Drag reducer for rear end of vehicle

A drag reducer adapted to be mounted on the rear face of a land vehicle. It is characterized by a large piece of flexible material adapted to be tightly fixed around the periphery of the rear surface adjacent the lateral faces of the truck. The piece of material has an area larger than the rear face of the truck so as to display a convex surface when fully extended. The drag reducer has one and preferably two openings located adjacent the periphery of the rear face of the truck and a tubular extends from each of the said opening in a direction towards the front of the truck so that upon forward movement of the truck, air is automatically introduced in said tubular members and projected between the rear face of the truck and automatically forming a plano-convex air bag which reduces the drag behind the truck.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention is directed to an inflatable appendage located at the rear of 
a vehicle and especially of a truck or trailer having a flat rear surface. 
The appendage modifies the aerodynamic shape of a truck so that the low 
pressure created at the rear of a moving truck which produces a drag on 
the latter, is replaced by a zone of high pressure. The present appendage 
which acts as a drag reducer operates in an autonomous manner without 
assistance from the vehicle operator. 
2. Prior Art 
U.S. Pat. No. 4,741,569 discloses an inflatable drag reducer made of 
non-porous air bags inflated with a blower motor. 
In U.S. Pat. No. 4,236,745, metal tubing, are used to support adjacent 
sleeve members, thereby necessitating an elaborate and heavy structure. 
The appendage contemplated by Paul D. Kerian in U.S. Pat. No. 4,601,508 
requires a duct beneath the truck to supply air to the plenum chamber 
(col. 4, line 23) at the center of the rear of the truck. 
E. L. Keedy discloses in U.S. Pat. No. 4,142,755 a drag reducer made of an 
assembly of rods or rigid panels hingedly mounted on the rear surface of 
the truck. These elements maintain the shape of the drag reducer with 
little use of an air scoop which is not described and which may have a 
preventive use only. 
SUMMARY OF THE INVENTION 
The drag reducer according to the invention is adapted to be fixed to the 
flat rear face of a land vehicle. It is characterized by a piece of 
flexible material fixed to the periphery of the rear face of the vehicle 
and having an area adapted to produce a plano-convex air bag when the 
latter is inflated. The air is introduced in the air bags through air 
inlet tubular members extending on the lateral faces of the vehicle and 
forwardly opening in the direction of movement of the vehicle. The air 
entering the tubular members, when the vehicle is moving, inflates the air 
bag. 
Very little air flows through the flexible material and its periphery and 
is constantly replaced by the air penetrating through the tubular members. 
The rear face of the vehicle is usually made of two doors and each door is 
covered by its own air bag. Each bag has its middle partition and the two 
partitions are adjacent and abutting against each other.

DETAILED DESCRIPTION OF THE INVENTION 
It is known that a truck, a van or the like having a flat rear panel 
produces a turbulence behind the rear panel when the truck is moving 
forwardly. FIG. 1 illustrates the air turbulence 12 when a truck 10 is 
moving in the direction of the arrow 14. This air turbulence 12 is 
characterized by a zone of low pressure which produces a drag on the 
truck, therefore reducing its speed and increasing the gaz consumption of 
the truck. 
It has been found that the drag on the truck can be reduced by installing a 
drag reducer 16 on the rear panel 18 of the truck 10 as illustrated in 
FIG. 2 when the truck moves in the direction of the arrow 14. 
One embodiment of the drag reducer according to the invention is 
illustrated in FIG. 3. In this embodiment, the truck 20 has a side door 22 
adjacent the rear panel 24 which is completely closed by the drag reducer 
26. The drag reducer 26 is made of a piece of flexible material such as 
nylon cloth which may be completely or partially air tight and which, when 
inflated, has substantially semi-spherical shape. The cloth constituting 
the drag reducer folds itself loosely when not inflated and drops along 
the rear panel 24. The inflation of the drag reducer 26 takes place 
through a pair of channels 30 and 32 located adjacent the side of the 
truck 34 and 36. The channels 30 and 32 are opened at both ends. The front 
end is located adjacent the side 34 of the truck and allows the air to be 
introduced into the channel 30 and to flow into the drag reducer 26. The 
latter displays a substantially semi-circular cross-section, whether the 
cross-section is horizontal, vertical or in between at 45.degree.. The 
semi-circular contour 40 of the drag reducer extends substantially from 
the side panels 34 and 36 of the truck. The tubular members 30 and 32 are 
generally curved so as to define a passage between a forward inlet 38 
adjacent the side panel 34 and an outlet 43 through the drag reducer 
defined by the contour 40 as shown in FIG. 4. Although, two channels such 
as 30 and 32 are preferred, one is sufficient. 
When the drag reducer has a semi-spherical volume such as illustrated in 
FIG. 4, the internal pressure on the peripheral walls is substantially 
identical for every portion of the surface. The contour 40 is also under 
the influence of an external pressure. 
A vectorial representation of the forces exerted on the periphery of the 
drag reducer as schematically shown in FIGS. 5 and 6 identifies a 
substantially radial internal pressure by letter A. The letters C and D 
identify the fabric used to make the drag reducer. Although the internal 
pressure A and the external pressure B on the fabric are equal in force, 
they are not the same in their direction. B is the vector representing the 
action of the surrounding air and is substantially tangential to the 
fabric CD. The value of B must be divided in the two coordinates Bx and By 
in order to obtain the external real pressure exerted on the textile of 
the drag reducer. The vector Bx as shown in FIG. 6 is the one which is 
opposed to vector A corresponding to the internal pressure. The length of 
the vector A compared to the length of the vector Bx shows that it is 
possible to obtain a rigid surface of the drag reducer. The resistance of 
the fabric compensates the internal flow of air with the tangential 
external flow caused by the movement of the vehicle. 
This combination produces an aerodynamic deflector having a variable 
internal pressure as well as a variable tension on the textile forming the 
drag reducer and this pressure and tension are automatically obtained to 
provide a complete autonomy on the performance of the drag reducer. 
Accordingly, the present drag reducer needs no mechanical support or 
external manual operation. 
FIG. 7 shows an isometric view of the drag reducer which corresponds to one 
quarter of a sphere. This representation corresponds to the 
cross-sectional view shown in FIG. 8. The drag reducer 42 as shown in 
FIGS. 7 and 8 are used when the truck or van 44 is provided with doors 46 
and 48 which are adapted to be opened along a central vertical line 50. 
Each half 42 and 42a of the drag reducer are respectively provided with a 
central partition 52 and 52a which closes each of the portions of the drag 
reducer. The two halves 42 and 42a of the drag reducer are easily provided 
with a central partition 52 and 52a which spreads from each other from the 
external contour 54 to a line 56 and 56a away from the central line 50. 
With this arrangement, the internal pressure such as identified by 58 can 
exert a tension on all peripheral surfaces of both halves 42 and 42a of 
the drag reducers and especially along the central partitions 52 and 52a. 
With this arrangement, the doors can be fully opened along the side 44 of 
the truck as shown in the position 48 while allowing the drag reducer to 
fold between the door 48 and the side 44 of the truck. When the air is 
allowed to fill the halves 42 and 42a of the drag reducer, the two central 
partitions 52 and 52a do not hinder each other when the doors are closed. 
As it may be seen from the position of the door 48 on the left-hand side of 
the truck in FIG. 8, the air inlet 60a is also folded against the side of 
the truck for this purpose, it is preferable that the air inlet 60 and 60a 
be made of flexible material and preferably of a material identical to the 
material or textile used to form the drag reducer. 
The textile of the drag reducer is substantially sealed to each door around 
its periphery and preferably in a manner identified in FIG. 10. 
Considering that the textile 62 forming the drag reducer is constantly 
under tension in operation, a seal must be maintained between the fabric 
and the door as illustrated in FIG. 10. For this purpose, the textile 62 
is folded over a flexible cable 66 and a portion of the double-folded 
textile adjacent the flexible cable 66 is fixed against the door with a 
securing plate 68 preferably held by screws (not shown). The double-folded 
textile can be additionally maintained in place by sewing the edge 62a 
with the outer portion 63 adjacent the securing plate 68. Obviously, the 
sewing may be replaced by glue or by a fusing process. The plates such as 
68 are disposed around the doors so as not to interfere any moving parts 
of the doors nor with the signaling tail lights such as identified by 
reference number 41 in FIG. 7 or 31 in FIG. 3. 
FIG. 9 is a schematic illustration of an arrangement which provides access 
to the locking system 72 of the door 73. The dotted lines 70 illustrate 
the shape of the deflector surrounding the handle which is used to lock 
the doors at the rear of the truck. Such locking mechanism is positioned 
between securing plates 68a corresponding to plate 68 shown in FIG. 10. 
The flexible material needed to make the drag reducer is not necessarily 
airtight as long as the material, when slightly torn does not split under 
the pressure of the air in the drag reducer. The size of the air inlet 30 
shown in FIG. 3 or 60 shown in FIG. 8, needs to be of a sufficient 
dimension so as to compensate for the loss of air tightness for a material 
which is not fully airtight and must also be sufficiently large to supply 
sufficient air if the drag reducer is torn within acceptable limits. 
It has been found that a truck having a rear panel of about 77 square feet 
has a drag of about 1248 pounds at 55 M.P.H. and a facing wind of about 15 
M.P.H. for a conventional flat surface and less than 574 pounds for a 
convex surface corresponding to the applicant's drag reducer. A reduction 
of 54% of the drag is obtained. 
The seal between the drag reducer and the door also need to be taken in 
consideration. For an opening being 1/64 of an inch wide and 640 inches 
long this corresponds to a 10 inches square opening. Accordingly, for the 
purpose of compensating such an opening, the air inlet such as 30 needs to 
be 10 inches square in cross-section. If the air inlet has a cross-section 
smaller than that, the drag reducer will never be allowed to reach its 
expected shape. Depending on the air tightness of the material per se, the 
cross-section of the opening 38, as shown in FIG. 4, will have to be 
computed accordingly. Furthermore, a security factor of two should be 
computed in case the material is slightly torn. In the case of the 
cross-section of 10 inches square, the dimension of the opening could be a 
rectangle 1.5 inch wide and 8 inches high, that is, 12 inches square. The 
long side of the opening lies against the side of the truck. It should be 
understood that the cross-section of the opening 38 should not be 
unecessarily large because too much pressure would be exerted on the 
material of the drag reducer and eventually could damage the latter. 
The number of securing plates or anchors 68 necessary to hold the drag 
reducer can easily be computed as needed. 
Although the shape of the drag reducer has been identified above as a 
semi-spherical dome, it is easier to manufacture the dome with material 
divided in a plurality of segments as shown in FIG. 3. Considering that 
the vertical cross-section of most of the trucks is rectangular, it is 
sufficient that the drag reducer has a substantially circular 
cross-section along a vertical and a horizontal plane defined by the lines 
33 and 35. 
It is pointed out that the present invention is not an inflatable balloon 
but should be refered to and was conceived as an aerodynamic deflector. A 
inflatable balloon can burst while the present invention remains 
operational even when it is torn. The present drag reducer makes use of a 
combined internal and external pressures. 
The embodiments of the invention illustrated in FIGS. 2, 3, 4 and 8 
identify the location of the air inlets such as 30 (FIG. 3) on the side 
near the upper level of the truck. This position does not interfere with 
the usual travelling conditions of the truck such as usual passageways for 
other vehicles travelling in the same or opposite direction. The air 
inlets can also be disposed at various levels on the side of the truck 
without changing the nature of the invention. 
It is pointed out that the present aerodynamic deflector reaches its 
inflated shape through a progressive accumulation of air pressure supplied 
in a natural manner.