FR3087180A1 - BODY ASSEMBLY FOR A MOTOR VEHICLE CHASSIS, COMPRISING A BUMPER AND A BOTTOM FAIRING ASSEMBLED ON A TRANSVERSE PANEL - Google Patents

Abstract

The bodywork sub-assembly comprises a panel (5), one edge (5a) of which is extended by a fixing lug (8) on which are fixed, via a nut (9), a rebate of a bumper and a flat wall ( 7a) of a fairing docked towards the bumper. An edge (7b) of said flat wall (7a) is interposed between said rebate and a seat (10a) of the nut (9) against the fixing lug (8). The flat wall (7a) is provided with a cleat (11a, 11b) which provides a ramp for spacing said edge (7b) of the flat wall (7a) relative to the fixing lug (8) during the docking of the flat wall (7a) towards the bumper.

Description

SUB-BODY ASSEMBLY FOR A MOTOR VEHICLE CHASSIS, INCLUDING A BUMPER AND A BOTTOM FAIRING ASSEMBLED ON A TRANSVERSE PANEL.

The present invention relates to the field of bodywork sub-assemblies equipping a chassis of a motor vehicle. The invention relates more specifically to such a bodywork sub-assembly comprising a bumper and a bottom fairing assembled on a transverse panel.

A motor vehicle comprises a chassis carrying various bodywork elements. Several bodywork elements are potentially assembled together, forming a bodywork sub-assembly mounted on the chassis. Within the framework of the invention, it is considered such a body sub-assembly comprising a bumper and a bottom fairing installed on a base of the chassis, being fixed to each other via a transverse body element mounted on the chassis and for example arranged in a skirt or panel.

As a reminder, a bumper conventionally extends transversely to the front or the rear of the chassis, to protect the chassis and / or the vehicle equipment in the event of a frontal or rear impact supported by the vehicle. A bottom fairing extends under the chassis base, to protect the equipment installed under a platform that includes the chassis base. The bottom fairings also form aerodynamic members which make it possible to improve the stability of the moving vehicle and / or reduce its drag. The bottom fairings also make it possible to reduce the noise pollution which is generated by the flow of air under the underbody of the chassis during the progression of the vehicle.

More particularly, a front or rear bottom fairing is commonly fixed under the platform, itself fixed on a base frame of the chassis comprising in particular spars braced by crosspieces. The bottom fairing essentially comprises a flat wall which extends parallel under the platform to which it is fixed at a vertical distance, in particular by bolting or by screwing. A front or rear bumper is fixed to the chassis via a transverse body element which is mounted on the chassis base at one of its front or rear ends. The transverse body element is then potentially exploited to form a fixing interface between the fairing and the bumper.

It should be taken into consideration that the methods of assembling the fairing and the bumper on said transverse bodywork element vary according to the architecture of the chassis, which determines their respective layouts and the organization of their docking and fixing to each other. other.

For example, as shown in document US2014070564 A1 (HENDRICKSON USA LLC), said transverse bodywork element can be formed of a skirt providing a flat wall extending under the platform of the chassis. The flat wall of the skirt is enhanced with a rebate via which the bumper is attached to the skirt. The fairing is fixed under the flat wall which is then placed in interposition between the bumper and the fairing which are jointly fixed to the flat wall, in particular by screwing or by bolting.

In general, depending on the architecture of the chassis, the fairing, the bumper and / or the transverse body element, are capable of individually or collectively taking up space and / or a conformation which can make it difficult to approach them by compared to others, and / or obtaining a robust attachment that is easy to carry out between them. A solution is then to be sought to allow easy and reliable mounting between the various components that comprises said sub-body assembly, in particular between on the one hand the transverse body element and on the other hand the fairing and the bumper.

In this context, the subject of the present invention is a body sub-assembly for a motor vehicle chassis, comprising a panel at the base of which a bumper and a bottom fairing are fixed. The invention also relates to a motor vehicle chassis equipped with a subset of bodywork elements according to the invention, as well as a method of mounting said bodywork subset of the invention on the chassis.

An object of the invention is to propose a solution to facilitate the task of an operator carrying out the assembly between them of the components of said body sub-assembly on the chassis.

Another object of the invention is to seek such a solution without affecting the quality of a desired robust connection between the components of said body sub-assembly, and this by avoiding unduly complexifying their structure and / or the methods of their fixing. between them, in particular by screwing or bolting.

Such research is in particular subject to the constraint of a reduction in the costs generated by the structure and / or by the mounting on the chassis of the components of said body sub-assembly, in the context of notoriously severe economic competition in the automotive field. can make a potential solution prohibitive due to the costs involved.

To describe the invention, relative concepts relating to directions of extension of a motor vehicle commonly used in the automotive field are introduced. As a reminder, a direction and / or a longitudinal orientation of a motor vehicle extends between the front and the rear of the vehicle, a direction and / or a transverse orientation of a motor vehicle extends between the right sides and left of the vehicle with respect to the driver's station in the vehicle, and a direction and / or a vertical orientation of a motor vehicle extends relative to its running plane on the ground.

To facilitate understanding of the invention and unless otherwise specified, such directions and / or orientations are used to describe the bodywork sub-assembly and the chassis of the invention, as well as the methods of assembling the components of the sub-assembly of bodywork between them and on the chassis. The concepts front and rear are defined according to the longitudinal direction and the concepts bottom and top, or other related concepts like under and above, are defined according to the vertical direction in adequacy with the position of the components of the sub-assembly of bodywork on the chassis with respect the vehicle driving schedule.

A body sub-assembly according to the invention is configured to equip a motor vehicle chassis. The bodywork sub-assembly of the invention is recognizable in that it has the following arrangements.

The bodywork sub-assembly comprises a vertically oriented panel, the edge of a transverse edge of which is longitudinally extended by at least one fixing lug. A vertical axis nut is mounted on said at least one fixing lug and cooperates with a threaded element by providing a joint fixing on the fixing lug of a rebate that comprises a bumper and of a plane wall of longitudinal extension. and transverse that includes a bottom fairing, said flat wall being longitudinally approached towards the bumper.

In this context, a transverse edge of the flat wall of the fairing is vertically interposed between the rebate of the bumper and at least one seat of the nut against the fixing lug. The flat wall is provided, on its face vertically oriented towards said at least one panel fixing lug, with at least one vertical extension cleat which is oriented in the longitudinal direction of docking of the fairing towards the bumper. Said at least one cleat provides a ramp for vertical separation of said transverse edge of the planar wall with respect to said at least one fixing lug, under the effect of a vertical support grip of said at least one cleat against said edge from the transverse edge of the panel during longitudinal docking of the flat wall towards the bumper.

In the context of the invention, consideration is given to the case in which the nut can be a cause of discomfort for the operator when he moves the bottom fairing longitudinally towards the bumper for docking. As a reminder, said transverse edge of the flat wall of the fairing is placed in vertical interposition between the seat of the nut and the rebate of the bumper which extends perpendicular to the overall plane of vertical extension of the bumper towards which the flat wall is longitudinally approached. The seat of the nut can then stand in the way of an easy passage by the operator of the transverse edge of the flat wall along the fixing lug, during the longitudinal displacement of the fairing towards a vertical wall of the bumper located at longitudinal distance from said at least one fixing lug.

More particularly, the discomfort caused to the operator during the installation of the fairing on the chassis is induced by the presence of the seat of the nut which extends vertically from the fixing lug towards the flat wall. . The seat of the nut then forms an obstacle against which the edge of the transverse edge of the plane wall can abut sliding along the fixing tab during the longitudinal displacement of the fairing towards the bumper. This complicates the maneuvering of the fairing carried out by the operator during its installation on the chassis, to avoid the obstacle formed by the seat of the nut.

In accordance with the arrangement of the bodywork sub-assembly of the invention, said at least one cleat vertically pushes back the transverse edge of the flat wall of the fairing, under the effect of a vertical support of the cleat against the edge of the transverse edge of the panel during the longitudinal displacement of the fairing towards the bumper by the operator. The cleat then causes a deflection of the flat wall of the fairing allowing passage under the rebate of the bumper of the transverse edge of the flat wall of the fairing at a vertical distance from the seat of the nut. When the cleat drops the edge of the transverse edge of the panel in the longitudinal docking position of the fairing towards the bumper, the flat wall of the fairing is released from the bending stress to which it was subjected and is then placed, via the seat of the nut, pressing against said at least one fixing lug.

Thus, the operator can easily install the fairing on the chassis without worrying about the presence of the nut and the possible discomfort which it may be the cause against the positioning of the fairing relative to the panel. and / or the bumper. It will now be noted that the invention is particularly useful when the nut is a collet nut according to an advantageous embodiment of the invention referred to below. In fact, in the absence of said at least one cleat, such a clamp nut can be removed from the fixing lug via the edge of the transverse edge of the flat wall of the fairing during the longitudinal displacement of the fairing towards the bumper.

According to one embodiment, the cleat extends longitudinally between said transverse edge of the panel and the edge of the transverse edge of the planar wall oriented towards the bumper.

According to one embodiment, a group of at least two tabs are transversely distributed on either side of the fixing lug.

According to one embodiment, as previously mentioned, the nut is integral with an elastic deformation clamp via which the nut is mounted on the fixing lug. The arms of the pliers elastically enclose the fastening tab vertically between them.

More specifically, a first branch of the clamp providing said seat of the nut, bears elastically against a first face of the fixing lug oriented towards the flat wall of the fairing. A second branch of the clamp carrying the nut elastically bears against a second face of the fixing lug vertically opposite to said first face of the fixing lug.

According to one embodiment, said rebate of the bumper is provided with at least one tab via which the rebate is fixed to the fixing lug.

Preferably, said tongue extends longitudinally towards the fixing lug from a transverse wing participating in the rebate of the fairing.

The invention also relates to a chassis for a motor vehicle, comprising a base equipped with at least one body sub-assembly according to the invention.

More particularly, the bottom fairing is mounted under a platform that includes the base. The panel is fixed to any one of the longitudinal ends of a framework that includes the base, the panel being oriented in its plane perpendicular to the plane of extension of the platform. It is understood here that the longitudinal end of the frame on which the panel receiving the bumper is fixed, is identified according to the rear or front location of the bumper on the chassis.

For example, according to one embodiment, the bumper is a rear bumper. In other words, the bodywork sub-assembly of the invention is installed at the rear of the chassis.

The invention also relates to a motor vehicle comprising a chassis according to the invention. In other words, a motor vehicle according to the invention is equipped with at least one body sub-assembly according to the invention arranged at the front and / or at the rear of the vehicle.

The invention also relates to a method for mounting the components of a bodywork sub-assembly according to the invention, on a motor vehicle chassis according to the invention. It is understood that said components of the bodywork sub-assembly include at least said panel, said bumper and said bottom fairing.

According to the invention, the method comprises the following operations:

-) fix the panel to one of the longitudinal ends of the base, orienting it along its extension plane vertically and transversely on the chassis, then

-) install the bumper in the mounting position on the chassis, by placing the bumper rebate under said at least one fixing lug, then

-) install the fairing under the platform by longitudinal displacement of the fairing towards the panel, by placing said transverse edge of the plane wall of the fairing in interposition between the rebate of the bumper and said at least one fixing lug. The longitudinal displacement of the fairing initially causes a vertical deflection of the flat wall of the fairing towards the bottom of the chassis under the effect of a bearing of said at least one cleat against said edge of the transverse edge of the panel, then secondly authorizing a vertical support grip of said transverse edge of the flat wall of the fairing against said at least one fixing lug as a result of a longitudinal distance of the cleat relative to the transverse edge of the panel, then

-) jointly fix the fairing and the bumper to the fixing lug by putting in cooperation between the nut and the threaded element, then

-) fix the fairing under the platform.

The invention will be better understood on reading the following detailed description of an embodiment of the present invention, in relation to the following figures:

[Fig. 1] Figure 1 is a partial illustration in perspective from below of an embodiment of a base formed by a chassis of a motor vehicle, configured to receive a sub-body assembly according to the invention.

[Fig. 2] Figure 2 is a partial illustration in perspective from below of the base shown in Figure 1, on which is installed a bumper participating in a body assembly according to the invention.

[Fig. 3] Figure 3 is a partial perspective illustration from below of the base shown in Figures 1 and 2, on which is installed a bottom fairing participating in a sub-body assembly according to the invention.

[Fig. 4] Figure 4 is a perspective illustration from below of the fairing shown in Figure 3.

[Fig. 5] Figure 5 is a partial perspective view from below of the base shown in Figures 1 to 3, illustrating the fairing shown in Figures 3 and 4 in the installation phase under the base.

[Fig. 6] Figure 6 is a partial perspective view from below of the base shown in Figures 1 to 3, illustrating the fairing shown in Figures 3 to 5 in the installation position under the base.

The figures and their nonlimiting detailed descriptions show the invention according to particular methods which are not restrictive as to the scope of the invention as defined by the claims. The figures and their detailed descriptions of an embodiment of the invention can be used to define it better, if necessary in relation to the general description which has just been made.

In FIGS. 1 to 3, a chassis 1 of a motor vehicle comprises a base 2, illustrated in a view from below. The chassis 1 extends in the three directions of an orthonormal reference, commonly identified in a longitudinal direction L1 extending from front AV1 to rear AR1 of the chassis 1, a transverse direction T1 extending between the right and left sides of the chassis 1 relative to the station of the driver of the vehicle, and a vertical direction V1 of extension of the chassis 1 in elevation from the rolling plane of the vehicle. The relative concepts used to describe the invention, such as for example front AV1 and rear AR1, or below and above and / or bottom B1 and top H1 or other related concepts like lower and upper, are defined with respect to the directions of extension of the chassis 1.

The base 2 conventionally comprises a frame 3a, 3b, in particular formed at least in part of longitudinal members 3a braced with crosspieces 3b, on which frame 3a, 3b is fixed a platform 4. A panel 5 participating in a body sub-assembly conforming to the invention is fixed to the framework 3a, 3b in the transverse direction T1 of extension of the chassis 1, being oriented in its plane in the vertical direction V1 of extension of the chassis 1. The panel 5 is placed at a longitudinal end of chassis 1, in particular rear according to the illustrated embodiment.

The panel 5 forms a support participating in the fixing to the chassis 1 of bodywork elements, such as in particular a bumper 6 and a bottom fairing 7 as successively illustrated in FIGS. 2 and 3. It is understood here that the panel 5 , the bumper 6 and the fairing 7 form a sub-body assembly, main object of the invention. The bumper 6 is for example arranged in a shell having a slight longitudinal extension, against which the fairing 7 is intended to be longitudinally docked L1.

To this end, a lower transverse edge 5a of the panel 5 comprises fixing lugs 8 formed in longitudinal extension L1 of the section 5b of said transverse edge 5a of the panel 5 towards the outside of the frame 1. The fixing lugs 8 are used to jointly fix on the panel 5, the bumper 6 oriented in its overall plane parallel to the panel 5 and the fairing 7 via a flat wall 7a which it comprises and which is oriented parallel to the platform 4.

According to a predefined mounting method, the panel 5 is in a first step fixed on the chassis 1, in particular at the longitudinal end of the side rails 3a which includes the framework 3a, 3b as illustrated in FIG. 1. Then the bumper 6 is installed in the mounting position on the chassis 1 as illustrated in FIG. 2. Then the fairing 7 is installed in the mounting position under the platform 4, being displaced S1 longitudinally L1 for its docking towards the bumper 6. Such docking is preferably produced by bringing into longitudinal contact L1 between the fairing 7 and the bumper 6, but a longitudinal play L1 can be provided between them without departing from the invention.

The bumper 6 has a rabbet 6a for fixing it to the fixing lugs 8 which the panel 5 comprises, preferably via tabs 6b integrated into the rabbet 6a. As shown in Figures 5 and 6, the fixing lugs 8 are each provided with a nut 9 of vertical axis V1 cooperating with a threaded element, such as in particular a screw not shown, for fixing on the fixing lugs 8 jointly the bumper 6 via the rebate 6a and the fairing 7 via its transverse edge 7b oriented longitudinally L1 towards the bumper 6.

The nut 9 extends vertically V1 upwards from the chassis 1, comprising a seat 10a bearing against the face of the fixing lug 8 which is oriented towards the flat wall 7a of the fairing 7.

As shown in FIG. 3 when the components of the bodywork sub-assembly are fixed to each other, the transverse edge 7b of the fairing 7 is interposed vertically between the fixing lugs 8 and the rebate 6a of the bumper 6. This poses a difficulty for an operator carrying out the longitudinal docking L1 of the fairing 7 towards the bumper 6, due to the presence of the seat 10a of the nuts 9 which can hinder the movement S1 of the fairing 7 towards the bumper 6.

More particularly in Figures 5 and 6 according to the illustrated embodiment, the nuts 9 are each advantageously formed of a clamp nut previously installed on a fixing lug 8 which is assigned to them. In this case, the nut 9 is integral with a clamp 10 with elastic deformation, the branches 10a, 10b respectively bear against the vertically opposite faces V1 of the fixing lug 8. Said seat 10a of the nut 9 is in this case formed by a first branch 10a of the clamp 10 bearing against a first face of the fixing lug 8 oriented towards the flat wall 7a of the fairing 7. A second branch 10b of the clamp 10 carrying the nut 9, takes support against a second face of the fixing lug 8 which is vertically V1 opposite its first face. Thus, the fixing lug 8 is elastically clamped between the branches 10a, 10b of the clamp 10.

The clamp 10 then encloses the fixing lug 8 between the branches 10a, 10b which it comprises, by being put in place by an operator in a direction S2 of installation which is longitudinally L1 opposite to the direction S1 of longitudinal movement L1 of the flat wall 7a of the fairing 7 towards the bumper 6. There emerges a risk of the nut 9 being pushed back out of the fixing lug 8 by the fairing 7, via the edge 7d of the flat wall 7a of the fairing 7 oriented towards the bumper 6, during the installation of the fairing 7 on the chassis 1 by the operator.

In Figures 4 to 6 to obviate the problem of discomfort for the operator caused by the presence of the nuts 9 on the fixing lugs 8, it is proposed to provide the flat wall 7a of the fairing 7 with a spacer ramp vertical V1 from the transverse edge 7b of the planar wall 7a relative to the fixing lugs 8. Said ramp is formed of cleats 11a, 11b of vertical extension V1 which are formed longitudinally L1 on the planar wall 7a at its transverse edge 7b oriented towards the bumper 6. The cleats 11a, 11b are preferably integrated into the flat wall 7a of the fairing 7, for example being arranged in a rib.

To avoid an overload of Figures 5 and 6, and thus facilitate their reading and understanding, the flat wall 7a of the fairing 7 is shown in transparency and the bumper 6 is not shown. This makes it possible in particular to highlight the tabs 11a, 11b and the methods of their implementation during the installation of the fairing 7 on the chassis 1.

It will be noted that the longitudinal extension L1 of the tabs 11a, 11b does not exclude their possible inclination in the plane of the planar wall 7a relative to the edge 5b of the lower transverse edge 5a of the panel 5 against which the tabs 11a, 11b are planned to take V1 vertically. It will also be noted that, as illustrated, the cleats 11a, 11b of the same pair of cleats 11a, 11b are capable of having longitudinal extensions L1 different from each other, depending on the more or less curved conformation of the edge transverse 5a of the panel 5.

In FIGS. 5 and 6, the lugs 11a, 11b are two in number for each of the fixing lugs 8. The lugs 11a, 11b of the same pair of lugs 11a, 11b are transversely T1 distributed on either side of the fixing lug 8 which is assigned to them, to promote a vertical distance V1 from the flat wall 7a relative to the fixing lug 8 which is balanced on either side of the fixing lug 8. The cleats 11a, 11b have a vertical extension V1 greater than the vertical extension V1 of the seat 10a of the nut 9 which rises under the fixing lug 8 towards the bottom of the chassis 1.

In FIG. 5, the fairing 7 is in the installation phase in the mounting position on the chassis 1. The operator moves S1 by longitudinal translation L1 the fairing 7 towards the bumper 6, from the front AV1 towards the rear AR1 of the chassis 1, in the illustrated case where the bumper 6 is a rear bumper AR1. It is understood here that in the case where the bumper 6 is a front bumper AV1, the displacement of the fairing 7 is effected longitudinally L1 from the rear AR1 towards the front AV1 in the direction of the bumper 6.

When the tabs 11a, 11b are placed in contact against the edge 5b of the transverse edge 5a of the panel 5, these cause a deflection F1 of the flat wall 7a downwards B1 of the frame 1. It will be noted that the resistance of the rebate 6a of the bumper 6 against the deflection F1 of the flat wall 7a, is attenuated due to the support of the rebate 6a against the fixing lugs via the tongues 6b with which it is provided, which are capable of bending without major resistance under the effect of the vertical thrust V1 exerted by the cleats 11a, 11b in reaction to their taking of support against the edge 5b of the transverse edge 5a of the panel 5.

Preferably, the leading edge 11 of the cleats 11a, 11b against the transverse edge 5a of the panel 5, or in other words the end face of the cleats 11a, 11b oriented towards the bumper 6, is generally inclined relative to the plane of the flat wall 7a being preferably curved upwards H1 of the chassis 1. The inclination of the leading edge 11 of the cleats 11a, 11b promotes the progressive taking of vertical support V1 of the cleats 11a, 11b against the edge 5b of the edge transverse 5a of the panel 5, and consequently promotes the deflection F1 of the flat wall 7a of the fairing 7 downwards B1 of the chassis 1.

The vertical extension V1 of the cleats 11a, 11b being greater than that of the nut 9 in its part extending from the fixing lug 8 towards the bottom of the chassis 1, a vertical clearance V1 for mounting is then provided between the edge transverse 7b of the flat wall 7a and the nut 9. Such a vertical clearance V1 then allows the flat wall 7a of the fairing 7 to overcome the obstacle presented by the seat 10a of the nut against displacement S1 longitudinal L1 of the transverse edge 7b of the flat wall 7a of the fairing 7 towards the bumper 6.

In FIG. 6 when the fairing 7 is in the fixing position on the fixing lugs 8 of the panel 5, the tabs 11a, 11b extend longitudinally L1 between the transverse edge 5a of the panel 5 and the edge 7d of the transverse edge 7b of the flat wall 7a oriented towards the bumper 6. As a result of the escapement of the tabs 11a, 11b relative to the transverse edge 5a of the panel 5, the flat wall 7a of the fairing 7 is no longer subjected to deflection F1 in its plane d 'extension. The transverse edge 7b of the flat wall 7a of the fairing 7 oriented towards the bumper 6, is then able to take vertically V1 support against the fixing lugs 8, via the first branch 10a of the clamp 10 providing the seat of the nut 9 which is interposed between the fixing lug 8 and the transverse edge 7b of the flat wall 7a of the fairing 7.

As visible in FIGS. 3 and 4, the transverse edge 7b of the flat wall 7a of the fairing 7 is provided with orifices 7c for passage of the threaded elements intended to cooperate with the nuts 9 fitted to each of the fixing lugs 8 for fixing together with the panel 5 the fairing 7 and the bumper 6. As shown in FIG. 3 when the fairing 7 is in the mounting position on the chassis 1, the transverse edge 7b of the flat wall 7a of the fairing 7 bears against the fixing lugs 8 to their downward-facing side B1 of the chassis 1. The rebate 6a of the bumper 6 bears against the fixing lugs 8 on their upward-facing side H1 of the chassis 1, preferably via the tongues 6b.

In the preferred case where the nut 9 is a collet nut, the range of the transverse edge 7b of the flat wall 7a of the fairing 7 against the fixing lugs 8 is produced via the first branch 10a of the clamp 10, and the range of the rebate 6a of the bumper 6 against the fixing lugs 8 is produced via the second branch 10a of the clamp 10. In other words when the fairing 7 is in the mounting position on the chassis 1, the following elements are vertically V1 superimposed from the bottom B1 upwards H1 of the chassis 1: the rabbet 6a of the bumper 6 preferably via the tongues 6b, if necessary the second branch 10b of the clamps 10, the fixing lugs 8 with which the panel 5 is provided, a seat of the nut 9 formed where appropriate by the first branch 10a of the clamp 10, and the transverse edge 7b of the planar wall 7a of the fairing 7.

The threaded elements are then placed in cooperation with the nut 9 to fix jointly on the fixing lugs 8 of the panel 5, the transverse edge 7b of the flat wall 7a of the fairing 7 and the rebate 6a of the bumper 6. The fairing 7 is then fixed to the platform 4 via threaded members 12 as shown in Figure 3, for example by screwing or bolting.

Claims (10)

1 Sub body assembly configured to equip a chassis (1) of a motor vehicle, characterized: -) in that the bodywork sub-assembly comprises a vertically oriented panel (5) (V1) whose edge (5b) of a transverse edge (5a) is longitudinally (L1) extended by at least one fixing lug (8 ), a nut (9) with a vertical axis (V1) being mounted on said at least one fixing lug (8) and cooperating with a threaded element by providing a joint fixing on the fixing lug (8) of a rebate (6a) that includes a bumper (6) and a flat wall (7a) of longitudinal (L1) and transverse (T1) extension that includes a bottom fairing (7), said flat wall (7a) being longitudinally ( L1) approached towards the bumper (6), and -) in that a transverse edge (7b) of the flat wall (7a) of the fairing (7) is vertically (V1) interposed between the rebate (6a) of the bumper (6) and at least one seat (10a) of the nut (9) against the fixing lug (8), the flat wall (7a) being provided, on its vertically facing side (V1) oriented towards said at least one fixing lug (8) of the panel (5), d '' at least one cleat (11a, 11b) of vertical extension (V1) which is oriented in the longitudinal direction (L1) of docking of the fairing (7) towards the bumper (6), said at least one cleat (11a, 11b) providing a vertical spacing ramp (V1) of said transverse edge (7b) of the flat wall (7a) relative to said at least one fixing lug (8), under the effect of a support vertical (V1) of said at least one cleat (11a, 11b) against said edge (5b) of the transverse edge (5a) of the panel (5) during longitudinal docking (L1) of the flat wall (7a) towards the bumper (6). 2, - Sub body assembly according to claim 1, characterized in that the cleat (11a, 11b) extends longitudinally (L1) between said transverse edge (5a) of the panel (5) and the edge (7d) of the edge transverse (7b) of the flat wall (7a) oriented towards the bumper (6). 3, - Sub body assembly according to any one of claims 1 and 2, characterized in that a group of at least two cleats (11 a, 11 b) are transversely (T 1) distributed on both sides other of the fixing lug (8). 4, - Sub body assembly according to any one of claims 1 to 3, characterized in that the nut (9) is integral with a clamp (10) with elastic deformation via which the nut (9) is mounted on the fixing lug (8), the arms (10a, 10b) of the clamp (10) elastically enclosing the fixing lug (8) vertically (V1) between them. 5, - Sub body assembly according to claim 4, characterized in that a first branch (10a) of the clamp (10) providing said seat of the nut (9) resiliently bears against a first face of the tab fixing (8) oriented towards the flat wall (7a) of the fairing (7), a second branch (10b) of the clamp (10) carrying the nut (9) resiliently bearing against a second face of the fixing lug (8) vertically (V1) opposite to said first face of the fixing lug (8). 6, - Sub body assembly according to any one of claims 1 to 5, characterized in that said rebate (6a) of the bumper (6) is provided with at least one tongue (6b) via which the rebate (6a) is fixed on the fixing lug (8). 7, - Chassis (1) of a motor vehicle, characterized in that the chassis (1) comprises a base (2) equipped with at least one body sub-assembly according to any one of Claims 1 to 6, the fairing ( 7) bottom being mounted under a platform (4) that includes the base (2) and the panel (5) being fixed to any one of the longitudinal ends (L1) of a frame (3a, 3b) that includes the base (2), the panel (5) being oriented in its plane perpendicular to the extension plane of the platform (4). 8, -The chassis (1) of a motor vehicle according to claim 7, characterized in that the bumper (6) is a rear bumper. 9, - Motor vehicle characterized in that the vehicle comprises a chassis (1) according to any one of claims 7 and 8. 10, -Process for mounting the components of a bodywork subassembly according to any one of claims 1 to 6, on a chassis (1) of a motor vehicle according to any one of claims 7 and 8, characterized in that the process which it comprises the following operations: -) fix the panel (5) to one of the longitudinal ends (L1) of the base (2), orienting it along its plane of extension vertically (V1) and transversely (T1) on the chassis (1), then -) install the bumper (6) in the mounting position on the chassis (1), by placing the rebate (6a) of the bumper (6) under said at least one fixing lug (8), then -) installing the fairing ( 7) under the platform (4) by longitudinal displacement (L1) of the fairing (7) towards the panel (5), by placing said transverse edge (7b) of the flat wall (7a) of the fairing (7) in interposition between the rebate (6a) of the bumper (6) and said at least one fixing lug (8), the longitudinal displacement (S1) (L1) of the fairing (7) initially causing a vertical deflection (F1) (V1) of the flat wall (7a) of the fairing (7) towards the bottom of the frame (1) under the effect of a support taking of said at least one cleat (11a, 11b) against said edge (5b) of the transverse edge ( 5a) of the panel (5), then authorizing in a second step a vertical support socket (V1) of said transverse edge (7b) of the flat wall (7a) of the fairing (7) against said at least one fixing lug ( 8) as a result of a longitudinal distance (L1) of the cleat (11a, 11b) relative to the transverse edge (5a) of the panel (5), then -) jointly fix the fairing (7) and the bumper (6) to the fixing lug (8) by cooperation between the nut (9) and the threaded element, then -) fix the fairing (7) under the platform (4).