Abstract:
A motor vehicle body includes a steel support structure surrounding a passenger compartment and a sidewall covering the support structure. The sidewall includes a front and a rear fender, at least one of which is realized in the form of a lightweight component of light metal, as well as a steel roof frame element that borders on both fenders.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to German Patent Application No. 102015014643.2, filed Nov. 12, 2015, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present disclosure pertains to a motor vehicle body, and in particular a lightweight body which utilizes light metal without compromising the dimensional stability of the passenger compartment. 
       BACKGROUND 
       [0003]    One way for meeting the increasingly stringent legal requirements with respect to the fuel consumption of vehicles is to reduce the weight of the vehicles by replacing their components, which are conventionally made of steel, with light metal or plastic components. DE 10 2010 019 999 A1 discloses a motor vehicle body, in which a steel support structure surrounding a passenger compartment is covered with planking parts of aluminum. Among other things, these planking parts include an outer wall section that extends around front and rear door cutouts on a side of the vehicle. However, the coefficients of thermal expansion of steel and aluminum differ significantly such that the length increase of such an outer wall section can be several millimeters greater than that of the underlying steel support structure when the vehicle body is subjected to a high temperature, e.g. while drying the paint applied thereon. Consequently, there is a significant risk of the outer wall section locally distorting to such a degree that permanently visible traces remain when it is subjected to a high temperature. 
       SUMMARY 
       [0004]    According to the present disclosure a motor vehicle body is disclosed, the weight of which is reduced due to the utilization of light metal without compromising the dimensional stability of the passenger compartment. In particular, the risk of a thermally induced distortion of the light metal leaving visible traces thereon is simultaneously minimized. 
         [0005]    According to an embodiment of the present disclosure, a motor vehicle body includes a steel support structure surrounding a passenger compartment and a sidewall covering the support structure. The sidewall includes a front and a rear fender, at least one of which is realized in the form of a lightweight component of light metal, as well as a steel roof frame element that borders on both fenders. Due to the fact that the roof frame element connects the two fenders, it is elongated in the longitudinal direction of the vehicle and simultaneously narrow such that it is on the one hand subjected to particularly high stresses in case its coefficient of thermal expansion differs from that of the steel support structure, but can on the other hand also be very easily distorted due to its small lateral dimension. Since the roof frame element is made of steel, it is protected from thermally induced tensions and a resulting distortion, wherein the contribution of the roof frame element to the overall weight of the body is due to its small lateral dimension so low that the issue of whether the roof frame element is made of steel or of light metal only has little influence to the overall weight of the body. The fact that the at least one fender is made of light metal has due to its large surface area a greater influence on the body weight. A thermal expansion that differs from that of the support structure only has a relatively insignificant effect on this fender due to its compact shape such that the fender only has a low tendency of permanently distorting under thermal stress. 
         [0006]    If the lightweight component of light metal includes a visible and a concealed metal sheet, only the concealed metal sheet is preferably anchored to the support structure. In this way, thermal stresses resulting from the connection of the light metal to the steel support structure are essentially limited to the concealed metal sheet and the visible metal sheet is protected from a potentially conspicuous deformation. 
         [0007]    In order to compensate different thermal expansions of the support structure and the fender, the roof frame element and the at least one fender should be separated by an expansion gap. 
         [0008]    The sidewall may furthermore include a B-column cover that is likewise realized in the form of a lightweight component made of light metal or plastic. A door sill cover of the sidewall may also be realized in the form of a lightweight component that, however, is preferably made of plastic rather than light metal. 
         [0009]    The support structure may include an elongate carrier flange on an edge of a door opening in order to mount parts of the sidewall. At least one of the lightweight components may include a contact flange that is held in contact with the carrier flange of the support structure by an elastic groove profile attached to the carrier flange and the contact flange. Such a groove profile can on the one hand ensure a rigid seat of the lightweight component on the support structure, but on the other hand also makes it possible to reduce thermal stresses in that the carrier flange and the contact flange can shift relative to one another along their contacting surfaces. 
         [0010]    The groove profile may include a clip with two legs that encompass a groove for accommodating the carrier flange and the contact flange on both sides. In order to ensure a rigid seat of the flanges on one another, the groove profile may furthermore include an elastically compressed element between one of the legs and the carrier flange and/or an elastically compressed element between the other leg and the contact flange. The carrier flange may be in contact with contact flanges of different lightweight components over its length; in this way, the flanges can form a frame that extends around the door opening. 
         [0011]    According to a preferred embodiment, the aforementioned groove profile is simultaneously realized in the form of a door seal profile. The door seal profile preferably extends around the door opening over the entire length of the adjoining carrier and contact flanges. 
         [0012]    The B-column cover may form one of the different lightweight components that are in contact with the carrier flange. In this case, a second contact flange of the B-column cover is preferably held on a second door opening by a second groove profile. 
         [0013]    If the lightweight component consists of a door sill cover, a second flange of the door sill cover, which faces away from the door opening, is preferably bonded on the support structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements. 
           [0015]      FIG. 1  shows a side view of an inventive motor vehicle body; 
           [0016]      FIG. 2  shows a section through the sidewall and the underlying support structure along the plane II-II in  FIG. 1 ; 
           [0017]      FIG. 3  shows a section along the plane II-III; 
           [0018]      FIG. 4  shows a section along the plane IV-IV; and 
           [0019]      FIG. 5  shows a section along the plane V-V in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description. 
         [0021]    The sidewall  1  of a motor vehicle body illustrated in  FIG. 1  includes multiple components that are not directly connected to one another, but rather only by an underlying support structure that is not visible in  FIG. 1  and conventionally forms a frame around a passenger compartment. The components of the sidewall include a roof frame element  2  that is made of steel analogous to the underlying support structure and continuously extends in one piece over the entire length of the passenger compartment, i.e. over a front and a rear door opening  3  and  4 . In a front region  5 , the roof frame element  2  forms a cover of the upper part of an A-column of the support structure extending between windshield and side window. A central region  6  forms a lateral end of the roof surface and a rear region  7  forms a cover of a C-column. 
         [0022]    A rear fender  8  made of light metal sheet, particularly an aluminum sheet, is separated from the lower edge of the rear region  7  by an expansion gap  9 . In  FIG. 1 , the roof frame element  2  is illustrated in a position, in which it is slightly shifted upward relative to its position on the finished motor vehicle body, such that the expansion gap  9  appears wider in the figure than on the finished body and an upper edge of the fender  8 , which is otherwise concealed by the rear region  7  on the completely assembled vehicle, is exposed. The upper boundary of the rear fender  8  is formed by a rear window opening  10  and a rear door opening  4  and its lower boundary is formed by a rear wheel cutout  11 . 
         [0023]    The fender  8  borders on a door sill cover  13  molded of plastic along a lower edge  12  between the rear wheel cutout  11  and the door opening  4 . Edges  14 ,  15 , at which the door sill cover  13  and a B-column cover  16 , as well as the door sill  13  and a cover  17  of the lower part of the A-column, respectively border on one another, extend at approximately the same height as the edge  12 . 
         [0024]    The upper edge of the door sill  13  bordering on the front and rear door openings  3 ,  4  is respectively formed by vertical flanges  18 ,  19  that are elongated in the longitudinal direction of the vehicle and referred to as contact flanges below. A contact flange  20  extending upward from the front edge of the B-column cover  16  flushly adjoins the contact flange  18  and is on its upper end extended by a flange of the roof frame element  2  that is concealed in  FIG. 1 . Only a small part of a contact flange  21  of the cover  17 , which once again flushly extends between the contact flange  18  and the flange of the roof frame element  2 , is visible in this figure. 
         [0025]    The contact flange  19 , a contact flange  22  of the rear fender  8 , a contact flange  23  on the rear edge of the B-column cover  16  and a once again concealed flange of the roof frame element  2  form a frame around the rear door opening  4  analogous to the contact flanges  18 ,  20 ,  21 . 
         [0026]    The sidewall furthermore includes a front fender, which like the rear fender  8  is made of an aluminum sheet. This front fender conventionally extends in front of the front ends of the roof frame element  2  and the door sill cover  13  and is at least spaced apart from the roof frame element  2  by an expansion gap. 
         [0027]      FIG. 2  shows a section through the B-column cover  16  and the B-column  24  of the support structure covered thereby. The B-column  24  is composed of two sheet metal walls  25 ,  26  that are welded together along their front and rear edges referred to the longitudinal direction of the vehicle in order to form a hollow profile with forwardly and rearwardly protruding carrier flanges  27 . The respective flanges  20  and  23  of the B-column cover  16  adjoin the carrier flanges  27 . They are fixed on the carrier flanges  27  by two door seal profiles  28  that respectively extend around the door openings  3 ,  4  in a seamless fashion. 
         [0028]    The door seal profiles  28  respectively include a groove profile  30  that is reinforced with an inserted metal rail  29 , wherein elastic lips  32  respectively engage into the groove from the two opposing legs  31  of the groove profile. In  FIG. 2 , the lips  32  are illustrated in the relaxed position; once the respective flanges  20 ,  27  and  23 ,  27  are inserted into the groove profile  30 , they are pressed against one another by the elastically deflected lips  32  such that the B-column cover  16  is held in contact with the carrier flanges  27 , but the respective flanges  20 ,  27  and  23 ,  27  can still slide along one another in order to reduce potential thermal stresses caused by the different coefficients of thermal expansion of the plastic B-column cover  16  and the steel B-column  24 . Hollow profiles  33  formed on an outer side of the groove profile  30  are conventionally provided for producing seals along the doors that are not illustrated in the figures and engage into the respective door openings  3  and  4 . 
         [0029]      FIG. 3  shows a section through the door sill cover  13  and an underlying door sill  34  along the plane III-III in  FIG. 1 . Analogous to the B-column  24 , the door sill  34  is also composed of two metal sheets  35 ,  36  that are welded to one another along upwardly and downwardly protruding flanges. The upper of these two flanges acts as a carrier flange  37  that is in contact with the respective flanges  18  and  19  of the door sill cover  13  and held by the door seal profile  28  extending around the door openings  3 ,  4 . A lower flange  38  of the door sill cover  13  is bonded along an underside of the outer sheet metal wall  35 . The bond extends continuously over the entire length of the flange  38  such that thermal stresses can occur along this bond due to different coefficients of thermal expansion of the sheet metal wall  35  and the door sill cover  13 ; since plastic has a relatively high elasticity in comparison with a light metal sheet, however, the door sill cover  13  is able to adapt to the thermal expansion of the sheet metal wall  36  along the flange  35  without tearing or buckling. 
         [0030]      FIGS. 4 and 5  shows two sections through the rear fender  8  of light metal and underlying parts of the support structure, in this case a wheel well  39 , along different planes IV-IV and V-V. Similar to the B-column  24  and the door sill  34 , the fender  8  is composed of an outer sheet metal wall  40  and an inner sheet metal wall  41  that are connected to one another along their edges. On their edges facing the rear door opening  4 , the welded sheet metal walls  40 ,  41  form the contact flange  21  as shown in  FIG. 4  and a corresponding flange  42  extends along an upper edge of the sheet metal walls  40 ,  41  bordering on the rear window opening  10  as shown in  FIG. 5 . On its lower edge bordering on the rear wheel cutout  11 , the outer sheet metal wall  40  is beaded around the edge of the inner sheet metal wall  41 . Only the inner sheet metal wall  41  is mounted on the flanges  43 ,  44  of the steel wheel well  37  such that thermal stresses occurring along these flanges  43 ,  44  are limited to the inner sheet metal wall  41  and cannot lead to a visible distortion of the outer sheet metal wall  40 . 
         [0031]    While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.