Patent Publication Number: US-6698052-B2

Title: Hydraulically assisted restraint device

Description:
FIELD OF INVENTION 
     This invention relates to a device for restraining the upward movement of a dock and particularly relates to a hydraulically assisted restraint device. This invention also relates to an assembly for holding a dock relative a vehicle as well as a method of holding down a spring loaded dock having a pivotal end and a moveable distal end. 
     BACKGROUND ART 
     Dock levellers generally comprise hinged ramp structures which are disposed in vehicle loading docks to provide a ramp extending between a vehicle load bed and the loading dock to facilitate movement of cargo between the dock and the vehicle and to overcome any difference in elevation between the floor of the vehicle load bed and the dock. 
     Various structures and devices have heretofore been manufactured and sold some of which include extension lip members. Each of the devices and assemblies in the prior art are subjected to the change in height of the vehicle load bed relative the dock during loading and unloading operations. 
     Generally speaking the dock has a hinged or pivotal end and a moveable distal end which can move vertically relative to the vehicle&#39;s load bed. Accordingly as the loaded vehicle is backed up towards the dock the distal end is adjusted so as to rest generally at the edge of the load bed of the vehicle. The suspension system of a vehicle is generally compressed due to the weight of the cargo when initially adjusting the dock relative to the load bed. Upon unloading of the cargo, whether by pallet truck or otherwise the weight of the cargo diminishes and the potential energy of the suspension system in the vehicle increases since the weight of the cargo is no longer there to balance the force in the suspension system which generally includes springs. Accordingly such dock levelling devices and apparatus are subject to rapid wear and unwanted damage as a result of this type of movement. 
     Various devices have heretofore been devised. For example, U.S. Pat. No. 6,327,733 B1 relates to a pit type dock leveller having a frame adapted to be fixedly mounted at a dock with a deck, pivotally mounted to the frame at one end thereof, and having a pivotal lip at the other end. A spring is mounted to the deck and the frame to support and raise the deck. A hydraulic actuator is coupled to the deck and to a pivotal link member that is mounted to the frame. In a powered mode, the hydraulic unit acts as a power assist for the springs to move the deck from a generally horizontal stored position to an operative position. Such device positions the dock by use of an electric hydraulic power utilizing the hydraulic cylinder to move the dock up. 
     Moreover U.S. Pat. No. 6,163,913 discloses a dock leveller including a pivotal mounted ramp and a lip member pivotally mounted to the distal end of the ramp and moveable between an extended position and a depending position for forming a path between a loading dock and a load bed of a vehicle. A motor operated linear power screw type actuator is connected to the ramp for moving the ramp to an elevated position and includes an extension member which is engageable with a second tube and telescope relationship in such a way that the actuator tube may be controlled after positioning the ramp to engage the load bed of a vehicle so that the actuator is not subject to forces exerted by the ramp during oscillatory movement while the vehicle is being loaded or unloaded. This device generally describes a hydraulic cylinder used to hold up the dock and protect the dock from sudden downward movements. 
     Moreover U.S. Pat. No. 5,832,554 relates to a dock leveller typically powered by electric actuator or other motive source having a frame and a deck pivotally mounted to the frame. 
     Furthermore U.S. Pat. No. 5,856,355 relates to a safety device for a vertically stored dock leveller. Electric power is required to allow the dock leveller to be lowered and the dock leveller will stop if electrical power to the control circuit is interrupted. 
     Furthermore U.S. Pat. No. 5,526,545 also relates to a dock moveable by hydraulic cylinder which mechanism returns a loading dock into a stored position automatically. 
     These and other devices illustrate the use of devices which hold up docks. There have also been mechanical devices such as wheel style pulley systems which hold docks downwardly as well as mechanical rachet type hold down systems, which can come apart if subjected to increased upward pressure due to unloading of a vehicle. 
     It is an object of this invention to provide an improved hydraulic hold down system. 
     It is an object of this invention to provide an improved device for restraining the upward movement of a dock and particularly an assembly for holding a dock relative a vehicle. 
     DISCLOSURE OF INVENTION 
     It is an aspect of this invention to provide a device for restraining the upward movement of a dock comprising a hydraulic cylinder having a fixed end; a piston slideably disposed in said cylinder so as to define opposed first and second chambers; a rod having one end connected to said slideable piston, extending through said first chamber and having another end adapted for connection to said dock; hydraulic reservoir containing hydraulic fluid communicating with said first chamber; valve means disposed between said reservoir and said first chamber, said valve means having open position permitting said hydraulic fluid to flow from said first chamber to said reservoir and extending said rod in response to said upward movement of said dock; a closed position stopping the flow of said hydraulic fluid from said first chamber to said reservoir and restraining the upward movement of said dock. 
     It is a further aspect of this invention to provide an assembly for holding a dock relative a vehicle comprising a dock having one end moveable relative said vehicle; means for urging said one end of said dock upwardly relative said vehicle; a hydraulic cylinder having a fixed end relative said dock; a piston slideably disposed in said cylinder so as to define opposed first and second chambers; a rod having one end connected to said slideable piston extending through said first chamber and having another end connected to said moveable dock; hydraulic reservoir containing hydraulic fluid communicating with said first chamber; valve means disposed between said reservoir and said first chamber having an open position permitting said hydraulic fluid to flow from said first chamber to said reservoir so as to extend said rod in response to said upward movement of said dock; a closed position stopping the flow of said hydraulic fluid from said first chamber to said reservoir and restraining said urging means from urging said upward movement of said one end of said dock; means for moving said valve means between said open and closed positions. 
     It is yet another aspect of this invention to provide a method of holding down a spring loaded dock having a pivotable end and a distal end with a hydraulic cylinder having a valve and a piston slideably disposed in said cylinder so as to define opposed first and second chambers, and a rod having one end connected to said piston, said rod extending through said first chamber and having another end extending outwardly of said first cylinder and connected to said dock comprising the steps of fixing one end of said cylinder relative said dock; connecting said another end of said rod to said dock; opening said valve so as to extend said rod as said spring loaded dock rises; closing said valve to lock said rod in said position and hold said spring loaded dock. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of the assembly for holding a dock relative a vehicle. 
     FIG. 2 is a full cross-sectional view through the hydraulic cylinder. 
     FIG. 3 is a side elevational view showing the hydraulic cylinder in a closed position and an open position. 
     FIG. 4 is a schematic diagram of the hydraulic cylinder. 
     FIG. 5 is another side elevational view of the invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     In the description that follows, like parts are marked throughout the specification and the drawings with the same respective reference numerals. The drawings are not necessarily to scale and in some instances proportions may have been exaggerated in order to more clearly depict certain features of the invention. 
     FIGS. 1 and 2 illustrate the device  2  for restraining the upward movement of a dock  4 . The dock  4  is generally comprised of a hinged or pivotal end  6  and a distal end  8  which may include an extendable lip  10  which is well known to those persons skilled in the art. The distal end  8  is adapted to be moved vertically upwardly or downwardly relative to a vehicle  12  as shown in FIGS. 3 and 4. The distal end  8  is adapted to be moved vertically up or down in a manner to be described herein so as to level the height H of the vehicle  12  relative to the height h of a loading platform  14 . 
     The dock  4  may include a frame  16  and may pivot about the pivotable end  6  above a pit  18  which pit  18  may include the various mechanisms for movement of the dock to be described herein. 
     Generally speaking the dock  4  is urged upwardly by means of structure which causes the dock to be moved upwardly. As shown in FIG. 1, such upwardly moving means may comprise of spring loaded means  20  having a plurality of springs  22 ,  24 ,  26  and  28 . One end  30  of each of the springs  22 ,  24 ,  26  and  28  are fixed or anchored to the pit  18  and the other end  32  of each of the springs  22 ,  24 ,  26  and  28  are connected to one end of an arm assembly  34  so as to cause the arm  36  to rotate about pivot  38  and thereby urge the dock upwardly. A roller  40  is generally utilized in order to reduce friction. 
     Any spring biasing means or upwardly moveable dock means may be utilized and the invention should not be limited to the spring loaded means shown in FIG.  1 . 
     Accordingly the dock is biased in an upward position by means of the spring loaded means  20 . 
     A device  2  is utilized to restrain the upward movement of the dock. Generally speaking the device comprises a hydraulic cylinder  50  having a fixed end. 52  and a piston  54  slideably disposed in the cylinder so as to define opposed first chamber  56  and second chamber  58 . A rod  60  has one end  62  connected to the slideable piston  54  and extends through the first chamber  56  and has another end  64  connected to the dock  4 . A hydraulic reservoir  66  contains hydraulic fluid  68  for communicating with the first chamber  56 . In other words, the first chamber  56  is filled with hydraulic fluid. Any suitable hydraulic fluid can be utilized, one example of which includes hydraulic aircraft fluid. 
     A valve means  70  is disposed between the reservoir  66  and the first chamber  56 . 
     FIG. 4 illustrates one example of the valve means  70  which comprises a ball  72 , a seat  74 . The valve means  70  as shown in FIG. 4 generally comprises a check valve which is biased in a closed or blocked position. The closed or blocked position corresponds to the ball  72  bearing against the seat  74 . Hydraulic fluid  68  can not communicate with the reservoir  66  in the closed position since the ball  72  bears against the seat  74 . However, the ball  72  may be separated from the seat  74  by utilizing separating means  80  which in the figures comprise a pull chain  82 . The pull chain  82  is connected at one end  84  to an assembly which will separate the ball  72  from the seat  74  thereby permitting communication of the hydraulic fluid  68  from the first chamber  56  to the reservoir  66 . Upon moving the valve means  70  to an open or unblocked position the upward movement of the spring means  20  will cause the deck  4  to move upwardly or pivot about the pivot end  6  thereby extending the rod  60  since the end of the rod  64  is connected to the deck  4 . 
     The pull chain  82  extends through an appropriate aperture  86  located in the deck  4 . Accordingly a user may pull on the pull chain  86  thereby releasing the locking device of the hydraulic cylinder  2  and therefore the springs  22  move the deck upwardly relative a vehicle. As the deck  4  moves upwardly by means of the spring means  20  the rod  60  is extended whereby the volume of the first chamber  56  diminishes while the volume of the second chamber  58  enlarges. Upon releasing the check valve  86  the valve means  70  closes stopping further communication of hydraulic fluid  68  from the first chamber  56  to the reservoir  68 . Accordingly the position of the deck  4  is “locked” and the hydraulic device  2  restrains further upward movement of the dock  4 . 
     The spring-loaded means  20  is selected to lift the dock  4  when the chain is released. Therefore once a user pulls the pull chain  80  the check valve  70  opens permitting hydraulic fluid  68  to move from the first cylinder  56  back into the reservoir  68  extending the rod  60  as the distal end  8  of the dock moves upwardly. 
     Thereafter a vehicle may be backed up against the dock  4  in which event the distal end  8  would be higher than the height H of the vehicle  12 . Thereafter a person may walk along the dock causing the distal end  8  to move downwardly due to the weight of the person until the height is substantially the same as the height H of the vehicle. The rod  60  in such event would be forced downwardly opening the check valve  70  causing hydraulic fluid to flow from the reservoir  66  back into the first chamber  56  thereby slightly expanding the volume of the first chamber  56 . Once the hydraulic cylinder  2  adjusts to the height of the vehicle  12  a tow motor may be used to unload the load from the vehicle unto the ramp  4  and platform  14 . 
     As the vehicle is unloaded the springs  90  of the vehicle would expand thereby creating an upward force on the distal end  8  of the dock  4 . 
     The hydraulic cylinder  2  is also equipped with a bypass valve  92  as shown in FIG. 2 which would automatically open at a preselected position when the force from the spring  90  reaches a selected value. Without the bypass valve  92  it  5  is possible that the end of the vehicle  12  may exert such a force at the distal end  8  to excessively wear out the dock mechanism. 
     The bypass valve  92  may be selected at a certain pressure such as for example 2000 pounds in which event hydraulic fluid  68  in the first chamber  56  would flow back into the reservoir  66  automatically extending rod  60  upwardly as well as the dock  4  to relieve the pressure at the distal end  8  created by the expansion of the vehicle&#39;s springs  90 . 
     FIG. 3 shows the device  2  and dock  4  in a down position (hidden lines)  15  as well as showing an extended or highest position where the chain has been pulled. FIG. 4 shows the dock  4  in a working or loading position, which may be in a horizontal position, but need not be. 
     The second chamber  52  includes a vent hole  94  which vents to the atmosphere. 
     Alternatively the valve means can comprise an electric operated lock valve for opening and closing the communication of the hydraulic fluid  68  between the reservoir  66  and the first chamber  56  electrically. In one example the electric operated lock valve may comprise a solenoid valve. 
     The assembly as shown in FIG. 1 holds the dock  4  relative the vehicle  12  and comprises: 
     (a) a dock  4  having one end  8  moveable relative the vehicle  12 ; 
     (b) means  20  for urging one end  8  of the dock  4  upwardly relative the vehicle  12 ; 
     (c) hydraulic cylinder  50  having: 
     (i) a fixed end  52  relative dock  4 ; 
     (ii) a piston  54  slideably disposed in the cylinder  50  so as to define opposed first and second chambers  56  and  58  respectively; 
     (iii) a rod  60  having one end  62  connected to the slideable piston  54  extending through the first chamber  56  and having another end  64  connected to the moveable dock  4 ; 
     (d) a hydraulic reservoir  66  containing hydraulic fluid  68  communicating with the first chamber  56 ; 
     (e) a valve means  70  disposed between the reservoir  66  and the first chamber  56  having: 
     (i) an open position permitting the hydraulic fluid  68  to flow from the first chamber  56  to the reservoir  66  so as to extend the rod  60  in response to the upward movement of the dock  4 ; 
     (ii) a closed position stopping the flow of the hydraulic fluid  68  from the first chamber  56  to the reservoir  66  and restrain the urging means  20  from urging the upward movement of one end  8  of the dock  4 ; 
     (f) means  80  for moving the valve means  70  between the open and closed positions. 
     Accordingly the device  2  and the assembly as shown in FIG. 1 discloses a method of holding down a spring loaded dock  4  comprising the steps of: 
     (a) fixing one end  52  of the cylinder  50  relative the dock  4 ; 
     (b) connecting the other end  64  of the rod to the dock  4 ; 
     (c) opening the valve  70  so as to extend the rod  60  as the spring loaded dock  4  rises 
     (d) closing the valve  70  to lock the rod  60  in said position and hold said spring loaded dock  4 . 
     Various embodiments of the invention have now been described in detail. Since changes in and/or additions to the above-described best mode may be made without departing from the nature, spirit or scope of the invention, the invention is not to be limited to said details.