Abstract:
The invention relates to a portable load lifting bed including a base frame and a bed frame moveably mounted for movement between an upper position and a lower position. A plurality of guides connect the bed to the base frame and at least one actuator provides force for moving the bed frame between the upper position and the lower position.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to a portable lifting bed for hauling cargo that is moveable between an upper position and a lower position. 
   U.S. Pat. No. 6,273,435 shows a trailer with a non-tilting movable bed. This trailer includes a hydraulic cylinder which is connected to a linkage between a base frame and a bed frame. Extension of the hydraulic cylinder causes the linkage to articulate and causes movement of the bed frame relative to the base frame. The bed frame is guided in a series of tracks between an elevated position and a lowered position. 
   The device of U.S. Pat. No. 6,273,435 has the disadvantage of requiring a complicated mechanical linkage between the hydraulic cylinder and the bed frame and the base frame. Furthermore, the hydraulic cylinder rises and lowers in unison with the bed frame, rather than being stationary relative to the base frame. 
   Therefore a primary objective of the present invention is to provide a portable lifting bed with a moveable bed that lowers to the ground for easy loading. 
   A further objective of the present invention is to provide a portable lifting bed that is suitable for use with a pull type trailer or a self-powered vehicle. 
   A further objective of the present invention is to provide a portable lifting bed which can be moved from an upper position to a lower position without tilting for easy loading and unloading of contents. 
   A still further object of the present invention is to provide a portable lifting bed having a new, safe design. 
   A still further objective of the present invention is to provide a portable lifting bed which has extensible lifters extending parallel to the direction of movement of the bed. 
   A still further objective of the present invention is to provide a portable lifting bed which is easy to use and economical to manufacture. 
   The means and method of accomplishing these and other objectives will become apparent in the following description of the invention. 
   BRIEF SUMMARY OF THE INVENTION 
   The foregoing objects may be achieved by a portable lifting bed supported on a supporting surface. The lifting bed comprises a base frame supported on the supporting surface. It includes a bed frame having an upwardly presented bed surface. At least two mounting mechanisms engage both the base frame and the bed frame and guide the bed frame for movement from an elevated position wherein the bed surface is elevated above the supporting surface to a lowered position wherein the bed surface is closely adjacent the supporting surface. An actuator includes a first elongated actuator member that is mounted to a second elongated actuator member for longitudinal extensible movement with respect to the second actuator member. The first actuator member is attached to the base frame and the second actuator member is attached to the bed frame for causing movement of the bed frame between its elevated and lowered positions. 
   According to one feature of the invention the two mounting mechanisms each comprise an elongated track on one of the bed frame and the base frame and a track follower guided in the track and connected to the other of the base frame and the bed frame. 
   According to another feature of the present invention the elongated tracks each extend from an upper track end in an inclined downward and horizontal direction to a lower track end. 
   According to another feature of the present invention the first and second actuator members include longitudinal first and second actuator member axes respectively. Those two actuator axes extend in a direction approximately parallel to the elongated tracks. 
   According to another feature of the present invention the bed frame and the base frame each include a forward end, a rear end, and opposite sides. The first actuator member always is positioned between the forward and rear ends of the base frame and the second actuator member is always positioned between the forward and rear ends of the bed frame throughout movement of the bed frame between the elevated and lowered positions. 
   According to another feature of the present invention, one of the first and second actuator members is a cylinder and the other is a piston and rod assembly that is longitudinally extensible and retractable with respect to the cylinder. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of the portable lifting bed attached to a self-powered vehicle. 
       FIG. 2  is a rear view of a portable lifting bed attached to a self-powered vehicle. 
       FIG. 2A  is an enlarged sectional view of the guide track with a roller assembly within. 
       FIG. 3  is a rear perspective view of the portable lifting bed attached to a self-powered vehicle, the moveable bed trailer in the raised position. 
       FIG. 4  is a rear perspective view of the portable lifting bed attached to a self-powered vehicle in the lower position. 
       FIG. 5  is an enlarged view of the diagonal guide and actuator in a raised position. 
       FIG. 6  is an enlarged view of the diagonal guide and actuator in a lower position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings, numeral  10  generally refers to the portable lifting bed. 
   As seen in  FIG. 1 , the portable lifting bed  10  may be attached to a self-powered vehicle  20  by a swivel hitch  22  and a tow bar  34 . The self-powered vehicle has wheels  24  supporting the self-powered vehicle  20  and the moveable bed trailer  10  a distance from the ground. 
   The self-powered vehicle  20  has an engine  25  that powers a lifting system or hydraulic system  26 . The engine  25  also powers the movement of the self-powered vehicle  20 . 
   The self-powered vehicle  20  is steered by a steering wheel  28 . 
   The self-powered vehicle  20  has seats  30  displaced from the steering wheel  28  for easy access by the driver to the lifting system  26  and the steering wheel  28 . 
   The self-powered vehicle also has a vehicle frame member  32 . As seen in  FIG. 1 , the vehicle frame member  32  is in alignment with the moveable bed trailer base frame  40 . In this configuration, the self-powered vehicle joins with the moveable bed trailer base frame. This provides structural integrity between the trailer and the moveable bed trailer wheels  42 . 
   Although  FIG. 1  as shown has a self-powered vehicle  20  on which is mounted the portable lifting bed  10 , it is to be understood that the portable lifting bed  10  may be manufactured as a pull-type trailer having the same inventive features as herein disclosed. 
   As seen in  FIGS. 1 and 2 , the portable lifting bed  10  has a base frame  40 . The base frame  40  has a forward cross member  44  and first and second longitudinal frame members or side members  46  extending in opposed relationship from the lateral frame member  44 . The tow bar  34  is approximately centered upon the lateral frame member  44  and attaches to the self-powered vehicle by a swivel hitch  22  that permits pivoting about a horizontal longitudinal axis of frame  40 . The base frame  40  has a back end  48  opposite the lateral frame member  44 . The base frame  40  has axles  50  upon which the wheels  42  attach. 
   A moveable bed frame  52  moves relative the moveable bed trailer base frame  40 . The bed frame  52  is mounted to the base frame  40  by a diagonal guide  54 . Also interconnecting the bed  52  and the base frame  40  are two actuators  100 . Actuators  100  are preferably hydraulic cylinders, but other power systems such as pneumatics or gear driven mechanisms may be used to move the bed frame  52  between an elevated position ( FIG. 3 ) and a lowered position ( FIG. 4 ). 
   The guide has an elongated guide track  70  and a track follower  80 . In the preferred embodiment, the guide track  70  is an elongated angle member and the track follower  80  is a roller assembly. The guide track  70  is fixed to the bed frame  52  and the track follower  80  is mounted on the base frame  40 . 
   The bed frame  52  has front and rear cross members  56  and longitudinal frame members or side members  58 . Bed frame  52  also includes upstanding side frames  58  on opposite sides thereof. The guide tracks  70  form a part of the side frames  58 . 
   Bed frame  52  also includes an upwardly facing bed surface  60  made of planks running longitudinally along with the bed longitudinal frame members  58 . Alternatively, the bed surface  60  may be a sheet of steel as seen in  FIG. 3 , which runs the complete longitudinal and latitudinal length of the bed frame  52 . 
   Upon the bed surface  60  may exist any number of moveable objects  62 . The self-powered lifting bed  10  is anticipated to have a capacity for moveable objects  62  in the order of 1000–2000 pounds. A portable lifting bed  10  adapted to be attached to a self-powered vehicle by a trailer hitch is anticipated to have a capacity for moveable objects  62  of approximately 6000 pounds. 
   As seen in  FIG. 3  and  FIG. 4 , the moveable objects  62  are easily slid upon the bed  52  when the bed frame  52  is in a lower position. To aid upon sliding the moveable objects upon the bed surface  60 , there may be positioned a ramp  114 . 
   The moveable bed frame  52  has a railing  64 . The railing is held in place by a railing support  66  and the diagonal guides  54 . 
   As seen in  FIG. 2 , the diagonal guide  54  has a guide track  70 . The guide track  70  has a lower end  72  and an upper end  74 . The lower end  72  is approximately parallel to the longitudinal frame member  58  and attached thereto. The lower end  72  runs horizontal for a distance sufficient to accommodate a roller assembly  80 . The roller assembly, as can be seen in  FIG. 2A , is made up of a roller  82  and spindle  84 . 
   The guide track  70  defines a roller assembly guide opening or channel  90 . The guide opening  90  extends the length of the first end  72 , the length of the angle member  70 , and the length of the second end  74 . The roller assembly  80  travels along the roller assembly guide opening  90  for moving the bed frame  52  from an upper position ( FIG. 3 ) to a lower position ( FIG. 4 ). When the bed frame  52  is in the upper position, the roller assembly  80  supports the weight of the bed frame  52  with assistance from actuators  100 . Illustrated in  FIG. 3  are actuators  100  holding the bed in an upper position.  FIG. 4  is an illustration of the actuators extending the bed to a lower position. 
   The actuators  100  have cylinder  102  and rod  104 . The cylinder  102  has an upper end  108  attached to the longitudinal frame member  46  of base frame  40  by an upstanding frame member  106  that is fixed to base frame  40 . The actuators  100  have a lower end  110  attached to the longitudinal frame member  46  at a point beyond the roller assembly  80 . 
   An enlarged view of the operation of the actuators  100  in use may be seen in  FIGS. 5 and 6 . 
   In the preferred embodiment, the actuators  100  are hydraulic cylinders. They are connected by hydraulic lines to a hydraulic master cylinder  26  on the self-powered vehicle  20 . 
   In use, the portable lifting bed  10  may be mounted on either a self-powered vehicle or as a trailer attached to a vehicle. 
   As seen in  FIG. 3 , the actuators  100  are retracted to hold the bed in an upper position during transportation. When the portable lifting bed  10  is held in the upper position, the roller  82  is in the lower end  72  of guide track  70 . In this position, the roller assembly  80  exerts a force against the angle member first end  72  to prevent weight of lift bed frame  52  from being applied to the actuators  100 . Additionally, safety features may be added to further prevent the bed frame  52  from moving from the upper position to the lower position. 
   When the user desires to lower the bed, the user manipulates the hydraulic system  26  to lower the bed frame  52  to the ground as seen in  FIG. 4 . 
   When the bed frame  52  is upon the ground, the rods  104  are in an extended state. During movement, the rods  104  move at an angle such that the longitudinal axes of actuators  100  are is approximately parallel to the longitudinal axes of guide tracks  70 . In this approximately parallel orientation, the guide tracks  70  move approximately the same distance as the extension of the rod  104  outside the cylinder  102 . To accommodate for slight deviation from parallel orientation, the actuators  100  may be pivotally mounted to the bed frame  52  and the base frame  54 . Alternatively, the guide tracks  70  may be pivotally mounted to the bed frame  52  and the base frame  54 . 
   When the rods  104  are extended at a point to which the bed is lowered to the ground, the roller assembly  80  is within the angle member upper end  74 . 
   With the bed frame  52  in the lower position, the user is free to insert cargo  62  upon the bed. To aid in placement of the cargo  62  upon the bed frame  52 , a ramp  114 , as seen in  FIGS. 3 and 4 , may be attached to the bed. 
   Once the user has completely loaded the bed with cargo  62 , the user is free to manipulate the hydraulic system  26 , which lifts the bed frame  52  from a lower position forcing the angle member upper end  74  of guide track  70  to travel along the roller assembly  80 , until the lower end  72  comes to rest with the roller assembly  80  supporting the lower end  72 . 
   The user with the bed frame  52  in the upper position can then transport the cargo  62 . 
   A dump system (not shown) comprising a pivot axis at the rear thereof may be used to enable the user to elevate the front end  118  of the bed frame  52  and to drop the back end  116 . A hydraulic cylinder may be used to elevate front end  118  to enable a user to dump the contents of the bed frame  52  out. This dump system can be integral with the bed  118  or a separate dump system may be inserted on top of bed  118 . 
   Thus a user would be able to load contents on the bed while it is in a lowered horizontal position and then lift the bed to an elevated horizontal position. The contents could then be dumped by elevating the front of bed  118  with the aforementioned cylinder. 
   In the drawings and specification there has been set forth a preferred embodiment of the invention, and although specific terms are employed, these are used in a generic and descriptive sense only and not for purposes of limitation. Changes in the form and the proportion of parts as well as in the substitution of equivalents are contemplated as circumstances may suggest of render expedient without departing from the spirit or scope of the invention as further defined in the following claims.