STRUCTURAL ASSEMBLY FOR AN ELECTRIC VEHICLE

Abstract

A structural assembly for an electric vehicle comprises a first and second longitudinal rail, a battery structure, and a retention element. The first longitudinal rail is positioned opposite the second longitudinal rail and defines a slot. The battery structure is located between the first and second longitudinal rails and is configured to accommodate two energy storage units. The battery structure includes a tab that extends laterally outward from a first side of the battery structure. The tab engages in the slot of the first longitudinal rail. The retention element engages the second longitudinal rail and the second side of the battery structure and is configured to secure the second side of the battery structure to the second longitudinal rail.

Description

AREA OF TECHNOLOGY

[0001] The present disclosure relates to a structural assembly for an electric vehicle. GENERAL STATE OF THE ART

[0002] The statements in this section merely provide background information relating to the present disclosure and may not represent the state of the art.

[0003] The desire to reduce the fuel consumption and emissions of automobiles is well-documented. Therefore, electric vehicles have been developed to significantly reduce reliance on internal combustion engines. Generally, electric vehicles differ from conventional motor vehicles in that they are powered by one or more rechargeable battery packs, which may contain, for example, lithium-ion batteries or any other suitable storage unit for electrical power. The battery pack typically supplies power to one or more motors to drive a set of wheels. The size and weight of the battery pack are typically greater for electric vehicles capable of long-distance travel (e.g., electric vehicles with a range exceeding 500 miles). Depending on its mounting location relative to the electric vehicle, the battery pack may be susceptible to various vehicle stresses.

[0004] Integrating rechargeable battery packs into the structure of existing vehicles and providing efficient load paths under a variety of operating conditions can be challenging, primarily due to the increased weight of the battery packs and their larger footprint within the vehicle. This disclosure addresses these problems related to the integration of rechargeable battery packs into electric vehicles. SUMMARY

[0005] This section provides a general summary of the revelation and is not a comprehensive revelation of its full scope or all of its features.

[0006] In one form, the present disclosure provides a structural assembly for an electric vehicle. The structural assembly includes a first and a second longitudinal rail, a battery structure, and a retaining element. The first longitudinal rail is located opposite the second longitudinal rail and defines a slot. The battery structure is positioned between the first and second longitudinal rails and is configured to accommodate two energy storage units. The battery structure includes a first lug that extends laterally outward from a first side of the battery structure. The first lug is received in the slot of the first longitudinal rail. The retaining element engages the second longitudinal rail and the second side of the battery structure and is configured to secure the second side of the battery structure to the second longitudinal rail.

[0007] In variations of the structural assembly described in the preceding paragraph, which may be implemented individually or in any combination, the following applies: the battery structure includes a battery carrier and a cover secured to the battery carrier; a variety of mechanical fasteners extend through the second longitudinal rail and the retaining element to secure the battery structure to the second longitudinal rail; the first longitudinal rail and the first lug do not include any mechanical fasteners; one shape of the first lug corresponds to one shape of the slot; the retaining element extends over the entire length of the battery structure;The battery structure includes a second nose extending laterally outward from a second side of the battery structure, the retaining element engaging the second longitudinal rail and the second nose such that the second nose is positioned between the retaining element and the second longitudinal rail; the retaining element includes an upper section that tapers inward; the battery structure includes a second nose extending laterally outward from a second side of the battery structure, the second nose including an edge corresponding to the tapered upper section of the retaining element; the retaining element includes a further upper end section that tapers inward; and the second longitudinal rail includes a further edge corresponding to the further tapered upper end section of the retaining element.

[0008] In another form, the present disclosure provides a structural assembly for an electric vehicle. The structural assembly includes a first and a second longitudinal rail, a battery structure, and a retaining element. The first longitudinal rail is located opposite the second longitudinal rail and defines a slot. The battery structure is positioned between the first and second longitudinal rails and is configured to accommodate two energy storage units. The battery structure includes a first lug extending laterally outward from a first side of the battery structure and a second lug extending laterally outward from a second side of the battery structure. The first lug is received in the slot of the first longitudinal rail.The retaining element engages the second longitudinal rail and the second lug of the battery structure and is configured to secure the second lug of the battery structure to the second longitudinal rail and the first lug of the battery structure to the first longitudinal rail. The slot of the first longitudinal rail defines a lower inclined surface, and the first lug includes an edge that corresponds to the lower inclined surface of the slot.

[0009] In variations of the structural assembly described in the preceding paragraph, which may be implemented individually or in any combination, the following applies: a plurality of mechanical fasteners extending through the second longitudinal rail and the retaining element to secure the battery structure to the second longitudinal rail; the first longitudinal rail and the first lug do not include any mechanical fasteners; the retaining element engages the second longitudinal rail and the second lug such that the second lug is positioned between the retaining element and the second longitudinal rail; the retaining element includes an upper section that tapers inwards; the second lug includes an edge corresponding to the tapered upper section of the retaining element; and the retaining element includes a further upper end section that tapers inwards;The second longitudinal rail includes another edge that corresponds to the further tapered upper end section of the retaining element.

[0010] In yet another form, the present disclosure provides a method for mounting a battery to a vehicle frame. The method includes moving the battery structure into a space defined between a first longitudinal rail and a second, opposing longitudinal rail of the vehicle frame, inserting a first lug extending laterally outward from a first side of the battery structure into a slot defined in the first longitudinal rail, moving a retaining element into engagement with the second longitudinal rail and a second side of the battery structure, and securing the retaining element to the second longitudinal rail.

[0011] In variations of the procedure described in the preceding paragraph, which may be implemented individually or in any combination, the following applies: securing the retaining element to the second longitudinal rail moves the first nose further into the slot of the first longitudinal rail, and securing the retaining element to the second longitudinal rail involves extending a plurality of mechanical fasteners through the second longitudinal rail and the retaining element.

[0012] Further areas of application will become apparent from the description provided in this document. It is understood that the description and specific examples serve only for illustration and are not intended to limit the scope of protection afforded by this disclosure. DRAWINGS

[0013] To fully understand the revelation, various forms of it will now be described by way of example with reference to the attached drawings, in which the following applies: Fig. Figure 1 is a schematic view of a vehicle comprising a battery housing assembly and a vehicle frame in accordance with the principles of the present disclosure; Fig. Figure 2 is a perspective view of a section of the vehicle frame and battery housing assembly. Fig. 1; Fig. Figure 3 is an exploded view of a section of the vehicle frame and battery housing assembly. Fig. 1; Fig. Figure 4 is a cross-sectional view of a section of the vehicle frame and battery housing assembly made of Fig. 1; Fig. Figure 5 is a perspective view of a section of the vehicle frame and a section of the battery housing assembly. Fig. 1, wherein a retaining element is shown separated from the section of the vehicle frame and the battery housing assembly; the Fig. Figures 6A-6D are cross-sectional views of the battery housing assembly. Fig. 1, which is attached to the vehicle frame Fig. 1 is mounted; and Fig. Figure 7 is a flowchart illustrating a method for mounting a battery housing assembly to a vehicle frame according to the principles of the present disclosure.

[0014] The drawings described in this document serve only for illustration and are not intended to limit the scope of the present disclosure in any way. DETAILED DESCRIPTION

[0015] The following description is merely exemplary and is not intended to limit the present disclosure, application, or uses. It is understood that reference numerals used throughout all drawings indicate identical or corresponding parts and features.

[0016] With reference to the Fig. 1 and Fig. Figure 2 provides a vehicle 10, such as an electric vehicle. In the example provided, the electric vehicle is a battery electric vehicle (BEV). In other examples, the electric vehicle could be, among others, a hybrid electric vehicle (HEV), a plug-in electric vehicle (PHEV), or a fuel cell vehicle. The vehicle 10 includes a vehicle frame 12, a battery housing assembly or battery structure 14, and an elongated retaining element 15 ( Fig. 2) The vehicle frame 12 is the main support structure of the vehicle 10, to which various components are attached either directly or indirectly. The vehicle frame 12 includes opposing longitudinal rails 18a, 18b. The rails 18a, 18b are spaced apart from each other and can define the length of the vehicle frame 12.

[0017] With reference to the Fig. 2-5 includes rail 18a with an L-shaped section 60, which provides a space 62 ( Fig. 4) defined, in which a section of the battery housing assembly 14 is included. The L-shaped section 60 includes a vertical wall 64a and a horizontal wall 64b extending perpendicularly from the vertical wall 64a. The vertical wall 64a is spaced from the battery housing assembly 14 and includes an outer surface 66a ( Fig. 4), which faces away from the battery housing assembly 14, and an inner side 66b ( Fig. 4), which faces the battery housing assembly 14. How best to in Fig. As shown in Figure 4, the inner surface 66b includes an inner surface or profile 68 that has a first vertical section 68a, a second vertical section 68b, and an inclined section 68c. The second vertical section 68b is located above the first vertical section 68a and above the inclined section 68c. The second vertical section 68b is also located further inward (i.e., closer to the battery housing assembly 15) than the first vertical section 68a. In the illustrated example, the first vertical section 68a extends over a greater distance in the vertical direction than the second vertical section 68b. In some forms, the second vertical section 68b extends over a greater distance in the vertical direction than the first vertical section 68a.The inclined section 68c is positioned between the first vertical section 68a and the second vertical section 68b and extends from the first vertical section 68a upwards and inwards to the second vertical section 68b.

[0018] The horizontal wall 64b extends inward from an upper end of the vertical wall 64a and covers an upper section or edge of the battery housing assembly 14. In the illustrated example, the horizontal wall 64b includes an upper side 70a facing away from the battery housing assembly 14 and a lower side 70b facing the battery housing assembly 14. The lower side 70b includes a lower surface or profile 72 that engages the upper section of the battery housing assembly 14. In the illustrated example, the lower surface 72 is flat. The horizontal wall 64b also includes a plurality of openings 75 ( Fig. 3), which extend through these. The openings 75 are aligned along the length of the rail 18a from a front end 83a of the rail 18a to a rear end 83b of the rail 18a.

[0019] With reference to Fig. Figure 4 includes the rail 18b with a section 79 having an outer surface 76a facing away from the battery housing assembly 14 and an inner surface 76b facing the battery housing assembly 14. The rail 18b includes a slot 78 formed therein, which receives a section of the battery housing assembly 14. The slot 78 opens to the inner surface 76b of the rail 18b. The slot 78 also defines a lower surface 80a and an upper surface 80b. In the illustrated example, the lower surface 80a is inclined and the upper surface 80b is flat. That is, the lower surface 80a slopes upward and outward from the inner surface 76b of the rail 18b to the outer surface 76a of the rail 18b. In some forms, the lower surface 80a may be flat and the upper surface 80b may be inclined. In other configurations, the lower surface 80a can be inclined and the upper surface 80b can also be inclined.

[0020] In some embodiments, the L-shaped section 60 can be a separate component secured to the rail 18a using mechanical fasteners, adhesives, or any other suitable fastening means. Likewise, the section 79 can be a separate component secured to the rail 18b using mechanical fasteners, adhesives, or any other suitable fastening means. In this way, the structural assembly of the present disclosure can be retrofitted to already manufactured electric vehicles. In the illustrated example, the electric vehicle is a ladder-frame vehicle. In some embodiments, the electric vehicle can have a unibody architecture, in which the L-shaped section 60 and the section 79 are, for example, part of sills or sleepers.

[0021] With renewed reference to Fig. 1 The battery housing assembly 14 supplies power to a rear electric motor (not shown) to drive rear wheels 20a, 20b of a set of rear wheels 20 via a rear axle. Likewise, the battery housing assembly 14 supplies power to a front electric motor (not shown) to drive front wheels 24a, 24b of a set of front wheels 24 via a front axle.

[0022] With reference to the Fig. 2, Fig. 3 and Fig. Figure 5 includes the battery housing assembly 14, comprising one or more battery banks or power storage units (not shown) and a battery carrier or battery housing 28. The battery housing 28 is an enclosure that provides a structurally surrounding and sealed compartment for the battery banks and other battery components, such as cooling lines, retaining clips, and wiring, located within it. The battery banks may be rechargeable and may contain lithium-ion batteries or any other suitable electrical power storage units. In some forms, the battery banks are stacked on top of each other.

[0023] The battery housing 28 can be located at various points on the vehicle 10 and is mounted on the vehicle frame 12. In this way, the battery housing 28 is supported by the vehicle frame 12 and is located away from the passenger compartment (not shown) and cargo compartments (not shown) of the vehicle 10, thus not occupying any space that would otherwise be available for passengers or cargo. In the illustrated example, the battery housing 28 is located between the rails 18a, 18b and includes a cover or lid 38 (shown schematically), a body 40, and a seal (not shown). The cover 38 is removably coupled to the body 40 by mechanical fasteners, such as bolts or screws (not shown). This allows the cover 38 to be removed for maintenance of the battery banks located inside the battery housing 28.

[0024] The body 40 comprises a bottom wall or plate 48 and one or more side walls or plates 50. The bottom wall 48 supports the battery banks arranged within the battery housing 28 and is attached to the lower sections of the side walls 50. For example, the bottom wall 48 is secured to the lower parts of the side walls 50 by welding, adhesive, or any other suitable fastening method. The side walls 50 are manufactured, for example, by stamping and extend in a vertical direction. The side walls 50 define an outer boundary of the body 40 and are joined to one another, for example, by welding or adhesive. The gasket is arranged around the circumference of the side walls 50 of the battery housing 28 and engages with the side walls 50 and the cover 38. This prevents fluids, dirt, and other materials from entering the battery housing 28.

[0025] The battery housing 28 includes a first lug 52 and a second lug 54. The first lug 52 extends laterally outwards from a first side of the battery housing 28 and is received in the space 62 of the rail 18a. In the illustrated example, the first lug 52 is spaced from the inner surface 68 of the rail 18a and engages with the retaining element 15, as described in more detail below. As is best done in Fig. As shown in Figure 4, the first lug 52 comprises an upper surface 58a, a vertical surface 58b, and an inclined surface 58c. The upper surface 58a is flat and engages the lower surface 72 of the rail 18a. The vertical surface 58b is located above the inclined surface 58c and above the retaining element 15. The inclined surface 58c extends upward and outward from the side wall 50 of the battery housing 28 to the vertical surface 58b. The inclined surface 58c engages the retaining element 15, so that the second lug 54 of the battery housing 28 is driven or pressed into the slot 78 of the rail 18b, as described in more detail below.

[0026] The second lug 54 extends laterally outward from a second side of the battery housing 28 and is securely received in the slot 78 of the rail 18b. In this way, the battery housing 28 is attached to the rail 18b without mechanical fasteners, as described in more detail below. The second lug 54 includes a top surface 82a, a vertical surface 82b, and an inclined surface 82c. The top surface 82a engages the top surface 80b of the slot 78 and has a shape that corresponds to the shape of the top surface 80b of the slot 78. In the illustrated example, the top surface 82a is flat to match the flat surface of the top surface 80b of the slot 78. The vertical surface 82b is located above the inclined surface 82c. The inclined surface 82c engages the lower surface 80a of the slot 78 and has a shape that corresponds to the shape of the lower surface 80a of the slot 78.The inclined surface 82c extends upwards and outwards from the side wall 50 of the battery housing 28 to the vertical surface 82b.

[0027] In some forms, the first and second noses 52, 54 are formed by a combination of the cover 38 and the body 40 (e.g., the cover 38 forms sections of the upper surfaces 58a, 82a of the first and second noses 52, 54, respectively). In other forms, the first and second noses 52, 54 are formed only by the body 40 (e.g., the cover 38 does not form sections of the upper surfaces 58a, 82a of the first and second noses 52, 54, respectively).

[0028] With reference to the Fig. 3-5 The retaining element 15 is made of a metal material, such as aluminum, and is located internally relative to the vertical wall 64a of the rail 18a. In other words, the retaining element 15 is positioned between the vertical wall 64a of the rail 18a and the battery housing 28. In the illustrated example, the retaining element 15 extends over the entire length of the battery housing 28 ( Fig. 3 and Fig. 5) In some forms, the retaining element 15 extends only over a section of the battery casing 28.

[0029] In the illustrated example, the retaining element 15 is a solid structure and generally has a rectangular shape. In some forms, the retaining element 15 may include a hollow structure. In the illustrated example, the retaining element 15 includes a planar top surface 84 and a pair of top end sections or end faces 86. The retaining element 15 also includes a reduced cross-sectional area near the end that is attached to the rail 18a (e.g., near the top end). A variety of mechanical fasteners 83 ( Fig. 2) extends through the planar upper surface 84 and the horizontal wall 64b of the rail 18a, thereby securing the retaining element 15 to the rail 18a. In some forms, the upper wall 84 is, for example, arcuate or curved instead of planar. When the retaining element 15 and the rail 18a are secured to one another, the planar upper surface 84 is spaced from the horizontal wall 64b of the rail 18a, and the pair of upper end sections 86 engage the inclined surfaces 58c, 68c. The upper end sections 86 are tapered inwards and have a shape that corresponds to the surfaces 58c, 68c. In this way, when the retaining element 15 is secured to the rail 18a, it can drive or push the second lug 54 of the battery housing 28 into the slot 78 of the rail 18b.

[0030] The upper end sections 86 of the retaining element 15 offer the advantage of facilitating the coupling of the battery housing 28 to the rail 18b without the use of mechanical fasteners extending through the rail 18b and the battery housing 28. This reduces the number of mechanical fasteners used to secure the battery housing 28 to the vehicle frame 12. In the illustrated example, the upper end sections 86 of the retaining element taper along the entire length of the retaining element 15. In some configurations, the upper end sections 86 of the retaining element 15 taper only at opposite ends of the retaining element 15.In other configurations, the upper end sections 86 of the retaining element 15 taper along some sections of the retaining element 15 and are, for example, square-cut along other upper end sections of the retaining element.

[0031] With reference to the Fig. 6A-6D and Fig. In section 7, a method 100 for mounting the battery housing assembly 14 to the vehicle frame 12 is described in detail. In section 104, the battery housing assembly 14 is moved into a space between the rail 18a and the rail 18b of the vehicle frame 12 ( Fig. 6A). At 108, the second lug 54 of the battery housing assembly 14 is inserted into the slot 78 of the rail 18b ( Fig. 6B). The first lug 52 of the battery housing assembly 14 engages the lower surface 72 of the rail 18a, thereby allowing the second lug 54 to align with the slot 78 of the rail 18b. In this way, the battery housing assembly 14 can be moved laterally relative to the rail 18b so that the second lug 54 is at least partially engaged within the slot 78 of the rail 18b.

[0032] At 112, the retaining element 15 is moved into engagement with the rail 18a and the battery housing assembly 14 ( Fig. 6C). In other words, the retaining element 15 engages the rail 18a and the battery housing assembly 14 such that one upper end section 86 of the retaining element 15 contacts the inclined surface 58c of the nose 52 and the other upper end section 86 of the retaining element 15 contacts the inclined surface 68c of the rail 18a. In this way, the retaining element 15 can laterally drive or push the battery housing assembly 14 so that the second nose 54 of the battery housing 28 is moved further into the slot 78 of the rail 18b, while the first nose 52 is securely held between the retaining element 15 and the rail 18a. In some forms, the second nose 54 and the slot 78 may have an interference fit, thus preventing the second nose 54 from being removed from the slot 78.

[0033] At 116, the retaining element 15 is secured to the rail 18a ( Fig.6D), thereby allowing the second lug 54 to be moved further into the slot 78 of the rail 18b. In the illustrated example, the mechanical fasteners 83 extend through the retaining element 15 and the horizontal wall 64b of the rail 18a, securing the retaining element 15 to the rail 18a. The present disclosure involves securing the retaining element 15, which has a predetermined shape, to the rail 18a using mechanical fasteners 83, which can further press the second lug 54 into the slot 78, thereby retaining the lug 54 in the slot 78. In this way, the battery housing assembly 14 is coupled to the rail 18b without the use of mechanical fasteners, thus reducing the number of mechanical fasteners used to secure the battery housing assembly 14 to the vehicle body frame 12.

[0034] Unless expressly stated otherwise in this document, all numerical values ​​indicating mechanical / thermal properties, percentages of compositions, dimensions and / or tolerances, or other parameters are to be understood as modified by the word "approximately" or "about" when describing the scope of this disclosure. This modification is desirable for various reasons, including industrial practice, material, manufacturing and assembly tolerances, and testability.

[0035] As used herein, the phrase "at least one of A, B and C" should be interpreted as meaning a logical (A OR B OR C) using a non-exclusive logical OR, and should not be interpreted as meaning "at least one of A, at least one of B and at least one of C".

[0036] The description of the revelation is merely exemplary, and therefore variations that do not deviate from the core of the revelation should be considered within its scope. Such variations are not to be regarded as a deviation from the nature and scope of the revelation.

[0037] According to the present invention, a structural assembly for an electric vehicle is provided, comprising: a first longitudinal rail and a second longitudinal rail opposite the first longitudinal rail, wherein the first longitudinal rail defines a slot; a battery structure arranged between the first longitudinal rail and the second longitudinal rail and configured to accommodate power storage units, wherein the battery structure includes a first lug extending laterally outward from a first side of the battery structure and a second lug extending laterally outward from a second side of the battery structure, the first lug being received in the slot of the first longitudinal rail;and a retaining element that engages the second longitudinal rail and the second lug of the battery structure and is configured to secure the second lug of the battery structure to the second longitudinal rail and the first lug of the battery structure to the first longitudinal rail, wherein the slot of the first longitudinal rail defines a lower inclined surface and the first lug includes an edge corresponding to the lower inclined surface of the slot.

[0038] According to one embodiment, the invention is further characterized by a plurality of mechanical fastening elements extending through the second longitudinal rail and the retaining element to secure the battery structure to the second longitudinal rail.

[0039] According to one embodiment, the first longitudinal rail and the first nose do not include any mechanical fastening elements.

[0040] According to one embodiment, the retaining element engages the second longitudinal rail and the second nose, such that the second nose is arranged between the retaining element and the second longitudinal rail.

[0041] According to one embodiment, the retaining element includes an upper section that tapers inwards.

[0042] According to one embodiment, the second nose includes an edge that corresponds to the upper section of the retaining element.

[0043] According to one embodiment, the retaining element includes a further upper end section that tapers inwards, and wherein the second longitudinal rail includes a further edge corresponding to the further upper end section of the retaining element.

Claims

[1] Structural assembly for an electric vehicle; wherein the structural assembly comprises: a first longitudinal rail and a second longitudinal rail opposite the first longitudinal rail, wherein the first longitudinal rail defines a slot; a battery structure arranged between the first longitudinal rail and the second longitudinal rail and configured to accommodate power storage units, the battery structure including a first nose extending laterally outward from a first side of the battery structure, the first nose being received in the slot of the first longitudinal rail; and a retaining element that engages the second longitudinal rail and a second side of the battery structure and is configured to secure the second side of the battery structure to the second longitudinal rail. [2] Structural assembly according to claim 1, wherein the battery structure includes a battery carrier and a cover attached to the battery carrier. [3] Structural assembly according to claim 1, further comprising a plurality of mechanical fastening elements extending through the second longitudinal rail and the retaining element to secure the battery structure to the second longitudinal rail. [4] Structural assembly according to claim 3, wherein the first longitudinal rail and the first nose do not include any mechanical fastening elements. [5] Structural assembly according to claim 1, wherein a shape of the first nose corresponds to a shape of the slot. [6] Structural assembly according to claim 1, wherein the retention element extends over the entire length of the battery structure. [7] Structural assembly according to claim 1, wherein the battery structure includes a second nose extending laterally outwards from a second side of the battery structure, and wherein the retaining element engages the second longitudinal rail and the second nose, such that the second nose is arranged between the retaining element and the second longitudinal rail. [8] Structural assembly according to claim 1, wherein the retaining element includes an upper section that tapers inwards. [9] Structural assembly according to claim 8, wherein the battery structure includes a second nose extending laterally outwards from a second side of the battery structure, and wherein the second nose includes an edge corresponding to the upper section of the retaining element. [10] Structural assembly according to claim 9, wherein the retaining element includes a further upper end section which tapers inwards and wherein the second longitudinal rail includes a further edge which corresponds to the further upper end section of the retaining element. [11] Structural assembly according to claim 1, wherein the slot of the first longitudinal rail defines a lower inclined surface and the first nose includes an edge corresponding to the lower inclined surface of the slot. [12] Method for mounting a battery structure on a vehicle frame, the method comprising: Moving the battery structure into a space defined between a first longitudinal rail and a second opposing longitudinal rail of the vehicle frame; Inserting a first nose extending laterally outwards from a first side of the battery structure into a slot defined in the first longitudinal rail; Moving a retaining element into engagement with the second opposing longitudinal rail and a second side of the battery structure; and Securing the retaining element to the second opposite longitudinal rail. [13] Method according to claim 12, wherein securing the retaining element to the second opposite longitudinal rail moves the first nose further into the slot of the first longitudinal rail. [14] Method according to claim 12, wherein securing the retaining element to the second opposite longitudinal rail comprises extending a plurality of mechanical fastening elements through the second opposite longitudinal rail and the retaining element.

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