Rear wedge device, releasable by rear impact, to increase the compressible efficiency of the structure

Description

[0001] The invention relates to the field of passive vehicle safety equipment. In particular, the invention relates to the field of protecting vehicles against rear-end collisions.

[0002] Current regulations require motor vehicle manufacturers to comply with certain safety constraints and to carry out tests in order to obtain the approvals necessary for their marketing. Thus, regulations in Europe, Japan and most countries around the world require the vehicle to be sized for a rear impact in which the vehicle is struck by a rigid barrier at a speed of 50 km / h. In the United States, the rear impact protocol is more stringent. In this protocol, the vehicle is struck from the rear by a 1368 kg NHTSA (National Highway Traffic Safety Administration) type barrier at high speed (80 km / h) and on an offset overlap zone, i.e. with 70% overlap of the vehicle width as measured at the rear right axle. These are therefore high-energy impacts, with a very stiff, large barrier that is very aggressive for the vehicle.

[0003] Furthermore, the development of hybrid vehicles comprising both an electric and a thermal engine may be accompanied by a new design of the vehicle structure, particularly at the level of the underbody and, for example, at the level of the rear part of this underbody. In certain cases, the installation of an electric motor at the rear of the vehicle may be accompanied by a change of the rear axle in favor of a multi-link axle with four attachment points on the side members and which may serve as a frame for said electric motor.

[0004] The use of a multi-link rear axle in the context of a hybrid vehicle is described in document FR3049920. This document relates to an arrangement of the rear part of an underbody structure for a plug-in hybrid motor vehicle comprising a rear cradle extended at each of its ends by two arms, front and rear, on which fixing points allow the cradle to be fixed to the bodywork and to the rear axle. The components of the vehicle include a low-voltage battery, a high-voltage battery, a battery charger, a fuel tank and an exhaust silencer which are arranged at the level of said rear part of the underbody structure.The position of the attachment points of the rear arms of the rear cradle define a reference position in the longitudinal direction of the vehicle, at the rear of which said exhaust silencer is arranged, and at the front of which the other aforementioned components of the vehicle are arranged.

[0005] Unfortunately, the use of such a multi-link rear axle limits the possibilities of deformation of the side members, reduces the energy absorption potential of the rear structure and therefore degrades the performance of the vehicle in the event of a high-speed rear collision. A solution remains to be found to address this problem.

[0006] Documents US 2020 / 102014 A1 and EP 3 069 962 A1 describe electrically powered motor vehicles comprising a pair of side members and a rear subframe.

[0007] The invention aims to address at least one of the problems or drawbacks encountered in the prior art. The invention therefore aims to propose a hybrid-powered vehicle comprising both a multi-link rear axle and improved high-speed rear impact damping performance. In particular, the invention aims to propose a hybrid-powered vehicle comprising both a multi-link rear axle and means for improving the vehicle's behavior in terms of compressibility of the rear underbody structure; preferably, said means are passive means.

[0008] To this end, and according to a first aspect, the invention relates to a motor vehicle with an electric or hybrid engine comprising a pair of side members and a rear cradle arranged to support an electric propulsion unit, the rear cradle comprises a central zone extending in the transverse direction of the vehicle and extended at each of its ends by two arms, respectively a front arm and a rear arm, the rear cradle is fixed to the side members by its front and rear arms; the vehicle is remarkable in that the fixing of each of the rear arms of the rear cradle on the side members is done by means of a fixing device in two parts configured to separate under the action of a tensile force greater than a predetermined threshold.

[0009] As will be understood from reading the definition just given, the invention allows a break in the attachment between the rear cradle and the side members at the rear arms of said rear cradle by the use of a fixing device in two parts assembled together which can, under certain conditions, detach from each other. The break in the rear attachment devices of the rear cradle allows the side member to continue its deformation and therefore improves the vehicle's ability to absorb impacts by increasing the compressibility of said structure during a rear collision. The invention thus makes it possible to reduce the size of the rear overhang of the vehicle thanks to the increase in the compressibility of the structure. In addition, the cost of the vehicle is not increased.

[0010] According to a preferred embodiment of the invention, the two parts are configured to separate under the action of a tensile force greater than a predetermined threshold, said tensile force being oriented in the longitudinal direction of the fixing device which is preferably oriented vertically. Thus, preferably, the fixing device is in two parts configured to separate under the action of a tensile force greater than a predetermined threshold, said tensile force being oriented vertically. Indeed, it has been observed that during a rear collision the side members tend to straighten while the rear cradle tends to flex towards the side. It will be understood that the separation kinematics in the vertical direction between the cradle and the side members only occurs in the event of high-speed impacts.The fastening device according to the invention takes advantage of this observation and is therefore made fusible in this direction. The fastening device according to the invention is remarkable in that it is suitable for being fusible under the conditions of a high-speed rear-end collision of a vehicle but not under normal vehicle driving conditions.

[0011] According to a preferred embodiment of the invention, the fixing device comprises an external part and an internal part, the external part forming a housing and the internal part comprising at least one block, the block(s) being arranged in the housing.

[0012] Thus, another definition of the invention will read: a motor vehicle with electric or hybrid motorization comprising a pair of side members and a rear cradle arranged to support an electric propulsion unit, the rear cradle comprises a central zone extending in the transverse direction of the vehicle and extended at each of its ends by two arms, respectively a front arm and a rear arm, the rear cradle is fixed to the side members by its front and rear arms; the vehicle is remarkable in that the fixing of each of the rear arms of the rear cradle on the side members is done by means of a two-part fixing device; one of the parts being fixed to a rear arm of the rear cradle and the other part being fixed to a side member;preferably, the fixing device comprises an external part and an internal part, the external part forming a housing and the internal part comprising at least one block, the block or blocks being arranged in the housing and the external part being fixed to a rear arm of the rear cradle.;

[0013] It will be noted that two-part fixing devices are known and used in the context of damping vibrations generated by the rolling of a vehicle. Thus, document US7104533 discloses a cylindrical vibration damping device comprising a rubber bushing having an elastic rubber body elastically connecting an inner sleeve and an outer sleeve made of resin; a rigid mounting member having a cylindrical bore into which the rubber bushing is press-fitted; an engaging stepped face formed on an inner surface of the mounting member; and an engaged stepped face produced on an outer surface of the outer sleeve once the outer sleeve is press-fitted into the cylindrical bore of the mounting member, by means of elastic deformation of the outer sleeve.The engaged stepped face opposes the engaging stepped face in an axial direction of the device, and is brought into engagement with the engaging stepped face so as to provide resistance to dislodgement of the rubber bushing from the mounting member in opposite axial directions.

[0014] Similarly, JP5291981 discloses a device for preventing generation of abnormal sound by contact between an outer cylinder and a sleeve. The sleeve mounting structure of a vibration control device is formed by frictionally engaging an outer peripheral surface of the outer cylinder with an inner peripheral surface of the sleeve, pressing the vibration control device having the outer cylinder and a rubber elastic body secured to an inner peripheral surface of this outer cylinder, into the sleeve under diametrically contracted deformation of the outer cylinder. The pressed-on length of the synthetic resin outer cylinder sleeve is formed shorter than the length in the axial direction of the sleeve.A projection strip protruding outward in the radial direction and extending in the peripheral direction of the outer cylinder is formed in an end portion of the sleeve on a tip outer peripheral surface in the driving direction.

[0015] As will be seen in detail, the invention differs from the devices described above, in particular in its function, since the dislodgement of the internal part is desired to promote the compressibility of the rear structure, but also in its structure, since the invention proposes an architecture allowing adjustment of the force necessary for the dislodgement of the internal part. Finally, the invention differs from the prior art by the installation of said fixing device at the interface between the rear cradle and the side members.

[0016] As will be understood, advantageously, the fixing device comprises two parts and one of the parts is fixed to one of the rear arms of the rear cradle and the other part is fixed to one of the side members.

[0017] Thus, preferably, the fixing device comprises an external part and an internal part and the external part is fixed to one of the rear arms of the rear cradle and the internal part is fixed to one of the side members by means of an axis; preferably, the axis has a diameter greater than or equal to 9 mm.

[0018] Alternatively, the fixing device comprises an external part and an internal part and the external part is fixed to one of the side members and the internal part is fixed to one of the rear arms of the rear cradle by means of an axle; preferably, the axle has a diameter greater than or equal to 9 mm.

[0019] Regardless of the configuration chosen, the fixing device preferably comprises an external part and an internal part, and the external part comprises at least one side wall and further comprises an upper wall and a lower wall and at least the upper wall and / or the lower wall comprises an opening for the passage of an axle.

[0020] According to one implementation of the invention, the ratio between the diameter of the opening shown by the upper wall and / or the lower wall and the diameter of the or at least one of the blocks is between 0.60 and 0.95; preferably between 0.75 and 0.90.

[0021] Additionally or alternatively, the opening shown by the upper wall and / or the lower wall is circumvented by a chamfer forming an angle with the side wall(s) of between 30 and 60°; preferably of between 30 and 45°.

[0022] Advantageously, the upper and / or lower wall is assembled to the side wall(s) by fixing screws; preferably, by at least three fixing screws.

[0023] Optionally, the upper or lower wall is joined to the side wall(s) by up to three fixing screws. This configuration allows separation of the upper wall or the lower wall under the pressure exerted by the block(s) and therefore the dislodgement of the internal part, taking with it one of the upper or lower walls.

[0024] According to a preferred embodiment of the invention, the fixing device comprises an external part and an internal part, the internal part comprising at least one block and the block(s) are made of a deformable elastic material chosen from the list comprising cis 4-polyisoprene, synthetic polyisoprene, polybutadiene, styrene-butadiene copolymer, polyisobutylene, chloroprene, butadiene-acrylonitrile copolymer, ethylene-propylene copolymer, terpolymer, polyether block amide, thermoplastic elastomers, polyurethanes, polysulfides, silicone elastomers, fluoroelastomers, perfluoroelastomers, ethylene-vinyl acetate copolymer, polyacrylic elastomers, chlorosulfonated polyethylene, epichlorohydrin elastomers; preferably chosen from the list including silicone elastomers, thermoplastic elastomers and polyurethanes.

[0025] Preferably, the fixing device comprises an external part and an internal part, the internal part comprising at least one block and the block(s) are mounted on an axis and held in position on said axis by at least one ring.

[0026] According to a second aspect, the invention relates to the use of a fixing device for fixing a rear arm of a multi-link rear cradle to a side member of a motor vehicle with an electric or hybrid engine, the use being remarkable in that the fixing device comprises two parts, respectively an external part and an internal part, the external part forming a housing and the internal part comprising at least one block, the block or blocks being arranged in the housing; the two parts being configured to separate under the action of a tensile force greater than a predetermined threshold; preferably, said tensile force is oriented vertically.

[0027] The invention will be well understood and other aspects and advantages will appear clearly on reading the following description given with reference to the attached drawings in which: [ Fig. 1 ] There figure 1 is a bottom view of a vehicle according to the invention. Fig. 2 ] There figure 2 illustrates the breaking kinematics of the fixing devices according to the invention. Fig. 3 ] There figure 3 is a perspective sectional view of the external part of the fixing device according to the invention. Fig. 4 ] There figure 4 is a view similar to that of the figure 3 in which the inner part was added. [ Fig. 5 ] There figure 5 is a sectional view of a fixing device according to the invention. Fig. 6 ] There figure 6 is a view similar to that of the figure 5 showing the compression deformation of a fixing device according to the invention. Fig. 7 ] There figure 7 illustrates the possibilities of deformation of the internal part. Fig. 8 ] There figure 8 is a view similar to that of the figure 5 showing the breaking kinematics of a fixing device according to the invention. [ Fig. 9 ] There figure 9 is a view similar to that of the figure 8 showing the continuation of the breaking kinematics of a fixing device according to the invention.

[0028] In the following description, the term "comprise" is synonymous with "include" and is not limiting in that it allows the presence of other elements or means in the vehicle to which it relates, or other steps in the use considered. It is understood that the term "comprise" includes the terms "consist of". Similarly, the terms "interior", "exterior", "front", "rear" will be understood in relation to the general orientation of the vehicle, as taken in its normal direction of travel. In the different figures, the same references designate identical or similar elements.

[0029] There figure 1 illustrates the general architecture of a vehicle 1 according to the invention as seen from below and in its rear part. The vehicle is a motor vehicle 1 with electric or hybrid motorization comprising a pair of side members 3 and a rear cradle 5 arranged to support an electric propulsion unit 7. The rear cradle 5 comprises a central zone extending in the transverse direction of the vehicle and extended at each of its ends by two arms (9, 11), respectively a front arm 9 and a rear arm 11. The rear cradle 5 is fixed to the side members 3 by its arms (9, 11). The side members 3 are connected to the rear bumper beam 13 of the vehicle by means of absorbers 15, and are designed to deform in the event of a sudden impact, so as to absorb the kinetic energy of the impact.

[0030] The invention is remarkable in that the fixing of at least one of the rear arms 11 and preferably of each of the rear arms 11 of the rear cradle 5 on the side members 3 is done by means of a fixing device 17 in two parts (19, 29) configured to separate under the action of a tensile force greater than a predetermined threshold; preferably, said tensile force is oriented vertically.

[0031] It will be understood that advantageously, the fixing device comprising two parts, one of the parts is fixed to one of the rear arms of the rear cradle and the other part is fixed to one of the side members.

[0032] According to a preferred implementation of the invention, the fixing devices 17 are in two parts (19, 29) configured to separate under the action of a tensile force greater than a predetermined threshold, said tensile force being oriented vertically. Indeed, it has been observed that during the kinematics of the rear impact the fixings of the rear arms 11 of the cradle are first stressed in compression, due to contact with the element with which the vehicle collided. Then, the fixing devices are stressed in traction in the vertical direction due to the straightening of the side members following their deformation and the downward bending of the rear cradle.

[0033] The invention takes advantage of this impact kinematics to make the fixing device(s) 17 fusible in the vertical direction, namely when they are subjected to a vertically oriented tensile force greater than a predetermined threshold value. The tensile force tends to separate the side members of the rear cradle in the vertical direction in order to allow the side members to impact. The gap between the rear cradle 5 and the side members 3 at the rear arms during an impact is illustrated in figure 2 It is understood that the fixing device opened, one part of the fixing device remained fixed to the side member while the other part remained attached to the rear cradle.

[0034] According to a preferred embodiment illustrated in figures 3 à 9 , the fixing devices 17 used for fixing the rear arms of the multi-arm cradle to the side member, comprise two parts (19, 29) respectively an external part 19 and an internal part 29, the external part 19 forming a housing and the internal part 29 comprising at least one block, the block or blocks being arranged in the housing.

[0035] There figure 3 represents the external part 19 of the fixing device. The external part 19 comprises at least one side wall 21 and further comprises an upper wall 23 and a lower wall 25. In the illustrated embodiment, the external part 19 comprises a cylindrical side wall 21. Advantageously, at least the upper wall 23 and / or the lower wall 25 comprises an opening for the passage of an axis 31 (represented in figures 4 et 5 ). The axis is advantageously of a diameter greater than or equal to 9 mm, for example 10 and 15 mm, to ensure solid fixing. It is understood that the external part 19 forms a housing which will receive the internal part 29 comprising at least one block as illustrated in figures 4 et 5 In the remainder of the description, reference will be made to an internal part 29 comprising a single block, however, those skilled in the art will easily adapt the following description to an internal part comprising two or more blocks.

[0036] The external part 19 is preferably made of a metallic material, for example steel. Advantageously, at least one of the upper 23 or lower 25 walls is assembled to the side wall(s) 21 by screwing, in order to allow the assembly of the fixing device and in particular the insertion of the internal part 29 into the housing.

[0037] Indeed, the internal part is of a size less than or equal to the size of the housing but shows a diameter greater than the size of the openings shown at the upper wall 23 and / or the lower wall 25 of the housing. Thus, the diameter D5 of the internal part is less than or equal to the internal diameter D2 of the external part, preferably less than 2 to 20%; more preferably, less than 4 to 15% or 6 to 10%. Thus the diameter D5 of the internal part is greater than or equal to the diameter D1 of the opening of the external part, preferably greater than 2 to 20%; more preferably, greater than 4 to 15% or 6 to 10%. The housing therefore constitutes a cage in which the block is enclosed. The block is mounted on an axis 31 passing through the opening of the upper wall 23 and / or the lower wall 25 of the housing, in the case of a plurality of blocks, the different blocks follow one another along the axis.The block is held in position on said axis 31 by at least one ring (33, 35) and preferably by two rings (33, 35), namely an upper ring 33 and a lower ring 35.

[0038] The block(s) 29 are preferably made of a deformable elastic material, for example a material chosen from the list comprising cis 4-polyisoprene, synthetic polyisoprene, polybutadiene, styrene-butadiene copolymer, polyisobutylene, chloroprene, butadiene-acrylonitrile copolymer, ethylene-propylene copolymer, terpolymer, polyether block amide, thermoplastic elastomers, polyurethanes, polysulfides, silicone elastomers, fluoroelastomers, perfluoroelastomers, ethylene-vinyl acetate copolymer, polyacrylic elastomers, chlorosulfonated polyethylene, epichlorohydrin elastomers. Preferably, the block(s) 29 are preferably made of a material chosen from the list comprising silicone elastomers, thermoplastic elastomers and polyurethanes. More preferably, the block(s) 29 are preferably made of polyurethane.

[0039] The use of an elastomeric material, capable of deformation, offers several advantages, such as absorption of vibrations and damping of stresses when the vehicle is moving.

[0040] According to the invention, the fixing device 17 acts as a fusible interface between the rear cradle and the side member. In a preferred implementation of the invention, the housing is fixed to the cradle and the axis carrying the block is fixed to the side member. The reverse configuration in which the housing is fixed to the side member and the axis carrying the block is fixed to the cradle is also possible.

[0041] Regardless of the configuration chosen, the fusible attachment device operates as follows. In normal operation, the inner part 29 (i.e. the block(s)) is arranged in the housing formed by the outer part 19. The inner part 29 is retained in said housing ensuring the attachment between the side member and the rear subframe. In the event of a rear impact, as illustrated in figure 6 , the presence of the internal part inside the external part will contribute to the resistance of the fixing device which is first subjected to compression. In fact, the external part sees its initial diameter D3 reduced to a compressed diameter D4. Advantageously, the narrowed diameter D4 is approximately 10% lower than the initial diameter. The internal part 29 is preferably also compressed in its transverse direction as illustrated in the figure 7 and begins a deformation in its longitudinal direction, which will allow it to begin its exit from the housing.

[0042] If the impact is sufficiently violent to generate a separation between the side members and the rear cradle, vertical tensile forces in opposite directions are then applied to the internal and external parts. The internal part 29 is then extracted from the housing through one of the openings allowing the passage of the axis 31 as illustrated in the figures 8 And 9 Once the internal part is out of the housing the fixing is broken and the spar can continue its deformation.

[0043] This break or disconnection between the internal and external parts can be done in several ways. In one embodiment illustrated in figures 8 And 9, the block will deform to exit the housing through the opening in the upper wall of the external part. In the case, not shown, where the axle is fixed to the rear cradle, the internal part (i.e. the block) will deform to exit the housing through the opening in the lower wall of the external part.

[0044] The exit of the internal part 29 of the housing through one of the openings assumes a solid fixing between the upper and / or lower walls of the external part and the side wall(s). This solid fixing can be obtained by the use of four or more fixing screws between the upper or lower wall and the side wall(s). In an embodiment not shown, one of the upper or lower walls is integral with the side wall so that it cannot be disassembled.

[0045] In an embodiment not shown, when three or fewer fixing screws are used, the outer part can be disassembled and the inner part can come out of the housing, taking with it the upper wall or the lower wall depending on the chosen configuration, without passing through its opening.

[0046] In the embodiments in which the internal part passes through the opening of one of the lower or upper walls to exit the housing, the person skilled in the art will benefit from placing a chamfer 27 between the side wall 21 and the upper wall 23 (or lower wall 25 as the case may be) inside the housing. The presence of a chamfer 27 makes it possible to initiate and facilitate the deformation of the block(s) forming the internal part 29 as it passes through the opening of the upper wall 23 or lower wall 25 of the external part 19.

[0047] The force required to break the fixing device 17, in this case, in the example illustrated, the force required to separate the internal 29 and external 19 parts by the passage of the block through the opening in the upper wall, will be adjusted by a person skilled in the art by varying the ratio between the diameter of the opening that the internal part 19 must pass through and the diameter of the internal part 19; and the presence or absence of a chamfer 27 circumscribing the opening that the internal part 19 must pass through (and if this chamfer 27 is present, the angle that it presents relative to the side wall, generally placed vertically). The three associated parameters are therefore the diameter of the internal part 19, the diameter of the opening and the angle of the chamfer 27 relative to the vertical (an angle of 90° being representative of an absence of chamfer).

[0048] For example, the angle of the chamfer 27 will be between 30 and 60° relative to the vertical, and preferably between 30 and 45°. For example, in the case of the application of the invention to a vehicle having a mass greater than 1900 kg, the person skilled in the art will benefit from favoring a significant output force and choosing a chamfer angle greater than 45°; for example, an angle between 45 and 90°; preferably, between 45 and 60°.

[0049] The ratio between the diameter D1 of the opening and the diameter D5 of the internal part is advantageously between 0.60 and 0.95; preferably between 0.65 and 0.90. The closer this ratio is to 1, the less the output force will be significant. For example, in the case of the application of the invention to a vehicle showing a mass less than 1900 kg, the person skilled in the art will benefit from favoring a less significant output force and choosing a diameter ratio D1 / D5 between 0.75 and 0.90. For example, an opening diameter of 40 mm associated with a diameter D5 shown by the 45 mm block gives a diameter ratio D1 / D5 of approximately 0.89.

Claims

1. An electric or hybrid motor vehicle (1) consisting of a pair of wrists (3) and a rear cradle (5) designed to support an electric propulsion group (7), the rear cradle (5) consists of a central area extending according to the transverse direction of the vehicle and extending at each end by two arms (9, 11), respectively a front arm (9) and a rear arm (11), the rear cradle (5) is attached to the longeronets (3) by its front and rear arms (9, 11); the vehicle (1) is characterized by the fact that each of the rear arms (11) of the rear cradle (5) is fastened on the ringpins by means of a two-part (19, 29) attachment device (17) configured to separate under the action of a tensile force greater than a predetermined threshold; preferably, the said traction force is oriented vertically.

2. Motor vehicle according to Claim 1, characterized as the attachment device (17) includes an external part (19) and an internal part (29), the external part (19) forming a housing unit and the internal part (29) comprising at least one block, the block(s) being arranged in the unit.

3. Motor vehicle according to Claim 1 or 2, characterized as one part (19, 29) is attached to one of the rear arm (11) of the rear cradle (3) and the other part (19, 29) is attached to one of the longeronets (5); preferably, the attachment device (17) includes an external part (19) and an internal part (29) and the external part (19) is attached to one of the rear arm (11) of the rear cradle (5) and the internal part (29) is attached to one of the longeronets (3) through an axis (31).

4. Motor vehicle according to one of claims 1 to 3, characterized as the attachment device (17) includes an external part (19) and an internal part (29), and as the outer part (19) includes at least one side wall (21) and also includes a upper wall (23) and a lower wall (25) and in that case at least the upper wall (23) and / or the lower wall (25) includes an opening for the passage of an axis (31).

5. Motor vehicle according to Claim 4, characterized as the ratio between the opening diameter shown by the upper wall (23) and / or the lower wall (25) and the diameter of the block(s) of at least one block is between 0,60 and 0,95; preferably between 0,75 and 0,90.

6. Motor vehicle according to one of claims 4 or 5, characterized as the opening shown by the upper wall (23) and / or the lower wall (25) is circumscribed by a chamfer (27) forming an angle with the side wall(s) (21) between 30 and 60°; preferably between 30 and 45°.

7. Motor vehicle according to one of claims 4 to 6, characterized as the upper wall (23) and / or lower wall (25) is assembled to the side wall(s) (21) by fastening screws; preferably with at least three fastening screws.

8. Motor vehicle according to one of claims 1 to 7, characterized as the fastening device (17) includes an external part (19) and an internal part (29), the internal part (29) includes at least one block and the block(s) are made up of a deformable elastic material chosen from the list comprising cis 4-polyisoprene, polyisoprene Synthetic ene, polybutadiene, styrene-butadiene copolymer, polyisobutylene, chloroprene, butadiene-acrylonitrile copolymer, ethylene-propylene copolymer, terpolymer, polyether block amide, elastomeric thermoplastics, polyurethanes, polysulfides, elastomers, fluoroelastomers, perfluoroelastomers, copolymers, Ethylene-vinyl acetate era, polyacrylic elastomers, polyethylene chlorosulfoné, epichlorhydrin elastomers; preferably, chosen from the list including silicone elastomers, elastomeric thermoplastics and polyurethanes.

9. Motor vehicle according to one of claims 1 to 8, characterized as the fastening device (17) includes an external part (19) and an internal part (29), the internal part (29) comprising at least one block and the block(s) are mounted on an axis (31) and held in position on that axis (31) by at least one ring (33, 35).

10. Use of a fastening device (17) for the attachment of a rear arm (11) of a multi-arm rear cradle (5) on a longeronnet (3) of a vehicle (1) electric or hybrid motor vehicle, the use being characterized by the fact that the fastening device (17) consists of two parts (19, 29), respectively. external part (19) and internal part (29), the external part (19) forming a housing unit and the internal part (29) comprising at least one block, the block(s) being placed in the housing, the two parts (19,29) being configured to separate under the action of a tensile force greater than a predetermined threshold; preferably, the said traction force is oriented vertically.