The invention relates to the reduction of aerodynamic drag for moving ground vehicles; specifically to an improved method and device for the reduction of aerodynamic drag and for improved performance of ground vehicles by reducing the mass and velocity of the air interacting with the wheel cavity. The air passing around a ground vehicle imparts a drag force to the vehicle when it flows into the cavity of a wheel and interacts with the outward facing surfaces of the wheel. The outward facing surfaces of a wheel is referred to as the wheel cavity. The ground vehicle class of particular interest is a motorized ground vehicle system. The subject invention controls the air passing over the wheel cavity and restricts air from entering the wheel cavity.
Prior art has attempted to reduce the aerodynamic drag of ground vehicles by reducing the aerodynamic drag of the wheels. For powered and un-powered vehicles with a large number of wheels the total wheel drag may comprise a significant portion of the total vehicle drag. The air passing around the tires and wheels of a vehicle will enter the outward facing wheel cavity referred to as the wheel cavity and interact with the surface of the wheel cavity resulting in low and high pressures acting on the wheel cavity surface which result in an aerodynamic drag force. Prior art has reduced wheel drag by fully covering the wheel cavity opening with a disc or panel that stops all air from entering the wheel cavity. These previous wheel cavity cover devices are circular in shape to match the wheel cavity opening and extended to the wheel outer rim. These previous devices typically attached to the wheel outer rim edge or other locations on the wheel structure. These devices were designed to prohibit external air passing over the outward facing external surfaces of the vehicle tire and wheel system from flowing into the wheel cavity and interacting with the wheel cavity surface. Several versions of these type of drag reduction devices were configured with openings in the covers to facilitate the movement of air from inboard of the tire and wheel assembly to flow into the cavity and then to the outer surface of the wheel cavity cover in an effort to promote air flow from inboard of the tire and wheel assembly through the wheel cavity to provide cooling to the brake systems.
Prior art that has used wheel cavity covers, see U.S. Pat. Nos. 6,820,475, 5,263,770, 5,135,289 and 6,794,178. These representative devices, while successful in reducing the mass of air interacting with the wheel assembly and thereby reducing the wheel drag, are complex devices that reduce access to the wheel cavity and therefore negatively impact operations and result in additional maintenance.
The object of the invention is to reduce vehicle drag and thereby increase vehicle performance by; controlling the air passing over the outer facing surfaces of the tire and wheel assembly, restricting air flow from entering the wheel cavity, and changing the wheel cavity flow characteristics by positioning a specifically sized and shaped panel shaped device in a plane that is coincident with or in close proximity the outer opening of the wheel cavity. The laterally projected area of the subject device is less than the maximum wheel cavity open area. The shape of the subject device may be either rectilinear or curvilinear. The positioning of the subject device is accomplished with various attachment means. The subject device may be fabricated with various geometric and material modifications to support operational, maintenance, and aesthetic requirements without altering the aerodynamic performance and flow control function of the device. The flow control function of the subject device is accomplished by two means; first the mass and velocity of air entering the wheel cavity is restricted and secondly the flow characteristics of the air that enters the wheel cavity is modified such that the entrained air in the wheel cavity works in partnership with the subject device to fundamentally change the wheel cavity flow features from an open cavity flow condition to a closed cavity flow condition. The subject device attaches to the wheel, rim, hub, axle cover or hubcap through the use of an attachment bracket or fitting. The subject device may be fabricated with an integral attachment bracket or fitting as such the integrated device attaches to the wheel, rim, hub, axle cover or hubcap. The subject device is centered in the wheel cavity opening, positioned laterally near the outer edge of the wheel rim and is sized with a laterally projected area that is larger than the area defined by the hub maximum diameter but less than the area defined by the wheel rim maximum inner diameter. The subject device comprising the subject invention is a light-weight and rigid device that attaches to either the surface of the wheel, rim, hub, axle cover or hubcap by means of an attachment bracket or fitting.
The subject device controls the air entering the wheel cavity by modifying the flow in the wheel cavity from an open cavity flow condition to a closed cavity flow condition. The air flow within the wheel cavity, without the subject invention installed, behaves as an open cavity in which the high velocity freestream air flow turns into the wheel cavity and imparts a low pressure on the forward section of the wheel cavity and a high pressure on the aft section of the wheel cavity. The low and high-pressure regions in the wheel cavity combine to produce a drag force. The open cavity flow conditions occur when the depth of the wheel cavity is less than the wheel cavity outer edge maximum diameter. This high drag open cavity flow condition can be minimized by covering a portion of the wheel cavity opening which thereby results in an increase in the effective aerodynamic depth-to-width ratio of the wheel cavity resulting in the wheel cavity flow changing from a open cavity flow to a closed cavity flow condition. Closed cavity flow is characterized by the external flow bridging the cavity. The high velocity freestream air does not enter the wheel cavity this results in free stream static pressures acting over the majority of the wheel cavity and thus resulting in a low drag force.
The use of a subject device that partially covers the wheel cavity to fully block air from entering the wheel cavity provides several operational and maintenance advantages over that of prior art.
Several objects and advantages of the present invention are:
Further objects and advantages are to provide a device that can be easily and conveniently used to minimize aerodynamic drag on any ground vehicle for the purposes of improving the operational performance of the vehicle. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.
The invention will be better understood in relation to the attached drawings illustrating preferred embodiments, wherein:
a is an oblique view of a single wheel, hub and tire system.
b is an oblique view of a dual wheel, hub and tire system.
a is a cross section view of a single wheel, hub and tire system.
b is a cross section view of a single wheel, hub and tire system showing the streamlines of the flow in the region of the wheel cavity.
a is an oblique view of a single wheel, hub and tire system with the subject invention installed.
b is an oblique view of a dual wheel, hub and tire system with the subject invention installed.
a is a cross section view of a single wheel, hub and tire system with the subject invention installed.
b is a cross section view of a single wheel, hub and tire system with the subject invention installed showing the streamlines of the flow in the region of the wheel cavity.
a is a cross section view of a single wheel, hub and tire system showing the critical dimensional parameters.
b is a cross section view of a single wheel, hub and tire system with the subject invention installed showing the critical dimensional parameters.
a are cross section views of a single wheel, hub and tire system with the subject invention illustrating hubcap attachment concept A.
b are cross section views of a single wheel, hub and tire system with the subject invention illustrating hubcap attachment concept B.
c are cross section views of a single wheel, hub and tire system with the subject invention illustrating wheel attachment concept A.
a through 7f are plan views of the subject invention illustrating various discoidal shape concepts.
a through 8e are cross section views of the invention illustrating various cross section concepts.
The following descriptions are of exemplary embodiments of the invention only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather the following description is intended to provide a convenient illustration for implementing various embodiments of the invention. As will become apparent, various changes may be made in the function and arrangement of the elements described herein without departing from the spirit and scope of the invention. For example, though not specifically described, many shapes, widths, diameters, placements, edge shapes, and orientation of the invention should be understood to fall within the scope of the present invention. The invention is applicable to all vehicles with wheels. The invention is not limited by fabrication means and material, attachments means and material such that all fabrication and attachment means and material should be understood to fall within the scope of the present invention.
Referring now in detail to the drawings, like numerals herein designate like numbered parts in the figures.
Ground vehicle wheel and tire systems are typically either single tire-and-wheel assemblies or dual tire-and-wheel assemblies as shown in
b shows an oblique view of a ground vehicle dual tire and wheel assembly 2. The assembly is comprised of an outer tire 12, outer wheel 22, inner tire 13, and inner wheel 23 (not shown) that mount to the vehicle by a mechanical attachment to the wheel hub 32. The shape and structure of a wheel 22 typically results in a wheel cavity 27. The wheel cavity 27 is the outward facing surface of the wheel located inboard of the wheel outer rim 28.
The wheel cavity 26 of a single wheel assembly 1 and the wheel cavity 27 of a duel wheel assembly 2 have similar geometric characteristics. For this reason the details of a wheel assembly and the air flow features will be discussed for a single wheel assembly 1 in
Cross section cuts through a single wheel assembly 1 are provided in
b shows a cross section view A-A of the single tire and wheel assembly 1 and the air flow-streamlines passing over and into the wheel cavity 26. The cross section view shows a typical relationship between the tire 11, wheel 21, and hub 31.
To control the air passing over a rotating tire and wheel assembly 1 and limit the external air from entering the wheel cavity 26 a minimally sized panel is positioned in the outer opening of the wheel cavity 26. The subject invention 50 is comprised of the minimally sized panel and associated attachment hardware. The subject invention 50 is sized and positioned according to the wheel cavity geometric characteristics. The subject invention 50 effectively closes the wheel cavity 26 to the external air flow.
The wheel 21 and wheel cavity 26 of a single wheel assembly 1 and the wheel 22 and the wheel cavity 27 of a duel wheel assembly 2 have similar geometric characteristics. For this reason the details of a wheel assembly, subject invention 50 and the air flow features will be discussed for a single wheel assembly 1 in
a shows a cross section view B-B of the subject invention 50 installed on a single tire, wheel, and hub assembly 1. The cross section view B-B shows a typical relationship between the tire 11, wheel 21, axle 41, hub 31, hubcap 33 and subject invention 50.
b shows a cross section view B-B of the air flow-streamlines passing over and into the wheel cavity 26 for a single tire, wheel, and hub assembly 1 with the subject invention 50 installed. The cross section view shows a typical relationship between the tire 11, wheel 21, axle 41, hub 31, hubcap 33 and subject invention 50.
The benefits of the subject invention 50 are the ability to use a minimally sized panel device to stop external air from entering the wheel cavity 26 and thereby reduce the aerodynamic drag force on a ground vehicle wheel assembly 1. The invention 50 accomplishes this goal with a minimum sized panel device specifically sized to take advantage of advanced aerodynamic flow control technology to create a virtual cover over the opening of the wheel cavity 26. For the subject invention 50 to effectively control the air passing over the wheel cavity 26 a number of geometric parameters related to the wheel cavity 26 and the subject invention 50 must be satisfied.
The subject invention 50 may be mounted to the wheel assembly 1 at various locations and through the use of various fastening devices.
b shows a second means for attaching the subject invention 50 to the hub 31 or hubcap 33 of a wheel assembly 1. The wheel assembly 1 is comprised of a tire 11, a wheel 21, axle 41, hub 31 and hubcap 33. The subject invention 50 is comprised of a panel device 51, an attachment bracket structure 53 and means for attaching the panel device 51 to the bracket structure 53 and means for attaching the bracket structure 53 to the hub 31 or hubcap 33.
c shows a means for attaching the subject invention 50 to the wheel 21 of a wheel assembly 1. The wheel assembly 1 is comprised of a tire 11, a wheel 21, axle 41, hub 31 and hubcap 33. The subject invention 50 is comprised of a panel device 51, an attachment bracket structure 54 and means for attaching the panel device 51 to the bracket structure 54 and means for attaching the bracket structure 54 to the wheel 21.
To accommodate various manufacturing requirements, materials, maintenance needs, and other engineering and operational concerns the subject invention may take various forms in planform shape and planform cross-section shape.
a through 8e show representative cross section cuts C-C of the panel device 51 of the subject invention 50. The panel device 51 of the subject invention 50 may take various forms to accommodate the operation, maintenance, cost, and aesthetic needs of the manufacturer and the user. The thickness TP of the panel device 51 shall be less than 50% of the wheel cavity height HW. The out-of-plane dimension OOP shall be less than 50% of the wheel cavity height HW
From the description provided above, a number of advantages of the subject device become evident:
Accordingly, the reader will see that the subject device can be used to easily and conveniently reduce aerodynamic drag on any ground vehicle for the purposes of improving the operational performance of the vehicle. Furthermore, the device has the additional advantages in that:
Although the description above contains many specifics, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. For example, the subject device can be composed of various rectilinear and curvilinear shapes such as ellipsoid, quadratic, etc.; the outer edge can be any rectilinear or curvilinear shape; the thickness and width of the subject panel device can vary; the material used to construct the panel device or attachment hardware can be any light-weight and structurally sound material such as wood, plastic, metal, composites, etc. The attachment hardware can be either conventional off the shelf or designed specifically for the subject invention.
The invention has been described relative to specific embodiments thereof and relative to specific vehicles, it is not so limited. The invention is considered applicable to any road vehicle including race cars automobiles, trucks, buses, trains, recreational vehicles, trailers, automobiles and campers. It is to be understood that various modifications and variation of the specific embodiments described herein will be readily apparent to those skilled in the art in light of the above teachings without departing from the spirit and scope.
Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.
This application claims benefit of U.S. Provisional Application No. 61068437, filed Mar. 3, 2008, the entire content of which is incorporated herein by reference.
The invention described herein was made by employees of the United States Government, and may be manufactured and used by or for the Government without payment of any royalties thereon or therefor.
Number | Date | Country | |
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61068437 | Mar 2008 | US |