Patent ID: 12195099

InFIG.19, an aerodynamic deflector panel and wheel skirt assembly is mounted underneath the trailer of an industrial truck in front of the rear wheel assembly.

DETAILED DESCRIPTION OF THE INVENTION

Description of Wheel Drag Mechanics:

As mentioned, drag force on exposed wheels increases more rapidly on upper wheel surfaces than on vehicle frame surfaces, causing a non-linear relation from rising wind speeds between net drag forces on vehicle frame surfaces versus net drag forces on vehicle wheel surfaces. Thus, vehicles having wind-exposed wheels are particularly sensitive to external headwinds reducing propulsive efficiency. As a result, there exists a need for an improved aerodynamic deflector and skirt for use on industrial trucks and trailers.

Because of this rising dominance of wheel drag in rising headwinds-due to the non-linear relation from rising wind speeds between net drag forces on vehicle frame surfaces versus net drag forces on vehicle wheel surfaces-a discussion of the wheel drag mechanics central to this non-linear relationship is presented herein. The upper wheel fairing is described below as a simple solution for reducing vehicle drag in rising headwinds on a cycle, and is presented herein as background for the present embodiment.

The shielding provided by fairing1inFIG.11is particularly effective since aerodynamic forces exerted upon exposed vehicle surfaces are generally proportional to the square of the effective wind speed impinging thereon. Moreover, the power required to overcome these drag forces is generally proportional to the cube of the effective wind speed. Thus, it can be shown that the additional power required to overcome these drag forces in propelling a vehicle twice as fast over a fixed distance, in half the time, increases by a factor of eight. And since this power requirement is analogous to rider effort—in the case of a bicycle rider—it becomes critical to shield the most critical drag-inducing surfaces on a vehicle from oncoming headwinds.

FIG.14shows the results of an analysis of the drag mechanics on a bicycle with shielded upper wheels. The curves indicate that a bicycle with shielded upper wheels is faster when facing headwinds. Moreover, the gains in propulsive efficiency are shown to quickly increase in only a modest headwind, but continue to rise as headwinds increase further.

In any wheel used on a vehicle, and in the absence of any external headwinds, the effective horizontal wind speed at a point on the wheel at the height of the axle is equal to the ground speed of the vehicle. Indeed, the effective headwind speed upon any point of the rotating wheel depends on that point's current position with respect to the direction of motion of the vehicle.

Notably, a point on the moving wheel coming into direct contact with the ground is necessarily momentarily stationary, and therefore is not exposed to any relative wind speed, regardless of the speed of the vehicle. While the ground contact point can be rotating, it is not translating; the contact point is effectively stationary. And points on the wheel nearest the ground contact point are translating with only minimal forward speed. Hence, drag upon the surfaces of the wheel nearest the ground is generally negligible.

Contrarily, the topmost point of the wheel assembly (opposite the ground) is exposed to the highest relative wind speeds: generally at least twice that of the vehicle speed. And points nearest the top of the wheel are translating with forward speeds substantially exceeding the vehicle speed. Thus, drag upon the surfaces of the upper wheel can be quite substantial. Lower points on the wheel are exposed to lesser effective wind speeds, approaching a null effective wind speed—and thus negligible drag—for points nearest the ground.

Importantly, due to the rotating geometry of the wheel, it can be shown that the effective combined frictional drag force exerted upon the wheel is typically centered in closer proximity to the top of the wheel, rather than centered closer to the axle as has been commonly assumed in many past analyses of total wheel drag forces. While the net pressure (or form) drag (P) force on the forwardly facing profile of the wheel is generally centered with elevation and directed near the axle on the wheel (as shown inFIG.17), the net frictional drag force (F) upon the moving surfaces is generally offset to near the top of the wheel (as shown inFIG.18).

Indeed, it is near the top of the wheel where the relative winds are both greatest in magnitude, and are generally oriented most directly opposed to the forward motion of rotating wheel surfaces. Moreover, in the absence of substantial external headwinds, the frictional drag exerted upon the lower wheel surfaces contributes relatively little to the net drag upon the wheel, especially when compared to the drag upon the upper surfaces. The combined horizontal drag forces (from pressure drag from headwinds deflected by both the leading and trailing wheel forwardly facing profiles, and from frictional drag from headwinds impinging upon the forwardly moving surfaces) are thus generally concentrated near the top of the wheel under typical operating conditions. Moreover, with the faster relative winds being directed against the uppermost wheel surfaces, total drag forces combine near the top to exert considerable retarding torque upon the wheel.

As mentioned, the horizontal drag forces are primarily due to both pressure drag forces generally distributed symmetrically across the forwardly facing vertical profiles of the wheel, and to winds in frictional contact with moving surfaces of the wheel. Pressure drag forces arise primarily from the displacement of air from around the advancing vertical profile of the wheel, whose circular outline moves at the speed at the vehicle. As discussed above, since the entire circular profile moves uniformly at the vehicle speed, the displacement of air from around the moving circular profile is generally uniformly distributed with elevation across the forwardly facing vertical profile of the wheel. Thus, these pressure drag forces (P, as shown inFIG.17andFIG.18) are also generally evenly distributed with elevation across the entire forwardly facing vertical profile of the wheel, and centered near the axle. And these evenly distributed pressure drag forces arise generally in proportion only to the effective headwind speed of the vehicle.

Frictional drag forces (F, as shownFIG.18), however, are concentrated near the top of the wheel where moving surfaces generally exceed vehicle speed—while the lower wheel surfaces move at less than the vehicle speed. Since drag forces are generally proportional to the square of the effective wind speed, it becomes apparent that with increasing wind speed, that these upper wheel frictional drag forces directed upon the moving surfaces increase much more rapidly than do pressure drag forces directed upon the forward profile of the wheel. Indeed, these friction drag forces generally arise in much greater proportion to an increasing effective headwind speed of the vehicle. Nevertheless, these increased frictional drag forces being directed on the upper wheel is only a partial factor contributing to augmented wheel drag forces being responsible for significantly retarded vehicle motion.

Significantly, both types of drag forces can be shown to exert moments of force pivoting about the point of ground contact. And as such, either type of drag force exerted upon the upper wheel retards vehicle motion considerably more than a similar force exerted upon a substantially lower surface of the wheel. Minimizing these upper wheel drag forces is therefore critical to improving propulsive efficiency of the vehicle.

Also important—and due to the rotating geometry of the wheel—it can be shown that the vehicle propulsive force on the wheel applied horizontally at the axle must substantially exceed the net opposing drag force exerted near the top of the wheel. These forces on a wheel are actually leveraged against each other, both pivoting about the same point—the point on the wheel which is in stationary contact with the ground—and which is constantly changing lateral position with wheel rotation. Indeed, with the geometry of a rolling wheel momentarily pivoting about the stationary point of ground contact, the lateral drag and propulsive forces each exert opposing moments of force on the wheel centered about this same point in contact with the ground.

Furthermore, unless the wheel is accelerating, the net torque from these combined moments on the wheel must be null: The propulsive moment generated on the wheel from the applied force at the axle must substantially equal the opposing moment from drag forces centered near the top of the wheel (absent other resistive forces, such as bearing friction, etc.). And the propulsive moment generated from the applied force at the axle has a much shorter moment arm (equal to the wheel radius) than the opposing moment from the net drag force centered near the top of the wheel (with a moment arm substantially exceeding the wheel radius)—since both moment arms are pivoting about the same stationary ground contact point. Thus, for these opposing moments to precisely counterbalance each other, the propulsive force applied at the axle—with the shorter moment arm-must substantially exceed the net drag force near the top of the wheel.

In this way, the horizontal drag forces exerted upon the upper surfaces of the wheel are leveraged against opposing and substantially magnified forces at the axle. Hence, a relatively small frictional drag force centered near the top of the wheel can have a relatively high impact on the propulsive counterforce required at the axle. Shielding these upper wheel surfaces can divert much of these headwind-induced drag forces directly onto the vehicle body, thereby negating much of the retarding force amplification effects due to the pivoting wheel geometry.

Moreover, since the propulsive force applied at the axle exceeds the combined upper wheel drag forces, a lateral reaction force (R, as shown inFIG.18) upon the wheel is necessarily developed at the ground contact point, countering the combined unbalanced propulsive and drag forces on the wheel: Unless the wheel is accelerating, the reaction force at the ground, together with the upper wheel net drag forces (F+P), combine (A=F+R+P, as shown inFIG.18) to countervail the lateral propulsive force (A) applied at the axle. This reaction force is transmitted to the wheel through frictional contact with the ground. In this way, an upper wheel drag force is further magnified against the axle. For these multiple reasons, it becomes crucial to shield the upper wheel surfaces from exposure to headwinds.

Given that the propulsive force (A) applied at the axle must overcome both the net wheel drag forces (F+P) and the countervailing lower reaction force (R) transmitted through the ground contact point, it can be shown that the net drag force upon the upper wheel can oppose vehicle motion with nearly twice the sensitivity as an equivalent drag force upon the static frame of the vehicle. Hence, shifting the impact of upper wheel drag forces to the static frame can significantly improve the propulsive efficiency of the vehicle.

Furthermore, as drag forces generally increase in proportion to the square of the effective wind speed, the more highly sensitive upper wheel drag forces increase far more rapidly with increasing headwind speeds than do vehicle frame drag forces. Thus, as the vehicle speed increases, upper wheel drag forces rapidly become an increasing component of the total drag forces retarding vehicle motion.

And given the greater sensitivity of speed-dependent upper wheel drag forces—as compared against vehicle frame drag forces—to the retarding of vehicle motion, considerable effort should first be given to minimizing upper wheel drag forces. And shielding the faster-moving uppermost surfaces of the wheel assembly from oncoming headwinds, by using the smallest effective fairing assembly, is an effective means to minimize upper wheel drag forces.

Contrarily, drag forces on the lower wheel generally oppose vehicle motion with reduced sensitivity compared to equivalent drag forces on the static frame of the vehicle. Propulsive forces applied at the axle are levered against lower wheel drag forces, magnifying their impact against these lower wheel forces. Shielding lower wheel surfaces can generally negate this mechanical advantage, and can actually increase overall drag on the vehicle.

Moreover, as discussed above, headwinds on the static frame generally exceed the speed of winds impinging on the lower surfaces of the wheel. Hence, frictional drag forces on the lower wheel surfaces are greatly reduced. Thus, it is generally counterproductive to shield the wheel below the level of the axle. Drag on a vehicle is generally minimized with upper wheel surfaces shielded from headwinds and with lower wheel surfaces exposed to headwinds.

Wheel drag sensitivity to retarding vehicle motion becomes even more significant in the presence of external headwinds. With external headwinds, the effective wind speed impinging on the critical upper wheel surfaces can well exceed twice the vehicle speed. Shielding protects the upper wheel surfaces both from external headwinds, and from headwinds due solely to vehicle motion.

Indeed, wheel surfaces covered by the shield are exposed to winds due solely to wheel rotation; headwinds are deflected. The effective drag winds beneath the shield are generally directed tangentially to rotating wheel surfaces, and vary in proportion to radial distance from the axle, reaching a maximum speed at the wheel rim equal to the vehicle speed, regardless of external headwinds. Since drag forces vary generally in proportion to the square of the wind speed, the frictional drag forces are considerably reduced on shielded upper wheel surfaces. Using these wind shields, shielded wheel surfaces are exposed to substantially reduced effective wind speeds—and to generally much less than half of the drag forces without shielding.

Diminished drag forces from external headwinds impinging on the slower moving lower surfaces of a rolling wheel generally oppose wheel motion with much less retarding torque than drag forces from winds impinging on the faster upper surfaces. Indeed, tests demonstrate that with upper shields installed on a suspended bicycle wheel, the wheel will spin naturally in the forward direction when exposed to headwinds. Without the shields installed, the same wheel remains stationary when exposed to headwinds, regardless of the speed of the headwind. And an unshielded spinning wheel will tend to stop spinning when suddenly exposed to a headwind. This simple test offers an explanation for the unexpected result and demonstrates that by minimally shielding only the upper wheel surfaces from external headwinds, the overall drag upon the rotating wheel can be substantially reduced.

Furthermore, as external headwinds upon a forwardly rotating vehicle wheel add relatively little frictional drag to the lower wheel surfaces—which move forward at less than the vehicle speed—but add far more significant drag to the upper wheel surfaces, which move forward faster than the vehicle speed and which can more significantly retard vehicle motion, shielding the upper wheel surfaces against headwinds is particularly beneficial. Since drag forces upon the wheel are generally proportional to the square of the effective wind speed thereon, and the additional drag on the wheel—and thereby on the vehicle—increases rapidly with headwinds, shielding these upper surfaces greatly reduces the power required to propel the vehicle. Moreover, the relative effectiveness of shielding upper wheel surfaces generally increases with increasing headwinds.

An examination of the retarding wind vectors on a rotating wheel can reveal the large magnitude of drag retarding moments upon the uppermost wheel surfaces, relative to the lower wheel surfaces. And an estimate of the frictional drag torque on the wheel can be determined by first calculating the average moments due to drag force vectors at various points—all pivoting about the ground contact point—on the wheel (results shown plotted inFIG.15), and then summing these moments at various wheel elevations above the ground and plotting the results (FIG.16). The area under the resulting curve (shown inFIG.16as a series of curves representing various headwind conditions) then represents the total frictional drag (absent profile drag) torque upon the wheel.

In order to determine the relationship between this torque and elevation on the wheel, the magnitudes of the drag wind vectors that are orthogonal to their corresponding moment arms pivoting about the point of ground contact must first be determined. These orthogonal vector components can be squared and then multiplied by the length of their corresponding moment arms, in order to determine the relative moments due to drag at various points along the wheel rim.

The orthogonal components of these wind vectors tend to increase linearly with elevation for points on the rim of the wheel, and also for points along the vertical mid-line of the wheel. Calculating the moments along the vertical mid-line of the wheel can yield the minimum relative drag moments at each elevation. Calculating an average of the maximum drag moment at the rim combined with the minimum drag moment along the mid-line can then yield the approximate average drag moment exerted at each elevation upon the wheel. Multiplying this average drag moment by the horizontal rim-to-rim chord length can yield an estimate of the drag torque exerted upon the wheel at each elevation level (FIG.16). These calculations are simply determined from the geometry of the rotating wheel; the object of this analysis is to determine the likely relative magnitudes of drag torques upon the wheel at various elevations.

From the resulting plots (FIG.16), it can be estimated that the uppermost approximate one-third section of the wheel likely contributes most of the overall drag torque upon the wheel. Thus, by shielding this upper section from headwinds, drag torque can be considerably reduced. With upper-wheel shielding, as noted above, the relative winds beneath the shield are due mostly to wheel rotation, and are generally directed tangentially to the wheel. The resulting drag torque under the shielded sections can then be determined as above, and compared with the unshielded drag torque for similar headwind conditions.

These calculations-generally confirmed by tests-indicate a substantial reduction in retarding drag torque upon the shielded upper wheel surfaces. In the absence of external headwinds, the plots ofFIG.16indicate that shielding the uppermost approximate one-third section of the wheel can reduce the drag torque of this section considerably, by as much as 75 percent. Moreover, repeating calculations and testing with an external headwind equal to the vehicle speed indicates that upper wheel shielding can reduce the comparative upper wheel drag torque of this section by still more, perhaps by as much as 90 percent. Hence, the potential effectiveness of shielding upper wheel surfaces can be significant, especially with surfaces having higher drag sensitivities, such as wheel spoke surfaces.

As discussed above, since upper wheel drag forces are leveraged against the axle—thereby magnifying the propulsive counterforce required at the axle—an increase in drag force on the wheels generally retards vehicle motion much more rapidly than does an increase in other vehicle drag forces. And while under external headwind conditions, the total drag on a vehicle with wheels exposed directly to headwinds increases still more rapidly with increasing vehicle speed.

Shielding upper wheel surfaces effectively lowers the elevation of the point on the wheel where the effective net drag force is exerted, thereby diminishing the magnifying effect of the propulsive counterforce required at the axle, as discussed above. As a result, the reduction in drag force upon the vehicle achieved by shielding the upper wheel surfaces is comparatively even more significant with increasing external headwinds. Shielding these upper wheel surfaces can thereby improve relative vehicle propulsion efficiency under headwinds by an even greater margin than under null wind conditions.

Moreover, shielding these upper wheel surfaces can be particularly beneficial to spoked wheels, as round spokes can have drag sensitivities many times greater than that of more streamlined surfaces. As round spokes—in some configurations—can have drag coefficients ranging from one to two orders of magnitude greater than corresponding smooth, streamlined surfaces, shielding the spokes of the upper wheel from external wind becomes particularly crucial in reducing overall drag upon the wheel.

Accordingly—given these multiple factors-a relatively small streamlined fairing attached to the vehicle structure and oriented to shield the upper surfaces of the wheel assembly from oncoming headwinds substantially reduces drag upon the wheel, while minimizing total drag upon the vehicle. Consequently, an embodiment includes the addition of such a fairing to any wheeled vehicle-including vehicles having spoked wheels, where the potential drag reduction can be even more significant.

The addition of such minimal fairings to each side of a traditional spoked bicycle wheel, for example, reduces windage losses and improves propulsive efficiency of the bicycle, particularly at higher cycle speeds or in the presence of headwinds, while minimizing cycle instability due to crosswind forces. Since crosswinds are a significant factor restricting the use of larger wheel covers, minimizing the fairing size is also an important design consideration. And minimizing form drag induced by the forward-facing profile of the fairing also will influence the fairing design. The preferred fairing size will likely substantially cover the upper section of the exposed wheel, and be placed closely adjacent to the wheel surfaces, consistent with general use in bicycles. In heavier or powered cycles, design considerations may permit somewhat larger fairings, covering even more of the wheel surfaces.

As shielding upper wheel surfaces can reduce overall drag on the vehicle, while simultaneously augmenting the total frontal profile area of the vehicle exposed to headwinds, a natural design constraint emerges from these competing factors: Shields should be designed sufficiently streamlined and positioned sufficiently close to wheel surfaces to provide reduced overall vehicle drag. And as shielding effectiveness potentially increases under headwind conditions, shields designed with larger surface areas and larger frontal profiles may still provide reduced overall vehicle drag under headwind conditions, if not under null wind conditions. Thus, a range of design criteria may be applied to selecting the best configuration and arrangement of the fairing, and will likely depend on the particular application. In any particular application, however, the embodiment will include a combination of design factors discussed above that will provide a reduction in overall vehicle drag.

In a cycle application, for example, fairings positioned within the width of the fork assembly will likely provide the most streamlined design which both shields spokes from headwinds but also minimizes any additional form drag profile area to the vehicle frame assembly. In other applications, insufficient clearances may preclude positioning the fairings immediately adjacent to moving wheel surfaces. In such situations, headwinds may be sufficient in magnitude to cause a reduction in overall vehicle drag to justify the use of wider upper wheel fairings-positioned largely outside the width of the fork assembly—with extended forward profile areas.

Furthermore, from the previous analysis a consideration the drag torque curves wholly above the level of the axle, it becomes apparent that shielding the wheel is best centered about an elevation likely between 75 and 80 percent of the diameter of the wheel, or near the center of the area under the unshielded torque curve shown inFIG.16. While drag forces are generally greatest in magnitude near the top of the wheel, the effective exposed topmost surface areas are much smaller, thereby limiting the magnitude of drag torques upon the uppermost surfaces of the wheel. Thus, the upper wheel fairing would best extend above and below this critical level (generally, between 75 and 80 percent of the diameter of the wheel) in order to optimally minimize drag upon the wheel. And as the surfaces forward of the axle are the first to be impacted by headwinds, shielding these surfaces is essential to deflecting headwinds from the rearward surfaces. Thus, the higher-sensitivity drag-inducing surfaces in the forward upper quadrant and centered about this critical elevation on the wheel generally need to be shielded for optimal minimization of drag. These higher-sensitivity drag-inducing surfaces generally centered about this critical elevation and extending to include those surfaces with higher drag-inducing sensitivities that are positioned mostly in the forward upper quadrant of the wheel, but likely also to include much of the wheel surfaces positioned in the rearward upper quadrant, are herein defined and later referred to as: major upper drag-inducing surfaces. And the critical level about which the major drag-inducing surfaces are generally centered in elevation is herein defined and later referred to as: critical elevation.

As discussed, the precise elevation about which the major upper drag-inducing surfaces are centered, as well as the precise extent to which surfaces in the forward quadrant and in the upper half of the wheel are included in the major upper drag-inducing surfaces, will depend on the particular application and operating conditions. Certain wheel surfaces with higher drag sensitivities, such as wheel spokes, generally need to be shielded when positioned within the region of the major upper drag-inducing surfaces. Other surfaces such as smooth tire surfaces having lower drag sensitivities may also benefit from shielding if their surface areas are extensive, are positioned near the critical level in elevation, or are the primary upper wheel surfaces exposed to headwinds. In the example analysis ofFIGS.15and16, a uniform surface across the wheel having a constant drag-sensitivity was assumed. In any particular application, the unique combination of different wheel surfaces with differing drag sensitivities will determine the particular height of the critical elevation level about which the major upper drag-inducing surfaces are centered.

A similar analysis can be performed for form drag forces on the moving forward vertical profiles of the wheel rim or tire. The results obtained are generally similar in form, though may differ somewhat in magnitudes as the effective wind speeds on the moving profiles are generally lower on the upper wheel—equal to the vehicle speed—and will depend on the particular application, including the total area of the wheel forward profile exposed to headwinds, and to headwind and vehicle speeds. Nevertheless, the net pressure drag torque caused by the moving outline of the wheel is also centered above the level of the axle, and thereby merits consideration in determining the particular height of the critical elevation level, and in the ultimate configuration of the fairing.

Hence, the fairing shown inFIG.13is best configured to shield the uppermost and forward wheel surfaces, and to extend rearward to at least partially shield the forward profile of the trailing portion of the upper wheel rim, consistent with the further requirement to extend downward as much as practical to the level of the axle. As mentioned, crosswind considerations will also influence the ultimate configuration for a particular application.

In consideration of further embodiments described below, the operating principles described above will generally apply, and may be referred thereto.

Description of Various Embodiments

Various embodiments are described below in detail, each providing means to deflect headwinds from directly impinging on the upper wheel surfaces and onto the lower wheel surfaces of a trailing wheel assembly, thereby reducing vehicle drag and increasing propulsive efficiency.

First Embodiment—FIGS.1and2

As shown inFIGS.1and2, an embodiment comprises an inclined aerodynamic wheel deflector panel assembly20attached to and mounted underneath the body of a trailer16for a commercial vehicle. The inclined wheel deflector panel assembly20is located forward of the rear wheel assembly17and located directly in front of a trailing wheel set18which would otherwise be exposed to headwinds when the vehicle is in forward motion. The inclined wheel deflector panel assembly20is planar in shape, mounted inclined in a forwardly—angled orientation with the upper edge more forwardly located and the lower surface located more rearward on the vehicle. The inclined wheel deflector panel assembly20spans the lateral width of the trailing wheel set18of the trailing rear wheel assembly17located on either side of the vehicle. The optimal inclined wheel deflector panel assembly20extends downward ideally to no lower than the level of the axle19and is located proximal to the trailing wheel set18in order to deflect upper wheel headwinds onto the exposed lower wheel surfaces.

It can be concluded from the discussion of wheel drag mechanics above, that since propulsive counterforces applied to the wheel at the axle have a mechanical advantage over lower wheel drag forces—which are necessarily applied to the wheel below the level of the axle-directing upper wheel headwinds onto the lower wheel surfaces can significantly reduce overall vehicle drag and improve propulsive efficiency. The reasons for these gains in vehicle efficiency become apparent by further considering how wheel drag forces compare with vehicle body drag forces.

As discussed earlier, drag forces on the wheel must be countered by a propulsive force from the vehicle body applied at the axle. And it can be established that drag forces on the upper wheel have a mechanical advantage over countervailing propulsive counterforces applied at the axle. And with the wheel deflector assembly attached to the vehicle body, drag on the deflector must also be countervailed by a propulsive counterforce applied to the vehicle body at a propulsive axle.

Thus, in order to determine the relative difference in total vehicle drag between the traditional extended height deflector diverting headwinds from impinging on both the upper and the lower wheels, and the improved reduced height deflector with the lower wheel surfaces ideally fully exposed to headwinds, the added vehicle drag derived from the surface of the deflector panel extending below the level of the axle must be compared against the vehicle drag arising from the corresponding additional surfaces of the lower wheel otherwise shielded by the extended deflector. And as already established above, the relative effects of these resistive forces on vehicle propulsion are non-linearly related, and vary considerably with increasing headwinds: for vehicles facing faster external headwinds the nonlinear effects quickly increase, as discussed above and as shown inFIG.14, where the results of an analysis of the drag mechanics of a bicycle facing increasing headwinds shows rapid increases in propulsive efficiency by shielding the upper wheels.

A skilled artisan will recognize from the curves shownFIG.14that as the relative external headwind increases on the vehicle, so does the increase in propulsive efficiency of the vehicle. And a skilled artisan will also recognize that the natural design constraint described above for the cycle wheel fairing ofFIG.13similarly applies to the wind deflecting fairing of the present embodiment.

This inherent design constraint implies that for a given vehicle under a given relative external headwind condition—as shown along the horizontal axis of the plots inFIG.14-awind-deflecting fairing of the present embodiment will similarly be constrained to have a limited overall wind-deflecting extent that will produce a reduction in overall vehicle drag. This limited wind-deflecting extent includes a limit on the total drag-inducing surface area extent of the wind-deflecting fairing, including a combined limit in both forward and downward extension of fairing surfaces.

And as discussed extensively above for the cycle wheel fairing ofFIG.13, the relative effects of drag forces on the fairing versus drag on the various points on the wheel are not simply related. Instead, the drag forces on various points on the wheel are magnified or de-magnified as applied against the axle, whereas the drag on either the cycle fairing or on the similar drag-inducing surfaces of the wind-deflecting fairing of the present embodiment are directly applied equivalently against the same axle.

Thus, since propulsive counterforces applied at the axle have a mechanical advantage over drag forces on the lower wheel surfaces, a simple comparison of the net drag force on either surface alone—either on the lower wheel or on the extended deflector surface—is entirely insufficient to determine the relative effect each has on vehicle propulsive efficiency. Instead, the magnitudes of the drag force from each surface must be reflected to an equivalent force applied at the same axle and compared against one another.

For the lower wheel surfaces, the net drag force as applied against the axle is diminished by leveraging about the point of ground contact, as previously discussed. For the lower deflector panel surface, the drag force is directed against the axle without magnification since it is transmitted directly through the body and frame of the vehicle. Although another axle of the vehicle may be the used as the propulsive axle, the two net drag forces must be compared against each other as reflected at the same affected axle in order to gauge their relative effects on overall vehicle drag.

For the lower deflector surface, the drag force on the surface is-like other vehicle body drag forces-directly countervailed by the propulsive counterforce applied at the driven axle. For the lower wheel surfaces, the situation is more complicated due both to the mechanical advantage that the propulsive forces have over lower wheel drag forces, and to the effects that the summation moments of drag force (FIG.15) at different points on the rotating wheel have on the net lower wheel drag force.

As noted earlier under the Description of Wheel Drag Mechanics, and as shown in the plot ofFIG.16, the average drag torque exerted against the lower wheel surfaces has far less impact on the total wheel drag as exerted upon the vehicle than does the average drag torque exerted against the upper wheel surfaces. This is due largely to the pivoting geometry of the rotating wheel, where wheel forces are levered about the same stationary point of ground contact at the bottom of the wheel. Owing in part to their longer moment arms, drag forces applied to the upper wheel produce far greater resistive torques on the wheel than do drag forces applied to the lower wheel.

Consequently, drag forces on the upper wheel surfaces are ideally shifted to the lower wheel surfaces in order to benefit the propulsive efficiency of the vehicle. As a result, deflecting headwinds from the upper wheel surfaces onto the lower wheel surfaces can substantially reduce overall vehicle drag and improve propulsive efficiency.

And in the case of industrial trucks having large wheels with larger tires, the relative effects of resistive pressure drag forces on the wheel over frictional drag forces is exacerbated over that of a spoked bicycle wheel as described above in the discussion of the wheel drag mechanics. As mentioned, the spoked wheels with thin tires and rims used on a bicycle can produce significant frictional drag effects resisting vehicle propulsion. Trucks with smooth wheels and tires are more significantly affected by pressure drag forces acting against the upper wheel forward-facing profile surfaces, than are bicycles with thin tires and rims.

Thus for trucks, deflecting upper wheel headwinds downward onto the lower wheel becomes an important operating function. Since propulsive counterforces at the axle have a mechanical advantage over lower wheel drag forces applied to the wheel below the level of the axle, deflecting headwinds downward onto the lower wheel can reduce overall vehicle drag and improve propulsive efficiency.

The natural design constraint method discussed above can also be used in combination with an accounting for the non-linear effects on vehicle drag from drag forces directed on various points on the wheel to determine the limited extent of the wind-deflecting fairing of the present embodiment that will also yield an overall reduction in vehicle drag, including the combined limit in both forward and downward extent of the fairing. And as is evident from the curves ofFIG.14, the combined limit for the overall drag-inducing extent of the wind-deflecting fairing of the present embodiment will vary with both vehicle configuration and relative external headwind condition.

From an examination of the curves ofFIG.14, it becomes evident that the worst-case limit for the overall extent of the fairing is while the vehicle is operated under null wind conditions, where the relative gains in vehicle efficiency are comparatively minimal, and as shown at the left vertical axis of the plots ofFIG.14. As the relative external headwind increases, the relative gains in vehicle efficiency quickly increase, as shown in the general trend of the efficiency curves rising toward the right side of the plots.

Therefore, a skilled artisan then will understand that the most restrictive limit for the overall extent of the fairing will be while the vehicle is operated under null external headwinds conditions. If the extent of the fairing is sufficiently limited to produce an overall reduction in vehicle drag under null operating conditions, then the thus limited fairing will also produce even more gains in vehicle efficiency under an external headwind condition.

And from the discussion above, it becomes evident that the fairing could be designed either to be more limited in forward extent and more extensive in downward extent or alternatively could be designed instead to be more extensive in forward extent and more limited in downward extent, and still produce the same measure of gains in overall vehicle propulsive efficiency.

Thus, the fairing could be designed to be somewhat limited in forward extent and to extend somewhat below the level of the axle while still yielding a reduction in overall vehicle drag, especially while the vehicle is operated under a substantial relative external headwind condition. This potential configuration for the fairing becomes quite evident both from an examination of the curves ofFIG.16, and from a consideration of how the very limited mechanical disadvantage that surfaces of the wheel located not very far below the level of the axle have over vehicle frame drag forces, such as wheel fairing or deflector drag forces.

Indeed,FIG.16shows that near the level of the axle, much less relative gains in propulsive efficiency are gained from shielding more centrally located wheel surfaces in elevation than from shielding the uppermost wheel surfaces positioned substantially above the axle near the critical elevation. AndFIG.16also shows that the relative gains in vehicle efficiency increase in rising relative external headwinds.

While the ideal configuration of the fairing includes a limit for fairing surfaces to extend downward to lower than the level of the axle, the discussion above makes clear that this is optimal limitation is not fully restrictive. Instead, a skilled artisan would recognize that a wind-deflecting fairing of the present embodiment could be designed to be somewhat limited in forward extent while also extending somewhat below the level of the axle while still yielding a reduction in overall vehicle drag, especially while the vehicle is operated under a variety of relative external headwind conditions.

Or alternatively, a wind-deflecting fairing of the present embodiment could be designed to be more extensive in forward extent, while being somewhat limited in extending to no lower than the level of the axle, while still yielding a reduction in overall vehicle drag, especially while the vehicle is operating under a variety of relative external headwind conditions. Thus, a variety of configurations for extending the surfaces of the wind-deflecting fairing of the present embodiment is included that will yield an effective reduction in overall vehicle drag.

In consideration of further embodiments described below, the operating principles described above will generally apply, and may be referred thereto.

Second Embodiment—FIGS.1and3

As shown inFIGS.1and3, an embodiment comprises an inclined aerodynamic deflector panel assembly15attached to and mounted underneath the body of a trailer16for a commercial vehicle. The inclined deflector panel assembly15is located forward of the rear wheel assembly17and located in front of trailing wheel sets18which would otherwise be exposed to headwinds when the vehicle is in forward motion. The inclined deflector panel assembly15is planar in shape, mounted inclined in a forwardly—angled orientation with the upper edge more forwardly located and the lower surface located more rearward on the vehicle. The inclined deflector panel assembly15spans the lateral width of the trailer17, and where aligned directly in front of the wheel sets18ideally extends downward to no lower than the level of the axle. The inclined deflector panel assembly15is located proximal to the trailing wheel assembly18in order to deflect headwinds onto the exposed lower wheel surfaces, and to deflect headwinds from directly impinging on the central axle assembly19, thereby reducing overall vehicle drag and improving propulsive efficiency.

Third Embodiment—FIGS.4and5

As shown inFIGS.4and5, an embodiment comprises a channeled aerodynamic wheel deflector panel assembly25attached to and mounted underneath the body of a trailer16for a commercial vehicle. The channeled wheel deflector panel assembly25is located forward of the rear wheel assembly17and located directly in front of a trailing wheel set18which would otherwise be exposed to headwinds when the vehicle is in forward motion. The channeled wheel deflector panel assembly25includes a deflector plate22which is generally planar in shape, mounted inclined in a forwardly—angled orientation with the upper edge more forwardly-located and the lower surface located more rearward on the vehicle. The channeled wheel deflector panel assembly25includes forwardly-projecting end plates24attached to either side edge of the deflector plate22, forming a channeled deflector panel assembly25to funnel headwinds directly onto the lower wheel surfaces, minimizing any outwardly deflected headwind from otherwise impinging on the trailing upper wheel surfaces.

The channeled wheel deflector panel assembly25ideally extends downward to no lower than the level of the axle19and is located proximal to the trailing wheel set18in order to deflect and funnel headwinds onto the exposed lower wheel surfaces, thereby reducing overall vehicle drag and improving propulsive efficiency.

Fourth Embodiment—FIGS.4and6

As shown inFIGS.4and6, an embodiment comprises a channeled aerodynamic deflector panel assembly30attached to and mounted underneath the body of a trailer16for a commercial vehicle. The channeled deflector panel assembly30is located forward of the rear wheel assembly17and located in front of both trailing wheel sets18which would otherwise be exposed to headwinds when the vehicle is in forward motion. The channeled deflector panel assembly30includes a deflector plate28which is generally planar in shape, mounted inclined in a forwardly—angled orientation with the upper edge more forwardly-located and the lower surface located more rearward on the vehicle. The deflector plate28spans the lateral width of the trailer16, and where directly aligned in front of the wheels ideally extends downward to no lower than the level of the axle19. The channeled deflector panel assembly30includes forwardly-projecting end plates32attached to either side edge of the deflector plate28, forming a channeled deflector panel assembly30to funnel headwinds directly onto the lower wheel surfaces and minimize any outwardly deflected headwind from otherwise impinging on the trailing upper wheel surfaces. Although not shown, between the wheel sets18, the deflector plate28may extend further downward to deflect headwinds well below the central axle assembly19.

The channeled deflector panel assembly30is located proximal to the trailing wheel set18in order to deflect headwinds onto the exposed lower wheel surfaces, and to deflect headwinds from directly impinging on the central axle assembly19, thereby reducing overall vehicle drag and improving propulsive efficiency.

Fifth Embodiment—FIGS.7and5

As shown inFIG.7in side view, and as shown inFIG.5when viewed in cross-section from the front of the vehicle, an embodiment comprises the channeled aerodynamic wheel deflector panel assembly25identical to that of the third embodiment above, together with removable upper wheel skirt panels38covering the outside of the trailing wheel sets18. The upper wheel skirt panels38also ideally extend downward to no lower than the level of the axle19.

The upper wheel skirt panels38extend from the deflector plate22rearward to cover adjacent trailing wheel sets18, thereby shielding the trailing upper wheels from external headwinds. The channeled wheel deflector panel assembly25used in combination with the upper wheel skirt panels38reduces overall vehicle drag and improves propulsive efficiency.

Sixth Embodiment—FIGS.7and6

As shown inFIG.7in side view, and as shown inFIG.6when viewed in cross-section from the front of the vehicle, an embodiment comprises the channeled aerodynamic deflector panel assembly30identical to that of the fourth embodiment above, together with removable upper wheel skirt panels38covering the outside of the trailing wheel sets18. The upper wheel skirt panels38also ideally extend downward to no lower than the level of the axle19.

The upper wheel skirt panels38extend from the deflector plate28rearward to cover adjacent trailing wheel sets18, thereby shielding the trailing upper wheels from external headwinds. The channeled deflector panel assembly30used in combination with the upper wheel skirt panels38reduces overall vehicle drag and improves propulsive efficiency.

Seventh Embodiment—FIGS.8and2

As shown inFIG.8in side view, and as shown inFIG.2when viewed in cross-section from the front of the vehicle, an embodiment comprises an aerodynamic wheel deflector panel45is attached to and mounted underneath the body of a trailer16for a commercial vehicle. The wheel deflector panel45is located forward of the rear wheel assembly17and located in front of a trailing wheel set18, which would otherwise be exposed to headwinds when the vehicle is in forward motion. The wheel deflector panel45is planar in shape, sufficiently wide to deflect headwinds from directly impinging on the upper wheels of the trailing wheel set, mounted vertically and shown oriented parallel to the axle19. The wheel deflector panel45ideally extends downward no lower than the level of the axle19, and is located proximal to the trailing wheel set18in order to deflect headwinds substantially toward either the outside or the inside of the wheel set18, or onto the lower wheel surfaces—thereby reducing overall vehicle drag and improving propulsive efficiency.

This simple wheel deflector panel configuration is appropriate for use when limited clearance space exists in front of the trailing wheel set.

Eighth Embodiment—FIGS.8and3

As shown inFIG.8in side view, and as shown inFIG.3when viewed in cross-section from the front of the vehicle, an embodiment comprises an aerodynamic deflector panel50is attached to and mounted underneath the body of a trailer16for a commercial vehicle. The deflector panel50is located forward of the rear wheel assembly17and located in front of a trailing wheel sets18which would otherwise be exposed to headwinds when the vehicle is in forward motion. The deflector panel50is planar in shape, spans the lateral width of the trailer16, and where aligned directly in front of the wheel sets18ideally extends downward to no lower than the level of the axle19. The deflector panel50is mounted vertically and parallel to the axle19. The deflector panel50is located proximal to the trailing wheel sets18in order to deflect headwinds substantially toward either the outside of the trailing upper wheels, under the central axle assembly, or onto the lower wheel surfaces—thereby reducing overall vehicle drag and improving propulsive efficiency.

This simple deflector panel configuration is appropriate for use when limited clearance space exists in front of the trailing wheel assembly.

Ninth Embodiment—FIGS.9and2

As shown inFIG.9in side view, and similar to as shown inFIG.2when viewed in cross-section from the front of the vehicle, an embodiment comprises the aerodynamic wheel deflector panel45identical to that of the seventh embodiment above, together with removable upper wheel skirt panels42covering the outside of the trailing wheel sets18. The upper wheel skirt panels42also ideally extend downward to no lower than the level of the axle19.

The upper wheel skirt panels42extend from the deflector panel45rearward to cover adjacent trailing wheel sets18, thereby shielding the trailing upper wheels from external headwinds. The wheel deflector panel45used in combination with the upper wheel skirt panels42reduces overall vehicle drag and improves propulsive efficiency.

This simple wheel deflector panel configuration is appropriate for use when limited clearance space exists in front of the wheel sets and where the use of exterior wheel skirts panels is permitted.

Tenth Embodiment—FIGS.9and3

As shown inFIG.9in side view, and similar to as shown inFIG.3when viewed in cross-section from the front of the vehicle, an embodiment comprises the aerodynamic wheel deflector panel50identical to that of the eighth embodiment above, together with removable upper wheel skirt panels42as used in the ninth embodiment above. The deflector panel50used in combination with the upper wheel skirt panels42reduces overall vehicle drag and improves propulsive efficiency.

This simple wheel deflector panel configuration is appropriate for use when limited clearance space exists in front of the wheel sets, where deflecting headwinds from directly impinging on the central axle assembly19is needed, and where the use of exterior wheel skirts panels is permitted.

Eleventh Embodiment—FIGS.10and11

As shown inFIGS.10and11, an embodiment comprises an aerodynamic vehicle skirt assembly60is attached to and mounted underneath the body of a trailer16for a commercial vehicle. The vehicle skirt assembly60is located forward of the rear wheel assembly17which would otherwise be exposed to headwinds when the vehicle is in forward motion. The vehicle skirt assembly60ideally extends downward to no lower than the level of the axle19of the trailing wheel set18, leaving lower wheel surfaces of the trailing wheel set18exposed to headwinds.

The vehicle skirt assembly60is shown mounted to the trailer16with the forwardmost end of the vehicle skirt assembly60inset toward the centerline of the trailer16to a position in general longitudinal alignment with the inside of—and thereby substantially in front of—the innermost surface of the trailing wheel set18. Extending rearward, the vehicle skirt assembly60progressively varies in position toward the outside of the body of the trailer16, extending more rapidly toward the outside wheel when nearest the rear end, which is located proximate to the trailing wheel set18. The rear end of the vehicle skirt assembly60is located near the outer side of the wheel set18, thereby deflecting headwinds substantially toward the outside of the upper wheel surfaces and below onto the lower wheel surfaces.

The vehicle skirt assembly60may be constructed from either a single panel or from multiple panels arranged end-to-end. The vehicle skirt assembly60may be constructed with resilient materials, especially along the lower edge that may occasionally contact road obstacles. The vehicle skirt assembly60may also be mounted to the trailer16by deflectable resilient means, returning the vehicle skirt assembly60to the proper aerodynamic position after contacting road obstacles.

Twelfth Embodiment-FIG.12

As shown inFIG.12, an embodiment comprises the aerodynamic vehicle skirt assembly60identical to that of the eleventh embodiment above, together with removable upper wheel skirt panels42covering the outside of the trailing wheel sets18as used in the tenth embodiment above.

The upper wheel skirt panels42extend from the aerodynamic vehicle skirt assembly60rearward to cover adjacent trailing wheel sets18, thereby ideally shielding the trailing upper wheel surfaces from external headwinds. The aerodynamic vehicle skirt assembly60used in combination with the upper wheel skirt panels42reduces overall vehicle drag and improves propulsive efficiency.

Advantages:

From the description above, a number of advantages of some embodiments become evident:(a) An improved aerodynamic wheel set deflector panel located in front of trailing wheels and ideally extending downward to no lower than the axle to thereby deflect headwinds onto mechanically disadvantaged lower wheel surfaces and to shield trailing mechanically-advantaged upper wheel surfaces from headwinds, thereby reduces overall vehicle drag improving propulsive efficiency.(b) An improved aerodynamic wheel assembly deflector panel which may deflect headwinds below the central axle assembly, and where in front of trailing wheels ideally extending downward to no lower than the axle to thereby deflect headwinds onto mechanically disadvantaged lower wheel surfaces and to shield trailing mechanically-advantaged upper wheel surfaces from headwinds, thereby reduces overall vehicle drag improving propulsive efficiency.(c) An improved aerodynamic deflector and skirt assembly where in front of trailing wheels ideally extending downward to no lower than the axle to thereby deflect headwinds onto mechanically disadvantaged lower wheel surfaces and to shield trailing mechanically-advantaged upper wheel surfaces from headwinds, thereby reduces overall vehicle drag improving propulsive efficiency.(d) An improved aerodynamic vehicle skirt panel assembly ideally extending downward to no lower than the axle to thereby deflect headwinds onto mechanically disadvantaged lower wheel surfaces and to shield trailing mechanically-advantaged upper wheel surfaces from headwinds, reduces total weight of the skirt assembly, improves the skirt ground clearance of road obstacles, and reduces overall vehicle drag improving propulsive efficiency.
Conclusions, Ramifications, and Scope:

Exposed wheels can generate considerable drag forces on a moving vehicle. These forces are directed principally near the top of the wheel, rather than being more evenly distributed across the entire profile of the wheel. Furthermore, these upper-wheel drag forces are levered against the axle, thereby magnifying the counterforce required to propel the vehicle. As a result, a reduction in drag upon the upper wheel generally enhances propulsive efficiency significantly more than a corresponding drag reduction on other parts of the vehicle.

With the net drag forces being offset and directed near the top of the wheel, nearly equivalent countervailing reaction forces—also opposing vehicle motion—are necessarily transmitted to the wheel at the ground. These reaction forces necessitate augmented down-forces to be applied in higher speed vehicles, in order to maintain static frictional ground contact and, thereby, vehicle traction and directional stability. As wings and other means typically used to augment these down-forces in such vehicles can add significant drag, it becomes evident that substantial effort should be made to reduce the upper wheel drag forces on most high-speed vehicles.

Moreover, since the lower wheel drag forces suffer a mechanical disadvantage over propulsive counterforces, using shielding devices to deflect headwinds from impinging on lower wheel surfaces can increase overall vehicle drag. Given these considerations, it becomes evident that drag-reducing vehicle deflectors and skirts should be ideally limited to lengths that inhibit vehicle headwinds from directly impinging on only the upper wheel surfaces, leaving the lower wheel surfaces exposed.

While the embodiments shown illustrate application generally to the trailers of industrial trucks, the embodiments could be similarly applied to other trucks and vehicle types having wheel assemblies exposed to headwinds. And while the embodiments shown include skirt assemblies formed from relatively inexpensive flat panels, somewhat curved panels could also be used. Further examples of alternative embodiments include having deflector panels mounted at various angles, all ideally limited in height to extend downward to no lower than the level of the axle. Although not shown, in the case where additional space exists in front of the wheel assembly, the wheel deflector panel of the ninth embodiment could instead be mounted in nonparallel to the axle in order to deflect winds not only downward, but also to either side of the trailing wheel assembly.

In addition, the embodiments generally can include various methods of resilient mounting to the vehicle body permitting the panels to deflect when impacted by road obstructions and return undamaged to their normal aerodynamic position.

Accordingly, the embodiments should not be limited to the specific examples illustrated and described above, but rather to the appended claims and their legal equivalents.