Abstract:
Inflatable drag reduction device ( 20, 22 ) for vehicles, comprising an inflatable bag of a durable, flexible and generally air-tight material, arranged for attachment to the vehicle. The bag comprises of a plurality of conjoined panels and an air duct arranged for allowing the inflow of air into the interior of the bag when the vehicle is in motion. The bag further comprises internal ribs of a generally non-elastic material attached to the internal surfaces of the panels, that assist the bag in assuming a predetermined geometrical shape in which the panels are prevented from billowing outward.

Description:
This application is a US national stage of PCT/NO2009/000185 filed 15 May, 2009, and claims the benefit under 35 USC §119 to U.S. provisional application 61/053,227, filed 15 May 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the invention 
     The present invention relates to inflatable devices for reducing air drag on moving vehicles. 
     2. Prior art 
     It is well known that a moving vehicle, and in particular a moving tractor trailer having a rectangular shape, will create an area of low pressure at the rear of the vehicle causing a significant amount of drag. The opening between sections of a tandem trailer will also experience turbulence and/or drag forces. Among other things, the drag forces cause increased fuel consumption. 
     A number of prior art devices have been proposed that attempt to improve the aerodynamic shape of a vehicle, in particular a tractor trailer, by providing an inflatable attachment at the rear of such a vehicle, or between sections of a tandem vehicle. Examples of such prior art devices include U.S. Pat. Nos. 6,409,252; 5,236,347; 4,978,162; 4,741,569; 4,688, 841; and CA2,470,291. 
     While all of these references are based upon the principle of creating a more streamlined shape for a moving vehicles, the inflatable devices disclosed therein do not assume an optimal and stable shape at highway speeds, and are cumbersome and difficult to install. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a first embodiment of the device attached to the rear of a tractor trailer, and a second embodiment of the device attached between sections of a tandem trailer. 
         FIG. 2  is a perspective view of the attachment arrangement for the first embodiment. 
         FIG. 3  and  FIG. 4  are sectional side views showing the internal arrangement of various components of the first embodiment. 
         FIG. 5  is a transparent perspective view showing internal structure of the first embodiment. 
         FIG. 6  is a transparent perspective view showing internal structure of the first embodiment as well as an embodiment of an air intake duct. 
         FIG. 7  and  FIG. 8  are perspective views of components of the attachment arrangement for the first and, second embodiments. 
         FIG. 9  is a perspective view of a first embodiment of the device attached to the rear of a tractor trailer. 
         FIG. 10  is an illustration of the lines of pulling forces experienced by the first and second embodiments caused by the expansion of the device when a vehicle is moving at highway speeds. 
         FIG. 11  is a side elevational view of the first embodiment partially expanded. 
         FIG. 12  is a perspective view of an alternative embodiment of an attachment ring 
         FIGS. 13 and 14  are perspective views of an alternative arrangement for an air intake duct. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a device  20  according to one aspect of the invention for attachment to the rear of a transport trailer, and a device  22  according to another aspect of the invention for attachment between sections of a tandem trailer. The device according to the invention is inflatable, and is therefore constructed of a durable, flexible and generally airtight material. 
     According to one aspect of the invention, devices  20  and  22  are modular, meaning that they may be easily attached to existing trailers without the need for modifications to the trailer itself.  FIG. 2  shows one embodiment of a removable attachment arrangement for the device according to the invention, in this instance showing an attachment arrangement for device  20 . For ease of illustration  FIG. 2  shows the device in the geometric shape that it will assume when inflated by moving air, but it should be understood that the device would actually be collapsed in an uninflated state. 
     As seen in  FIG. 2 , the removable attachment arrangement comprises a cincture strap  24  secured around the outside perimeter of the trailer. Attachment rings  26  are connected to the cincture strap  24  and arranged at the upper corners of the trailer, as shown in more detail in  FIG. 7 . While the preferred embodiment contemplates a removable attachment arrangement, according to another aspect of the invention an attachment ring member  27 , as shown in  FIG. 12 , can be permanently affixed to the upper corners of the back of the vehicle. In some cases the container may have openings in the corners of the appropriate size, in which case those openings may be employed instead of an attachment ring. 
     Each attachment ring  26  is adapted to receive the lip of a removable hook member  28 . As shown in  FIG. 8 , hook members  28  comprise a clasp  30  and a collar  32 . Collar  32  is adapted for receiving one end of a mounting pole  34  as shown in  FIG. 2 , which is used to lift the hook member  28  up and into engagement with attachment rings  26 . According to one aspect of the invention, collar  32  and the corresponding end of pole  34  are rectangular to permit rotational manipulation of the pole, however any appropriate shape could be employed. 
     As shown in  FIG. 2 , an attachment strap  36  is attached to each of the upper corners of the back side of device  20  or  22  at attachment points  38 . Each strap  36  passes through clasp  30  of its corresponding hook  28 , and thereafter through one of two slits  40  integrated into the lower corners of the back side of the device. Straps  36  further comprise an adjustable attachment loop  42  at their lower ends. 
     The device according to the invention is easily mounted to any existing trailer by first securing cincture strap  24  near the rear of the trailer. Pole  34  is inserted into collars  32  of hook members  28  and used to lift them into engagement with rings  26 . The user secures adjustable loop  42  to a convenient structure near the bottom of the trailer, such as a bumper or the like, and pulls on the free end of strap  36  until the upper corners of the device are raised into position. Loop  42  is thereupon tightened and secured. The mounted device will, in an uninflated, collapsed state, have a shape similar to that illustrated in  FIG. 4 . For the device according to a second embodiment  22  for use between trailer sections of a tandem trailer, only one side of the device will be mounted to the back end of one trailer section, with the other side free as shown in  FIG. 1 . 
     As seen in  FIG. 1 , the first embodiment of the invention assumes a triangular cross section when inflated.  FIGS. 3 ,  4 ,  5  and  6  show the internal structure of the first embodiment, one function of which is to maintain the stability and shape of the triangular cross section when subjected to strong airflows at highway speeds. While the following description relates to the triangular cross section of the first embodiment, it will be appreciated by one skilled in the art that corresponding structures can be employed for the rectangular cross section of the second embodiment. 
     As seen in  FIG. 5 , the device comprises a plurality of internal rib members  44 . Rib members  44  are preferably made of a nonelastic material and according to one aspect of the invention of the same material as the outer panels of the device. The rib members are in the form of three strips sewn together at adjacent ends, and sewn into the material along their outer edges to the inside surface of the side panels of the device. A vertical triangular channel will thus be formed in the interior of the device. The ribs serve to impart rigidity to the device, allowing it to maintain the triangular cross section when subjected to the forces depicted in  FIG. 10 . A tension cord  46  is attached to the top panel and bottom panel of the device. When inflated, the ribs prevent the device from billowing outward from the sides, and tension cord  46  prevents the device from billowing out at the top and bottom. 
     The device further comprises means for automatically assuming the compact, collapsed configuration shown in  FIG. 4  when the vehicle slows below a predetermined speed. The device therefore further comprises a vertical, internal sleeve member  48  affixed to the inside surface of the back side of the device. According to one aspect of the invention, the sleeve is preferably sewn from the same material as the device. A weight member  50  is arranged in the sleeve, and connected by a cord  52 , via a pulley  54 , to a fan-shaped plurality of cords  56  attached to the bottom panel of the device, shown in  FIG. 6 . Pulley  54  is suspended from a strap  55 . When the vehicle is in motion, air pressure from air entering in through an air duct  58  will cause an increase in the air pressure inside the device, tending to causing it to expand. Air duct  58  is preferable located slightly to the side of the vehicle as shown in  FIG. 9 , and is secured to the vehicle a strap  59 . When the vehicle reaches a predetermined speed, the inside air pressure will exceed the weight of member  50 , which will be raised inside sleeve  48 , as depicted in  FIG. 3 . When the vehicle slows below a predetermined speed, the weight of member  50  will exceed the pressure acting on the inside of the device, and fall inside sleeve  48 , drawing the device closed by pulling on cords  56 , whereby the device will assume a collapsed shape as shown in  FIG. 4 . 
     The length of cord  52  may be chosen so as to determine the degree of tapering of the top and bottoms panels of the device. The illustrations shown in the figures show a preferred embodiment having a degree of taper of zero degrees, wherein the side panels of the device are essentially rectangular. In such case the length of cord  52  will be essentially equal to the height of the trailer section. By choosing a shorter length for cord  52  (and making corresponding adjustments to the geometric shape of the side panels), a greater degree of taper can be selected. According to one aspect of the invention, the degree of taper is 17 degrees or less. 
     An alternative arrangement for an air intake duct  58 , on the top of the bag, is shown in  FIGS. 13 and 14 . The upper edge of the inflatable device is illustrated in  FIGS. 13 and 14  by reference number  65 . Reference number  66  shows a portion of the duct arranged inside the inflatable device. The duct further comprise an opening  62 , an strap lock  63  attached to duct  58  where strap  69  goes into and around duct  58 . Strap  69  is attached in the bag in a zone  67  and has an overlapping joint attached with a ring  64 . The exposed portion of duct  58  can be regulated by opening the strap lock  63  and retracting/pushing in the duct to the desired position, in order to arrive at an optimal position in relation to the vehicle.