Top cover for a battery pack with integral reinforcement, battery pack, and method for assembling a battery pack

Abstract

A top cover assembly (1) for a battery pack (201) comprising: a top cover (10) generally having an inverted tab shape; an inner reinforcing structure (11) having at least one lateral inner reinforcing element (111) extending substantially laterally into the interior of the top cover (10); and an outer reinforcing structure (12) having at least a left outer reinforcing element (121L) and a right outer reinforcing element (121R).

Description

[Technical Field]

[0001] The present invention relates to a battery pack for an electric vehicle, and particularly to the design of the top cover of the battery pack, the overall design of the battery pack, and the assembly process of the battery pack. [Background technology]

[0002] Electric vehicles are a solution to the increasingly urgent need to reduce the carbon dioxide emissions of each individual journey. The battery pack, located below the floor panel, is a key element of said electric vehicle. One of the main challenges that battery packs must address is optimizing the structural resistance of the pack while maintaining the maximum possible battery cell capacity. In practice, reinforcing the battery pack involves adding structural elements such as cross beams, which occupy space at the expense of battery cell capacity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 153781 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides an innovative battery pack design, and in particular an innovative design for the battery pack top cover, which allows for maximizing cell space while ensuring excellent structural integrity of the pack.

[0005] The present invention also provides an innovative assembly sequence for the battery pack that simplifies the overall process, resulting in increased productivity and reduced costs. [Means for solving the problem]

[0006] The object of the present invention is achieved by providing a top cover for a battery pack according to claim 1, which optionally comprises the features of claims 2 to 10 individually or in any possible combination. A further object of the present invention is achieved by providing a battery pack according to claim 11. A further object of the present invention is to provide an assembly sequence for a battery pack according to the present invention according to claim 12.

[0007] Other aspects and advantages of the present invention will become apparent from a reading of the following description, given by way of example and with reference to the accompanying drawings, which are in no way limiting. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is an overall perspective view of the electric vehicle showing the position of the battery pack. [Figure 2] 1 is a perspective view of an embodiment of a battery pack according to the present invention, showing the top cover assembly and battery tray assembly before being assembled together. FIG. [Figure 3] 1 is a perspective view of an embodiment of a top cover assembly according to the present invention; [Figure 4] FIG. 1 is an exploded perspective view of an embodiment of a top cover assembly according to the present invention. [Figure 5] 1 is a perspective view of an embodiment of a corner of a top cover assembly according to the present invention; [Figure 6] FIG. 1 is a perspective view of an embodiment of a battery tray assembly according to the present invention. [Figure 7] FIG. 1 is an exploded perspective view of an embodiment of a battery tray assembly according to the present invention. [Figure 8] 1A-1C are diagrams illustrating an embodiment of an assembly process for a battery pack according to the present invention. [Figure 9] 1A-1C are diagrams illustrating an embodiment of an assembly process for a battery pack according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] In the following description and claims, directional terms are defined according to the normal directions of the vehicle in which they are installed.

[0010] In particular, terms such as "upper", "above", "upper", "above", "lower", "lower", "below" and the like are defined according to the ascending direction of the vehicle. Terms such as "forward", "rear", "rear", "front", "forward", "rearward" and the like are defined according to the longitudinal direction of the vehicle, i.e., the direction in which the vehicle moves forward when following a straight line. Terms such as "left", "right", "lateral" and the like are defined according to an orientation parallel to the width of the vehicle. The terms "inner" and "outer" are to be understood according to the width direction of the vehicle: "inner" is closest to the central axis of the vehicle, i.e., closest to the interior of the vehicle, while "outer" is located further from said central axis of the vehicle and substantially closer to the exterior of the vehicle. The same applies to the terms "distal" and "central": a "distal" part is closest to the exterior of the vehicle and a "central" part is closest to the center of the vehicle. The term "horizontal" refers to an orientation in a plane including the longitudinal and lateral directions. The term "vertical" refers to any orientation including the ascending direction.

[0011] In the following figures, all orientation and spatial references are made using an X, Y, Z coordinate reference, where Z is the vehicle's uphill direction, X is the vehicle's longitudinal direction, and Y is the vehicle's lateral direction. The coordinate references are represented in each figure. When a figure is a 2D flat representation, according to established conventions, axes that are external to the figure are represented by a dot within a circle when pointing towards the reader, and by a cross within a circle when pointing away from the reader.

[0012] By "substantially parallel" or "substantially perpendicular" is meant a direction that can deviate from the parallel or perpendicular direction by no more than 15°.

[0013] A steel plate refers to a flat sheet of steel. The steel plate has a top face and a bottom face, also referred to as a top side and a bottom side, or a top surface and a bottom surface. The distance between the faces is designated as the thickness of the plate. The thickness may be measured, for example, using a micrometer, with the micrometer spindle and anvil placed on the top and bottom faces. Similarly, the thickness may also be measured on a formed part.

[0014] By average thickness of a part or portion of a part, what is meant is the overall average thickness of the material that makes up the part after the part has been formed from an initially flat sheet into a three-dimensional part.

[0015] To optimize part performance in different areas of the part, to reduce the overall part weight, to reduce the overall part cost, and to reduce material scrap, tailor welded blanks are made by assembling several plates or cut-out blanks of steel, known as sub-blanks, together, for example, by laser welding. The sub-blanks that form the tailor welded blank may be assembled with or without overlap, for example, laser butt-welded (no overlap) or spot welded to each other (with overlap).

[0016] Contrary to tailor-welded blanks, monolithic blanks refer to blanks that consist of one single sub-blank, without several sub-blanks being joined together.

[0017] A tailor rolled blank is a blank with multiple plate thicknesses obtained by differential rolling during the steel plate production process.

[0018] Ultimate tensile strength, yield strength, and elongation are measured according to ISO standard ISO 6892-1, published in October 2009. Tensile test specimens are cut from flat areas. If necessary, smaller sized tensile test specimens are taken to cover the entire available flat area on the part.

[0019] The bending angle is measured according to the VDA-238 bending standard. For the same material, the bending angle depends on the thickness. For simplicity, the bending angle values ​​in this invention refer to a thickness of 1.5 mm. If the thickness is different from 1.5 mm, the bending angle value should be normalized to 1.5 mm by the following calculation, where α1.5 is the normalized bending angle at 1.5 mm, t is the thickness, and αt is the bending angle for thickness t: α1.5=(αt×√t) / √1.5

[0020] Cold stamping is a metal forming technique that involves forcing a metal sheet between upper and lower dies, called a cold stamping tool, into a formed part. For example, a cold stamping tool may have a blank holder, which allows the metal sheet to be held by its sides. For example, a cold stamping tool may consist of several steps, each with an upper and lower die for generating complex shapes and / or for further manipulation, such as punching holes in the part or trimming its sides. Other cold forming techniques exist, such as roll forming, which involves bending a continuous sheet between successive sets of rolls, and simple bending, which involves simply bending a steel sheet using a press and upper and lower bending tools.

[0021] Roll forming is a continuous metal forming process that takes a sheet, strip, or coil and bends or forms it into successive cross sections. The process takes place between successive pairs of shape-changing rolls until the desired cross section is completed. The cross section is called the roll-forming cross section, and the direction in which the material is roll-formed, i.e., the direction separating two successive pairs of rolls, is called the roll-forming direction.

[0022] Hot stamping is a forming technique for steels that involves heating a steel blank or a preformed part made from a steel blank to a temperature at which the microstructure of the steel is at least partially transformed to austenite, forming the blank or preformed part by stamping at high temperature, and simultaneously quenching the formed part to obtain a microstructure with very high strength, possibly with further division or tempering steps in the heat treatment.

[0023] A multi-step hot stamping process is a specific type of hot stamping process that consists of at least two process steps, including at least one stamping step, performed at temperatures above 300°C. For example, a multi-step process can include a first stamping operation and a subsequent hot trimming operation, so that the finished part does not need to be further trimmed upon completion of the hot stamping process. For example, a multi-step process may include several consecutive stamping steps to produce parts with more complex shapes than can be achieved using a single stamping operation. For example, parts are automatically transferred from one operation to another in a multi-step process, for example, using a transfer press. For example, parts remain in the same tool, which is a multi-purpose tool that can perform different operations, such as a first stamping and a subsequent in-tool trimming operation.

[0024] A partial-hardening hot stamping process is a hot stamping process in which the thermal profile to which the blank is subjected is intentionally tailored to be different in different areas of the blank so that different material properties are obtained in these areas at the end of the hot stamping process. For example, this allows a single metal blank made of a single material to be used to produce a blank hot-stamped part that will have different levels of hardness and elongation in different areas of the final part. For example, this allows for the production of a part with soft zones that can deform under impact loads to absorb energy and hard zones that will resist deformation and therefore penetration. There are several different techniques for achieving partial hardening. For example, the material may be heated to different temperatures in different areas of the blank, with the higher temperature areas becoming fully austenitic at the exit of the austenitizing furnace, resulting in a very hard microstructure after hot stamping, and the lower temperature areas having an intercritical ferrite / austenite microstructure at the exit of the austenitizing furnace, resulting in a less hard microstructure after hot stamping. For example, the material may be quenched at different quench rates in different areas of the blank during the hot stamping step itself, with the areas quenched at a higher quench rate having a higher hardness than the areas quenched at a lower rate.

[0025] Referring to FIG. 1 , an electric vehicle 200 has a battery pack 201 located below the floor panel. The electric vehicle has a front electric motor 202 powered by, for example, an energy storage unit located inside the battery pack 201. The battery pack 201 is typically attached to the vehicle structure on its sides by assembling it into the vehicle's left and right rocker assemblies 203 (also known as side sills), which are long longitudinal assemblies often made up of several parts assembled together. The rocker assemblies 203 run along the lower edge of the body-in-white between the front and rear wheel housings. The object of the present invention is the design of the battery pack 201 and a method for assembling the battery pack.

[0026] Referring to FIG. 2 , a battery pack 201 includes at least a top cover assembly 1 and a battery tray assembly 2 to which an energy storage unit 3 is attached. The energy storage unit 3 houses battery cells used to power a vehicle. In certain embodiments, the energy storage unit 3 consists of the battery cells themselves in a so-called cell-to-pack concept. In certain embodiments, the energy storage unit 3 consists of battery cells and a packaging element known as a battery module to protect the cells, in what is known as a module-to-pack architecture. The present invention is compatible with both cell-to-pack and module-to-pack architectures by providing a fully reinforced battery pack that can efficiently protect the battery cells directly without the need for a dedicated reinforced module.

[0027] If a vehicle is involved in a collision, protecting the energy storage unit 3 is of paramount importance. Indeed, damage to the energy storage unit 3 can result in the leakage of toxic chemicals, the release of toxic gases, and can lead to electrical or fire hazards. For the safety of the occupants and surroundings, the energy storage unit 3 must be kept safe from harm, even in the event of a severe collision. This is the role of the battery pack itself.

[0028] It is known from the prior art to provide a reinforced battery tray assembly having inner and outer reinforcing elements for protecting the energy storage unit and providing a non-structural top cover for the battery pack that acts simply as a closing plate, see for example patent application WO2018153781.

[0029] There are several drawbacks associated with such a design. One drawback is that the battery pack can only be attached and reinforced by fastening it to the body-in-white by its lower portion. While this is not an issue when attaching it to the rocker assembly, it proves problematic when attaching it to a floor panel or floor reinforcement, because the fasteners run through the entire height of the battery pack. In fact, the battery pack is very often at least partially attached to the floor panel or floor reinforcement structure. In fact, this allows the load of a very heavy battery pack (typically around 500 kg) to be distributed over a large area of ​​the lower portion of the body-in-white. It also helps improve the Noise Vibration Harshness (NVH) performance of the vehicle: without a central attachment to the floor panel or floor reinforcement, the battery pack would drop between the rocker panels and vibrate up and down when the vehicle is moving, which significantly affects occupant comfort and also puts additional pressure on the rocker panel mounts. Another identified drawback to the above-described design relates to the presence of an upper flange in such architecture, which extends horizontally above the sidewall of the reinforced battery tray and serves as an assembly area between the tray and the top cover. Because the flange is located toward the top of the battery pack, it occupies space within the volume located between the left and right rocker elements. The volume occupied by the assembly flange is unavailable for the energy storage unit, thereby reducing the overall energy storage capacity of the battery pack and, consequently, the vehicle's driving autonomy.

[0030] The present invention aims to overcome the identified shortcomings of the prior art by providing a battery pack having a reinforced top cover assembly and an assembly flange between the top cover assembly and the battery tray assembly that is located toward the bottom of the battery pack. By applying the present invention, it is possible to manufacture battery packs that can be attached to a vehicle rest in a wide variety of ways, such as by the bottom, side, or top, or by a combination of the three possibilities. Furthermore, the assembly flange between the top cover assembly and the tray assembly is located toward the bottom of the battery pack and can slide below the packaging volume occupied by the rocker assembly, thus making the entire transverse space between the bulk of the rocker assembly available for the energy storage unit, thereby maximizing the amount of energy storage unit that can fit inside the battery pack.

[0031] 3 and 4, the top cover assembly according to the present invention comprises: - an upper cover 10 having a generally inverted tab shape and consisting of an upper plate 101 extending generally in a horizontal plane bounded by a left side wall 102L, a right side wall 102R, a front side wall 102F and a rear side wall 102B, the height of said side walls 102 in an upward direction being at least 0.5 times, preferably 0.75 times, the height between the lowest point of the battery tray assembly 2 and the highest point of the upper cover assembly 1, said side walls 102 being extended by four flanges 103 extending generally in the horizontal plane; an internal reinforcing structure 11 located inside the top cover 10, i.e. below the top plate 101, comprising at least one transverse internal reinforcing element 111 extending substantially transversely between said left side wall 102L and said right side wall 102R of the top cover; an external reinforcing structure 12 located outside the top cover 10, i.e. above the top cover 10, comprising at least a left external reinforcing element 121L and a right external reinforcing element 121R, each of said external reinforcing elements 121 having at least a side portion 1212 extending over at least a part of said left wall 102L and right wall 102R, so that the surface area of ​​each of said external reinforcing side portions 1212 is at least equal to 0.75 times, preferably equal to 0.8 times, and even more preferentially equal to 0.9 times, the surface area of ​​the corresponding side wall 102 over which said external reinforcing side portion 1212 extends.

[0032] The top cover assembly according to the present invention is particularly well reinforced on the left and right sides to withstand intrusion into the battery pack in the event of a side impact. Generally speaking, side impacts are most critical to the battery pack because the sides of the battery pack are closest to the exterior of the vehicle and are only protected by the rocker assembly. The front and rear ends of the battery pack are less exposed to direct intrusion from an external impacting object due to the presence of the front and rear crash management systems between the impacting object and the battery pack. However, the front and rear ends of the battery pack will still be exposed to crash energy transmitted by the front and rear crash management systems—thus, it may be advantageous to further reinforce these areas with the outer reinforcing structure 12. Accordingly, in certain embodiments, the outer reinforcing structure 12 further includes a rear outer reinforcing element 121B and a front outer reinforcing element 121F, each of which includes at least a side portion 1212 extending over at least a portion of the rear sidewall 102B and the front sidewall 102F. In certain embodiments, at least one of the rear or front stiffening element side portions 1212B, 1212F extends over a surface that covers at least 80%, preferably 90%, of the respective sidewall surface over which it extends.

[0033] The outer reinforcement element 121 is assembled to the top cover 10, for example, by spot welding. As depicted in Figure 5, spot welding may be performed, for example, to attach the outer reinforcement top portion 1211 (said top portion overlapping the top plate 101) to the top plate 101 by spot welding 1211w. Spot welding may also be performed, for example, to attach the outer reinforcement side wall portion 1212 to the corresponding side wall 102 by spot welding 1212w.

[0034] The use of an inverted tab design with high side walls allows the flanges 103 used to assemble the top cover assembly to the battery tray assembly to be positioned toward the bottom of the battery pack, which in some cases allows the left and right flanges 103, 103 to slide below the left and right rocker assembly packaging space, thereby providing additional space for the energy storage unit 3, as previously described.

[0035] By providing a reinforced top cover assembly, the present invention allows the battery pack to be directly mounted to the vehicle chassis via the top or reinforced sides of the top cover, which is extremely beneficial when the battery pack is directly mounted to a floor panel or floor reinforcement element, thereby improving the NVH performance of the vehicle and efficiently distributing the load of the battery pack, as previously mentioned.

[0036] Thanks to the presence of the inner reinforcing structure 11, which includes at least one inner transverse reinforcing element 111 extending between the left side wall 102L and the right side wall 102R of the upper cover, the reinforced upper cover can withstand a side impact with little deformation, thereby efficiently protecting the energy storage unit 3. As depicted in FIGS. 3 and 4 , in a specific embodiment, the inner reinforcing structure 11 includes at least two transverse inner reinforcing elements 111 spaced apart from one another in the longitudinal direction. Advantageously, this allows for higher resistance to intrusion and deformation of the battery pack in the event of a side impact. Furthermore, the presence of transverse reinforcing elements at different longitudinal positions prevents deformation in the event of a side impact at various longitudinal positions, thereby making the battery pack more robust in the event of different side impact situations. This further provides a higher overall rigidity to the battery pack.

[0037] 3 and 4, the inner reinforcing structure 11 further comprises a longitudinal reinforcing element 112 extending between the rear side wall 102B and the transverse reinforcing element 111, and at least a longitudinal reinforcing element 112 extending between the front side wall 102F and the transverse reinforcing element 111. Advantageously, this makes it possible to reinforce the battery pack in the event of a front or rear impact.

[0038] The presence of the side outer reinforcement structure 12 allows the battery pack to be efficiently attached to the vehicle chassis in various ways as previously described. Furthermore, the outer reinforcement structure 12 resists deformation of the battery pack and pack intrusion, while at the same time dispersing the load of a side, front, or rear impact on the chassis of the reinforcement structure and transmitting it to the inner reinforcement structure 11.

[0039] In a particular embodiment as depicted in FIG. 5 , at least one of the outer reinforcing elements 121L, 121R, and optionally 121F, 121B, comprises a flange portion 1213 that extends over at least a portion of the corresponding flange 103 of the top cover. Said flange portion 1213 may extend further outward than the flange 103 over which said flange portion 1213 extends, as depicted in FIG. 5 . Advantageously, the presence of such an outer reinforcing flange portion 1213 allows for further reinforcement of the top cover assembly 1 and may further serve as an attachment point to the vehicle structure, e.g., to the rocker assembly in the case of the left and right outer reinforcing elements 121L, 121R. In a particular embodiment as depicted in FIG. 5 , said flange portion 1213 comprises a closed section portion that encloses a hollow volume 1214. For example, this is done by manufacturing the outer reinforcing element 121 by roll forming, which makes it possible to create closed section portions in the outer reinforcing element - the outer reinforcing element depicted in Figure 5 may, for example, be manufactured by roll forming. Advantageously, the presence of the hollow volume 1214 in the flange portion 1213 makes it possible to very efficiently withstand applied compressive forces applied in a direction substantially perpendicular to the side walls of the top cover, such as occurs, for example, for the left reinforcing element 121L or the right reinforcing element 121R in the event of a side impact. The presence of the hollow volume 1214 further provides increased stiffness for the corresponding reinforcing element 121.

[0040] In certain embodiments, the outer reinforcement structure 12 further comprises an outer corner reinforcement 123, as depicted in Figures 3 to 5. The outer corner reinforcement 123 is attached to two adjacent outer reinforcement elements. For example, the outer corner reinforcement is between at least one of the following outer reinforcement elements: - front lateral reinforcement 121F and left lateral reinforcement element 121L, - left lateral reinforcement element 121L and rear lateral reinforcement 121B, - Rear outer reinforcement 121B and right outer reinforcement 121R, - Right lateral reinforcement 121R and front lateral reinforcement 121F.

[0041] In certain embodiments, there are outer corner reinforcements 123 at all four of the above possible locations, in other words at all four corners of the outer reinforcement structure 12.

[0042] Advantageously, the outer corner reinforcements make it possible to further stiffen the structure and ensure that the different reinforcement elements 121 of the outer reinforcement structure 12 cooperate with each other in the event of an impact. Indeed, for example, if the battery pack is impacted on its left side, the presence of the outer corner reinforcements between the left outer reinforcement element 121L and the rear outer reinforcement 121B and between the left outer reinforcement element 121L and the front outer reinforcement 121F ensures that the displacement of the left outer reinforcement 121L upon impact is limited by the resistance to deformation of the front and rear outer reinforcements. Furthermore, if outer corner reinforcements are present at all four corners, the outer reinforcement structure 12 will form a rigid annular structure, thereby increasing the overall stiffness of the assembly.

[0043] For example, the outer corner reinforcements 123 are attached to the flange portions 1213 of the corresponding outer reinforcement elements 121, as depicted in Figures 3, 4, and 5. Other configurations are possible. For example, the outer corner reinforcements 123 are attached to the sidewall portions 1212 of the corresponding outer reinforcement elements 121.

[0044] In the particular embodiment as depicted in Figure 5, the outer corner reinforcements 123 are assembled by inserting and attaching them into the hollow volumes 1214 of the corresponding outer reinforcement elements 121. Advantageously, this allows for a very solid connection and offers several industrial advantages, such as ease of positioning the elements to be assembled (e.g. the corner reinforcements 123 are press-fit into two adjacent hollow volumes 1214 and are held in place against the outermost walls of the closure sections enclosing said hollow volumes 1214 before being assembled).

[0045] In certain embodiments, the inner reinforcing structure 11 further comprises inner corner reinforcements 113 as depicted in FIG. 4. The inner corner reinforcements 113 are located at the corners of the inner reinforcing structure and are attached to at least two portions of the top cover 10 extending in different planes. For example, the inner corner reinforcements 113 can be attached to the top plate 101 and one side wall 102. For example, the inner corner reinforcements 113 can be attached to two adjacent side walls, such as the left side wall 102L and the front side wall 102F. For example, the inner corner reinforcements 113 can be attached to three different portions of the top cover 10 simultaneously: the top plate 101 and two adjacent side walls—this is the case for the inner corner reinforcement depicted in FIG. 4. In certain embodiments, the inner corner reinforcements are located at all four corners of the inner reinforcing structure 11.

[0046] Advantageously, the presence of said inner corner reinforcements makes it possible to increase the resistance of the reinforced top cover to deformation under impact, making it possible to increase the rigidity of the top cover.

[0047] A battery pack 201 according to the present invention comprises a top cover assembly 1 having the above-mentioned characteristics and a battery tray assembly 2 to which an energy storage unit 3 is attached. The battery pack typically comprises additional elements not detailed in this invention, such as a lower shield located at the bottom of the battery pack and serving to prevent any possible intrusion from below the battery pack. The battery pack also typically comprises a cooling circuit, typically located on or below the tray, serving to regulate the temperature of the energy storage unit, which should be maintained as close as possible to the optimum operating temperature of the battery cells.

[0048] 6 and 7, the battery tray assembly 2 comprises the battery tray 20 itself having a shallow tab shape, including a flat or corrugated lower portion 201 surrounded by shallow side walls 202 and extended by a horizontal flange 203. The purpose of having the corrugated tray lower portion 201 is to increase the rigidity of that portion and, in some cases, to provide clearance for a cooling system. The corrugations can also play a role in assembling the battery tray to the lower portion of the battery pack structure, i.e., to a shield that may include a reinforcing cross-member. The battery tray 20 does not itself serve a structural role; its purpose is to support the energy storage unit 3.

[0049] To reinforce the battery tray 20 itself, a battery tray inner reinforcing structure 21 and an outer reinforcing structure 22 are provided. The inner reinforcing structure 21 is made up of elements attached to the inside of the battery tray hollow tab, i.e., on top of the tray itself. The outer reinforcing structure 22 is made up of elements attached to the outside of the battery tray shallow tab, i.e., below the tray.

[0050] The battery tray inner reinforcing structure 21 includes at least a left inner lateral reinforcing element 211L and a right inner lateral reinforcing element 211R, and optionally further front and / or rear inner lateral reinforcing elements 211F, 211B. The inner lateral reinforcing elements 211 cover at least a portion of the tray bottom 201 and, optionally, at least a portion of the corresponding side wall 202 and at least a portion of the corresponding flange 203. The inner lateral reinforcing elements 211 provide the battery tray assembly 2 with further reinforcement and rigidity to protect the energy storage unit 3 in the event of a collision. The inner lateral reinforcing elements 211 can also serve as elements to which the energy storage unit 3 is attached.

[0051] The inner reinforcing structure 21 optionally further comprises at least one transverse reinforcing element 212 attached to the lower tray portion 201 as depicted in Figures 6 and 7, either to two opposing side walls 202 or to two opposing lateral reinforcing elements 211 - said transverse reinforcing element being longitudinal (as depicted, reinforcing element 212 in Figure 6 is attached between opposing lateral reinforcing elements 211F and 211B) or transverse. The optional transverse reinforcing element 212 serves to further strengthen and stiffen the lower tray portion 201, which is a large component that supports the heavy weight of the energy storage unit 3. The optional transverse reinforcing element 212 can also serve as an element to which the energy storage unit 3 is attached.

[0052] The battery tray outer reinforcement structure 22 includes at least a left side outer reinforcement element 221L and a right side outer reinforcement element 221R, and optionally rear and / or front side outer reinforcement elements 221F, 221B, which cover at least a portion of the corresponding side wall 202 of the battery tray 20, optionally at least a portion of the corresponding flange 203, and optionally a portion of the tray bottom itself 201.

[0053] The top cover assembly 1 and the bottom tray assembly 2 are assembled by attaching them together at least along their respective flanges 103, 203. For example, the top cover assembly 1 and the bottom tray assembly 2 are attached by spot welding them along the flanges. For example, the top cover assembly 1 and the bottom tray assembly 2 are attached by mechanically fastening them along the flanges, such as by bolting, riveting, etc. For example, the top cover assembly 1 and the bottom tray assembly 2 are attached by both spot welding and mechanical fastening techniques.

[0054] To assemble a reinforced battery pack according to the present invention, follow the assembly sequence depicted in FIGS. 8 and 9:

[0055] If the optional inner corner reinforcement 113 is used, the top cover 10 and the inner corner reinforcement 113 are assembled together, for example by spot welding, as depicted in the upper left-hand side of FIG.

[0056] As depicted in the upper right-hand side of Figure 8, an inner reinforcing structure 11 is provided. For example, said inner reinforcing structure 11 is manufactured by assembling together transverse reinforcements 111 and longitudinal reinforcements 112. Said reinforcements are assembled together, for example, by spot welding. In a particular embodiment, a bracket is used between the parts to be assembled, acting as a connecting element between the two reinforcing elements - in that configuration, said bracket is provided with two sets of flanges on opposite sides of the bracket, each set facing one of the parts to be assembled - the parts are assembled by welding them to the bracket using said flanges as welding surfaces. In a particular embodiment, the inner reinforcing structure 11 further comprises brackets on the surface to be welded to the top cover 10, so that they can be assembled to the top cover using said brackets in a subsequent step.

[0057] The outer reinforcing structure 12, the top cover 10 and the inner reinforcing structure 11 are assembled together, for example by spot welding, as depicted in the lower part of FIG.

[0058] Optionally, if external corner reinforcements 123 are used, said external corner reinforcements 123 are added by attaching them to the external reinforcement structure 12 already installed on the top cover 10, as depicted in the top part of Figure 9. For example, the external corner reinforcements 123 are welded or bolted to two continuous external reinforcement elements 121, respectively.

[0059] - Next, the upper cover assembly 1 assembled in this way is assembled to the battery tray assembly 2, and an energy storage unit 3 is fixed on the battery tray assembly 2 as depicted in the lower part of FIG. 9. This assembly is performed at least by attaching the upper cover assembly 1 and the battery tray assembly 2 along their respective flanges 103, 203. The assembly is performed, for example, by spot welding, or by mechanical fastening such as bolting, or by using a combination of both techniques.

[0060] In a specific embodiment, in order to prevent water from entering the inside of the battery pack that would damage the energy storage unit, and conversely, to ensure that the chemicals in the energy storage unit do not leak out of the battery pack, a sealing material is applied to cover at least the sides of the flanges 103, 203.

[0061] In a specific embodiment, the following materials are used to manufacture the above-described elements of the upper cover assembly 1 and the battery tray assembly 2 according to the present invention:

[0062] - Steel having a chemical composition of 0.13% < C < 0.25%, 2.0% < Mn < 3.0%, 1.2% < Si < 2.5%, 0.02% < Al < 1.0% by weight, 1.22% < Si + Al < 2.5%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5%, Ti < 0.05%, with the balance being Fe and unavoidable impurities, having a microstructure containing 8% to 15% retained austenite, and the balance being ferrite, martensite, and bainite, and the total proportion of martensite and bainite being included between 70% and 92%. In this composition, when measured in the roll direction, the steel sheet has a yield strength included between 600 MPa and 750 MPa and an ultimate tensile strength included between 980 MPa and 1300 MPa while maintaining an elongation over 19%. For example, this material is used at least for a part of the elements constituting the outer reinforcement structures 12, 22 or the inner reinforcement structures 11, 21.

[0063] - A steel having a chemical composition containing, in weight percentages, 0.15% < C < 0.25%, 1.4% < Mn < 2.6%, 0.6% < Si < 1.5%, 0.02% < Al < 1.0%, with 1.0% < Si + Al < 2.4%, Nb < 0.05%, Cr < 0.5%, and Mo < 0.5%, the balance being Fe and inevitable impurities, having a microstructure containing 10% to 20% retained austenite, and the balance being ferrite, martensite, and bainite. In this composition, when measured in the rolling direction, the steel sheet has a yield strength within the range of 850 MPa to 1060 MPa and an ultimate tensile strength within the range of 1180 MPa to 1330 MPa while maintaining an elongation over 13%. For example, this material is used, at least, for a part of the elements constituting the outer reinforcing structures 12, 22 or the inner reinforcing structures 11, 21. For example, the corresponding elements are produced by bending, stamping, or roll-forming them into the desired shape using such steel. <s

[0064] - A fully martensitic steel having a composition containing, in weight percentages, 0.15% ≤ C ≤ 0.5%. For example, this material is used, at least, for a part of the elements constituting the outer reinforcing structures 12, 22 or the inner reinforcing structures 11, 21. For example, the corresponding elements are produced by roll-forming them into the desired shape using such steel.

[0065] - A duplex steel having a microstructure containing at least martensite and ferrite and having a UTS of at least 590 MPa. For example, this material is used, at least, for a part of the elements constituting the outer reinforcing structures 12, 22 or the inner reinforcing structures 11, 21.

[0066] - A duplex steel having a microstructure containing at least martensite and ferrite and having a UTS of at least 780 MPa. For example, this material is used, at least, for a part of the elements constituting the outer reinforcing structures 12, 22 or the inner reinforcing structures 11, 21.

[0067] a dual-phase steel having a microstructure containing at least martensite and ferrite and an ultimate tensile strength of at least 980 MPa, for example, used for at least part of the elements making up the outer reinforcing structure 12, 22 or the inner reinforcing structure 11, 21;

[0068] In certain embodiments, at least some of the elements making up the outer reinforcing structure 12, 22 or the inner reinforcing structure 11, 21 are made by hot stamping, by multi-step hot stamping, or by partial cure hot stamping of at least one of the following combinations of materials in the form of a monolithic blank, in the form of a tailor rolled blank, or in the form of a tailor welded blank:

[0069] Steel having a composition in weight percent of: 0.06%≦C≦0.1%, 1%≦Mn≦2%, Si≦0.5%, Al≦0.1%, 0.02%≦Cr≦0.1%, 0.02%≦Nb≦0.1%, 0.0003%≦B≦0.01%, N≦0.01%, S≦0.003%, P≦0.020%, less than 0.1% Cu, Ni and Mo, the remainder being iron and unavoidable impurities resulting from refining, in which the yield strength of the corresponding area after hot stamping is between 700 and 950 MPa, the tensile strength is between 950 and 1200 MPa, and the bending angle is greater than 75°.

[0070] - Steels having an ultimate tensile strength after hot stamping comprised between 1300 MPa and 1650 MPa and a yield strength comprised between 950 MPa and 1250 MPa.

[0071] - Steels having an ultimate tensile strength after hot stamping comprised between 1300 MPa and 1650 MPa, a yield strength comprised between 950 MPa and 1250 MPa and a bending angle greater than 75°.

[0072] Steel having a composition, in weight percent, of 0.20%≦C≦0.25%, 1.1%≦Mn≦1.4%, 0.15%≦Si≦0.35%, Cr≦0.30%, 0.020%≦Ti≦0.060%, 0.020%≦Al≦0.060%, S≦0.005%, P≦0.025%, 0.002%≦B≦0.004%, the remainder being iron and unavoidable impurities resulting from refining, in which the ultimate tensile strength of some corresponding areas after hot stamping in this composition range is between 1300 MPa and 1650 MPa, and the yield strength is between 950 MPa and 1250 MPa.

[0073] - Steels with a tensile strength after press hardening greater than 1800 MPa.

[0074] - Steel having a composition, in weight percent, of the following: 0.24%≦C≦0.38%, 0.40%≦Mn≦3%, 0.10%≦Si≦0.70%, 0.015%≦Al≦0.070%, Cr≦2%, 0.25%≦Ni≦2%, 0.015%≦Ti≦0.10%, Nb≦0.060%, 0.0005%≦B≦0.0040%, 0.003%≦N≦0.010%, S≦0.005%, P≦0.025%, the remainder being iron and unavoidable impurities resulting from refining.

[0075] A steel having a composition, in weight percent, including: C: 0.15-0.25%, Mn: 0.5-1.8%, Si: 0.1-1.25%, Al: 0.01-0.1%, Cr: 0.1-1.0%, Ti: 0.01-0.1%, B: 0.001-0.004%, P≦0.020%, S≦0.010%, N≦0.010%, and optionally including one or more of the following elements in weight percent: Mo≦0.40%, Nb≦0.08%, Ca≦0.1%, with the remainder being iron and unavoidable impurities resulting from smelting. With this composition range, the tensile strength of the corresponding area of ​​the dash panel assembly after hot stamping is higher than 1350 MPa, and the bending angle is greater than 70°.

[0076] a steel having a composition in weight percent comprising: C 0.26-0.40%, Mn 0.5-1.8%, Si 0.1-1.25%, Al 0.01-0.1%, Cr 0.1-1.0%, Ti 0.01-0.1%, B 0.001-0.004%, P≦0.020%, S≦0.010%, N≦0.010%, and optionally containing one or more of the following elements in weight percent: Ni≦0.5%, Mo≦0.40%, Nb≦0.08%, Ca≦0.1%, with the remainder of the composition being iron and unavoidable impurities resulting from smelting. In this composition range, the tensile strength of the corresponding area after hot stamping is higher than 1350 MPa and the bending angle is greater than 70°.

[0077] Steel having a composition in weight percent comprising: C: 0.2-0.34%, Mn: 0.50-1.24%, Si: 0.5-2%, P≦0.020%, S≦0.010%, N≦0.010%, and optionally containing one or more of the following elements in weight percent: Al≦0.2%, Cr≦0.8%, Nb≦0.06%, Ti≦0.06%, B≦0.005%, Mo≦0.35%, the remainder of the composition being iron and unavoidable impurities resulting from smelting. In this composition range, the corresponding steel after hot stamping has a tensile strength of 1000 MPa or more and a bending angle of greater than 55°.

[0078] - Steel having a composition comprising, in weight percent, C: 0.13-0.4%, Mn: 0.4-4.2%, Si: 0.1-2.5%, Cr≦2%, Mo≦0.65%, Nb≦0.1%, Al≦3.0%, Ti≦0.1%, B≦0.005%, P≦0.025%, S≦0.01%, N≦0.01%, Ni≦2.0%, Ca≦0.1%, W≦0.30%, V≦0.1%, Cu≦0.2%, which confirms the following combination: 114-68*C-18*Mn+20*Si-56*Cr-60*Ni-36*Al+38*Mo+79*Nb-17691*B<20, the remainder of the composition being iron and unavoidable impurities resulting from smelting. For example, the composition is used when hot stamping parts using a multi-step process.

[0079] - Steel coated with an aluminum-based metallic coating. By aluminum-based is meant a coating containing at least 50% aluminum by weight. For example, the metallic coating is an aluminum-based coating containing 8-12% Si by weight. For example, the metallic coating is applied by dipping the base material into a molten metal bath. Advantageously, applying an aluminum-based metallic coating avoids the formation of surface scale during the heating step of the hot stamping process, thereby making it possible to produce parts by hot stamping without a subsequent sandblasting operation. Furthermore, the aluminum-based coating also provides corrosion protection to the part while in service on the vehicle.

[0080] - Steel coated with an aluminum-based metallic coating consisting of 2.0 to 24.0% by weight of zinc, 1.1 to 12.0% by weight of silicon, optionally 0 to 8.0% by weight of magnesium, and optionally a further element selected from Pb, Ni, Zr, or Hf, the content by weight of each further element being less than 0.3% by weight, the remainder being aluminum and optionally unavoidable impurities. Advantageously, this type of metallic coating provides very good corrosion protection for the part as well as an excellent surface appearance after hot stamping.

[0081] In a particular embodiment, at least some of the elements constituting the outer reinforcing structure 12, 22 or the inner reinforcing structure 11, 21 are made by hot stamping a laser-welded blank comprising at least one sub-blank with an aluminum-based metal coating, said aluminum-coated sub-blank having been previously prepared by ablating at least part of the metal coating on the edges to be welded, thereby advantageously removing part of the aluminum present in the coating that would contaminate the weld seam and deteriorate its mechanical properties.

[0082] In a specific embodiment, at least some of the elements constituting the outer reinforcing structure 12, 22 or the inner reinforcing structure 11, 21 are produced by hot stamping a laser-welded blank including at least one sub-blank having at least one side on which an emissivity-enhancing top layer rests. The emissivity-enhancing top layer is applied to the outermost surface of the sub-blank. The emissivity-enhancing top layer allows the surface of the sub-blank to have a higher emissivity compared to the same sub-blank not coated with the emissivity-enhancing top layer. The emissivity-enhancing top layer may be applied to either the top or bottom side of the sub-blank. The emissivity-enhancing top layer may also be applied to both sides of the sub-blank. If the sub-blank includes a metal coating as described above, the emissivity-enhancing top layer is applied on top of the metal coating. In fact, for the emissivity-enhancing top layer to enhance the surface emissivity, it must cover the outermost surface of the sub-blank. Advantageously, the emissivity-enhancing top layer increases the heating rate of the sub-blank, thus increasing the productivity of the heating step of the hot stamping process. When using several sub-blanks of different thicknesses, said emissivity-enhancing top layer is advantageously applied to the thickest sub-blank, in order to reduce the difference in heating times between the different sub-blanks and thus increase productivity, the duration of the hot stamping process and, overall, to make it possible to obtain a final part with homogeneous surface properties.

Claims

1. A top cover assembly (1) for a battery pack (201) designed to be assembled to a battery tray assembly (2) that supports an energy storage unit (3) for an electric vehicle (200), comprising: - an upper cover (10) consisting of an upper plate (101) having a generally inverted tab shape and extending generally in a horizontal plane bounded by a left side wall (102L) and a right side wall (102R), and a front side wall (102F) and a rear side wall (102B), wherein the height of said side walls (102) in the upward direction is at least 0.5 times the height between the lowest point of the battery tray assembly (2) and the highest point of the upper cover assembly (1), and said side walls (102) are extended by four flanges (103) extending generally in the horizontal plane; an internal reinforcing structure (11) comprising at least one lateral internal reinforcing element (111) extending substantially laterally inside the top cover (10) between the left side wall (102L) and the right side wall (102R); an external reinforcing structure (12) comprising at least a left external reinforcing element (121L) and a right external reinforcing element (121R), each of said external reinforcing elements (121) comprising at least a side portion (1212) extending over at least a portion of the exterior of said left side wall (102L) and said right side wall (102R), whereby the surface area of ​​each of said external reinforcing side portions (1212) is at least equal to 0.75 times the surface area of ​​the corresponding side wall (102) over which said external reinforcing side portion (1212) extends; A top cover assembly (1) comprising:

2. 2. The top cover assembly (1) of claim 1, further comprising a rear outer reinforcing element (121B) and a front outer reinforcing element (121F), each comprising at least a side portion (1212) extending over at least a portion of the rear side wall (102B) and the front side wall (102F).

3. 3. A top cover assembly (1) according to claim 1 or 2, comprising at least two transverse inner reinforcing elements (111) spaced apart from one another in the longitudinal direction.

4. 4. The upper cover assembly (1) according to claim 1, wherein the inner reinforcing structure (11) further comprises a longitudinal reinforcing element (112) extending between the rear side wall (102B) and the transverse reinforcing element (111), and at least a longitudinal reinforcing element (112) extending between the front side wall (102F) and the transverse reinforcing element (111).

5. 5. The top cover assembly (1) according to claim 1, wherein the outer reinforcing structure (12) comprises at least one outer reinforcing element (121) further comprising a flange portion (1213) extending over at least a portion of a corresponding flange (103) of the top cover (10).

6. 6. The top cover assembly (1) according to claim 5, wherein the flange portion (1213) of at least one outer reinforcing element (121) comprises a closed section portion enclosing a hollow volume (1214).

7. 7. The top cover assembly (1) according to any one of claims 1 to 6, wherein the outer reinforcing structure (12) further comprises at least one outer corner reinforcement (123) attached between two adjacent outer reinforcing elements (121).

8. 8. The top cover assembly (1) according to claim 7, wherein the outer reinforcing structure (12) comprises four outer corner reinforcements (123) at all four corners of the outer reinforcing structure (12).

9. 9. The top cover assembly (1) according to any one of claims 1 to 8, wherein the inner reinforcing structure (11) comprises at least one inner corner reinforcement (113) located at a corner of the inner reinforcing structure (11) and attached to at least two portions of the top cover (10) extending in different planes.

10. 10. The top cover assembly (1) according to claim 9, wherein the inner reinforcing structure (11) comprises four inner corner reinforcements (113) at all four corners of said inner reinforcing structure (11).

11. A battery pack (201) for an electric vehicle, comprising: a top cover assembly (1) according to any one of claims 1 to 10; and a battery tray assembly (2) having an energy storage unit (3) mounted thereon, wherein the battery tray assembly (2) a battery tray (20) having a tray bottom (201) surrounded by side walls (202) and extended by a horizontal flange (203); an inner reinforcing structure (21) comprising at least a left inner lateral reinforcing element (211L) and a right inner lateral reinforcing element (211R) covering at least a part of the interior of the battery tray lower part (201) on its left and right sides, respectively; an external reinforcing structure (22) comprising at least a left lateral external reinforcing element (221L) and a right lateral external reinforcing element (221R) covering at least a part of the exterior of the corresponding side wall (202L), (202R); Equipped with A battery pack (201) wherein the top cover assembly (1) and the battery tray assembly (2) are attached together by at least their respective flanges (103), (203).

12. A process for manufacturing a battery pack (201) according to the present invention, comprising: - providing a top cover assembly (1) according to any one of claims 1 to 10, - providing a battery tray assembly (2) according to claim 11, having an energy storage unit (3) attached thereto; - attaching said top cover assembly (1) to said battery tray assembly (2) by fastening said top cover assembly (1) and said battery tray assembly (2) together at least along the flanges (103), (203) of said top cover assembly (1) and said battery tray assembly (2), respectively; A process including:

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