Abstract:
The current invention is a portable wheel lift device for lifting and towing vehicles comprising a boom which pivots up and down for connecting to and raising a portion of a vehicle which is to be towed. The invention comprises a mounting frame adapted to be attached to a towing vehicle and a two-stage cylinder assembly operatively connected to the mounting frame and the boom for tilting the pivoting boom relative to the mounting frame.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a device which can be attached to a vehicle and used for lifting and towing other vehicles. Specifically, this invention relates to a double cylinder tilt recovery system. 
     Many types of devices have been used in the past for connecting and towing vehicles. These types of devices generally operate with one or more hydraulic cylinders to raise the vehicle which is to be towed. One problem with these type of devices is, however, that in order to get the strength from a hydraulic cylinder to raise a heavy vehicle the hydraulic cylinder must be very large. The downfall of a large cylinder is that it operates or extends very slowly. Therefore, when the operator is done using the towing device and wishes to stow the boom of the towing device getting the boom to the stowed position is a very slow process. Thus, there is a need for an improved and faster operating towing device. 
     In light of the foregoing, it is a primary feature or advantage of the present invention to provide an improved double cylinder tilt recovery system. 
     A further feature or advantage of the current invention is a towing device which can be easily attached to vehicles, such as a road tractor. 
     A further feature or advantage of the current invention is a two-stage cylinder which is faster than traditional single stage cylinders. 
     A further feature or advantage of the invention which has power to lift vehicles, yet stows faster than comparable powered lifts. 
     A further feature or advantage of the current invention is the provision of a double cylinder tilt recovery system which is economical to manufacture, durable in use, and efficient in operation. 
     One or more of these or other features or advantages of the invention will become apparent from the specification and claims that follow. 
     BRIEF SUMMARY OF THE INVENTION 
     The foregoing features or advantages may be achieved by a portable wheel lift device for lifting and towing vehicles comprising a boom which pivots up and down for connecting to and raising a portion of a vehicle which is to be towed, a mounting frame, a means for attaching the mounting frame to a towing vehicle, and a two-stage cylinder assembly operatively connected to the mounting frame and the boom for tilting the pivoting boom relative to the mounting frame. 
     A further feature or advantage of the current invention is a portable wheel lift device for lifting and towing vehicles which has a boom that is a telescoping boom. 
     A further feature or advantage of the current invention is a portable wheel lift device for lifting and towing vehicles which has a two-stage cylinder that has a first stage piston and a smaller second stage piston. 
     A further feature or advantage of the current invention is a portable wheel lift device for lifting and towing vehicles wherein a second stage of a two-stage piston extends only after the first stage piston has fully extended. 
     A further feature or advantage of the current invention is a portable to about vertical stowing position when the device is mounted to a towing vehicle and both stages of a two-stage cylinder are extended. 
     A still further feature or advantage of the current invention is a two-stage cylinder wherein the second stage piston travels within a small piston tube and the small piston tube is affixed within a large cylinder rod and the large cylinder rod is affixed to the large piston. 
     A further feature or advantage of the current invention is a portable wheel lift device for lifting and towing vehicles which has a boom that pivots up and down. 
     A further feature or advantage of the current invention is a portable wheel lift device for lifting and towing vehicles which has a two-stage cylinder wherein the small piston travels within a small piston tube and the small piston tube is affixed within a large cylinder rod and the large cylinder rod is affixed to the large piston. 
     A further feature or advantage of the current invention is a portable wheel lift device for lifting and towing vehicles which has a kingpin for mounting to a road tractor. 
     A further feature or advantage of the current invention is a portable wheel lift device for lifting and towing vehicles which has one or more lift cylinders for lifting the towing device relative to the mounting frame. In addition, the device may have guide rollers which travel in a track to guide the lifting with the cylinders and the boom. The device may also comprise a push rod operatively connected between the two-stage cylinder and the boom. 
     One or more of the foregoing features or advantages may be achieved by a vehicle towing device for mounting to a road tractor comprising a towing vehicle attachment assembly for mounting the device to the road tractor, a boom lift assembly operatively connected to the towing vehicle attachment assembly, the boom lift assembly having one or more hydraulic cylinders for lifting the boom assembly in a linear plane and a two-stage cylinder assembly operatively connected between the boom lift assembly and the boom for pivoting the boom about a pivot point for lifting vehicles attached to the boom for towing. 
     One or more of the foregoing features or advantages may also be achieved by a two-stage hydraulic cylinder assembly comprising a large cylinder body, a large piston which travels linearly within the cylinder body, a large hollow piston rod connected to the large piston which travels linearly with the large piston and extending out of the large cylinder body, a small hollow piston tube connected within the large piston rod which travels linearly with the large piston rod, a small piston which travels linearly within the small piston tube and a small piston rod connected to the small piston which travels linearly with the small piston within the small piston tube and extends outside of the small piston tube. 
     A further feature or advantage of the present invention involves a two-stage hydraulic cylinder assembly wherein a small piston tube is welded to a large cylinder rod. 
     A further feature or advantage of the present invention involves a two-stage hydraulic cylinder assembly where a large piston extends linearly within the large cylinder body before a small piston extends linearly within the small piston tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one embodiment of the current invention with a boom shown in multiple locations. 
         FIG. 2  is a perspective view of one embodiment of the current invention with the boom shown in multiple locations. 
         FIG. 3  is an elevation view of one embodiment of the boom lift assembly. 
         FIG. 4  is a cut away side view of one embodiment of the boom lift assembly. 
         FIG. 5  is another elevation view of one embodiment of the boom lift assembly. 
         FIG. 6  is a cut away view showing one embodiment of the two-stage cylinder assembly. 
         FIGS. 7-10  are side cut away views showing one embodiment of the tilt recovery auto lift system of the current invention with the boom in multiple positions. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIGS. 1 and 2  show one embodiment of the tilt recovery auto lift system assembly  10  of the current invention. The invention is a device which mounts to a towing vehicle and connects to and lifts a vehicle which is to be towed. A two-stage cylinder assembly  38  for tilting a boom  14  allows the boom to be raised and lowered, for use and stowing, much faster than traditional vehicle towing recovery systems. 
     Both  FIGS. 1 and 2  show the lift system  10  with the boom assembly  14  in multiple positions. It is preferred, but not necessary, that the boom  14  be a telescoping boom. In addition, the lift system assembly  10  generally comprises a vehicle towing attachment assembly  12 . The vehicle towing attachment assembly  12  preferably has a kingpin for attaching to a towing vehicle (not shown) at a fifth wheel plate of a road tractor. The preferred towing vehicle attachment assembly  12  is like that shown in U.S. Pat. Nos. 5,823,735 and 6,036,428 for Kooima, which are both herein incorporated by reference in their entirety. However, any towing vehicle attachment assembly  12  which allows the tilt recovery auto lift system assembly  10  of the current invention to be attached to a towing vehicle will work with the current invention. 
     The invention also has a boom lift assembly  16  which attaches to a boom lift assembly mounting frame  20  and preferably uses one or more vertical hydraulic lift cylinders  18  attached between the boom lift assembly mounting frame  20  and the boom lift assembly lifting frame  22  for raising and lowering the boom lift assembly  16  and the boom assembly  14 . 
       FIG. 3  shows a close-up side view of one embodiment of the boom lift assembly  16 . The boom lift assembly  16  has a boom lift assembly mounting frame  20  which mounts to a towing vehicle attachment assembly  12 . The boom lift assembly mounting frame  20  can be permanently mounted or affixed to the towing vehicle attachment assembly or may be removable. 
     The vertical hydraulic lift cylinders  18  which can raise or lower the boom lift assembly  16  including the boom lift assembly lifting frame  22  with respect to the boom lift assembly mounting frame  20 . One or more vertical guide rollers  24  are preferred to travel within a vertical lift guide track  26 . The rollers  24  guide the travel of the boom lift assembly lifting frame  22 . It is preferred that the vertical lift guide track  26  be linear so that when the boom lift assembly lifting frame  22  raises and lowers the boom lift assembly  16  can travel in a linear motion up and down raising and lowering the boom assembly  14 . 
     The boom assembly  14  pivotally mounts to the boom lift assembly  16  with connector rods or pins (not shown) at the boom pivot point  30  on the boom pivot bracket  28  and also at the push rod  32 . This is best shown in  FIGS. 7-10 . 
       FIG. 4  shows a cut away view of the boom lift assembly  16  of  FIG. 3 . This view shows back ribs  36  attached to the boom lift assembly mounting frame  20 . In addition, the two-stage cylinder assembly  38  is shown attached to the boom lift assembly lifting frame  22  at the two-stage cylinder pivot point  34 . The two-stage cylinder pivot point  34  is preferably a pin which allows the two-stage cylinder assembly  38  to rotate about the two-stage cylinder pivot  34 . 
     A large cylinder rod  52  and a small piston rod  58  travel in and out of the two-stage cylinder assembly  38  and move a clevis  42 . It is preferred that the clevis  42  be attached with a pin to both the push rod  32 , for pivoting the boom assembly  14 , and a cylinder containment roller  44 . A cylinder containment roller  44  preferably travels within cylinder roller track  46  to guide the travel of the large cylinder rod  52  and the small piston rod  58  within the boom lift assembly  16 . This helps to prevent damage or binding of the two-stage cylinder assembly  38  when lifting heavy vehicles. 
       FIG. 5  shows an elevation view of the boom lift assembly  16  as viewed from the boom assembly  14  towards a towing vehicle. In this view, a vertical hydraulic lift cylinder  18  and the back ribs  36  are not shown on the right hand side for clarity sake. 
       FIG. 6  shows a cut away view of the preferred embodiment of the two-stage cylinder assembly  38 . The two-stage cylinder assembly  38  is constructed with a large cylinder body  48 . The cylinder body is preferably steel or some other rigid material capable of withstanding the pressures generated within the two-stage cylinder assembly  38 . 
     A large piston  50  travels linearly within the large cylinder body  48 . The large piston  50  should be sized large enough to be able to generate enough lifting force to be able to lift and tow vehicles which are to be towed with the current invention. There should be a small gap between the inside of the large cylinder body  48  and the large piston so as to allow lubricant or pressurizing fluid to pass between the inside of the large cylinder body  48  and the large piston. However, a gap between the piston  50  and the large cylinder body  48  should still be small enough to seal so that fluid pressure can move the piston  50  within the large cylinder body  48  as is customary in hydraulic cylinders. Additionally, the large piston  50  may be encircled by one or more piston rings or seals to help create the needed seal to build pressures to move the large piston  50  within the large cylinder body  48 . 
     Pressurized fluid enters the large cylinder body  48  through the large piston extend fluid port  66  to create greater pressure or force above the large piston  50  and pushes the large piston  50  downward within the large cylinder body  48 . As the large piston  50  moves downward it displaces the fluid below the piston so that the fluid flows out of the large piston retract fluid port  68 . To retract the large piston  50 , fluid then flows into the large piston retracted fluid port  68  creating a greater pressure or force below the large piston  50  and displacing the fluid above the large piston  50  so that the fluid then flows out of the large piston extend to the fluid port  66  and the large piston  50  is able to move upward. 
     A rigid large piston rod/tube  52  is attached to the large piston  50 . The large piston rod/tube  52  will be referred to as a rod because it is attached to the large piston  50  and travels linearly with the large piston  50  to extend and retract in and out of the large cylinder body  48 . However, the large piston rod  52  is hollow inside thereby resembling a tube. There are one or more large rod seals  62  which keep the pressurizing fluid within the large cylinder body  48 . 
     A small piston tube  54  is attached within the large piston rod  52 . It is preferred that a weld joint  60  attach to the small piston tube  54  within the large piston rod  52 . However, any attachment means to attach the small piston tube  54  within the large piston rod  52  can be used. A fluid passageway  74  should be maintained between the small piston tube  54  and the large piston rod  52  so that fluid may flow between the two parts for actuating the second stage of the two-stage cylinder assembly  38 . 
     A small piston  56  is located within the small piston tube  54  and travels linearly within the small piston tube  54 . The small piston  56  travels linearly within the small piston tube  54  as fluid enters the small piston extend fluid port  70  with a force or pressure to slide the small piston  56  within the small piston tube  54 . A small gap should be between the small piston  56  and small piston tube  54  for allowing a lubricant to lubricate the sliding action of the two parts. However, as with the large piston  50 , one or more seals or piston rings may be used to reduce flow of pressurizing fluid past the small piston  56 . 
     To retract the small piston  56 , fluid flows through the small piston retract fluid port  72  in the large piston rod  52  and through the small piston retract fluid port  73  in the small piston tube  54  for pushing the small piston  56  back through the small piston tube  54 . 
     A rigid small piston rod  58  is attached to the small piston  56  and travels linearly with the small piston  56  within the small piston tube  54 . A small rod seal  64  seals the bottom end of the small piston tube  54  to prevent leakage of pressurizing fluid. It is preferred that a clevis  42  be attached to the end of the small piston rod  58  for pushing the push rod  32  thereby pivoting the boom assembly  14  about the boom pivot point  30 . The clevis  42  can also rest on the ends of the large piston rod  52  for added pressure and strength when pushing the clevis  42  for operating the boom assembly  14 . This only works for the travel distance of the large piston rod  52 . Then, once the large piston rod  52  reaches the extent of its travel, the second stage of the two-stage cylinder assembly  38 , the small piston  56  and the small piston rod  58  travel beyond the travel distance of the large piston  50  and the large piston rod  52 . At this point, the clevis  42  is moved by the small piston rod  58 . 
       FIGS. 7-10  show cut away views of the tilt recovery auto lift system  10  with the boom assembly  14  in various positions. The cut away views  7 - 10  show how the two stages for the two pistons  50 ,  56  and rods  52 ,  58  travel within the two-stage cylinder assembly  38  and pivot the boom assembly  14  about the boom pivot point  30  to attach to and tow a vehicle, and also to store the boom assembly  14  when not in use. 
       FIG. 7  shows both the small piston  56  and the large piston  50  in an unextended or retracted position thereby causing the boom assembly  14  to be approximately 10° below horizontal position.  FIG. 8  shows the small piston  56  unextended and the large piston  50  approximately halfway extended, thereby causing the boom assembly  14  to be approximately horizontal.  FIG. 9  shows the small piston  56  unextended and the large piston  50  fully extended, as would be in many situations for towing a vehicle, thereby causing the boom assembly  14  to be approximately 20° above horizontal.  FIG. 10  shows both the small piston  56  and the large piston  50  fully extended to place the boom assembly  14  in an approximately vertical stowing position. The boom assembly  14  is shown in these positions for example only and is not meant to limit the invention with extension of pistons and boom assembly  14  position. 
     In summary, the invention comprises a two-stage cylinder assembly  38 . A large bore diameter piston  50  has a large rod  52  with a small cylinder with a small piston  56  built into the large piston rod  52 . The force of the large piston  50  is necessary to properly tilt the boom assembly  14  with a full load on it. This action with the large piston  50  is very slow and is not acceptable to entirely stow the boom assembly  14  to its full vertical position. Therefore, the small piston  56  will take over and promptly finish storing the boom assembly  14 . An advantage of the two-stage lift is that it has the power to lift heavy vehicles, yet can stow the boom much more quickly than similarly powered single stage lifts. This is because large powerful cylinders are inherently slower than smaller cylinders under similar conditions. 
     The small piston rod  58  has a clevis so the large piston rod  52  can push the clevis  42  when tilting and lifting a heavy load. The two-stage cylinder assembly  38  will be contained within the boom lift assembly  16  by rollers  44  placed on a through pin that rides in a track  46  which is attached to each inside of the boom lift assembly  16 . 
     Being built in this manner, the boom assembly  14  will have a pivot point  30  close to the vertical movement of the boom assembly  14 , giving maximum boom tilt with minimum distance between pivot points. This will also give a true tilt without moving the crossbar and load forward or back during the tilting operation as in other towing devices. The boom lift assembly  16  will raise approximately straight up and down via one or more vertical cylinders  18  placed along the side of the boom lift assembly  16 . The boom lift assembly  16  will ride up and down between pairs of rollers  24  mounted to ribs  36  that are a part of the mounting frame  20 . The boom lift assembly  16  preferably has a track  26  attached to each side to accommodate and guide the vertical guide rollers  24 . 
     Designs of the current invention can fit to both trucks and road tractors. The device can be mounted to the towing vehicle in any manner, such as mounted to the frame, or the fifth wheel plate or any other means to attach the current invention to a towing vehicle. 
     The invention has been shown and described above with the preferred embodiments, and it is understood that many modifications, substitutions, and additions may be made which are within the intended spirit and scope of the invention. From the foregoing, it can be seen that the present invention accomplishes at least all of its stated objectives.