Trailer drag reduction system

[0002] 1. Field of the Invention

[0003] This invention relates generally to over-the-road semi-trailers and, more specifically, to a system for reducing aerodynamic drag incurred by the shape and speed of the trailer.

[0004] 2. Prior Art

[0005] Over-the-road semi-trailers are usually shaped like rectangular solids. This shape maximizes the loadable volume of the trailer for its size. It has long been known that shape causes substantial aerodynamic drag, which increases with the speed of the trailer, and increases fuel consumption. This drag was not a significant economic problem when gasoline and diesel fuel were inexpensive. However in recent years, fuel prices have skyrocketed and continue to be quite unstable. Thus, reduction in drag has a significant impact on gas mileage of tractor-trailers, which affects operation costs and, ultimately on profitability.

[0006] This drag has two components. One is the headwind resistance caused by the large flat front of the trailer impacting the air mass as it moves through it. For this reason, many commercial shippers mount a bubble on the upper front of the trailer, or provide the tractor with a wind deflector. The other component is rear turbulence, caused by the flat rear of the trailer, which causes eddying of the air as it passes around the trailer.

[0007] Many attempts have been made to reduce this eddying, most notably the addition of a “bustle” to the rear of the trailer. This approach can be seen in U.S. Pat. No. 5,375,903—Lechner, U.S. Pat. No. 4,978,162—Labbe, and U.S. Pat. No. 5,236,347—Andrus, for example. All of these devices are bulky, cumbersome and expensive. They effectively reduce the length, and necessarily carg capacity, of the trailer in states where there are length restrictions. None of them have been commercially successful.

[0008] Another approach has been to duct air from the front of the trailer through ducting within the trailer and eject this air at the rear of the trailer. This approach dates back nearly a century in application to rail cars, as exemplified by U.S. Pat. No. 926,971—Ahrens. More recent examples of this approach applied to semi-trailers are seen in U.S. Pat. No. 5,782,521—Anderson, and U.S. Pat. No. 2,514,695—Dempsey. In all of these, the ducted aor occupies internal volume of the trailer, necessitating a reduction in cargo capacity.

[0009] Thers is a need for a system of reducing drag for a trailer that is simnple, and does not reduce the cargo capacity of the trailer.

[0010] It is therefore an object of this invention to provide a system of improving gas mileage of a tractor-trailer by reducing drag, that is simple, and does not reduce the cargo capacity of the trailer.

[0011] In one aspect, this invention features a system for reducing the drag on a trailer, comprising air ducting mounted beneath the trailer which has an intake located beneath the trailer, and an outlet located on the flat rear surface of the trailer, whereby movement of the trailer forces air to flow into the intlet, through the ducts and out the outlets. Preferably, the duct inlets face the front and the side of the trailer, and the ducting forces all inlet air into a common plenum, through a venturi and out through a series if outlets spaced about the rear surface of the trailer.

[0012] These and other objects and features of this invention will become more readily apparent from reference to the following detailed description of a preferrred embodiment and the attached drawings, in which:

[0013] FIG.1 is a partial perspective view of a trailer drag reduction system according to this invention;

[0014] FIG. 2 is an enlarged detail view of a portion of FIG. 1;

[0015] FIG. 3 is a partial sectional view, taken along line 3—3 of FIG. 1;

[0016] FIG. 4 is a bottom view of the system of FIG. 1; and

[0017] FIG. 5 is a side view of FIG. 4.

[0018] As shown in FIG. 1, a semi-trailer 10 is of the type which is conventionally supported on, and pulled by a tractor (not illustrated). Trailer 10 includes spaced sides 12 and 14, a top 16 and a floor 18 which define a cargo-carrying interior that has the shape of a rectangular solid. Trailer 10 is conventionally supported on a dual axle undercarriage 20. Access to the trailer interior is through a pair of rear doors 22 (shown open) and 24 (shown closed).

[0019] Each rear door 22, 24 mounts three spaced, identical vertical pipes 26, each of which has a plurality of spaced outlet holes 28 for discharging air, as will be described later, to break up the air turbulence which conventionally occurs adjacent the doors when the trailer is at highway speeds. As illustrated, a manifold 30 extends horizontally adjacent the lower edge of doors 22, 24 and has six spaced transfer ports 32, each of which registers with an inlet port 34 at the lower end of a pipe 26.

[0020] As seen in FIGS. 4 and 5, manifold 30 is provided with air from a ducting system 36 located beneath floor 18. Ducting system 36 includes a wide forward-facing inlet 38 and a pair of side inlets 40, 42. As trailer moves through the air mass, ambient air is forced through inlets 38, 40 and 42 into a plenum 44. From there air flows through a venturi 46 and a delivery channel 48 to manifold 30. From there, the air is forced vertically up pipes 26 and out of outlet holes 28 to break the partial mmediately behind trailer, as best seen in FIGS. 1 and 2. Note that the sizes of holes 28 are graduated, from the smallest at the bottoms of pipes 26, to the largest at the tops of pipes 26. This approximately equalizes the volume of air discharges from all holes 28. Vortex generators may be added adjacent inlets 38, 40, 42 to disrupt and channel air flow to venturi 46.

[0021] To aid in air flow, a spoiler or air deflector 50 is fitted to the top rear edge of trailer 10, as shown in FIG. 3, while the bottom of plenum 30 is rounded (FIGS. 2 and 5).

[0022] This system will reduce the drag caused by the turbulence in the partial vacuum that conventional trailers normally create immediately behind them during motion. All parts are designed as add-ons that may be retrofitted to any conventional trailer. Ducting system 36 is easily mountable between the undercarriage 20 and trailer floor 18, while manifold 30 mounts just below doors 22, 24 and pipes 26 are easily secured to the rear face of doors 22, 24. Because of this design, no cargo space is lost or sacrificed, and the system can be mounted as original equipment or as an aftermarket add-on. As an alternative, the system could easily be accommodated in the original trailer design and offered as original equipment. In this case, the air discharge ducting could easily be designed as an integral part of the rear trailer doors Optionally, doors incorporating the. ducting could be offered as an aftermarket conversion.

[0023] It is thought that venturi 46 improves air flow through the system, but that it is not absolutely necessary to the functioning of this invention. Similarly spoiler 50 may be optionally omitted, although it is thought that it facilitates air flow.

[0024] While only a preferred embodiment of this invention has been disclosed and described, obvious modifications will occur to those skilled in the art and are within the scope of this invention, as defined by the appended claims.