Abstract:
A mechanism raises and lowers a tailgate provided on a dump box of a dump truck, trailer, or similar vehicle. The dump box has an open end and is supported on the frame for movement between a lowered position for storing and transporting items and a raised position for dumping the items out of the dump box. A tailgate is supported on the bump box for movement between a closed position, wherein the tailgate closes the open rear end of the dump box, and an opened position, wherein the tailgate is spaced away from the open end of the dump box. A double cylinder assembly extends between the dump box and the tailgate for selectively moving the tailgate between the closed and opened positions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/959,394, filed Jul. 13, 2007, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates in general to mechanisms for raising and lowering a tailgate provided on a dump box of a dump truck, trailer, or similar vehicle. In particular, this invention relates to a double cylinder assembly for raising and lowering such a tailgate that is pivotably supported on the dump box. 
     A typical dump truck includes a dump box that is movable (usually by pivoting) between a lowered position (for storing and transporting items) and a raised position (for dumping the items out of the dump box). A typical dump box includes a floor, a pair of side walls, a front wall, and an open rear end for accomplishing this function. Frequently, the open rear end of the dump box includes a pair of upstanding corner posts that are each formed from a hollow rectangular member. A tailgate is supported on the side walls of the dump box adjacent to the open rear end for pivoting movement between a closed position (wherein the tailgate closes the open rear end of the dump box for facilitating the storing and transporting of the items therein) and an opened position (wherein the tailgate is pivoted away from the open rear end of the dump box for facilitating the dumping of the items out of the dump box). 
     In many instances, the tailgate is affirmatively moved between the opened and closed positions by means of a cylinder (typically a pneumatic cylinder) that extends between the dump box and the tailgate. When the cylinder is extended, the tailgate is pivoted away from the open rear end of the dump box to the opened position. When the cylinder is retracted, the tailgate is pivoted toward the open rear end of the dump box to the closed position. In this manner, the operation of the cylinder controls the movement of the tailgate between the opened and closed positions. 
     In the past, the cylinder has typically been provided on the dump truck in one of two locations. In a first generally vertical orientation, a cylinder has been located within either or both of the hollow upstanding corner posts provided on the open rear end of the dump box. This generally vertical orientation is desirable because it does not expand the overall width of the vehicle, which can be limited by practical considerations or by regulation. However, the internal space that is available within each of these corner posts is limited, thus limiting the size of the cylinder that can be provided within each of the corner posts (and, as a result, the amount of force that is available to move the tailgate between the opened and closed positions) is relatively limited. In a second generally horizontal orientation, a cylinder has been located on the outside of either or both of the side walls of the dump box. This generally horizontal orientation is desirable because it is simple and inexpensive to install. However, as mentioned above, it does undesirably expand the overall width of the vehicle. Thus, it would be desirable to provide an improved mechanism for raising and lowering a tailgate provided on a dump box of a dump truck, trailer, or similar vehicle that avoids these problems. 
     SUMMARY OF THE INVENTION 
     This invention relates in general to an improved mechanism for raising and lowering a tailgate provided on a dump box of a dump truck, trailer, or similar vehicle. The dump box has an open end and is supported on the frame for movement between a lowered position for storing and transporting items and a raised position for dumping the items out of the dump box. A tailgate is supported on the bump box for movement between a closed position, wherein the tailgate closes the open rear end of the dump box, and an opened position, wherein the tailgate is spaced away from the open end of the dump box. A double cylinder assembly extends between the dump box and the tailgate for selectively moving the tailgate between the closed and opened positions. 
     Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a prior art dump truck including a conventional single cylinder assembly. 
         FIG. 2  is an enlarged perspective view of a portion of the prior art dump truck illustrated in  FIG. 1 . 
         FIG. 3  is a further enlarged perspective view, partially broken away, of a portion of the prior art dump truck illustrated in  FIGS. 1 and 2 . 
         FIG. 4  is a perspective view of a dump truck including a first embodiment of a double cylinder assembly in accordance with this invention. 
         FIG. 5  is an enlarged perspective view of a portion of the dump truck illustrated in  FIG. 4 . 
         FIG. 6  is a further enlarged perspective view, partially broken away, of a portion of the dump truck illustrated in  FIGS. 4 and 5 . 
         FIG. 7  is a further enlarged perspective view of the double cylinder assembly illustrated in  FIGS. 4 ,  5 , and  6  shown in a retracted position. 
         FIG. 8  is a side elevational view of the double cylinder assembly illustrated in  FIG. 7 . 
         FIG. 9  is a top plan view of the double cylinder assembly illustrated in  FIGS. 7 and 8 . 
         FIG. 10  is a perspective view similar to  FIG. 7  showing the double cylinder assembly in an extended position. 
         FIG. 11  is a side elevational view similar to  FIG. 8  showing the double cylinder assembly in an extended position. 
         FIG. 12  is a side elevational view of a dump truck including a second embodiment an alternate embodiment of a double cylinder assembly in accordance with this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, there is illustrated in  FIG. 1  a dump truck, indicated generally at  10 , including a frame that supports a prior art dump box  11  that is pivotable between a lowered position (for storing and transporting items) and a raised position (for dumping the items out of the dump box  11 ). The prior art dump box  11  includes a floor  12 , a pair of side walls  13 , a front wall  14 , and an open rear end  15 . The open rear end  15  of the prior art dump box  11  has a pair of upstanding corner posts  16  that are each formed from a hollow rectangular member. A tailgate  17  is supported on the side walls  13  of the prior art dump box  11  adjacent to the open rear end  15  for pivoting movement between a closed position (wherein the tailgate  17  closes the open rear end  15  of the prior art dump box  11 ) and an opened position (wherein the tailgate  17  is spaced away from the open rear end  15  of the prior art dump box  11 , as shown in  FIG. 1 ). The tailgate  17  is moved between the opened and closed positions by means of one or more single cylinders that, as described above, have been secured to the dump truck  10  in one of two locations. 
     As more clearly shown in  FIGS. 2 and 3 , a conventional single cylinder assembly, indicated generally at  20 , is provided in a vertical orientation within each of the hollow rectangular beams of the corner posts  16  of the prior art dump box  11 , as described above. As shown therein, each of the conventional single cylinder assemblies  20  includes a single cylinder  21 . The single cylinder  21  is conventional in the art and may be embodied as a hydraulically or pneumatically actuated cylinder. The single cylinder  21  has a piston rod  22  associated therewith. As is well known in the art, the piston rod  21  can be extended from or retracted within the single cylinder  21  as desired. The end of the piston rod  22  is connected through a yoke  23  to the tailgate  17  of the prior art dump box  11 . 
     To open the tailgate  17  of the prior art dump box  11 , the single cylinder assembly  20  is actuated in a conventional manner to extend the piston rod  22  from the cylinder  21 . As a result, the tailgate  17  of the prior art dump box  11  is caused to pivot from a closed position to an opened position. To close the tailgate  17  of the dump box  11 , the single cylinder assembly  20  is actuated in a conventional manner to retract the piston rod  22  within the cylinder  21 . As a result, the tailgate  17  of the prior art dump box  11  is caused to pivot from the opened position to the closed position. 
     Referring now to  FIGS. 4 ,  5 , and  6 , there is illustrated a dump truck, indicated generally at  30 , in accordance with a first embodiment of this invention. The dump truck  30  includes a frame supporting a dump box  31  that is pivotable between a lowered position (for storing and transporting items) and a raised position (for dumping the items out of the dump box  31 ). The dump box  31  includes a floor  32 , a pair of side walls  33 , a front wall  34 , and an open rear end  35 . The open rear end  35  of the dump box  31  has a pair of upstanding corner posts  36  that are each formed from a hollow rectangular member. A tailgate  37  is supported on the side walls  33  of the dump box  31  adjacent to the open rear end  35  of the dump box  31  for pivoting movement between a closed position (wherein the tailgate  37  closes the open rear end  35  of the dump box  31 ) and an opened position (wherein the tailgate  37  is spaced away from the open rear end  35  of the dump box  31 , as shown in  FIG. 4 ). 
     A double cylinder assembly, indicated generally at  40 , is provided within each of the hollow rectangular members of the corner posts  36  of the dump box  31  for moving the tailgate  37  between the opened and closed positions. The structure of one of the double cylinder assemblies  40  is illustrated in detail in  FIGS. 7 through 11 . As shown therein, each of the double cylinder assemblies  40  includes first and second cylinders  41  and  42  that are disposed adjacent to one another. The first and second cylinders  41  and  42  are, of themselves, conventional in the art and may be embodied as hydraulically or pneumatically actuated cylinders. Each of the first and second cylinders  41  and  42  has a respective piston rod  41   a  and  42   a  associated therewith. As is well known in the art, the piston rods  41   a  and  42   a  can be extended from or retracted within the associated first and second cylinders  41  and  42  as desired. The piston rods  41   a  and  42   a  are connected to a cross bar  43  for concurrent extending and retracting movement. The cross bar  43  is connected to a yoke  44  that, in turn, is connected to the tailgate  37  of the dump box  31 . As best shown in  FIG. 7 , each of the double cylinder assemblies  40  is generally rectangular in shape when viewed from each end thereof. 
     To open the tailgate  37  of the dump box  31 , the double cylinder assemblies  40  are actuated in a conventional manner to extend the piston rods  41   a  and  42   a  from the respective first and second cylinders  41  and  42 . As a result, the cross bar  43  and the yoke  44  are similarly extended, causing the tailgate  37  of the dump box  31  to pivot from a closed position to an opened position. To close the tailgate  37  of the dump box  1131 , the double cylinder assemblies  40  are actuated in a conventional manner to retract the piston rods  41   a  and  42   a  within the respective first and second cylinders  41  and  42 . As a result, the cross bar  43  and the yoke  44  are similarly retracted, causing the tailgate  37  of the dump box  31  to pivot from the opened position to the closed position. 
     The two double cylinder assemblies  40  fit more efficiently within the respective hollow rectangular shape of the corner posts  36  than a conventional single pneumatic cylinder having a square or circular cross sectional shape. Therefore, the two double cylinder assemblies  40  provide more force than the single pneumatic cylinder could provide for a given size of the corner posts  36 . 
     Referring now to  FIG. 12 , there is illustrated a dump box, indicated generally at  50 , in accordance with a second embodiment of this invention. The dump truck  50  includes a dump box  51  that is pivotable between a lowered position (for storing and transporting items) and a raised position (for dumping the items out of the dump box  51 ). The dump box  51  includes a floor  52 , a pair of side walls  53  (only one of which is shown in  FIG. 12 ), a front wall  54 , and an open rear end (not shown in  FIG. 12 ). A tailgate  57  is supported on the side walls  53  of the dump box  51  adjacent to the open rear end  55  of the dump box  51  for pivoting movement between a closed position (wherein the tailgate  57  closes the open rear end  55  of the dump box  51 ) and an opened position (wherein the tailgate  57  is spaced away from the open rear end  55  of the dump box  51 . A double cylinder assembly, indicated generally at  60 , is provided on either or both of the side walls  53  of the dump box  51 . The structure and manner of operation of the double cylinder assemblies  60  can be the same as described above in connection with  FIGS. 7 through 11 . 
     The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.