Patent Publication Number: US-2007095616-A1

Title: Forklift trucks

Description:
INTRODUCTION  
      The present invention relates to a forklift for mounting on the rear of a carrying vehicle of the type comprising a U-shaped chassis having a rear leg bridged by a pair of forwardly projecting side legs, ground engaging wheels, a driver station mounted on one chassis leg, a motor drive mounted on the other chassis leg and forks mounted on a mast assembly located between the side legs of the chassis. The invention relates particularly to the mast assembly.  
     BACKGROUND OF THE INVENTION  
      Such forklift trucks are often referred to as piggy-back forklift trucks and many constructions of such forklift trucks have been sold under the Trade Mark MOUNTY. Very often, they comprise a pair of front wheels and a rear steering wheel. However, equally well, two rear steering wheels are often used and in other embodiments, front steering wheels are used.  
      It is known to provide a forklift of this type in which the mast assembly comprises a mast assembly in the form of a telescopic mast that can be tilted to provide reach for the forklift. Such a construction of forklift is the telescopic boom forklift and is described in European Patent Specification No. 0 701 963 (Manitou). There are, however, certain problems with such a telescopic boom forklift which, while it allows extended reach for the forks of the forklift to engage a load, it has the disadvantage that as the height of the platform supporting load increases, it becomes increasingly difficult for the telescopic forklift to reach sufficiently far across the platform or vehicle from which the load is being removed or placed on. Obviously, the further the load is spaced-apart from the chassis, the less weight can be carried without causing the forklift to become unstable.  
     OBJECTS OF THE INVENTION  
      The present invention is directed towards providing an improved construction of such a forklift which will overcome these problems.  
     SUMMARY OF THE INVENTION  
      The invention provides a forklift for mounting on the rear of a carrying vehicle of the type comprising a U-shaped chassis comprising a rear leg bridged by a pair of forwardly projecting side legs. A driver station is mounted on one of the side legs and a motorised drive on the other side leg and there are ground engaging wheels, generally one wheel towards the front of each side leg and one rear wheel on the rear leg. An upright mast is mounted on the chassis between the side legs and there is means for moving the mast back and forth between the side leg towards and away from the rear leg. A telescopic boom is slidably mounted on the mast to project substantially orthogonal to the mast. There are also provided means for moving the boom up and down the mast. A fork carrier is generally mounted on the free end of the boom and lifting forks are then mounted on the front carrier. Finally, there are means for extending or reducing the length of boom to move the fork carrier towards and away from the mast.  
      By providing this arrangement, it is possible to move the load back and forth across a platform, without tipping the forklift. Generally, the mast is mounted on a support frame and there is a pivot mounting between the mast and the support frame, and a tilting ram is connected to the support frame and the mast to tilt the mast on the support frame. The support frame carries rollers to engage in sockets or slots in each side leg. A frame moving ram is connected between the rear leg and the support frame to move the mast back and forth between the side legs.  
      Generally, the mast is a two-part telescopic mast and comprises a lower inner portion and an upper outer portion embracing the lower inner portion. An actuating ram is housed within the inner portion and connected between the two portions. A pair of pulleys, namely an upper pulley and a lower pulley, is mounted on the outer portion adjacent each end and a pair of drive chains is connected to a mounting bracket secured on the outer portion intermediate its ends, one of the chains being led across one of the pulleys and secured to the boom and the other chain being led across the other pulley and secured to the boom.  
      In another embodiment, there is provided, rather than two drive chains, an endless drive chain connected again to the mounting bracket and led across each of the pulleys and secured to the boom. The boom will generally be mounted on a sleeve and preferably, adjacent the free end of the boom, there are ground engaging wheels to support the boom on, for example, a platform.  
      The main advantage of the present invention is that the arrangement of raising and lowering the boom, while also extending the telescopic mast with both operations being carried out synchronously, is particularly advantageous with a piggy-back forklift because the minimum height extension of the mast is provided as the forks are raised and/or extended. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which:  
       FIG. 1  is a perspective view of a forklift according to the invention,  
       FIG. 2  is a side view of the forklift,  
       FIG. 3  is a front view of the forklift,  
       FIG. 4  is a perspective view of a mast assembly according to the invention,  
       FIG. 5  is a side cut-away view of the mast assembly,  
       FIG. 6  is an enlarged perspective view of the rear of portion of the mast assembly;  
       FIG. 7  is a perspective view showing the forklift loading a trailer,  
       FIG. 8  is a side view of the forklift loading the trailer,  
       FIG. 9  is a perspective view of another construction of forklift according to the invention, and  
       FIG. 10  is a side view of the forklift of  FIG. 9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Referring to the drawings, there is provided a forklift, indicated generally by the reference numeral  1 , for mounting on the rear of a carrier vehicle. Neither the carrier vehicle or the means for mounting the forklift  1  on it are illustrated as they have no relevance to this description. The forklift  1  comprises a U-shaped chassis, indicated generally by the reference numeral  2 , having a rear leg  3  bridged by a pair of forwardly projecting side legs  4 . The chassis  2  is mounted on ground engaging wheels, namely, front wheels  5  and rear wheels  6 . A driver station  7  is mounted on one side leg  4  and a motor drive  8  is mounted on the other side leg  4 . The driver station has a conventional steering wheel and operating equipment. Similarly, the motor drive  8  is again of conventional construction.  
      Forks  9  are mounted on a mast assembly, indicated generally by the reference numeral  10 , between the side legs  4 . The mast assembly  10  comprises an upright mast  11  carrying a boom, indicated generally by the reference numeral  12 , substantially orthogonal thereto. The boom  12  is so mounted to be slidable up and down the mast  11  by means, indicated generally by the reference numeral  16 , for raising and lowering the boom  12  on the mast  11 . The forks are mounted on a fork carrier, indicated generally by the reference numeral  13 , mounted on a free end  14  of the boom  12 . Means, indicated generally by the reference numeral  17 , are provided for moving the fork carrier  13  towards and away from the mast  11 .  
      The upright mast  11  is a telescopic two-part mast comprising a lower inner portion  20  and an upper outer portion  21 . The lower inner portion  20  houses a hydraulic actuating ram  22  connected to a bracket  30  on the upper outer portion  21 . An actuating or drive chain  31  is mounted on the interior of the outer portion  21  by a bracket  32  and led over a pulley wheel  33  on the bracket  30  and connected to the sleeve  15  by a connector  34 . The chain  31  is then led down to a pulley wheel  35  on the exterior of the lower outer portion  21  and back inside the outer portion  21  to the bracket  32 . The chain  31  and ram  22  together form the means  16 . The pulley wheels  33  and  35  are idler pulleys.  
      The boom  12  is also a telescopic boom having an inner section  25  slidable within an outer section  26  which are together mounted within the sleeve  15  and movable relative to the sleeve  15  by the actuating ram  17  which is mounted by a bracket  36  on the sleeve  15  and engages at its other end  31 , a bracket  37  on the free end  14  of the inner section  25  of the boom  12 .  
      The free end  14  of the boom  12  carries a pair of depending brackets  40  between a cross member  41  which mounts the fork carrier  13 . The fork carrier  13  comprises a pair of transverse fork carrying beams, namely, an upper beam  42  and a lower beam  43  connected together by brackets  44 . The upper beam has conventional fork engaging slots  48 . The brackets  44  are connected by fork frame guide rods  45  which project through the brackets  40 . Thus, the beams  42  and  43  are laterally slidable relative to the boom  12 . Mounted between the brackets  40  is a cylinder  46  of a double acting side shift ram having piston rods  47  connected to each bracket  44 . Thus, the fork carrier  13  and hence the forks  9  can be moved laterally with respect to the boom  11 .  
      Referring specifically to  FIGS. 1, 4  and  8 , the mast  11  is illustrated mounted on a rectangular frame  50  carrying rollers  51  which engage within grooves  52  in the side legs  4 . A pair of frame moving rams  53  are mounted between the frame  50  and the chassis  2  for movement of the frame  50  towards and away from the chassis  2 . A tilting ram  55  is mounted by a bracket  56  on the frame  50  and is also connected to the chassis  2  to allow tilting of the mast  11 .  
      In operation, the forklift  1  is mounted on the rear of a carrying vehicle in conventional manner such as described in our European Patent No. 0 816153.  
      In use and referring specifically to  FIGS. 7 and 8 , where there is illustrated a trailer  60 , onto which is placed a load  61 . The forks  9  are illustrated carrying the load  61  in conventional manner. The boom  12  can be moved inwards and outwards by the ram  17  to have the fork carrier  13  assume a position, as illustrated in  FIG. 2 , close against the mast  11  or in the fully spaced-apart or extended position, as illustrated in  FIG. 8 .  
      The mast  11  can be extended or retracted by the actuating ram  22 . As the mast  11  is extended, the chain  31  between the pulley  33  and the sleeve  15 , shortens and pulls the boom  12  up the mast  11 . Simultaneously, the chain between the sleeve  15  and the pulley  35  extends. The reverse motion occurs when the mast  11  is retracted. Similarly, the mast  11  can be moved forwards and backwards by the frame moving ram  53 . Thus, loads can be moved across platforms or vehicle bodies in an efficient and easily controlled manner. For very heavy loads, it can be advantageous to have the mast  11  as near as possible to the centre of gravity of the forklift  1 . At the same time, the use of the moving support frame can be particularly advantageous where the forklift  1  can only be moved against a platform and not beneath it, where a load is being taken or removed from the platform. There is full, vertical and horizontal control of the movement of the load. This is advantageous as compared to a telescopic boom forklift, which telescopic boom forklift pivots about the vertical to allow the forks engage a load.  
      Instead of an endless chain, two chains may be used or indeed, wire ropes or any flexible connector.  
      Referring to  FIGS. 9 and 10 , there is illustrated an alternative construction of forklift, again identified generally by the reference numeral  1 , in which parts similar to those described with reference to the previous drawings, are identified by the same reference numerals. In this embodiment, on the fork carrier  13 , is mounted, by means of retractable rams  65 , a pair of ground engaging wheels  66 . In operation, the wheels  66  can be raised and lowered to help support the load. This will also tend to equalise the loading on the forklift and reduce the movement causing the rear wheels of the forklift  1  to raise off the ground. Suitable controls can be provided to raise and lower the wheels  66 . It is envisaged that instead of being mounted, as illustrated, with the rams outside the fork carrier, preferably they may be mounted within the frame of the fork carrier.  
      While in the embodiment described above, the boom is a telescopic boom, it is not necessary to have a telescopic boom and the forks, or more strictly, the fork carrier, could be slidable on a rigid boom. All that is required is that the forks be movable in the x and y axis.  
      In the specification the terms “comprise, comprises, comprised and comprising” or any variation thereof and the terms “include, includes, included and including” or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.  
      The invention is not limited to the embodiment hereinbefore described, but may be varied in both construction and detail within the scope of the appended claims.