Abstract:
An aerodynamic test stand ( 1 ) is provided for determining forces acting on a vehicle. The test stand has a stationary floor ( 2 ), at least two supporting devices ( 4 ) for supporting the motor vehicle, and at least one band unit moving in relation to the floor, for influencing air flow behavior in the floor region. The band unit is composed, segment-like, of runway sections ( 9, 10, 11, 20, 21, 22, 23, 24, 25, 26, 27, 28 ) to accurately detect forces acting on the vehicle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an aerodynamic test stand. 
     2. Description of the Related Art 
     Aerodynamic test stands serve for determining aerodynamic properties, particularly in vehicles. As a rule, a wind tunnel is provided, which by means of a blower generates an airflow which is routed via straighteners to the aerodynamic test stand uniformly, in parallel and with low turbulence and noise. 
     It is known that, for the near-reality simulation of a road journey, it is advantageous to illustrate a moved roadway and wheel rotation, since the boundary layer flow on the ground and the flow around or through the moved wheel influence the forces acting on the vehicle. For this purpose, it has become known to arrange between the wheel rotation units, on which the vehicle is set down, a continuous runway which revolves at an appropriate speed. 
     DE 10 2005 040 445 A1 and DE 103 38 638 A1, furthermore, disclose a moved runway which simulates the roadway and which not only extends between the wheel rotation units, but beyond these. The vehicle is held laterally by means of fixing devices. The wheels of the vehicle are set down on standing surfaces which are located directly below the runway. The test stand shown in DE 103 638 A1 comprises a stationary floor on which the runway is mounted as an entire unit on a weighbridge. The forces in the vehicle longitudinal direction and vehicle transverse direction are measured at the bearings of the weighbridge, while the forces in the Z-direction are measured through the runway at the standing surfaces of the vehicle. It is advantageous that a road journey can be simulated optimally by means of the large-area runway. In this arrangement, however, the measurement data are influenced by aerodynamic interaction with the runway and have to be balanced accordingly. 
     The object of the invention is to provide an aerodynamic test stand which as accurately as possible detects the forces acting on the vehicle. 
     SUMMARY OF THE INVENTION 
     There is provision, according to the invention, for the aerodynamic test stand to comprise a stationary floor and at least two supporting devices for the support of the vehicle. To simulate a road journey, at least one band unit moving in relation to the floor is provided. This band unit is composed, segment-like, of runway sections. The crux of the invention, therefore, is not to provide a single large-area runway, but, instead, a plurality of smaller adjustable runway sections which together produce a band unit. The supporting devices are therefore arranged between the runway sections. Consequently, the forces which act on the supporting devices due to the vehicle can be introduced directly to an underfloor weighing appliance. In this case, the forces both in the X- and Y-direction and in the Z-direction can be measured directly. It is in this case advantageous if the active force pick-up surfaces within the band unit are kept as small as possible, so that, in actual fact, only those forces are measured which the vehicle exerts on the supporting devices. Flow forces which act on the runway sections are not detected. The flow topology across the runway sections therefore has no influence on the measurement results. Owing to the segment-like division and the adjustability of the runway sections, a variable band unit can be implemented, which can be used for the most diverse possible vehicle types. 
     In order to obtain as large a coherent runway surface as possible, runway sections may be arranged in each case in front of, behind or between the supporting devices. The more closely the individual runway sections lie together, the more positively the boundary layer flow can be influenced. 
     There may be provision for at least one of the supporting devices to be held so as to be relatively movable with respect to the other supporting device. Consequently, the distance between the two supporting devices can be selected freely, so that a modular assembly of the test stand is possible. In a preferred refinement of the invention, overall, four supporting devices are provided, in order to make a supporting device available for each wheel in four-wheel motor vehicles. The supporting units are anchored on an underfloor weighing appliance as a function of the wheel base or track of the motor vehicle. It is conceivable that even two-wheel or three-wheel vehicles can be investigated by means of the aerodynamic test stand, since the supporting devices can be converted correspondingly. 
     The dimensions of the runway section extending between two supporting devices can be set according to the distance between the two supporting devices. It is in this case advantageous if the runway sections can be lengthened or shortened correspondingly. 
     In order also to simulate the flow through or around the wheel, the vehicle does not stand, unmoved, on the supporting device, but rotatably. For this purpose, the supporting device may be designed as a wheel rotation device. 
     Preferably, the wheel rotation device may be formed by a belt band rotating about a pair of rollers. 
     The runway sections may comprise a runway belt rotating about carrying rollers, an additional deflection unit being provided. The deflection unit has the effect that the runway belt rotates about the carrying rollers with a sufficient frictional connection. 
     For maximum flexibility, the distance between two carrying rollers may be adjustable. In the case of the offset of the supporting device, the length of the runway can be adapted by increasing or reducing the distance between the two carrying rollers. To ensure frictional connection, the position of the additional deflection unit may likewise be variable, in order to keep the runway belt under pretension. 
     Further advantageous embodiments of the invention are explained in more detail below with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a view of an aerodynamic test stand from above. 
         FIG. 2  shows a view according to  FIG. 1  without a vehicle. 
         FIG. 3  shows a sectional illustration along the line III-III in  FIG. 1 . 
         FIG. 4  shows a second embodiment of the aerodynamic test stand. 
         FIG. 5  shows a third embodiment of the aerodynamic test stand. 
         FIG. 6  shows an illustration of the wheel rotation unit according to  FIG. 3  in the form of a detail. 
         FIG. 7  shows a second embodiment of a wheel rotation unit. 
         FIG. 8  shows a third embodiment of a wheel rotation unit. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The views from above according to  FIGS. 1 and 2  and also the side view according to  FIG. 3  show a first preferred embodiment of an aerodynamic test stand  1 . In the wind tunnel, not illustrated in any more detail, an airflow A is generated by means of a nozzle  40  and is routed via straighteners to the aerodynamic test stand  1  uniformly, in parallel and with low turbulence and noise. The flow profile is illustrated by flow lines  41 . Behind the test stand  1 , the airflow A is conveyed to the nozzle  40  again by means of a collector  42 . The aerodynamic test stand  1  is delimited downward by a stationary floor  2 . A vehicle  3  can be set down on supporting devices  4  which are designed as wheel rotation devices  5 ,  6 ,  7  and  8 . The wheel rotation devices  5 ,  6 ,  7  and  8  are preferably designed as a drive unit, so that the wheels of the vehicle can be driven. Alternatively, it is also conceivable that the wheel rotation devices are suitable for decreasing the power of an engine-powered vehicle  3 . 
     The two wheel rotation devices  5  and  6  or  7  and  8  lying next to one another are spaced apart from one another according to the track s, while the wheel rotation devices  5  and  7  or  6  and  8  lying one behind the other are spaced apart from one another according to the wheel base r of the vehicle  3 . 
     Arranged in front of the two front wheel rotation devices  5  and  6  is a first runway section  9  which has a width B and an adjustable length  11 . The width B is greater than the track s, so that the runway section  9  extends laterally beyond the two wheel rotation devices  5  and  6 . 
     Behind the two front wheel rotation devices  5  and  6  is arranged a second runway section  10  which covers the distance between the front and rear wheel rotation devices. The second runway section  10  has the same width B as the first runway section  9 , and the likewise adjustable length  12  is to be selected as a function of the wheel base r and in this exemplary embodiment is lower than the length  11 . 
     A third runway section  11  is provided behind the wheel rotation devices  7  and  8 . Its length  13 , too, is adjustable. The length  13  can be kept longer, precisely in the rear region of the vehicle  3 , than that of the two front runway sections as a function of the interfacial flow to be achieved. The width B of the third runway section corresponds to the width of the front runway sections  9  and  10 . 
     The band unit influencing the flow behavior in the floor region is therefore formed from three runway sections  9 ,  10  and  11 , the band unit being interrupted in its longitudinal extent L by the wheel rotation devices  5  to  8 . 
     The wheel rotation devices  5  to  8  may be mounted together on a common underfloor weighing appliance  50 . By means of the underfloor weighing appliance  50 , the forces acting in the X-, Y- and Z-directions can be picked up. Alternatively or additionally, force pick-ups under each wheel rotation device are possible, in order to detect the individual forces acting in each case. The detection of acting moments, such as a pitching, yawing and tilting moment, is consequently likewise possible. 
     The side view, illustrated in  FIG. 3 , along the line III-III in  FIG. 1  shows the arrangement of the runways  9 ,  10  and  11 . 
     The runway section  9  is equipped with two carrying rollers  12  and  13 , about which a runway belt  14  rotates clockwise according to the direction of the arrow B. In addition, a deflection unit  15  is provided within the circumference enclosed by the runway belt  14 . The carrying rollers  12  and  13  can be displaced towards one another or away from one another according to the direction of the arrow X. Displacement may take place via spindle drives, rack drive or hydraulic/pneumatic drives. In order to ensure a sufficient frictional connection for the uniform rotation of the runway belt  14 , the position of the additional deflection unit  15  is variable. For this purpose, it can be held displaceably in vertical and/or horizontal guides. Thus, for example, the belt slack can be taken out of the runway belt  14  by the deflection unit being displaced according to the direction of the arrow Z. However, a displacement of the deflection unit  15  in the Z- and X-direction is also possible. The length  11  of the runway section  9  is thus variably adjustable. 
     The length  12  or  13  of the runway sections  10  and  11  can be adjusted in exactly the same way as the runway section  9 . For the sake of clarity, the same components are designated by the same reference numerals, but with an apostrophe. Thus, the runway section  10  is equipped with two carrying rollers  12 ′ and  13 ′, a runway belt  14 ′ and a deflection unit  15 ′. Similarly, the runway section  11  is equipped with 2 carrying rollers  12 ″ and  13 ″ and a deflection unit  15 ″. 
     The wheel rotation devices  5  and  7  are formed by a belt band  19  rotating about two rollers  17  and  18 . The illustration D of the wheel rotation device  5  in  FIG. 3  in the form of a detail is illustrated, enlarged, in  FIG. 6 . Wedges  30  are inserted on both sides next to the pair of rollers  16 , so that the wheel rotation device  5  and the adjacent runway sections  9  and  10  adjoin one another with flush surfaces . 
     According to  FIG. 7 , an alternative embodiment of the wheel rotation device  5  may be one where only a single roller  31  is arranged between the two runway sections  9  and  10 . Reference numeral  33  denotes the motor vehicle wheel set down on the wheel rotation device  5 . 
     A third embodiment of the wheel rotation device  5  becomes possible, according to  FIG. 8 , by means of a pair of rollers  32  without a rotating belt band. 
     Each of the wheel rotation devices  5  and  7  can be positioned according to the wheel base r or the track s of the motor vehicle to be tested. If, for example, a larger wheel base than is shown in  FIG. 3  should be required, the wheel rotation device  7  can be displaced to the right into the position indicated by dashes. The rear carrying roller  13 ′ of the runway  10  is likewise displaced to the right, while the deflection unit  15 ′ is displaced vertically upward into the position indicated by dashes. The length  12  of the runway  10  is consequently lengthened. 
     The length  13  of the runway section  11  is shortened in a similar way. For this purpose, the front carrying roller  12 ″ is displaced to the right, while the deflection unit  15 ″ has to be displaced downward, in order to tension the runway section  11 . 
     The orientation of the vehicle and consequently the positioning of the wheel rotation devices  5 ,  6 ,  7  and  8  may take place at the center of the aerodynamic test stand. That is to say, the vehicle center is positioned at the center of the aerodynamic test stand. Alternatively, an orientation of the vehicle via a constant distance between the vehicle nose and the nozzle is possible. The advantage of this is that the onflow forces are constant in this position. Theoretically, the displaceability of the front supporting devices  5  and  6  could then be dispensed with. 
     The great variance in the possibilities for arrangement affords the advantage that virtually any desired vehicle can be tested in the aerodynamic test stand and yet a coherent band unit is preserved. It is even conceivable to push the wheel rotation units  5  and/or  6  and  7  and/or  8  lying next to one another into the center, so that the flow can be applied to two-wheel vehicles such as, for example, motor cycles or bicycles, with the band unit running. Alternatively, in this application, one of the front and one of the rear wheel rotation units could be dispensed with, and the two remaining wheel rotation units could be oriented in alignment with one another in a longitudinal direction. It goes without saying that, in this arrangement, it is even possible for the flow to be applied to three-wheel vehicles, with the band unit running. 
     In addition to the variant, shown in  FIGS. 1 to 3 , with three runway sections, there may alternatively be provision, as shown in  FIG. 4 , for a further runway section  20  and  21  to be provided between the wheel rotation units  5  and  6  or  7  and  8 . With the track s being increased, this runway section  20  or  21  would have to be such that it could be exchanged for a wider runway section, in order to form a corresponding width. Further runway sections could also be provided in addition to the wheel rotation devices  5 ,  6 ,  7  or  8 . 
     A third embodiment of the invention is shown in  FIG. 5  in which a middle runway  22  is arranged between the wheel rotation units  5 ,  6  and  7 ,  8 . Further runway sections  23  and  24  are then provided in front of the wheel rotation units  5  and  6  in each case on the right and on the left of the middle runway  22 . The band unit is virtually assembled by means of the further runway sections  25 ,  26 ,  27  and  28 . 
     A version, not illustrated, could be one in which a runway of equal length is arranged in each case on the outside of the wheel rotation units with respect to the middle runway section  22 , so that three runway sections of equal length are provided. The free sections between the front wheel rotation device  5  or  6  and the rear wheel rotation device  7  or  8  may be closed in each case by means of a runway section. 
     From the exemplary embodiments explained above, it becomes clear that virtually any desired arrangement of runway sections is possible by means of the solution according to the invention. A band unit assembled in a modular way can thereby be produced.