Abstract:
A crossmember ( 20 ) for a front bumper of a motor vehicle ( 10 ) has at least one throughflow opening for air. At least one exit-air opening ( 51, 52 ) is provided on a rear side ( 44 ) of the crossmember ( 20 ) to accommodate a discharge of exit air from a cooler of the motor vehicle.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 USC 119 to German Patent Appl. No. 10 2014 104 286.7 filed on Mar. 27, 2014, the entire disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a crossmember for a front bumper of a motor vehicle having at least one throughflow opening for air. The invention also relates to a motor vehicle having such a crossmember and a method for operating a motor vehicle. 
         [0004]    2. Description of the Related Art 
         [0005]    DE 10 2009 056 841 A1 discloses a front part of a motor vehicle body having a cooler and having a bumper support extending transversely in front of the cooler. An air passage is formed in bumper support there and is directed toward the cooler. DE 10 2012 015 336 A1 discloses a crossmember for a bumper of a passenger motor vehicle. The crossmember has at least one throughflow region in the vehicle transverse direction and at least one throughflow opening for air. The throughflow region is adjoined to the inside by a central region and to the outside by an outer region that are free from throughflow openings for air. 
         [0006]    It is an object of the invention to improve the discharge of exit air from a cooler in motor vehicles having a crossmember for a front bumper. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention relates to a crossmember for a front bumper of a motor vehicle having at least one throughflow opening for air. The crossmember has rear side with at least one exit-air opening that allows exit air to enter the crossmember from the rear. The crossmember preferably is hollow to allow air to pass through the crossmember. The exit air entering the crossmember at the rear side through the exit-air opening is guided through the crossmember, preferably to the ends thereof. By contrast to known crossmembers, the crossmember of the invention does not allow cooling air to pass through to a cooler arranged behind the crossmember. Rather, the crossmember of the invention is used for discharging exit air. Exit air refers, for example, to air that has been conducted through a cooler for cooling purposes. The use of the crossmember for discharging the exit air advantageously enables the exit air to be discharged laterally. Thus, the exit air is not discharged in the direction of the road surface, and the emergence of underbody air below the vehicle is prevented. 
         [0008]    The crossmember may have a closed front side, a closed underside and a closed top side. The crossmember advantageously has at least one exit-air opening for air only on its rear side. Thus, the stability of the crossmember is improved in this way. 
         [0009]    Openings may be formed on the underside to allow exit air to enter the crossmember from below. 
         [0010]    The exit-air opening on the rear side of the crossmember may be assigned an exit-air guiding device that extends down to a cooler. The cooler may be arranged below the crossmember and may have a multiplicity of air passage openings from which the exit air emerges. The cooler preferably is a relatively small cooler such as is used in sports cars. The relatively small cooler may be arranged centrally below the crossmember. Air is conducted through the air passage openings of the cooler for cooling purposes. The air that emerges on the rear side of the cooler is referred to as exit air. The exit air emerging from the cooler may be guided or conducted at least partially by the exit-air guiding device to the exit-air opening on the rear side of the crossmember. 
         [0011]    Exit-air ducts may extend laterally from the exit-air guiding device below the crossmember. A part of the exit air may be discharged via the exit-air ducts and a further part of the exit air may be conducted via the exit-air guiding device into the crossmember. 
         [0012]    The exit-air ducts may extend toward wheel arches. The exit-air ducts extend from the exit-air guiding device below the crossmember to the wheel arches. 
         [0013]    Additional exit-air ducts may extend from the ends of the crossmember and may be connected by the crossmember to the at least one exit-air opening on the rear side of the crossmember. Exit air that enters the at least one exit-air opening on the rear of the crossmember may pass through the crossmember into the additional exit-air ducts. The additional exit-air ducts in the connecting region to the crossmember, preferably have substantially the same cross section as the crossmember. However, the additional exit-air ducts advantageously are formed from a different material than the crossmember. 
         [0014]    The additional exit-air ducts may extend toward wheel wells and may end laterally in a nose part of the motor vehicle in front of the wheel wells. 
         [0015]    The invention also relates to a motor vehicle having a crossmember as described above and having at least one cooler arranged below the crossmember and a multiplicity of air passage openings. The crossmember preferably constitutes the front end of a supporting structure of the motor vehicle. A so-called front nose part is for example fastened to the crossmember. 
         [0016]    Exit air may emerge on the rear side of the cooler and may be guided by the exit-air guiding device and the exit-air ducts. The exit air then is discharged entirely or partially laterally through the crossmember. This offers the advantage that the exit air is not discharged in the direction of the road surface, thereby preventing the emergence of underbody air below the vehicle. 
         [0017]    An exit-air outflow at the outlet openings of the additional exit-air ducts is generated from a combination of a dynamic pressure on the rear side of the cooler and a suction effect of a negative pressure at outlet openings of the additional exit-air ducts. This advantageously leads to calming of an air flow that emerges from the wheel arches of the motor vehicle. The aerodynamics of the motor vehicle are improved in this way. 
         [0018]    Further advantages, features and details of the invention will emerge from the following description, in which various exemplary embodiments will be described in detail with reference to the drawings 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a perspective view of a motor vehicle having a crossmember according to the invention. 
           [0020]      FIG. 2  is a front perspective view of the crossmember from  FIG. 1  with an exit-air guiding device and exit-air ducts. 
           [0021]      FIG. 3  is a rear perspective view of the crossmember of  FIG. 2  with the exit-air guiding device and the exit-air ducts. 
           [0022]      FIG. 4  is a rear perspective view of the crossmember on its own. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]      FIG. 1  is a perspective view of a motor vehicle  10  having a front part  12 , with a front nose part omitted from the perspective view of the front part  12  of  FIG. 1 . 
         [0024]    The front part  12  of the motor vehicle  10  comprises parts of a body with two wheel arches  14  and  15 . The body comprises a supporting structure  16  with two longitudinal members  18 ,  19 . A crossmember  20  is fastened to the front ends of the longitudinal members  18 ,  19 . 
         [0025]    Two exit-air ducts  21 ,  22  are assigned to the crossmember  20 . The exit-air duct  21  issues into the wheel arch  14  and the exit-air duct  22  issues into the wheel arch  15 . The associated outlet openings  23 ,  24  of the exit-air ducts  21 ,  22  are denoted in  FIGS. 2 and 3  by  23  and  24 . 
         [0026]    Additional exit-air ducts  25 ,  26  extend from the ends of the crossmember  20 . The additional exit-air duct  25  opens out laterally at an outlet opening  27  in front of a right wheel well of the motor vehicle  10 , and the additional exit-air duct  26  opens out laterally at an outlet opening  28  in front of a left wheel well of the motor vehicle  10 . 
         [0027]    A relatively small cooler  30  is arranged centrally below the crossmember  20 . The cooler  30  comprises a multiplicity of passage openings (not illustrated) for cooling air. The cooling air is supplied to the cooler  30  from the front and emerges, as exit air, on the rear side of the cooler. 
         [0028]      FIG. 2  shows an exit-air guiding device  35  that is arranged behind the cooler  30  shown in  FIG. 1 . The exit air emerging on the rear side of the cooler is collected in the exit-air guiding device  35  with a dynamic pressure being generated. 
         [0029]    The two exit-air ducts  21  and  22  extend laterally from the exit-air guiding device  35 . The exit-air ducts  21 ,  22  extend below the crossmember  20  and below the additional exit-air ducts  25 ,  26 . 
         [0030]    The exit-air ducts  21  and  22  extend from a lower part  36  of the exit-air guiding device  35 , as shown in  FIG. 3 . The lower part  36  is connected integrally to an upper part  38  of the exit-air guiding device  35 . The upper part  38  of the exit-air guiding device  35  bears against the rear side  44  of the crossmember  20 . 
         [0031]    As shown in  FIG. 4 , the rear side  44  of the crossmember  20  has two exit-air openings  51 ,  52  that allow exit air to enter the crossmember  20  from the rear. The crossmember  20  is of closed form on its top side  41 , its underside  42  and its front side  43 . 
         [0032]    The interior of the crossmember  20  has a dividing body  54  that divides a cavity in the interior of the crossmember  20  into two crossmember exit-air ducts. During the operation of the motor vehicle  10 , air for cooling the cooler  30  initially is conducted through the cooler. 
         [0033]    A part of the exit air that emerges on the rear side of the cooler  30  is discharged laterally via the exit-air ducts  21  and  22 , with their outlet openings  23  and  24 , into the wheel arches  14  and  15 . However, a part of the exit air also is conducted via the exit-air guiding device  35  into the crossmember  20  from the rear through the exit-air openings  51 ,  52 . This part of the exit air is conducted out through the crossmember  20 , and via the additional exit-air ducts  25 ,  26  with their outlet openings  27 ,  28 , into regions on the nose part or front nose part where a negative pressure prevails during operation due to the flow around the motor vehicle  10 . 
         [0034]    A useful throughflow of the additional exit-air ducts  25 ,  26  arises from the combination of the dynamic pressure downstream of the cooler  30  and the suction effect of the negative pressure at the outlet openings  27 ,  28  of the additional exit-air ducts  25 ,  26 . This throughflow emerges from the additional exit-air ducts  25 ,  26  at the outlet openings  27 ,  28  in front of the wheel wells or wheel arches  14 ,  15 , and advantageously calms the flow emerging from the wheel arches  14 ,  15 . The flow emerging from the wheel arches  14 ,  15  may be part of a brake-cooling arrangement. The throughflow of the additional exit-air ducts  25 ,  26  advantageously leads to an improvement of the aerodynamics of the motor vehicle  10 .