Abstract:
An actuation mechanism for a tarping system includes a double coil spring mountable on a pivot shaft of the mechanism. A bushing is mounted on the pivot shaft and within the double coil spring. The bushing includes an eccentric external periphery that limits the deflection of the spring, particularly at the transition points between the center portion and each of the coil portions of the spring. As the spring winds or coils, the coil portions progressively contact the eccentric periphery of the bushing to not only limit further movement of the coil portions, but also to provide support for those portions under load.

Description:
REFERENCE TO RELATED APPLICATION 
     The present application claims priority to co-pending provisional application No. 61/088,368, filed on Aug. 13, 2008. 
    
    
     BACKGROUND 
     The present invention relates to covers or tarping systems for open-topped containers, and more specifically to an actuation mechanism for pivoting the cover over a truck bed. 
     Some hauling vehicles, such as dump trucks, include open-topped containers used for hauling or storing various materials. For example, in a typical dump truck application, the dump body is used to haul a variety of particulate material, such as gravel, aggregate or similar products. In addition, some hauling vehicles carry organic materials, such as grain or produce. 
     Depending upon the nature of the materials stored in the open-topped container, it is often desirable to provide a cover for the container. Of course, rigid covers are well known that may be hinged from one end of the container body. These rigid covers have gradually given way in the industry to flexible tarping systems because the flexible tarpaulin can be easily stowed when a cover is not necessary, such as when the dump bed is being loaded. Moreover, the flexible tarp is much easier to deploy than a rigid cover. 
     One tarping system for use with dump trucks is the EASY COVER® Tarping System, of Aero Industries, Inc. The EASY COVER® Tarping System includes a U-shaped bail member that is pivotally mounted at its ends to the base of the container body. The horizontal section of the U-shaped bail is attached to the tarp, while the free ends of the vertical elements are pivotally mounted. 
     As shown in  FIG. 1 , a vehicle  10  having an open-topped dump body  11 , such as a dump truck, includes a tarpaulin cover  12 , which is shown in its deployed configuration spanning the length of the container. The tarp cover  12  is wound onto a tarp roller  14  at the forward end of the bed. 
     A U-shaped bail member  16  is connected to one end of the tarp cover  12  and is pivotally mounted to the truck body  11  by way of an actuation mechanism  20 . This actuation mechanism can take a variety of forms including extension springs, compression spring, and coil torsion springs which apply a torque or moment to arms  17  of the U-shaped bail member  16 . When the actuation mechanism is released, it automatically pivots the bar, thereby unfurling the tarp from the tarp roller  14 . A hand crank or powered motor can be provided to rotate the tarp roller in the opposite direction to wind the tarp onto the roller when it is desired to open the container top. The hand crank or motor mechanism must be capable of providing sufficient mechanical advantage to overcome the deployment force of the actuation mechanism. 
     One such actuation mechanism implemented in the Easy Cover® Tarping System incorporates a “double-coil” spring as more fully described in U.S. Pat. No. 6,318,790 to Henning, the disclosure of which is incorporated herein by reference. As shown in  FIG. 2 , this actuation mechanism  20  includes an elastically deformable double-coil spring  21  with two coil portions  23  and  24  concentrically wound around each other and disposed in a common plane with an integral center anchor section  28  between each of the coil portions  23  and  24 . Each of the coil portions include a free reaction end connected to arm  17  of the bail member  16  through a pair of reaction posts  26  and  27  mounted on the arm. The center anchor section  28  is held fixed relative to the pivoting bail arm  17  and is generally fixed to the dump body  11  by a pivot shaft  18  mounted thereto. The double-coil spring  21  is arranged to apply a torsional force to the bail arm  17  to deploy the tarp cover  16 , as described above. 
     As shown in  FIG. 3 , the mechanism  20  includes a housing  32  that sandwiches the double coil spring  21  between opposed housing halves. After the spring is fitted into the housing halves, the reaction posts  26  and  27  extend through openings in the housing halves. The pivot shaft  18  passes through an opening in the housing  32  to engage the center anchor section  28  of the spring. It is understood that the housing pivots about the pivot shaft to pivot the bail member arm  17  secured to the housing  32 . 
     It has been found in practice that the double coil springs of the actuation mechanism endure their greatest stress at the transition portions  35  (see  FIG. 2 ) between the center anchor section  28  and the coil portions  23  and  24 . Repeated deployment of heavy tarps by the actuation mechanism means repeated coiling and uncoiling of the spring, which may lead to eventual fatigue of the coil springs. Since metal fatigue typically occurs at a location of greatest stress, for the double coil springs the transition portion  35  is a potential site for failure. 
     The weight of the tarp and its deployment mechanism may be minimized to lower the stress on the springs of the actuation mechanism and to lengthen the fatigue life of the springs. Also the fatigue life of the springs can be lengthened by increasing the number of springs and the size of the springs. However, weight reduction of the tarp and its mechanism is constrained by the need to maintain a durable tarp and mechanism. Similarly, increasing the number and size of the springs is limited by cost, space and weight considerations. 
     Consequently, there remains a need for improvements to a double coil torsion spring actuation mechanism, and particularly to eliminate stress or fatigue points in the spring. 
     SUMMARY 
     According to an embodiment of the present disclosure an improvement to coil spring actuation mechanism for a cover system on an open-topped container is provided. The cover system includes a cover extendable from a stowed position to a deployed position covering the container and a bail member attached to the cover and movable relative to the container to move the cover between the stowed and deployed positions. The mechanism includes a pivot shaft mountable on the container and a double coil spring mountable on the pivot shaft. The improvement comprises a bushing mountable on the pivot shaft and within the double coil spring. 
     In accordance with certain features, the bushing has an eccentric external periphery that is progressively increasingly spaced from the coil portion of the spring as the coil portion diverges from the mounting portion of the spring. The eccentric external periphery limits the deflection of the spring at the transition points between the center portion and each of the coil portions. In particular, at some point in the coiling of the spring, the coil portions contact the eccentric periphery of the bushing to not only limit further movement of the coil portions, but also to provide support for those portions under load. 
     One important benefit of the present invention is that it significantly reduces the stress concentration in the bend points of the double coil spring. Another benefit is that the bushing provides an inexpensive solution that will significantly prolong the life of the spring in the actuation mechanism. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate embodiments of the present disclosure and together with a description serve to explain the principles of the disclosure. 
         FIG. 1  is a perspective view of a vehicle utilizing a tarping system to cover the open-topped body of the vehicle. 
         FIG. 2  is a side perspective view of an actuation mechanism of the prior art. 
         FIG. 3  is a top exploded view of the actuation mechanism depicted in  FIG. 2 . 
         FIG. 4  is a perspective view of a bushing for use with the double coil torsion spring shown in  FIG. 2 . 
         FIG. 5  is an elevational view of a double coil spring and the bushing of  FIG. 4  shown in their assembled configuration. 
         FIG. 6  is an enlarged detail view of the spring and bushing of  FIG. 5  particularly illustrating the transition points of the double coil spring. 
         FIG. 7  is a side view of the bushing shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. The invention includes any alterations and further modifications in the illustrated devices and described methods and further applications of the principles of the invention which would normally occur to one skilled in the art to which the invention relates. 
     According to the present disclosure, the actuation mechanism  20  incorporates a bushing  100  shown in  FIGS. 4-7  that helps reduce stress and fatigue in the transition portions  35  of an elastically deformable double-coil spring  21 . The mechanism  20  itself is otherwise similar to the mechanism shown in  FIGS. 2 and 3 . It should be appreciated that the mechanism  20  may be retrofitted with the bushing  100  without modification to the housing  32  or any other components of the mechanism. 
     The bushing  100 , as shown in  FIG. 4 , includes a body  102  that is generally in the form of a hollow cylinder with a central opening  105 . The body  102  includes a cam portion  104  and a collar  106 . The cam portion  104  defines an eccentric external periphery  107  which itself includes a first cam surface  108  and a second cam surface  110  that are diametrically opposite each other on the periphery. The first cam surface  108  is separated from the second cam surface  110  by a slot  112  that extends across the diameter of the body  102 . The first cam surface  108  extends from a small end  114  to a large end  116 , with the small end defined at a radius that is less than the radius at which the large end is defined. Similarly, the second cam surface  110  extends from a small end  118  to a large end  120  preferably having the same dimensions and dimensional relationship as the ends of the first cam surface. 
     To conform to the contour of the coil spring  21 , the first cam surface  118  includes a first coil contact surface  122  which increases in radius, as measured from the axis  124  through the central opening  105  of the bushing  100 , in the direction from small end  114  to large end  116  of the first cam surface  108 . Similarly, the second cam surface  110  includes a second coil contact surface  126  which continually increases in radius from the small end  118  to the large end  120  of the second cam surface  110 . The height of the two coil contact surfaces  122 ,  126  is sufficient to fully bear against the full diameter of the coil spring when the bushing  100  is placed within the actuation mechanism  20 , as described herein. The height of the bushing may also be adjusted to account for multiple springs in a particular mechanism. 
     As shown in  FIG. 4 , the first and second coil contact surfaces  122  and  126  extend from outer face  128  of the cam portion  104  of the bushing  100  to inner face  130  of the cam portion  104  of the bushing  100 . A collar  106  then extends upward from the inner face  130  of the cam portion  104  and defines an upper outer face  129 . It can be appreciated that the collar  106  essentially supports the two parts of the cam portion  104 . Moreover, the collar  106  supports the bushing  100  on the center portion  28  of the double-coil spring  21  when the center portion extends through the slot  112 . The collar, in effect, closes one end of the slot. The bushing  100  is preferably molded as a single piece, with an integral collar and cam portion. 
     Referring now to  FIG. 5 , the double coil spring  21  is shown supported on the pivot shaft  18  mounted to housing  32  of the mechanism  20  with the first and second coil portions  23  and  24  engaged at their respective ends  44  and  46  to a corresponding reaction post  26  and  27  of the mechanism. The bushing  100  is placed on the pivot shaft  18  before the double coil spring  21  with the collar  106  of the bushing  100  placed toward the center of the truck body  11 . The pivot shaft  18  is slotted and the slot  112  of the bushing  100  is aligned with the slot of the pivot shaft  18  to allow the center anchor portion  28  of the double coil spring  21  to be placed into both slots. The spring  21  and the bushing  100  are shown assembled together to form coil spring assembly  132 . The center anchor section  28  of the spring  21  is fitted into slot  112  of bushing  100 . 
     As shown in more detail in  FIG. 6 , the first cam surface  108  is positioned adjacent and cooperates with the first coil portion  23  of the spring  21  while the second cam surface  110  cooperates with the second coil portion  24  of the spring  21 . The large ends  116 ,  120  of the first and second cam surfaces  108 ,  110 , respectively, closely conforms to corresponding inner periphery  38  of the first coil portion  23  and inner periphery  40  of the second coil portion  24  of the spring  21 . The large ends are particularly oriented at the coil transition portion  35  where the greatest support is needed, thereby reducing the stress at the transition portions  35  of the spring  21 . 
     The pivot shaft  18  of the mechanism  20  extends through the central bore  105  of the bushing while the center section  28  of the spring fits within the slot  112  of the bushing  100 . The eccentric external periphery  107  of the cam portion  104  of the bushing  100  is increasingly spaced from the coil portions  23 ,  24  of the spring  21  when the spring  21  is in its initial state within the actuation mechanism. The eccentric external periphery  107  cooperates with the spring  21  to limit the amount of deflection the coil portions may experience under load to improve the fatigue life of the spring  21 , while having minimal effect upon the torsional capacity of the spring  21 . In other words, it can be appreciated that as the spring winds, the coil portions  23 ,  24  will contact an increasing amount of a respective cam surface  108 ,  110 . The eccentric nature of the periphery allows the spring to operate at its highest torque position in which the coil portions are tightly wound around the center section  28  of the spring. 
     The first coil portion  23  and the second coil portion  24  of the spring  21  are shown in  FIG. 6  in solid lines in an initial position  134  of the spring in which the spring is unloaded or only slightly torqued. In the initial position  134 , the inner periphery  38  of the first coil portion  23  is in intimate contact with the first coil contact surface  122  of the first cam surface  108  only at the large end  116  of the first cam surface  108 . Similarly, the inner periphery  40  of the second coil portion  24  is in intimate contact with the second coil contact surface  126  of the second cam surface  110  only at the large end  120  of the second cam surface  110 . 
     A controlled deflected position of the spring is shown as a dashed line  140  in  FIG. 6 . It should be appreciated that, in the controlled deflected position  140  the inner peripheries  38  and  40  of the coil portions  23  and  24 , respectively, of the spring  21  are in intimate contact with the coil contact surfaces  122  and  126  of the cams  108  and  110 , respectively, of the bushing  100 . Such intimate contact defines an angular relationships of a between the center anchor section  28  and each of the coil portions  23  and  24  of spring  21 . 
     The spring  21  is shown in an uncontrolled deflected position as a phantom line  142 , representing the deflection of the spring  21  with the bushing  100  removed. In this position, the inner peripheries  38  and  40  of the coil portions  23  and  24 , may contact pivot shaft  18 . The transition portions  35  of the spring  21  are deflected such that the angles between the center anchor section  28  of the spring  21  and each of the coil portions  23  and  24  of the spring  21  are defined by angle α′, which is significantly less than the angle α in the controlled deflected position  140  with the bushing  100  in place. Providing the bushing  100  such that the larger angles α within the transition portions  35  of the spring  21  may be maintained, the stress on the spring  21  is reduced and the resulting fatigue life of the spring  21  is lengthened. 
     The increasing radial dimension of the cam surfaces may be accomplished by configuring the first coil contact surface  122  and the second coil contact surface  126  such that the center of the contact surfaces  122  and  126  are defined by a dimension offset from the axis  124  through the central opening  105  of the bushing  100 . For example, and as shown in  FIG. 6 , the first coil contact surface  122  of the first cam surface  108  may be defined by radius FCR measured from a point  136  extending a horizontal distance HO, measured along the length of the slot  112 , and a vertical distance VO from the axis  124  of the bushing  100 . Similarly, the second coil contact surface  126  of the second cam surface  110  may be defined by radius SCR extending from a point  138  spaced a horizontal distance HO and a vertical distance VO from axis  124  of the bushing  100  (it is understood that  FIG. 6  is not drawn to scale). It should be appreciated that the contact surfaces  122  and  126  of the cams  108  and  110 , respectively, may be defined with other geometry provided that the contact surfaces  122  and  126  at the large ends  116  and  120 , respectively, of the bushing  100  closely conform to the inner peripheries  38  and  40 , respectively, of the spring  21 . For instance, rather than being defined at a constant radius offset from the axis  124  of the bushing, each camming surface may be defined at a radius measured from the axis  124  that gradually increases from the smaller end  118  to the larger end  120 . 
     As depicted in  FIG. 7 , the slot  112  of the bushing  100  may be tapered outwardly from inner face  130  to the outer face  128  of the cam portion  104 . This taper facilitates introduction of the bushing over the spring and mounting post. 
     It should be appreciated that the bushing  100  of the present disclosure may include complimentary right and left versions of the bushing for use in complimentary right and left actuation mechanisms. For example, the actuation mechanism  20  as shown in  FIG. 2 , represents a left actuation member suitable for the left side of a vehicle. It should be appreciated that the mirror image or symmetrical construction of an actuation member would be appropriate on the right side of the vehicle. Further, multiple springs may be used in the actuation system to obtain greater spring force to actuate larger, heavier mechanisms. Each spring may have its own bushing or a single bushing may be made longer to accommodate a stack of double coil springs within a single actuation mechanism. In some cases it may be desirable to orient successive springs in a stack at different angular orientations or pre-loaded. In such cases, the configuration of the cam surfaces may be modified accordingly. 
     The bushing  100  may be made of metal or a polymer. Preferably, the bushing  100  may be molded of a suitable polymer such as a polyoxymethylene (POM) such as DELRIN® sold by DuPont. 
     While the actuation system bushing described herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the actuation system bushing to the particular forms disclosed. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.