Abstract:
Disclosed is a gearbox for a powered leg assembly for trailers. The gearbox includes a plurality of gears mounted in a cage, the cage being displaceable from a first low speed position through a neutral position to a second high speed position, and a lever coupled to an eccentric whereby movement of the lever causes displacement of the cage causing the gears to mesh to assume a low speed, neutral and high speed configurations.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Australian Patent Application Nos. 2012904072, filed Sep. 18, 2012 and 2013202391, filed Apr. 4, 2013, the disclosures of which are incorporated by reference in their entireties herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a powered jacking leg that forms part of the landing gear for articulated trailers. 
     2. Description of Related Art 
     For many years articulated trailers have included manually operable jacking legs located at the forward end of the trailer. The manual raising or lowering of jacking legs is an onerous task requiring a significant degree of strength. Current laws relating to health and safety are raising serious questions about the potential hazards of manually operating the jacking legs of trailers. 
     There have been a number of proposals to automate the raising and lowering of the legs of trailers. One solution to this problem is suggested in our earlier patent application WO 00/51859. This application relates to a demountable system that could be attached to existing jacking leg structures to provide a powered drive through the use of an electric motor. Most jacking systems incorporate a gearbox that facilitates a speed change so that when the forces are low the leg can be moved at high speed but when a heavy load has to be lifted, the ratios can be substantially reduced to render the task easier. 
     A problem with the use of the existing speed change systems is that the speed change mechanism is cumbersome and at times difficult to operate. When the leg is under load it is very difficult to move the gear wheels from one position to another. Thus, the demountable powered systems tend to be bulky and at times difficult to operate. 
     It is these issues that have brought about the present invention. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention there is provided a gearbox for a powered leg assembly for trailers, the gearbox comprising a plurality of gears mounted in a cage, the cage being displaceable from a first speed position through a neutral position to a second speed position, and a lever coupled to an eccentric whereby movement of the lever causes displacement of the cage. 
     Preferably there is provided a powered jacking system for use with articulated trailers, the system comprising a pair of opposed legs having feet that can be powered from a operational load supporting position to a retracted position, a screw drive in each leg operable to drive the feet, a transverse shaft connecting the screw drives and a gearbox of the kind described above secured to one leg to impart drive to each leg. 
     Preferably it is further provided with respect to the powered jacking system that each screw drive is positioned to be rotatable about a cage that moves up and down the screw drive to displace the foot, the cage abutting the end of the leg in the retracted position, damping means being positioned between the cage and the leg to reduce impact loads as the cage abuts the leg. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view of a jacking leg assembly of a trailer with a powered drive means attached to the leg, 
         FIG. 2  is a perspective view on one leg of the assembly illustrating the drive means, 
         FIG. 3  is an exploded perspective view of a gearbox of the drive means, 
         FIG. 4 a    is a rear elevational view of the gearbox with parts removed showing the box in a high speed mode, 
         FIG. 4 b    is a front elevational view of the gearbox in a high speed mode, 
         FIG. 5  is a rear elevational view of the gearbox with parts removed in a neutral mode, 
         FIG. 6  is a side elevational view of the gearbox in the neutral mode, 
         FIG. 7 a    is a rear elevational view of the gearbox in a low speed mode, 
         FIG. 7 b    is a front elevational view of the gearbox in a low speed mode, 
         FIG. 8 a    is a front elevational view of one jacking leg, 
         FIG. 8 b    is a cross sectional view taken along the lines A-A of  FIG. 8A , 
         FIG. 8 c    is an enlarged view of the top of the leg shown in the circle B of  FIG. 8   b,    
         FIG. 9  is a rear view of a plate forming part of the gearbox in an engaged mode, 
         FIG. 10  is a rear view of the plate in a neutral mode, 
         FIG. 11  is a front view of a housing of the drive means, and 
         FIG. 12  is a cross sectional view taken along the lines D-D of  FIG. 11 . 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The trailer jacking leg assembly  10  illustrated in the accompanying drawings comprises two spaced leg structures  11  and  12  that are secured to the underside of the front of an articulated trailer (not shown). Each leg structure  11 ,  12  includes a foot  13 ,  14  that is displaceable vertically relative to the leg structure  11 ,  12 . Each leg structure  11 ,  12  also includes a drive mechanism that is interconnected by a drive shaft  15  that extends across the leg structures so that rotation of the drive shaft  15  causes the feet  13 ,  14  to be raised or lowered as required. 
     As shown in  FIG. 1  a powered drive mechanism  20  is secured to the front of one leg structure  12  to be coupled to the drive shaft  15  to provide a powered drive to raise or lower the feet  13 ,  14  of both leg structures  11 ,  12 . 
     The powered drive means  20  essentially comprises a housing  21  that is adapted to be bolted to the forward face of the leg  12 . The housing contains a gearbox that imparts drive to the forward projection of a stub axle that projects through the housing to locate in a socket on the front face of the leg. Although not shown the socket is geared to the drive shaft  15 . The housing  21  also incorporates a control panel  50  that is located in a recess  23  in the front of the housing  21 . An electric motor  60  is secured to the underside of the housing  21  to impart drive to the gearbox. Where necessary, a separate power pack  70  is mounted on the other side of the leg  12  to provide power to the motor  60 . It is however understood that power could be driven by the prime mover or another source of power, namely the batteries located elsewhere on the trailer. 
     As shown in the exploded view of  FIG. 3  the housing  21  encloses the gearbox  30  that includes a series of gear wheels mounted on a carriage  31  about a main shaft  32 . The carriage  31  is mounted to a lever  33  that in operation causes the carriage  31  to move from three different orientations within the housing  21  to reflect connection of different gears to impart a speed change and a position of neutrality where the main shaft  32  can be manually turned to raise or lower the feet  13 ,  14 . 
     The housing  21  is in two halves  25 ,  26  that are bolted together. The rear half  25  is firmly secured to the front face of the leg  12  via screws  27 . This firm location has been designed to absorb the torque from the electric motor  60  through the gearbox  30 . The front half  26  of the casing has a peripheral skirt  28  that is bolted to a similarly shaped skirt  29  on the lower half  25 . The main shaft  32  extends through apertures  35 ,  36  in the housing halves  25 ,  26  to project forwardly from the front of the housing  21  to be connectable to a manual crank when necessary. The rearward extension of the main shaft  32  is the sub axle. 
     The front half  26  of the housing has a rectangular recess  23  into which is located the control panel  50 . When the housing halves  25 ,  26  are assembled the underside of the housing defines a plate  61  with a central aperture  62 . The electric motor  60  is bolted to the plate  61  so that a bevel gear (not shown) mounted on the output shaft of the electric motor  60  extends though the aperture  62  into the housing  21  to engage the gear assembly. 
     The gearbox has a primary gear  35  having a bevelled front face  36  to be driven by the bevel gear (not shown) mounted on the output shaft of the electric motor  60 . The rear side of the primary gear  35  has a gear  37  that in turn meshes with a high speed lay gear  38  to drive a tertiary gear  39  that is mounted on the main shaft  32 . The front of the primary gear has a smaller gear  40 . A low speed drive is effected through the meshing of the smaller gear  40  with a secondary gear  41 . Secondary gear  41  has a solidly coupled pinion gear  42  on its rear side which in turn meshes and imparts a drive to the tertiary gear  39  that is mounted on the main shaft  32 . 
     The change between low speed to high speed is effected by pivotal movement of the carriage  31  and in the low speed mode the carriage assumes the position shown in  FIGS. 7 a  and 7 b    where the secondary gear  41  is meshing with the smaller gear  40  on the primary gear  35 . In the high speed mode the carriage  31  is moved to the position shown in  FIGS. 4 a  and 4 b    in which the secondary gear  41  is now moved away from the smaller gear  40  on the primary gear  35  and the drive is imparted through the larger gear  37  on the rear of the primary gear  35  which drives the high speed lay gear  38  which in turn meshes with the tertiary gear  39  on the main shaft  32 . The low speed gear operates at a speed of about 6% of the speed of the high speed gear. 
     The carriage  31  is in the form of two plates  31   a ,  31   b  spaced in a parallel array with appropriately positioned apertures with bearings to support the main shaft  32 , and the shafts supporting the secondary gear  41  and high speed lay gear  38 . The primary gear  35  is supported by the housing halves and the tertiary gear  39  is on the main shaft  32 . The movement of the front face  31   a  of the carriage to effect gear changes is by an eccentric  43  driven by a shaft  44  that extends through the front of the housing  21  to be attached to a small lever  33  which, as can be seen from  FIGS. 4, 5 and 7  can be moved from three positions namely, a position pointing to the left to determine a high speed mode and a position pointing to the right to determine a low speed mode. If the lever  33  is moved to the vertical configuration ( FIG. 5 ), the drive from the electric motor is disengaged, which means that the main shaft  32  is free to rotate without causing rotation of the primary gear in the gearbox and subsequently the electric motor. This provides manual operation with minimum drag. 
     As shown in  FIGS. 9 and 10  a coil spring  90  extends between the eccentric  43  and a bolt  91  on the front plate  31   a . When the lever  33  is in either of the engaged positions  FIGS. 4 a , 7 a    and  9 , the spring  90  is compressed state of reduced tension. When the lever is in the neutral position  FIGS. 5 and 10 , the spring  90  is extended to a higher state of tension. A force is required to extend the spring  90  to move away from either engaged positions. Thereby ensuring the gears stay in the engaged state until the eccentric  43  is operated to change the gears state of engagement. 
     The electric motor is provided with a pair of pins that operate as the electrical terminals, these pins are arranged to extend through the housing and engage the underside of female recesses in the control panel. In this way, power from the control panel is fed directly to the electric motor. The power to the control panel comes from separate wiring from the power source (not shown). The control panel  50  includes an stop switch  51  and a raise and lower buttons  52 ,  53 . The control panel is a modular unit that has tabs on the rear side (not shown) and is simply slotted into the recess  23  and held therein by the pins of the motor. The motor is secured to the casing by two bolts that extend into the mounting flange. The drive mechanism  20  is comparatively slim and thus causes minimum obstruction to the leg assembly. 
       FIGS. 8 a , 8 b  and 8 c    show one of the legs  11  supporting a foot  13 . The stub axle  32  from the drive mechanism includes a gear  34  that imparts drive to the gear  80 . Gear  80  includes a bevel gear  86  on its inboard face that inturn drives bevel gear  81 . Bevel gear  81  is supported on the end of a rotating elongate screw  82  that is in turn threaded engagement with a cage  83 . The screw is free for axial rotation about a bearing  84 . The bevel  81  meshes with the shaft  80  and the main drive shaft  15  that extends between the legs  11 ,  12 . In each leg  11 ,  12  a Belleville washer  85  is positioned between the bearing  84  and the cage  83 . When the drive mechanism  20  drives the foot of the leg upwardly the cage  83  ultimately engages the end of the leg to stop the movement. The increase in current that takes place when the end of the cage  83  engages the leg causes the motor  60  to switch off. However, the high speed of the leg when it is lifting under no load has a tendency of causing severe shocks as the cage  83  hits the end of the leg. To reduce these shocks the Belleville washer  85  is positioned in between the bearing  84  and the cage  83 . When the cage  83  first contacts the Belleville washer  85  the current increases causing the electric motor  60  to switch off and the flexing of the Belleville washer  85  absorbs the shock loads whilst the motor  60  is switching off and reduces the impact load that would otherwise be between the cage  83  and the top of the leg  11 . 
       FIGS. 11 and 12  illustrate a mechanism to reduce the likelihood of crashing or crunching of the gears during a speed change operation. 
     A rare earth magnet  62  is seated in a non magnetic plastics seat  63  within the front gear carriage plate  31   a , when the gear carriage plate  31   a  is rotated by use of the gear change lever  33  the magnet  62  moves through an arc. This action sweeps the magnet past a magnetic switch (not shown) positioned within the control panel  50  and activates the switch when the plate and the gear lever is in the neutral gear position as shown in  FIG. 11 . The switch is located behind an aperture  64  in the housing recess  23  that supports the control panel  50 . When the switch is activated the power to the motor is disabled thereby ensuring that the motor only operates whilst in gear. If the gear change lever  33  is activated whilst the motor is running power will be cut off to the motor before the gears have a chance to engage the non-spinning gear side. This reduces the damage to the gears and simplifies the gear changing operation. 
     In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.