Abstract:
A control linkage system for opening and closing a door at least partially covering an opening to a large container such as a transfer trailer. The linkage system maintains constant control over the door during rotation, using mechanical linkage providing increased rotational motion and enhanced mechanical advantage. The linkage system employs hydraulic cylinders pivotally attached to the side wall of the container. The linkage system alse employs a curved link joined to a straight link in the same plane as the mechanical linkage.

Description:
BACKGROUND OF THE INVENTION 
     The invention generally relates to covers over the openings of large containers, such as transfer trailers. More specifically, the invention relates to a control mechanism for opening and closing such covers. 
     Many different types of large containers are used for hauling loads and waste, such as solid waste, construction debris, landscape materials, recyclables, etc. One such type are wheeled containers designed for hauling by trucks, known as “transfer trailers”. Transfer trailers are typically rectangular-shaped with open tops. Covers over the open tops are typically provided to prevent the load from spilling, sliding or being blown out the top of the container during transport. These covers have taken various forms in the past, including tarpaulin, lightweight nylon doors, open mesh plastic screens, etc. Some past trailer cover doors have consisted of two half-doors each rotating about a pivot point located adjacent each sidewall of the trailer. However, the doors may be 45 feet in length, and may each weigh 400 pounds, for example. Thus, the doors may be too heavy to manually open and close, and for this purpose hydraulic power mechanisms have been employed. 
     Known rotation control mechanisms for flip tops have disadvantages. They do not maintain control of the cover door(s) during their entire rotation. Thus, once a door has been rotated over-center, conventional powering mechanisms allow it to free fall down and possibly be damaged upon impact with the outer sidewall of the container. In the case of hazardous waste, for example, the doors need to be tightly sealed, such as by using a rubber gasket seal, and this may be impossible if the doors are sufficiently damaged, such as being bent. Further, such powering mechanisms have been relatively expensive since they have required relatively large hydraulic pressures to accomplish door rotation. 
     Accordingly, it is an object of the present invention to provide a control mechanism for a trailer cover which maintains control of the cover doors during their entire rotation, preventing damage to the doors and/or the trailer. 
     It is another object of the invention to provide a control mechanism for covering a container opening which requires relatively low hydraulic or air pressure as compared to conventional control mechanism, enabling the more economic manufacture and use of the trailer. 
     DEFINITION OF CLAIM TERMS 
     The following terms are used in the claims of the patent as filed and are intended to have their broadest meaning consistent with the requirements of law. Where alternative meanings are possible, the broadest meaning is intended. All words used in the claims are intended to be used in the normal, customary usage of grammar and the English language. 
     Container: Any large receptable, including but not limited to a transfer trailer, such as containers used for holding and/or hauling loads or waste. 
     Linkage mechanism: A system of links or bars which are joined together. 
     SUMMARY OF THE INVENTION 
     The objects mentioned above, as well as other objects, are solved by the present invention, and overcome disadvantages of prior art mechanisms for controlling the opening and closing of large container covers, such as transfer trailer doors, while providing new advantages not believed associated with such mechanisms. 
     In one preferred embodiment, a device is provided for controlling the opening and closing of at least one door covering at least part of an opening of a container, such as a transfer trailer or other container. The door(s) may be pivotally or otherwise attached to various locations on the container such as at an upper edge of the container, for example. The device includes one or more power mechanisms attached to the container for driving rotation of the door. The power mechanism may include a hydraulic cylinder or an air-powered cylinder, for example. At least one linkage mechanism is connected to the power mechanism, and transfers force from the power mechanism to open or close the door, such as by driving its rotation. Preferably, the door(s) remains under constant control, such as under constant rotational control, of the power mechanism during its opening and closing. Preferably, the door rotates through at least about 180° and, more preferably, rotates through at least about 270°. 
     In a preferred embodiment, at least one arm is provided which is slidably and pivotally connected to the at least one door and also pivotally connected to the container, and the linkage mechanism substantially increases the rotational mechanical advantage imparted by the power mechanism to the at least one arm. In a preferred embodiment, the linkage mechanism may include first and second links. The first link may be pivotally connected to the power mechanism and to a wall of the container, and the second link may be pivotally connected to the first link and to the arm. In one embodiment, one link may be curved and the other may be straight, allowing the use of links in the same or substantially the same plane. The curved link may be pivotally attached to the container, and the straight link may be pivotally attached to an intermediate portion of the arm and also pivotally attached to the curved link. In an alternative embodiment, two straight links may be used, in which case they may be designed to be in different or substantially different planes. In a particularly preferred embodiment, a first four-bar linkage connected to the power mechanism drives a second four-bar linkage connected to the door. 
     In a particularly preferred embodiment, the ratio of cylinder pressure (psi) to door weight (pounds), or the “cylinder pressure-to-door weight ratio” is preferably less than about 3.0, and more preferably less than about 2.0. Also with the present invention the ratio of cylinder force to door weight, or the “cylinder force-to-door weight ratio” is about 22, and in preferably in the range of about less than 30, and more preferably less than about 25. In a preferred embodiment, a power mechanism employs at least one hydraulic cylinder under pressure of less than about 2000 psi, and more preferably less than about 1000 psi. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features which are characteristic of the invention are set forth in the appended claims. The invention itself, however, together with further objects and attendant advantages thereof, will be best understood by reference to the following description taken in connection with the accompanying drawings, in which: 
     FIGS. 1 and 2 are partial perspective views of the upper portion of a trailer equipped with a preferred embodiment of the trailer cover control mechanism of the present invention; 
     FIGS. 3-5 are partial, enlarged views showing sequential movement of the right-side control mechanism shown in FIGS. 1 and 2; and 
     FIGS. 6-8 are partial, enlarged views showing sequential movement of the linking mechanisms which form a portion of the right-side control mechanism shown in FIGS.  3 - 5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Set forth below is a description of what are currently believed to be the preferred embodiments and/or best examples of the invention claimed. Future and present alternatives and modifications to these preferred embodiments are contemplated. Any alternatives or modifications which make insubstantial changes in function, in purpose, in structure or in result are intended to be covered by the claims of this patent. 
     Referring first to FIGS. 1-2, a container, designated generally as  20 , is shown. Container  20  may be a transfer trailer, or other large container, having sidewalls  20   a  and end walls  20   b.  Doors  27  are pivotally attached at upper end  26  via pivotable brackets  26   a  or other means. Instead of two doors, as shown, a single cover or door may be used. Container  20  may be unloaded, for example, by opening a door forming end wall  20   b  opposite the end wall carrying the control mechanism, designated generally as  25 , for the door(s). 
     Referring now to FIGS. 1-5, a preferred embodiment of control mechanism  25  is shown. Control mechanism  25  controls rotation of flip top doors  27  about pivot point(s)  27   b  on the upper end  26  of transfer trailer  20 . A rubber gasket or seal strip (not shown) may cover upper ends  26  to provide a tight seal between doors  27  to upper end  26  of the trailer. Control mechanism  25  may possibly be directly attached to a sidewall or end wall of container  20 . Alternatively, a rigid support bar, such as support bar  30 , may carry control mechanism  25  and be rigidly attached to a container wall as shown in the drawings. A power mechanism, such as one or more hydraulic cylinders  35 , may be rigidly attached to support bar  30 . 
     In one particularly preferred embodiment, shown in FIGS. 3-8, curved link  43  is attached at one end to an end of support bar  30  at pivot point “A”, and is attached at a second end to link  45  at pivot point “B”. Link  45 , which may be curved and need not be straight, as shown, is pivotally attached at “C” to arm  50 , which is pivotally attached at “D 1 ” to support  30 . Arm  50  is pivotally and slidably attached at point “D 2 ”, such that arm  50  slides within passage  27   a  of door  27 . The ends of cylinder rods  37  are also each pivotally attached to straight link  45  at pivot point B. The other end of straight link  45  is pivotally attached to an intermediate point on arm  50  at pivot point “C”. Cylinders  35  are each free to pivot about fixed pin E. 
     In operation, and referring now to the sequence of FIGS. 3-5 and  6 - 8  showing the portion of control mechanism  25  associated with the right-hand side door, rotation of doors  27  is accomplished as follows. When cylinder rod  37  is extended, curved link  43  is rotated clockwise, as indicated by the arrow in FIG. 4, about point A. This exerts a force on straight link  45 , causing right-hand side door  27  to be rotated clockwise about point  27   b;  as this rotation occurs, end D 2  of arm  50  slides along passage  27   a  first in a direction toward point  27   b  and then, as door  27  traverses over-center, in a direction away from point  27   b  and toward the distal end  27   c  of door  27 . Rotation of the left-hand side door is simultaneously accomplished in a similar manner. 
     Cylinders  35  are free to pivot about pin E, and no external limits such as stops or other means limit the rotation of the cylinders, other than the door itself when it is in an open or closed position. This rotation of cylinders  35  about pin E allows the cylinders to maintain a direct pushing arrangement and limits sideloads which would otherwise be exerted on these cylinders, and which might have a deleterious impact on the packing material (bearings, rings) within the cylinder, potentially allowing the cylinders to leak. 
     It can be seen that in this preferred embodiment one four-bar linkage (consisting of links  43 ,  45  and arm  50 ) drives a second four-bar linkage (consisting of arm  50 , slide opening  27   a  and door  27 ). 
     This preferred embodiment shown in the drawings and described above has been found to provide the beneficial result that, for hydraulic cylinders with a bore size of 4 inches, a relatively small cylinder pressure, e.g., about 700 psi (preferably less than about 2000 psi and more preferably less than about 1000 psi), imparting a relatively small cylinder force, e.g., about 8800 pounds of force, is sufficient to rotate open and closed a door that weighs about 400 pounds, for example, through 270°. (This is in contrast to applicant&#39;s own prior art system, for example, which requires two to three times this cylinder pressure (about 2400 psi) and cylinder force (about 25,000-27,000 pounds), using the same size cylinder and the same door weight, to rotate open or closed the door.) In a preferred embodiment of the invention, for example, the ratio of cylinder pressure (psi) to door weight (pounds) (“X”) is about 1.75, and is preferably in the range of about less than 3.0, and more preferably less than about 2.0. With the present invention the ratio of cylinder force to door weight (“Y”) is about 22, and in preferably in the range of about less than 30, and more preferably less than about 25. In contrast, these ratios X and Y are about 6 and 60, respectively, for Applicants&#39; own prior art system. The lowered ratios realized by preferred embodiments of the present invention represent increased mechanical advantages provided by improved linkage mechanisms disclosed here. 
     Another advantage of the present invention is that constant rotational control is maintained over the door, so that the door is not permitted to rotate freely under the forces of gravity and/or to impact or otherwise damage either the container walls or the door itself. Further, the forces within the mechanical linkage and at the pivot points are minimized, extending the life of the control mechanism and the doors. For example, a relatively low lifting and rotating moment around pin  27   b  is exerted on door  27  by control mechanism  25 . 
     Various alternative embodiments within the spirit and scope of the invention are possible. For example, air cylinders or a hydraulic motor may be used instead of hydraulic cylinders. Also, one cover or door may be used instead of two. The power mechanism may also be configured such that if two or more doors are used, the doors may be rotated separately or at different times. Hydraulic controls (not shown) may be attached to a sidewall of the container. It will also be appreciated that rather than using cylinders, movement of a suitable linkage mechanism (e.g., links  43 ,  45  and arm  50 ) may be accomplished using a hydraulic/torque motor, a rack and pinion mechanism, a chain link, or other suitable power or drive mechanisms. 
     While in the particularly preferred embodiment the use of a curved link  43  and a straight link  45  is disclosed, this is not a requirement. Instead, for example, each link could be straight. Use of a curved link enables this link to curve around and not interfere during its movement with pivot pin D 1 , and thus allows links  43 ,  45  to be provided in the same, or substantially the same, plane. If two straight links are provided, each link may preferably be located in different planes to avoid the links from contacting each other during their rotation. Of course, it will be understood that links  43 ,  45  may be provided with varying shapes and configurations. 
     In yet another alternative embodiment, which is a modification of the preferred embodiment shown in FIGS. 3-8, bar  50  may be removed, and link  45  may be attached directly to door  27 ; for this purpose, link  45  may be lengthened, or control mechanism  25  may be located at a higher elevation on the container wall. 
     In still another alternative embodiment, arm  50  need not be slidably attached to lid or door  27 . Instead, a third link could be used, rotatably pinned to an end of arm  50  and also rotatably pinned to door  27  at a point approximately where opening  27   a  terminates toward the distal end  27   c  of the door. This arrangement would still allow door  27  to rotate through about 270°, without the requirement that door  27  be slidably attached to arm  50 . 
     In yet another alternative embodiment, the cylinder rod end and the two links  43 ,  45  need not meet at common pivot pin B, but instead could be commonly attached through one or more brackets or further links, for example. 
     The above description is not intended to limit the meaning of the words used in the following claims that define the invention. For example, it will be understood that other control mechanisms specifically mentioned here that accomplish the same general operations may do so in substantially different ways, while still providing a mechanism for controlling container door movement that operates within the principles of the present invention. Rather, it is contemplated that future modifications in structure, function or result will exist that are not substantial changes and that all such insubstantial changes in what is claimed are intended to be covered by the claims.