Abstract:
A hydraulic lift for mobile living quarters having a liftable top. A fluid pressure source communicates fluid through fluid lines connected to a plurality of lifting members that extend upon receipt of fluid and retract upon discharging fluid. The rate at which fluid is discharged from the lifting members is a function of how much weight each lifting member bears. Each of the fluid lines has a flow control valve between the pressure source and each lifting member. Fluid is communicated through the flow control valve to the lifting member connected to the pressure source the fluid is also communicated through the flow control valve when fluid is discharged from the lifting member. The flow control valve limits the flow rate of the fluid to a constant predetermined rate when the fluid is discharged from the lifting member.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit and priority of U.S. Provisional Patent Application Ser. No. 60/806,677, filed Jul. 6, 2006, the subject matter of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Camping trailers have long been provided with lift mechanisms for raising and lowering the top. Some lifts use telescoping corner posts to accomplish this task. 
     U.S. Pat. No. 3,363,932 uses a single pumping piston which supplies four separate hydraulic cylinders in four corner posts and has adjustable valves to allow each of the corner posts to descend at an equal rate to the other posts. The valves restrict the flow of fluid returning from the hydraulic cylinders in the corner posts, which adjusts the rate of descent for the cylinder in line with the adjustable valve. If the posts do not descend evenly, binding and excessive wear can occur. In use the weight of the camper top would almost never be evenly distributed to all of the posts. There would almost certainly be some posts which would carry more weight than others. Generally a post with more weight will descend faster than a post with less weight. To compensate for this a user of this disclosed invention would have to adjust each of the four individual valves through trial and error to restrict fluid flow from the individual cylinders in the corner posts until they all descended at the same rate. If a user guessed wrong in his adjustment of one or more of the posts, the camper could bind due to an uneven rate of descent. Also, if the weight distribution changed in any way due to different loading conditions, a user would have to readjust the valves. It is unsafe and unreasonable to expect a consumer to properly adjust the valves each time the camper top is raised or lowered. 
     SUMMARY OF THE INVENTION 
     The present invention is a liftable top for mobile living quarters. The top is supported by lifting members which are a piston retained in a cylinder. The lifting members extend when receiving fluid and retract when fluid is discharged from the lifting members. Fluid is discharged at a rate which is a function of the weight borne by the lifting member. A pump communicates fluid to the lifting members through fluid lines. Each fluid line connected to the lifting members has a flow control valve therein. Each line also has a release valve to allow fluid to be discharged from the lifting members. The release valves may be contained in the pump or in the fluid lines. In either case, the release valves are operated simultaneously to allow fluid to be discharged from the lifting members, thereby lowering the top. As the top lowers, flow control valves limit the fluid discharged from the lifting members to a predetermined flow rate. This causes the lifting members to lower the top evenly despite different weight borne by each lifting member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a camper with a liftable top; 
         FIG. 2  is a perspective view of the camper shown in  FIG. 1  with the top partially raised; 
         FIG. 3  is a perspective view of the camper shown in  FIGS. 1 and 2  showing the fluid lines connected to lifting members in the corners of the liftable top, with the liftable top being fully raised; 
         FIG. 4  is a perspective view of a first embodiment of a pump; 
         FIG. 5  is a section view of the pump shown in  FIG. 4 , showing the piston in the upstroke as the handle is raised; 
         FIG. 6  is a section view of the pump shown in  FIG. 4 , showing the piston in the downstroke as the handle is lowered; 
         FIG. 7  is a section view of the pump shown in  FIG. 4 , showing a ball valve open returning fluid to the reservoir; 
         FIG. 8  is a perspective view of the handle that attaches to the ball valves; 
         FIG. 9  is a perspective view of the handle shown in  FIG. 8  partially disassembled; 
         FIG. 10  is a perspective of a second embodiment pump; 
         FIG. 11  is a section view of the pump shown in  FIG. 10  with the piston on the downstroke; 
         FIG. 12  is a section view of the pump shown in  FIG. 11  with the cams engaged to activate pins which release fluid back to the reservoir; 
         FIG. 13  is a section view of the flow control valve; 
         FIG. 14  is a section view of the flow control valve with the spool in its equilibrium position; 
         FIG. 15  is an exploded perspective view of the flow control valve shown in  FIGS. 13 and 14 ; 
         FIG. 16  is an exploded perspective view of the lower end of a lifting member as it is mounted in a camper; 
         FIG. 17  is a perspective view of the upper end of a lifting member, shown in  FIG. 16 , as it is mounted in a camper; 
         FIG. 18  is a section view of a lifting member shown in  FIGS. 16 and 17 ; and 
         FIG. 19  is a partial section view of a lifting member fully extended. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     The hydraulic lift of this invention is used to lift a structure. This structure may be any structure that requires uniform lifting, as well as uniform and controlled descent. The embodiment detailed as follows, pertains to a camper  30 , but may be used for boat lifts, work benches, tables, etc. 
     The hydraulic lift of this invention has four lifting members  12  that are placed near corners of a camper top  14 . The lifting members  12  have a piston  16  and a cylinder  18 . The piston  16  and cylinder  18  form a chamber  20  that receives fluid through a fluid line  22 . The piston  16  may have a bore  4  running its entire length, as shown in  FIG. 18 , that is capped with a threaded plug  6 . This allows bleeding of air form the chamber  20  when hydraulic fluid is used as the fluid. When the piston  16  has a bore  4 , as shown in  FIG. 18 , the piston  16  is preferably a rod having the same diameter along its entire length. When fluid is forced into the chamber  20  through the fluid line  22  the lifting member  12  extends, as fluid leaves the chamber  20  the lifting member  12  retracts. The rate that fluid leaves the chamber  20  of the lifting member  12  is a function of the weight borne by the lifting member  12 . When more weight is borne by the lifting member  12 , fluid will leave at a faster rate. 
     A pump  28  is put into a camper  30 , as shown in  FIG. 3 , and connected with fluid lines  22  to the lifting members  12 . The pump  28  has four pistons  32  that are sealed with O-rings  36  and slide in cylinders  40 . The cylinders  40  are threaded into a block  42 . A removable handle  66  is connected to a linkage  68 , which is connected to a connecting rod  70 . The connecting rod  70  is received in each of the four pistons  32 . Set screws  72  are threaded into the ends of each piston  32  and are tightened until each piston  32  is tightened against the connecting rod  70 , which removes any free play between the connecting rod  70  and pistons  32 . When the handle  66  is raised, the linkage  68  lifts the connecting rod  70  and raises all of the pistons  32  at the same time. When the handle  66  is lowered, the pistons  32  are lowered at the same time. The set screws  72  tightened onto the connecting rod  70  ensure that each time the handle  66  is raised or lowered, the pistons  32  travel the same amount. When a piston  32  is raised, fluid is drawn into the pump  28  through an inlet hole  52  which is connected to a reservoir  59  with an inlet fluid line  21 . As fluid is drawn through the inlet hole  52 , a first ball  78  lifts from an inlet seat  76  to allow fluid to pass into the chamber  53  formed by the piston  32  in its cylinder  40 . When the piston  32  travels downward, as shown in  FIGS. 6 and 11 , the first ball  78  is forced into the inlet seat  76  preventing flow of fluid back into the inlet hole  52  while fluid is forced past a second ball  80  toward an outlet  82  of the pump connected to the chamber  53 . Each of the four outlets  82  are only connected to one chamber  53  and are independent of all other chambers  53  of the pump  28 . The pump  28 , shown in  FIGS. 4 ,  5 ,  6 , and  7 , is a first embodiment of the pump  28  that serves only the function of a pump. 
     The second embodiment shown in  FIGS. 10 ,  11 , and  12 , in addition to being a pump, contains a set of four pressure release valves  84  connected to each fluid line  22 . In the second embodiment, pressurized fluid in communication to the pump  28  through the fluid lines  22  is prevented from flowing back to the reservoir through the pump by the second ball  80  and a third ball  86 . When a user desires to return pressurized fluid from the four lifting members  12  to the reservoir  59 , a handle  88  attached to a cam rod  89  having four cams  90  may be rotated which moves a set of pins  92  downward, thereby pushing the third ball  86  from its seat and allowing pressurized fluid to return to the inlet hole  52 . Each pin  92  is associated with a single outlet  82 . The cam rod  89  moves all four pins  92  at the same time. 
     When the first embodiment of the pump  28  is used, fluid is returned to the reservoir  59  through the use of ball valves  96 . Each fluid line  22  has a ball valve  96  between the pump  28  and a lifting member  12 . A second fluid line  98  is attached to each ball valve  96  and is connected to the reservoir  59 . Each ball valve is connected to a handle  100  that simultaneously opens and closes all of the ball valves  96 . The handle  100 , as shown in  FIG. 8 , may be disassembled, as shown in  FIG. 9 , to open or close individual ball valves  96 . 
     As fluid is communicated from the pump  28  it is pushed into the lifting members  12 . The cylinder  18  of the lifting member  12  rests on a frame bracket  105  of the camper  30 . The piston  16  and cylinder  18  are surrounded by telescoping members  106 , as shown in  FIG. 3 . The piston  16  carries a pulley  108  on its upper end and the pulley  108  receives a cable  110 . The cable  110  is locked near the bottom of the cylinder into a plate  111 , and also locked into the uppermost telescoping member  112 . The uppermost telescoping member  112  is affixed to the camper top  14  and the lowermost telescoping member  113  is held by a tab  118  locked into the plate  111  by a pin  120 . As fluid enters the lifting member  12 , the piston  16  extends and raises the pulley  108 . This pulls the cable  110  upward, and raises the top  14 . 
     Each of the fluid lines  22  are connected to a flow control valve  24 , as shown in  FIGS. 4 ,  5 ,  6 ,  7 ,  11 ,  12 . The flow control valve  24  limits the rate of fluid flow leaving the chamber  20  of the lifting member  12  to which it is connected. The flow control valve  24  has a housing  31  that has an inner sleeve  33  mounted therein. The inner sleeve  33  has holes  34  through which fluid may pass. A spool  37  is slidably retained in the inner sleeve  33 . The spool  37  receives a spring  39  in one end. The opposite end of the spool  37  has an orifice  43  that communicates fluid through the center of the spool  37 , and out holes  48  in the spool. The spring  39  presses against an end plug  50  received in the downstream end of the housing  31  to urge the spool  37  against an inner face  51  in the housing  31 . The end plug  50  has a first O-ring  57  that seals against the inner sleeve  33  and a second O-ring  54  that seals against housing  31 . The first O-ring  57  seals a first chamber  58  that is defined by the inner face  51  of the housing  31 , the inner sleeve  33  and the end plug  50 . Holes  34  in the inner sleeve  33  allow fluid to pass from the first chamber  58 . The second O-ring  54  seals a second chamber  64  defined by the housing  31 , the inner sleeve  33  and the end plug  50 . Holes  67  in the end plug  50  allow fluid to pass from the second chamber  64  and out of the flow control valve  24 . When fluid is discharged from a lifting member  12  it enters the flow control valve  24  through the orifice  43 . The fluid is communicated through the center of the spool  37 , through holes  48 , then passes into the first chamber  58 , out holes  34  in the inner sleeve  33  to the second chamber  64 , and through holes  67  out of the flow control valve  24 . The arrows in  FIGS. 13 and 14  show the flow path through the flow control valve  24  when fluid is discharged from the lifting members  12 . As fluid flow increases the spool  37  is pushed toward the end plug  50  which partially covers holes  34 , thereby slowing the flow rate due to the restriction of the spool valve partially covering holes  34 . The flow rate is slowed until the force on the spool  37  due to the fluid flow through the orifice  43  is equal to the spring force on the spool  37 . When this occurs an equilibrium position of the spool  37  is established, which is shown in  FIG. 14 . 
     When a user of the camper  30  wishes to raise the top  14  he will attach the handle  66  to the linkage  68 . The user will then raise and lower the handle  66  which forces fluid through the fluid lines  22  and into the respective lifting members  12  attached to each fluid line  22 . Each lifting member  12  will raise by the same amount each time the handle  66  is lowered until the top  14  is fully raised. When the user has fully raised the top a safety piece  130  may be inserted around the telescoping members  106  to support the weight of the top  14  in case it were to be unexpectedly lowered as shown in  FIG. 3 . When the user wants to put the camper top  14  down he will then use the handle  100  to open the ball valves  96  if the first embodiment pump  28  is used. If the second embodiment pump  28  is used, the user will rotate the handle  88  by ninety degrees. The use of either will allow fluid to flow back to the reservoir  59 . When this happens, the flow control valves  24  ensure that the fluid flow leaving the lifting members  12  is uniform even if one corner of the camper top  14  carries more weight than others. Having fluid leave all lifting members at the same rate will cause the top  14  to descend in a level manner and prevent binding. At any point during the lowering, the user can close the ball valves  96  with handle  100 , or use the handle  88  to stop the fluid flow to the reservoir  59 . This will stop the camper top  14  at any point between fully raised and fully lowered so that the user may have an opportunity to tuck in canvas sidewalls as the top  14  descends. 
     Variations from the described embodiments may be made by one skilled in the art without departing from the scope of the invention. The above described invention is not to be limited to the details given but may be modified within the scope of the following claims.