A battery enclosure for an electric vehicle

Abstract

A battery enclosure 1 for an electric vehicle comprising a tray 100 and opening for insertion, containment and removal of at least one battery cell 2a and a lid 200 for closure of the opening. The bas

Description

The invention relates to battery enclosures suitable for electric vehicles, as well as hybrid electric vehicles, and to methods of manufacture of such battery enclosures. BACKGROUND Modem electric vehicles typically comprise a plurality of individual battery modules. These battery modules are often contained within a battery enclosure, or case, which is installed within an electric vehicle during its manufacture. A key purpose of a battery enclosure is to house and protect the individual battery modules from damage. Such enclosures normally form a substantial part of the floor of an electric vehicle and are affixed to vehicle’s chassis using mechanical fasteners. Battery enclosures therefore form a significant part of the structure of electric vehicles. In the event of a collision involving an electric vehicle comprising a battery enclosure, it is important that the battery enclosure maintains its structural integrity so as to protect the contents of the battery enclosure and support the chassis of the vehicle. This protects the passengers travelling within the vehicle and prevents damage to the battery cells contained in the enclosure. Battery enclosures must therefore be strong structures. The footprint of a battery enclosure is limited by the footprint of a vehicle. Furthermore, it is desirable to minimise the thickness of the battery enclosure to maintain space in the vehicle for other purposes. Nonetheless, the contents of a battery enclosure generally do not have a uniform thickness, and some battery elements may extend higher than others, or some battery elements may need to pass over other battery elements or parts of the battery enclosure. For example, electrical connectors or coolant conduits may need to pass over battery modules or internal walls of the battery enclosure. In other cases, in order to meet requirements as to the range of the electric vehicle, it may be necessary to double stack battery cells within part of the battery enclosure. To avoid enclosing empty space in the battery enclosure, this has led to battery enclosures that have bases and / or lids that are shaped to match the profile of the contents of the enclosures. However, requiring that the base and / or lid of the battery enclosure is to be formed to match the shape of the contents of the battery enclosure limits the material that can be used for the base to only those materials that can be formed into the required shape. This means that the strength of the battery enclosure is compromised. It is desirable to provide a battery enclosure for an electric vehicle in which more types of material can be used for the major structural surfaces, i.e. the lid and the base, of the battery enclosure without compromising on the tight packaging of the contents of the battery enclosure. SUMMARY OF INVENTION In accordance with a first aspect of the invention, there is provided a battery enclosure for an electric vehicle, comprising: a tray defining an interior for containing at least one battery cell and an opening into the interior for insertion and removal of the at least one battery cell, the tray comprising a base opposite the opening; a lid arranged so as to close the opening of the tray, thereby enclosing the interior of the tray; wherein the base of the tray and / or the lid comprises: a sheet extending across the opening, said sheet comprising a hole therethrough, through which at least one element may pass from the interior of the tray to the opposite side of the sheet; and a housing joined to the sheet and extending over said hole through the sheet for enclosing said at least one element on said opposite side of the sheet. The present battery pack thus uses a respective sheet for the lid and / or base, which can be formed of a relatively strong material that does not need to be formed into complex shapes, but through which a hole can be simply provided. A separate housing is then provided to enclose any elements that pass through the sheet. This housing can be formed of a material that may be more readily formed into complex shapes, while the overall strength remains high due to the presence of the stronger sheet. Thus, tight packaging of the contents of the battery enclosure may be achieved while retaining high strength of the base of the tray and / or the lid. It should be noted that the housing joined to the sheet is said to extend over the hole. In this context, the term “over” does not imply a relative orientation between the housing and the sheet, and the housing should extend on the opposite side of the sheet to the interior of the tray, regardless of the orientation of the enclosure. In the case that both the base of the tray and the lid are formed using a sheet and housing arranged as described, then housing on the lid and the housing on the base will be arranged to extend on opposite sides of their respective sheet, each nonetheless being considered to extend over its respective opening. The sheet of the base of the tray and / or lid is said to extend across the opening. It will be understood that the base of the tray is generally spaced from the opening in a direction perpendicular to the plane of the sheet forming the base of the tray. The sheet of the lid may substantially coincide with the opening, or the lid may also be shaped generally like a tray, such that the sheet of the lid is spaced from the opening in a direction perpendicular to the plane of the sheet in the lid. Generally, the sheet forming the base of the tray, the opening into the tray and the sheet forming the lid will all have approximately the same footprint. However, this is not essential. For example, the walls of the tray may taper inwards or outwards such that the opening is larger or smaller than either sheet. It is therefore not essential that the sheet extends across the entire area of the opening. However, preferably the sheet in the lid and / or base extends across substantially the entire area of the opening. The tray of the battery enclosure will generally comprise a base and one or more sidewalls extending from the base to define the tray. Generally, two pairs of opposing sidewalls will be provided along corresponding edges of the base defining a battery enclosure with a generally rectangular footprint; however, other shapes are also possible. The sidewalls may be joined to the base in any manner desired, and in some embodiments the whole tray could be formed as a single moulded piece. Other techniques for forming the tray would include overmoulding the sidewalls onto a sheet acting as the base, or joining sidewalls to a base using mechanical fasteners and / or adhesive. The tray will generally define a peripheral edge, to which the lid is joined to form the battery enclosure. Preferably, the sheet comprises a composite material. Composite materials may provide very high strength, especially when they are only required to be provided in sheet form. Preferably, the composite material is a fibre-reinforced polymer. Preferably the fibres are so-called “long fibres” or “continuous fibres”, which provide significant strength, but are difficult or impossible to use in processes such as injection moulding, which are capable of providing complex shapes. In particular, preferably the fibres have a median length of at least 1 mm, more preferably at least 5 mm, more preferably at least 10 mm, more preferably at least 20 mm, more preferably at least 50 mm, more preferably at least 100 mm, most preferably at least 200 mm. In some cases, the fibres are continuous fibres that extend along at least 50% of the length or width of the sheet, preferably along 70%, more preferably along 80%, more preferably along 90% of the length or width of the sheet, wherein more preferably the continuous fibres extend along substantially the entire length or width of the sheet. Preferably, the housing either comprises no reinforcing fibres, or comprises reinforcing fibres wherein the median fibre length of the sheet is greater than the median fibre length of the housing, preferably at least two times greater, more preferably at least five times greater, most preferably at least ten times greater. Fibre length may be measured, for example, by dissolving the matrix of the composite material in a solvent, or otherwise removing the matrix material, and inspecting the fibres by optical microscopy. In some embodiments, the sheet may be a multi-layer sheet. This may allow different layers to be provided for reinforcement or other purposes and such a multi-layer sheet may be particularly difficult to form into a shape while maintaining the integrity of the multi-layer sheet. In some embodiments, the sheet comprises a layer of metal. The layer of metal may comprise a continuous metal layer or a layer of a mesh or the like. The present arrangement provides advantages even in the cases where the lid is formed of a castable material, like a metal, as it allows the enclosure to be formed with a flat sheet of metal without requiring a large custom cast to be developed or without requiring a flat metal sheet to be stamped. Rather, the flat sheet may have holes cut through it and smaller housing joined to it to enclose elements that pass through the holes. A metal layer may be used for electromagnetic shielding but may be unsuitable for providing the strength of the sheet without being too heavy, and so could be paired with layers of other materials for strength. In other embodiments, the sheet could consist of one or more metal layers. As noted previously, an advantage of the present arrangement is that a strong, difficult to form sheet may be used for the base and / or lid. In particular, relatively thick sheets may be used. Preferably, the median thickness of the sheet is at least 1,5mm, preferably at least 2 mm, preferably at least 3mm, preferably at least 5mm, preferably at least 10mm, more preferably at least 20 mm. The median thickness of the sheet will be understood to be the thickness value that divides the sheet's thickness distribution into two equal parts. Even where a thick sheet is used, it may still be possible to somewhat form areas of the sheet to conform to certain contents of the battery enclosure that do not require significant height variation of the sheet. In some embodiments, the maximum height and / or depth of any reliefs formed in the sheet, measured perpendicular to the plane of the sheet, does not exceed 10 times the median thickness of the sheet, preferably does not exceed 8 times the median thickness of the sheet, more preferably does not exceed 5 times the median thickness of the sheet. In other embodiments, the maximum height and / or depth of any reliefs formed in the sheet, measured perpendicular to the plane of the sheet, does not exceed 20 cm, preferably 10cm, more preferably 5cm. The sheet may also be kept relatively flat, with little deforming of the sheet required in forming the battery enclosure. Therefore, preferably, at least 50% of the area of the sheet is substantially planar, preferably at least 70%, more preferably at least 80%, more preferably at least 90%, more preferably at least 95%, most preferably at least 99% of the area of the sheet is substantially planar. As noted above, there could, however, be localised regions in which the sheet is deformed from its primary plane. While it is preferred to keep the sheet relatively flat, the housing on the sheet may nonetheless provide significant depth for housing elements above the sheet. In some embodiments, the height of the housing above the sheet may be at least 10% of the depth of the tray, preferably at least 20%, more preferably at least 50%, most preferably at least 100%. Here, height and depth are measured along the same direction, which is the direction generally perpendicular to the plane of the sheet which is also generally perpendicular to the plane in which the tray defines its largest footprint. In other embodiments, the height of the housing above the sheet may be at least 5 cm, preferably at least 10 cm, more preferably at least 15 cm, most preferably at least 20 cm. In some embodiments, the tray comprises a base and at least one pair of opposing sidewalls, and the sheet extends between the opposing sidewalls, i.e. from one opposing side wall to the other. The sheet may also extend beyond one or more sidewalls to define a reinforced flange of the tray. Preferably, the sheet is substantially planar between the sidewalls along at least 50% of the length of the sheet along the direction of the sidewalls, preferably along at least 75%, more preferably along at least 90% of said length. The assessment of planar areas of the sheet will be considered to ignore the presence of any holes through the sheet. In most embodiments, the housing has a different material composition to the sheet. However, in alternative embodiments, the housing may be formed of the same material but in a thinner form. It will be appreciated that the housing and the sheet may comprise some of the same materials, but nonetheless be different. For example, the housing may be formed of polypropylene and the sheet formed of carbon fibre-reinforced polypropylene. Alternatively, they may be formed of the same materials but in different proportions. For example, both may be a fibre reinforced polymer, but they may comprise different proportions of fibre reinforcement by weight. In particularly preferable embodiments, the housing is formed of a polymeric material, but other materials, such as metals, may also be used. In some embodiments, the housing may be formed by a single, integral piece. For example, the housing may be a single injection moulded component. As described above, because of the reduced structural role performed by the housing, the housing may be formed of materials that can be more readily formed or moulded, and so forming the housing as a single, integral piece may provide a number of advantages. In particularly preferable embodiments, the housing is at least partially defined by an overmoulded material, the overmoulded material being overmoulded onto the sheet. Overmoulding provides a simple process for forming the housing and joining the housing to the sheet in a single step. While preferred, in other embodiments, the housing may be formed by as an injection moulded component and then joined to the sheet. As described above, because of the reduced structural role performed by the housing, the housing may be formed of materials that can be more readily formed or moulded, and so forming the housing in this way may provide a number of advantages. In many embodiments, the housing is joined to an exterior face of the sheet, facing away from the interior of the tray. This means that no part of the housing needs to be packaged within the tray. In alternative embodiments, the housing could be joined to an interior face of the sheet, i.e. with the housing itself extending through the hole to the exterior side. Preferably, the housing extends away from the hole in at least one direction in a plane of the sheet, such that a portion of an interior of the housing is provided over an area of the sheet not having the hole. In this way, at least some of the contents of the housing may be separated from the contents in the interior of the tray by the sheet. This may prevent damage in the event of battery failure. In particular, preferably the interior of the tray comprises at least one battery cell and the portion of the interior of the housing provided over the area of the sheet not having the hole comprises at least one battery cell, such that the sheet extends between the at least one battery cell in the interior of the tray and the at least one battery cell in the interior of the housing. This can prevent a chain reaction of battery cell failures between battery cells arranged over one another in the present arrangement. While the above has referred to a single housing on each sheet, some embodiments further comprise a second housing joined to the sheet for enclosing a further at least one element on the opposite side of the sheet to the interior of the tray. While the use of the present housing is particularly advantageous for when an element must pass through a hole in the sheet, it is also possible that the sheet may extend continuously between the second housing and the interior of the tray, isolating an interior of the second housing from the interior of the tray. In some examples, the interior of the tray comprises at least one battery cell, and the interior of the second housing comprises at least one battery cell, such that the sheet extends continuously between the at least one battery cell in the interior of the tray and the at least one battery cell in the interior of the second housing. In this way, battery cells in the interior of the tray can be completely isolated from battery cells in the second housing. This embodiment may require electrical connections and / or coolant connections to be made through the second housing, or electrical connections or cooling systems may pass through the sheet at the first housing and then pass from the first housing to the second housing on the exterior side of the sheet, avoiding the need for a hole through the sheet in the vicinity of the second housing. This may improve the safety of the battery enclosure. The at least one element, i.e. which may pass through the hole in the sheet, could be any element contained within the battery enclosure, typically a battery element, such as one or more of electrical connectors, coolant conduits, coolant fluids, battery cells, and battery modules. Preferably, the battery enclosure comprises at least one battery cell located in the interior of the tray. The battery cells may be provided directly in the tray, or a plurality of battery cells may be provided in a battery module, provided in the tray. As noted above, one or more battery cells or battery modules may extend into or be provided in the interior of the housing on the exterior side of the sheet. Preferably, the battery enclosure has a length of at least 50 cm, preferably at least 100 cm, more preferably at least 150 cm, most preferably at least 200 cm. Preferably, the or each sheet has a length a length of at least 50 cm, preferably at least 100 cm, more preferably at least 150 cm, most preferably at least 200 cm, e.g. substantially the same as the length of the battery enclosure. The battery enclosure may also have a width of at least 50 cm, preferably at least 100 cm, more preferably at least 150 cm. Preferably, the battery enclosure has a maximum height of no more than 50 cm, preferably no more than 40 cm, more preferably no more than 30 cm. There may be one or more holes through each sheet. A plurality of holes in one sheet may be closed by a single housing, or each hole may have a respective housing. Preferably, holes make up no more than 25% of the area of the sheet, preferably no more than 20%, more preferably no more than 15%, most preferably no more than 10% of the area of the sheet. Reducing the area of the holes improves the strength of the sheet and hence the battery enclosure. Preferably, one or more holes through the sheet have a largest dimension no greater than 25% of the length of the sheet, more preferably 20%, more preferably 15%, most preferably 10%. Again, smaller holes through the sheet improve the strength of the sheet and hence the battery enclosure. In accordance with a second aspect of the invention, there is provided a method of manufacturing a battery enclosure for an electric vehicle, comprising: providing a tray defining an interior for containing at least one battery cell and an opening into the interior for insertion and removal of the at least one battery cell, the tray comprising a base opposite the opening; providing a lid arranged so as to close the opening of the tray, thereby enclosing the interior of the tray; wherein providing the base of the tray and / or the lid comprises: providing a sheet configured to extend across the opening, said sheet comprising a hole therethrough, through which at least one element may pass from the interior of the tray to the opposite side of the sheet; and joining a housing to the sheet such that it extends over said hole through the sheet for enclosing said at least one battery element on said opposite side of the sheet. The present method corresponds to a method of manufacturing a battery enclosure according to the first aspect and so all of the optional features described above may be incorporated into the method of this aspect. The present method preferably involves moulding the housing, typically using a polymeric material. However, the housing could alternatively be assembled by separate pieces joined together. Joining the housing to the sheet may comprise overmoulding the housing onto the sheet. Overmoulding is a convenient process for simultaneously forming a complex structure and joining it to the sheet. In alternative embodiments, the housing may be manufactured in other processes, such as injection moulding away from the sheet and separately arranged on and joined to the sheet, e.g. by adhesive or bolts. In accordance with a third aspect of the invention, there is provided a battery enclosure for an electric vehicle, comprising: a tray defining an interior for containing at least one battery cell and an opening into the interior for insertion and removal of the at least one battery cell, the tray comprising a base opposite the opening; a lid arranged so as to close the opening of the tray, thereby enclosing the interior of the tray; wherein the base of the tray and / or the lid comprises: a sheet extending across the opening; and a housing joined to the sheet, the housing defining an interior of the housing on an opposite side of the sheet to the interior of the tray for containing a second at least one battery cell, wherein the sheet extends substantially continuously between the interior of the tray and the interior of the housing. In the present aspect, the sheet extends continuously between the interior of the tray and the interior of the housing, thus improving the safety of the enclosure. In particular, the contents of either interior may be protected by the failure of battery cells in the contents of the other interior. All of the optional features described above with respect to the first aspect of the invention may be incorporated into this aspect of the invention. In accordance with a fourth aspect of the invention, there is provided a method of manufacturing a battery enclosure for an electric vehicle, comprising: providing a tray defining an interior for containing at least one battery cell and an opening into the interior for insertion and removal of the at least one battery cell, the tray comprising a base opposite the opening; providing a lid arranged so as to close the opening of the tray, thereby enclosing the interior of the tray; wherein providing the base of the tray and / or the lid comprises: providing a sheet configured to extend across the opening; and joining a housing to the sheet, the housing defining an interior of the housing on an opposite side of the sheet to the interior of the tray for containing a second at least one battery cell, wherein the sheet extends substantially continuously between the interior of the tray and the interior of the housing. This corresponds to a method of manufacturing a battery enclosure according to the third aspect of the invention. All of the optional features described above may be incorporated into the method of this aspect. In accordance with a further aspect of the invention, there is provided an electric or hybrid electric vehicle comprising a battery enclosure according to either the first or third aspects of the invention. Preferably, the electric or hybrid electric vehicle is a passenger vehicle. These is also provided a method of manufacturing an electric or hybrid electric vehicle comprising manufacturing a battery enclosure according to either the second or fourth aspects of the invention. BRIEF DESCRIPTION OF DRAWINGS The invention will now be described with reference to the accompanying Figures, of which: Figure 1 is a perspective view of a battery enclosure according to a first embodiment; Figure 2 is perspective view of the tray of the battery enclosure of Figure 1; Figure 3 is a perspective view of the base assemblies of the tray and lid of the battery enclosure of Figure 1; Figure 4 is an enlarged perspective view of part of the battery enclosure shown in Figure 1; Figure 5 is an enlarged perspective view of another part of the battery enclosure shown in Figure 1; Figure 6 is a schematic cross-section through the battery enclosure of Figure 1; Figure 7 is an enlarged perspective view of part of a battery enclosure according to a second embodiment; Figure 8 is a flow diagram illustrating a method of manufacturing a battery enclosure; Figure 9 is a schematic view of an overmoulding tool for overmoulding the tray; Figure 10 is a cross-section through part of the tool of Figure 9; and Figure 11 is a schematic cross-section through a tool for overmoulding a housing sidewall over a hole through a sheet. DETAILED DESCRIPTION Figure 1 is a perspective view of a battery enclosure 1 of an electric vehicle in an embodiment of the invention. The battery enclosure comprises a tray 100 closed by a lid 200. Figure 2 is a perspective view of the tray 100 with the lid 200 omitted. The tray is shown without any battery cells or modules in this Figure to reveal the internal structure. The tray 100, comprises a base provided by a sheet 112, discussed in more detail below, with two pairs of opposing sidewalls 120a, 120b, 120c, 120d, defining the perimeter of the tray and an opening into the tray through which battery modules and the like may be placed inside the tray. The sidewalls also define an upper flange 160, to which the lid 200 is secured, e.g. by bolts, in order to close the tray and secure the contents inside. The tray may be approximately 2.5 m long, 1.5 m wide, and 20 cm deep, being of an appropriate size to sit within the floor of an electric vehicle. The lid 200 comprises a sheet 212 that extends across the opening into the tray, extending between the sidewalls 120a, 120b, 120c, 120d of the tray. As will be discussed in more detail below, the lid is formed by providing a flat sheet that is then thermoformed to define a plurality of recesses 213 into the sheet, as well as a raised section 214, and are lowered peripheral edge 215, although any technique for forming by means of mechanical pressure and / or thermal / chemical energy input may be used . The raised section 214 may be raised approximately 5 cm above the original plane of the sheet 212 and extends along the length of the battery enclosure 1, being provided down the centre of the lid and may accommodate cooling conduits extending along the centre of the battery enclosure. The recesses 213 may each be recessed approximately 3 cm into the original plane of the sheet 212 and are provided in parallel rows on either side of the raised section 214 in order to more closely follow the profile of the battery modules that will be located in the tray 100. The periphery 215 of the lid 200 is thermoformed towards the tray 100 to define a peripheral edge of the lid 200 that may be secured to the upper flange 160 of the tray, e.g. by bolts. Due to the raised section 214, recesses 213 and edge 215, in this embodiment approximately 40% of the area of the sheet 212 is provided by areas deformed out of the original plane of the sheet 212, while the remaining approximately 60% remains in the original plane of the sheet 212. The lid 200 also comprises a first housing 20 and a second housing 30, each joined to the upper face of the sheet 212. The first housing 20 is provided at a first longitudinal end of the battery enclosure and extends along the width direction of the battery enclosure. The second housing 30 is provided at the opposite longitudinal end of the battery enclosure to the first housing 20 and extends along approximately half the length of the battery enclosure from the edge of the battery enclosure, extending along the raised section 214 of the sheet 212. As will be discussed in more detail below, in the present embodiment, each housing 20, 30 is provided by overmoulded sidewalls 21,31, which are overmoulded directly onto the sheet 212, and each housing 20, 30 is closed by a respective moulded lid 22, 32. In particular, the overmoulded sidewalls 21, 31 each define an upper peripheral edge to which the respective moulded lid 22, 32 may be joined by mechanical fasteners, such as bolts. These housings have depths that are approximately the same depth or more than the depth of the tray 100, and so it would not be possible to mould these housings directly into the sheet 212 without forming the sheet 212 of a material that would be much weaker. The housings 20, 30 will be described in more detail below. The construction of the tray 100 and lid 200 will now be described in more detail. The tray 100 and the lid 200 each comprise a preliminary assembly 110, 210 shown in Figure 3. For the tray, this preliminary assembly is provided by a flat sheet 112 to which a series of parts are joined prior to overmoulding of certain features of the tray, described in more detail below. For the lid, this preliminary assembly 210 simply comprises a flat sheet 212. The tray preliminary assembly 110 comprises a rectangular sheet 112 provided with a hole 112a therethrough, a plurality of side elements 114a, 114b, 114c, 114d, and two central transverse elements 116a, 116b. The sheet 112 is a composite material comprising an aluminium mesh and continuous glass or carbon fibres embedded in a polypropylene matrix, the fibres extending along substantially the entire the length of the sheet 112. The aluminium mesh provides electromagnetic shielding for the battery enclosure, while also contributing to the strength of the sheet along with the continuous glass or carbon fibres. The sheet 112 has a thickness of at least 20 mm to ensure that it is highly impact resistant. The hole 112a may be cut through the sheet 112 after the sheet is provided or the sheet may be produced with the hole 112a in situ. The side elements comprise longitudinal and transverse side elements 114a, 114b and 114c, 114d, arranged along or near to the edges of the rectangular sheet 112, so that they define side walls of the assembly 110. The side elements 114a, 114b are referred to herein as longitudinal side elements as their longitudinal axes are arranged in parallel with the longitudinal axis of the sheet 112 and the tray 100. The longitudinal side elements 114a, 114b are arranged proximal to the longer edges of the sheet 112. The side elements 114c, 114d are referred to herein as transverse side walls as their longitudinal axes are arranged perpendicular the longitudinal axis of the sheet 112 and the tray 100, but in parallel with the plane of the sheet 112. The transverse side elements 114c, 114d are arranged at the shorter edges of the sheet 112. The longitudinal side elements 114a, 114b are greater in length than the transverse side elements 114c, 114d. Each of these side elements may be formed of similar materials to the sheet 112, e.g. continuous fibre reinforced polypropylene with embedded aluminium mesh, but will typically be thinner than the sheet 112 in order to allow the side elements to be thermoformed into the shapes shown in Figure 2. The preliminary assembly 110 of the tray also comprises two central traverse elements 116a, 116b, which are arranged parallel to the transverse side elements 114c, 114d, and are each about halfway between the transverse side elements 114c, 114d. The central transverse element 116a is arranged to extend perpendicularly from the longitudinal side element 114a towards the centre of the tray, and the central transverse element 116b is arranged to extend perpendicularly from the longitudinal side element 114b towards the centre of the tray. A small gap is left between the central transverse elements 116a, 116b at the centre of the tray to allow for connections to be made between the front and rear halves of the tray, defined by the central transverse elements 116a, 116b. The side elements 114a, 114b, 114c, 114d and the central traverse elements 116a, 116b are each joined to the sheet 112 prior to any overmoulding, for example by an adhesive or by mechanical fasteners. Returning to the tray shown in Figure 2, the tray 100 generally comprises a base provided by the sheet 112, two pairs of opposing side walls 120a, 120b and 120c, 120d arranged perpendicular to one another, a plurality of ribs 130 and a busbar housing 140. The side walls 120a, 120b, 120c, 120d, the ribs 130 and the busbar housing 140 are defined integrally and are each overmoulded to the preliminary assembly 110 to form the tray 100. Each side wall 120a, 120b, 120c, 120d is defined by overmoulded material that been overmoulded onto each of the respective side elements 114a, 114b, 114c, 114d and onto the sheet 112. The sheet 112 of the preliminary assembly 110 defines a lower flange 150 and the upper sections of the side walls 120a, 120b, 120c, 120d define an upper flange 160. The sheet 112 of the preliminary assembly 110 forms the base of the tray 100 and it extends between each of the two pairs of side walls 120a, 120b and 120c, 120d. The sheet 112 is planar between each of the two pairs of side walls 120a, 120b and 120c, 120d. In this particular embodiment, the sheet 112 extends beyond the side walls 120a and 120b in a direction parallel to a direction of the sheet 112 so as to define a lower flange 150 that may act to protect the contents of the battery pack in the case of a side impact. As mentioned above, the side elements 114a, 114b, 114c, 114d of the preliminary assembly 110 partially define the side walls 120a, 120b, 120c, 120d. Material is overmoulded onto the side elements 114a, 114b, 114c, 114d such that the side element 114 and the overmoulded material together define the respective side wall 120. In other words, the side walls 120a, 120b, 120c and 120d are formed of overmoulded material and a respective side element 114a, 114b, 114c, 114d within the overmoulded material, wherein the respective side element forms a reinforcing internal element of the side wall. The side walls 120a, 120b are longitudinal side walls, which are greater in length than transverse side walls 120c, 120d. The side walls 120a, 120b, 120c and 120d form a continuous perimeter of the tray which surround its centre. As mentioned above, their upper sections form an upper flange 160. The side walls 120a, 120b define an array of open hexagonal cells having a honeycomb-like structure extending across the upper face of the sheet 112. These open hexagonal cells provide a floor of the tray on which battery modules may sit so that they are lifted off the sheet 112. The tray 100 further comprises overmoulded central transverse parts 118a, 118b. Material is overmoulded onto central transverse elements 116a, 116b in order to form the central transverse parts 118a, 118b. The central transverse parts 118a, 118b are therefore similar in structure to the side walls 120a, 120b, 120c, 120d. These central transverse parts 118a, 118b meet the overmoulded material forming the sidewalls 120a, 120b and extend toward the centre of the tray 100. Although not shown in Figure 2, the overmoulded material may additionally extend between the central transverse parts 118a, 118b to form a reinforced central cross member that may effectively transmit impact forces between the sidewalls 120a, 120b to protect the battery modules provided in the tray. The ribs 130 are formed of overmoulded material which is overmoulded to sheet 112. Each of the ribs 130 extend between, and are integral with, the two opposing longitudinal side walls 120a, 120b. The longitudinal axes of each of the ribs 130 are parallel to the longitudinal axes of the transverse side walls 120c, 120d. In this embodiment, seven ribs 130 are provided. However, in other embodiments, greater or fewer ribs may be provided. The ribs 130 further help to transmit impact forces between the opposing overmoulded sidewalls 120a, 120b to shield the battery modules within of the tray from damage. The ribs 130 also form individual housing units within the tray 100 to separate individual battery modules from one another. The busbar housing 140 is arranged to house two busbars arranged over the sheet 112. The busbar housing 140 is formed of overmoulded material and extends between, and is integral with, the transverse side walls 120c, 120d. The busbar housing 140 also extends through and is integral with each of the ribs 130. The longitudinal axis of the busbar housing 140 is arranged in parallel with that of the sheet 112. The direction of longitudinal axis of the busbar housing 140 is therefore perpendicular to the direction of the longitudinal axes of each of the ribs 130. In accordance with the above, the tray 100 is provided by the preliminary assembly 110 which is overmoulded to define the walls and interior of the tray, with the result being a tray having a hole 112a therethrough, through which an element may pass from the inside of the tray to below the sheet 112. As will be described further below, a housing is provided on the lower face of this sheet 112 in order to enclose the space below this hole. As noted above, the lid assembly 210 in this embodiment simply comprises sheet 212, provided with a first hole 212a through a first area of the sheet and a second hole 212b through a second area of the sheet 212. The first hole 212a is a larger hole located centrally close to one of the transverse edges of the sheet 212 corresponding to the sidewall 120d of the tray 100. The first hole 212a has a generally rectangular shape, with a narrower projecting part of the hole projecting from the edge facing towards the centre of the sheet 212. The second hole 212b is a smaller generally rectangular hole located close to the opposite transverse edge of the sheet 212, corresponding to the sidewall 120c of the tray 100, located slightly off centre towards the sidewall 120a of the tray. Like the sheet 112 in the preliminary assembly 110, the sheet 212 of the lid is a composite material comprising an aluminium mesh and continuous glass or carbon fibres embedded in a polypropylene matrix, the fibres extending along substantially the entire the length of the sheet 212. The sheet 212 again has a thickness of at least 20 mm to ensure that it is highly impact resistant. As noted above, whereas the sheet 112 in the tray retained its planar shape in the overmoulded tray, in the present embodiment, the sheet 212 of the lid is formed by thermoforming and provided the relief discussed above to improve the packaging of the battery enclosure contents. This may be achieved by taking the flat sheet 212, as shown in Figure 3, and providing this to a thermoforming machine in order to form the relief shown in in Figure 1. In other embodiments, the sheet of the lid may be injection moulded with fibres of lengths of around 25 mm. In these embodiments, the relatively flat shape of the sheet facilitates injection moulding with longer fibres, hence allowing a stronger injection moulded sheet to be formed. Figure 4 shows the interior of the first housing 20, in more detail. In particular, Figure 4 shows the overmoulded sidewall 21 with the lid 22 omitted to reveal the interior 20a, 20b, 20c of the housing. As shown in Figure 4, the first housing 20 is located over the first opening 212a through the sheet 212, with the overmoulded sidewall 21 extending around the periphery of the opening 212a such that the overmoulded sidewall 21 entirely encompasses the opening 212a. The overmoulded sidewall extends beyond the opening 212a towards both longitudinal side edges of the sheet 212, so that a central interior region 20a is provided inside the housing over the opening 212a, but also so that two side interior regions 20b are provided on opposite sides of the opening. In these side interior regions 20b, when the lid 200 is fixed to the tray 100, the sheet 212 is present between the side interior regions 20b of the housing 20 and the interior of the tray 100. The overmoulded sidewall 21 is generally rectangular in plan view, but comprises a sloped section 23 that projects towards the centre of the sheet 212 over the projecting part of the first hole 212a, described above. This sloped section 23 may provide room for cooling conduits and electrical connectors to extend from the interior of the tray 100 to the inside of the housing 20. The overmoulded sidewall 21 also comprises a section 24, opposite the sloped section 23, in which the sidewall steps back towards the transverse edge of the sheet 212, and an internal wall 25 separates the main interior region 20a, 20b of the housing 20 from a separate interior region 20c bounded by the stepped back section 24 and the internal wall 25. The overmoulded sidewalls 21 also comprise struts 21a in the exterior surface of the sidewall, which increases the strength of the overmoulded sidewalls. The housing 20 also comprises base elements 26 that extend between opposing sides of the housing sidewall 21 in contact with the sheet 212 so as to increase the bond strength between the overmoulded material and the sheet 212. Figure 5 shows the interior of the second housing 30, in more detail. Again, this shows the overmoulded sidewall 31 with the lid 32 omitted to reveal the interior 30a, 30b of the housing. The second housing 30 is located over the second opening 212b through the sheet 212, with the second opening being positioned in one corner of the interior of the housing 30. The overmoulded sidewall 31 extends around the opening 212b such that the overmoulded sidewall 31 entirely encompasses the opening 212b. The overmoulded sidewall extends along the raised portion 214 of the sheet 212, so that only a small interior corner region 30a of the interior of the housing 30 is provided over the opening 212a, with the main part of the interior 30b being provided so that the sheet 212 is present between that main part of the interior region 30b and the interior of the tray 100. The overmoulded sidewall 31 is generally rectangular in plan view, extending along the raised section 214 of the sheet, but the side wall tapers outward towards the transverse edge of the sheet 212. In the sidewall running along the transverse edge of the sheet, connection points 33 are provided. These connection points 33 may be used for coolant and electrical connections into the interior of the battery enclosure 1, with the connections extending down through the hole 212b inside the housing 30 to connect through to the modules in the interior of the tray, and with connectors extending back up through the hole 212a to connect to the battery modules in the first housing 20. The overmoulded sidewalls 31 also comprise struts 31a in the exterior surface of the sidewall, which increases the strength of the overmoulded sidewalls 31. The housing 30 also comprises base elements 36 that extend between opposing sides of the housing sidewall 31 in contact with the sheet 212 so as to increase the bond strength between the overmoulded material and the sheet 212. Figure 6 shows a schematic cross-section through the assembled battery enclosure 1. As shown, the tray 100 of the battery enclosure 1 is provided with a series of battery modules 2a containing battery cells. The battery modules 2a provided in the tray 100 make up the majority of the battery capacity provided by the battery enclosure. However, due to the footprint of the battery enclosure being limited by the size of the vehicle, and this therefore limiting the number of battery modules that can be arranged in a single layer inside the tray 100, further battery modules 2b, 2c and 2d are provided. The battery module 2b is an enlarged battery module that extends above the height of the tray 100 so that it extends through the hole 212a through the sheet 212 of the lid 200 and into the interior region 20a of the first housing 20. While not shown in this schematic cross-section, two such enlarged battery modules extend through this hole 212a, one on either side of the busbar, and further battery modules are provided inside the first housing 20 inside the two side interior regions 20b, shown in Figure 4. The battery modules 2c are located in the main part of the interior 30b of the second housing 30, extending along the length of this second housing. Finally, battery modules 2d are provided in a third housing 40, which is provided on the underside of the sheet 121 of the tray 100, over the opening 112a. The third housing 40 is not visible in Figure 1, but is formed in the same manner as the first and second housings 20, 30, being provided by a sidewall overmoulded onto the lower face of the sheet 112 and closed by a lid. In order to electrically interconnect and cool the battery modules 2a, 2b, 2c and 2d, electrical connections and coolant conduits are provided that extend away from the connection ports 33, through the sidewall 31 of the second housing 30. The electrical connections and coolant conduits are represented in Figure 6 by the elements 3a, 3b, 3c and 3d. In particular, the battery modules in the tray 100 are provided with electrical connections and coolant by connecting elements 3a, which extend along the inside of the tray 100, enclosed between the sheet 112 of the tray and the sheet 212 of the lid. In order to connect the battery modules in the first housing 10, a connecting element 3b is provided, which extends up through the first hole 212a in the sheet 212 and through the sloped section 23 of the first housing 20, where the connecting element 3b may connect to the battery modules located in the two side interior regions 20b. Likewise, connecting element 3c is provided that extends through the second hole 212b through the sheet and into the second housing, where the connection is made not only to the modules 2c located in the second housing, but also to the connection ports 33, which serve as the electrical and coolant connection ports for the entire battery module. Finally, connecting element 3d is provided, which extends down through the hole 112a through the sheet 112 forming the base of the tray 100, where it may connect to the battery modules 2d located in the third housing 40 in the same way. Thus, all battery modules may be connected together, including those enclosed inside the tray 100 and those enclosed inside the moulded housings 20, 30, 40, via the openings through the sheets 112, 212. Figure 7 shows a variant of the embodiment described above with respect to Figure 1 to 6. In particular, Figure 7 shows a similar view to Figure 5, showing the interior of the second housing 30 in this variant, with the lid of the second housing removed and the contents of the housing omitted. This embodiment differs from that described above in that no second opening is provided through the sheet 212 in the region of this second housing 30, so that the sheet 212 extends continuously between the interior of the tray 100 and the interior of the second housing 30. In order to accommodate this variant embodiment, in which the contents of the second housing 30 are entirely isolated from the contents of the tray 100, it will be necessary to provide a second set of connection ports through to the interior of the tray. This may be provided through one of the sidewalls 120a, 120b, 120c, 120d of the tray if all other housings are also isolated from the interior of the tray, or could be provided through a sidewall of the first housing 20 or third housing 40, if they are provided over openings through the sheets 112, 212. The manufacture of a battery enclosure will now be described with reference to Figures 8 to 11. Figure 8 is a flow diagram illustrating the steps of manufacturing the battery enclosure. In step S1 a tray assembly is provided comprising sidewall elements 114a, 114b, 114c, 114d, joined to a sheet 112 having a hole 112a therethrough. This corresponds to the preliminary assembly 110 of the tray shown in Figure 3 and described above. In step S2, the tray interior is overmoulded onto the tray preliminary assembly 110. Figures 9 and 10 show the overmoulding tool used for this step. The overmoulding tool comprises a set of tools A, B, shown in an open configuration in Figure 9. This set of overmoulding tools A, B can be used to produce the tray 100. The set of overmoulding tools comprises an upper overmoulding tool A and a lower overmoulding tool B. The upper overmoulding tool A comprises a main body tool part A1 and first and second side tool parts A2, A3. The first and second side tool parts A2, A3 coincide with the longitudinal side elements 114a, 114b respectively. The main body tool A1 may also be broken down into transverse side elements, depending on the geometry of the transverse side elements 114c, 114d and shape of the corresponding sidewalls to be moulded. In the open configuration, with the first and second side tool parts A2, A3 removed, the base assembly 110 and the busbars can be loaded into the main body tool A1 of the upper overmoulding tool A. The first and second side tool parts A2, A3 can then be closed with the main body tool part A1 to enclose the base assembly 110 and the busbars 145a, 145b within the upper overmoulding tool A. The sheet 112 may then be loaded into the lower tool B, before the upper and lower tools are closed. A section of the lower tool B extends into the hole 112a and contacts the upper tool A so as to preserve the hole 112a after overmoulding. The overmoulding tool will then define spaces within and between the tools for overmoulding structures onto the sheet 112. Figure 10 shows a partial cross-sectional diagram of the overmoulding tools A, B in the closed configuration. This Figure depicts the spaces provided around the longitudinal side element 114b and the base plate 112 by the main body tool part A1 and the second side tool part A3. Overmoulding material can be injected into these spaces between these components of the base assembly 110 and the upper overmoulding tool A to form the side wall 120b, the lower flange 150 and the hexagonal cells depicted in Figure 2. With the tray 100 formed, in step S3, the lid assembly is provided comprising a hole. This may be the sheet 212 shown in Figure 3, comprising first and second hols 212a, 212b. However, more complex lid assemblies are possible, including sidewall elements similar to the tray. In step S4, the sheet 212a of the lid is thermoformed to form the relief comprising recesses 213, raised section 214 and the depressed rim 215, as described above. This step is not essential, and instead the sheet may be used in a flat configuration. On the other hand, the sheet 112 of the tray assembly may also be thermoformed, typically before the other preliminary elements are joined to the sheet, in order to make the base of the tray conform to certain battery elements. In steps S5 and S6, the housing sidewalls 21, 31, 41 are overmoulded onto the respective sheets 112, 212, over the respective holes 112a, 212a, 212b. Figure 11 shows a schematic cross-section through an overmoulding tool for overmoulding the housing sidewalls. The overmoulding tool comprises an upper tool comprising a plurality of elements D1, D2, D3 and a lower tool E. The lower tool contacts and conforms to the interior surface of the sheet 112, 212 across and around the respective hole 112a, 212a, 212b. In the case of the lid sheet 212, this lower tool conforms to the relief in the sheet, and in the case of the tray, the lower tool conforms to overmoulded elements inside the tray. In the upper tool, a main element D1 is provided that is inserted into the hole 112a, 212a, 212b along a direction perpendicular to the sheet and meets the lower tool E in the hole so that the hole is preserved after overmoulding. This main element D1 also defines the inner surface of the housing sidewall 21, 31, 41 and the upper flange of the sidewall 21, 31, 41. The upper tool also comprises side elements, of which two D2, D3 are shown in this Figure. The side elements D2, D3 are moved into place laterally and define the outer surface of the housing sidewall 21, 31, 41, including the reinforcing ribs 21 a, 31 a. Typically, at least four of these side elements will be provided to define four sidewalls of a generally rectangular housing. However, the number and arrangement of these side elements may vary depending on the shape of the housing to be overmoulded. The main element D1 may also be further broken down as needed, for example with laterally moved elements configured to be arranged inside the housing to define any interior structures, such as the sloped section 23, described above, or broken into elements defining different interior regions separated by internal walls, such as the regions 20a and 20c separated by wall 25, described above. With all overmoulding tool elements in place, defining between and within them the spaces that will form the overmoulded sidewalls 21, 31, 4,1 of the housings 20, 30, 40, the overmoulding material can be injected into these spaces in order to overmould the housings onto the respective sheets 112, 212 surrounding the hole. Next, in step S7, battery elements, including the battery modules 2a, 2b, cooling conduits and electrical connecting elements are provided into the tray 100 and then the lid 200 is secured to the tray, e.g. using bolts at the periphery of the lid and tray rim, to enclose these elements within the tray, with any elements that project above the rim of the tray either being received in the moulded raised section 214 of the lid 200 or extending through one of the openings 212a, 212b, and with connections 3d extending through the opening 112a. Finally, in step S8, battery elements, including battery modules 2c, 2d, are provided inside the housings 20, 30, 40, through the openings defined by the overmoulded sidewalls 21, 31, 41. The housings 20, 30, 40 may then finally be closed by respective lid elements 22, 32, 42, which may have been injection moulded separately, for example, and then joined to the upper flange of the overmoulded sidewalls 21, 31,41, for example by bolts.

Claims

1. A battery enclosure for an electric vehicle, comprising:a tray defining an interior for containing at least one battery cell and an opening into the interior for insertion and removal of the at least one battery cell, the tray comprising a base opposite the opening;a lid arranged so as to close the opening of the tray, thereby enclosing the interior of the tray;wherein the base of the tray and / or the lid comprises:a sheet extending across the opening, said sheet comprising a hole therethrough, through which at least one element may pass from the interior of the tray to the opposite side of the sheet; anda housing joined to the sheet and extending over said hole through the sheet for enclosing said at least one element on said opposite side of the sheet.

2. A battery enclosure according to claim 1, wherein the sheet comprises a composite material.

3. A battery enclosure according to claim 2, wherein the composite material is a fibre-reinforced polymer, the fibres preferably having a median length of at least 1 mm, more preferably at least 5 mm, more preferably at least 10 mm, more preferably at least 20 mm, more preferably at least 50 mm, more preferably at least 100 mm, most preferably at least 200 mm.

4. A battery enclosure according to claim 3, wherein the fibres comprise glass fibres, carbon fibres and / or aramid fibres.

5. A battery enclosure according to claim 3 or claim 4, wherein the fibres are continuous fibres that extend along at least 50% of the length or width of the sheet, preferably along 70%, more preferably along 80%, more preferably along 90% of the length or width of the sheet, wherein more preferably the continuous fibres extend along substantially the entire length or width of the sheet.

6. A battery enclosure according to any of the preceding claims, wherein the sheet is a multi-layer sheet.

7. A battery enclosure according to any of the preceding claims, wherein the sheet comprises a layer of metal.

8. A battery enclosure according to any of the preceding claims, wherein the median thickness of the sheet is at least 1.5mm, preferably at least 2mm, preferably at least 3mm, preferably at least 5mm, preferably at least 10mm, more preferably at least 20 mm.

9. A battery enclosure according to any of the preceding claims, wherein the maximum height and / or depth of any reliefs formed in the sheet, measured perpendicular to the plane of the sheet, does not exceed 10 times the median thickness of the sheet, preferably does not exceed 8 times the median thickness of the sheet, more preferably does not exceed 5 times the median thickness of the sheet.

10. A battery enclosure according to any of the preceding claims, wherein at least 50%, of the area of the sheet is substantially planar, preferably at least 70%, more preferably at least 80%, more preferably at least 90%, more preferably at least 95%, most preferably at least 99% of the area of the sheet is substantially planar.

11. A battery enclosure according to any of the preceding claims, wherein the housing has a different material composition to the sheet.

12. A battery enclosure according to any of the preceding claims, wherein the housing is formed of a polymeric material.

13. A battery enclosure according to any of the preceding claims, wherein the housing is at least partially defined by an overmoulded material, the overmoulded material being overmoulded onto the sheet.

14. A battery enclosure according to any of the preceding claims, wherein the housing is joined to an exterior face of the sheet, facing away from the interior of the tray.

15. A battery enclosure according to any of the preceding claims, wherein the housing extends away from the hole in at least one direction in a plane of the sheet, such that a portion of an interior of the housing is provided over an area of the sheet not having the hole.

16. A battery enclosure according to claim 15, wherein the interior of the tray comprises at least one battery cell and the portion of the interior of the housing provided over the area of the sheet not having the hole comprises at least one battery cell, such that the sheet extends between the at least one battery cell in the interior of the tray and the at least one battery cell in the interior of the housing.

17. A battery enclosure according to any of the preceding claims, further comprising a second housing joined to the sheet for enclosing a further at least one element on the opposite side of the sheet to the interior of the tray.

18. A battery enclosure according to claim 17, wherein the sheet extends continuously between the second housing and the interior of the tray, isolating an interior of the second housing from the interior of the tray.

19. A battery enclosure according to claim 18, wherein the interior of the tray comprises at least one battery cell, and wherein the interior of the second housing comprises at least one battery cell, such that the sheet extends continuously between the at least one battery cell in the interior of the tray and the at least one battery cell in the interior of the second housing.

20. A battery enclosure according to any of the preceding claims, wherein the at least one element comprises a battery element, preferably one or more of electrical connectors, coolant conduits, coolant fluids, battery cells, and battery modules.

21. A method of manufacturing a battery enclosure for an electric vehicle, comprising:providing a tray defining an interior for containing at least one battery cell and an opening into the interior for insertion and removal of the at least one battery cell, the tray comprising a base opposite the opening;providing a lid arranged so as to close the opening of the tray, thereby enclosing the interior of the tray;wherein providing the base of the tray and / or the lid comprises:providing a sheet configured to extend across the opening, said sheet comprising a hole therethrough, through which at least one element may pass from the interior of the tray to the opposite side of the sheet; andjoining a housing to the sheet such that it extends over said hole through the sheet for enclosing said at least one element on said opposite side of the sheet.

22. A method according to claim 21, comprising moulding the housing.

23. A method according to claim 22, wherein joining the housing to the sheetcomprises overmoulding the housing onto the sheet.

24. A method according to any of claims 21 to 23, adapted to manufacture a battery enclosure according to any of claims 1 to 20.

25. A battery enclosure for an electric vehicle, comprising:a tray defining an interior for containing at least one battery cell and an opening into the interior for insertion and removal of the at least one battery cell, the tray comprising a base opposite the opening;a lid arranged so as to close the opening of the tray, thereby enclosing the interior of the tray;wherein the base of the tray and / or the lid comprises:a sheet extending across the opening; anda housing joined to the sheet, the housing defining an interior of the housing on an opposite side of the sheet to the interior of the tray for containing a second at least one battery cell, wherein the sheet extendssubstantially continuously between the interior of the tray and the interior of the housing.

26. A method of manufacturing a battery enclosure for an electric vehicle, comprising:5 providing a tray defining an interior for containing at least one battery celland an opening into the interior for insertion and removal of the at least one battery cell, the tray comprising a base opposite the opening;providing a lid arranged so as to close the opening of the tray, thereby enclosing the interior of the tray;10 wherein providing the base of the tray and / or the lid comprises:providing a sheet configured to extend across the opening; and joining a housing to the sheet, the housing defining an interior of the housing on an opposite side of the sheet to the interior of the tray for containing a second at least one battery cell, wherein the sheet extends15 substantially continuously between the interior of the tray and the interiorof the housing.

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