Abstract:
The present invention relates to a device for minimizing the aerodynamic drag that results when tractors, trailers, rigid trucks, lorries, and other vehicles are moving through air. In particular the invention relates to a plate-shaped flow conductor having a front edge, a lower edge, a rear edge and an upper edge. The flow conductor is mountable along the upper edge in a substantially vertical position to a body portion of a pulled vehicle of a vehicle combination of at least two pivotally connected vehicles. When mounted the flow conductor extends at least partially under the body portion in a longitudinal direction of the pulled vehicle. Characteristic for the flow conductor according to the invention is that the flow conductor comprises locally in conjunction with the front edge a thickened portion, which has a streamlined outer contour in a cross section transversally to the front edge.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is the National Phase of International Application no. PCT/NL2008/000187, filed 4 Aug. 2008, which claims priority to and the benefit of U.S. provisional patent application No. 60/955,524, filed 13 Aug. 2007, and NL patent application no. 1034363, filed 11 Sep. 2007, the contents of which are incorporated by reference as if fully set forth herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a flow conductor for minimizing the aerodynamic drag that results when tractors, trailers, rigid trucks, lorries, and other vehicles are moving through air. In particular the invention relates to a plate-shaped flow conductor for use as a side skirt having a front edge, a lower edge, a rear edge and an upper edge. The flow conductor is mountable along the upper edge in a substantially vertical position to an outer lower edge of a body portion of a pulled vehicle of a vehicle combination of at least two pivotally connected vehicles. When mounted the flow conductor extends at least partially at the outside under the body portion in a longitudinal direction of the pulled vehicle. The flow conductor as a side skirt reduces aerodynamic drag, but reduces also noise and spray of rainwater from the wheels. 
     BACKGROUND 
     It is a well known fact that the aerodynamic performance of the external shape of a vehicle and its movement through a medium can be defined in a certain non-dimensional quantity called the drag coefficient C D . The drag coefficient at lower speeds of a body is mainly dependent on the aerodynamic configuration of the body and the Reynolds number, which is a measure for the ratio of inertia forces to viscous forces in a flow. The drag coefficient and the corresponding aerodynamic forces are directly related to the driving speed to the second power, and to the fuel consumption, thus the operational economics, of that corresponding vehicle. 
     Heavy road transport vehicles can be characterized in an aerodynamically sense as bluff shapes. This means that the aerodynamic properties of these road vehicles are strongly influenced by flow separation. Flow separation occurs when the boundary layer, which is a thin layer that bridges the velocity difference between the moving vehicle and the lower air speed, encounters a sufficiently large adverse pressure gradient due to, for instance, abrupt geometrical changes in the body like for instance at the back of bluff road vehicles. 
     The term bluff most commonly refers to bodies which have leading-edge flow separation, as most vehicles do at large side wind angles. The flow which is touching the front of the vehicle, goes, for instance, along the side of the trailer to the back of the same trailer where it is not able to follow a 270 degrees corner comprising the side and back surfaces. For example the squared edges found at most corners of bulk commercial road and rail cargo carriers. The effects of these flow separations are most apparent in their high aerodynamic drag levels, where the pressure drag component is many times higher due to flow separation than the drag due to skin friction as with airfoils. The aerodynamic drag of a bluff shape is mainly due to the pressure difference of the front and rear faces of the body, with respect to the environment pressure, with only a secondary contribution due to skin friction. 
     Fuel economy and the associated fuel cost of heavy transport vehicles are very important issues within the operational cost of national and international transport companies. Till this day transportation of goods over the roads is one of the most efficient and flexible methods within the field of freight transportation. A large amount of engine power is required to overcome the aerodynamic forces that are acting on a road vehicle, due to the passage of the vehicle through air. Besides reducing the aerodynamic drag with special designed devices or aerodynamically well streamlined bodies, also other measures may positively effect the fuel consumption of vehicles. For instance by introducing vehicle weight reduction through designing lightweight structures, by improving tire friction coefficients which reduce the tire friction forces and by increasing mechanical efficiency of the mechanical parts like the engine, the gear box and the driving shafts. An improved aerodynamic behaviour of a vehicle will, besides an increased fuel economy, decrease the belch of environmental unfriendly exhaust gasses as well as introducing a more save traffic situation because of the decreased tire wear. 
     Due to the aerodynamic instabilities in the flow around and in the wake behind the vehicle, the vehicle is bucketing slowly over the road which results in tire wear and possible tire burst and thus an unsafe traffic situation. 
     As a road vehicle is progressing along its path, the volume of air in the near front of the vehicle actually acts as a frontal barrier which causes stagnation drag and thus a loss in fuel economy. Significant advances have already been made in aerodynamic design of the cabin of the tractor and of trucks in general. Rounded cabin corners, side and roof deflectors, aerodynamic mirrors, and side fenders to close the gab between the cabin and the trailer are commonly adopted. Also several aerodynamic devices for the back end of the vehicle, like the boat tail, splitter plates, guiding vanes, air deflectors, and pneumatic systems, are developed and reduce the total drag of the road vehicle significantly. Since the undercarriage of a trailer usually includes transverse chassis beams, a pallet box, axles, support legs, equipment storage volumes, and other irregular elements, this region is characterized by highly turbulent and separated flows. 
     The present invention relates to vehicles having highly turbulent regions as a result of an interrupted flow at a position of a pivotal connection between at least two parts of the total vehicle combination. Such turbulent regions for example occur typically at the pivotal connection point between a trailer and a tractor or at the position of the connection by a drawbar of one or multiple lorries to a rigid truck. Another example of a vehicle combination is a railway train comprising a locomotive and several wagons. The locomotive and wagons are all pivotally connected to each other. At each connection, regions occur with large pressure differences. At those positions, the flow along the vehicle is interrupted, which adversely affect the aerodynamic behaviour of the total vehicle combination. 
     U.S. Pat. No. 6,974,178 to Ortega and Salari illustrates several baffle assemblies adapted to be positioned upstream of the wheel assembly for deflecting airflow away from the wheel assembly so as to reduce the incident pressure on the wheel assembly. 
     A first embodiment of the apparatus of U.S. Pat. No. 6,974,178 shows a wedge-shape side skirt arrangement. The skirt arrangement is mounted on the underside of the vehicle body portion in front of the rear wheel assembly using fasteners or other mounting hardware of a type known in the relevant arts. The skirt arrangement has right and left panels extending down from the underside of the body portion and angled to deflect airflow away from the rear wheel assembly. It is appreciated, that the left and right panels are part of unitary construction and the leading ends thereof may be integrally connected, either at an angle, or with a curvilinear or otherwise continuous shape. The straight panels themselves may also have a concave or convex curvilinear configuration. 
     A second embodiment of U.S. Pat. No. 6,974,178 shows a wedge-shaped skirt portion with a left and a right panel similar but shorter than the first embodiment and a third forward panel connected to the wedge-shaped portion at a forward location thereof. This third forward panel is centrally aligned with the longitudinal central axis of the trailer. 
     A third embodiment is compromising a pair of side-skirts which are mounted parallel at or near the transversely opposite side of the body vehicle. In particular, the side skirts may be directly mounted to the underside of the body portion to extend there below, or mounted to the side of the body portion to extend down to a level below the body portion. The side skirts are located near the left and right side lower edges to impede airflow into and across the underside of the trailer. 
     A first problem of the first and second embodiment of U.S. Pat. No. 6,974,178 is that units, like the battery box, pallet box, storage volume and other necessary parts, which are present on a regular trailer, can not be mounted anymore due to the present side skirts. 
     Another problem of the three embodiments of U.S. Pat. No. 6,974,178 is the fact that the underside of the body portion of the vehicle is not accessible if necessary for certain tasks like maintenance or storekeeping of parts and the like. 
     A further problem of the three embodiments of U.S. Pat. No. 6,974,178 is that there are still zones with a high level of turbulence caused by released flows and felt by the passing flow, which adversely affect the aerodynamic behaviour of the vehicle. Especially when the vehicle is subjected to horizontally inclined flows, eddies and heavy irregularities in the flow are occurring. 
     SUMMARY 
     It is an object of the present invention to overcome at least one of the abovementioned drawbacks, at least partially, and/or to provide a usable alternative. In particular, it is an object of the invention to provide an improved streamlined vehicle comprising a flow conductor that guides the flow properly if it is liable to horizontal inclined and straight forward flows. This object is achieved with a flow conductor for use as a side skirt, which is plate-shaped having a front edge, a lower edge, a rear edge and an upper edge, wherein the flow conductor is mountable along the upper edge in a substantially vertical position to a body portion of a pulled vehicle of a vehicle combination of at least two pivotally connected vehicles, and wherein the flow conductor extends at least partially under the body portion in a longitudinal direction along an outer edge of the pulled vehicle. 
     Characteristic for the flow conductor according to the invention is that the flow conductor comprises locally in conjunction with the front edge a thickened portion, which has a streamlined outer contour in a cross section transversally to the front edge. In a vertically mounted flow conductor an inner and outer surface may be defined. The inner surface is positioned inwards with respect to the pulled vehicle, like a trailer, lorry or wagon. Advantageously according to the invention the airflow which hits the flow conductor at the front edge is conducted in a stable manner in airflows along the inner and outer surface of the flow conductor. The front edge comprises a streamlined outer contour which guides the airflow along the surfaces of the flow conductor. The risk on separation of the airflow at the front edge is strongly reduced. According to the invention the turbulence of the airflow in the region around the front edge is strongly reduced, which positively affect the aerodynamic performance of the complete vehicle combination. The improved aerodynamic performance has an appreciable effect on the fuel consumption of the vehicle combination. During several tests it has been established that fuel consumption savings of about 5% and more may be achieved with the flow conductor according to the invention. 
     Herewith the present invention provides a device for reducing aerodynamic drag of a wheeled vehicle in an air stream. This vehicle may be represented as a tractor-trailer combination, where the trailer has several wheel assemblies supporting the vehicle body. Preferably, the aerodynamic device as a drag reduction apparatus for the trailer comprises two panels with a geometry in substantially mirror symmetry and curvatures at the inside at the front vertical edges. The panels are mounted in the longitudinal direction of the trailer beneath a lower outer edge. The panels are side skirts which extend along the sides of the trailer adjacent the ground. 
     In an alternative embodiment the present invention provides a flow conductor in a device for reducing aerodynamic drag for an alternative wheeled vehicle in an air stream. This vehicle can be described as a rigid truck with a lorry and a drawbar, where the lorry has several wheel assemblies supporting the vehicle body. The drag reduction apparatus for this type of trailer comprises two equal panels with, at the inside curvatures at the front vertical edges. The panels are mounted in the longitudinal direction of the lorry. 
     In a preferred embodiment of the flow conductor according to the invention the outer contour of the thickened portion in cross-section comprises a curvature with an airfoil part, which is in conjunction with the front edge. The airfoil part is positioned at the front edge of the flow conductor to guide an approaching airflow along the inner and outer side of the flow conductor. Advantageously, the airfoil geometry like a wing profile is optimally suitable to guide the airflow, reduce turbulence and preventing flow separation in a zone around the front edge. 
     In an alternative embodiment of the flow conductor according to the invention the outer contour comprises a curvature with a circular part having a radius of at least 100 mm which is in conjunction with the front edge. In a further alternative embodiment according to the invention the outer contour comprises a curvature with an elliptical part, which is in conjunction with the front edge. These embodiments are advantageous, because the production of these flow conductors is relatively cost-efficient and the reduction of the turbulence is considerable. 
     To obtain a relevant reduction of the turbulence, it is important that the thickened portion has suitable dimensions. In a particular embodiment the thickened portion has a height dimension in a direction perpendicular to the outer surface of the flow conductor of at least 50 mm. Preferably the height dimension is 100 mm, in particular 200 mm. 
     In an embodiment according to the invention the thickened portion of the flow conductor extends through an imaginary plane which is parallel to the outer surface of the flow conductor at a distance of 100 mm. Preferably, the geometry of the front edge is smooth and sharp edges are avoided to prevent the creation of swirls in the guided airflow. It is important that the airflow keeps following the surface of the flow conductor. A continuous flow along the flow conductor must not be interrupted by a sudden change in the geometry of the flow conductor. It also depends on the speed of the airflow, if a change in geometry turns out in an interruption of the continuous airflow. The minimum dimensions of the thickened portion of the flow conductor are in a particular embodiment according to the invention related to the higher speeds of airflow which occur during a ride. The geometry of the thickened portion of the flow conductor may preferably not have abrupt changes and have minimum dimensions. According to the invention it is established that it is advantageous to gradually conduct the airfoil with a thickened portion which is arranged with a minimum dimension in a direction perpendicular of the outer surface of the plate-shaped flow conductor. This minimum dimension is defined as a perpendicular distance between the outer surface of the flow conductor and a parallel positioned imaginary plane. In a preferred embodiment it has been established that it is favorable if the imaginary plane is parallel to the outer surface of the flow conductor at a distance of 200 mm. 
     In an embodiment according to the invention the mountable plate-shaped flow conductor comprises an inner and an outer surface. When the flow conductor is mounted onto a vehicle, the inner surface is arranged inwards with respect to the pulled vehicle. Advantageously, the thickened portion is positioned at the inner surface of the flow conductor. The outer surface is flat and not equipped with a thickened portion. Herewith, the turbulence in the region around the front edge is considerably reduced. 
     In an embodiment according to the invention the flow conductor comprises a front and/or rear chamfer between the front edge and the lower edge. These chamfers improve the conduction of the airflow and therefore further improve the aerodynamic performance. 
     In a particular embodiment the front and/or rear chamfer have a dimension in a direction of the front edge of at least 100 mm. From this minimum dimension a better performance is established. 
     In a particular embodiment of the flow conductor according to the invention the flow conductor is made of dicyclopentadiene, also known as Telene. This material has a high impact resistance, which is advantageously for reducing damages caused by road metal. Dicyclopentadiene is further advantageous, because it may reduce the total weight of the flowconductor. In addition, it is advantageous that the dicyclopentadiene material allows the manufacture of large 3D geometries in one piece, which allows to integrate the thickened portion in the plate-shaped part of the flow conductor according to the invention. 
     Further the invention relates to an aerodynamic device comprising a set of two flow conductors which have a corresponding geometry in mirror symmetry. 
     In an embodiment according to the invention, the flow conductor extends over the whole length of the vehicle to guide an air stream from the front of the vehicle along the underside of the body portion to the back of the vehicle. Advantageously, turbulent zones along the whole length of the vehicle are reduced. Components, like pillars and storage containers which could cause disturbances of the airflow are arranged behind the flow conductor and no longer adversely affect the guided airflow. 
     It is advantageous to sustain the flow path to the back of the body portion. Herewith also the aerodynamic drag behind the vehicle is reduced. The guidance of air to the back of the vehicle reduces the pressure drop behind the vehicle, which positively affect the aerodynamic performance of the total vehicle combination. 
     A further embodiment of the present invention comprises a longitudinal flow conductor that can be flapped up along the longitudinal axis of the vehicle in order to guarantee the accessibility of the underside of the vehicle. Preferably, the accessibility of the underside of the body portion of the vehicle is assured via a leaf mechanism as a hinge to which the flow conductor is connected. Herewith, it is also convenient to mount indispensable parts at the underside of the body portion of the same vehicle. 
     Further the invention relates to an advantageous trailer provided with a flow conductor according to the invention. In a particular embodiment of the trailer according to the invention the flow conductor covers at least partially a wheel of the wheel assembly. Preferably there are cool gaps provided in the flow conductor at a position near the wheel assembly to provide a passage for air to cool the tires and the braking system of the trailer. This reduces the risk of an overheated tire. 
     Further the invention relates to a vehicle which can be pulled in a vehicle combination, like a lorry or wagon provided with a flow conductor according to the invention. In an embodiment according to the invention the front edge of the flow conductor is substantially aligned with the front surface of the body portion of the lorry or wagon. This is favorable, because in this embodiment turbulence regions are reduced. 
     Further preferred embodiments are defined in the Detailed Description below and in further dependent claims presented herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in further detail with reference to the attached drawings which show a practical embodiment of the invention, but which should not be seen as being limiting. 
       The accompanying drawings, which are incorporated into and form a part of the disclosure, are as follows: 
         FIG. 1  is a frontal oriented perspective view of one of the vehicles, referred to as a tractor-trailer combination, on which the flow conductor according to the present invention can be mounted; 
         FIG. 2  is an underside oriented perspective view of a first embodiment of the flow conductor according to the invention mounted underneath a trailer of a tractor-trailer combination; 
         FIG. 3  is a side view of the tractor-trailer of  FIG. 1  comprising the flow conductor; 
         FIG. 4A  is a bottom view of the trailer out of  FIG. 3  as a pulled vehicle; 
         FIG. 4B  is a bottom view in detail of the flow conductor out of  FIG. 4A  focussing on the geometry of the region adjacent the front edge of the flow conductor; 
         FIG. 5  is a frontal oriented perspective view of one of the vehicles, referred to as rigid truck with a drawbar and a lorry, on which the flow conductor according to the present invention can be mounted. 
         FIG. 6  is an underside oriented perspective view of a first embodiment of the flow conductor of the present invention mounted underneath a lorry of the rigid truck with drawbar and lorry. 
         FIG. 7  is a side view of the device of  FIG. 6 . 
         FIG. 8  is a bottom view of the device of  FIG. 6 . 
         FIG. 9  is an underside oriented perspective view of a second embodiment of the apparatus of the present invention mounted underneath a trailer of a tractor-trailer combination. 
         FIG. 10  is a bottom view of the device of  FIG. 9 . 
         FIG. 11  is an underside oriented perspective view of a third embodiment of the apparatus of the present invention mounted underneath a trailer of a tractor-trailer combination. 
         FIG. 12  is a bottom view of the device of  FIG. 11 . 
         FIG. 13  is an underside oriented perspective view of a fourth embodiment of the apparatus of the present invention mounted underneath a trailer of a tractor-trailer combination. 
         FIG. 14  is a bottom view of the device of  FIG. 13 . 
         FIG. 15  is an underside oriented perspective view of a fifth embodiment of the apparatus of the present invention mounted underneath a trailer of a tractor-trailer combination. 
         FIG. 16  is a side view of the device of  FIG. 15 . 
         FIG. 17  is an underside oriented perspective view of a sixth embodiment of the apparatus of the present invention mounted underneath a trailer of a tractor-trailer combination. 
         FIG. 18  is a side view of the device of  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION 
     In the end of this detailed description a legend is presented indicating the names of components with corresponding reference numbers. 
     The present invention is an aerodynamic drag reduction device to be used with wheeled vehicles of a type generally having a vehicle body portion supported by one or more wheel assemblies located below the body volume where it is exposed to an airflow that contributes to the total drag of the vehicle. The proposed aerodynamic device, which will be named as longitudinal flow conductor, can be applied on different transportation vehicles including automobiles, trains, aircraft or any other vehicle having one or more wheel assemblies located or extending below a body portion of the vehicle which is exposed to an airflow resulting in aerodynamic drag. 
     In  FIGS. 1-18  of the drawings and in the following discussion, a conventional trailer of a tractor-trailer combination and a rigid truck with a drawbar and a lorry have been selected as representative wheeled vehicles to illustrate the aerodynamic drag, as well as showcase the solution provided by the various embodiments of the present invention. 
     Referring to  FIG. 1 , a typical tractor-trailer combination  1 , indicated generally as the tractor  2  and the trailer  3 , is illustrated in perspective view, as observed from an elevated position forward and to the left of the vehicle combination. The tractor  2  is a well known object which is not of interest and will not be described in further detail. The trailer  3 , in such a vehicle, travels upon one or more wheel assemblies  26 , with its forward end portion pivotally supported by a rear portion of the tractor through the king-pin  29 . In order to describe the trailer  3 , within the tractor-trailer combination, it is generally configured as a structure enclosing a rectangular body volume  4 . This volume has a front surface  5 , a left side surface  6 , a right side surface  9 , a top surface  7 , a rear surface  10  and a lower surface  8 , a supporting chassis  30 , and other equipments, amongst others, indicated generally as left and right supports legs, respectively pillars  23  and  24 , a pallet box  25  and possible left and right storage volumes  27  and  28 . As used in this detailed description and in the claims, the wheel assembly includes any combination of wheels, (single or double) tires, axles, differentials, and other wheel-related structure, such as struts, shock, springs (or air bellows), control arms, brakes, etc., or any portions thereof, located or extending below the body portion as a unit group. The location as well as the number of the wheel assemblies are not predefined, and are arbitrary. The presence as well as the location of the pallet box  25  and both the storage volumes  27  and  28  are not compulsory and defined. 
     Referring to  FIG. 5 , a rigid truck with drawbar and lorry  51 , indicated generally as the rigid truck  52  and the lorry  53  with drawbar  74 , is illustrated in perspective view, as observed from an elevated position forward and to the left of the vehicle combination. The rigid truck  52  comprises a driver&#39;s cabin  92 , a body volume  93 , multiple wheel assemblies  94  and possible storage volumes  95 , for instance, for fuel or electrical units. The lorry  53 , in such a vehicle, travels upon one or more wheel assemblies  73 , with its forward drawbar  74  pivotally connected by the rear portion of the rigid truck  52  through the king-pin of the same rigid truck  52 . 
     In order to describe the lorry  53 , within the rigid truck with drawbar and lorry configuration  51 , the lorry is generally configured as a structure enclosing a rectangular body volume  54 . This volume has a front surface  55 , a left side surface  56 , a right side surface  59 , a top surface  57 , a rear surface  60  and a lower surface  58 , a supporting chassis  75 , and other equipments, amongst others, indicated generally as possible left and right storage volumes  76  and  77  for the placement of, for instance, electrical units. As used in this detailed description and in the claims, the wheel assembly includes any combination of wheels, (single or double) tires, axles, differentials, and other wheel-related structure, such as struts, shock, springs (or air bellows), control arms, etc., or any portions thereof, located or extending below the body portion as a unit group. The location and the number of the wheel assemblies are not predefined, but are arbitrary. 
       FIGS. 2-4A  show an exemplary first embodiment for a trailer  3  of the present invention having an aerodynamic drag reduction device such as the straight longitudinal flow conductors  31  and  38 . The aerodynamic devices can be described as a combination of two thin walled plates with, considering the left longitudinal flow conductor  31 , a horizontal lower edge  32 , a vertical rear edge  33 , a horizontal upper edge  34 , and a vertical front edge  35 , and, considering the right longitudinal flow conductor  38 , a horizontal lower edge  39 , a vertical rear edge  40 , a horizontal upper edge  41 , and a vertical front edge  42 . The starting point of the most forward edges,  35  and  42 , of both the longitudinal flow conductors,  31  and  38 , lies beyond the lower horizontal front edge  19  of the body volume  4  of the trailer  3 . The rear edges  33  and  40  of both longitudinal flow conductors,  31  and  38 , reach until the lower rear edge  20  of the body volume  4  of the trailer  3 . The left and right flow conductors, respectively indicated as  31  and  38 , are vertically mounted along its upper edges  34  and  41  to the horizontal outer lower edges  11  and  15  of body volume  4  of the trailer  3 . Both the left and right longitudinal flow conductors,  31  and  38 , are regarded to be identical in this detailed description, therefore only the left longitudinal flow conductor  31  will be considered further in this detailed description. However, the left and the right longitudinal flow conductors,  31  and  38 , can be configured differently with respect to each other, according to the requirements of the user. 
     The straight front edge  35  of the device splits the flow, that comes from the side and the rear of the tractor  2 , into two different flows; one at the outside and one at the inside of the trailer  3 . As  FIG. 4A  indicates that the flow at the outside of the device is guided along the pillar  23 , the pallet box  25  (if present), along the wheels assemblies  26  and along the storage volume  27  (if present) to the rear of the trailer  3 . At the inside of the front of the aerodynamic device, as can be seen in  FIG. 4A , the flow comes along a curvature  36  and a sloping edge  37  preventing the same flow from separating, which reduces the aerodynamic drag locally of the vehicle, and accelerates this inside flow, due to the curvature  36 , creating an underpressure. This curvature  36  can be defined as a quarter of an ellipse with a gradually sloping back end  37 , as indicated in  FIG. 4A . This elliptical curvature with sloping back end will be referred to as elliptical longitudinal flow conductor. The favorable pressure gradient of the profile decelerates the flow again and guides it to the rear of the vehicle, where the flow is expanded into the wake of the vehicle decreasing the underpressure in the wake and thus reducing the aerodynamic drag at the back of the trailer  3 . 
       FIG. 4B  shows a view in detail of the flow conductor out of  FIG. 4A . The detailed view is focussed on the geometry of the region adjacent to the front edge  35  of the flow conductor  38 . The flow conductor is plate shaped having a thickness of at least 5 mm. The region adjacent to the front edge  35  of the flow conductor is thickened and is characterised by the fact that it comprises a curvature  36  defining an elliptical surface. The elliptical curvature  36  is defined by two radii “c” and “b”. Preferably the ratio of ‘c’ over ‘b’ is between at least 1 and at most 3. More preferably the ratio ‘c’ over ‘b’ is at most 1.5. A ratio of about 1 defines a circular curvature  36  in the cross section transversely over the flow conductor. The height dimension of the thickened portion in conjunction with the front edge is formed by the dimension ‘b’. The dimension ‘b’ is in a direction perpendicular to the longitudinal direction of the flow conductor. Preferably this dimension ‘b’ is at least 50 mm, in particular 100 mm, but even more preferable is a height dimension of 200 mm. 
     With a height dimension of at least 50 mm the thickened portion extends through an imaginary plane  47  parallel to an outer surface  45  of the flow conductor. The substantially flat surface over the substantially full length at the outer side of the flow conductor defines the outer surface  45 . Most embodiments of the flow conductor comprise at the inner side an inner surface which is parallel to the outer surface. However, in a particular embodiment according to the invention only a thickened portion may be provided at the inner side or outer side of the flow conductor. The imaginary plane  47  is positioned parallel to the outer surface at a distance ‘a’ of at least 100 mm at the innerside of the flow conductor. 
     The thickened portion in  FIG. 4B  is in cross section defined by the elliptical curvature  36  and the reducing curvature  37 . Along the reducing curvature  37 , the thickened portion is reduced to the thickness of the plate shaped flow conductor. In  FIG. 4B  the curvature  36  comprises at least two radii ‘d’ and ‘e’ of at least 100 mm. The geometry of the thickened portion ensures a stable guidance of the airflow in a longitudinal direction. 
     To obtain a streamlined outer contour, the thickened portion, comprising the curvature and the decaying part, preferably extends in a longitudinal direction of the flow conductor over a distance of at least 100 mm. 
       FIGS. 6-8  show the first embodiment for a lorry  53 , within the vehicle known as a rigid truck with a drawbar and lorry  51 , of the device of the present invention having an aerodynamic drag reduction device such as the straight longitudinal flow conductors  78  and  85 . The aerodynamic devices can be described as a combination of two thin walled plates with, considering the left longitudinal flow conductor  78 , a horizontal lower edge  79 , a vertical rear edge  80 , a horizontal upper edge  81 , and a vertical front edge  82 , and, considering the right longitudinal flow conductor  85 , a horizontal lower edge  86 , a vertical rear edge  87 , a horizontal upper edge  88 , and a vertical front edge  89 . The starting point of the most forward edges,  82  and  89 , of both the longitudinal flow conductors,  78  and  85 , lies at the lower horizontal edge  69  of the body volume  54  of the lorry  53 . The rear edges  80  and  87  of both longitudinal flow conductors,  78  and  85 , reach until the lower rear edge  70  of the body volume  54  of the lorry  53 . The left and right flow conductors, respectively indicated as  78  and  85 , are mounted vertically along its upper edges  81  and  88  to the horizontal lower edges  61  and  65  of body volume  54  of the lorry  53 . Both the left and right longitudinal flow conductors,  78  and  85 , are regarded to be identical in this detailed description, therefore only the left longitudinal flow conductor  78  will be considered further in this detailed description. However, the left and the right longitudinal flow conductors,  78  and  85 , can be configured differently with respect to each other according to the requirements of the user. 
     The straight front edge  82  of the device splits the flow, coming from the side and the rear of the rigid truck  52 , into two different flows; one at the outside and one at the inside of the lorry  53 . As  FIG. 8  indicates the flow at the outside of the device is guided along the wheel assemblies  73  and along the storage volume  76  (if present) to the rear of the lorry  53 . At the inside front of the aerodynamic device, as can be seen in  FIG. 8 , the flow comes along a curvature  83  and a sloping edge  84  preventing the same flow of separating, which reduces the aerodynamic drag locally of the vehicle, and accelerates this inside flow, due to the curvature  83 , creating an underpressure. This curvature  83  can be defined as a quarter of an ellipse with a gradually sloping back end  84 , as indicated in  FIG. 8 . This elliptical curvature with sloping back end will be referred to as elliptical longitudinal flow conductor. The favorable pressure gradient of the profile decelerates the flow again and guides it to the rear of the vehicle, where the flow is expanded into the wake of the vehicle decreasing the underpressure in the wake and thus reducing the aerodynamic drag at the back of the lorry  53 . 
     The subsequent embodiments can be preferably utilized on both vehicles, described above, commonly known as a trailer  3  and a lorry  53  with a drawbar  74 . The vehicle set-up referred to as a trailer  3  will be further considered in this detailed description. 
     In  FIGS. 9 and 10  an exemplary second embodiment of the present invention is shown, generally indicated at reference characters  102  and  109 , and having an aerodynamic drag reduction device such as the longitudinal flow conductors with a back step. The aerodynamic devices comprise a combination of two thin walled plates with, considering only the left longitudinal flow conductor  102 , a horizontal lower edge  103 , a vertical rear edge  104 , a horizontal upper edge  105 , and a vertical front edge  106 . The starting point of the most forward edge  106  the longitudinal flow conductors  102  lies beyond the lower horizontal edge  19  of the body volume  4  of the trailer  3 . The rear edge  104  of longitudinal flow conductor  102  reaches until the lower rear edge  20  of the body volume  4  of the trailer  3 . The longitudinal flow conductor with a back step, indicated as  102 , is mounted vertically along its upper edge  105  to the vertical lower edge  11  of body volume  4  of the trailer  3 . 
     The straight front edge  106  of the device splits the flow, coming from the side and the rear of the tractor  2 , into two different flows; one at the outside and one at the inside of the trailer  3 . As  FIG. 10  indicates the flow at the outside of the device is guided along the pillar  23 , the large pallet box  101 , over the wheels assemblies  26  and along the storage volume  27  (if present) to the rear of the trailer  3 . At the inside front of the aerodynamic device, as can be seen in  FIG. 10 , the flow comes along a curvature  107  and a back step  108 , which creates room for the pallet box  101 . This curvature  107  can be defined as a quarter of an ellipse with a straight back step  108 , as indicated in  FIG. 10 . This curvature with back step will be referred to as longitudinal flow conductor with back step. 
     In  FIGS. 11 and 12  an exemplary third embodiment of the present invention is shown, generally indicated with reference numbers  120  and  127 , and having an aerodynamic drag reduction device such as the longitudinal flow conductors with a circular curvature. The aerodynamic devices comprise a combination of two thin walled plates with, considering only the left longitudinal flow conductor  120 , a horizontal lower edge  121 , a vertical rear edge  122 , a horizontal upper edge  123 , and a vertical front edge  124 . The starting point of the most forward edge  124  of the longitudinal flow conductors  120  lies beyond the lower horizontal edge  19  of the body volume  4  of the trailer  3 . The rear edge  122  of longitudinal flow conductor  120  reaches until the lower rear edge  20  of the body volume  4  of the trailer  3 . The flow conductor, indicated as  120 , is mounted horizontally along its upper edge  123  to the horizontal lower edge  11  of body volume  4  of the trailer  3 . 
     The straight front edge  124  of the device splits the flow, coming from the side and the rear of the tractor  2 , into two different flows; one at the outside and one at the inside of the trailer  3 . As  FIG. 12  indicates the flow at the outside of the device is guided along the pillar  23 , the large pallet box  25 , over the wheels assemblies  26  and along the storage volume  27  (if present) to the rear of the trailer  3 . At the inside front of the aerodynamic device, as can be seen in  FIG. 12 , the flow comes along a curvature  125  and a sloping edge  126  preventing the same flow of separating, which reduces the aerodynamic drag locally of the vehicle, and accelerates this inside flow, due to the curvature  125 , creating an underpressure. This curvature  125  can be defined as a quarter of a circle with a gradually sloping back end  126 , as indicated in  FIG. 12 . This circular curvature will be referred to as circular longitudinal flow conductor. The favorable pressure gradient of the circular flow conductor decelerates the flow again and guides it to the rear of the vehicle, where the flow is expanded into the wake of the vehicle increasing the pressure in the wake and thus also reducing the aerodynamic drag at the back of the trailer  3 . 
     In  FIGS. 13 and 14  an exemplary fourth embodiment of the present invention is shown, generally indicated at reference characters  140  and  146 , and having an aerodynamic drag reduction device such as the longitudinal flow conductors with an airfoil curvature. The aerodynamic devices comprise a combination of two thin walled plates with, considering only the left longitudinal flow conductor  140 , a horizontal lower edge  141 , a vertical rear edge  142 , a horizontal upper edge  143 , and a vertical front edge  144 . The starting point of the most forward edge  144  of the longitudinal flow conductors  140  lies beyond the lower horizontal edge  19  of the body volume  4  of the trailer  3 . The rear edge  142  of longitudinal flow conductor  140  reaches until the lower rear edge  20  of the body volume  4  of the trailer  3 . The flow conductor, indicated as  140 , is mounted vertically along its upper edge  143  to the vertical lower edge  11  of body volume  4  of the trailer  3 . 
     The straight front edge  144  of the device splits the flow, coming from the side and the rear of the tractor  2 , into two different flows; one at the outside and one at the inside of the trailer  3 . As  FIG. 14  indicates the flow at the outside of the device is guided along the pillar  23 , the large pallet box  25 , over the wheels assemblies  26  and along the storage volume  27  (if present) to the rear of the trailer  3 . At the inside front of the aerodynamic device, as can be seen in  FIG. 14 , the flow comes along a curvature  145  preventing the same flow of separating, which reduces the aerodynamic drag locally of the vehicle, and accelerates this inside flow, due to the curvature  145 , creating an underpressure. This curvature  145  can be defined as any kind of airfoil, as indicated in  FIG. 14 . This airfoil based curvature will be referred to as an airfoil based longitudinal flow conductor. The favorable pressure gradient of the airfoil based flow conductor decelerates the flow again and guides it to the rear of the vehicle, where the flow is expanded into the wake of the vehicle decreasing the underpressure in the wake and thus also reducing the aerodynamic drag at the back of the trailer  3 . 
       FIGS. 15 and 16  shows an exemplary fifth embodiment for a trailer  3  of the device of the present invention having an aerodynamic drag reduction device such as the longitudinal flow conductors  160  and  167 . The aerodynamic devices can be described as a combination of two thin walled plates with, considering the left longitudinal flow conductor  160 , a horizontal lower edge  161 , a vertical rear edge  162 , a horizontal upper edge  163 , and a chamfered edge  164  between the lower edge  161  and a vertical edge. The starting point of the most forward chamfered edge  164  of the longitudinal flow conductors  160  lies beyond the lower horizontal edge  19  of the body volume  4  of the trailer  3 . The vertical rear edge  162  of longitudinal flow conductor  160  reaches until the lower rear edge  20  of the body volume  4  of the trailer  3 . The flow conductor, indicated as  160 , is mounted vertically along its upper edge  163  to the vertical lower edge  11  of body volume  4  of the trailer  3 . 
     The chamfered front edge  164  of the device splits the flow, coming from the side and the rear of the tractor  2 , into two different flows; one at the outside and one at the inside of the trailer  3 . The flow at the outside of the device is guided along the pillar  23 , the pallet box  25  (if present), over the wheels assemblies  26  and along the storage volume  27  (if present) to the rear of the trailer  3 . At the inside front of the aerodynamic device, as can be seen in  FIG. 15 , the flow comes along a curvature  165  and a sloping edge  166  preventing the same flow of separating, which reduces the aerodynamic drag locally of the vehicle, and accelerates this inside flow, due to the curvature  165 , creating an underpressure. The favorable pressure gradient of the profile decelerates the flow again and guides it to the rear of the vehicle, where the flow is expanded into the wake of the vehicle decreasing the underpressure in the wake and thus also reducing the aerodynamic drag at the back of the trailer  3 . As  FIG. 16  indicates that the front edge  164  of the longitudinal flow conductor is inclined under a certain angle with respect to the horizontal resulting in a higher efficiency during side wind conditions. This chamfered edge  164 , to which any angle or outline required by the user can be assigned, will be referred to as longitudinal flow conductor with chamfered front. 
       FIGS. 17 and 18  shows an exemplary sixth embodiment for a trailer  3  of the device of the present invention having an aerodynamic drag reduction device such as the longitudinal flow conductors  180  and  187 . The aerodynamic devices can be described as a combination of two thin walled plates with, considering the left longitudinal flow conductor  180 , a horizontal lower edge  181 , a chamfered rear edge  182  between the lower edge  181  and a vertical edge, a horizontal upper edge  183 , and a vertical front edge  184 . The starting point of the most forward vertical edge  184  of the longitudinal flow conductors  160  lies beyond the lower horizontal edge  19  of the body volume  4  of the trailer  3 . The chamfered rear edge  182  of longitudinal flow conductor  180  reaches until the lower rear edge  20  of the body volume  4  of the trailer  3 . The flow conductor, indicated as  180 , is mounted vertically along its upper edge  183  to the vertical lower edge  11  of body volume  4  of the trailer  3 . 
     The vertical front edge  184  of the device splits the flow, coming from the side and the rear of the tractor  2 , into two different flows; one at the outside and one at the inside of the trailer  3 . The flow at the outside of the device is guided along the pillar  23 , the pallet box  25  (if present), along the wheels assemblies  26  and along the storage volume  27  (if present) to the rear of the trailer  3 . At the inside front of the aerodynamic device, the flow comes along a curvature  185  and a sloping edge  186  preventing the same flow of separating, which reduces the aerodynamic drag locally of the vehicle, and accelerates this inside flow, due to the curvature  185 , creating an underpressure. The favorable pressure gradient of the profile decelerates the flow again and guides it to the rear of the vehicle, where the flow is expanded into the wake of the vehicle decreasing the underpressure in the wake and thus also reducing the aerodynamic drag at the back of the trailer  3 . 
       FIG. 18  shows an inclined rear edge  182  of the longitudinal flow conductor under a certain angle with respect to the horizontal resulting in a higher efficiency during side wind conditions. This chamfered edge  182 , to which any angle and outline required by the user can be assigned, will be referred to as longitudinal flow conductor with chamfered rear edge. 
     An exemplary seventh embodiment for a trailer  3  of the present invention having an aerodynamic drag reduction device such as the longitudinal flow conductors which can flap away by means of a support structure. This support structure comprises four rods forming a parallelogram with hinged corners providing the desired freedom to translate the longitudinal flow conductor in an upward direction. The support structure is connected to the lower surface  8  of the body volume  4  parallel to its longitudinal lower edge  11  according to the known art of mechanical fixation. The longitudinal flow conductor has to be equipped with several supporting structures to ensure the desired stiffness and flexibility. 
     Numerous variants are possible in addition to the embodiment shown, but these will remain within the scope of the invention as defined in the claims. 
     Thus, the invention provides a flow conductor comprising a streamlined outer contour at the front edge. The invention provides a flow conductor which may lead to better aerodynamic performances of vehicle combinations, which may result in great savings in fuel consumption. 
     LEGEND 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 1 
                 tractor-trailer combination 
               
               
                 2 
                 tractor 
               
               
                 3 
                 trailer 
               
               
                 4 
                 trailer body 
               
               
                 5 
                 front surface trailer body 
               
               
                 6 
                 left surface trailer body 
               
               
                 7 
                 top surface trailer body 
               
               
                 8 
                 bottom surface trailer body 
               
               
                 9 
                 right surface trailer body 
               
               
                 10 
                 rear surface trailer body 
               
               
                 11 
                 lower trailer body edge left 
               
               
                 14 
                 front trailer body edge left 
               
               
                 15 
                 lower trailer body edge right 
               
               
                 19 
                 lower front trailer body edge 
               
               
                 20 
                 lower rear trailer body edge 
               
               
                 23 
                 left support leg trailer 
               
               
                 24 
                 right support leg trailer 
               
               
                 25 
                 pallet box trailer 
               
               
                 26 
                 wheel assembly trailer 
               
               
                 27 
                 left storage volume trailer 
               
               
                 28 
                 right storage volume trailer 
               
               
                 29 
                 king-pin trailer 
               
               
                 30 
                 supporting structure 
               
               
                 31 
                 left flow conductor with elliptical curvature 
               
               
                 32 
                 lower edge left flow conductor 
               
               
                 33 
                 rear edge left flow conductor 
               
               
                 34 
                 upper edge left flow conductor 
               
               
                 35 
                 front edge left flow conductor 
               
               
                 36 
                 elliptical curved edge left flow conductor 
               
               
                 37 
                 slooping/dcaying edge left flow conductor 
               
               
                 38 
                 right flow conductor with elliptical curvature 
               
               
                 39 
                 lower edge right flow conductor 
               
               
                 40 
                 rear edge right flow conductor 
               
               
                 41 
                 upper edge right flow conductor 
               
               
                 42 
                 front edge right flow conductor 
               
               
                 45 
                 outer suface 
               
               
                 46 
                 innder surface 
               
               
                 47 
                 imaginary plane 
               
               
                 51 
                 rigid truck with drawbar and trailer 
               
               
                 52 
                 rigid truck 
               
               
                 53 
                 lorry 
               
               
                 54 
                 lorry body 
               
               
                 55 
                 front surface lorry body 
               
               
                 56 
                 left surface lorry body 
               
               
                 57 
                 top surface lorry body 
               
               
                 58 
                 bottom surface lorry body 
               
               
                 59 
                 right surface lorry body 
               
               
                 60 
                 rear surface lorry body 
               
               
                 61 
                 lower lorry body edge left 
               
               
                 65 
                 lower lorry body edge right 
               
               
                 69 
                 lower lorry front body edge 
               
               
                 70 
                 lower lorry rear body edge 
               
               
                 73 
                 wheel assembly lorry 
               
               
                 74 
                 drawbar lorry 
               
               
                 75 
                 supporting structure lorry 
               
               
                 76 
                 left storage volume lorry 
               
               
                 77 
                 right storage volume lorry 
               
               
                 78 
                 left flow conductor lorry with elliptical curvature 
               
               
                 79 
                 lower edge left flow conductor 
               
               
                 80 
                 rear edge left flow conductor 
               
               
                 81 
                 upper edge left flow conductor 
               
               
                 82 
                 front edge left flow conductor 
               
               
                 83 
                 elliptical curved edge left flow conductor 
               
               
                 84 
                 slooping/dcaying edge left flow conductor 
               
               
                 85 
                 right flow conductor lorry with elliptical curvature 
               
               
                 86 
                 lower edge right flow conductor 
               
               
                 87 
                 rear edge right flow conductor 
               
               
                 88 
                 upper edge right flow conductor 
               
               
                 89 
                 front edge right flow conductor 
               
               
                 92 
                 drivers cabin rigid truck 
               
               
                 93 
                 body volume rigid truck 
               
               
                 94 
                 wheel assemblies rigid truck 
               
               
                 95 
                 storage volume rigid truck 
               
               
                 101 
                 big pallet box 
               
               
                 102 
                 left flow conductor with back step 
               
               
                 103 
                 lower edge left fllow conductor 
               
               
                 104 
                 rear edge left flow conductor 
               
               
                 105 
                 upper edge left flow conductor 
               
               
                 106 
                 front edge left flow conductor 
               
               
                 107 
                 elliptical curvature left flow conductor 
               
               
                 108 
                 back step left flow conductor 
               
               
                 109 
                 right flow conductor with back step 
               
               
                 120 
                 left flow conductor with circular curvature 
               
               
                 121 
                 lower edge left flow conductor 
               
               
                 122 
                 rear edge left flow conductor 
               
               
                 123 
                 upper edge left flow conductor 
               
               
                 124 
                 front edge left flow conductor 
               
               
                 125 
                 circular curvature left flow conductor 
               
               
                 126 
                 slooping/decaying edge left flow conductor 
               
               
                 127 
                 right flow conductor with circular curvature 
               
               
                 140 
                 left flow conductor with airfoil based profile 
               
               
                 141 
                 lower edge left flow conductor 
               
               
                 142 
                 rear edge left flow conductor 
               
               
                 143 
                 upper edge left flow conductor 
               
               
                 144 
                 front edge left flow conductor 
               
               
                 145 
                 airfoil based curvature left flow conductor 
               
               
                 146 
                 right flow conductor with airfoil based profile 
               
               
                 160 
                 left flow conductor with chamfered front 
               
               
                 161 
                 lower edge left flow conductor 
               
               
                 162 
                 rear edge left flow conductor 
               
               
                 163 
                 upper edge left flow conductor 
               
               
                 164 
                 chamfered front edge left flow conductor 
               
               
                 165 
                 elliptical curvature left flow conductor 
               
               
                 166 
                 slooping/decaying edge left flow conductor 
               
               
                 167 
                 right flow conductor with chamfered front 
               
               
                 180 
                 left flow conductor with chamfered rear 
               
               
                 181 
                 lower edge left flow conductor 
               
               
                 182 
                 chamfered rear edge left flow conductor 
               
               
                 183 
                 upper edge left flow conductor 
               
               
                 184 
                 front edge left flow conductor 
               
               
                 185 
                 elliptical curvature left flow conductor 
               
               
                 186 
                 slooping/decaying edge left flow conductor 
               
               
                 187 
                 right flow conductor with chamfered rear