Abstract:
A portable load transporting dolly having a mechanism manually operable for selectively ascending or descending steps is shown. The dolly has generally cross-shaped wheels and a pivotal driving lever is located at its handle. A cable couples the pivotal driving lever to the rotating shaft of the cross-shaped wheels through a plurality of pulleys and ratchet gears such that the wheels may be rotated easily by gripping the lever. The radial arms of the cross-shaped wheels have sliding reciprocative rods which react with the steps of the staircase to enhance the climbing action of the dolly on the staircase.

Description:
FIELD OF INVENTION 
     This invention relates to a portable dolly operable manually by a single person for safely transporting a relatively heavy load up or down various staircases having steps of different heights and depths. 
     BACK GROUND OF THE INVENTION 
     A portable dolly is commonly used for transporting a heavy load such as furniture or a large appliance. The dolly is provided with rotary wheels and the load is mounted or rested securely on a support shelf on the dolly so that the load may be transported by simply wheeling the dolly from one location to another location on a ground or a floor. However, it has been problematic to move a heavy load up or down a staircase, since it is not possible to push the dolly up the steps of the staircase and it is very hazardous to attempt to push the dolly down the steps in such instances since it would drop from one step to a lower step. The drop could cause damage to the dolly and the load and also the dolly could continue to roll down the steps uncontrollably due to the falling momentum. Therefore, it is necessary that the dolly with the load resting thereon must be lifted and carried up or down the staircase. Such operation is difficult, if not impossible in most instances, for one person to carry out. 
     There are some dollies such as that shown in U.S. Pat. No. 2,633,363 issued to J. M. Marshall on Mar. 31, 1953 and U.S. Pat. No. 3,698,501 issued to E. S. Gross on Oct. 17, 1972 which are provided with a star-shaped rotary support having wheels mounted at its corners. The rotary support is rotatable to position the neighboring wheels at its corners on consecutive steps of a staircase such that the dolly may be pushed up or down the staircase. In both these devices, the above stated problem of the dolly continuing to roll down the steps by momentum still exists, and the dolly would still roll down the steps by the wheels of the star-shaped rotary support. Furthermore, the Gross device has an electric motor incorporated therein, which can be energized to drive the star-shaped rotary support. Such dolly is rather complex in structure and the motor and the associated driving gear mechanism would invariably increase the weight of the device such that it would be difficult to handle by a single person. Moreover, since the electric motor must be connected to a nearby electrical supply with a power cable for its operation; it is awkward to use or is useless if no power supply outlet is close by. Also, the star-shaped rotary support in both devices shown in these patents has a fixed size so that it can only operate on a staircase having steps of a predetermined height and depth. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide a manually operable dolly which is operable for transporting a load up or down a staircase with ease in a controlled manner. 
     It is another object of the present invention to provide a dolly which is operable on various staircases having steps of different heights and depths. 
     It is another object of the present invention to provide a dolly having a relatively light weight and may be operated by a single person. 
     It is still another object of the present invention to provide a dolly having a simply construction and is easy to operate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments thereof in connection with the accompanying drawings, in which 
     FIG. 1 is a perspective rear elevation view of the manually operable dolly according to the present invention. 
     FIG. 2 is an isolated enlarged partial sectional side view of the pivotal lever operable for moving the dolly of the present invention. 
     FIG. 3 is an isolated enlarged partial section view of the pulley system for coupling the cable to the drive shaft of the dolly. 
     FIG. 4 is an isolated enlarged partial sectional view of the cross-shaped wheel of the dolly of the present invention showing the reciprocative sliding rods. 
     FIG. 5 is a side elevation view showing the operation of the dolly of the present invention on a staircase. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the drawings in which like reference numerals designate corresponding parts in the several views, the portable dolly  10  of the present invention has a main frame consisting of two elongated mutually parallel tubular support columns  11  and  12 . Two curved handles  13  and  14  are located at the upper ends of the support columns  11  and  12  respectively and curving slightly rearwardly to facilitate the ease of handling the dolly  10 . The support columns  11  and  12  are mounted together by one or a plurality of horizontal cross brace  15 . One cross braces  15  is shown in FIG. 1 for ease of illustration. A rectangular pulley housing  16  is also provided between the support columns  11  and  12  and preferably located just below the handles  13  and  14 . The pulley housing  16  is provided with a cover  17  either provided on the front or the back therein; a rear cover is shown as an example. The interior compartment  18  of the pulley housing  16  is in communication with the interior channels  19  and  20  of the support columns  11  and  12  respectively through openings  21  and  22 . A load support shelf  23  extends horizontally outwards at the front of the dolly  10  and is adapted for supporting the load which may be additionally secured to the support columns  11  and  12  by restraining straps in a conventional manner. A driving gear housing  24  is provided at the lower end of the support column  11  and a bearing housing  25  is provided at the lower end of the support column  12 . The driving gear housing  24  and the bearing housing  25  extend rearwardly relative to the support columns  11  and  12 . A hollow rotary shaft  26  extends horizontally through the driving gear housing  24  and bearing housing  25 . Ratchet driving gears are provided in the driving gear housing  24  which are operable for rotating the rotary shaft  26 . 
     Three cross-shaped drive wheels  27  are provided on the rotary shaft  26 . Each drive wheel  27  consists of four sleeves  28 ,  29 ,  30  and  31  mounted perpendicular to the rotary shaft  26  and are positioned 90 degrees from the neighboring sleeves. Elongated sliding rods  32 ,  33 ,  34  and  35  are slidably located within the sleeves  28 ,  29 ,  30  and  31  respectively. The inner ends of the sliding rods  32 ,  33 ,  34  and  35  are coupled to one another by elongated bendable push rods  36 ,  37 ,  38  and  39  as best shown in FIG. 4 such that retraction of any one sliding rod would cause the adjacent pair of the sliding rods located 90 degrees to it to extend outwards; for example, when sliding rod  34  is pressed inwards to retract into the sleeve  30 , it would push on the push rods  37  and  38  to cause the sliding rods  33  and  35  located 90 degrees to the sliding rod  34  to extend outwards of the sleeves  29  and  31  respectively. The outward extension of the sliding rods  33  and  35  would in turn pull on the push rods  36  and  39  to cause the sliding rods  32  and  34  to also retract into the sleeves  28  and  30  respectively. Four guiding rollers  40 ,  41 ,  42  and  43  are located within the rotary shaft  26  to facilitate the secure and smooth operation of the push rods  36 ,  37 ,  38  and  39  respectively. 
     A pivotal lever  44  is mounted to the handle  14  by a pin  45  in a cantilever manner. A torsion spring  46  is also mounted to the pin  45 . The torsion spring  46  maintains the lever  44  in a normally outward angular position relative to the handle  14 , and the lever  44  may be operated against the resilient force of the torsion spring  46  by gripping it by hand to lie close to the handle  14 . It will return to the outward angular position when the grip is released. One end of an elongated cable  47  is connected to the lever  44 . The cable  47  extends through the hollow channel  20  of support column  12  into the interior compartment  18  of the pulley housing  16  through the opening  22 . 
     The cable  47  is wound through a plurality of pulley assembly  48 . For simplicity of illustration, two pulleys  49  and  50  are shown in the pulley assembly as representative. It will be appreciated by those skilled in the art that more than two pulleys may be provided. The cable  47  extends through opening  21  and downward through the hollow channel  19  of support column  11  to connect to a ratchet drive gear mechanism located in the drive gear housing  24 . Two guiding rollers  51  and  52  are provided in the interior compartment  18  adjacent to the openings  22  and  21  respectively to lead the cable  47  through the pulley housing  16 . Thus, when the lever  44  is operated to pull and release the cable  47  in a reciprocative manner it would cause the ratchet gear mechanism to rotate the drive shaft  26  to drive the cross-shaped wheels  27 . The ratchet geat mechanism provides the mechanical advantage for the operation such that only a light gripping action is required to operate the lever  44  to rotate the rotary shaft  26  for transporting a heavy load mounted to the dolly. Additional gearing arrangement may also be provided in the drive gear to provide further mechanical advantage. 
     In operation, as best shown in FIG. 5, the dolly  10  climbs the steps by operating the lever  40  to rotate the cross-shaped wheels  27  mounted on the rotary shaft  26 . When the first sliding rod of the cross-shaped wheels is pressing down on the first step, it would cause the next sliding rod located 90 degrees from it to extend outwards from its sleeve to contact the next step. Thus, when the cross-shaped wheels are then rotated it would raise the dolly to the next step. Particularly, in the descending operation, the extended next sliding rod would contact the lower step to prevent the dolly from dropping onto the next lower step. The operation continues until the dolly is moved to the top of the staircase or down to its bottom. The extensible rods also facilitate the device to be operated in various staircases having steps of different heights and depths. Furthermore, since no wheels are provided at the outer end of the sliding rods of the cross-shaped wheel, the dolly would not roll down the steps due to its downward momentum. Accordingly, the dolly may be operated in a controlled manner to transport the heavy load up or down the staircase by a relatively light gripping action of the lever  44 . 
     While the present invention has been shown and described in the preferred embodiment thereof, it will be apparent that various modifications can be made therein without departing from the essential attributes thereof, for example, the cross-shaped wheels with the sliding reciprocative rods may have other application than that shown, and it is desired therefore that only such limitations be placed thereon as are imposed by the appended claim.