Abstract:
A support structure ( 1 ), in particular an axle support for a motor vehicle, which is made as a single-shell or multi-shell frame element ( 7 ) of fiber-reinforced plastic. The frame element ( 7 ) has at least one elastic connection point ( 9, 9′, 9″, 9′″ ) for connection to an aggregate such that the at least one elastic connection point ( 9, 9′, 9″, 9′″ ) is formed integrally with the frame element ( 7 ). Additionally, a method for producing such a support structure ( 1 ) is disclosed.

Description:
This application is a National Stage completion of PCT/EP2013/074005 filed Nov. 18, 2013, which claims priority from German patent application serial no. 10 2013 201 075.3 filed Jan. 24, 2013. 
     FIELD OF THE INVENTION 
     The invention concerns a support structure, in particular an axle support for a motor vehicle and a method for producing a support structure of that type. 
     BACKGROUND OF THE INVENTION 
     To hold chassis components such as control arms, suspensions, etc, motor vehicles (passenger cars and utility vehicles) comprise a support structure in the form of an axle support or auxiliary frame. This axle support distributes the loads to suitable connection points on the body and at the same time also offers an elastic decoupling of the chassis relative to the body. The elastic decoupling is particularly advantageous in relation to driving comfort and the acoustics during driving. Moreover, the axle support also serves to facilitate the fitting of the chassis as a pre-assembled module. 
     From the prior art axle supports are known, which consist of welded metallic structures made for example from steel sheet or cast aluminum assemblies combined with extruded sections. Furthermore, from the prior art it is also known to make axle supports from fiber-reinforced plastic. 
     For example, from DE 695 22 950 T3 a front and/or rear suspension assembly with a substantially Omega-shaped chassis component made from fiber-reinforced plastic is known, which is integrated in a two-shell auxiliary frame. The auxiliary frame can be made from steel, aluminum or magnesium. Alternatively, the auxiliary frame can also be made from fiber-reinforced plastic. 
     Until now, due to the complex requirements relating to mechanical properties such as strength and rigidity at the force transfer points of the known auxiliary frames or axle supports, there has still not been any solution for economical mass production. In that respect it is particularly problematic that the known designs require elastic mountings, for example in the form of rubber mountings, which have to be designed in such manner that they have high elasticity parallel to the longitudinal axis of the vehicle, but high rigidity perpendicular to that axis. An additional disadvantage of the known designs is, moreover, that in the case of axle supports or auxiliary frames made from fiber-reinforced plastic, during production a lot of excess material is produced at the corners, which has to be removed, in particular cut away in an additional process step. 
     SUMMARY OF THE INVENTION 
     Accordingly one objective of the present invention is to provide a support structure, in particular an axle support for a motor vehicle, which can be produced economically but which still satisfies the mechanical requirements particularly at the force transfer points of the support structure. A further objective of the present invention is to provide an appropriate production method for such a support structure. 
     These objectives are achieved by a support structure having the characteristics described below and a method for producing a support structure having those characteristics. 
     A support structure, in particular an axle support for a motor vehicle is provided, which is made as a single-shell or multi-shell frame element from fiber-reinforced plastic, wherein the frame element has at least one elastic connection point for connection to an aggregate, the at least one elastic connection point being made integrally with the frame element. By virtue of this configuration of elastic connection points made integrally with the frame element, economical production can be ensured while at the same time satisfying the strict mechanical requirements demanded from the support structure. Moreover, by designing the connection points themselves elastically, the need for additional rubber mountings is avoided, which further improves the economy of the production process since, on the one hand, costs for the additional rubber mountings can be saved and, on the other hand, an additional production step for fitting the rubber mountings can be omitted. 
     In a preferred embodiment the support structure comprises at least two elastic connection points, in particular four elastic connection points. The number of elastic connection points provided can be varied depending on the field of use or the requirements demanded from the support structure. 
     In another preferred embodiment the frame element is designed with two shells, in particular with an upper shell and a lower shell, such that between the upper and the lower shell a hollow space is formed. Alternatively, however, the frame element can also be of single-shell design with an open profile, which saves material costs and renders superfluous an additional step of joining the upper and lower shells to one another, for example by adhesive bonding. 
     Preferably, the frame element has a substantially S-shaped cross-section. The S-shaped design has the advantage that when the upper and lower shells are bonded together, this can take place on substantially straight surfaces. 
     Moreover, it is advantageous for the at least one elastic connection point to be substantially elastic in the direction of a longitudinal axis of the motor vehicle and substantially rigid in a direction perpendicular to the longitudinal axis. The high elasticity in the vehicle&#39;s longitudinal direction enables a parallel displacement backward and forward along the longitudinal axis of the vehicle, which serves to reduce the bumpiness of the chassis, for example when driving over uneven ground. In practice the displacement can be up to 6 mm. Furthermore, it should be noted that the elasticity at the elastic connection points is achieved by virtue of a small cross-section and a low area moment of inertia of the support structure in the area of the elastic connection points. In contrast, the high rigidity in the transverse direction is enabled by force transfer over the entire area, which is in the form of or acts as a compression or tension strut. This is ensured by a corresponding orientation of the fibers in a lateral surface of the support structure. 
     Preferably, the at least one elastic connection point is formed by folding a textile, which simplifies the production process. 
     Preferably, the fiber-reinforced plastic is reinforced with long-fiber and/or continuous-fiber plastic fibers (organic sheet). In particular, continuous fibers are advantageous for textile folding. 
     It is also advantageous for the frame element to taper down in the area of the at least one elastic connection point. In particular, in the connection area to the vehicle&#39;s body, depending on the required connection rigidity, the hollow space formed by the upper and lower shells is of tapered shape. This still further reduces the above-mentioned bumpiness of the chassis when driving over uneven ground. 
     In a further preferred embodiment the frame element has a substantially rectangular body with four corner sections, such that from each corner section an elastic connection point projects in the direction transverse to the longitudinal axis of the motor vehicle. In this case it is advantageous for the elastic connection points to be arranged substantially in the transverse direction of the vehicle and to project from the support structure, so that the rubber mountings used in the prior art can thereby be effectively replaced and the above-mentioned elastic properties in the longitudinal direction of the vehicle can be achieved. 
     However, as an alternative the frame element can have only two elastic connection points, which are then connected by a bracket-like element. 
     A further advantage can be achieved by forming the support structure with reinforcing elements, in particular reinforcing ribs, the reinforcing elements being made as plastic moldings of long-fiber-reinforced thermoplasts or SMC/BMG (Duroplast). This advantageously ensures that the strict mechanical demands made on the support structure can be satisfied and no premature failure of the support structure takes place. The plastic moldings can be provided on the inside and/or outside of the frame element. The textile reinforcing structure can be a scrim, a fabric, a woven material, a knitted material or a mat, and can contain quasi-continuous or cut long fibers. The textile finished product can be dry or pre-impregnated, and can contain a hybrid yarn or a binder for fixing dry layers. For the production and shaping of dry textile semifinished products, the use of thermoplastic or reactive binders, for example based on a resin component, is advantageous. As resins, thermoplasts such as polyamides (PA), polysulfones (PS), polypropylene (PP) or PEEK can be used. As Duroplasts, epoxide resins, polyurethane, vinyl ester or hybrid resin systems are suitable. As the production process, preferably hot-molding can be used for pre-impregnated semifinished products and a Liquid Composite Molding (LCM) process (RIM, RTM, etc.) can be implemented for the use of dry textile semifinished products. 
     In a further preferred embodiment the upper and lower shells are joined to one another by a joining method, in particular by adhesive bonding, riveting or screwing, or by welding. Welding by ultrasound, laser or vibration is particularly advantageous when thermoplastic materials are used for the support structure. 
     The hollow space can be filled with a low-density material, in particular a foam, honeycomb material or balsa-wood. During the production process this can advantageously be used in order to shape the upper and lower shells in one step. 
     According to the invention, in addition a method for producing a support structure is provided, the method comprising the following steps: production of a textile semifinished product or a semifinished product made of textile-reinforced plastic for forming the support structure, having a substantially rectangular body with four corner sections; deforming the textile semifinished product or semifinished product made of textile-reinforced plastic, from an initial circumference to a smaller, second circumference displaced relative to a reference plane of the textile semifinished product or semifinished product made of textile-reinforced plastic; forming folds from the areas compressed during the deformation step, in order to form two, more particularly four, elastic connection points and further force transfer points formed by the folds. This process is particularly economical, since as already described earlier, additional rubber mountings are rendered superfluous and the support structure can be made in one piece in a simple manner, since the excess material of the upper and lower shells no longer has to be cut away, but is used further for the elastic connection point(s). 
     Preferably, the construction of the support structure is multi-layered, the layers being fixed in intermediate steps in a so-termed pre-forming process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Below, an embodiment of the invention is described in greater detail with reference to the attached drawings, which show: 
         FIGS. 1A-1C : Various views of a support structure according to an embodiment of the invention; and 
         FIG. 2 : A perspective view of a front portion of a support structure according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1A to 1C  show various views of a support structure  1  according to an embodiment of the invention,  FIG. 1A  shows a perspective view of the support structure,  FIG. 1B  a view of the support structure seen from above, and  FIG. 1C  a section along the line  1 C- 1 C shown in  FIG. 1B . The support structure  1  is an axle support or auxiliary frame for a motor vehicle. In the embodiment shown here the support structure  1  is in the form of a two-shell structure with an upper shell  2  and a lower shell  3  (see in particular  FIG. 1C ), the shells being firmly joined to one another to form a frame element  7 . The upper shell  2  and the lower shell  3  are in each case S-shaped (in this case shown as back-to-front mirror images), so that the upper shell  2  can be joined to the lower shell  3  along their respective, substantially straight upper and lower surfaces  4 ,  4 ′,  5 ,  5 ′, for example by bonding. Between the upper shell  2  and the lower shell  3  a hollow space  6  is formed, which however, can also be filled with a low-density material as already described earlier. The wall thickness of the upper and lower shells  2 ,  3  is 4 to 5 mm. The frame element  7  is made of a fiber-reinforced plastic and has a substantially rectangular shape with four corner sections  8 ,  8 ′,  8 ″,  8 ′″, such that from each corner section  8 ,  8 ′,  8 ″,  8 ′″ an elastic connection point  9 ,  9 ′,  9 ″,  9 ′″ projects in the direction transverse to the longitudinal axis L of the motor vehicle. The elastic connection points  9 ,  9 ′,  9 ″,  9 ′″, which serve as force transfer points, are formed integrally with the frame element  7  by textile folding. By virtue of the connection points  9 ,  9 ′,  9 ″,  9 ′ so formed, there is elasticity or flexibility in the direction of the longitudinal axis L and at the same time rigidity in the direction transverse to the longitudinal axis L. 
     To further reduce the bumpiness of the chassis as already described earlier, in the area of connection to the body, i.e. at the elastic connection points  9 ,  9 ′,  9 ″,  9 ′″ the support structure  1  is formed with a taper, i.e. the hollow space  6  between the upper shell  2  and the lower shell  3  becomes narrower. The distance between the upper and lower shells  2 ,  3  is at most 5 mm at the tapered elastic connection points  9 ,  9 ′,  9 ″,  9 ′″. Along the respective elastic connection points  9 ,  9 ′,  9 ″,  9 ′″ in the direction toward the four-cornered frame element  7 , the upper shell  2  and the lower shell  3  are V-shaped over a length of 10 to 20 cm in an aperture distance of 10 cm. 
     In an alternative embodiment not shown in detail here, if the support structure  1  has only two elastic connections  9 ,  9 ′″, then the frame component  7  would end approximately at the broken line indexed  10  in  FIG. 1B , so that the elastic connection points  9 ,  9 ′″ are only connected by a bracket-like element, in this case indexed  11 . In contrast, in the variant with four elastic connection points  9 ,  9 ′,  9 ″,  9 ′″ there are also four bracket-like elements  11 ,  11 ′,  11 ″,  11 ′″, which then form the frame element  7 . 
     By providing the elastic connection points  9 ,  9 ′,  9 ″,  9 ′″ made integrally with the frame element  7  as described above, the provision of additional rubber mountings is superfluous. The folds  12 ,  12 ′ (see  FIG. 2 ) formed by textile folding along the edges of the support structure  1  and the likewise formed elastic connection points  9 ,  9 ′,  9 ″,  9 ′″ serve as force transfer points by virtue of the through-going fiber structure of long or continuous fibers in the plastic of the support structure  1 . 
       FIG. 2  shows a perspective view of a front portion of a support structure  1  according to an embodiment, in which the support structure  1  is additionally provided with reinforcing elements  13 , here in the form of reinforcing ribs. The collars  14  also formed by textile folding on the underside  15  of the support structure  1  can additionally be provided with reinforcing elements. The reinforcing elements  13  can be made as plastic moldings, in particular of fiber-reinforced thermoplasts or Duroplasts. 
     INDEXES 
     
         
           1  Support structure 
           2  Upper shell 
           3  Lower shell 
           4 ,  4 ′ Upper straight surfaces 
           5 ,  5 ′ Lower straight surfaces 
           6  Hollow space 
           7  Frame element 
           8 ,  8 ′,  8 ″,  8 ′ Corner sections 
           9 ,  9 ′,  9 ″,  9 ′ Elastic connection points 
           10  Broken line 
           11 ,  11 ′,  11 ″,  11 ″ Stirrup-like elements 
           12 ,  12 ′ Folds 
           13  Reinforcing element 
           14  Collar 
           15  Underside