Patent Publication Number: US-2005127620-A1

Title: Trailer with mechanically activated dolly legs

Description:
FIELD OF THE INVENTION  
      The present invention relates to a trailer having dolly legs, which can be mechanically extended or retracted.  
     BACKGROUND OF THE INVENTION  
      Large trailer units have underlying dolly legs positioned at their hitch end. These dolly legs are extended down to the ground to provide support, when the trailer is not attached to and supported by a tow vehicle. Most trailers dolly legs are presently extended and retracted by means of a mechanical crank mechanism.  
     SUMMARY OF THE INVENTION  
      What is required is an alternative form of mechanically activated dolly legs.  
      According to the present invention there is provided a trailer with mechanically activated dolly legs, which includes a trailer body having a front towing end and a rear end. Ground engaging support wheels are positioned at the rear end. Means are provided for attachment to a tow vehicle at the front towing end. Dolly legs are positioned spaced from and underlying the front towing end. The dolly legs are housed in a housing and are movable relative to the housing between an extended position and a retracted position. At least one air bag is positioned between the dolly legs and the housing. The air bag is adapted to move the dolly legs from the retracted position to the extended position.  
      With the trailer, as described above, the dolly legs are air activated for movement from their retracted position to their extended position. Once the basic teachings of this invention are understood, there are additional features which may be added to further enhance performance.  
      Although beneficial results may be obtained through the use of the trailer, as described above, even more beneficial results may be obtained when a spring is provided in the housing which is adapted to exert a biasing force urging the dolly legs from the extended position back into the retracted position.  
      Although beneficial results may be obtained through the use of the trailer, as described above, when the trailer has an air suspension system with an air supply tank, even more beneficial results may be obtained by having air supplied to the air bag or air bags from the air supply tank.  
      Although beneficial results may be obtained through the use of the trailer, as described above, it would be undesirable for the dolly legs to retract due to a sudden or gradual loss of air pressure. Even more beneficial results may, therefore, be obtained when the dolly legs have apertures adapted to receive locking pins to maintain the dolly legs in the extended position, should a loss of air pressure occur.  
      Although beneficial results may be obtained through the use of the trailer, as described above, there are limits on the distance that the dolly legs can be moved using an air bag. If the distance exceeds the manufacturers specifications for the air bag, stability problems will be encountered. Even more beneficial results may, therefore, be obtained when the dolly legs have telescopic leg extensions. Each of the leg extensions have an upper end and a lower end. The lower end of each of the leg extensions terminates in a support foot. The upper end of each of the leg extensions extends telescopically into the dolly legs. Means are provided to fix the leg extensions in a selected telescopic position. In the illustrated embodiment, the leg extensions screw into the dolly legs, however, locking pins or other means could also be used. The leg extensions are initially set to accommodate the stroke of the air bag or air bags. They can be adjusted, as required. For example, when the trailer is parked with the dolly legs positioned over a hollow, the leg extensions can be extended. When travelling over uneven ground where additional clearance is desired, the leg extensions can be retracted. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to in any way limit the scope of the invention to the particular embodiment or embodiments shown, wherein:  
       FIG. 1  is a side elevation view, in section, of a trailer with mechanically activated dolly legs constructed in accordance with the teachings of the present invention, with the dolly legs in the retracted position.  
       FIG. 2  is a detailed side elevation view, in section, of the trailer illustrated in  FIG. 1 , with the dolly legs in the extended position.  
       FIG. 3  is a side elevation view, in section, of an alternative embodiment of trailer with mechanically activated dolly legs constructed in accordance with the teachings of the present invention, with the dolly legs in the retracted position.  
       FIG. 4  is a detailed side elevation view, in section, of the dolly legs illustrated in  FIG. 3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The preferred embodiment, a trailer generally identified by reference numeral  10 , will now be described with reference to  FIGS. 1 and 2 . An alternative embodiment will be described with reference to  FIGS. 3 and 4 .  
      Structure and Relationship of Parts:  
      Referring to  FIG. 1 , trailer  10  has a trailer body  12  with a front towing end  14  and a rear end  16 . Mounted on trailer body  12  is an air suspension system  18  supplied with air from an air supply tank  20 . Body  12  is further adapted with ground engaging support wheels  22  at rear end  16  and a hitch  24  adapted for attachment to a tow vehicle  26  at front towing end  14 . Dolly legs  28  (one profile is shown) are spaced from and underlie front towing end  14  of body  12 . Dolly legs  28  are housed in a housing  30  which is attached to body  12 . The housing may also have rigid depending sleeves  31  adapted to provide enhanced lateral stability to the dolly legs. Dolly legs  28  are movable relative to housing  30  between an extended position as illustrated in  FIG. 2  and a retracted position as illustrated in  FIG. 1 . Referring to  FIG. 2 , in the illustrated embodiment, two air bags  32  are positioned between dolly legs  28  and housing  30 . Air bags  32  are adapted to move dolly legs  28  from the retracted position to the extended position. Air is supplied to air bags  32  from air supply tank  20 . A control valve  34  is provided to control the flow of air to air bags  32  and exhaust air from air bags  32 . A spring  36  is positioned in housing  30 . Spring  36  is adapted to exert a biasing force, (as indicated by arrows  38 ), urging dolly legs  28  from the extended position back into the retracted position. Dolly legs  28  have apertures  40  adapted to receive locking pins  42  to maintain dolly legs  28  in the extended position should air bags  32  experience a loss of air pressure. Dolly legs  28  are further adapted with telescopic leg extensions  44 . Each of leg extensions  44  having an upper end  46  and a lower end  48 . Each lower end  48  terminates in a support foot  50 . Each upper end  46  extends telescopically into each dolly leg  28 . In the illustrated embodiment, a latch  52  is provided to fix each leg extension  44  in a selected telescopic position.  
      Operation:  
      The use and operation of trailer with mechanically activated dolly legs will now be described with reference to  FIGS. 1 and 2 . Referring to  FIG. 1 , where trailer  10  is being towed by vehicle  26  and is in active operation, air bags  32  are deflated and spring  36  exerts a biasing force  38  to retract dolly legs  28  into housing  30 . Leg extensions  44  are fixed at a desirable height for ground clearance and retract upwards along with dolly legs  28 . Referring to  FIG. 2 , where trailer  10  is no longer attached to vehicle  26  and is in a resting mode, control valve  34  allows air from supply tank  20  into air bags  32  which exert a force (indicated by arrow  54 ) extending dolly legs  28  from housing  30  toward ground surface  56 . Where a user desires to adjust the moment of contact of support foot  50  with ground surface  56 , leg extensions  44  are telescopically extended from dolly legs  28  and fixed in place by latch  52 . In order to guard against the accidental deflation of air bags  32 , locking pins  42  are engaged with an appropriate one of apertures  40  to ensure safety and maintain trailer  10  in a stable position.  
      It will be appreciated that although  FIG. 1  uses an air supply tank  20  as the air supply for the air suspension system  18 , it will be understood that it would be possible to supply air from another source. For example, air could be supplied from an air supply tank on a tow vehicle.  
      Variations:  
      An alternative embodiment, a trailer generally identified by reference numeral  100 , will now be described with reference to  FIGS. 3 and 4 . Referring to  FIG. 3 , with alternative embodiment  100 , dolly legs, generally referenced by numeral  128  (one profile is shown) are spaced from and underlie front towing end  114  of body  112 . Dolly legs  128  are movable relative to body  112  between an extended position as illustrated with respect to dolly legs  38  of embodiment  10  in  FIG. 2  and a retracted position as illustrated in  FIG. 1 .  
      Referring to  FIG. 3 , in the illustrated embodiment, two air bags  132  are positioned between dolly legs  128  and body  112 . Air bags  132  are adapted to move dolly legs  128  from the retracted position to the extended position. Air is supplied to air bags  132  from air supply tank  120 . A control valve  134  is provided to control the flow of air to air bags  132  and exhaust air from air bags  132 .  
      Referring to  FIG. 4 , dolly legs  128  have apertures  140  adapted to receive locking pin  142  to maintain dolly legs  128  in the extended position should air bags  132  experience a loss of air pressure. With embodiment  100 , dolly legs  128  are further adapted with telescopic leg extensions  144 . A first section  146  of telescopic leg extensions  144  is fixed to body  112 . A second section  148  is received within first telescopic leg extensions  144 . Second section  148  extends into a third section  149  which terminates in a support foot  150 . A second section  148  is telescopically movable within first section. The position of second section  148  within first section  146  can maintained by to inserting locking pin  142  into one of the apertures  140  on first section  146 . Likewise, second section  148  can also move telescopically within third section  149 . The position of second section  148  within third section  149  can maintained inserting locking pin  142  into one of the apertures  140  on third section  146 .  
      In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements.  
      It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiment without departing from the spirit and scope of the invention as hereinafter defined in the claims.