Abstract:
An apparatus and method of articulating a vehicle is disclosed using a rotatable shackle connected to the frame and the suspension system of the vehicle. As one side of an axle is moved to a different level from the other side, the shackle rotates, allowing the vehicle to articulate and assisting the spring eye of a leaf spring suspension system to remain substantially in its resting position. Pivoting connections may be provided where the rotatable shackle is connected to the frame, where the rotatable shackle is connected to the suspension system, and within the rotatable shackle itself. The rotatable shackle is self supporting and may include a bushing to receive a portion of the rotatable shackle.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention generally relates to structures and methods for increasing articulation in a vehicle, and more particularly, to hinged shackles for connecting leaf spring suspension assemblies to the frame of an off road vehicle.  
         BACKGROUND  
         [0002]    Vehicles designed, built and marketed for off road use are increasingly being driven in more severe off road applications, while also being driven on paved highways and streets. One type of more severe off road driving is “rock crawling,” which is commonly referred to as slowly driving a four wheel drive vehicle over, through or between natural or even man made obstacles of a wide variety of shapes, angles, heights, widths, depths, compositions, etc. Such natural obstacles may include rocks, gulleys, ravines, stream beds, inclines or drops, among other things. Rock crawling refers not only to traversing the typically uneven rock surfaces, but also a variety of natural and man made surface material, including gravel, sand, dirt, concrete or metal barriers, and vegetation including exposed roots and tree stumps.  
           [0003]    Rock crawling, and other types of off road use, can place severe demands on the suspension system of the vehicle. To maximize traction and control, it is generally advantageous to maintain each tire in full contact with the surface being driven, or at least as many tires and as much of each tire as possible. Similarly, it is also generally advantageous to keep the weight of the vehicle evenly distributed over each of the tires, or at least as much as possible. Because each axle of most non-military off road vehicles extend to at least one wheel on each side, driving on an uneven surface often means one wheel is significantly lower than the other, resulting in one or more tires losing maximum contact, or even being lifted off the surface. This is an even greater issue when the front and rear axles are at different levels or even at different angles. The relative ability of a vehicle to keep the tires on the ground during such maneuvering is commonly referred to as the articulation of the vehicle.  
           [0004]    Off road vehicles commonly employ either a leaf spring or a coil spring suspension system to suspend the vehicle over the axles. Generally, in a leaf spring suspension system, a series of elongated bands of metal, or leaves, of varying lengths are stacked and banded together. One end of the assembly is bolted or otherwise fixed to the bottom of the vehicle, typically towards the center of the vehicle and away from the axle to be suspended. In a stock configuration, the leaves are commonly positioned under the axle, with a shallow U-shaped arc extending towards the outside of the vehicle. The end of the leaves near the outside of the vehicle typically terminates with a spring eye that allows a connection to a movable bar or shackle or other device that in turn is connected to the vehicle. One such leaf spring assembly is installed near each wheel. When at rest or under compression, the conventional leaf spring assembly typically presses the shackle up against the vehicle frame.  
           [0005]    During compression of the leaf spring, this type of suspension allows the leaf spring to flatten and move toward the direction of the shackle. When the leaf spring is required to droop, or stretch as far as possible, it is restricted by the flex of the leaf spring itself For this type of primarily vertical suspension, the bolted inner end of the leaf spring and the plates that make up the shackle limit the amount the leaf spring assembly can move.  
           [0006]    The conventional leaf spring assembly is limited in articulation, e.g., when one side of the axle compresses and the other side does not compress as much, does not compress at all, or is required to droop. The axle is no longer level and the vehicle tilts. Because the leaf spring at the inner end is bolted and at the outer end has only limited vertical and forward movement, but no lateral movement, the leaves themselves must twist or flex to try to accommodate the changing lateral angle between the axle and the vehicle. Reliance on the leaf spring twisting not only limits articulation, but also can cause metal fatigue in the leaf spring assembly and result in premature failure.  
           [0007]    To increase articulation, several modifications to leaf spring assemblies have been attempted, generally by allowing the leaf spring to more readily drop away from the frame. For example, in one configuration, the inner end of the leaf spring remains bolted to the vehicle frame and the spring eye remains connected to a shackle. However, the arm of the shackle is lengthened, which provides more droop. Although this configuration provides enhanced vertical suspension, it still relies on the leaf springs to twist to provide articulation. Also, lengthening the arm of the shackle generally reduces the lateral stability of the vehicle, particularly at higher speeds.  
           [0008]    In another design, known as a folded hinged shackle, the shackle has a first arm with one end connected to the vehicle and the other end pivotally connected to a second arm, that in turn is connected to the spring eye of the leaf spring. When at rest or under compression, the folded hinged shackle is pressed up against the vehicle and the leaf springs primarily provide for compression. When the leaf spring is required to droop, however, the folded hinged shackle opens, providing increased droop. Again, articulation is limited by the amount of twisting of the leaf springs.  
           [0009]    Another attempt to increase articulation is commonly referred to as a “buggy spring” suspension. Again, the end of the leaf spring towards the center of the vehicle is bolted to the vehicle frame. The outer shackle is replaced essentially with a second, shorter leaf spring assembly. The end of the shorter leaf spring assembly towards the center of the vehicle is bolted to the vehicle between the spring eye of the main leaf spring and the axle. The end of the shorter leaf spring assembly near the outside of the vehicle is connected to the spring eye of the main leaf spring by a conventional shackle design. This buggy spring assembly provides another level of vertical suspension and may provide more droop. It also increases articulation, as both the main and the shorter leaf springs will twist somewhat. However, articulation is still limited by the amount of twisting of the leaf springs. As with lengthening the shackle arm, replacing the shackle with a second leaf spring assembly generally reduces the lateral stability of the vehicle, particularly at higher speeds.  
           [0010]    A more complicated assembly to try to increase articulation, known as a “four link” suspension, is commonly installed to greatly increase droop of the rear axle. This assembly again has the inner end of the leaf spring bolted to the vehicle, but is inverted, i.e., the leaf spring forms a concave shape opening downward. The outer end of the leaf spring extends only just past the axle and is not fixed to another component. Rather, it merely rests on top of the axle. To protect the vehicle from the slapping of the leaf springs, a small bumper is commonly inserted on the vehicle frame between the two ends of the leaf spring. The relative vertical drop is controlled by a four arm link system, with two arms for each side of the axle. One arm is pivotally connected at the outer end of the vehicle and extends to rest under the axle. A shorter arm is pivotally connected toward the inside of the longer arm and extends to suspend above the axle. The inverted leaf springs provide compression and the arms can be set to provide little or no pressure, resulting in very large amounts of droop if both sides of the axle are required to droop. This four link assembly is commonly used in faster off road races with big, fast jumps requiring large droop of both rear wheels. The rear axle essentially is momentarily free hanging, supporting little or no weight of the vehicle. In part because one end of the leaf spring is unattached, articulation is increased, although it is still limited by the amount of twist of the leaf springs. Again, the four link system reduces the lateral stability of the vehicle, particularly at the higher speeds on the road.  
           [0011]    A more simple approach to increase articulation is to simply move the leaf springs of a conventional leaf spring assembly from under the axle to over the axle. This is commonly referred to as a “spring over” suspension or a “lift,” as it literally lifts the body of the vehicle several inches relative to the axle. Because the leaf springs are above the axle, they are able to flatten more during compression and may twist more to increase articulation. However, the amount of articulation is still limited by the amount of twist of the leaf springs. Also, the increased ability of the leaf spring to twist and the raised center of gravity reduces the lateral stability of the vehicle.  
           [0012]    Another more complicated approach, known as a “¾ elliptical” suspension, uses the spring over suspension, leaving the leaf springs unattached to the axle. Instead, a long arm is pivotally connected at the outer end of the vehicle and extends to rest under the axle. A shorter arm connected to the longer arm extends to suspend above the axle. As with the four link system, the leaf springs provide compression and the arms can be adjusted to provide little or no pressure, resulting in very large amounts of droop if both sides of the axle are required to droop. Articulation is increased, but still is limited by the twist or flex of the leaf springs.  
           [0013]    Many other attempts have been made to increase the articulation of off road vehicles, particularly leaf spring assemblies of four wheel drive vehicles and all terrain vehicles. Nonetheless, a need exists for a new or modified leaf spring assembly and method to increase articulation, while decreasing the lateral twisting forces on the leaf springs. A further need exists to provide such an assembly and method that is sufficiently stable to allow the vehicle to be driven both off road and on road.  
         SUMMARY  
         [0014]    The present invention is directed to a structure and method for increasing articulation of a vehicle. In one embodiment of the invention, a shackle comprises a first section having a proximal end and a distal end for connection to a vehicle, a second section having a proximal end connected to the proximal end of the first section and a distal end, a third section having a proximal end rotatably connected to the distal end of the second section and a distal end for connection to a suspension assembly of the vehicle.  
           [0015]    A further embodiment of the invention is directed to a shackle for suspension assemblies in vehicles comprising a first section having a first leg, a second leg and a piece connecting the first and second legs. The first and second legs each comprise a distal end for connection to the frame of a vehicle and a proximal end that is rotatably connected to the proximal end of a second section. The second section further comprises a cylindrical distal end that is rotatably connected to the cylindrical proximal end of a third section. The third section also comprises a distal end for connection to the suspension assembly of the vehicle.  
           [0016]    Yet another embodiment of the invention comprises a method for articulating a vehicle comprising rotating at least part of the suspension in a direction substantially parallel to the axle of the vehicle.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a side view of a rotating shackle in a closed position.  
         [0018]    [0018]FIG. 2 is a perspective view of the rotating shackle shown in FIG. 1.  
         [0019]    [0019]FIG. 3 is a front plan view of a bushing for the rotating shackle shown in FIG. 1.  
         [0020]    [0020]FIG. 4 is a side plan view of the bushing shown in FIG. 3.  
         [0021]    [0021]FIG. 5 is a perspective view of the rotating shackle shown in FIG. 1 showing rotation of the shackle while in a closed position.  
         [0022]    [0022]FIG. 6 is a perspective view of the rotating shackle shown in FIG. 1 showing rotation of the shackle while in an open position.  
         [0023]    [0023]FIG. 7 is a perspective view of the rotating shackle shown in FIG. 1 showing rotation of the shackle while in an open position.  
         [0024]    [0024]FIG. 8 is a side view of the rotating shackle shown in FIG. 1 in a closed position and connected to a vehicle and to a leaf spring suspension assembly.  
         [0025]    [0025]FIG. 9 is a side view of the rotating shackle shown in FIG. 1 in an open position and connected to a vehicle and to a leaf spring suspension assembly.  
         [0026]    [0026]FIG. 10 is a back view of a vehicle having rotating shackles, in closed, non-rotating positions, connected to its frame and to its leaf spring suspension assemblies.  
         [0027]    [0027]FIG. 11 is a back view of a vehicle having rotating shackles, one in an open, rotating position and the other in a closed, rotating position, connected to its frame and to its leaf spring suspension assemblies.  
         [0028]    [0028]FIG. 12 is perspective view of an alternative embodiment of a rotating shackle in a partially open position to show a bushing. 
     
    
     DETAILED DESCRIPTION  
       [0029]    One embodiment of the present invention is shown in FIGS.  1 - 5 . A rotating shackle  10  comprises a first section  11 , a second section  30  and a third section  40 , each of which have a distal end and a proximal end, and a bushing  60 . Generally, the first section  11  has a distal end for connection to the frame of a vehicle and a proximal end for connection to the proximal end of the second section  30 . Both of these preferably are pivoting connections, as set forth in more detail below. The third section  40  has a proximal end rotatably connected to the distal end of the second section  30  and a distal end for connection, preferably a pivoting connection, to a suspension assembly of the vehicle. The size, shape, dimensions, materials, number and configuration of the sections and other variations and details of the shackle  10  depend on, among other things, the configuration of the suspension system and vehicle on which it is to be used, as would be recognized by one of ordinary skill in the art.  
         [0030]    The embodiment shown in FIGS.  1 - 5  is specifically designed for use with Jeep YJ and CJ models manufactured from about 1976 to about 1996. Similar or alternative embodiments will work for vehicles from many other manufacturers, including Toyota, Isuzu, Suzuki and International Harvester. For example, FIG. 12 shows an alternative embodiment of the invention for installation on a Jeep XJ model manufactured since about 1984. Similar or alternative embodiments also will work for other types of vehicles, such as all terrain vehicles.  
         [0031]    As shown in FIGS.  1 - 5 , the first section  11  preferably comprises a first leg  12  having a hole  20  at a distal end and a hole  16  at a proximal end, a second leg  14  having a hole  22  at a distal end and a hole (not shown) at a proximal end, and a plate  24  connecting the first leg  12  and the second  14 . The second section  30  comprises a base  32 , a neck  34  and preferably an over extension stop  36 . The third section  40  comprises a neck  42  and a U-shaped member  44 , which further comprises a base  46 , a bolt  47 , a first flange  48  having a hole  52 , a second flange  50  having a hole  54 , and a port  56 .  
         [0032]    The first section  11  comprises holes  20 ,  22  to allow the shackle  10  to be connected to the vehicle, preferably by fastening a bolt through each of holes  20 ,  22  and through the stock holes on the bottom side of the vehicle located approximately above the spring eye of the leaf spring assembly. Alternatively, first section may be connected with other types of connector known in the art. Most preferably, the first section  11  is allowed to pivot about this connection with the vehicle.  
         [0033]    The first leg  12  and the second leg  14  are preferably fabricated from {fraction (5/16)} inch mild steel and are preferably approximately the same dimensions. For example, the preferred length of both legs  12  and  14  is about 4 inches to about 5¼ inches from the center of hole  16  to the center of hole  20 , depending on the vehicle. For the Jeep CJ, the legs  12  and  14  will be about 4 inches in this dimension. The plate  24  is preferably mild steel approximately ½ inch deep by 1 inch wide and welded to the first leg  12  and to the second leg  14  about 1 inch below the center of hole  16  and the corresponding hole (not shown) of the second leg  14 . The length of plate  24 , and therefore the distance between the first leg  12  and the second leg  14 , must be sufficient to accommodate the width of the leaf springs. Typically, the leaf springs installed on recreational off road vehicles vary from about 2 inches to about 2½ inches in width and the plate  24  preferably is about ½ inch longer than the width of the leaf springs. In Jeep YJ, the leaf springs are about 2½ inches wide and the preferred length of the plate  24  is about 3 inches.  
         [0034]    If present, first section  11  may take any number of alternative configurations, including a solid single piece, that provide a connection, preferably pivoting, to the rotating portion of the shackle  10  and another connection, preferably pivoting, to the frame of the vehicle. Variations of materials, including other metals, alloys, composites and polymers, as well as variations of dimensions and configurations, would be recognized by one of ordinary skill in the art.  
         [0035]    The second section  30  comprises a base  32  to connect the second section  30  to the first section  11 . Although this connection may fixed, preferably it is pivoting. Preferably, the base  32  spans substantially the entire distance between the first leg  12  and the second leg  14  and comprises an opening to insert a pin  58 , bolt or other fastener through the first leg  12 , the base  32  and the second leg  14  to provide a pivotal connection.  
         [0036]    The second section  30  also preferably comprises a neck  34  extending from the base  32 . Most preferably, second section  30  is generally T-shaped, with base  32  and neck  34  being welded together. Preferably, base  32  is a hollow cylinder formed of drive line or D.O.M. tubing, with a 1 inch inside diameter and a 1¼ inch outside diameter, and neck  34  has a  1  inch outside diameter and a ½ inch threaded hole approximately 2⅛ inch deep. Variations of materials, including other metals, alloys, composites and polymers, as well as variations of dimensions and configurations, would be recognized by one of ordinary skill in the art.  
         [0037]    The third section  40  comprises a generally cylindrical neck  42  fixed, preferably by welding, to a U-shaped member  44 . The neck  42  of the third section  40  has at least a slightly larger inside diameter than the outside diameter of the neck  34  of the second section  30 , preferably about 0.003 inch to about 0.005 inch larger. Most preferably, the neck  42  of the third section  40  is fabricated of drive line or D.O.M. tubing having a 1 inch inside diameter and a 1{fraction (5/16)} inch outside diameter. Port  56  may be added to introduce grease or other lubricants to the interior surface of neck  42 . Variations of materials, including other metals, alloys, composites and polymers, as well as variations of dimensions and configurations, would be recognized by one of ordinary skill in the art.  
         [0038]    Referring particularly now to FIG. 5, the neck  34  of the second section  30  is generally cylindrical and is fitted for at least partial insertion into the generally cylindrical neck  42  of the third section  40 . Bolt  47  preferably rotatably connects the U-shaped member  44  of the third section  40  to a threaded hole in the neck  34  of the second section  30 . Most preferably, bolt  47  is about {fraction ( 1 / 2 )} inch by 1½ inch long. The connection allows the third section  40  to rotate relative to the second section  30 .  
         [0039]    The U-shaped member  44  comprises a first flange  48  having hole  52  and a second flange  50  having hole  54  for connecting the shackle  10  to the spring eye of the suspension system. Preferably, a bolt or pin or similar fastener is used to allow the third section  40  to pivot about this connection. The holes  52  and  54  preferably are sized and located for connection at or near the stock, or standard manufactured, location of the leaf spring assembly. The U-shaped member  44  may have an alternative size, shape or configuration, even one that is not U-shaped, depending on the suspension system that is to be connected, preferably by a pivoting connection, to the shackle  10 .  
         [0040]    The distance between the first flange  48  and the second flange  50  should be sufficient to accommodate the width of the leaf spring, and preferably is about the same distance as that between the first leg  12  and the second leg  14  of the first section  11 . The U-shaped member  44  is preferably fabricated by bending a single piece of mild steel about ¼ inch deep and about 1¾ inch wide to form the base  46 , the first flange  48  and the second flange  50 .  
         [0041]    As shown in FIGS.  1 - 5 , shackle  10  further comprises a bushing  60 , sized to fit between the first leg  12  and the second leg  14 , as well as between the plate  24  and the neck  34  of the second section  30  when the shackle  10  is in the closed position. To accommodate the shape of the neck  34  and thereby support the second section  30  when the shackle  10  is in a closed position, the bushing  60  preferably has a semi-circular cutout having about a 1 inch diameter. The bushing  60  is fixed in place by bolts  62  and  64 , which extend through the bushing  60  and into the plate  24 . Most preferably, bushing  60  comprises a Delrin block having a ¼ inch hole, with a ⅜ inch countersink, for bolts  62  and  64 , and also a slight taper of about 25 degrees from the side view, on which the neck  34  may rest. The bushing  60  may be fabricated from a variety of materials, and preferably is fabricated of resilient and durable polymers such as nylon, teflon, urethane, or Delrin. Most preferably, bushing  60  is constructed of Delrin, a polymer mix of nylon and teflon manufactured by U.S. Plastic of Lima, Ohio.  
         [0042]    Now referring to FIG. 8, a revolving shackle  10  is shown installed on a vehicle. The first section  11  is attached to frame  80 , preferably by bolt  82  and washer  84 . The third section  40  is attached to spring eye  88  of the leaf spring assembly  86 , preferably by bolt  90  and washer  92 . When the vehicle is at rest, the shackle is in a “closed position,” as shown in FIG. 8. The first section  11  typically will extend back toward the axle. The second section  30  and the third section  40  typically will extend away from the axle, forming an acute angle with the first section  11 . The weight of the vehicle presses the first section  11 , particularly the plate  24 , and the bushing  60  onto the neck  34  of the second section  30 . In this way, the shackle  10  is self-supporting, i.e., the shackle  10  contacts the frame of the vehicle only where it connects with the first section  11  and contacts the suspension system only where it connects with the third section  40 .  
         [0043]    The shackle  10  could be installed such that there is little or no pivoting movement at any of the connections 1) between the first section  11  and the frame  80 , 2) between the first section  11  and the second section  30  and 3) between the third section  40  and the spring eye  88 . If the leaf spring  86  were required to droop or compress in a vertical direction only, the leaf springs would be forced to provide the extension for the droop and the upward/forward movement for the compression.  
         [0044]    However, in actual operation, there is typically a significant lateral component to such droop and compression, and particularly so in rock crawling, when one side of the axle compresses, and the other side does not compress as much, does not compress at all, or is required to droop. Then the third section  40  of the shackle  10  rotates relative to the second section  30 , which allows the spring eye  88  of the leaf spring assembly  86  to remain essentially in its resting position, approximately parallel to the axle. From full compression, even with a negative arch, to fully extended droop, the rotating shackle  10  allows the spring eye  88  to remain essentially in its resting position.  
         [0045]    Rotating the third section  40  of the shackle  10  results in significantly greater articulation, as articulation is no longer limited by the twist or flex of the spring leaves. Instead, the rotating shackle  10  provides the articulation, minimizing the twist or flex of the leaf spring assembly  86  and leaving the leaf spring assembly  86  to provide the vertical movement of the suspension. By maintaining the resting position of the spring eye  88 , rotating the shackle  10  also reduces metal fatigue, and thereby increases the life, of the leaf spring assembly  86 .  
         [0046]    Preferably, the shackle  10  comprises a pivotal connection between the first section  11  and the second section  30 , and most preferably also comprises pivotal connections between the first section  11  and the frame  80 , as well as between the third section  40  and the spring eye  88 . As shown in FIG. 9, when the leaf spring assembly  86  is required to droop, the shackle  10  then is allowed to “open.” Rotating the shackle  10  on both the compression and droop sides of the axle, coupled with opening the shackle  10 , greatly increases articulation of the vehicle.  
         [0047]    Because the rotating shackle  10  is self-supporting, the leaf spring assembly  86  is able to start compression earlier, resulting in a softer action and a more comfortable ride. For example, as can be seen from FIG. 8, on initial compression of the suspension, the shackle  10  can close slightly, compressing the bushing  60  and allowing the leaf spring  86  to start to move before the leaf spring  86  starts to straighten out. This results in a quicker spring action and a better ride.  
         [0048]    Referring now to FIGS.  10 , shackles  10 A,  10 B are installed on the frame  80  of vehicle  100  and to spring eyes  88 A,  88 B of leaf spring assemblies  86 A,  86 B, respectively. Vehicle  100  is at rest on level ground, with no compression, other than the weight of the vehicle, and no droop on either side of axle  94 . Base  32  of the second section  30  is essentially parallel to spring eye  88 , as well as to the leaves of the leaf spring assembly  86  and the axle  94 . That is, there is little or no twist or flex of the leaf spring assembly  86  in this position, which is the “resting” position of spring eye  88 .  
         [0049]    Vehicle  100  is then subjected to being driven onto an uneven surface, as shown in FIG. 11. Leaf spring assembly  86 B compresses to accommodate the higher terrain and shackle  10 B rotates, maintaining the spring eye  88 B essentially in its resting position. This minimizes the pressure on, and therefore the twist or flex of, the leaves of the leaf spring assembly  86 B.  
         [0050]    At the same time, the lower terrain on the other side of the axle  94  requires that the axle  94  droop from the vehicle frame  80 . Shackle  10 A rotates and opens, allowing the axle  94  to droop. If additional droop is required, the leaf spring assembly  86 A extends the droop further. Again, the rotation of the shackle  10 A allows the spring eye  88 A to remain essentially in its resting position, which minimizes the twist or flex on the leaf spring assembly  86 A. In contrast, in a conventional leaf spring assembly, the droop side leaf spring will rotate laterally with the axle, thereby limiting the amount of articulation by the twist or flex of the leaf springs.  
         [0051]    The rotation of the compression side shackle  10 B is an important element in the ability of the droop side shackle  10 A to fully open and to fully droop. On the compression side of the vehicle  100  during articulation, the compression side shackle  10 B rotates and allows the compression side leaf spring  86 B to stay essentially parallel to the axle  94 , which will bring the compression side wheel into its wheel well. In turn, this allows the suspension system to increase the angle between the vehicle frame  80  and the axle  94 , allowing the vehicle to droop further on the droop side.  
         [0052]    The rotating shackle  10  has improved lateral stability, particularly for higher speed and on road use, over other designs to increase articulation. During such driving conditions, the shackle  10  is in a closed position, with the vehicle weight supported by the shackle  10 , including the bushing  60 . The primary lateral movement of the suspension system is in the bushings of the frame  80  and spring eye  88 .  
         [0053]    The rotating shackle of the present invention may take other forms in addition to those described herein. For example, the first section  11  may be essentially omitted or combined with second section  30  or third section  40 , as long as at least a portion of the shackle, or other structural piece, rotates to assist the spring eye  88  in remaining substantially in a resting position or substantially parallel to the rest of the leaf spring and the axle. The size, shape, dimensions, materials, number and configuration of the sections and other variations and details of the shackle  10  depend on, among other things, the configuration of the suspension system and vehicle on which it is to be used, as would be recognized by one of ordinary skill in the art.  
         [0054]    The foregoing description of the present invention has been presented for purposes of illustration and description. The description is not intended to limit the invention to the forms disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and the skill or knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain the best mode known for practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims be construed to include embodiments to the extent permitted by the prior art.