Abstract:
A trailer jack having a low profile which will not interfere with opening of a towing vehicle&#39;s tailgate. The jack has tubes telescopically contained within each other. A threaded rod has a threaded tube slidingly placed over it. The threaded tube has slots and a pin in the threaded rod slides within the slots for synchronous rotation. This provides even extension and retractions for the telescoping tubes relative to each other. The jack has a low profile that extends above the trailer tongue a minimal amount when the jack is extended. When the jack is retracted, no parts of the jack are raised above the tongue. Thus, the tailgate of the towing vehicle may be operated without hitting any part of the jack.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Trailer jacks are commonly used to hold and lift a trailer tongue before hitching to a vehicle. The jacks extend to contact the ground and push against it and also must be retracted to provide clearance for when the trailer is being towed. When the jack is retracted, typically parts of the jack that were below the tongue must be moved above the tongue to provide the necessary ground clearance for being towed. This is a problem because, often times the tailgates of towing vehicles can hit the jack after it is retracted and sticking up above the tongue. Ideally, a trailer jack when fully retracted would have no parts above the trailer tongue to obstruct operation of a towing vehicle&#39;s tailgate. 
       SUMMARY OF THE INVENTION 
       [0002]    The present invention has a first tube that contains a threaded member that is rotatably held within the first tube. The threaded member is fixed from axial movement relative to the first tube. A second tube is telescopically contained within the first tube and has female threads that engage the first threaded member so that rotation of the first threaded member causes the second tube to slide axially within the first tube. A second threaded member engages the first threaded member for synchronous rotation with the first member and is movable axially relative to the first threaded member. The second threaded member is fixed from axial movement relative to the second tube. A third tube is telescopically contained within the second tube and has female threads that engage the second threaded member so that rotation of the first and second threaded members causes the third tube to slide axially within the second tube. 
         [0003]    The first threaded member can be a threaded rod and the second threaded member can be a threaded tube having external threads. In this case, the inner diameter of the threaded tube is larger than the outer diameter of the threaded rod. 
         [0004]    The third tube may include either a flat foot, which is just a piece for resting on a ground surface, or a pivotal foot. The pivotal foot has a gear that is fixed to a shaft that is pivotally retained within the third tube and affixed through the foot. The gear mates with a rack that is fixed relative to the third tube. Movement of the gear over the rack pivotally extends or retracts the foot. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a perspective of the trailer jack with a pivotally extendable foot; 
           [0006]      FIG. 2  is a side view of the jack in  FIG. 1 ; 
           [0007]      FIG. 3  is a sectional view taken about line  3 - 3  in  FIG. 2 ; 
           [0008]      FIG. 4  is a sectional view taken about line  4 - 4  in  FIG. 2 ; 
           [0009]      FIG. 4A  is a detail view near the top of the threaded rod; 
           [0010]      FIG. 4B  is a detail view near the top of the threaded tube; 
           [0011]      FIG. 5  is a sectional view taken about line  5 - 5  in  FIG. 3  of the threaded rod and threaded tube together, not showing the tubes; 
           [0012]      FIG. 6  is a perspective view of the jack in  FIG. 1  retracted; 
           [0013]      FIG. 7  is a view of the third tube of the jack shown in  FIG. 1 , near the ground with the foot not bearing weight; 
           [0014]      FIG. 8  is a side view of the third tube of the jack shown in  FIG. 7 , near the ground with the foot not bearing weight; 
           [0015]      FIG. 9  is a view of the third tube shown in  FIG. 7-8  touching the ground and bearing weight; 
           [0016]      FIG. 10  is a side view of the third tube shown in  FIG. 9  touching the ground and bearing weight; 
           [0017]      FIG. 11  is a perspective view of the jack with a flat non pivoting foot; 
           [0018]      FIG. 12  is a perspective view of the jack having only a first and second tube with a pivotal foot; 
           [0019]      FIG. 13  is a front view of the jack having a fixed foot in its extended position; 
           [0020]      FIG. 13A  is a sectional view of the jack taken about line  13 A- 13 A in  FIG. 13 ; 
           [0021]      FIG. 14  is a front view of the Jack shown in  FIG. 13  in its retracted position; and 
           [0022]      FIG. 14A  is a sectional view of the jack taken about line  14 A- 14 A in  FIG. 14  similar to  FIG. 13  with the jack in its retracted position. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0023]    The present invention is a jack  10  used near the tongue  12  of a trailer to support it when it is unhitched.  FIG. 1  shows the tongue  12  without the hitch. The jack  10  shown in  FIG. 1  is shown sectioned along its length in  FIG. 4 . It has an outermost first tube  16  that is fixed to the tongue  12  as shown in  FIG. 1 . The first tube  16  contains a second tube  18  that is telescopically slidable within the first tube  16 . The second tube  18  telescopically contains a third tube  22  that is slidable within the second tube  18 . Each of the first, second and third tubes  16 ,  18 ,  22  includes a crease  24  as shown in  FIG. 3 . The creases  24  prevent rotation of each tube  16 ,  18 ,  22  with respect to the other tubes, yet allows axial movement. It is contemplated that the tubes  16 ,  18 ,  22  could be square or rectangular tubing if desired and using such a tube would eliminate the need for the creases  24  to prevent relative rotation of the tubes  16 ,  18 , and  22 . The tubes  16 ,  18 ,  22  may be made of any material that can support the weight of a trailer tongue  12  and may be cost effectively made from steel. The first tube has a stop block  28  fixed at its upper end as shown in  FIG. 4 . The stop block  28  does not move with respect to the first tube  16 . It may be secured using semi-pierces or dimples within the outer tube  16  that impinge on the stop block  28  to lock it into place. The stop block  28  has a hole  30  with a smooth inner diameter that accepts a first threaded member that is a threaded rod  32 . The threaded rod  32  rotates freely within the stop block  28 . The threaded rod  32  is held within the stop block  28  near its upper end  29  with a snap ring  34  above and a thrust bearing  36  below the block  28 . This is shown in detail in  FIG. 4A . The thrust bearing  36  is between the stop block  28  and a shoulder  40  on the threaded rod  32 . The threads on the threaded rod  32  are Acme threads. Turning the threaded rod  32  will move the second tube  18  axially within the first tube  16 . 
         [0024]    The second tube includes a threaded block  42  having female threads that engage the threaded rod  32 . The threaded block  42  is fixed within the second tube  18  and cannot rotate with respect to the second tube  18 . As the second tube  18  moves with respect to the first tube, the block  42  moves with the second tube  18 . The second tube  18  also includes a second stop block  46 . The second stop block  46  is fixed within the second tube  18  and does not move with respect to the second tube  18 . The second stop block  46  rotatively holds a second threaded member, which is a threaded tube  48 . The threaded tube  48  is held within the stop block above by a snap ring  50  and below by a thrust bearing  52  that rests on a shoulder  54  of the threaded tube  48 . The threads on the threaded tube  48  are Acme threads of the same pitch as those on the threaded rod  32 . The inner diameter of the threaded tube  48  is slightly larger than the outer diameter of the threaded rod  32 . This allows the threaded tube  48  to move axially with respect to the threaded rod  32 . The threaded rod  32  includes a pin  55  that protrudes from the threaded rod  32  on both sides and rides in slots  56  on opposite sides the threaded tube  48 .  FIG. 5A  shows a slot  56  in which the pin  55  rides. Thus, the threaded rod  32  and the threaded tube  48  are linked for synchronous rotation and the threaded tube  48  is not prevented from axial movement with respect to the threaded rod  32 . During rotation of the threaded rod  32  and threaded tube  48 , the position of the pin  55  will change in the slots  56  because the threaded tube  48  will move with the second tube  18 , which moves with respect to the first tube  16 , and the threaded rod  32  will not move with respect to the first tube  16 . 
         [0025]    The third tube  22  includes a threaded block  60  having female threads that engage the threaded tube  48 . Threaded block  60  is fixed at the upper end of the third tube  22  and cannot rotate with respect to the third tube  22 . Rotation of the threaded rod  32  and the threaded tube causes the third tube  22  to move with respect to the second threaded tube  18 . As the third tube moves with respect to the second tube  18 , the threaded block  60  moves with the second tube  18 . 
         [0026]    The threaded rod  32  may be rotated using the motor  71  and gear box  73 . This is done by use of a pinion (not shown) that is fixed to the upper end  29  of the threaded rod  32 . The threaded rod  32  may also be turned using a fold down handle, as is often done in prior art trailer jacks. In either case, rotation of the threaded rod  32  causes synchronous rotation of the threaded tube  48 . Rotation of the threaded rod  32  and tube  48  in one direction causes the jack  10  to extend and rotation in the opposite direction causes the jack  10  to retract. When standard right hand Acme threads are used, turning the threaded rod  32  counterclockwise as viewed from above will extend the jack  10  whereas clockwise rotation will retract the jack  10 .  FIG. 13  shows a section of a jack  10  using standard Acme threads having a flat foot  61  that does not pivot, with the jack  10  in its extended position.  FIG. 14  shows the jack  10  in its retracted position. When the jack  10  is in its retracted position, the threaded block  42  in the second tube is close to the stop block  28  in the top of the first tube  16 . The threaded block  60  in the third tube  22  is near the second stop block  46  in the second tube  18 . As the threaded rod  32  and tube  48  rotate counterclockwise, the threaded blocks  42 ,  60  move away from the stop blocks  28 ,  46  respectively. The fully extended position of the jack  10  shown in  FIG. 13A  shows the threaded blocks  42 ,  60  and stop blocks  28 ,  46  at their farthest apart locations. During extension of the jack  10 , the second tube  18  is extended axially from the first tube at a predetermined rate based on rotation of the threaded rod  32 , and the third tube  22  is extended axially from the second tube  18  at the same rate. This is because the threads on the threaded rod  32  and threaded tube  48  are the same pitch and they both rotate at the same rate at all times. Thus, the jack  10  is may be rapidly deployed. The thrust bearings  36 ,  52  support the weight of the tongue  12  when lifted. When the jack  10  is retracted and the foot  61  is not touching the ground  63 , the snap rings  34 ,  50  prevent the threaded rod  32 , and threaded tube  48  respectively from falling out of the jack  10 . 
         [0027]    In the embodiment shown in  FIG. 1 , the lower end of the third tube  22  has slots  64  on opposite sides of the tube  22 , each having an upper end  66  and a lower end  68 .  FIG. 4  shows the slots  64 . The slots  64  carry a shaft  68  that rides within them and is rotatable within the slots  64 . The shaft  68  is fixed from rotation with respect to a foot  69  that is held onto the third tube  22  by the shaft  68 . A gear  70  fixed on the shaft outside the third tube  22  and rotates with the shaft  68 . The shaft  68  also includes a first locking feature  72  that is rigidly affixed to the shaft  68  and rotates with the shaft  68 . Although the FIGS. show the gear  70  and locking feature  72  on opposite sides of the shaft, it is contemplated that both could be on the same side of the shaft  68 . This might be desirable if the locking feature  72  and gear  70  were cast at the same time. The third tube  22  has a second locking feature  76  rigidly affixed thereon that is complementary to the first locking feature  72 . The second locking feature  76  has a negative profile of the protruding triangular shape contained on the first locking feature  72 . The second locking feature  76  may be a welded metal boss. It is not necessary that the locking features  72 ,  76  have complementary triangular shapes as shown in  FIGS. 7-10 , just that the shapes complement each other when the mating surfaces  78 ,  80  are in contact. For instance, a rectangle rigidly affixed to the shaft  68  in place of the first locking feature  72  would complement a flat surface on a raised rectangle in place of the second locking feature  76 . 
         [0028]    A rack  84  is fixed to the first tube  12  and is designed to mate with the gear  70 . When the third tube  22  is positioned near its fully retracted position the gear  70  will be moved along the rack. The fully retracted position of the jack  10  is shown in  FIG. 6 , and the foot  69  is in its fully retracted position along with the fully retracted third tube  22 . As can be seen in  FIG. 3  the foot  69  is open facing the rear of the trailer. This allows the foot  69  to be pivoted as the gear  70  is moved along the rack. When the jack  10  is extended, the third tube  22  will be moved downward relative to the stationary rack  84 . This will cause the gear  70  to rotate, and thus, rotate the foot downward into its extended position, shown in  FIG. 1 . The gear  70  and rack are positioned so that approximately 180 degrees of the gear contacts the rack  84 . Therefore, the foot  69  will never be rotated more than the necessary 180 degrees needed to move it from its retracted to extended position and vice versa. 
         [0029]    As the jack  10  is extended downward it will ultimately contact the ground  63 , which is necessary to support and lift the tongue  12 .  FIG. 1  shows the jack  10  immediately before the foot  69  contacts the ground  63 .  FIGS. 7-10  show the third tube  22  on the jack in  FIG. 1  in a larger more detailed view near the ground  63 .  FIGS. 7 and 8  show the foot  69  as it nears the ground surface. In  FIGS. 7 ,  8  the weight of the foot  69  keeps the shaft  68  in the bottom of slots  64 . Also, with the foot  69  in the extended position, the first locking feature  72  is pointed upward.  FIGS. 9 ,  10  show the foot  69  on the ground and with the jack  10  bearing weight. In this position, the third tube  22  is pushed down until the first locking feature is contacting the second locking feature  76 . The mating surfaces  78 ,  80  are meshed together and the shaft  68  is in the top of the slot. The position shown in  FIGS. 7 ,  8  provides stability because the foot  69  is prevented from pivoting. This is a safety feature that prevents the foot  69  from accidentally pivoting if the trailer were to roll forward, such as if chocks were not used on the wheels. If the trailer were to roll backward, the shape of the foot would catch on the third tube  22  due to the closed front of the foot  69  even in the absence of the locking features  72 ,  76 . 
         [0030]    The pivotal foot  69  provides an extremely rapid extension and retraction of the jack  10 . During extension of the jack  10 , all that is necessary to extend the jack  10  the entire length of the foot  69  is movement enough to turn the gear  70 , 180 degrees. For instance, if a one inch gear is used, the jack  10  must extend only half of the circumference of the gear. This corresponds to a distance of π*radius; (½ inch*3.14)=1.57 inches. Thus, the foot  69  is extended or retracted in a mere 1.57 inches. If the foot is twelve inches tall a rather large amount of travel is obtained rather quickly, and this is done before weight is placed on the foot  69 . Because of the rapid increase in length that may be made by a jack  10  of the configuration shown in  FIG. 1 , in certain applications it may be desirable to have the foot  69  placed in the second tube  18  and have no third tube  22 .  FIG. 12  shows a jack  10  having only a first and second tube  16 ,  18  with a foot  69 . 
         [0031]    When a user of the jack  10  wishes to extend the jack  10  to lift the tongue  12  of a trailer he will move the toggle switch  90  located on the back of the gear box  73  to turn the motor  71  in the direction necessary to extend the jack  10 . As mentioned above, in all the embodiments, the tubes  16 ,  18 ,  22  will extend with respect to each other until reaching the ground  63 . At that point the user will hold the toggle switch  90  until the tongue  12  is lifted to its desired height. Electronic controls within the gear box  73  will prevent the jack from overextending. Once the trailer is hitched to a towing vehicle, the jack  10  is retracted with the opposite procedure. 
         [0032]    In its fully retracted position, the jack  10  has no parts extending over the gear box  73 . Because of the telescoping design, achieving ground clearance beneath the tongue  12  necessary to tow the trailer can be had without moving any parts of the jack  10  above the tongue  12 . This enables tailgates of towing vehicles to be opened above the tongue  12  without hitting parts above the tongue, which is a problem with prior art trailer jacks. 
         [0033]    The invention is not limited to the details given above, but may be modified within the scope of the following claims.