Abstract:
A damping spring assembly particularly but not exclusively useful for damping the motion of rake wheels in agricultural wheel rakes. The damping spring includes a pair of extended U-bolts and a coil compression spring. The extended U-bolts are connected to spring holder bushings which bear on the ends of the coil compression spring. As the coil compression spring is compressed, a constrained resilient damping rod located within the extended shafts of the extended U-bolts is likewise compressed in length and expands in diameter to bear against the extended shafts of the extended U-bolts, thus providing a damping action to prevent snapping back of the damping spring.

Description:
RELATED APPLICATION 
   The present application claims the benefit of U.S. Provisional Application No. 60/607,813 filed Sep. 8, 2004, which is incorporated herein in its entirety by reference. 

   FIELD OF THE INVENTION 
   The invention relates to agricultural implements and more particularly to springs for damping of the motion of rake wheels used in wheel rakes that are useful to form windrows from cut forage. 
   BACKGROUND OF THE INVENTION 
   A primary goal in the harvesting of hay or forage is to dry the hay as soon as possible and then to remove it from direct exposure to sunlight. The hay must be dried before storage to avoid the problems of mold and spontaneous combustion. Exposing the cut hay to sunlight longer than is required to adequately dry it, however, can result in unacceptable loss of nutritive value of the hay due to deterioration of the protein level. 
   Typically, hay is harvested into approximately five-foot swaths along the ground, and is exposed to sunlight for the initial stage of the drying process. These swaths spread out the hay to maximize exposure to the sun and air to speed initial drying. The swaths of hay are then raked into narrow windrows to remove most of the hay from direct contact with the moist ground. The windrow enhances air circulation within the hay, thereby hastening the drying process. Raking hay into windrows also facilitates gathering of hay by providing rows of forage for a hay baler or other harvesting device to follow. 
   Many types of wheel rakes have existed for decades. Wheel rakes utilize angled, tined “pinwheels” that are propelled across the ground of a field of cut forage. Contact with the ground while traveling across the ground rotates the wheels and thereby rakes the hay in a desired direction. Of particular interest are V-rakes in which at least two banks of rake wheels are deployed in the shape of a V during operation. Generally, V-rakes employ an arm on each side of a frame to support the wheel rakes. Such V-rakes are used to rake forage into a windrow by raking the forage from the outer edges of the implement inward. V-rakes are preferably adjustable so that the width of the windrow produced is variable and the swath raked on each pass is optimal for the circumstances encountered. For optimal operation, it is preferable that the relative angle of the wheel banks and the width of their separation be independently adjustable. 
   Wheel rakes are subject to repeated structural stresses due to uneven ground and irregular distribution of forage material when propelled through fields of cut hay to form the hay into windrows. The assemblies supporting the rake wheels must have considerable strength in order to bear such stresses successfully. Welded assemblies are thus preferred for their robustness and durability. In addition, a certain degree of flexibility in motion of the rake wheels is desirable. Some flexibility of the assembly is desired as well. 
   Wheel rakes convert the forward motion of the rake into a lifting and sideward motion by interaction of the rake wheels with the ground as the wheel rake is drawn forward. Compacted, damp or unusually heavy forage can create problems in that the rake wheels may tend to roll over or skip over areas of heavy compacted forage rather than lifting it and raking it toward the desired windrow. If this occurs, loss of production and increased costs result. Loss of production occurs if forage is left in the fields to decay rather than being harvested. Increased costs can occur if it is necessary to pass through the fields several times to accomplish sufficient raking to gather all of the forage desired. 
   Rake wheels include a plurality of tines extending from the rim of the wheel. Flexible metal tines lift and move forage to one side as the rake wheels rotate. 
   Thus, wheel rakes generally have adjustable tension springs that allow the wheels to float. The spring tension can be adjusted to cause more or less of the wheel&#39;s weight to bear on the ground. If wheel float is too light, wheels will pass over the crop and leave some of the crop unraked. If wheel float is too heavy, wear on the rake wheels is increased and the rake wheel will dislodge more soil and rocks from the earth and increase contamination of the hay. 
   Traditionally, and sometimes today, tines extend the entire distance from the rake wheel hub beyond the rim. More commonly tines are attached to the wheel rim and the rim to the hub via spokes or a wheel disk. In the event that spokes are utilized, a plastic disc often covers the spokes. This arrangement keeps forage from passing through the wheel instead of being raked as desired. 
   Modern rake wheels often utilize metal tines mounted in flexible rubber bases. The rubber bases secure the tines to the wheel rim and provide a measure of controlled flexibility so that each tine can flex in response to loads in all directions without bending or breaking. 
   Wheel rakes are typically constructed so that multiple rake wheels are mounted side by side mounted on long beams. It is desirable that the beams be adjustable in width or separation and in the angle that the beams make with the path of travel as viewed from above. 
   Rake wheels are flexibly supported as they pass over the ground so that the full weight of the rake wheel does not rest on the ground. Rake wheel are typically biased upward by springs so that the rake wheels may resiliently flex upwardly as the wheel rake passes over a bump and so that the rake wheels can move downward when the wheel rake passes over a depression in the ground. 
   Commonly, tension springs are used in cooperation with a bellcrank to resiliently support the rake wheels. The tension springs are generally oriented horizontally while the motion of the rake wheel is along a generally vertical arc. The tension springs are often linked directly to the to the bellcrank or via short chains connected to eyes at the end of the springs. Several problems arise with this arrangement. With repeated stress the spring eyes may suffer metal fatigue and break. This not only interferes with proper raking action but also may cause damage to the rake wheel and cause loss of the spring in the field where it may later cause damage to other farm implements or equipment. For example, a lost spring may interfere with a hay mower during the next mowing of the field and damage the hay mower. 
   Tension springs may also be damaged by being overextended. If the tension spring is stretched too far it may no longer recoil as it once did. This will cause the rake wheel to bear on the ground to a greater degree than it should and may cause excess wear and or damage. 
   Further, the tension spring supporting the rake wheel may “snap back” when the spring is loaded and then the load on the tension spring is abruptly released. This can also damage the rake wheel assembly. 
   Thus the agricultural arts would benefit from a device to provide spring tension for supporting rake wheels and the like that is less prone to breakage and that does not “snap back” when released. It would be beneficial if the device were resistant to overextension as well. 
   SUMMARY OF THE INVENTION 
   The present invention is a damping spring that solves many of the above problems. In one embodiment, the damping spring of the present invention generally includes a pair of opposed extended U-bolts, a coil compression spring, a pair of spring holder bushings, a pair of spring holder washers, a resilient damping rod, and nuts to secure the extended U-bolts. 
   The coil spring is capped on each end by the pair of spring holders. Each spring holder has four holes bored therethrough. The extended U-bolts pass through an opposed pair of holes in a first spring holder, then through the interior space surrounded by the coils of the coil spring and through another pair of opposed holes in the second spring holder. A spring holder washer is placed over the threaded ends of the extended U-bolt and two nuts are threaded on to the ends of the extended U-bolt to secure the extended U-bolt to the second spring holder. A second extended U-bolt is passed from the opposite end of the damping spring through the spring holder washer, the second spring holder, the interior of the coil spring, through a pair of opposed holes in the first spring holder, and through a spring holder washer, where the threaded ends of the second U-bolt are secured with nuts. Once the extended U-bolts are placed in this orientation, they form a cage surrounding a space formed by the four shafts of the extended U-bolts. In this space is placed the resilient damping rod. 
   Thus, the assembled damping spring in this embodiment, as viewed in cross-section at the center of the spring, includes the coils of the coil spring on the outside, a space, the four shafts of the two extended U-bolts forming a substantially square cage formed of four straight shafts, and within that cage a resilient damping rod. 
   In another embodiment, the assembled damping spring includes one U-bolt and an eyebolt positioned between the legs of the U-bolt and an annular damping member surrounding the shaft of the eyebolt. In yet another embodiment two eyebolts are utilized with a resilient damping member located between their shafts. 
   Thus, when tension is applied to the first and second U-bolts, the U-bolts transfer the load to the nuts at the ends thereof. The nuts contact the spring holder washer which transfers the load to the pair of spring holders which bear against the ends of the compression coil spring. Thus, tension applied to the U-shaped ends of the first and second extended U-bolts causes the coil compression spring to be compressed. The length of the resilient damping rod may be less than the length of the coil compression spring. Thus, the spring may be compressed a limited amount before the spring holders come into contact with the ends of the resilient damping rod. Alternately, the damping rod may be partially compressed when the spring is at its maximum extended length if preloading of the resilient damping rod is desired. When the spring holders come into contact with the resilient damping rod, the resilient damping rod is shortened in length but thickens in diameter. As the resilient damping rod thickens in diameter it begins to rub against the shafts of the first and second extended U-bolts from the inside. As the resilient damping rod is further compressed end to end it will expand further flexing and bowing outward the shafts of the first and second extended U-bolts. 
   As tension on the U-shaped ends of the two extended U-bolts is relieved, the coil compression spring tends to return to its extended length. As this occurs, the two extended U-bolts move in opposite directions while rubbing against the sides of the resilient damping rod. Thus, the resilient damping rod will slow the motion of the two extended U-bolts as they pass by each other and damp the action of the coil compression spring as it returns to its extended length. In addition, as the extended U-bolts may be forced into a bowed or flexed position by expansion of the resilient damping rod, friction occurs between the two extended U-bolts and the spring holders where the U-bolts pass through the opposed holes in the spring holders. This also contributes to the damping action of the resilient damping rod. 
   The degree of damping can be adjusted by adjusting the length of the resilient damping rod. A longer resilient damping rod will expand more readily as the coil compression spring is compressed, thus increasing damping. A shorter resilient damping rod will reduce damping because the resilient damping rod will not be compressed until the compression coil spring is further compressed by the motion of the two extended U-bolts. 
   In addition, the compression coil spring only compresses until its coils come into contact with one another thus limiting the extend to which the spring can be compressed. Thus the spring is resistant to being over extended. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a damping spring in accordance with the present invention; 
       FIG. 2  is an exploded perspective view of the damping spring of the present invention; 
       FIG. 3  is a perspective view of the damping of the present invention with the coil compression spring removed to show the interior parts with greater clarity; and 
       FIG. 4  is a fragmentary view of a wheel rake including a damping spring with a rake wheel depicted in schematic, and in contact with the ground; 
       FIG. 5  is a fragmentary view of a wheel rake including a damping spring with a rake wheel depicted in schematic, and raised from contact with the ground; 
       FIG. 6   a  is a cross-sectional view of the damping spring including a resilient damping member of circular cross section; 
       FIG. 6   b  is a cross-sectional view of the damping spring including a resilient damping member of cruciform cross section; 
       FIG. 6   c  is a cross-sectional view of the damping spring including a resilient damping member of modified cruciform cross section; 
       FIG. 6   d  is a cross-sectional view of the damping spring including a resilient damping member of square cross section; 
       FIG. 6   e  is a cross-sectional view of the damping spring including a U-bolt, and eyebolt and a resilient damping member of annular cross section; 
       FIG. 6   f  is a cross-sectional view of the damping spring including another resilient damping member having a diamond cross section; 
       FIG. 6   g  is a cross-sectional view of the damping spring including a resilient damping member of circular cross section including channels therethrough to accommodate U-bolt shafts; 
       FIG. 6   h  is a cross-sectional view of the damping spring including two eyebolts and a resilient damping member of H-shaped cross section; 
       FIG. 7  is a perspective view of a wheel raking including damping springs in accordance with the present invention; and 
       FIG. 8  is a partial perspective view of the wheel rake of  FIG. 7 . including damping springs in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1-3 , damping spring  10  of the present invention generally includes first extended U-bolt  12 , second extended U-bolt  14 , coil compression spring  16 , first spring holder bushing  18 , second spring holder bushing  20 , first spring holder washer  22 , second spring holder washer  24 , resilient damping member  26 , and nuts  28 . First extended U-bolt  12  and second extended U-bolt  14  are substantially similar and include U-shaped ends  30 , extended shafts  32  and threaded ends  34 . First extended U-bolt  12  and second extended U-bolt  14  may be formed from stainless steel or other high strength, corrosion resistant material. 
   Coil compression spring  16  is a generally conventional compression spring of a size appropriate to contain first extended U-bolt  12  and second extended U-bolt  14  within its inner diameter. 
   First spring holder bushing  18  and second spring holder bushing  20  are substantially similar in construction. First spring holder bushing  18  and second spring holder bushing  20  both include a small diameter portion  36  and a large diameter portion  38 . Small diameter portion  36  and large diameter portion  38  are concentrically positioned to form shoulder  40 . First and second spring holder bushings  18 ,  20  are desirably formed of unitary piece of material. For example, ultra high molecular weight polyethylene may be used to form first and second spring holder bushings,  18 ,  20 . First and second spring holder bushings  18 ,  20  are pierced by four substantially evenly spaced holes  42 . Holes  42  are desirably arranged in a four cornered or square pattern. 
   Small diameter portion  36  is sized to fit within the inside diameter of coil compression spring  16 . Large diameter portion  38  is sized to substantially equal the outside diameter of coil compression spring  16 . 
   First spring holder washer  22  and second spring holder washer  24  are substantially similar in construction. First and second spring holder washers  22 ,  24  are substantially equal in diameter to large diameter portion  38  of first and second spring holder bushings  18 ,  20 . First and second spring holder washer  22 ,  24  are pierced by four holes  44 . Holes  44  are located to align precisely with holes  42  located in first and second spring holder bushings  18 ,  20 . 
   Resilient damping member  26  may be shaped as an elongate cylinder and is formed of a resilient material that desirably has a significant surface friction. Resilient damping member  26 , as depicted in examples in  FIG. 6 , may also be shaped in a polygonal cross section or in a cross section that partially or completely surrounds some or all of extended shafts  32 . Resilient damping member  26  may be formed of rubber or another resilient material. One material that may be used to form resilient damping member  26  is rubber O-ring material. Resilient damping member  26  is dimensioned so that it has a diameter or cross sectional dimension slightly smaller than the space between extended shafts  32  of first extended U-bolt  12  or second extended U-bolt  14 . The length of resilient damping member  26  may be more or less than the length separating first spring holder bushing  18  and second spring holder bushing  20  when coil compression spring  16  is uncompressed. The length of resilient damping member  26  relative to coil compression spring  16  may be varied to adjust the damping qualities of resilient damping member  26 . In addition, the diameter of resilient damping member  26  may be varied to increase or reduce the frictional interaction of resilient damping member  26  with extended shafts  32 . 
   Nuts  28  are generally conventional but may be self locking nuts. 
   Damping spring  10  may be connected to other assemblies by chains  46 . For use with a wheel rake, short chain  48  and long chain  50  may be utilized to interconnect damping spring  10  with the wheel rake assembly. 
   Referring to  FIG. 4 , damping spring  10  is connected to bell crank  52  by short chain  48 . In turn, bell crank  52  supports rake wheel  54 . Bell crank  52  is movably supported at pivot  56 , which is in turn supported by rake beam  58 . Preferably, damping spring  10  is located substantially horizontally, but damping spring  10  may be located in any position as decided by those skilled in the art. Long chain  50  is desirably connected to rake wheel lift tube  60 . Rake beam  58  may be attached to any wheel rake known to the agricultural arts. For example, rake beam  58  may be utilized in a V-rake. 
   Referring to  FIG. 6 , resilient damping member  26  can be formed with many different cross-sections. For example,  FIG. 6   a  depicts an embodiment of the invention including a resilient damping member  26  of round cross-section  62 .  FIG. 6   b  depicts a resilient damping member  26  having a cruciform cross-section  64 .  FIG. 6   c  depicts a resilient damping member  26  having a modified cruciform cross-section  66 .  FIG. 6   d  depicts a resilient damping member  26  having a quadrilateral or square cross-section  68 .  FIG. 6   e  depicts a resilient damping member  26  including one U-bolt  12  and one eyebolt  69  and a resilient damping member  26  having an annular cross-section.  FIG. 6   f  depicts a resilient damping member  26  having a diamond cross-section  72 .  FIG. 6   g  depicts a cross-sectional view of including a resilient damping member  26  having a circular cross-section  76  with channels therethrough. In this embodiment of the invention, first extended U-bolt  12  and second extended U-bolt  14  pass through channels  76  in resilient damping member  26 . 
   Referring to  FIG. 6   h , an embodiment of the invention utilizing two eyebolts  69  and a resilient damping member  26  having an H-shaped cross section  78  located therebetween. In this embodiment, two eyebolts are utilized with their extended shafts  32  parallel and a resilient damping member  26  with H-shaped cross section  78  located between them. 
   Damping spring  10  is described here as utilized to support rake wheels  54  in an agricultural wheel rake. Indeed, damping spring  10  is particularly useful in this circumstance. However, the use of damping spring  10  in wheel rakes should not be considered to be limiting as damping spring  10  may be utilized for other purposes within the agricultural arts. 
   Damping spring  10  is assembled, so that first extended U-bolt  12  is passed through first spring holder washer  22 , then through spring holder bushing  18 . First extended U-bolt  12  then is further extended into the interior of coil compression spring  16 . Threaded ends  34  of first extended U-bolt  12  then pass through second spring holder bushing  20  and second spring holder washer  24 . The threaded ends  34  then receive nuts  28  which are tightened to prevent threaded ends  34  from pulling through holes  44  in second spring holder washer  24 . 
   Second extended U-bolt  14  passes through second spring holder washer  24 , then through second spring holder bushing  20  through the interior of coil compression spring  16 , then through first spring holder bushing  18  and first spring holder washer  22 . The exposed threaded ends of second extended U-bolt  14  are then secured with nuts  28 . Prior to completely assembling damping spring  10 , resilient damping member  26  is placed within the space formed by extended shafts  32  of first extended U-bolt  12  and second extended U-bolt  14 . Chains  46  may be secured to U-shaped ends  30  of first extended U-bolt  12  and second extended U-bolt  14  by passing a link of chain  46  over one of extended shafts  32 . 
   When used, damping spring  10  may be installed on an agricultural implement such as a wheel rake as depicted in  FIGS. 7 and 8 . A typical wheel rake  79  includes carriage  80  and rake assemblies  82 . Rake assemblies  82  are typically mirror images of on another and are supported by carriage  80 . 
   Carriage  80  includes ground engaging wheels  84  and drawbar  86 . Drawbar  86  may be attached to a prime mover such as a tractor (not shown) to provide motive force to wheel rake. 
   Rake assemblies  82  include rake beam  58  supporting bellcranks  52  at pivot  56 . Bell cranks  52  support rake wheels  54 . Damping spring  10  connects bellcrank  52  to lift tube  60 . Typically, long chain  50  connects damping spring  10  to lift tube  60  and short chain  48  connects damping spring  10  to bellcrank  52 . Thus, damping spring  10  resiliently supports rake wheel  54  via bellcrank and allows rake wheels  54  to flex upwardly and downwardly as they pass over irregularities of the ground. Thus, the full weight of rake wheels  54  do not bear on the ground since the weight is partially supported by damping spring  10 . 
   When assembled, the ends of coil compression spring  16  rest against shoulder  40  of first spring holder bushing  18  and second spring holder bushing  20 . Nuts  28  bear against first spring holder washer  22  and second spring holder washer  24 . Thus, loads applied to U-shaped ends  30  of first extended U-bolt  12  and second extended U-bolt  14  are transmitted through first spring holder washer  22  and second spring holder washer  24  to first spring holder bushing  18  and second spring holder bushing  20 . First spring holder bushing  18  and second spring holder bushing  20  then apply force to coil compression spring  16 . As coil compression spring  16  is compressed, first spring holder bushing  18  and second spring holder bushing  20  are brought closer together. 
   When first spring holder bushing  18  and second spring holder bushing  20  are close enough together they begin to encounter resilient damping member  26 . Thus, resilient damping member  26  is compressed in length and expands in diameter. As resilient damping member  26  expands in diameter it creates an outward force on extended shafts  32  of first extended U-bolt  12  and second extended U-bolt  14 . The greater the compression of resilient damping member  26  the greater the force applied against extended shafts  32 . As this force is applied, extended shaft may bow outwardly, thus increasing friction against first spring holder bushing and second spring holder bushing  20 . This friction also serves to increase damping as force as tension is applied to U-shaped ends of first extended U-bolt  12  and second extended U-bolt  14 . 
   Thus, damping spring  10  does not snap back when tension upon U-shaped ends  30  is released. Damping spring  10  returns to its untensioned length more gradually than an undamped spring. In addition, the greater the compression of coil compression spring  16  the greater the damping force created by the action of resilient damping member  26 . Thus, the damping action is proportional to the force exerted by the spring in returning to its uncompressed length. 
   The present invention may be embodied in other specific forms without departing from the spirit of any of the essential attributes thereof, therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.