Abstract:
A body shell structure of a motor vehicle includes a side superstructure of the body shell defining on either side of the vehicle two recess portions for wheel arch housings of the vehicle connected by a floor of the vehicle. The body shell structure includes, in each of the two recess portions for wheel arch housing, a wheel arch housing part and at least one mount for attaching the rear shock absorber, assembled by edges thereof to each of the wheel arch housing parts. The wheel arch housing part defines at least one substantially oblique surface portion around and beyond the edges of the mount. The superstructure also includes a structural plate rigidly connected to an oblique surface portion of the wheel arch housing part and secured to a substantially vertical surface portion of the superstructure.

Description:
BACKGROUND 
     The object of the invention is motor vehicle bodyshell structures and more particularly the points of anchoring of the rear shock absorbers of the vehicle on these bodyshells. 
     With the development of electric or hybrid vehicles, vehicle architectures are being increasingly frequently encountered in which the rear floor of the vehicle is raised, meaning that it disposed more at the top level of the wheel well instead of being disposed at an intermediate height between the base of the bodyshell and the top of the wheel wells. 
     As an example, these raised floors make it possible to free up space to install electric storage batteries. But the requirements of impact resistance of the vehicle, especially resistance to certain types of rear-end impact, applied at a standardized height relative to the vehicle, are more favorable to low positioning of the frame rails of the longitudinal structural reinforcements of the vehicle. 
     To be able to free up the space necessary for positioning of the batteries and at the same time to satisfy the requirements of rear-end impact, certain vehicle architectures therefore have frame rails that are locally offset upwards at the rear of the vehicle. Because of this offset, the rear frame rail, assuming equal section, is more subject to deformation during an impact than an equivalent straight frame rail. 
     In addition, the rear end of the frame rail in these architectures is no longer positioned facing the normalized point of impact during rear-end impact tests. 
     This therefore necessitates increasing the section and therefore the mass of the frame rails, as well as adding complementary structure portions designed to transfer the impact energy from the height at which it is applied to the front of the frame rail. 
     Another problem resulting from the elevation of the rear floor of the vehicle is that the shock absorber fixation towers, which traditionally are attached to the frame rails, tend to be disposed below the vehicle floor and are no longer connected in optimum manner to the upper part of the bodyshell. Thus they cannot be fixed in synergy with this upper part of the bodyshell in order to dissipate part of the forces transmitted by the shock absorber. 
     BRIEF SUMMARY 
     The object of the invention is to provide a motor vehicle bodyshell structure that makes it possible to limit the total weight of the bodyshell while making it possible to ensure good resistance of the vehicle to rear-end impact and to assure favorable distribution of the stresses resulting from the shock absorber fixation points, especially for the rear shock absorbers of the vehicle. 
     To this end, the invention proposes a motor vehicle bodyshell structure comprising a lateral bodyshell superstructure defining, on both sides of the vehicle, two housing portions for wheel wells of the vehicle. The two wheel well housing portions, wherein each housing can receive at least one wheel, are connected by a floor of the vehicle. At the level of each of the two wheel well housing portions, the bodyshell structure comprises a wheel well part and at least one rear shock absorber fixation tower assembled by its rims on each of the wheel well parts. Most often, each wheel well part contributes to bounding a housing that shelters a single vehicle wheel, but in certain alternative embodiments one housing could shelter several wheels of two adjacent axles. The wheel well part defines at least one substantially oblique surface portion around and outside the flanges of the tower. The superstructure additionally comprises a structural metal sheet integral with an oblique surface portion of the wheel well part and integral with a substantially vertical surface portion of the superstructure. Advantageously the floor is a rear floor of the vehicle, and the wheel wells are rear wheel wells of the vehicle. According to an alternative embodiment, the oblique surface portion may be horizontal. 
     According to a preferred embodiment, the tower has two first substantially vertical walls, substantially parallel to the structural metal sheet, each assembled by at least one flange with the wheel well part, and at least one of which is situated, relative to the structural metal sheet, at a distance that is smaller than or equal to the largest dimension of the tower. 
     The structure may additionally comprise a rear reinforcing frame rail, wherein the lateral bodyshell superstructure rises above the frame rail. The tower may be assembled with the frame rail by means of an extension piece forming a beam and connecting the frame rail and the tower. Preferably the wheel well portions are offset vertically upward relative to the frame rail. 
     Preferably the shock absorber fixation tower is assembled with the lateral superstructure and assembled with a reinforcing longitudinal frame rail by means of an extension piece connecting the tower and only a portion of the frame rail. By only a portion of the frame rail there will be understood only a portion of the length of the frame rail in the longitudinal direction of the vehicle. The extension piece has a width, measured in longitudinal direction of the vehicle, substantially equal to that of the tower. The maximum width of the extension piece may typically range between 0.9 and 1.3 times the maximum width of the tower, the term width being used here to designate a dimension along the longitudinal axis of the vehicle. The extension piece positions the tower above the frame rail, meaning in a position offset vertically relative to the frame rail. Advantageously the assembly points between the extension piece and the frame rail are substantially aligned in vertical direction with a rim of the tower. Preferably the vertical offset between the base of the tower and the point closest to the frame rail is at least equal to the height of the tower; the vertical offset between the base of the tower and the point closest to the frame rail may be, for example, between two and ten times the height of the tower. By height there will be understood a dimension measured in a vertical direction of the assembled part in the vehicle. Thus the extension piece has a width that makes it possible to transmit the vertical forces between the tower and the frame rail without closing the entire width of the vertical space between the floor and the frame rail. In this way it is possible, with a part that consumes little material, to transfer the vertical forces of the shock absorber to the frame rail while nevertheless assuring good lateral accessibility to the elements located between the wheels and under the floor. Advantageously the floor is positioned above a limit height of the wheel well openings that are visible on the coachwork exterior to the vehicle. 
     According to a particularly advantageous embodiment, several parallel structural metal sheets are disposed on both sides of the tower relative to the longitudinal axis of the vehicle. 
     At least one structural metal sheet can be part of a structure portion forming a four-sided box and a bottom, one side of which is a substantially vertical surface portion of the superstructure and the bottom of which is a portion of the wheel well part. 
     According to an advantageous embodiment, the shock absorber fixation tower is positioned to be substantially in the horizontal prolongation of the rear floor. For example, the minimum rear floor height can be located between the assembled height of the tower bottom and a maximum height of a rim of the tower. 
     Advantageously the extension piece has a beam geometry of substantially U-shaped section, wherein the beam axis is oriented substantially vertically and at least two parallel rims of the U-shaped section are placed in the prolongations of the two first substantially vertical walls of the tower. 
     The two first parallel rims of the U-shaped section are preferably assembled, for example by welding, with the two first substantially vertical walls of the tower. The U-shaped section may transition between the point or points of fixation on the frame rail and between the assembly zones between tower and extension piece. For example, the U-shape may not be entirely symmetric, and the height of the rims of the U-shape may increase between the frame rail and the tower. At the level of the zones of assembly with the tower, the height of the U-shape may be chosen to be sufficient that the rims of the beam completely surround the two first walls of the tower, at least in a right section plane of the beam. The two first walls of the tower may be completely lined over their vertical portion by two first rims of the U-shaped beam of the extension piece. 
     According to one embodiment, the tower has at least one third substantially vertical or oblique lateral wall joining the two first walls, and the tower has a substantially horizontal bottom wall joining the two first walls and placed in the continuity of the third wall. By oblique, there will be understood here a direction that is neither vertical not horizontal, when the vehicle is placed in usual riding position on a level road. 
     According to a preferred embodiment, the open side of the U-shaped section of the extension piece is turned toward the lateral side of the vehicle which is exterior to the vehicle, and the third lateral wall of the tower is located on the side exterior to the vehicle, and therefore on the open side of the U-shape. The tower may not have a fourth wall, or it may have a substantially vertical fourth wall facing the third wall. The first, second, third and fourth walls may each be connected to the bottom wall of the tower by a curved wall portion in order to limit the stress concentrations in the transition zones between the bottom wall of the tower and at least one of the lateral walls of the tower, each comprising preferably at least one vertical wall portion. According to a preferred embodiment, the height of the fourth wall is smaller than the height of the third wall. Of course, other embodiments can be envisioned. The third and the fourth walls of the tower may be of substantially equal height, or the highest wall may border the tower on the side interior to the vehicle. The open side of the U-shape may be turned toward the interior of the vehicle, and/or the base of the U-shape may be disposed in the continuity of the third wall. 
     The bottom wall of the tower may typically be perforated to receive, for example, a fixation screw of the shock absorber. 
     A reinforcing part may be assembled on the bottom of the tower to increase the bending resistance of the bottom of the tower. Ribs may be formed by deep drawing so as to connect the bottom of the tower and at least one of the substantially vertical walls of the tower along a curved path, in such a way as to stiffen the tower as a whole and to facilitate the transmission of forces between the bottom of the tower, where the end of the shock absorber is assembled, and the walls of the tower connected to the sides of the U-shaped beam. 
     Advantageously, the two first walls and the third wall may be assembled with the wheel well part by welding two first flanges of the two first walls and by welding a third flange of the third wall, the flanges being folded so as to be disposed substantially in a common plane with an interior flange of an opening of the wheel well part. According to a preferred embodiment, the tower is open upwards, meaning that the shock absorber is braced on the bottom of the tower while remaining outside the tower. The tower is preferably assembled with the lateral superstructure in such a way that the opening of the tower is flush at the bottom with the level of an opening of the wheel well part. This orientation of the tower makes it possible to assemble the tower via three of its vertical walls with the U-shaped beam, and makes it possible to assemble the tower via the flanges of the tower with the wheel well part. In this way the distribution of forces of the shock absorber between the U-shaped beam and the wheel well part is optimized. According to an advantageous embodiment, the wheel well part has a lower rim that is on the same level as a rim of the floor and that is assembled with this floor rim. 
     The tower may have at least one third substantially vertical or oblique third wall joining the two first walls, it may have a substantially horizontal bottom wall joining the two first walls and placed in the continuation of the third wall, and it may be assembled via the flanges of the two first walls and of the third wall with the wheel well part. 
     Advantageously, the tower is also assembled with the wheel well part along a flange that is disposed along the bottom wall of the tower or along a flange that is disposed along a fourth wall of the tower. According to an advantageous embodiment, the third wall of the tower may be lined by a central portion of the U-shaped beam, wherein the central portion is the central web of the beam joining the two webs forming the sides of the U-shape of the beam. According to another embodiment, it is a flange of the bottom of the tower, i.e. the fourth wall, or it is a flange of the fourth wall that is assembled with the central portion of the U-shaped beam. The U-shaped beam therefore surrounds the tower over at least two faces and preferably over three faces. The faces in question are the first wall, the second wall and either the third or the fourth wall. 
     The tower may also be assembled with the wheel well part along a flange that is disposed along either the bottom wall of the tower or along a fourth wall opposite the third wall and of height smaller than the height of the third wall. 
     According to a preferred embodiment, the extension piece is assembled with the tower in at least several different points of each of the two first walls of the tower. 
     Preferably the extension piece is assembled with the tower in at least three points of each of the two first walls of the tower. According to an advantageous embodiment, the extension piece may additionally be assembled directly with the wheel well part along certain portions of the interior flange of the opening of the wheel well part. 
     The invention also proposes a motor vehicle comprising a lateral bodyshell superstructure defining, on both sides of the vehicle, two portions, right and left, of wheel well housings of the vehicle. The two right and left wheel well housing portions are connected by a floor of the vehicle. At the level of each wheel well housing portion, the vehicle comprises a wheel well part and at least one shock absorber fixation tower assembled with each of the wheel well parts. The wheel well part defines at least one substantially oblique surface portion around and beyond the flanges of the tower. The superstructure additionally comprises a structural metal sheet integral with an oblique surface portion of the wheel well part and integral with a substantially vertical surface portion of the superstructure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objectives, characteristics and advantages of the invention will become apparent upon reading the description hereinafter, given merely by way of example, which is in no way limitative, and referring to the attached drawings, wherein: 
         FIG. 1  is a simplified sectional view of a bodyshell structure portion according to the invention, 
         FIG. 2  is an overhead view of the bodyshell structure portion of  FIG. 1 , 
         FIG. 3  is a perspective view of some characteristic elements of another bodyshell structure according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIGS. 1, 2 and 3 , the x-axis represents a longitudinal axis of the vehicle, the y-axis represents a transversal axis of the vehicle and the z-axis represents a vertical axis. 
     The structures represented in  FIGS. 1, 2 and 3  are present at least two times in the vehicle, in each case with two structures that are symmetric relative to an axis parallel to the x-axis and passing through the middle of the vehicle. 
     As illustrated in  FIGS. 1 and 2 , a motor vehicle bodyshell structure  1  (not represented) according to the invention comprises a frame rail  2  disposed in longitudinal manner along the vehicle and extending at least partly to the rear end of the vehicle. The structure comprises a substantially vertical portion  3  of a lateral superstructure  9  in which there is made a wheel well opening  29  making it possible to mount a wheel on the vehicle below lateral superstructure  9 , and comprises a rear floor  5  that is raised, i.e. placed vertically above frame rails  2 . 
     Rear floor  5  is not necessarily located directly above frame rails  2  but in any case is offset vertically upward relative thereto. Floor  5  is connected to lateral superstructure  9  by a wheel well part  7 , which defines at least one oblique surface portion  30  and is assembled, on the side interior to the vehicle (relative to a transversal direction of the vehicle), with rear floor  5 , and is assembled, on the side exterior to the vehicle, with lateral superstructure  9 . 
     Lateral superstructure  9  comprises at least one substantially vertical portion  3 , which may comprise, for example, an exterior portion of guard  3   a , comprising an exterior finishing metal sheet, an interior guard portion  3   c  on which are assembled diverse elements interior to the vehicle, and an intermediate guard portion  3   b  connecting exterior guard portion  3   a  and interior guard portion  3   c  in such a way as to leave an empty space between the interior and exterior portions to facilitate assembly of diverse elements on interior portion  3   c . Intermediate portion  3   b  defines a radially exterior portion of a wheel well housing  4 , in the interior of which a vehicle wheel may be inserted by passage through opening  29 . The rest of the depth (along the y-axis) of wheel well housing  4  is defined by wheel well part  7 . 
     A shock absorber fixation tower  10  is assembled on wheel well part  7 . An opening  8  is made in wheel well part  7 , below which tower  10  is assembled underneath wheel well part  7 , wherein the rims of tower  10  are braced on wheel well part  7  and are assembled therewith around opening  8 . Bottom  15  of tower  10  is offset downward relative to wheel well part  7 . 
     Bottom  15  may be perforated with a bore  16  that permits the assembly of the end of the rear shock absorber (not represented). This bottom  15  may if necessary be lined with a reinforcing metal sheet (not represented). 
     Tower  10  is connected to frame rail  2  by an extension piece  20 , which thus connects lateral superstructure  9  with frame rail  2 . 
     Extension piece  20 , as can be seen in the overhead view of  FIG. 2 , has a U-shaped beam section, wherein the two arms  17 ,  18  of the U-shape extend in the y-axis transversal to the vehicle and the base  19  of the U-shape extends in the x-axis. Extension piece  20  is welded to or otherwise assembled on frame rail  2 , and is also integral, via portions forming arms  17 ,  18  of the U-shape, with tower  10 . As can be seen in  FIG. 2 , extension piece  20  surrounds tower  10 , which has a substantially rectangular or square section. Tower  10  has a first tower wall  11  and a second tower wall  12  substantially parallel to the transversal y-axis. Tower  10  has a third tower wall  13  bordering the tower on the side exterior to the vehicle (relative to the y-axis) and a fourth wall  14  that may if necessary be of zero height and that borders tower  10  on the side interior to the vehicle. 
     Of course, elements common to  FIG. 1  are shown in  FIG. 2 , where like elements are represented by like reference numerals. However, to simplify the drawing, floor  5  and frame rail  2  have not been represented in  FIG. 2 . 
     Extension piece  20  has a U-shaped section, wherein this section comprises a first parallel rim  17  and a second parallel rim  18 , both parallel to the transversal y-axis of the vehicle (or at least forming a symmetric angle relative to this y-axis transversal to the vehicle), and it has a third rim  19  forming the base of the U-shaped section and which is substantially parallel to the longitudinal direction x of the vehicle. 
     The first and second walls of the tower are substantially vertical or end in a substantially vertical portion. The first rims, second rims and base rims of the U-shaped section of extension piece  20  also form substantially vertical planes. The parallel first and second rims of extension piece  20  are assembled with the first and second walls  11  and  12  respectively of tower  10 . The third rim or base rim of the U-shaped section is assembled here with the fourth wall of the tower, which is situated on the side interior to the vehicle. It is also possible to envision alternative embodiments in which this third rim of extension piece  20  is assembled with the third tower wall disposed on the side exterior to the vehicle. 
     Tower  10  is assembled with wheel well part  7  via tongues  27  disposed along the rims of the first, second, third and fourth walls of tower  10 . 
     Extension piece  20  may also have one or more tongues  28  for making extension piece  20  integral with wheel well part  7 , possibly by interposing a tongue  27  of tower  10  between a tongue  28  and wheel well part  7 . 
     As is visible in both  FIGS. 1 and 2 , motor vehicle bodyshell structure  1  also comprises a structural metal sheet  22  of substantially square shape. Structural metal sheet  22  comprises at least one substantially vertical force-absorbing portion  22   a , which is substantially parallel to first wall  11  and to second wall  12  of tower  10 , as well as to first parallel rim  17  and to second parallel rim  18  of extension piece  20 . 
     All of these vertical portions  22   a ,  11 ,  12 ,  17 ,  18  of bodyshell structure parts are all parallel to a geometric plane  21  which is vertical and transversal relative to the vehicle. Plane  21  is represented in  FIG. 3 , and has the y-axis and z-axis as director axes. It is possible to envision alternative embodiments in which plane  21 , which is common to structural sheet  22 , first and second walls  11 ,  12  of tower  10 , first and second parallel rims  17 ,  18  of the U-shaped section of extension piece  20 , is not strictly vertical, or is not strictly transversal relative to the vehicle. Preferably, however, plane  21  remains inclined by less than 10° relative to the vertical and preferably remains inclined by less than 5° relative to the vertical. 
     The inclination of plane  21  relative to the y-axis may depend on a local curvature of frame rail  2  on which extension piece  20  is assembled. Plane  21  may then be perpendicular to the frame rail. It is possible to envision alternative embodiments in which first and second rims  17 ,  18  of extension piece  20  would not be parallel but would be convergent or divergent (as viewed over a cross section of the beam forming the extension piece). First and second tower walls  11 ,  12  may then be convergent or divergent, in such a way that the first tower wall is assembled with the first rim of the extension piece and the second tower wall with the second rim of the extension piece. A structural metal sheet  22  may then be positioned in such a way that it is parallel to the one of first and second tower walls  11 ,  12  which is closest to structural metal sheet  22 , or may be in a plane transversal to the vehicle. 
     Structural metal sheet  22  is placed close to at least one among the first and second tower walls, in such a way that it can efficiently absorb part of the vertical forces transmitted by the shock absorber to tower  10  then via tower  10  to wheel well part  7 . Structural metal sheet  22  may comprise a portion  22   b  that is also vertical and substantially perpendicular to force-absorbing portion  22   a . Portion  22   b  is assembled with the interior portion of guard  3   c  and makes it possible to transfer the vertical forces received by force-absorbing portion  22   a  to the interior portion of guard  3   c . Structural metal sheet  22  is also integral with wheel well part  7  over at least one portion of the lower rim of force-absorbing portion  22   a . An assembly tongue (not represented) of structural metal sheet  22  may make an angle with portion  22   a  and be assembled on oblique surface portion  30  of wheel well part  7 . According to another alternative embodiment, force-absorbing portion  22   a  may be assembled in the lower part with a substantially vertical portion  31  of wheel well part  7 , bordering wheel well part  7  in a plane direction substantially perpendicular to the interior portion of guard  3   c . According to yet another embodiment, which may be combined with those in the foregoing, structural metal sheet  22  may be assembled via its portion  22   a  with a third part (not represented) comprising a metal sheet portion that is also parallel to plane  21  and is placed in the prolongation of force-absorbing portion  22   a , wherein that third part is itself also integral with wheel well part  7 . 
     Thus the vertical forces transmitted by the rear shock absorber (not represented) to tower  10  can be transmitted by the rims of tower  10  via extension piece  20  of frame rails  2  and can also be partly transmitted by tower  10  to wheel well part  7 , then by structural metal sheet  22 , then toward lateral superstructure  9 , the direction of which is favorable for absorption of vertical forces. It is possible to envision alternative embodiments in which wheel well part  7  is not oblique but is horizontal. 
     In order to favor the transfer of vertical forces to the upper part of the bodyshell structure, especially to lateral superstructure  9 , structural metal sheet  22  is situated close to tower  10 , typically at a distance shorter than the largest dimension of the tower itself, this minimum distance being respected both concerning the distance along the x-axis and concerning the distance along the y-axis. 
     According to an advantageous embodiment, structural metal sheet  22  is assembled with wheel well part  7  in such a way that the total assembly length along the y-axis, between structural metal sheet  22  and wheel well part  7 , is at least equal to half and preferably two thirds of the minimum distance along this y-axis between one of the lateral walls of the tower and a substantially vertical portion of the superstructure, for example interior guard portion  3   c . In certain particularly advantageous embodiments, the total assembly length is even greater than this minimum distance, in such a way that a portion of structural metal sheet  22  is disposed along at least one portion of a lateral wall  11 ,  12  of tower  10 . In this way the absorption, by the structural metal sheet, of the forces transmitted by tower  10  to wheel well part is improved. 
     Structural metal sheet  22  may be assembled with wheel well part  7  by tongues parallel to oblique surface portion  30  of wheel well part  7 , or by a portion of wheel well part  7 , which in contrast is vertical and assembled on a vertical portion of structural metal sheet  22 . 
     Furthermore, structural metal sheet  22  may result from an assembly of several parts, each containing at least one substantially plane portion parallel to axis  21 , wherein all of the portions parallel to axis  21  are assembled to form a force transfer plate both integral with wheel well part  7  and integral with portion  3  of lateral superstructure  9 . 
     In order to improve the transfer of vertical forces from wheel well part  7  close to tower  10  to lateral superstructure  9  even more, other vertical force-transferring elements may be added that are integral both with wheel well part  7  and lateral superstructure  9 . 
     These elements preferably have one or more vertical planes connecting wheel well part  7  and lateral superstructure  9 . At least some of these vertical planes are preferably parallel to plane  21  and parallel to first and second walls  11 ,  12  of tower  10 . At least one of these parallel vertical planes is disposed close to tower  10 , i.e. at a distance along the x-axis and at a distance along the y-axis that is smaller than the largest dimension of the tower. 
     Thus, in  FIG. 2 , it is possible to see a belt winding box  23  comprising a front part  24  and a rear part  25 . Rear part  25  comprises a bottom portion  25   c  joined to and fixed on the interior portion of guard  3   c , and it comprises two lateral walls  25   a  and  25   b  parallel to force-transmission plane  21 . 
     Box  23  also comprises a front part  24  comprising a front wall  24   c  parallel with rear wall  25   c  and comprising two lateral walls  24   a  and  24   b  assembled on lateral walls  25   a  and  25   b  of rear part  25 . Front part  25  additionally comprises assembly tongues  26  for making the base of front piece  24  integral with wheel well part  7 . 
     Assembly tongues  26  are disposed along a length greater than at least half of the length of lateral walls  24   a  and  24   b  along the y-axis, in such a way that the vertical forces can be transmitted effectively from wheel well part  7  to winder box assembly  23  then to lateral superstructure  9 . 
     Winder box  23  is not visible in  FIG. 1 , because it is disposed in front of the section plane of that figure. 
       FIG. 3  is a perspective representation of a bodyshell structure similar to that represented in  FIGS. 1 and 2 . Elements common to  FIGS. 1 and 2  are also shown in  FIG. 3 , where like elements are denoted by like reference numerals. In particular, an extension piece  20  in the form of a beam with right U-shaped section is shown in  FIG. 3 , the rims of the U-shape surrounding the lateral walls of a shock absorber fixation tower  10 . 
     Wheel well part  7  is not represented in  FIG. 3 , so that the contours of tower  10  and of extension piece  20  can be better seen. On the other hand, structural metal sheet  22  in square shape and a belt winder box  23  disposed in this case toward the rear of the vehicle relative to structural metal sheet  22  are shown in  FIG. 3 . 
     Floor  5  is not represented in  FIG. 3 , but it is possible to see a rear floor crossbeam  6  indicating the assembly height of the floor. 
     By virtue of the bodyshell structure according to the invention, a space can be made available underneath the rear floor of the vehicle while still retaining good resistance to rear-end impact of the vehicle by virtue of a low position of the longitudinal reinforcing frame rails. 
     Extension piece  20 , which represents a reduced material cost, makes it possible to transmit the forces from the rear shock absorber (not represented) to reinforcing frame rail  2 . Force-transferring elements  22 ,  23  make it possible to transmit the forces from the rear shock absorber (not represented) to lateral superstructure  9 . 
     The invention is not limited to the described exemplary embodiments and may be developed into numerous variants. It is possible to envision a bodyshell structure containing an extension piece  20  such as described in the foregoing and not containing structural metal sheets  22 . 
     It is possible to envision a bodyshell structure in which tower  10  would be connected to frame rail  2  by a part other than the U-shaped beam described in the foregoing, and in contrast containing one or more structural metal sheets  22  and/or a force-transferring element in the form of a box such as winder box  23 . 
     It could be that preferential plane  21  for absorbing vertical forces is not parallel to the y-axis transversal to the vehicle. The tower could be assembled in such a way that the tower bottom is turned toward the top of the vehicle. Extension piece  20  in the form of a U-shaped beam could have the opening of the U-shape turned toward the interior of the vehicle. Extension piece  20  could have a shape surrounding tower  10  in the upper part and transitioning toward a beam of different section in the lower part, for example toward a closed rectangular section or a closed triangular section, The contour of the tower itself in overhead view could be triangular or trapezoidal. The part of the beam surrounding the tower may have a closed section surrounding all of the lateral walls of the tower. It could be that the level of the rear floor does not correspond to the base of the opening of wheel well part  7  receiving tower  10 . 
     Demountable assemblies could completely or partly replace the welded assemblies connecting frame rail  2 , extension piece  20 , tower  10 , wheel well part  7 , structural metal sheet  22 , front part  24  and rear part  25  of belt winding box  23 .