Abstract:
A rear region of a motor vehicle has an underbody with at least one air-guiding element that is adjustable from a rest position into various operative positions. One operative position increases negative lift and another operative position reduces aerodynamic drag. The air-guiding element is adjustable into the individual operative positions via a central, transversely arranged pivot axis.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 USC 119 to German Patent Appl. No. 10 2013 105 843.4 filed on Jun. 6, 2013, the entire disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a motor vehicle with an adjustable air-guiding element. 
         [0004]    2. Description of the Related Art 
         [0005]    FR 2 856 974 A1 discloses an adjustable air-guiding element in the region of a vehicle rear and forming part of an underbody or to an underbody covering. 
         [0006]    It is the object of the invention to provide a motor vehicle with an adjustable air-guiding element in conjunction with a rear diffuser to influence vehicle forces and/or aerodynamic properties of the vehicle. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention relates to a vehicle that combines a rear diffuser and an associated air-guiding element to obtain higher negative lift forces in a targeted manner and to achieve an optimum adaptation of the aerodynamic properties of the motor vehicle to the driving state. More particularly, at least one holding and adjustment device is below an underbody or an underbody covering and can extend at least one air-guiding element from an upper rest position down toward the ground contact area of the vehicle. The holding and adjusting device also can cause the air guiding element to rise in the manner of a diffuser counter to the direction of travel. The at least one air-guiding element that is in an extended position also can be adjusted about an axis of rotation into a plurality of operative positions. The axis of rotation preferably is in the center of the air-guiding element and runs transversely. This pivotability of the air-guiding element and of the vehicle underbody rising in the manner of a diffuser makes it possible to vary both the negative lift of the rear axle and the coefficient of aerodynamic drag of the vehicle. 
         [0008]    The holding and adjustment device can move the air-guiding element substantially vertically between a rest position where the air-guiding element bears against the underbody and a first operative position where the air-guiding element is parallel to and spaced from the underbody. Negative lift is obtained in this first operative position, thus resulting in improved driving dynamics during rapid travel and on a racing track. 
         [0009]    The holding and adjustment device also can pivot the air-guiding element about the axis of rotation from the downwardly extended first operative position into a second operative position in which the air-guiding element is set at an angle to the underbody with a front edge of the air-guiding element bearing against the underbody. This second operative position results in reduced aerodynamic drag and brings about low fuel consumption. 
         [0010]    A control element preferably is provided to control the holding and adjustment device for pivoting the air-guiding element into positions between the two operative positions, the rest position and intermediate positions. The control element activates the air-guiding element depending on the current driving state and determines the individual positions that can be provided. 
         [0011]    The vehicle preferably has an underbody or an underbody covering that rises from a region of the rear axle of the motor vehicle to the rear end of the vehicle to form a rear diffuser with a diffuser angle of approximately ≧25° between the underbody and a horizontal. This diffuser angle enables the aerodynamic properties of the motor vehicle to be influenced optimally by the adjustable air-guiding element. 
         [0012]    The air-guiding element also preferably is arranged below the underbody covering to overlap approximately ⅓ to ½ of the length of the underbody covering of the diffuser. This diffuser angle and the length of the air-guiding element result in maximum effectiveness of the rear diffuser on the vehicle. 
         [0013]    The air-guiding element preferably is arranged in the rear region of the diffuser so that a rear edge of the air-guiding element is substantially flush with an edge of a rear-part of the vehicle. 
         [0014]    The air-guiding element may be divided in the longitudinal direction and the individual elements may be activated jointly or separately. The rear diffuser according to this embodiment preferably comprises air-guiding elements that form lower wings in a longitudinal channel of the underbody and may be adjustable individually or jointly about a transverse axis within the longitudinal channel to achieve different operative positions. 
         [0015]    In summary, the invention enables negative lift forces from the rear diffuser and air-guiding element to accumulate. More particularly, the combination of the rear diffuser with the air-guiding element enables higher negative lift forces than can be realized by using a diffuser or air-guiding element by itself. The air-guiding element additionally deflects the airflow up. Thus, the combination of the rear diffuser and the air-guiding element enables steeper and shorter diffusers to be used without the flow separating. The pivotability of the air-guiding element about the transverse axis makes it possible to optimally influence the setting angle and the outflow direction of the air. The pivotability of the air-guiding element permits a reduction in the lifting effect of the rear axle or in the aerodynamic drag. By this means, the aerodynamic properties of a motor vehicle can be adapted to match requirements. 
         [0016]    Exemplary embodiments of the invention are illustrated in the drawings and are described in more detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a side view of a vehicle with a rear diffuser shown in two operative positions. 
           [0018]      FIG. 2  is a side view of the vehicle of  FIG. 1  showing a retracted rest position and extended operative position of the air-guiding element. 
           [0019]      FIG. 3  is a side view of the vehicle with an air-guiding element extended parallel to the underbody in a first operative position. 
           [0020]      FIG. 4  is a side view of the vehicle with an air-guiding element pivoted at an angle with respect to the rear diffuser, in a second operative position. 
           [0021]      FIG. 5  is a bottom perspective view of a rear diffuser with an air-guiding element divided in two and pivotable in longitudinal channels of the underbody. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    A motor vehicle  1  comprises an adjustable air-guiding element  4  or plural air-guiding elements  4   a,    4   b  on the underbody  2  or underbody covering in the region of a vehicle rear  3 . 
         [0023]    The underbody  2  or underbody covering rises in the manner of a diffuser counter to the direction of travel FR, and the air-guiding element  4  is below the underbody  2  or underbody covering. Additionally, the air-guiding element  4  is extendable from an upper rest position I down with respect to the ground contact area  5  of the vehicle into operative positions II and III that have different settings. 
         [0024]    In these extended positions, the air-guiding element  4  is mounted in a holding and adjustment device  6  and is pivotable about an axis of rotation  7  into the operative positions II and III ( FIGS. 3 and 4 ). The axis of rotation  7  is in the center of the air-guiding element  4  and runs transversely. 
         [0025]    The air-guiding element  4  is movable via the device  6  from the rest position I bearing against the underbody  2  ( FIG. 2 ) vertically down to the first operative position II where the air-guiding element  4  is parallel to the underbody  2 . The first operative position II forms a negative lift position in which an air gap  8  is formed between the air-guiding element  4  and a diffuser surface  9  of the underbody  2  ( FIG. 3 ). The air flows up past the diffuser  10  and past the air-guiding element  4 , with air flowing around the air-guiding element  4  on all sides. Thus, the diffuser  10  and the air-guiding element  4  exert a force on the air that results in a downward reaction force with increased negative lift forces arising at the rear axle  11 . 
         [0026]    The air-guiding element  4  can be pivoted from the parallel first operative position II into the second operative position III ( FIG. 4 ), in which the air-guiding element  4  is set at an angle α with respect to the underbody  2 . In the operative position III, the air-guiding element  4  is oriented approximately horizontally or set parallel to the ground contact area  5  of the vehicle. There is only a small gap S, if any at all, between the air-guiding element  4  and the diffuser surface  9 . The air L flows off virtually parallel to the ground contact area  5  of the vehicle. There is no deflection of the air and therefore no reaction force arises. Hence, a reduced aerodynamic drag is achieved in this position. 
         [0027]    The air-guiding element  4  is pivotable into at least one third operative position between the first operative position II and the second operative position III. The air-guiding element  4  can be adjusted via a control element that acts depending on the current driving state. 
         [0028]    The underbody  2  preferably has an underbody covering  2  that rises from the rear axle  11  a lower edge  12  of the vehicle rear  3  and forms the rear diffuser  10 . A diffuser angle of approximately ≧25° is formed between the underbody covering  2  and a horizontal H by the rising underbody covering ( FIG. 3 ). 
         [0029]    The air-guiding element  4  arranged below the underbody  2  or the underbody covering has approximately a length of ⅓ to ½ of the length of the diffuser  10 , preferably with a length of the diffuser  10  being 300 to 500 mm. 
         [0030]    The air-guiding element  4  preferably is arranged in the rear region of the diffuser  10  so that a rear edge  14  of the air-guiding element  4  is flush with the lower edge  12  ( FIG. 3 ) and the air-guiding element  4  extends with the rear diffuser  10  over the entire width between the rear wheels  15  of the vehicle  1 . 
         [0031]    According to a further embodiment according to the invention, the rear diffuser  10  can be divided in the longitudinal direction. In this case, the rear diffuser  10  has the air-guiding element  4  defined by two air-guiding elements  4   a,    4   b  forming lower wings in a longitudinal channel  17 ,  17   a  of the underbody  2 . The air-guiding elements  4   a,    4   b  are adjustable about a transverse axis  18 ,  18   a  within the longitudinal channel  17 ,  17   a  with respect to the channel base, as is illustrated in  FIG. 5 . A plurality of operative positions can be set by the pivotability of the two air-guiding elements  4   a,    4   b.    
         [0032]    The air-guiding element  4  preferably has of a wing profile with a convex lower surface  16 . The upper surface  17  of the air-guiding element  4  is adapted to the shape profile of the underbody  2  or to the underbody covering so that the air-guiding element  4  bears tightly against the latter in the rest position I.