatively thin and generally flat pouch.

However, the lack of air gaps between the cells can lead to the build up of heat. It is therefore known to provide battery packs with cooling systems in order to cool the cells and thereby extend their operating life.

In order to assist with servicing of the battery pack, the battery modules may be exchangeable. In this case it is necessary to ensure that the removable battery modules are adequately restrained within the battery pack. This may be achieved using some form of clamping arrangement.

When using exchangeable battery modules, the battery modules themselves typically do not contribute to the structure of the battery pack. As a consequence, it may be necessary to provide the battery pack with structural features to ensure that it has sufficient overall strength. Furthermore, the cooling system may be required to absorb loads from the battery modules. Therefore, the cooling system may need to be relatively heavy, in order to ensure that it has the required mechanical strength. These (and other) requirements can make it difficult to achieve a high energy density pack with regards to total pack volume and mass of the pack, which are critical parameters in mobile battery pack applications.

The cooling system for a battery pack may include cooling plates. Normally a separate cooling plate is provided adjacent to each battery module. The cooling plates include a chamber through which a cooling fluid can flow in order to conduct heat away from the battery module. In order to ensure good thermal performance, a good thermal contact is desirable between the cooling system and the battery module. However, at the same time, it is also necessary to ensure that creepage and clearance distance requirements are achieved between electrical parts of the system. This may reduce the ability of the cooling system to conduct heat away from the battery modules.

It would therefore be desirable to provide a clamping arrangement which can help to ensure structural rigidity and module constraint, while at the same time helping to reduce battery pack volume and weight. It would also be desirable to provide good thermal contact between the cooling system and battery module, while achieving desired creepage and clearance distances.

According to one aspect of the invention there is provided a clamping arrangement for clamping a battery module in a battery pack, the battery pack comprising a cooling system, the clamping arrangement comprising: means for applying a clamping force to the battery module such that the battery module maintains contact with the cooling system; and support means for supporting the battery module, the support means comprising a compression stop.

This aspect of the invention may provide the advantage that, by providing a support means with a compression stop, it may be possible for the battery module to maintain thermal contact with the cooling system, while ensuring that any additional forces are transferred through the support means rather than through the cooling system. This may allow the cooling system to be lighter than would otherwise be the case, thereby helping to reduce the weight of the battery pack. Furthermore, by providing the compression stop, deformation of the cooling system may be avoided. This may help to avoid constriction of the flow of coolant, which if it were to occur could compromise the cooling of the battery cells. In addition, this aspect of the invention may allow a single cooling plate to be used for two or more battery modules, which may help to reduce the cost and weight of the cooling system and/or improve the efficiency of coolant flow.

The clamping arrangement is preferably arranged such the battery module contacts the compression stop when the clamping force is above a predetermined value. The predetermined value is preferably a value which is sufficiently high to ensure thermal contact between the battery module and the cooling system and/or sufficiently low to avoid deformation of the cooling system.

Preferably the clamping arrangement further comprises means for providing a counter force to the cooling system. The means for providing a counter force may be, for example, compression foam, or any other suitable elastic material. For example, in one embodiment, a counter clamping part includes a layer of foam on the opposite side of the cooling system to the battery module. In this case, the size, type and/or compression curve of the foam may be selected, together with other parameters of the clamping arrangement, to provide the required counter force to ensure that thermal contact is maintained between the battery module and the cooling system.

The counter force is preferably less than the clamping force applied to the battery module. This may help to ensure that the battery module maintains contact with the cooling system and with the compression stop. This in turn may allow dynamic loads to be passed through the support means rather than the cooling system.

Thus, the clamping arrangement may be arranged such that dynamic loads are passed through the support means. This may help to ensure that, even if the battery pack is subjected to dynamic loads due to shocks or other movements, such dynamic loads are not passed through the cooling system. This may allow the cooling system to be lighter than would otherwise be the case, and/or may help to prevent deformation of the cooling system. On the other hand, the pressure between the battery module and the cooling system may be sufficient to maintain thermal contact between the two even when dynamic loads are applied.

In one embodiment, the battery pack comprises a frame and a plurality of cross members. The cross members may be provided on either side of the battery module, or a row of battery modules. In this case, the clamping arrangement may comprise a clamping plate attached to two adjacent cross members (preferably cross members on either side of the battery module). The clamping plate may be arranged to apply the clamping force to the battery module. This may help to ensure that an even pressure is applied to the battery module, helping to ensure even contact with the cooling system. Furthermore, by attaching the module clamping plate to adjacent cross members, the structural rigidity of the battery pack may be improved. This may allow the battery pack to have a lower weight than would otherwise be the case.

According to another aspect of the invention there is provided a clamping arrangement for clamping a battery module in a battery pack, the battery pack comprising a frame and a plurality of cross members, the clamping arrangement comprising a clamping plate attached to two adjacent cross members.

A gap may be provided between the clamping plate and the cross members. This may help to ensure that the clamping plate is able to provide the required clamping force.

The clamping plate may be arranged to apply a clamping force to the battery module such that the battery module maintains thermal contact with the cooling system. However, it will be appreciated that other mechanisms for applying the required clamping force may be used instead.

In a preferred embodiment, as well as providing a compression stop, the support means is also arranged to locate the battery module. This may help to ensure that, when inserting or replacing a battery module, it is correctly located within the battery pack. However, means for locating the battery module may also be provided separately from the support means, if desired.

In one embodiment, the support means comprises a plurality of pins. The pins may be connected to a support structure (such as a housing panel) and may be arranged to engage with the battery module.

At least one of the pins may be a location pin, which may be arranged to engage with a corresponding hole in the battery module. The location pin may include a shoulder which may act as a compression stop. Alternatively or in addition, at least one of the pins may be a support pin, which may be arranged to engage with a pad on the battery module. The pins may have any appropriate cross section, such as circular, oval, rectangular, square, hexagon and so forth.

By providing a plurality of pins for supporting the battery module, more accurate positioning of the module may be achieved than would otherwise be the case.

Accurate module positioning may help to ensure uniform pressure on the cooling plate, reducing the risk of pressure drop in the cooling system, and may help to achieve better flexibility in module placement.

In a preferred embodiment, the support means comprise at least one location pin with a shoulder which acts as a compression stop. For example, the support means may comprise a plurality of location pins (for example, three location pins) and at least one support pin for each battery module. This may help to ensure that the battery module is correctly located while allowing for some tolerance and/or expansion of the battery module, as well as providing a compression stop, Alternatively, at least some of the pins and/or pads could be provided the other way around, that is, one or more of the pins could be provided on the battery module and be arranged to engage with a hole or a pad on a support structure.

According to another aspect of the invention there is provided a clamping arrangement for clamping a battery module in a battery pack, the clamping arrangement comprising a plurality of location pins arranged to locate and to support the battery module.

In any of the above aspects, the battery module may comprise at least one hole for receiving part of the support means and/or at least one pad for engaging with the support means. For example, where one or more location pins are provided, the battery module may comprise one or more holes for receiving the location pins. In this case, one or more of the holes may have a shape which corresponds to the cross section of a location pin. Alternatively or in addition, one or more of the holes may have a shape which is elongated with respect to the cross section of a location pin. For example, one or more of the holes may be a slot. Where a pad is provided, this may be arranged to engage with a support pin. These arrangements may help to ensure that the battery module is correctly located while allowing for some tolerance and/or expansion of the battery module.

Preferably the support means are arranged to pass past the cooling system. For example, the support means may pass through or next to the cooling system. In one embodiment, the cooling system comprises cooling plates which may have holes through which the support means pass. For example, where the support means comprises pins, then the pins may pass through the holes. This may help to ensure that a dynamic load can be passed through the support means rather than through the cooling system.

In a preferred embodiment, the battery pack comprises a housing panel, and the support means are attached to the housing panel. In this case, the housing panel may act as a counter clamp. This may provide the advantage that, by using the housing panel as a counter clamping part for the battery module, it may be possible to reduce or avoid the need for other counter clamping parts. This may help to reduce the overall weight and cost of the battery pack, and thus may help to achieve higher energy density in the pack.

This aspect of the invention may also be provided independently. Thus, according to another aspect of the invention, there is provided a clamping arrangement for clamping a battery module in a battery pack comprising a cooling system and a housing panel, the clamping arrangement comprising means for applying a clamping force to the battery module such that the battery module maintains contact with the cooling system, wherein the housing panel is arranged to act as a counter clamp.

In a preferred embodiment, the housing panel comprises a carbon fibre material, such as a carbon fibre reinforced polymer. For example, the housing panel may comprise layers of carbon fibre sheets. Carbon fibre may provide various advantages including high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and/or low thermal expansion. Thus, the use of a carbon fibre material may help to ensure that the housing panel has sufficient strength, while minimising the weight. However, any other appropriate material could be used instead or as well.

As discussed above, the clamping arrangement may comprise support means which may be attached to the housing panel. Thus, the housing panel may comprise a plurality of pins, such as one or more location pins and/or one or more support pins, which may be in any of the forms described above.

The housing panel may include an area of increased thickness in the region of the support means. This may help to ensure that the housing panel has the necessary strength, while avoiding unnecessary weight. The housing panel may also include an upturned edge or sidewall, which may help to provide stiffness.

Preferably, means for applying a counter force to the cooling system are provided between the housing panel and the cooling system. For example, a layer of support foam or any other suitable elastic material may be provided between the housing panel and the cooling system. This may help to ensure that the required counter clamping force to maintain thermal contact between the battery module and the cooling system is applied.

Preferably the clamping arrangement further comprises a thermally conductive pad for providing thermal contact between the battery module and the cooling system. The thermally conduct pad may help to compensate for any variations in the surface height of the battery module and/or cooling system, thereby helping to ensure good thermal contact.

In a preferred embodiment, the thermally conductive pad comprises a layer of electrically insulative film and at least one layer of thermally conductive plastic material (i.e. a material which exhibits plastic deformation). This may allow the thermally conductive pad to deform so as to conform to the shape of the battery module and/or the cooling system.

This aspect of the invention may also be provided independently. Thus, according to another aspect of the invention there is provided a thermally conductive pad for providing thermal contact between a battery module and a cooling system in a battery pack, the thermally conductive pad comprising a layer of electrically insulative film and at least one layer of thermally conductive plastic material.

By providing a thermally conductive pad comprising a layer of electrically insulative film and a layer of thermally conductive plastic material, it may be possible to maintain creepage and clearance values, while ensuring good thermal contact between the cooling system and battery module. For example, the thermally conductive plastic material may help to compensate for differences in height between the cells within a battery module caused by tolerance stack up and assembly tolerances. Furthermore, if it is necessary to replace a battery module, then the pad can easily be replaced at the same time, allowing good thermal contact to be achieved with the new module. In addition, use of the pad may avoid the need for the cooling system to have a coating or film to provide electrical insulation, which may simplify the cost and complexity of manufacture.

Preferably the thermally conductive pad comprises two layers of thermally conductive plastic material, one on each side of the electrically insulative film.

This may help to ensure that the thermally conductive pad can conform to the shape of the battery module and the cooling system.

The electrically insulative film is preferably chosen so as to provide sufficient electrical isolation between the battery module and the cooling system, while maintaining thermal conductivity between the two. This may be achieved, for example, through appropriate selection of the type and thickness of the material.

Preferably the layer of electrically insulative film extends beyond the or each layer of thermally conductive plastic material. Thus, the thermally conductive pad may include a skirt of electrically insulative film which extends beyond the thermally conductive plastic material. This may help to maintain creepage distances. Furthermore, the skirt may include alignment features which may be used to locate and retain the pad.

Preferably the thermally conductive pad comprises at least one alignment hole for locating the pad. For example, where the pad includes a skirt of electrically insulative film, the skirt may comprise one or more alignment holes. In the case of a clamping arrangement comprising support means for supporting the battery module, the support means may pass through the holes. Thus, the skirt may comprise one or more holes through which the support means may pass. This may help to ensure that the thermally conductive pad is correctly located, without the need to provide separate alignment features.

According to another aspect of the invention there is provided a battery pack comprising a clamping arrangement and/or a thermally conductive pad in any of the forms described above. Preferably the battery pack comprises a plurality of battery modules. The battery modules may be arranged in row, and cross members may be provided between adjacent rows. The cross members may be used, together with a clamping plate, to apply a clamping force to a battery module.

According to a further aspect of the invention there is provided a method of clamping a battery module in a battery pack, the method comprising clamping the battery module using a clamping arrangement, a thermally conductive pad and/or a battery pack in any of the forms described above.

Features of one aspect of the invention may be used with any other aspect. Any of the apparatus features may be provided as method features and vice versa.

Further details of the battery pack, battery module and clamping arrangement may be, for example, as disclosed in co-pending UK patent applications entitled "Battery Module Assembly", "Battery Antipropagation Techniques" and "Battery Pack' in the name of the present applicant, the subject matter of each of which is incorporated herein by reference.

Preferred features of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an overview of a battery pack; Figure 2 shows parts of a battery module; Figure 3 is an exploded view of a battery module; Figure 4 illustrates the basic principles of a module clamping assembly in an embodiment of the invention; Figure 5 shows an example of a module clamp plate; Figure 6 is a cross section through part of the module clamping assembly; Figure 7 shows parts of the clamping assembly in more detail; Figure 8 shows parts of a battery pack with modules and module clamps in place; Figures 9(A) and 9(B) show examples of a location pin and a support pin; Figure 10 shows schematically positions of the location pins and the support pin relative to a battery module; Figure 11 shows schematically holes in the bottom of the module to receive location pins; Figure 12 shows the bottom of the battery module; Figure 13 shows schematically part of the clamping arrangement; Figure 14 shows an example of a battery pack bottom panel; Figure 15 shows parts of a thermally conductive pad in an embodiment of the invention; Figure 16 is a side view of a thermally conductive pad; and Figure 17 shows a detail from Figure 16.

Battery pack Figure 1 shows a battery pack of a type with which embodiments of the invention may be used. The battery pack of Figure 1 is designed to be used with electric and hybrid vehicles, particularly in high horsepower applications as buses, trucks, vans, construction equipment, and so forth. However, the principles of the present invention may be applied to any type of battery pack for use in any suitable application.

Referring to Figure 1, the battery pack 10 comprises a plurality of battery modules 12, a plurality of cooling plates 14, cross members 15, a battery management system 16, a module retainer 18, a surround frame 20, a top panel 21 and a bottom panel 22. In this example, fifteen battery modules 12 are provided in five rows of three modules. Each row of three battery modules 12 is located on a corresponding cooling plate 14. The cooling plates 14 are hollow to allow the flow of coolant. Cross members 15 are provided between rows of battery modules. The battery management system 16 is located at one end of the battery pack. In the assembled state, the cross members 15 are attached to the surround frame 20 and span the frame from one side to the other. The top panel 21 and the bottom panel 22 are attached to the top and bottom respectively of the frame 20 and the cross members 15. The battery modules 12, cooling plates 14, battery management system 16 and retainer 18 are housed inside the frame 20 and panels 21, 22. The module retainer 18 is used to hold the battery modules 12 and other components in place.

Battery module Figure 2 shows parts of a battery module in an embodiment of the present invention. Referring to Figure 2, in this example the battery module 12 comprises twenty-four battery cell units 24 stacked together side by side. The battery cell units 24 are electrically connected in series and/or parallel to achieve the target module voltage. End plates 26 are provided on each side of the module. The battery cell units 24 and end plates 26 are held together by steel bands 28. A removable cover 30 is provided at one end of the module. A battery management unit is integrated with the module 12 beneath the cover 30 to monitor and manage cell charge and other aspects of cell operation.

Figure 3 is an exploded view of a battery module. Referring to Figure 3, the battery module 12 is formed by stacking together a plurality of battery cell units 24. A compression foam expansion pad 36 is provided between adjacent cell units. Each of the battery cell units 24 is in the form of a pouch cell 32 held within a cell tray 34. In this example the cell trays 34 are made from a plastic polymer material such as a thermoplastic. Each of the battery cell units 24 includes electrical terminal blocks 38, which are connected to the electrical terminals of the pouch cell 32. Each of the battery cell units 24 also has a cooling sheet 40 which is used to conduct heat away from the pouch cell 32. The cooling sheets 40 are provided on the rear sides of the cells in Figure 3. Each cooling sheet includes tabs 41 which extend around the bottom of the cell tray 34. The tabs 41 are designed to contact cooling plates such as those shown in Figure 1, in order to conduct heat away from the cells. The cooling sheets 40 are made from a thermally conductive material such as aluminium or graphite. A thermally conductive electrically insulative film is provided on the cooling sheets.

In the arrangement of Figure 3, a laminated busbar 42 is used to make electrical connections to the various cell units 24. The laminated busbar 42 is connected to the cell units 24 by means of electrically conducting pins 44. The pins 44 pass through holes in the busbar 42 and into corresponding holes in the terminal blocks 38 of the cell units in order to provide electrical and mechanical connections between the two. The laminated busbar 42 includes electrical conductors (busbars) which connect the battery cell units 24 in the required series and/or parallel connections to achieve the target voltage. The laminated busbar 42 also connects to positive and negative terminals 45 which provide electrical connections to and from the battery module.

Also shown in Figure 3 is a battery management unit 46. The battery management unit 46 is used to monitor and manage cell charge and other aspects of cell operation, in cooperation with the battery management system shown in Figure 1. The battery management unit 46 is provided on a circuit board, which is mounted on the laminated busbar 42 via an electrically insulating barrier plate 48. A plurality of temperature sensors and voltage sensors are provided on the laminated busbar 42, and are used by the battery management unit 46 to monitor cell temperature and voltage. The battery management unit 46 is protected by removable cover 30. The removable cover 30 is made from a plastic polymer material such as a thermoplastic.

In order to assemble the battery module, the various battery cell units 24 (comprising pouch cell 32, cell tray 34, terminal blocks 38, cooling plate 40, and cell cover 50) are stacked together with a thermally conductive foam expansion pad 36 between each adjacent cell unit. The cell trays include location features such that the cell units can only be stacked in one orientation. The end plates 26 are then added to each side of the stack of cell units. The stack of cell units is then compressed to the required pressure. This ensures that the foam expansion pads 36 apply pressure to each of the pouch cells 32. The steel bands 28 are placed around the stack of cells as it is held under pressure. The ends of the steel bands are then crimped together. The steel bands ensure that the required pressure is maintained against the cells in the module, as well as maintaining the size and shape of the battery module.

Referring again to Figure 1, an advantage of providing a battery pack comprising a plurality of battery modules is that individual modules can be replaced should they fail without the need to replace the whole battery pack. However, when using exchangeable battery modules, it may be difficult to achieve a high energy density pack with regards to total pack volume and mass of the pack, which are critical parameters on the market.

As will be discussed below, embodiments of the invention relate to battery module assemblies which help to ensure structural rigidity and module constraint, while at the same time helping to reduce pack volume and weight.

Module clamping When the battery modules are assembled in the battery pack, it is necessary to ensure that they are properly retained and that optimal contact with the cooling plate is maintained.

In embodiments of the invention, module clamp plates are used to secure the battery modules in the battery pack. The module clamp plates are attached to battery pack cross members, which run across the width of the surround frame 20 shown in Figure 1. The module clamp plates also connect adjacent cross members to increase the rigidity of the structure. The module clamp plates utilise a designed-in gap between the cross-members and module clamps to apply the required compressive force through support foams for optimal thermal contact of the module cooling sheets with the cooling plate. Epoxy coating may be used for electrical isolation of the module clamp plates from the modules.

Figure 4 illustrates the basic principles of the module clamping assembly.

Referring to Figure 4, the clamping assembly comprises module clamp plate 52, battery pack cross members 15, gap pad 54, location pins 56, cooling plate 14, cooling plate support foam 58, and battery pack bottom panel 22. Also shown in Figure 4 are the battery module 12, and the battery pack top panel 21.

In the arrangement of Figure 4, the module clamp plate 52 is connected on each side to a battery pack cross member 15. This applies downward pressure to the battery module 12. Some of this downward pressure is applied from the battery module 12, through the gap pad 54 to the top of the cooling plate 14. Counter pressure is applied from the bottom panel 22 through the support foam 58 to the bottom of the cooling plate. The battery module 12 is located on location pins 56. The location pins 56 are connected to the bottom panel 22 and pass through holes in the support foam 58 and the cooling plate 14. The tops of the location pins 56 engage with holes in the bottom of the battery module 12. The location pins include shoulders which act as a compression stop. This limits the load which is applied to the cooling plate. The rest of the load is applied through the location pins 58 to the bottom panel 22.

Figure 5 shows an example of a module clamp plate. Referring to Figure 5, the clamp plate 52 is substantially flat, and has dimensions slightly larger than those of the top of the battery module 12. Slots 60 are provided in the clamp plate to allow air flow and to reduce the weight. The clamp plate includes holes 62, 63 which allow the clamp plate to be connected to the battery pack cross members. In this example the clamp plate 52 is made from a metal with a high strength to weight ratio, such as an aluminium alloy. An epoxy coating is applied for electrical isolation.

Figure 6 is a cross section through part of the module clamping assembly, showing how the module clamp plates are connected to the cross members.

Referring to Figure 6, the module clamp plates 52 are attached to the cross members 15 via module clamp bushes 64. The module clamp plates 52 are attached to module clamp bushes 64 using bolts 65. The module clamp bushes 64 are attached to the cross members 15 using bolts 66, which pass through holes in the bushes 64 and into threaded holes at the top of the cross members 15. Figure 7 shows parts of the clamping assembly around the clamping bush in more detail.

In the arrangement of Figures 6 and 7, the dimensions of the module and the module clamping assembly are such that a small gap 68 is left between the bushes 64 and the cross members 15. This small gap ensures that the clamping plates 52 can apply downward pressure to the modules 12. The amount of downward pressure can be adjusted by adjusting the amount by which bolts 66 are screwed into the cross members. During assembly, the required pressure can be achieved by tightening the screws to the required torque.

Figure 8 shows parts of a battery pack with the modules and module clamps in place. Referring to Figure 8, a module clamp plate 52 is placed over each of the battery modules 12 and attached to the cross members 15 in the way described above.

The clamping arrangement described above can allow uniform pressure to be applied through the battery module 12 to the cooling plate 14. This can help to ensure uniform cooling of the battery cells within the module, which may help to prolong the life of the module. In addition, it has been found that by connecting the battery pack cross members 15 using the module clamp plates 52 the structural stiffness of the battery pack may be improved. In particular, connecting the cross members may improve the torsional stiffness of the battery pack, which may help to prevent twisting of the battery pack in use.

A gap is designed into the clamping arrangement between the module clamping plate and the cross members in order to apply compressive force to ensure thermal contact pressure between the module and the cooling plate.

Module constraint When the battery modules are assembled in the battery pack, it is necessary to ensure that they are properly constrained and that optimal contact with the cooling plate is maintained. However, expansion of the cells during use and tolerance build up may make this difficult to achieve.

Referring back to Figure 4, the clamping assembly includes location pins 56, which are used to locate the battery module in the battery pack. The location pins 56 are attached to the bottom panel 22 and pass through holes in the cooling plate 14. The tops of the location pins 56 engage with holes in the bottom of the battery module 14.

In embodiments of the invention, three location pins and one support pin are used to locate and support each module. Figures 9(A) and 9(B) show respectively an example of a location pin and a support pin.

Referring to Figure 9(A), the location pin 56 comprises a base portion 70, a pin portion 72, and a shoulder 74. The bottom of the base portion 70 is designed to fit into a shallow hole in the battery pack bottom panel 22. The top of the base portion 70 is designed to pass through a hole in the battery pack cooling plate 14.

The pin portion 72 is designed to fit into a hole or slot in the battery module 12. The hole or slot in the battery module is sized such that the battery module sits on the shoulder 74 of the location pin.

Referring to Figure 9(B), the support pin 76 comprises base portion 78 and pin portion 80. The bottom of the base portion 78 is designed to fit into a shallow hole in the battery pack bottom panel 22. The top of the pin portion 80 is at approximately the same height (relative to the bottom panel 22) as the shoulder 74 of the location pin 56.

Figure 10 shows schematically the positions of the location pins and the support pin relative to a battery module. Referring to Figure 10, each location pin 56 is located at one of three corners of the battery module. The support pin 76 is located at the fourth corner of the battery module. The position of the battery module relative to the pins is shown by the dashed line.

Figure 11 shows schematically the holes which are provided in the bottom of the module to receive the location pins. In Figure 11, the x-direction is longitudinal along the battery pack, the y-direction is transversal across the pack and the z-direction is vertical within the pack. Referring to Figure 11, the module comprises one circular hole 82 and two slotted holes 83, 84. The circular hole 82 is used as a positional constraint, to constrict movement of the battery module in both the x and y directions. The slotted hole 82 is used to constrict movement of the battery module in the y-direction but allow some movement in the x-direction. This allows for some end-to-end tolerance in the battery module. The slotted hole 83 is used to constrict movement of the battery module in the x-direction but allow some movement in the y-direction. This allows for some side-to-side tolerance in the battery module. Also shown in Figure 11 is the location of a pad 84 which is provided on the bottom of the battery module. The pad 84 is designed to rest on the support pin 76. This helps to ensure even compression of the battery module on the cooling system.

Figure 12 shows the bottom of the battery module in one embodiment. Referring to Figure 12, the battery module 12 comprises a stack of battery cells 24 and two end plates 26 held together by steel bands 28. The circular hole 82 and the slotted hole 83 are provided in one of the end plates 26. The slotted hole 83 and the pad 84 are provided on the other end plate 26.

The arrangement described above helps to improve the thermal conductivity between the module and the cooling system, and also allows for expansion of the cells and tolerance build up.

In an alternative arrangement, it would be possible for one or more of the pins to be provided on the battery module, and to engage with one or more holes or pads in the bottom panel 22 Dynamic loading In existing battery packs, the battery modules are normally placed on the cooling system. Thus, when the battery pack is in use, the battery modules place a static and dynamic load on the cooling system. This requires the cooling system to be strong enough to absorb dynamic loads caused by shocks and other movements. In particular, it is necessary for the cooling system to have sufficient mechanical strength to avoid constricting the supply of cooling fluid. If the cooling plate were depressed or deformed, this would restrict the flow of cooling fluid, which could lead to uneven cell cooling, and ultimately cell failure. However, the need to provide the required mechanical strength means that existing cooling systems tend to be relatively heavy.

Referring back to Figure 1, the battery pack 10 includes a cooling system comprising a plurality of cooling plates 14. Each of the cooling plates is hollow to allow a cooling fluid to pass through it. The cooling plates are connected together via ports which allow cooling fluid to pass from one cooling plate to another. Input and output ports 15 are used to provide cooling fluid to and from the battery pack.

In the arrangement of Figure 1, the cooling plates 14 run from side to side across the battery pack. Three battery modules 12 are provided on each cooling plate 14. The cooling plates are thermally connected to the battery modules 12 in order to conduct heat away from the battery cells.

In embodiments of the present invention, rather than placing the entire dynamic load of the battery module on the cooling system, a dynamic load path is provided through the location pins 56 and the support pin 76. This can allow the weight of the cooling system to be reduced, as it is no longer necessary for it to take the dynamic load of the battery module.

Figure 13 shows schematically part of the clamping arrangement illustrating how the dynamic loading is applied through the location pins. Referring to Figure 13, the location pins 56 (and support pin 76) are attached to the battery pack bottom panel 22. The panel 22 is composed mainly from carbon fibre panels. The battery module 12 sits on the location pins 56 and support pin 76, which pass through holes in the cooling system. The module 12 is being pushed downwards by the module clamp plate described above. The module is stopped on the location pins 56 and support pin 76 with the clamp's force F. Between the module and the bottom panel there are, from top to bottom, thermal conductive pad (gap pad) 54, cooling plate 14 and support foam 58. The support foam 58 is attached to the bottom panel 22. The support foam distributed loads from the cooling plate 14 to the bottom panel, so as not to damage the cooling plate. The cooling foam also provides thermal isolation between the cooling plate and the bottom panel.

In the arrangement described above, the battery module 12 is clamped on the location pins 56 and support pin 76, and located in all three axes. All mounting and shock loads are primarily passed through the location pins and support pin into the base panel 22. The cooling system is located in the x and y-directions on the location pins and the support pin.

A key feature of this arrangement is that the cooling system is allowed to 'float' in the z-direction via equilibrium of forces between thermal gap pad and the compressed support foam.

In the arrangement described above, the amount of load applied to the cooling plate by the battery module can be adjusted based on selection of the thickness of the cooling foam, as well as the properties of the foam such as the foam material and its compression curve. Thus, the pressure which is applied to the cooling plate is that which is required to compress the foam (and gap pad) sufficiently for the battery module 12 to rest on the shoulders of the location pins 56 and on the support pin 76. This pressure is chosen to be large enough to ensure good thermal contact between the module and the cooling plate, but small enough to avoid deforming the cooling plate. Any additional force is transferred through the location pins and the support pin rather than through the cooling plate. Thus, if a dynamic load is produced through shocks or other movement of the battery pack, this dynamic load will be transferred through the pins rather than the cooling system.

An advantage of the above arrangement is that the cooling plate can be made lighter and thinner than would otherwise be the case, because it does not need to absorb dynamic loads. Furthermore, deformation of the cooling plate which might otherwise occur due to dynamic loading may be avoided. In addition, a single cooling plate can be used for one row of battery modules, rather than providing a separate cooling plate for each module. This can lead to further reduction in the weight of the cooling system and/or improvements in the flow of coolant and thus the cooling efficiency.

Bottom panel In this embodiment, the bottom panel 22 acts as a counter clamping part for the exchangeable battery modules. The battery modules sit on the pin and pads, which leads to a uniform pressure distribution between the battery module cooling sheets and cooling plate interfaces. Accurate module positioning helps to keep the cooling plate at the same level, helping to avoid pressure drop in the cooling system. Furthermore, the above arrangement helps to achieve better flexibility in battery placement in a vehicle regarding other packs in a system.

Figure 14 shows an example of the bottom panel. Referring to Figure 14, the bottom panel 22 comprises base plate 86 and side edges 88. The bottom panel 22 is composed mainly of carbon fibre layers. Location pins 56 and support pins 76 are attached to the bottom panel at the required locations. The location pins 56 and support pins 76 are designed to pass through holes in the cooling plates and to engage with the battery modules in the way described above. The bottom panel also includes corrugations (areas of increased thickness) 90. The corrugations 90, together with the side edges 88, add stiffness to the bottom panel. The bottom panel is designed to be attached to the surround frame 20 as shown in Figure 1.

Gap pad In a battery pack arrangement such as that described above, it is necessary to provide good thermal contact between the cooling system and the battery module. However, at the same time it is necessary to meet creepage and clearance distance requirements of the electrical components. The need to provide the appropriate creepage and clearance distances may reduce the ability of the cooling system to conduct heat away from the battery modules.

In embodiments of the present invention, a thermally conductive pad is provided in order to help provide good thermal contact between the cooling system and the battery module, while meeting creepage and clearance distance requirements.

The thermally conductive pad uses the concept of layering to help achieve these conflicting requirements. This involves using a layer of electrically insulative film between two layers of thermally conductive putty material.

Figure 15 shows parts of the thermally conductive pad in an embodiment of the invention. Referring to Figure 15, the thermal conductive pad (gap pad) 54 comprises a layer of electrically insulative film 92, on the top of which is provided a layer of thermally conductive putty (plastic) material 94. A separate layer of thermally conductive putty material is provided on the underside of the film 92, in a similar way to that on the top. The film is extended outwards around the edge of the thermally conductive putty to form a skirt 95. The skirt is used to maintain creepage distance and provide some alignment features. In the arrangement shown, the skirt 95 comprises four holes 96 and a notch 98. The four holes 96 are used to locate the pad 54 on the location pins 56 and support pins 76. The notch is provided to avoid contact with lifting features on the battery pack cross members. In this arrangement, one gap pad is used for each battery module. The skirts of adjacent gap pads overlap with each other to increase the creepage distances.

A side view of the thermally conductive pad 54 is shown in Figure 16. Figure 17 shows detail A from Figure 16. Referring to Figures 16 and 17, it can be seen that the thermally conductive putty 94 is provided on both sides of the electrically insulative layer 92. The electrically insulative layer 92 has a thickness Li while the thermally conductive putty layers each have a thickness Lz. The total thickness of the thermally conductive pad 50 is LT.

The electrically insulative layer may be made from any suitable material having the required thermal and electrical characteristics. In one embodiment, the electrically insulative layer is made from a thermoplastic polymer such as PET (polyethylene terephthalate) or a polyamide. Such materials have a high dielectric strength, even at small thicknesses. The thickness Li of the electrically insulative film 92 is chosen such that, on one hand, it is thick enough to ensure that sufficient electrical isolation is provided to achieve the creepage/clearance requirements, while on the other hand it is thin enough to ensure little loss of thermal conductivity. In one embodiment a suitable thickness has been found to be around 0.025 mm giving a dielectric strength of around 8 kVAC and a nominal thermal conductivity of around 3 W/MK, although of course other values could be used depending on the circumstances.

The thermally conductive putty material 94 may be in the form of a silicone thermal pad. Such pads are known in the art and are typically used to aid the conduction of heat away from CPUs. The thermal pad may be provided as a preformed rectangle of material which is tacky on one side to allow it to adhere to the electrically insulative film. The other side of the thermal pad is preferably non-tacky, to allow it to be easily removed from the underside of a module. The thermal pad may be relatively firm at room temperature and may soften at higher temperatures. This may allow the pad to deform so as to conform to the underside of the battery module and the top side of the cooling module when in use. A suitable material for the thermal pad is ceramic filled silicone, although other suitable plastic materials may be used instead. In one embodiment the thickness L2 of the thermal pad 94 is around 0.75mm, although other values can be used instead. The two layers of putty material 54 may have the same thickness, or different thicknesses.

By having the thermally conductive putty on both sides of an electrically insulative layer, the putty material compensates for the difference in height between each cooling sheet 40 within a battery module 12 (using a pouch cell/cooling fin arrangement) caused by tolerance stack up and assembly tolerances, and for any variations in height of the cooling plate. The thermally conductive putty is a plastic material (i.e. exhibits plastic deformation) essentially like clay or putty.

Thus the thermally conductive putty deforms under load.

The electrically insulative layer helps to maintain creepage and clearance values, without the need for the cooling plate to have a coating or film to provide electrical insulation. The thermally conductive pad 54 is easy to renew if there is a problem of if a battery module needs to be changed. This can make servicing and repair more cost effective since it may be possible just to replace a single or a few pads, rather than requiring a cooling system replacement.

Thus, the thermally conductive pad 54 can help to ensure good thermal contact between the tabs 41 on the cooling sheets 40 in the battery cell units 24, and the cooling plate 14 in the cooling system, while helping to meet creepage and clearance distance requirements.

The support foam is under compression when system is being built. This provides a constant load into the gap pad (but lower than the clamping load to prevent structural failure of the clamp). This provides even and consistent pressure to the gap pad. This in turn leads to consistent thermal performance over product life.

In the above description, preferred features of the invention have been described with reference to various embodiments. It will be appreciated that features of one embodiment may be used with any other embodiment. Furthermore, the invention is not limited to these embodiments, and variations in detail may be made within the scope of the appended claims.

Claims

CLAIMS1. A clamping arrangement for clamping a battery module in a battery pack, the battery pack comprising a cooling system, the clamping arrangement 5 comprising: means for applying a clamping force to the battery module such that the battery module maintains contact with the cooling system; and support means for supporting the battery module, the support means comprising a compression stop.
2. A clamping arrangement according to claim 1, wherein the clamping arrangement is arranged such the battery module contacts the compression stop when the clamping force is above a predetermined value.
3. A clamping arrangement according to claim 2, wherein the predetermined value is a value which is sufficiently high to ensure thermal contact between the battery module and the cooling system and/or sufficiently low to avoid deformation of the cooling system.
4. A clamping arrangement according to any of the preceding claims, further comprising means for applying a counter force to the cooling system.
5. A clamping arrangement according to any of the preceding claims, wherein the clamping arrangement is arranged such that dynamic loads are passed through the support means.
6. A clamping arrangement according to any of the preceding claims, wherein the battery pack comprises a frame and a plurality of cross members, the clamping arrangement comprising a clamping plate attached to two adjacent 30 cross members.
7. A clamping arrangement according to any of the preceding claims, wherein the support means are arranged to locate the battery module.
8. A clamping arrangement according to any of the preceding claims, wherein the support means comprise a plurality of pins.
9. A clamping arrangement according to any of the preceding claims, wherein the support means comprise at least one location pin with a shoulder which acts as a compression stop.
10. A clamping arrangement according to any of the preceding claims, wherein the battery module comprises at least one hole for receiving part of the support means and/or at least one pad for engaging with the support means.
11. A clamping arrangement according to any of the preceding claims, wherein the support means are arranged to pass past the cooling system.
12. A clamping arrangement according to any of the preceding claims, wherein the battery pack comprises a housing panel, and the support means are attached to the housing panel.
13. A clamping arrangement according to claim 12, wherein the housing panel acts as a counter clamp.
14. A clamping arrangement for clamping a battery module in a battery pack comprising a cooling system and a housing panel, the clamping arrangement comprising means for applying a clamping force to the battery module such that the battery module maintains contact with the cooling system, wherein the housing panel is arranged to act as a counter clamp.
15. A clamping arrangement according to any of claims 12 to 14, wherein the housing panel comprises a carbon fibre material.
16. A clamping arrangement according to any of claims 12 to 15, wherein support means are attached to the housing panel, and the housing panel includes an area of increased thickness in the region of the support means.
17. A clamping arrangement according to any of claims 12 to 16, wherein means for applying a counter force to the cooling system are provided between the housing panel and the cooling system.
18. A clamping arrangement according to any of the preceding claims, further comprising a thermally conductive pad for providing thermal contact between the battery module and the cooling system.
19. A clamping arrangement according to claim 18, wherein the thermally conductive pad comprises a layer of electrically insulative film and at least one layer of thermally conductive plastic material.
20. A thermally conductive pad for providing thermal contact between a battery module and a cooling system in a battery pack, the thermally conductive pad comprising a layer of electrically insulative film and at least one layer of thermally conductive plastic material.
21. A clamping arrangement or thermally conductive pad according to claim 19 or 20, wherein the thermally conductive pad comprises two layers of thermally conductive plastic material, one on each side of the electrically insulative film.
22. A clamping arrangement or thermally conductive pad according to any of claims 19 to 21, wherein the layer of electrically insulative film extends beyond the or each layer of thermally conductive plastic material.
23. A clamping arrangement or thermally conductive pad according to any of claims 19 to 22, wherein the thermally conductive pad comprises at least one alignment hole.
24. A battery pack comprising a clamping arrangement and/or a thermally conductive pad according to any of the preceding claims.
25. A method of clamping a battery module in a battery pack, the method comprising clamping the battery module using a clamping arrangement, a thermally conductive pad and/or a battery pack according to any of the preceding claims.