Abstract:
In a loading platform system for mounting on a vehicle, especially a truck provided with a loading platform mounted to the vehicle by a lift support structure which is operated by a lift actuator for lifting and lowering loads onto, and from, a vehicle loading bed by way of the loading platform, means are provided for locking the loading platform in its raised position in which its surface is in planar alignment with the vehicle loading bed, thereby preventing exposure of the lift actuator to the stresses generated by heavy loads disposed on the loading platform during loading and unloading of the vehicle.

Description:
[0001]    The invention relates to a loading platform system for mounting on vehicle, particularly on trucks, comprising a platform lifting structure, an essentially plate-like loading platform for lifting and lowering loads and at least one lifting actuator mechanism for lifting and lowering the loading platform.  
           [0002]    Such a loading platform system is described for example in EP-A-0 808 747. Loading platform systems of various designs have long been known. They are used particularly in connection with trucks in order to facilitate the lowering of loads carried by the truck from the truck loading bed to the ground on which the truck stands. From there, the load can be transported to its final destination by other means. The same is true for the loading of a truck. The load is first placed onto the loading platform while the loading platform is at ground level. The loading platform is then raised to the level of the loading bed of the truck and the load is then moved onto the loading bed.  
           [0003]    In some designs of loading platform systems, the platform is pivoted, after completion of the unloading and loading procedure, from its horizontal position in which the loading and unloading occurs, to a vertical position for closing the rear access opening of the loading bed or a trunk-like loading space.  
           [0004]    In other loading platform system designs, so-called folding loading platforms, the loading platform is not pivoted from a horizontal to a vertical position and vice versa. Rather, after the loading or, respectively, unloading procedure, the loading platform is folded and moved below the loading bed, that is, below the rear part of the loading bed of the truck.  
           [0005]    For the raising and lowering of the loading board platform in an essentially horizontal orientation for the loading and unloading of a truck, a so-called lift actuator structure is used. Such an actuator structure is operated hydraulically, pneumatically, electrically or in another suitable way. For the pivoting of the loading platform from the vertical to a horizontal position and vice versa, that is, for the opening and closing of the loading bed space, a pivot actuator structure is used which operates hydraulically, pneumatically, electrically or in some other suitable way. Loading platform systems of the type referred to above therefore include at least two actuator structures. Generally, the lift actuator cooperates with one support structure for the loading platform whereas the pivot actuator cooperates with another loading platform support structure. The loading platform support structures may, but do not need to, include parallelogram type support lever arrangements. A loading platform pivot structure however is—as previously mentioned—only provided if the loading platform needs to be pivoted from a horizontal to a vertical position and vice versa.  
           [0006]    It is known that, during loading and unloading, the raised loading platform, which then forms an extension of the loading bed of the truck, may be subjected to extremely high loads. For example fork lifts may be used for the loading and unloading procedure. In that case, the loading platform is not only subjected to the weight of the load but also the weight of the forklift used in the loading and unloading procedure.  
           [0007]    The truck may be loaded or unloaded for example from the ramp of a warehouse while the loading platform is raised and disposed adjacent the ramp. A forklift carrying a load may then drive over the loading platform for loading the loads onto the truck bed or removing them therefrom.  
           [0008]    In this way, the loading platform may be subjected to substantial loads, which increases the wear of the loading platform system. However, also from a safety point of view such loading of the loading platform is highly problematic since already partial failure of individual elements of the loading platform system may have fatal results for the persons performing the loading and unloading tasks. Also the loads being handled and the components of the loading platform system may be damaged upon failure of a component of the loading platform system.  
           [0009]    It is the object of the present invention to provide a loading platform system of the type as described above, which is safely held in its raised position and wherein, in the raised position of the loading platform, the actuating structure remains free from stresses even when the loading platform is subjected to high loads. The system should furthermore be easy and inexpensive to manufacture and easy to handle during operation and wear of the actuating mechanism should be essentially eliminated while the loading platform is held in its raised position for loading and unloading.  
         SUMMARY OF THE INVENTION  
         [0010]    In a loading platform system for mounting on a vehicle, especially a truck provided with a loading platform mounted to the vehicle by a lift support structure which is operated by a lift actuator for lifting and lowering loads onto, and from, a vehicle loading bed by way of the loading platform, means are provided for locking the loading platform in its raised position in which its surface is in planar alignment with the vehicle loading bed, thereby preventing exposure of the lift actuator to the stresses generated by heavy loads disposed on the loading platform during loading and unloading of the vehicle.  
           [0011]    The arrangement according to the invention has the advantage, that with the loading platform locked in its raised position, for example fork lifts can drive onto and over the loading platform while the loading platform remains firmly positioned without transmitting the load to the lift support structure and the actuating mechanism. The arrangement is simple and can easily be retrofitted to existing loading platform systems. It may also be installed in newly manufactured loading platform systems, without the need for changes of the current design. The arrangement is furthermore inexpensive and simple to operate.  
           [0012]    In a preferred embodiment concerning a loading platform system, in which the loading platform is pivotable from a horizontal to a vertical position for closing the load bed of the truck, the loading platform can also be locked in the vertical position. With the arrangement as shown in FIG. 2, the loading platform is safely locked in the vertical truck bed closing position so that it cannot be opened without disengaging the locking means. No stresses are transmitted to the actuating mechanism while the loading platform is locked in its vertical load bed closing position.  
           [0013]    Basically only one locking means is needed to lock the loading platform in a particular position but two or more locking means may be used if it is expected that the loading platform will be subjected to large loads.  
           [0014]    The locking means may be constructed in various ways. Preferably, the locking means includes a pin-like locking bolt, which is mounted on the vehicle and by which the loading platform is engaged or disengaged while the loading platform is raised and/or pivoted to a vertical position.  
           [0015]    A pin-like locking bolt represents a simple embodiment as it requires merely a linear guide structure or bearing in which the bolt can be moved axially back and forth in order to engage or disengage an abutment structure on the loading platform.  
           [0016]    The locking bolt can be engaged with, or disengaged from, the loading platform in any suitable way, for example, by electric motors or electromagnetic means. Preferably, however, the locking bolt is moved into, and held in, its engagement position by a pressure means, especially by a hydraulically or pneumatically operated piston and cylinder structure. A very simple pressure means is a compression spring.  
           [0017]    If the loading platform is for example in a raised position at the same level as the loading bed of the truck and the pin-like locking bolt is in engagement with the locking structure on the loading platform, the loading platform could be unlocked manually. For example a handle may be provided which is connected to the locking bolt by a cable or a linkage for moving the locking bolt out of its locking position.  
           [0018]    It is however particularly advantageous if the arrangement is such that the locking bolt can be moved to its unlocking position by initiating actuation of the lift actuator mechanism for lowering the loading platform. In this case, there is a coupling between the lowering that is the initiation of the lowering movement and the disengagement action of the locking bolt from the loading platform. This is possible for a system with a hydraulic, a pneumatic, electric, electric-motor or other kind of operating means. The same is true for the disengagement, which can be achieved by the source operating means. It is however also possible to use different power means for operating the lift actuator mechanism on one hand and the disengagement of the locking bolt from the loading platform on the other.  
           [0019]    The engagement structure on the loading platform may comprise one or more sleeves—depending on the number of locking bolts used—into which the locking bolts are inserted. However, because of the possibly high bending moments generated, upon loading of the loading platform, on the lifting and possibly also the tilting structure of the loading platform when it is locked in the raised position, the engagement structure of the loading platform preferably includes a roller element or, respectively, several roller elements under which the locking member or pin moves in the locking position. An elastic deformation of the loading platform when loaded while being locked and a slight pivoting because of the moment applied to the support structures will then not detrimentally affect the locking bolt as the roller elements permit slight movement of the bolt relative to the loading platform.  
           [0020]    Below, an embodiment of the invention will be described in greater detail with reference to the accompanying schematic drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIGS. 1 a,    1   b  and  1   c  show the loading platform in different positions as it is moved upwardly up to the level of the loading bed of a truck, in which position it is locked by a locking bolt,  
         [0022]    [0022]FIG. 2 a  shows the loading platform system of FIGS. 1 a - 1   c , wherein the loading platform however is in a vertical position just before being locked in this position,  
         [0023]    [0023]FIG. 2 b  shows the loading platform locked in the vertical position,  
         [0024]    [0024]FIG. 3 shows a hydraulic or pneumatic control arrangement for operating the locking bolt in connection with the operation of the platform lift and pivot actuators, and  
         [0025]    [0025]FIG. 4 shows another embodiment of the locking mechanism. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]    Loading platform systems  10  for mounting on vehicles  11 , particularly trucks, are well known to the art. Such loading platform systems are described in detail for example in U.S. Pat. No. 6,082,958. The specific design of such systems is therefore described herein only in as much as it is necessary for an understanding of the present invention. Basically, a loading platform system comprises a lift support structure  12  and a pivot support structure  13  for supporting an essentially plate-like loading platform  15 . The lift support structure includes a lift actuator  16  for raising the loading platform for example from ground level to the loading bed level of the truck and vice versa and the tilt support structure includes a tilt actuator  17  for pivoting the loading platform  15  from a horizontal position to a vertical position and vice versa.  
         [0027]    The basic version of a loading platform system  10  is shown schematically in FIGS. 1 a - 1   c  to which reference is now made. The figures show schematically only a lift or, respectively, tilt support structure  12 ,  13 . The lift support structure  12  includes a lift actuator  16 , which is indicated in the figure as a piston-cylinder arrangement, which may be operated hydraulically or pneumatically. However, the lift actuator  16  may also be an electrically driven mechanism. The lift or respectively, tilt support structure is, at one end, pivotally connected to the loading platform  15  and, at the other end, supported by a suitable structure on the vehicle  11 . The lift support structure and, respectively, the tilt support structure of the loading platform  15  may include parallelogram-like support arms as they are well known to the persons knowledgeable in the field. A particular support arrangement is shown and described in the aforementioned U.S. Pat. No. 6,082,958, which is included herein by reference thereto. Each loading platform system however includes at least one lift support structure  12  and, if the loading platform system  10  includes a pivotal loading platform, at least one tilt support structure  13  for pivoting the loading platform from a horizontal to a vertical position and vice versa.  
         [0028]    The loading platform system  10  includes at least one locking means  18  by which the loading platform  15  can be releasably locked in its raised end position (see FIG. 1 c ). The locking means  18  consists essentially of a pin-like locking bolt  19 , which is movably supported in a locking bolt guide structure  190  so as to be slideable back and forth in the direction as indicated by the double arrow  191 . In addition to the locking bolt  19  and the locking bolt guide structure  190 , the locking means  18  includes an engagement structure  20  formed on the loading platform  15 . In the embodiment of the loading platform system  10  as shown in the figures, the locking means  18  or rather the pin-like locking bolt  19  is biased by a pressure structure, which is shown as a compression spring  21 , in a locking position  22 . From this position the locking bolt  19  can be retracted to an unlocking position  23  against the force of the pressure means for the release of the loading platform. It is pointed out that the pressure means  21  may be in another form. It may be, for example, in the form of a hydraulically and/or pneumatically operated piston-cylinder arrangement.  
         [0029]    The locking bolt  19  is connected to an operating lever  24  by a cable or a rod  27 . The operating lever  24  may be lockable to prevent unintended actuation thereof.  
         [0030]    [0030]FIG. 1 a  shows a position of the loading platform system  10  wherein the surface of the loading platform  15  approaches the surface plane of the loading bed  110 . The locking bolt  19  is seated in its guide structure  190  in a locking position under the force of the spring  21  against which it can be moved out of its locking position. As the loading platform  15  is further raised by the lift support structure  12  through actuation of the lift actuator  16 , the locking bolt  19  is contacted by the engagement structure  20 . The engagement structure  20  comprises a roller element  200 , by which the locking bolt  19  is pushed back against the force of the spring  21 . Upon further raising of the loading platform  15  by the lift actuator  16  the locking bolt  19  can move below the engagement structure  20  (see FIG. 1 c ), that is, below the roller element  200 . In this position in which the locking bolt  19  is held by the spring  21 , the loading platform  15  is prevented from being lowered. When the loading platform  15  is to be lowered, the locking bolt  19  must first be retracted by the operating lever  24 , whereby the locking bolt is moved out from under the roller element  200 . This permits the loading platform  15  again to be lowered by the lift actuator  16 .  
         [0031]    The loading platform system may also include a platform tilt mechanism  17  (see FIGS. 2 a,    2   b ) for locking the loading platform in a vertical position. The loading platform may then be pivoted from a position as shown in FIG. 1 b  upwardly in the direction of arrow  29  by actuating the tilt mechanism  17  until it reaches a vertical position as shown in FIG. 2 a.    
         [0032]    The vehicle body  11  includes a clamp  26 , which is open downwardly. When the loading platform  15  is now moved further upwardly the tip of the loading platform  15  (see arrow  26 ) is engaged by the clamp  26  so that down-pivoting of the loading platform  15  is prevented. At the same time, the locking bolt  19  is moved by the force of the spring  21  below the roller element  20 , thereby firmly holding the free end of the loading platform  15  in engagement with the clamp  26 . In this way, the loading platform  15  is firmly locked in its vertical position.  
         [0033]    Again, the loading platform can be unlocked by retracting the locking bolt  19  by moving the actuating lever  24  thereby pulling the locking bolt  19  out from under the roller element  200  by means of the pull-rod or cable  27 . Then the loading platform  15 , still in its vertical position, is slightly lowered until its tip or free end is released from the clamp  26 . Upon release of the free end of the loading platform  15  from the clamp  26 , the loading platform  15  can be pivoted down to a horizontal position in a direction opposite to the direction of the arrow  29 .  
         [0034]    [0034]FIG. 3 shows an embodiment of the invention with a control arrangement for disengaging the locking bolt  19  from the engagement structure  20  of the loading platform. In this embodiment, a pressure medium is utilized. In loading platform systems, a liquid or gas under pressure is generally provided for operating the lift actuator mechanism  16  hydraulically or pneumatically. The pressure medium for operating the lift actuator  16  is supplied to the lift actuator  16  by way of a conduit  14 , which, in the present case, is for example a hydraulic line. A magnetic valve  30  is so designed and controlled that the hydraulic medium is admitted to the lift actuator  16  for initiating movement of the loading platform  15  toward the loading bed  110  of the vehicle  11 . The lift speed is determined by the amount of the hydraulic medium per time supplied to the lift actuator  16  through the conduit  14 . In a loading platform system  10  according to the invention, wherein the loading platform  15  can be locked in its raised position, a magnetic valve  33  is provided which is arranged so as to be energized in parallel with the magnetic valve  30  for controlling a fluid supply to operating means for the lock operating mechanisms. The lock operating mechanism includes a piston cylinder system  31 , which is connected to the pressure medium conduit  14  by way of the magnetic valve  33 . In this way, hydraulic fluid can be supplied to the cylinder-system  31  whenever hydraulic fluid is supplied to the lift actuator  16 . This generates at the same time a force biasing the locking bolt  19  into locking direction.  
         [0035]    In a loading platform system  10 , the conduit for the pressure medium is normally directly connected to a pressurized medium storage (not shown). When the loading platform  15  is raised, the lift actuator  16  is under pressure. The loading platform  15  exerts a counter pressure by its weight and, if present, a load deposited on the loading platform  15 . The pressure of the pressure medium in the lift actuator  16  is selected to be high enough to prevent an uncontrolled lowering of the loading platform  15 . When the lowering of the loading platform  15  is desired, this is the medium is released from the lift actuator  16  in a controlled manner. This is done by releasing the pressure medium through a flow controller  34  which is arranged in series with the magnetic valve  30 .  
         [0036]    In the loading platform system  10  according to the invention, which includes an arrangement for locking the loading platform  15  in a raised position, the valves  30  and  33  are energized in parallel as already mentioned. The valve  32 , which is arranged in series with the magnetic valve  30  and the flow controller  34  opens only when the cylinder system  31  is not under pressure. In this way, it is insured that the lowering of the loading platform can be initiated only when the locking bolt  19  is in a retracted position that is when it does not engage the loading platform  15 . The valve  32  can be by-passed by way of a check valve  35  for pressurizing the actuator  16 .  
         [0037]    The arrangement of the loading platform system  10  as described with regard to FIG. 3 can easily be retrofitted to loading platform systems, which are already installed in vehicles but which do not have a locking arrangement for the loading platform  15  in a raised position. It is an important advantage of the arrangement as shown in FIG. 3 that, upon retrofitting, the normal control arrangement for the loading platform system is not disturbed.  
         [0038]    [0038]FIG. 4 shows another arrangement for the locking means  18  of FIG. 3, wherein the structure enclosed by the dash-dotted line of FIG. 3 is combined to a locking unit. Here, the locking bolt  19 ′ is mounted directly onto a piston rod  36  of the piston-cylinder system  31 . The pressure medium or, respectively, the locking spring  37 , comparable to the spring  21  of the arrangement of FIG. 3, is integrated into the piston rod  36 . The interlocking spring  38  disposed in the cylinder  31  in the form of a compression spring is schematically shown.