Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to a device for
improving the aerodynamic characteristics of a closed
trailer of a tractor-trailer combination and more particularly
to the shape of the front wall of the trailer to thereby
reduce aerodynamic drag.
Closed box-like trailers, as opposed to "flat
bed" trailers or low profile tankers present a serious
aerodynamic drag problem. For instance, studies conducted
by the University of Maryland for the American Trucking
Association showed that at 58 mph, 50% of the total horsepower
developed by a fully loaded tractor trailer of the bluff
body type, is used to overcome aerodynamic drag. At 70 mph,
59% of the horsepower is used to overcome aerodynamic drag.
Many attempts have been made to reduce the air
resistance on bluff bodies such as tractor trailers.
Canadian Patent 809,545, Saunders, is an example
of a popular attempt to overcome this problem. Following
the Saunders patent, thousands of tractor cabs were equipped
with air deflectors of the type mounted at the rear of
the cab, a few inches above the roof thereof and extending
at an acute angle from the vertical. This attempt did
much to reduce aerodynamic drag particularly with head wind
conditions. However, although some improvement was noted,
the cross wind or yaw air flow problem was not resolved.
It has been established that in at least a third
of all travel conditions even at speeds of 50 mph, there is
present a yaw air flow angle of greater than 5 and up to 20.
Canadian Patent 1,021,376 Hersh, 1977 and U. S.
Patent 4,210 354 Canning, 1980, show blister type fairings
which are added to the front of the flat bluff wall of
the trailer in a tractor trailer combination. In the case
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of Hersh, the blister is in the form of a paraboloid with
a point of maximum forward extension ~eing near the bottom
of the fairing. The point of maximum extension is substantial-
ly in line with the plane of the roof of the cab in the case
of a tractor trailer combination.
The Canning blister fairing on the other hand uses
elliptical curves. The Canning fairing has a lower part of
constant semi-elliptical cross section which extends but
a small distance below the plane of the roof of the cab
and includes a baffle in the median plane including the
longitudinal axis of the trailer. The baffle is said to
provide a trap for pockets of air on either side creating
areas of pressurized air to deflect sidewinds in the gap
between the tractor and the trailer~
It is an aim of the present invention to provide
a fairing device for the front of a trailer in a tractor
trailer combination which will improve the aerodynamic drag
coefficient thereof as a result of improved yaw air flow
treatment.
A construction in accordance with the present
invention includes a bluff-type trailer in a trailer tractor
combination, the trailer having an elongated body with upstanding
flat side walls and a flat top wall normal to the side walls,
the front wall being formed by surfaces extending from the top
and side walls which are smooth concavely curved aerodynamic
surfaces such that at least one half of the area of the front
wall is in the form of an aerodynamic fairing and the remaining
of the surface of the front wall being flat and extending
upwardly from the bottom thereof to merge with the fairing
portion of the front wall.
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In a more specific construction of the present
invention, the fairing portion of the trailer front wall
occupies approximately 2/3 of the total area of the front
wall including an upper portion and a central portion of
the front wall. The upper portion is characterized by
smooth aerodynamic curves merging with th~ flat side and
top walls of the trailer with all surfaces converging on a
vertical line of maximum forward projection in the central
portion. The top point of the line coincides with the
intersection of the apices of a parabolic curve of a surface
traced in a horizontal plane and the apex of a parabolic
curve of a surface traced in a vertical plane which includes
the longitudinal axis of the trailer. The central portion of
the front wall has a surface with a vertical extent of constant
cross section and includes a series of parallel horizontal
parabolic curves identical to the parabolic horizontal curve
passing through the top point of the line of maximum projection.
The lower portion includes a downwardly sloped surface extending
towards the trailer which merges smoothly with the flattened
surface forward of the front of the trailer and the flattened
surface merges smoothly with the sidewalls of the trailer.
The advantage of the above construction is that all
of the surfaces of the fairing, and thus most of the front
wall of the trailer, are formed of smooth curves thus greatly
improving the aerodynamic drag coefficient of the trailer.
Furthermore, since the front wall per se is the
fairing, the weight factor is greatly reduced as compared
with add-on blisters and the merging of the side surfaces of
the front wall with the sidewalls is designed to obtain the
best aerodynamic drag reduction coefficient which is not possible
with add-on blisters since the add-on blisters must be added
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to existing trailer bodies having squared off edges.
Further, the fact that the fairing fills a major
portion of the gap between the cab and the trailer, will
result in the aerodynamic drag coefficient being reduced
no matter what the yaw angle.
Having thus generally described the nature of
the invention, reference will now be made to the accompanying
drawings, showing by way of illustration, a preferred
embodiment thereof, and in which:
Figure 1 is a perspective view of a trailer
body incorporating the present invention,
Figure 2 is a side elevation showing a tractor
and the trailer body;
Figure 3 is a top plan view of the trailer body
shown in Figures 1 and 2;
Figure 4 is an enlarged top plan view partly in
cross-section of the front walls of the
trailer;
Figure 5 is a front elevation partly in cross-section
of the trailer; and
Figure 6 is a fragmentary side elevation of a detail
of a construction of the front wall of
the trailer.
A tractor 10 shown in dotted lines in Figure 2
represènts a conventional tractor with a cab 12 and an
engine covering hood 14v The roof 16 of the cab is lower
than the height of a trailer 18 having a top wall 20, sidewalls
22 and 24. The trailer walls in the present embodiment are
made of laminated panels and are assembled forming a cargo
receiving body of rectangular cross-section and outline.
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Front wall 26 includes a fairing segment 30 and
a bulkhead segment 28. In other words, there is no
conventional front wall to the trailer but the fairin~
segment 30 is the integral front wall and is attached to the
- sidewalls 22 and 24.
The trailer includes a frame construction in the
front wall section, upstanding channel shape columns 32
and end columns 34 mounted to a bulkhead 35 including beam
36, 38 and columns 40, 34. A beam 44 extends above the
columns 32. At the top of the frame there is provided a
laterally channel member 46 having inwardly extending flanges
48 and 50,curved connecting members 52 extend between the
channel member 46 and the column 34. The top edge of the
fairing segment is riveted to the flange 48 as shown in
Figure 4. The side edges of the fairing segment 30 are
riveted or otherwise fastened to the sidewalls 22 and 24 of
the trailer. The roof panel member 54 is similarly riveted
to the opposite flange 50 of the channel 46 as shown in
Figure 6.
The bulkhead segment 28 includes curved corner panels
56 and 58, the radius of the curvature of these corner panels
56 and 58 is approximately 10 inches.
The top 2/3 of the front wall is covered by the
fairing segment 30 which is a fiberglass shell in the present
embodiment and which includes an upper section A, a central
section B and a lower section C.
The upper section A formed of side surfaces 62
traced by vertical lines and a top sloping surface 64 traced
by horizontal lines. The fairing segment 30 is symmetrical
of course, and only one side is shown in Figures 4 and 5.
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The surfaces 62 and 64 all merge towards an apex 66 which
is a top point in a vertical line 68 of forward projection.
The point 66 is the intersection of a parabolic curve located
in the vertical plane and following the contour of t~e top
surface 54 as well as a parabolic curve traced along the side
surface 52 in a horizontal plane through the point 66. Towards
the rear edges of the fairing segment 30, the side surfaces
and top surface 62 and 64 respectively merge into arcuate
surfaces and terminate tangentially in the plane of the
sidewalls 22 and 24 and the top wall 20 respectively. The
radius of curvature of the arcuate section approximately 16
to 20 inches, the curve of the rear sections of the fairing
segment 30, in fact overlap approximately twelve inches
behind the frame of the front wall thereby providing gradual
aerodynamic curved surfaces.
The middle section B of the fairing segment 30 is
essentially formed by a series of straight vertical lines
intersecting a horizontal parabolic curve with an apex of
the parabola at the vertical line 68 projected at the point
66. The furthest projecting line of the fairing segment 30
is therefore the line 68 which is a vertical line passing
through point 66. The lowest section C of the segment 30 is
the rearwardly extending flat sloping surface interrupted by
a slight reinforcing V-shape projection 72.
The central section B fills a major portion of the
gap between the rear wall of the cab 12 and the trailer 18.
The parabolic horizontal curve of the central section B
provides reasonable maneuverability for the tractor 12 when
the tractor 12 is steered relative to the trailer 18. Further
the smooth curves formed by the parabolic contours of the
central section B and the top section A as well as the rounded
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gradual smooth curves of the panels 58 and 56 greatly
improve the coefficient aerodynamic drive of the vehicle
particularly in yaw flow conditions.
In a typical example of a fairing 30, the width
thereof was 104 inches while the overall height of the
wall 26 was 114 inches. The full front projection of
the fairing at its most forward point 66, was 33 inches
measured from the bulkhead, while no surface of the
fairing had a radius of less than 6 inches.
The projection of section B and to a certain
extent section C reduces the amount of air flow which
can enter the gap and provide drag against what is
normally a flat front surface. Furthermore, the aero-
dynamic curves of this section reduce drag particularly
under yaw conditions. The channel 46 permits easy
replacement of the roof panel 20 without having to remove
the overlapping front wall fairing segment 30 as is the
case with blister construction. The channel 46 also
acts as a form of gutter.
