Abstract:
A motor vehicle, especially a cabriolet vehicle, with a motor vehicle chassis is provided to whose underbody area at least two reinforcing struts are allocated, each of which trends from a chassis attachment with a component in the direction of a vertical longitudinal mid-plane. A connection support is provided free under the underbody and with a distance to it, at which support two of these struts are held in close distance to each other with respect to the vehicle transverse direction, as well as two further struts, which from there extend away, in each case, with a component in the direction of the vertical longitudinal mid-plane, wherein the connection support is angled about at least one axis extending transverse to the vehicle between the mountings for the two struts and the mountings for the two further struts.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is a US National Phase of International Application No. PCT/DE 2005/000691, filed Apr. 15, 2005, which claims priority to German 10 2004 018 977.3, filed Apr. 20, 2004. The entire contents of the above identified applications are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a motor vehicle, especially a cabriolet vehicle, with struts associated with its underbody area according to the preamble of claim  1 . 
       BACKGROUND OF THE INVENTION 
       [0003]    With motor vehicles there is the problem, in general, that outside stimuli of vibrations occurring during driving operation, such as when driving over uneven roadways, for example potholes or upwards projecting swells, can cause undesired vibrations and torsions of the chassis. Thus, driving safety and comfort can be impacted and the vehicle structure can be placed under strain. This problem occurs notably in cabriolet vehicles having an integral body-frame, which, due to the non-rigid roof, which especially in the open state cannot reinforce the chassis, have a stability disadvantage in comparison with closed vehicle bodies. In particular, noticeable torsions of the vehicle can occur around a longitudinal axis located in the direction of travel. In principle, the problem is more or less pronounced for all vehicle types. 
         [0004]    It is known, in the underbody area to allocate separate, reinforcing struts to the chassis, of which, for example, one strut pair can extend from the outer edge area, in the vehicle transverse direction, in front of the rear wheel arch to an area lying further inward in proximity to a vertical vehicle longitudinal mid-plane behind the rear wheel arch, and can be fixed there to a spare wheel well provided with webs, beading, or similar bracing. 
         [0005]    For vehicles with a low lying rear axle or other special geometric characteristics, the difficulty occurs that the struts usually lying horizontally under the bottom would hit on an obstacle, and the prior possibility of strut localization on the underbody is more difficult, or is completely impossible. 
         [0006]    DE 102 14 372 C1 shows a vehicle in which two struts, which run toward the rear up to a vehicle transverse middle, are fixed with their backward ends on the chassis via a connection area. The connection area is, with respect to the vehicle longitudinal direction towards the back, fixed via three mounts to the chassis in proximity to the vehicle transverse middle. Thereby, the supports counteract a bending stress around a horizontal axis lying transverse to the vehicle. Additionally, a rear strut pair is provided, which likewise on one end is held at the connection area, and is intended to counteract a torsional stress of the vehicle about a vehicle longitudinal axis. However, for torsion the system is over-determined. Elongation or compression strains introduced via one of the forward struts are counteracted in part via a bending of the connection area, and in a further part via the supports lying in the vehicle transverse middle, where the supports on the basis of their proximity to the vehicle transverse middle offer no effective support against torsions, and only a further part of the introduced force is picked up by the struts. Therefore, the reduction of the torsions is degraded. In addition, for adverse chassis conditions, such as a low-lying rear axle, such a construction cannot be assembled. 
       SUMMARY OF THE INVENTION 
       [0007]    The objective of the invention is to broaden the possibilities for the course of the struts and their connection to the chassis for a motor vehicle. 
         [0008]    The invention solves this problem through a motor vehicle having the features of claim  1 . Advantageous embodiments of the objective of the invention arise from the further claims  2  to  10 . 
         [0009]    With the freely suspended arrangement of the connection support beneath the underbody, an optimal counteraction results against the torsional deformations of the vehicle occurring about a longitudinal axis. The connection support requires no further connection beyond the struts that are held there and respectively run toward the transverse vehicle edges. Due to the spacing of the connection support to the underbody, this is also installable in adverse chassis conditions, and can also, in particular, be located in front of a rear axle in the direction of travel. Whether the projection of the struts in the horizontal plane form a large or small angle outgoing from the connection support has no effect at all on the minimization of the torsion. Furthermore, through the close spacing of the strut ends to the connection support in relation to the vehicle transverse direction, it is assured that the connection support will not be subject to bending stress. 
         [0010]    The latter is especially true when the spacing of the strut mountings at the connection support in the vehicle transverse direction is less than 120 millimeters. 
         [0011]    Because the connection support is angled about at least one axis extending transverse to the vehicle between the mountings for two struts and the mountings for two additional struts, the front and rear struts do not need to lie in the same plane, instead the rear struts can, for example, trend sharply upwards from the connection support, such that they can be fixed, for example, at a cross support lying in front of the rear axle in the direction of travel. 
         [0012]    The avoidance of a bending stress results, in particular, when the spacing of the strut mountings at the connection support in the vehicle transverse direction is less than 120 millimeters. 
         [0013]    With this, a particularly effective cancellation of the torsion is achieved when the rear pair of struts is fixed to a transverse support of the chassis by connection flanges that encompass the supports at least in areas on the front and back sides. 
         [0014]    It is also possible that the struts are formed to be vibration selective, and associated with these are a pick-up unit for the take-up of longitudinal stresses occurring during driving, and at least one actuator element for effecting a force to counteract the longitudinal stresses, so that an active stabilization of the vehicle against outside stimuli is possible. 
         [0015]    Further advantages and features of the invention arise from a practical example of the object of the invention represented in the drawings and described in the following. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The drawings show: 
           [0017]      FIG. 1  a schematic, perspective view of an underbody area of a motor vehicle formed/constructed according to the invention, 
           [0018]      FIG. 2  an enlarged view of the detail II in  FIG. 1 , 
           [0019]      FIG. 3  a similar view to  FIG. 2 , however, instead of the front struts, associated force vectors are shown, 
           [0020]      FIG. 4  a detailed view from below of the strut arrangement according to  FIG. 2 , 
           [0021]      FIG. 5  the area according to  FIG. 2  in a perspective view, obliquely from below, 
           [0022]      FIG. 6  a similar view to  FIG. 5 , without the chassis parts shown, 
           [0023]      FIG. 7  a detailed view corresponding to the section VII in  FIG. 6 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    In the illustrated practical example according to  FIG. 1 , a first pair of bracing struts  4 ,  5  that are at least nearly symmetrical about a vertical longitudinal mid-plane  3 , is associated, at least in the rear half of the vehicle, with the underbody  2  of a vehicle  1 —here a cabriolet vehicle, which is not essential. In addition, further struts can lie in the front area of the vehicle. The number and symmetrical arrangement of the struts  4 ,  5  shown in the drawing are only to be viewed as an example, as is their trend. 
         [0025]    The struts  4 ,  5  here are mounted via brackets, in each case, with their forward ends  6 ,  7  in the direction of travel F, to the underbody  2  of the vehicle  1  in its outer transverse edge area, for example, at side beams. In the present practical example, they are detachably screwed to the underbody  2 , to which end above the underbody  2  there are provided, in each case, abutments—not shown—that are separate and supplied with internal threads. Also, a riveting or welding can be considered. 
         [0026]    The struts  4 ,  5  extend in their trend from their forward ends  6 ,  7  in front of the rear wheel arches  9  up to the rear ends  10 ,  11 , which, with respect to the direction of travel F, can lie behind or even in front of the wheel arches  9 , with a component toward the vertical longitudinal mid-plane  3 . The struts  4 ,  5  can be formed, for example, as flat steel or profiles, such as tubular or rectangular profiles, from metal, or also, for instance, from fiber reinforced plastics. The ends  6 ,  7 ,  10 ,  11  can be compressed, also for profile struts  4 ,  5 , in order to simplify the reach-through of fastening means. The form of the struts  4 ,  5  can deviate significantly from the straight-line form shown here. Also, components that are somewhat angled and/or flat in areas can be considered as struts. 
         [0027]    The rear ends  10 ,  11  of the struts  4 ,  5  are attached at a common connection support  12 , which is lying underneath the underbody  2 , and with a vertical offset from it. 
         [0028]    Here, the rear ends  10 ,  11  of the two struts  4 ,  5  lie transverse to the direction of travel F, in close proximity to each other; their transverse distance  8  is a maximum of 120 millimeters, and generally it is much less than 100 millimeters, in order to avoid a bending stress on the connection support  12 . 
         [0029]    Additionally, two further struts  13 ,  14  with their ends  15 ,  16  are held at the connection support  12 , and extend with their ends  17 ,  18 , facing away turning outwards from the vertical longitudinal mid-plane  3 . 
         [0030]    Thus the connection support  12  is held solely by the two strut pairs,  4 ,  5  and  13 ,  14  from the underbody  2 , and otherwise is freely suspended. Further chassis connections are completely dispensable. The position of the connection support  12  can thus vary significantly, according to the geometry of an underbody  2 , in particular, depending upon space conditions, it can be located either in front of or behind the rear axle. The struts  4 ,  5 ,  13 ,  14  are detachably held here to the connection support  12  via screw connections, so that a simple disassembly is possible, such as for an exchange of the exhaust system. The connection support  12  can also be built—not shown here—as one piece with one of the struts  4 ,  5 ,  13 ,  14 , or with a strut pair  4 ,  5  or  13 ,  14 . 
         [0031]    Also, the transverse distance  19  of the ends  15 ,  16  of the additional struts  13 ,  14  at the connection support  12  is as small as possible, and amounts to clearly less than 120 millimeters, in the practical example less than 40 millimeters. 
         [0032]    The further struts  13 ,  14 , with the ends  17 ,  18  facing away, are fixed to the underbody  2  in an area of rigid sections, which are supporting and lying transverse to the direction of travel, such as at the spare wheel well, on lateral longitudinal supports, or—as here—on a transverse support  20 . 
         [0033]    There the struts  13 ,  14  are fixed via connection flanges  21 ,  22  that at least partially surround the transverse support  20  on the front and back sides, and which, especially as is seen in  FIG. 7 , like the strut arrangement, need not be symmetrical. The flange  22  reaches around, for example, two bolts  23 , which in the connection position lie horizontal and parallel to the longitudinal plane  3 , which attach through the transverse support  20 . Thus the struts  13 ,  14  are held particularly stable against elongation or compression force effects in their direction of extension. The ends  17 ,  18  of the struts  13 ,  14  end via the flanges  21 ,  22  also not parallel to the underbody, rather they rise nearly perpendicular to it, as can be seen in the example in  FIG. 7 . Therefore, during torsion a bending of these struts  13 ,  14  about their y-axis is necessary so that the struts  13 ,  14  can oppose this force effect with especially high resistance. 
         [0034]    The connection support  12  can be formed by a flat body, angled about an axis  24  that is horizontal and transverse to the direction of travel F. Considered here, for example, is a steel body from ST  52  in a thickness of 5 millimeters. The support  12  can have, for example, dimensions of 10*30 millimeters. The angle lies between the connection points of the front struts  4 ,  5  and the rear struts  13 ,  14 . Because in the practical example, a low lying rear axle  25  is provided, the resulting bending is a large angle of, for example, 60° to 80°, so that the rear struts  13 ,  14  can also be fixed, still before the rear axle, in the direction of travel, to the underbody  2 —here to the transverse support  20 . Also, foregoing a bending, or a bending of more than 90° is possible here, if the configuration of the underbody requires this. This results from the fact that the strut arrangement shown here is to function alone against torsion, and a reinforcement of the vehicle against bending need not be incorporated with it. As explained below using  FIG. 3 , during torsion, resulting forces occur only in the vehicle transverse direction and not in the vehicle longitudinal direction. Also, it is not necessary that the connection support  12  lie in the longitudinal mid-plane  3 , rather an off-center position of some tens of millimeters is easily possible. The connection support  12  can be bent differently depending on the vehicle, and is therefore applicable to various vehicles. 
         [0035]    In projection onto a plane that is bent corresponding to the bending about the axis  24 , the struts  4 ,  5 ,  13 ,  14  result in nearly an X-shape that is very favorable for the torsional rigidity about a vehicle longitudinal axis, wherein the connection sheet metal  12  forms the vertex of the X. 
         [0036]    During stimulation of a torsion of the vehicle  1  about a longitudinal axis by the fact, for example, that the right front vehicle area, in the direction of travel F, experiences an upward directed impulse, ( FIG. 3 ), the strut  4  is subjected to a tensile force, whereas the opposing strut  5  is subjected to a compressive force. The resulting force acts completely in the vehicle transverse direction, so that no support in the vehicle longitudinal direction is needed. The resulting force is then counteracted by the two rear struts  13 ,  14 , which are also fixed to areas of the underbody  2  that are rigid in the vehicle transverse direction, here to the transverse support  20 . Also, the localization via the flanges  21 ,  22  is formed such that large forces in the vehicle transverse direction can be absorbed. In particular, the strut ends  17 ,  18  are fixed as far outward as possible at the underbody  2 . 
         [0037]    The struts  4 ,  5  of the chassis can serve not only as customary reinforcement components, but also—not shown—as adaptive vibration dampers, i.e. that they, along with their passive reinforcement function, also enable an active influence on the vibration behavior of the chassis. 
         [0038]    For this, the struts  4 ,  5  can respectively be built from multiple parts, and detect via piezoelectric crystals a change in length of the struts  4 ,  5 , such as while driving over a pothole or a bump, and actively counteract this via actuators with a short response time. 
         [0039]    The tensile or compressive force on the struts  4 ,  5  is detected by the receiving unit that contains, for example, compressive strain transducers, and is transformed into an electrical signal for the actuator, which counteracts the outside force. The two struts  4 ,  5  are then lengthened or contracted against each other in opposite phases by the actuators. Both struts  4 ,  5  thereby brace the chassis at the same time, and effect an active damping. With this, the effect of the outside stimuli is nearly cancelled. The actuator and the receiver unit have very short response times, so that the excitation frequencies of a few Hz up to 10 s of Hz can be effectively counteracted. 
         [0040]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.