1. Area of Invention
The invention is a device, capable of self-stowing, to improve the aerodynamics and/or reduce base drag at the aft end of bluff bodies, such as box shaped heavy trailers towed by powered tractor trucks and similarly shaped cargo and passenger vehicles, that does not impede trailer docking and is capable of incorporating air blowing techniques.
2. Essential Perameters
The purpose of the invention is to improve of the aerodynamics at the aft end of a heavy trailer or other vehicle having a bluff body to reduce aerodynamic drag. The reduction of drag lessens the energy required from, and therefore the fuel consumption, of the powered vehicle or towing vehicle. A device producing this effect is economically beneficial to the operator and will lessen national fuel consumption and emissions.
The design of the vast majority of existing and newly constructed heavy trailers incorporates a pair of outwardly hinged doors that cover the entire aft end of the trailer and are capable of swinging through an arc of 270 degrees from the closed position to a position parallel to the outside of the sides of the trailer. This feature is essential to efficient loading and docking but presents a major obstacle to the application of aft end aerodynamic devices.
Aerodynamic devices that need to be removed or partially disassembled to enable door function are cumbersome, costly, subject to loss and can be accidentally dislodged; they require temporary storage and entail lost time and added effort to the operator, to the economic disadvantage of the freight carrier.
Because heavy trailers frequently wait in the yard between transits, and because the cost of fuel saved by the device is a finite number, there exists an economic threshold to the cost to manufacture and install the device, precluding complex devices with multiple components.
To become widely accepted by the trucking industry an aft end aerodynamic device must be functional, low in cost, easily retrofitted, permanently attached, allow normal door function, and require little or no operator intervention in its use.
3. Technical Considerations
Extensive studies have been performed to demonstrate and evaluate the efficacy in drag reduction of various aerodynamic alterations to and of aerodynamic devices for the traditional, rectangular box shape of the heavy trailer and other similarly shaped highway vehicles. Herein, only those modifications relating to the trailing or aft end of the heavy trailer will be addressed.
In an SAE (Society of Automotive Engineers) technical paper presented in May 2001 [Advanced Aerodynamic Devices to Improve the Performance, Economics, Handling and Safety of Heavy Vehicles; 2001-01-2072], the author, Robert J, Englar, Principal Research Engineer, Georgia Tech Research Institute, summarizes the results of research conducted for the DOE Office of Heavy Vehicle Technologies. Computer and wind tunnel tests indicated that applying a fixed curved surface to the aft edges of the trailer produced a 7.3% reduction in drag.
Furthermore, by blowing compressed air tangentially over that surface, the reduction of aerodynamic drag can be significantly enhanced as the blown air entrains air passing along the sides of the vehicle (the so called Coanda Effect); and when the blowing is selectively applied, stability of the trailer can be improved.
An AIAA (American Institute of Aeronautics and Astronautics) paper presented in July, 2004 [DOE's Effort to Reduce Truck Aerodynamic Drag—Joint Experiments and Computations Lead to Smart Design; UCRL-CONF-204819], summarizes the results of further DOE sponsored testing of various devices and recites positive drag reduction results of 10-12% from corner rounding and an additional 15% from tangential blowing.
According to a July 2001 article in Trailer-body Builder Magazine [Winds of Change; http://trailer-bodybuilders.com/mag], in which Robert J. Englar was interviewed, The American Trucking Associations determined that each 3% reduction in a vehicle's drag coefficient equates to about 1% in fuel savings. Englar is said to have described the device to be used in testing as “90 degree arcs”, and as “a patented curved surface 6-9″ in radius attached . . . to the four corners of the back end of the trailer” (quotes from the article, not directly from Englar).
A Georgia Tech Research News release [Jan. 2, 2005, Low-Drag Trucks: Aerodynamic Improvements & Flow Control System Boost Fuel Efficiency in Heavy Trucks; http://gtresearchnews.gatech.edu/newsrelease/truck fuel.htm] further describes the road test devices and their application to vehicle stability as well as drag reduction.
The engineering and aerodynamic principles involved in the creation of the cited drag reductions and contributions to trailer stability are fully described in the afore-mentioned engineering papers and need not be recited herein.
U.S. Pat. Nos. 5,863,090 and 7,192,077 to Englar pertain to racing cars and ground vehicles, respectively, and disclose the theory, application and methods of generation, expulsion and control of air blown over surfaces of a vehicle to create the Coanda Effect with resultant effects on aerodynamic drag and vehicle stability. Devices to enable the production of these effects at the aft of a heavy trailer or other vehicle having a box like shape and bluff aft end is the subject of the invention.
The actual rounding of the corners of the trailer is impractical due to considerations of cargo space, loading and the sealing of the rear doors. In light of the above, a need exists for a device to be attached to the aft of the trailer to accomplish the same effect as corner rounding while meeting the essential parameters outlined in [0002-0006] above. The device is to be capable of manufacture in a shape to suit optimal aerodynamic requirements, and to be easily adapted for tangential blowing. [See DOE 21st Century Truck Partnership White Paper, 21CTP-003, pg. 38].
4. Prior Art
Numerous aerodynamic devices have been patented that are designed to attach to the rear of the trailer. Because of the narrow scope of the invention, only prior art pertaining to permanently attached devices that simulate the rounding of the corners of the aft end of the trailer, that relate to the blowing of air at the corners or relate to a self-stowing or non-removable concept or system for aft-of-trailer will be considered.
While the means and method of blowing air tangentially over the device of this invention is a part hereof, neither the inventions, per se, of the tangential blowing of air to reduce aerodynamic drag, nor a control system for this purpose, nor a means to generate air for this purpose are a part on the invention, as these are contained in prior art.
U.S. Pat. No. 6,854,788 to Graham discloses a self-deploying device, which attaches to the rear doors and to the sides of the aft end of the trailer. Flexible flat sheets positioned at the sides of the trailer when the doors are open. As the doors close, the motion of the doors cause the sheets to be forced aft and formed into curved surfaces (airfoils) by means of and with the support of struts acting on them. The device consists of a minimum of 22 individual parts (not counting fasteners).
While these airfoils may serve to reduce aerodynamic drag, they are large and rigid when deployed, making them subject to damage if accidentally contacted. In addition the plurality of parts and interconnections, and multiple fastening points make them costly to manufacture and install. Even if constructed, as suggested, of aluminum, they add considerable weight and the scrap value of this material makes them targets of theft.
U.S. Pat. No. 5,824,734 to Lechner discloses a design for the aft end of a vehicle causes the top and sides of the vehicle to be angled toward the center at a suggested angle of 10 to 20 degrees. It is unclear whether these surfaces are formed into the body of the vehicle or whether the angled surfaces are rigidly attached extensions. In either case this device is not suitable for application to heavy trailers due to door function and loading requirements, and is not retrofittable.
Lechner further claims devices to blow air at an angle at the outer edge of the rear end of the device, invoking the Coanda Effect, but does not define the configuration or placement of the nozzles to be used to achieve this. It is questionable whether this is a proper application of the Coanda effect.
U.S. Pat. No. 7,129,077 to Hilleman discloses hollow, rounded devices attached to the vertical edges of the aft of the trailer. These appear at first to be corner rounding devices but are in fact scoops that gather air at the sides and direct it into the space at the aft of the trailer. Although the devices move forward so as to not project behind the aft end of the trailer, there is no provision to allow the doors to be swung flush to the sides of the trailer.
U.S. Pat. No. 5,280,990 to Rinard discloses a system or combination of individual devices that are to be applied in concert to the Class 8 truck, both to tractor and trailer. The claims include right and left side “arcuate” devices of a deformable, resilient material attached to the aft vertical edges of the trailer to direct air “passing along” the sides of the trailer transversely into the area at the rear of the trailer. These are vanes or deflectors and have no relation to corner rounding.
The devices referred to in [0023] are attached to the trailer by articulated support brackets that allow the devices, through the action of opening the doors, to pivot in such a way as to lie between the sides of the trailer and the outer faces of the doors when the doors have been swung 270 degrees from the closed position.
The attachment devices referred to in [0024] appear to consist of a minimum of 32 components (not counting fasteners). In the deployed orientation, the vanes and brackets extend aft of the end of the trailer making them susceptible to accidental damage from rear or side impact. Due to these features, the self-stowing aspect of the devices is impractical and requires high cost to manufacture, install and maintain.
U.S. Pat. App. Pub. No. US2007/0024087 (Skopic) discloses a pair of symmetrical devices consisting of “flexible vanes” attached by cables or “mesh” vertically at both aft corners of the trailer and intended to redirect air “flowing” along the sides of the vehicle into “a volume of low pressure air” aft of the vehicle. The vanes are formed with 2 angles and three faces and approximate a 90 degree short-sided angle with a flatted point.
The devices described in [0026] are not intended for corner rounding, but as deflectors. Their ability to self-store between the sides of the trailer and the outer faces of the doors, when opened 270 degrees from the closed position, requires the use of the aforementioned cables or extremely flexible mesh. This makes them subject to damage or dislodgement and reduces their real world practicality.
U.S. Pat. No. 6,485,087 to Roberge and Boivin discloses a device for attaching flat, hinged, side extensions to the aft vertical and top corners of the trailer and has no relevance to corner rounding. The attaching features of this device use the expedient of replacement of the existing trailer door hinges. Position when deployed is maintained by one or more cables in conjunction with pressure exerted by top flaps, powered by pneumatic springs.
U.S. Pat. No. 6,257,654 to Boivin, et al. discloses a device for attaching flat, hinged, side extensions to the aft vertical corners of the trailer and has no relevance to corner rounding. The attaching features of this device use the expedient of replacement of the existing trailer door hinges. Position when deployed is maintained through a combination of cables, springs, pneumatic cylinders or the like. A top flap on each door is similarly attached and controlled.
The devices described in [0028] and [0029] extend rigidly straight back from the aft of the trailer making them susceptible to accidental damage from rear or side impact. The plurality of parts increases the cost, weight and difficulty of installation.
The device described in [0029] differs from that described in [0028] in that the side extensions are shortened at their tops to clear the top of door flaps when stowed. The devices of both these inventions are stowed and deployed by the action of swinging the rear doors 270 degrees from and back to the closed position, requiring the aforementioned springs as a power source, and some sort of restraint.
U.S. Pat. App. Pub. No. 2007/0089531 (Wood) discloses a device generally referred to a “boattail plates”, and has no relation to corner rounding. The device self stows and deploys by the action of swinging the rear doors 270 degrees from and back to the closed position. A spring hinge, pneumatic cylinder or mechanical brace is employed to hold the device against a stop in its deployed position. Friction occasioned by the trailing edge of the device riding on the outer sidewalls of the trailer during door opening is dealt with through the commonly invoked use of rollers and/or antifriction materials applied to the contact surfaces.
The devices described in [0028, 0029 and 0031] all involve flat, essentially rectangular panels, seeming to be 15 to 20″ in length, that extend rigidly straight back from the aft face of the trailer. This makes the devices susceptible to damage from accidental side or rear impact.
U.S. Pat. App. No. 2002/0030384, Basford, employs drag vortex generators in conjunction with boattail plates and claims that the effective length of the boattail plates can thereby be decreased. A length of 12″ is described for these plates that are not self-stowing. Even this reduced length does not alleviate the potential for accidental damage.
German Pat. No. DE2218300 discloses design features for corner contours to reduce aerodynamic drag on vehicles. These are intended to be formed on the actual exterior of the vehicle body and do not apply to added devices for heavy trailers.