Patent Publication Number: US-8528622-B2

Title: Overhead door assembly for a storage container

Description:
This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/348,392 entitled OVERHEAD DOOR ASSEMBLY FOR A STORAGE CONTAINER and filed May 26, 2010, the entirety of which is hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a movable overhead door assembly for a storage container, such as a truck trailer or garage, for example. 
     BACKGROUND 
     Many storage containers, such as large truck trailers and garages, for example, include an overhead door constructed from longitudinal panels hingedly joined together and supported by rollers that ride in a pair of door guide tracks. The weight of the door may be balanced by a counterbalance mechanism including either a torsion spring system or a pair of extension springs, for example. The counterbalance mechanism is typically mounted on the header wall above the door of the trailer. The guide tracks are typically positioned on the outer sidewalls of the trailer and extend vertically upward from the floor of the opening to the top of the opening, where they then extend backward in a horizontal direction slightly below the roof of the enclosure. During operation, the rollers of the overhead door travel within the guide track and allow the door to be moved between a closed, vertical position to an opened, horizontal position. 
     SUMMARY 
     The present invention may comprise one or more of the features recited in the attached claims, and/or one or more of the following features and combinations thereof. 
     According to one aspect of the present disclosure, an overhead door assembly is configured to be coupled to a storage container, such as a truck trailer. The overhead door assembly includes a guide track system configured to be coupled to one of the sidewalls of the storage container. The guide track system includes a first guide track and a second guide track. The overhead door assembly further includes a door assembly including a door and plurality of rollers coupled to the door and extending outwardly from a lateral edge of the door. Each of the plurality of rollers is received within one of the first and second guide tracks. Further, the plurality of rollers includes an end roller positioned adjacent an upper edge of the door. A shaft of the end roller is positioned above the upper edge of the door when viewed from the side when the door is in a closed, generally vertical position. The end roller rotates about an axis aligned with the longitudinal axis of the lateral edge of the door while each of the plurality of offset rollers rotate about an offset axis spaced-apart from the longitudinal axis of the lateral edge of the door. 
     In one illustrative embodiment, the plurality of rollers may also include a plurality of offset rollers which may each rotate about an offset axis spaced-apart from the longitudinal axis of the lateral edge of the door. Further, the end roller may rotate about an axis aligned with a longitudinal axis of the lateral edge of the door. 
     In another illustrative embodiment, a generally vertical plane defined by the outer surface of the door may be aligned with or positioned forward of a rearmost portion of the end roller when the door is in the closed, generally vertical position. Further illustratively, an axis of rotation of the end roller may be laterally spaced-apart from the longitudinal axis of the door. 
     In still another illustrative embodiment, the first guide track may be positioned generally above the second guide track such that the first guide track is configured to be adjacent to and engaged with one or more roof bows of the storage container. 
     In one illustrative embodiment, the first guide track may include a first horizontal section and a first curved section. Similarly, the second guide track may include a second horizontal section parallel to the first horizontal section, and a second curved section. Further illustratively, the first curved section may define a radius of curvature different from that of the second curved section. In particular, the radius of curvature of the first curved section may be smaller than the radius of curvature of the second curved section. The first guide track may be positioned generally above the second guide track. 
     In another illustrative embodiment, the end roller may be positioned within the first guide track and the plurality of offset rollers may be positioned within the second guide track. 
     In yet another illustrative embodiment, the overhead door assembly may further include a counterbalance mechanism configured to be positioned at a location spaced-apart from a rear end of the storage container. The door of the door assembly is configured to be moved between a vertical, closed position and a horizontal, opened position. Further, the counterbalance mechanism may be positioned forward of the door when the door is in the horizontal, opened position. The overhead door assembly may also include a cable system having a first pulley coupled to a vertical section of the first track and a second pulley coupled a horizontal section of the first track. The cable system may also include a cable having one end coupled to the counterbalance mechanism and another end coupled to one of the plurality of rollers. The overhead door assembly may also include a housing configured to extend downwardly from an inner surface of the roof of the storage container. The counterbalance mechanism may be contained within the housing. Illustratively, a height of the housing may be configured to be approximately the same as a height of a header of the storage container. Accordingly, the door may be configured to be positioned between the header and the housing when the door is in the horizontal, opened position. 
     According to another aspect of the present disclosure, an overhead door assembly configured to be coupled to a storage container, such as a truck trailer includes a guide track system configured to be coupled to the sidewall of the storage container and a door assembly including a door and a plurality of rollers coupled to the door and positioned within the guide track system. The overhead door assembly further includes a counterbalance mechanism coupled to the guide track system and the door assembly. Illustratively, the counterbalance mechanism is configured to be spaced-apart from a rear end of the storage container. 
     In one illustrative embodiment of this disclosure, the door is configured to move between a vertical, closed position and a horizontal, opened position. Illustratively, the counterbalance mechanism may be positioned forward of the door when the door is in both the closed and opened positions. 
     In another illustrative embodiment of this disclosure, the overhead door assembly may also include a cable system having a cable with a first end coupled to the counterbalance mechanism and a second end coupled to a shaft of one of the plurality of rollers. Further illustratively, the second end of the cable may be coupled to an upper half of the door. 
     In still another illustrative embodiment of this disclosure, the guide track system may include an upper track configured to be coupled to a sidewall of the storage container and a lower track configured to be coupled to the same sidewall of the storage container. Illustratively, the plurality of rollers may include an end roller adjacent an upper edge of the door and an offset roller adjacent a lateral edge of the door. Further illustratively, the end roller may be received within the outer track and the offset roller may be received within the inner track. Accordingly, the axis of rotation of the end roller may be aligned with the longitudinal axis of the lateral edge of the door and the axis of rotation of the offset roller may be spaced-apart from the longitudinal axis of the lateral edge of the door. Further, a generally vertical plane defined by the outer surface of the door may be aligned with or positioned forward of a rearmost portion of the end roller when the door s in the closed, generally vertical position. 
     According to still another aspect of the present disclosure, an overhead door assembly configured to be coupled to the rear end of a storage container, such as a truck trailer, includes a guide track system configured to be coupled to the sidewall of the storage container. The guide track system includes a vertical section, a curved section, and a horizontal section. A door assembly includes a door and a plurality of rollers coupled to the door and positioned within the guide track system. The door is movable between a vertical, closed position and a horizontal, opened position. The overhead door assembly further includes a counterbalance mechanism coupled to the guide track system and the door assembly, and a cable system. Illustratively, the cable system includes a cable having a first end coupled to the counterbalance mechanism and a second end coupled to one of the plurality of rollers of the door assembly. 
     In one illustrative embodiment, the cable system may include a first pulley coupled to the vertical section adjacent the curved section of the guide track and a second pulley coupled to the horizontal section adjacent the curved section of the guide track. Further illustratively, the cable may be engaged with the first and second pulleys when the door is in the closed position and the cable may be disengaged from the first and second pulleys when the door is in the opened position. 
     In another illustrative embodiment of this disclosure, an axis of rotation of each of the plurality of rollers is offset from a longitudinal axis of the door. Further illustratively, the cable may be coupled to the upper-most roller of the plurality of rollers. 
     In still another illustrative embodiment, the counterbalance mechanism may be located forward of the door when the door is in the horizontal, opened position. Further illustratively, the counterbalance mechanism may be positioned between the door and a front end of the storage container when the door is in both the vertical, closed position and the horizontal, opened position. 
     In yet another illustrative embodiment of this disclosure, a bottom end of the door may be positioned adjacent a horizontal section of the guide track system when the door is in the horizontal, opened position. 
     In another illustrative embodiment, the overhead door assembly may further include a pull strap assembly. The pull-strap assembly may include a pull-strap configured to be coupled at a first end to an inner surface of the sidewall of the storage container and coupled at a second end to a bottom-most roller of the plurality of rollers. Illustratively, the pull strap may include an elastic portion and a non-elastic portion. Further illustratively, the pull-strap may be engaged with first and second pulleys of the cable system when the door is in the horizontal, opened position and may be disengaged from the first and second pulleys when the door is in the vertical, closed position. 
     In still another illustrative embodiment, a pulling force of the cable may be redirected from that of a vertical force to a horizontal force as the one of the plurality of rollers of the door assembly to which the cable is coupled is moved through the curved section of the guide track when the door assembly is moved to the opened position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a rear, perspective view of a portion of a truck trailer including an overhead door assembly and showing a door of the assembly in a partially-opened position. 
         FIG. 2A  is a perspective view of the overhead door assembly of  FIG. 1  showing a door in a closed, vertical position. 
         FIG. 2B  is a side, sectional view of a guide track system of the overhead door assembly again showing the door in the closed, vertical position. 
         FIG. 3A  is a perspective view similar to  FIG. 2A  showing the door in an opened, horizontal position. 
         FIG. 3B  is a side, sectional view similar to  FIG. 2B  again showing the door in the opened, horizontal position. 
         FIG. 4  is side view of a portion of the overhead door assembly showing a cable of the overhead door assembly coupled to a roller of the door. 
         FIG. 5  is a plan view of the portion of the overhead door assembly shown in  FIG. 4 . 
         FIG. 6  is an enlarged view of a portion of  FIG. 2B  showing an end roller of the overhead door assembly. 
         FIG. 7  is an enlarged, side sectional view of a portion of the door, similar to  FIG. 6 , showing an alternative end roller assembly. 
         FIG. 8  is an enlarged, side sectional view of a portion of the door, similar to  FIGS. 6 and 7 , showing another end roller assembly. 
         FIG. 9  is an enlarged, side sectional view of a portion of the door, similar to  FIGS. 6-8 , showing yet another end roller assembly. 
     
    
    
     DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to illustrative embodiments shown in the attached drawings and specific language will be used to describe the same. While the concepts of this disclosure are described in relation to a truck trailer, it will be understood that they are equally applicable to other mobile or stationary storage containers, as well as refrigerated and un-refrigerated trailers or storage containers, which include an overheard door assembly. 
     As shown in  FIG. 1 , a truck trailer  10  includes an overhead door assembly  12  at the rear of the trailer  10 . Illustratively, as is discussed in greater detail below, the overhead door assembly  12  includes first and second guide track systems  14  each coupled to one of the two sidewalls  16  of the trailer  10 , a rotational counterbalance mechanism  18  coupled to the roof  20  of the trailer  10 , and an overhead door  22  coupled to both the guide track systems  14  and the counterbalance mechanism  18 . The overhead door  22  operates to close a rear door opening  24  of the trailer  10  defined by the sidewalls  16  of the trailer  10 , a floor  26  of the trailer  10 , and the roof  20  of the trailer  10 . 
     Illustratively, the overhead door  22  is movable relative to the guide track systems  14  between a vertical, closed position (shown in  FIGS. 2A and 2B ) and a horizontal, opened position (shown in  FIGS. 3A and 3B ). The overhead door  22  includes a plurality of lateral panels  30  coupled together by hinges  32  (shown in  FIGS. 2A and 5 ) to allow the door  22  to move along the track systems  14  between the opened and closed positions. In other words, the lateral panels  30  are disposed one on top of the other with each panel  30  hinged to the panel above  30 . Illustratively, each panel  30  of the door  22  includes a pair of lateral edge surfaces  34  (shown in  FIG. 5 ) which extend parallel to the direction of movement of the door  22  between the opened and closed positions. A series of rollers  36  is spaced along the length of each of the lateral edge surfaces  34  of the door  22  and is attached to the door  22  by a series of shafts  38 . As shown in  FIG. 5 , a roller  36  is associated with each hinge  32  such that the door  22  includes a roller  36  located at the junction between each lateral panel  30  of the door  22 . Each roller  36  is able to rotate about the respective shaft  38  and is positioned within one of the respective first and second guide track systems  14 . Each roller  36  and shaft  38  cooperate to define a roller assembly such that the door  22  includes a plurality of roller assemblies adjacent the opposite, lateral edges  34  thereof. Illustratively, while the rollers  36  are coupled to each hinge  32 , it is within the scope of this disclosure to couple the rollers  36  to the door panels  30  at other suitable locations and to provide any suitable numbers of rollers  36  on the door  22  in order to allow the door  22  to move along the guide track systems  14  between the opened and closed positions. 
     Illustratively, the overhead door assembly  12  includes the right and left guide track systems  14  such that each guide track system  14  is rigidly coupled to one of the two sidewalls  16  of the trailer  10 . The first and second guide track systems  14  are provided on either side of the doorway  24  at the rear end of the trailer  10  for receiving the rollers  36  disposed on the adjacent edges  34  of the panels  30 . While the overhead door assembly  12  includes two separate guide track systems, i.e., the right and left guide track systems  14 , for purposes of simplicity, only the left guide track system  14  is described in detail herein. It should be understood, however, that the right guide track system is generally identical to the left guide track system and includes the same or similar components. Accordingly, although only the left guide track system  14  is described, an identical, right guide track system is positioned along the interior of the opposite sidewall  16 , as shown in  FIGS. 2A and 3A  such that the rollers  36  on each lateral edge  34  of the door  22  are positioned within one of respective guide track systems. In this manner, the rollers  36  travel within a guide track system and enable the overhead door  22  to move from the vertical, closed position to the horizontal, opened position. 
     As shown in  FIGS. 2A-3B , the guide track system  14  includes first and second guide tracks  40 ,  42 . The first guide track  40  is positioned slightly below the roof  20  of the trailer  10  and includes a curved portion  52  adjacent the rear end of the trailer  10  near the door opening  24  and a generally horizontal section  48  extending parallel to the roof  20  in a direction toward a front end of the trailer  10 . In particular, the generally horizontal section  48  of the first guide track  40  is positioned adjacent to and generally abutting a bottom portion of the roof bows  97  of the trailer  10 . In other words, the first guide track  40  is positioned just below the roof bows  97  in order to optimize the location of the door  22  in the opened, horizontal position such that the door  22  is generally located in an out-of-the-way position providing an increased distance between the floor  26  of the trailer  10  and the door  22  when the door  22  is in the opened, horizontal position, as is discussed in greater detail below The second guide track  42  extends upwardly from the floor  26  of the door opening  24  and along the interior surface of the sidewall  16  of the trailer  10  until the track  42  reaches a position slightly below the roof  20  of the trailer  10 . Upon reaching an area near the roof  20 , the guide track  42  bends to create a curved portion and then continues in a generally horizontal direction parallel to the roof  20 . As such, the second guide track  42  includes a vertical section  46 , a horizontal section  50  positioned just below the horizontal section  48  of the first track  40 , and a curved section  54  interconnecting the respective vertical and horizontal sections  46 ,  50 . Illustratively, the horizontal section  48  of the first guide track  40  is positioned generally outside, or above, the horizontal section  50  of the second, or inner, guide track  42 . 
     As shown in  FIGS. 2A ,  2 B,  3 A and  3 B, the horizontal sections  48 ,  50  of the first and second guide tracks  40 ,  42  are parallel to each other. However, the radius of curvature of the curved section  52  of the guide track  40  is different from the radius of curvature of the curved section  54  of the guide track  42 . Illustratively, the curved section  52  of the first, or outer, guide track  40  defines a smaller radius of curvature than the curved section  54  of the second, inner guide track  42 . However, it is within the scope of this disclosure to provide curved sections  52 ,  54  having the same or similar radii of curvature. Further illustratively, the curved section  52  of the upper track  40  may alternatively include a larger radius of curvature than that shown in  FIGS. 2A-3B  by curving the upper track  40  up to the roof  20  of the trailer  10  in an open area between the header  61  and the first (or rear-most) roof bow  97  of the roof  20 . Illustratively, while a larger radius of curvature generally operates to provide a smoother movement of the door  22  between the vertical and horizontal positions, it is within the scope of this disclosure to provide any suitable radius of curvature for each of the curved sections  52 ,  54  to allow movement of the door between the vertical and horizontal positions. 
     As shown in  FIG. 5 , the guide track  42  has a generally “c-shaped” cross-section including a curved, inner wall  60 , a generally straight outer wall  62 , and a back wall  64 . This generally c-shaped structure of the track  42  operates to maintain the rollers  36  therein during movement of the door  22  between the closed position and the opened position. Illustratively, the back wall  64  of the guide track  42  is in contact with or in close proximity to the sidewall  16  of the trailer  10 . Although not shown, the overhead door assembly  12  includes mounting brackets to mount the guide tracks  40 ,  42  to the sidewalls  16  of the trailer  10 . Further, though not shown, the cross-sectional shape of the guide track  40  is generally the same as or similar to the cross-sectional shape of the guide track  42  to maintain any rollers of the door  22  therein during operation of the door assembly  12 . While the particular shape and structure of the guide tracks  40 ,  42  is shown and described herein, it is within the scope of this disclosure for the guide tracks  40 ,  42  to define other cross-sectional shapes suitable for guiding rollers of the door  22  during movement of the door  22  between the opened and closed positions. 
     Illustratively, the rollers  36  of the door  22  are offset rollers  36  in that the shaft  38  associated with each roller  36  is positioned adjacent and coupled to the inside surface  21  of the door  22 . As such, the axis of rotation  43  of these offset rollers  36  (i.e., along the longitudinal axis of the respective shaft  38 ) is laterally offset, or spaced-apart, a distance  45  from a longitudinal, or centerline, plane  41  extending through the door  22 . The door  22  further includes an end roller  37  (shown in  FIGS. 2B and 3B ) adjacent an upper edge  35  of the door  22 . Illustratively, the upper edge  35  of the door  22  is the upper end of the door  22  when the door  22  is in the vertical, closed position, shown in  FIGS. 2A and 2B . Illustratively, the end roller  37  is mounted via a bracket  47  on the centerline of the door  22  such that the shaft  38  of the end roller  37  defines an axis of rotation  39  that is generally aligned with (i.e., intersects) the longitudinal, centerline plane  41  through the door  22 , as shown in  FIG. 6 . To contrast, as noted above, the axis of rotation  43  of each of the remaining rollers  36  is offset from, and does not intersect, the longitudinal plane  41  of the door  22 . Further, the axis of rotation  39  of the end roller  37  is positioned above the upper edge  35  of the door  22  when viewed from the side or cross-sectionally as shown in  FIG. 6 . To contrast, the axis of rotation  43  of the offset rollers  36  is adjacent the inside surface  21  of the door  22 . Accordingly, the axis of rotation  39  of the end roller  37  is spaced laterally apart from the axis of rotation of the offset rollers  36  such that the end roller  37  is positioned within the first, or outer, track  40  of the guide track system  14  whereas the offset rollers  36  are each positioned within the second, or inner, track  42  of the system  14 , as shown in  FIGS. 2B and 3B . As is discussed in greater detail below, the end roller  37  remains within the first track  40  during movement of the overhead door  22  between the vertical, closed position and the horizontal, opened position, whereas the offset rollers  36  each remain within the second track  42  during this movement. 
     Illustratively, a diameter of the end roller  37  is smaller than a diameter of the offset rollers  36 . Accordingly, a width of the first track  40  is smaller than a width of the second track  42 . Illustratively, for example, the second track  42  may have approximately a 2 inch width while the first, or upper, track  40  may have a 1¼ inch width. It is also within the scope of this disclosure, however, for the diameter of the end roller  37  to be the same size as or larger than the diameter of the offset rollers  36 . As such, the rollers  36 ,  37  and the corresponding tracks  42 ,  40  may be any suitable size. Further illustratively, while the end roller  37  is mounted on the centerline, or longitudinal axis  41 , of the door, it is within the scope of this disclosure to mount the end roller  37  in an offset manner similar to that of the offset rollers  36 . 
     In particular, as shown in  FIGS. 7-9 , the location of the end roller  37  may be moved laterally to position the end roller  37  in a number of suitable locations on the door  22 . For example, as shown in  FIG. 7 , the end roller  37  of the door  22  is coupled to the door using a mounting bracket  147  similar to the mounting bracket  47  shown in  FIG. 6 . The mounting bracket  147  is bolted to the inside surface  21  of the door and positioned such that the shaft  38  of the roller  37  is located above the upper edge  35  of the door  22 . Further illustratively, a rearmost point or portion  55  of the end roller  37  is generally aligned with a plane  65  parallel to an outer surface  23  of the door  22 . In other words, the rearmost portion  55  of the end roller  37  is tangent to the plane  65  formed by the outer surface  23  of the door  22 . In particular, while the axis of rotation  39  of the roller  37  intersects the centerline plane  41  of the door, other arrangements may be provided wherein the axis of rotation  39  of the end roller  37  is offset from the centerline plane  41  of the door  22 . 
     For example, looking to  FIG. 8 , an alternative bracket  247  and end roller  37  arrangement is provided wherein the rearmost portion  55  of the end roller  37  is positioned rearward of the plane  65  defined by the outer surface  23  of the door  22 . Further, the axis of rotation  39  of the end roller  37  shown in  FIG. 8  is laterally offset from the centerline plane  41  of the door  22 . In particular, the axis of rotation  39  of the end roller  37  shown in  FIG. 8  is offset rearwardly from the centerline plane  41  of the door  22 . Alternatively, as shown in  FIG. 9 , an alternative bracket  347  and alternative, larger end roller  337  arrangement is provided wherein the rearmost portion  55  of the end roller  37  is tangent to, or aligned with the plane  65  defined by the outer surface  23  of the door  22 . Further, the axis of rotation  39  of the end roller  37  shown in  FIG. 9  is laterally offset from the centerline plane  41  of the door  22 . In particular, the axis of rotation  39  of the end roller  37  shown in  FIG. 9  is offset forwardly from the centerline plane  41  of the door  22 . 
     Illustratively, while the various illustrative embodiments are shown in  FIGS. 6-9 , it is within the scope of this disclosure to position the end roller  37  in any suitable location whereby an outer surface  23  of the door  22  is aligned with or forward of the rearmost point or portion  55  of the end roller  37  when the door assembly is viewed from the side, as shown in  FIGS. 6-9 , for example. In other words, the outer surface  23  of the door  22  does not extend rearward, or to the left as viewed in  FIGS. 6-9 , of the rearmost point or portion  55  of the end roller  37 . It should be noted that the shaft  38  of the end roller  37 , and thus the axis of rotation  39  of the end roller  37 , remains positioned above the upper edge  35  of the door  22 , as viewed from the side in  FIGS. 6-9 , for example, when the door  22  is in the closed position. It should further be understood that the size of the end roller  37  may be smaller or larger than that which is illustratively shown in the figures. 
     Looking still to  FIGS. 2A-3B , the overhead door assembly  12  further includes the counterbalance mechanism  18 . As is generally understood by one skilled in the art, overhead doors generally require a counterbalancing force which allows the door to be more easily moved between the opened and closed positions. Such counterbalancing force for the overhead door assembly  12  of the present disclosure is provided by the illustrative counterbalance mechanism  18 . 
     Illustratively, the counterbalance mechanism  18  is a torsion spring counterbalance mechanism and includes a lateral torsion bar  70 , a cable drum  72  positioned at each end of the bar  70 , and one or more torsion springs  71  wound around the bar  70 . Illustratively, the torsion springs may be helical torsion springs or other suitable springs or tensioning devices known to those skilled in the art. Further, while the particular counterbalance mechanism  18  disclosed herein is a torsion spring counterbalance mechanism, it is within the scope of this disclosure to alternatively provide a counterbalance mechanism using extension springs as well. 
     As is generally understood by one skilled in the art, the torsion spring  71  includes a first end operatively connected to the torsion shaft  70  and another end operatively connected to a winding mechanism  73  of the counterbalance mechanism  18 . During operation, the torsion shaft  70  rotates to allow the raising and lowering of the door. The winding mechanism  73  may be supported by a fixed support  75  at each end of the torsion shaft  70 . The torsion shaft  70  is supported for rotation between the fixed supports and the drums  72 , which are rigidly affixed to the torsion shaft  70 , and is urged to rotate therewith. The torsion springs  71  of the counterbalance mechanism  18  are typically wound during the installation of the overhead door assembly  12  such that they are provided with the necessary preset torque. The gear winding mechanism  73  is provided for setting the appropriate torque or number of winds in the spring  71 . A counter may also be provided to indicate to the installer the number of winds being given to the spring. One illustrative counterbalance mechanism, including an illustrative winding mechanism, is disclosed in U.S. Pat. Nos. 5,632,063 and 4,882,806, the disclosures of which are hereby incorporated by reference herein. 
     As further shown, the counterbalance mechanism  18  is contained within a counterbalancing housing  80 . Illustratively, the counterbalance housing  80  may include an aperture  87  therethrough to allow an operator to wind the winding mechanism  73  or another such mechanism as that disclosed in the &#39;063 patent, for example. Alternatively, the sidewall  16  of the trailer  10  may include an aperture (not shown) to provide an operator access to the end of an alternative counterbalance mechanism (not shown). This alternative counterbalance mechanism may include a ratchet and winding mechanism positioned at one end of the counterbalance mechanism in order to allow the operator to wind the counterbalance mechanism from outside the trailer  10  via the access aperture through the trailer sidewall  16 . Illustratively, the counterbalance housing  80  further includes a pair of second apertures  77  through a front sidewall of the counterbalance housing to provide an operator access to each drum  72 . 
     Looking now to  FIGS. 2A and 3A , the torsion spring, shaft  70 , and drums  72  of the counterbalance mechanism  18  are all located within the housing  80 . The housing is coupled to and extends downwardly from an inside surface of the roof  20  of the trailer  10 . Illustratively, the housing  80  has a height  82  of approximately three inches and extends laterally across the width of the trailer  10 , as shown in  FIGS. 2A and 3A  and in phantom in  FIG. 1 . As shown in  FIGS. 1 , and  2 A- 3 A, the housing  80 , and thus the counterbalance mechanism  18  contained therein, is spaced-apart a distance  84  from the rear end of the trailer  10 . Illustratively, the distance  84  is approximately 10 feet such that the housing  80  and counterbalance mechanism  18  are positioned approximately ten feet forward of the rear end of the trailer  10 . As such, and as is discussed in greater detail below, the counterbalance mechanism  18  is located forward of the door  22  when the door  22  is in the horizontal, opened position, as shown in  FIGS. 3A and 3B  such that the counterbalance mechanism  18  is always positioned between the door  22  and a front end (not shown) of the trailer  22  regardless of whether the door  22  is in the closed or opened positions. 
     While the counterbalance mechanism  18  is spaced approximately 10 feet forward of the rear end of the trailer  10 , it is within the scope of this disclosure to position the counterbalance mechanism  18  at any suitable location spaced-apart from the rear end of the trailer  10 . Illustratively, the housing  80  for the counterbalance mechanism  18  may include one or more windows, cut-outs, apertures or removable panels to allow an operator access to the components of the counterbalance mechanism  18  contained therein. As is discussed in greater detail below, the housing  80  for the counterbalance mechanism  18  operates both to protect the components of the counterbalance mechanism  18  contained therein, as well as to protect, or shield, the upper edge  35  of the door  22  (when in the opened, horizontal position) from being unintentionally impacted and moved by freight during an unloading process, for example. 
     Looking now to  FIGS. 2A-5 , the overhead door assembly  12  further includes a pair of cable systems  90  coupled to both the counterbalance mechanism  18  and the door  22  and associated with each of the right and left guide track assemblies  14 . While the overhead door assembly  12  includes both right and left cable systems  90 , only the left cable system associated with the left guide track system  14  is shown and described herein. It should be understood, however, that the right cable system is generally identical to the left cable system and includes the same or similar components. 
     Illustratively, the cable system  90  includes a first cable pulley  92  coupled to the sidewall  16  of the trailer  10  adjacent the vertical section  46  of the inner guide track  42  and a second cable pulley  94  coupled to the sidewall  16  of the trailer  10  adjacent the horizontal section  50  of the inner guide track  42 . Illustratively, as shown in  FIGS. 2A-3B , each of the first and second cable pulleys  92 ,  94  is also positioned adjacent the curved section  54  of the inner guide track  42 . In particular, the pulleys  92 ,  94  are placed at or near the radius tangent points of the curved section  54 . As shown in  FIGS. 2B ,  3 B, and  5 , each pulley  92  includes a wheel  89  defining a cable-receiving groove  91  therein, and an axle, or shaft,  93  about which the wheel  89  freely rotates. The shaft  93  of each pulley  92 ,  94  is coupled to the sidewall  16  of the trailer. 
     The cable system  90  further includes a steel counterbalance cable  96  having a first end (not shown) coupled to the counterbalance mechanism  18  and a second end  98  coupled to one of the offset rollers  36  associated with each lateral edge  34  of the door assembly  12 . In particular, the first end of the cable  96  is coupled to the respective cable drum  72  of the counterbalance mechanism  18  and is configured to be wound around the drum  72  as the door  22  is moved to the opened position. Each cable  96  extends from the respective drum  72  such that, as shown in  FIGS. 4 and 5 , the second end  98  of the cable  96  is coupled to the shaft  38  of one of the offset rollers  36 . In particular, the cable  96  is coupled to the upper-most offset roller  36 , as shown in  FIGS. 2B and 3B , and is coupled to the door  22  at a location generally within the upper half of the door  22 . Further illustratively, the attachment point of the cable  96  to the shaft  38  of the upper-most offset roller  36  is in-line with the cable pulleys  92 ,  94 , as shown in  FIGS. 4 and 5 . It should be understood, however, that the cable  96  may be coupled to any of the offset rollers  36 . As is discussed in greater detail below, the pulleys  92 ,  94  operate to pick up or “grab” the cable  96  as it passes over each pulley  92 ,  94  during movement of the door  22  between the opened and closed positions. 
     The overhead door assembly  12  further includes a rebound spring  86  coupled to the counterbalance mechanism  18  and/or the housing  80  containing the counterbalance mechanism  18 . Illustratively, the rebound spring  86  is coupled to each end of the counterbalance housing  80 . In particular, the rebound spring  86  is positioned within the horizontal portion  48  of each outer track  40  adjacent the counterbalance mechanism housing  80 . The rebound spring  86  is provided to prevent the upper end of the door  22  from forcefully engaging the counterbalance mechanism  18  when the door  22  is moved to the opened position. While the rebound spring  86  is positioned within the track  40 , it should be understood that the rebound spring  86  may be located in any suitable position along the width of the housing  80  such that the spring  86  will be impacted by the door  22  when the door  22  is moved to the opened position. In particular, each rebound spring  86  is impacted by a corresponding bumper plate  81  coupled to the upper edge  35  of the door  22 . While two illustrative rebound springs  86  are provided, it is within the scope of this disclosure to include any number of rebound springs between the counterbalance mechanism  18  and the upper edge  35  of the door  22 . Further illustratively, it is within the scope of this disclosure to use a pneumatic plunger and/or other suitable dampening or bumper-like device to prevent the upper end of the door  22  from forcefully engaging the counterbalance mechanism  18  and/or housing  80  when the door is moved to the opened position. 
     In use, the overhead door assembly  12  operates to allow the door  22  to move between the closed, vertical position shown in  FIGS. 2A and 2B  and the opened, horizontal position shown in  FIGS. 3A and 3B . In particular, when the door  22  is in the closed, vertical position, the offset rollers  36  are located within the second, or inner, guide track  42 . Specifically, the offset rollers  36  are located within the vertical section  46  of the inner guide track  42 , as shown in  FIGS. 2A and 2B . The end roller  37 , however, is positioned within the first, or outer, guide track  40 . Specifically, as shown in  FIGS. 2A and 2B , the end roller  37  is positioned within the curved section  52  of the guide track  40  at the open, front end of the guide track  40 . The cable  96  associated with each guide track system  14  is engaged with and received within a cable-receiving groove  91  of each of the cable pulleys  92 ,  94 . Illustratively, in the fully-closed position, the uppermost offset roller  36  to which the cable  96  is coupled is positioned vertically below (and offset from) the first cable pulley  92 . 
     When the door  22  is raised and moved toward the opened position, the torsion spring  71  of the counterbalance mechanism  18  unwinds such that stored tension in the spring operates to help lift the door  22  by turning the torsion shaft  70 , thus turning the cable drums  72  in the counterclockwise direction shown in  FIGS. 2A and 2B  in order to wrap the cable  96  around cable-receiving grooves in the cable drum  72 . In other words, the counterbalance mechanism  18  is used to help lift the weight of the door  22  while the cable  96  operates to first pull the door  22  vertically and then horizontally along the guide track system  14 . Illustratively, when the door  22  is lowered, the cable  96  unwraps from the drum  72  and the torsion spring  71  is rewound about the torsion shaft  70  to full tension. 
     As the door  22  is raised, the end roller  37  rides along the outer guide track  40  from its location within the curved section  52  into the horizontal section  48  of the outer guide track  40 , as shown in  FIGS. 3A and 3B . The offset rollers  36 , on the other hand, remain within the inner guide track  42  during movement of the door  22  from the closed position to the opened position. As such, the offset rollers  36  each move from their location within the vertical section  46  of the inner guide track  42 , through the curved section  54  of the inner guide track  42 , and into the horizontal section  50  of the inner guide track  42 . 
     As the door  22  is raised to the fully-opened position shown in  FIGS. 3A and 3B , the cable  96  coupled to the shaft  38  of the upper-most offset roller  36  is pulled by the rotation of the cable drum  72  to provide an upward, vertical pulling force on the door  22  to help pull the door  22  upwardly. As the door moves upwardly, the cable  96  operates to allow the cable  96  to pull the door  22  vertically along the track system  14 . As the upper-most offset roller  36  (to which the cable  96  is attached) moves along the inner guide track  42  past the first pulley  92 , the pulling force of the cable  96  is redirected and the second pulley  94  operates to pull the door  22  horizontally along the track system  14  toward the closed position. The cable  96  becomes disengaged from each of the pulleys  92 ,  94  once the upper-most roller  36  moves past the pulleys  92 ,  94  as the door  22  is raised to the fully-opened position. 
     Once in the fully-opened position, the end roller  37  is located within the horizontal section  48  of the outer guide track  40  and each of the offset rollers  36  is located within the horizontal section  50  of the inner guide track  42  in order to fully locate the entire door  22  in a horizontal position generally parallel to the roof  20  of the trailer  10 . In other words, all panels  30  of the door  22  are positioned adjacent the horizontal sections  48 ,  50  of the guide tracks  40 ,  42  when the door  22  is in the fully-opened position. Generally, no portion of the door  22  is left to rest along the curved sections  52 ,  54  of the guide tracks  40 ,  42  and into the rear door opening  24 . Accordingly, in the fully-opened position, the door  22  does not extend into the rear door opening  24  to block or obstruct any portion of the rear door opening  24 . The forward position of the counterbalance mechanism  18  from the rear door opening  24  of the trailer  10  allows the door  22  to be pulled fully to this horizontal position. Illustratively, the door opening  24  defines a height  99  of approximately 110 inches. Thus, when the door  22  is in the opened position, access to the entire, unobstructed 110 inches of the rear door opening  24  is possible. 
     As noted above, the overhead door assembly  12  includes the rebound springs  86 . As the door  22  moves to the full-opened position, the counterbalance mechanism  18  operates to pull the door  22  until the upper edge  35  of the door  22 , and specifically the bumper plates  81  of the door, engage the rebound springs  86 , which are positioned just rearward of the counterbalance housing  80 . By absorbing the impact of the door  22 , therefore, the rebound springs  86  prevent the door  22  from forcefully crashing into and potentially damaging the counterbalance housing  80  as the door  22  is moved to the fully-opened position. 
     As the door  22  is moved from the fully-opened position back to the closed position, the torsion spring  71  of the counterbalance mechanism  18  is stretched to provide a force which counteracts the weight of the door  22 . As such, the torsion spring  71  controls the descent of the door  22  as the door  22  moves toward the closed position. As the door  22  moves toward the closed position, the end roller  37  remains within the outer guide track  40  while the offset rollers  36  remain within the inner guide track  42 . As the upper-most offset roller  36  moves through the curved section  54  of the inner track  42 , the cable  96  attached to the shaft  38  of that roller  36  is laid over the second pulley  94  and then the first pulley  92  to rest within the grooved section  91  of the respective pulleys  92 ,  94 . Once the cable  96  is laid onto the first pulley  92 , the force provided by the cable  96  is redirected from that of a horizontal force to a vertical force. Accordingly, in use, the cable pulleys  92 ,  94  allow the cable  96  to be redirected as the upper-most offset roller  36  to which the cable  96  is attached goes around the curved section  54  of the inner guide track  40 . Thus, as the door  22  is moved to the opened position, the cable  96  begins by pulling in the vertical direction, and then as the upper-most offset roller  36  goes around the curved section  54 , the cable operates to pull the door  22  in the horizontal direction. Illustratively, it should be noted that the cable  96  of the cable system  90  is located entirely on the inside of the trailer  10 . As such, the cable  96  does not interrupt any seal between the door  22  and the trailer  10  when the door  22  is in the closed, vertical position. 
     As noted above, the counterbalance housing  80  is positioned approximately ten feet forward of the rear door opening  24  of the trailer  10 . The housing  80  is coupled to the roof  20  of the trailer  10  and depends downwardly from the roof  20  approximately three inches. Illustratively, the height of the housing  80  is approximately the same as the height of a header  61  of the trailer  10 . The housing  80  extends laterally across a width of the trailer  10  and is generally parallel to the header  61  of the trailer. When the door  22  is in the fully-opened position, the door is generally positioned between the header  61  and the counterbalance housing  80 , as shown in  FIGS. 3A and 3B . In other words, the horizontal sections  48 ,  50  of the guide tracks  40 ,  42  are located between the header  61  and the housing  80  to support the door  22  on the rollers  36 ,  37  thereon. 
     Accordingly, because the door  22  is maintained in the space between the header  61  and the housing  80 , the upper edge  35  of the door  22  is protected or blocked by the housing  80  in order to prevent this edge  35  of the door  22  from being hit or bumped by freight during an unloading process, for example. In other words, the counterbalance housing  80  operates as a bumper to protect the upper edge  35  of the door  22  when the door  22  is in the opened position. As such, the location of the counterbalance housing  80  allows the door  22  to be located in a protected and out-of-the-way position when the door  22  is in the opened position such that persons, freight, or vehicles, such as forklifts, which are used to carry freight into and out of the trailer  10  do not accidentally bump the upper edge  35  of the door  22 , thus potentially causing the door  22  to unintentionally move toward the closed position onto any persons or freight which may be positioned in the rear door opening  24 . Furthermore, the housing  80  also operates to protect the torsion shaft  70 , the torsion spring  71 , and the cable drums  72  located therein from persons, freight, or vehicles which might otherwise accidentally run into the counterbalance mechanism  18  and/or the door  22 . 
     Looking to  FIGS. 2A and 3A , a pull-strap assembly  100  is provided to allow an operator to more easily move the door  22  from the horizontal, opened position to the vertical, closed position. As shown in  FIGS. 2A and 3A , the pull-strap assembly  100  includes a spool  104  pivotally coupled to the inner surface of the sidewall  16  by a mounting plate  102 . The pull-strap assembly  100  further includes a pull-strap  106  having a first end wound around the spool  104  and a second end attached to the axle  38  of the bottom-most roller  36  of the door  22 . While the Illustratively, the pull strap  106  includes an elastic portion  108  coupled to the sidewall  16  and a generally non-elastic portion  110  coupled to the door  22 . The elastic and non-elastic portions  108 ,  110  are coupled to each other. 
     In use, as the door  22  is moved to the horizontal, opened position, the non-elastic portion  110  of the pull-strap  106  is laid across the cable pulleys  92 ,  94 . Illustratively, once the non-elastic portion  110  of the pull-strap  106  engages the cable pulley  92 , the elastic portion  108  pull-strap  106  is stretched and thus tensions itself as the door  22  is moved to the horizontal, opened position. As noted above, when the door  22  is in the horizontal, opened position, the door  22  is fully positioned on the horizontal sections  48 ,  50  of the tracks  40 ,  42 . In other words, generally no portion of the door  22  is position in the curved sections  52 ,  54  of the tracks  40 ,  42  such that generally no portion of the door  22  is left to hang downwardly into the rear door opening  24 . Thus, in order to move the door  22  from this horizontal, opened position to the vertical, closed position, an operator grabs the portion of the pull-strap  106  positioned below the pulley  92  and pulls downwardly on the pull-strap  106 . The pulleys  92 ,  94  operate to translate this downward force into a horizontal, pulling force on the door  22  in order to move the door  22  horizontally and then vertically toward the closed position. 
     While the invention has been illustrated and described in detail in the foregoing drawings and description, the same is to be considered as illustrative and not restrictive in character, it being understood that only illustrative embodiments thereof have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.