CA2358484A1

CA2358484A1 - Truck trailer drag reducer

Info

Publication number: CA2358484A1
Application number: CA 2358484
Authority: CA
Inventors: Paul G. Andrus
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-09-19
Filing date: 2001-09-19
Publication date: 2003-03-19

Abstract

The invention comprises an inflatable bag mounted on each of the rear trailer doors of a standard tractor-trailer unit. The optimum aerodynamic shape of the bags with stable flat external surfaces for air to pass over is created by a series of internal cords extending horizontally in a radial array from the medial edge of the base of each bag to its corresponding lateral surface, and vertically form the top to the bottom surfaces of each bag.

Description

Background of the Invention: The invention relates to add-on aerodynamic air deflectors for the rear surface of a transport trailer. Inflatable drag reducers have been described (e. g. McDonald ( 1977) U. S Patent No. 4,006,932, Ryan { 1998) U.
S. Patent No. 5,823,610), and are more practical than rigid versions (e.g. Lechner (1994) U.S.
Patent No. 5,375,903, Switlik (1996) U.S. Patent No. 5,498,059, Boivin (2001) U.S
Patent No. 6,257,654 B 1), because inflatables are light-weight and collapsible to a very thin state so as not to interfere with complete trailer door opening which is important because there is limited room to maneuver at most loading docks. However, given that the standard long-haul trailer in North America is a double door configuration, this requires that the drag reducer have two separate halves meeting medially along a planar surface when inflated. The external surfaces over which the airstream passes should also be planar for minimum turbulence creation and maximum drag reduction.
Inflatables naturally tend towards a spherical shape without an internal means of controlling the position of the surface. The present invention describes a novel configuration of internal cords that allows the two bags to meet neatly along a common. plane, while having grossly flat external surfaces that are held firmly in place even in heavy crosswinds.
To achieve auto-inflation the present invention employs a flexible air-scoop extending above the roofline from each bag to capture air pressure from the over-passing air stream.
Similar such means have been used for inflation purposes in prior art (e.g.
McDonald (1977) U.S. Patent No. 4,006,932, Needy (1979) U.S. Patent :loo. 4,142,755, Lechner (1994) U.S. Patent No. 5,375,903).
To achieve bag stability and avoid surface flailing during inflation and deflation, an elastic cord oriented in a circular fashion on the medial surface of each bag is employed as disclosed in Andrus (1993) U.S. Patent No. 5,236,347. The present disclosure further teaches that the placement of such an elastic cord for a double; bag configuration is best on the medial surface of each bag thereby drawing the bags together and away from traffic during conditions of partial inflation.

summary of the Invention: The invention solves the problem of creating an aerodynamically optimal shape with flat surfaces from a soft inflatable material, as well as the problem of the inherent lateral instability of a double bag configuration. The novel aspect disclosed herein is a network of internal cords consisting of a radially oriented array of horizontal cords that stabilize and flatten the lateral surfaces of the bags, and a parallel array of vertical cords that flatten the upper and lower surfaces.
Brief description of the drawings: Figure I is a side view of a trailer with the invention mounted. Figure 2 is a face-on view showing the internal cordls. Figure 3 is a top view showing the 5 columns of horizontal cords splaying out radially, and the I O
vertical cards per bag end-on. Figure 4 shows the medial surface of ane half' of the invention with the elastic recoil system exposed.
Detailed description of the preferred embodiment: Each h,~lf of the invention is a fully enclosed bag 10 mounted permanently onto each of the o-ear doors I I of the trailer.
A flexible rubber air-scoop I Z feeds air into each bag to provide inflation pressure with trailer motion. A circular series of outside patches 13 on the medial side I4 of each bag I O pauses an elastic cord 15 that functions to draw the bags 1 ~0 together by contracting when inflation is only partial, thereby maintaining stability and preventing lateral flailing of the bags. An array of horizontal inelastic cards I6 originate from the medial edge I7 of the base 18 and splay out to insert at equally spaced points on the inner surface of the lateral side 19 and trailing surface 20. There are twenty-seven horizontal cords 16 per bag 10, twenty-four on the lateral side 19 and three on the trailing surface 20.
An array of vertical inelastic cords 21 connects the upper surface 22 and lower surface 23 of each bag 10, and intersects with the horizontal cords 16. The horizontal cords 16 and the vertical cords 2I are attached to inside patches 24 that are heat sealed to the inside surface of the bags 10. A rubber tube 25 that easily disconnects in its middle feeds air from one bag to the other in the event of partial air scoop l2 failure or a significant surface hole in one bag so as to maintain relatively equal bag pressure and thereby symmetry of drag reducer shape. Each bag has a zipper 2~ which can be undane to allow rapid deflation at the loading dock. Air leakage through the closed zippers 2fi during operation also serves to bleed unnecessary pressure from the bags so that the seams and attachment points are not unduly loaded. At 60 mph airspeed, the available static head of air pressure is about 2.5 inches of water or 0.1 psi. half of which is lost through the closed zippers 2b leaving about O.OS psi. 'The bag's surface tension will overcome the tension of the elastic cord 1~
and allow full inflation as iow as 0.025 psi. At 0.05 psi (typical highway operating conditions), each of the inelastic cords is loaded with about 7 pounds tension.

Claims

1. An inflatable drag reducer adapted to be mounted on the rear doors of a standard transport trailer, said drag reducer comprising an enclosed bag mounted on each of the two trailer doors, said bag having a base surface adjacent to said trailer door, said bag having a medial surface adjacent the to medial surface of the other of the two said bags, said bag having lateral, upper, and lower surfaces over which air passes during forward motion of said trawler, said bag containing an array of internal inelastic cords extending horizontally from the medial edge of said base surface to insert into said lateral surface at equally spaced points, said bag containing a second array of internal inelastic cards extending vertically from said upper surface at equally spaced points to insert into said lower surface at equally spaced points, such that upon inflation of said drag reducer the two said bags together assume a pyramidal shape with said lateral, upper and lower surfaces being substantially planar.

2. An inflatable drag reducer as recited in Claim 1 wherein a flexible tubular member connects the inside of one of said two bags to the inside of the other of said two bags, such that when the air pressure in one bag is greater that the air pressure in the other bag, then air shall freely pass from the higher pressure bag to the lower pressure bag.

3. An inflatable drag reducer as recited in Claim 1 wherein said bag has a zipper in one of its surfaces, such that under typical operating conditions approximately half of the available static head of air pressure is lost through said zipper.

4. An inflatable drag reducer as recited in Claim 1 wherein an elastic cord is mounted in a circular orientation onto said medial surfaces of each said bag, such that when said bags are only partly inflated, said elastic cord draws the bags medially toward one other.