Abstract:
A trailer tongue jack includes a grease (or zerk) fitting for providing grease to internal parts The jack includes an outer tube and an inner telescoping tube. A threaded insert (or nut) is fixedly attached inside an upper end of the inner telescoping tube. A screw shaft threadedly cooperates with the insert to extend or retract the inner telescoping tube from a lower end of the outer tube. A crank is provided to turn the screw shaft either directly or through gears, and a thrust bearing carries a vertical load between the screw shaft and the outer tube. The grease fitting allows the internal parts, and the thrust bearing in particular, to be easily lubricated.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to accessories for trailers and in particular to an improved tongue jack. 
   When a trailer is parked and detached from a tow vehicle, a support is required for the trailer tongue. Although other objects might be used, generally a special purpose jack (called a trailer jack or tongue jack) attached to the tongue is used. Trailer jacks generally are mounted vertically, or are pivotable to a vertical position, and have a telescoping portion and a crank for upwardly and downwardly moving the telescoping portion. Such jack provides static support, leveling, and facilitates detaching the tongue from the trailer hitch on the tow vehicle by allowing the tongue to the raised relative to the hitch and thereby disengaging from the hitch. Large trailers generally have significant tongue weight for safety and control. The tongue jack much be able to support the tongue weight, and allow operation without undue effort. 
   Devices for supporting trailer tongues are well known. U.S. Pat. No. 2,159,395 for “Trailer Control,” describes a pivotable wheel assembly which may be cranked to a down position whereby the trailer tongue is supported. U.S. Pat. No. 2,638,315 for “Trailer Attached Jack,” describes a simple telescoping jack for supporting a trailer tongue. U.S. Pat. No. 2,638,315 for “Trailer Attached Jack,” describes a telescoping tongue jack similar to modern jacks. The jack of the &#39;315 patent includes a crank for turning a screw shaft, which screw shaft is held in place by a thrust bearing, and cooperates with a nut attached to an inner telescoping tube to extend or retract the inner tube. 
   U.S. Pat. No. 3,314,693 for “Retractable Trailer Tongue Jack,” describes a jack having a screw shaft with a ring gear. A crank turns a pinion gear engaging the ring gear to turn the screw shaft, thereby extending or retracting an inner tube. U.S. Pat. No. 5,435,523 for “Trailer Tongue Jack,” describes a tongue jack with a pair of cooperating beveled gears coupling a crank to a screw shaft. 
   When known tongue jacks are used with heavy trailers having substantial tongue weight, the thrust bearings require lubrication to reduce wear and provide easy use. Commonly, such lubrication is provided by opening the trailer jack assembly and applying grease to internal parts. Unfortunately, such opening and applying may be a messy operation, and the grease frequently escapes the jack assembly, resulting in the grease on hands and clothing. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention addresses the above and other needs by providing a trailer tongue jack which includes a grease (or zerk) fitting for providing grease to internal parts The jack includes an outer tube and an inner telescoping tube. A threaded insert (or nut) is fixedly attached inside an upper end of the inner telescoping tube. A screw shaft threadedly cooperates with the insert to extend or retract the inner telescoping tube from a lower end of the outer tube. A crank is provided to turn the screw shaft either directly or through gears, and a thrust bearing carries a vertical load between the screw shaft and the outer tube. The grease fitting allows the internal parts, and the thrust bearing in particular, to be easily lubricated. 
   In accordance with one aspect of the invention, there is provided a trailer jack comprising an outer tube having a first top end, and a first bottom end, an inner tube having a second top end, a second bottom end, and being slidable inside the outer tube. A threaded insert is fixedly attached to the inner tube proximal to the second top end of the inner tube. A rotatable screw shaft is translationally fixed relative to the outer tube and is threadedly coupled to the insert. Turning the screw shaft a first direction extends the inner tube from the first bottom end of the outer tube, and turning the screw a second direction retracts the inner tube into the first bottom end of the outer tube. A thrust bearing is adapted to carry a vertical load between the screw shaft and the outer tube, and a grease fitting attached to the top end of the outer tube and adapted to provide grease to the thrust bearing. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
       FIG. 1A  is a trailer connected to a tow vehicle. 
       FIG. 1B  depicts the trailer detached from the tow vehicle with a trailer jack supporting a tongue of the trailer. 
       FIG. 2A  shown a first trailer jack with a first crank attached to a top end of the jack. 
       FIG. 2B  shows a second trailer jack with a second crank attached to a side of the jack. 
       FIG. 3  is a cross-sectional view of the first trailer jack taken along line  3 — 3  of  FIG. 2A . 
       FIG. 3A  is a detailed view of a top portion of the first trailer jack taken along line  3 — 3  of  FIG. 2A . 
       FIG. 3B  is a second detailed view of a top portion of the first trailer jack taken along line  3 — 3  of  FIG. 2A  with an inner tube partially extended. 
       FIG. 4  is a cross-sectional view of the second trailer jack taken along line  4 — 4  of  FIG. 2B . 
       FIG. 4A  is a detailed view of a top portion of the second trailer jack taken along line  4 — 4  of  FIG. 2B . 
       FIG. 4B  is a detailed view of the top portion of the second trailer jack rotated 90 degrees, taken along line  4 — 4  of  FIG. 2B . 
       FIG. 5  is a detailed view of a notch in a top end of the inner tube. 
       FIG. 6  is a thrust bearing comprising ball bearings held in a bearing race. 
       FIG. 6A  is a cross-sectional view of the thrust bearing taken along line  6 A— 6 A of  FIG. 6 . 
   

   Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
   A trailer  10  connected to a tow vehicle  12  is shown in  FIG. 1A . The trailer  10  includes a trailer tongue  14  which is connected to a trailer hitch  16  of the tow vehicle  12 . The tongue  14  and hitch  16  combine to provide a connection for pulling the trailer  10 , and vertical support for the tongue  14 . The total weight transferred from the tongue  14  to the hitch  16  is called “tongue weight”, and heavy trailers often have significant tongue weight. The trailer  10  is shown detached from the tow vehicle  14  in  FIG. 1B . A trailer jack  18  is used to support the tongue weight. 
   A first trailer jack  18   a  with a first crank  26   a  attached to a top end of the jack  18   a  is shown in  FIG. 2A . The jack  18   a  includes a first outer tube  20   a , a first inner tube  22   a , and a first crank  26   a . The outer tube  20   a  includes a flange  24  for mounting the jack  18   a  to the tongue  14 , and the crank  26   a  includes a handle  28 . A second trailer jack  18   b  with a second crank  26   b  attached to a side of the jack  18   b  near the top of the outer tube  20   b  is shown in  FIG. 2B . 
   A cross-sectional view of the first trailer jack  18   a  taken along line  3 — 3  of  FIG. 2A  is shown in  FIG. 3 . A threaded insert (or nut)  32  is fixedly attached to the inner tube  22   a  proximal to the top end of the inner tube  22   a . A first screw shaft  30   a  is translationally fixed relative to the outer tube and threadedly coupled to the threaded insert  32 , wherein turning the screw shaft  30   a  a first direction extends the inner tube  22   a  from the bottom end of the outer tube  20   a , and turning the screw a second direction retracts the inner tube  22   a  into the bottom end of the outer tube  20   a . A lubrication fitting  34  is shown attached to the top end of the outer tube  20   a  and adapted to provide lubrication to a jack interior portion defined by the interiors of the outer tube  20   a  and the inner tube  22   a . The lubrication fitting  34  is preferably a grease (or zerk) fitting, and a preferred lubricant is grease. 
   A detailed view of a top portion of the first trailer jack  18   a  taken along line  3 — 3  of  FIG. 2A  is shown in  FIG. 3A . The first crank  26   a  is attached to a first shaft top  31   a  by a crank bolt  29   a  and crank nut  29   b . When the crank  26   a  is turned to extend the inner tube  22   a , an upward vertical force (to the right in the figures) results on the screw shaft  30   a . An opposing force is required to retain the screw shaft  30   a  in the outer tube  20   a . The opposing force is provided by a thrust bearing assembly  41  (see  FIG. 3B ) sandwiched between a shaft shoulder  46  and a retainer (e.g., tube cap  36 ) attached to the outer tube  20   a . The thrust bearing assembly  41  comprises a lower thrust washer  44 , a thrust bearing  40 , a bearing spacer  42 , and a upper thrust washer  38 . The upper tube cap  36  acts as a retainer for the first jack  18   a . The lubrication fitting  34  is positioned to provide lubricant to the thrust bearing  40 . The thrust bearing  40  is preferably a ball bearing (see  FIGS. 6 ,  6 A). 
   The jack  18   a  with the internal tube  22   a  extended from a bottom end of the outer tube  20   a  is shown in  FIG. 3B . The screw shaft  30   a  is turned to thus extend the inner tube  22   a  from the outer tube  20   a , and the screw shaft  30   a  is held in place by the cooperation of the shaft shoulder  46  with the thrust bearing assembly  41 . A notch  62  in the top end of the inner tube  22   a  is aligned with the lubrication fitting  34  and allows lubricant to reach the thrust bearing assembly  41  when the inner tube  22   a  is in the full upward position (see  FIG. 3A ). 
   A cross-sectional view of the second trailer jack  18   b  taken along line  4 — 4  of  FIG. 2B  is shown in  FIG. 4 . The jack  18  be includes gears  50 ,  52  for operationally connecting the second crank  26   b  to the second screw shaft  30   b.    
   A detailed view of a top portion of the second trailer jack  18   b  taken along line  4 — 4  of  FIG. 2B  is shown in  FIG. 4A . The thrust bearing assembly  41  is sandwiched between the shoulder  46  and a retainer comprising a retainer plate  48 . Gears comprise a driven bevel gear  50  and a drive bevel gear  52 . While beveled gears  50 ,  52  are preferred, other operational connections, for example a ring gear and a pinion gear, or a ring gear and screw, may be used. A cap  54  covers the top end of the outer tube  22   b.    
   A second detailed view of the top portion of the second trailer jack rotated 90 degrees, taken along line  4 — 4  of  FIG. 2B , is shown in  FIG. 4B . The retainer plate  48  extends through the outer tube  20   b  to fix the position of the retainer plate  48 . The gear  50  is fixed to the screw shaft  30   b  by a first pin  56 , and the gear  52  is fixed to the crank  26   b  by a second pin  58 . A gear plate  60  resides in the crank  26   b  to provide backing for the gear  52 , thereby holding the gear  52  against the gear  50 . The lubrication fitting  34  may be further adapted to provide lubrication to the gears  50 ,  52 , and to the gear plate  60 , thereby extending the life of the gears  50 ,  52  and gear plate  60 , and reducing the effort required to extend the inner tube  22   b  from the outer tube  20   b.    
   A detailed view of the notch  62  in a top end of the inner tubes  22   a ,  22   b  is shown in  FIG. 5 , which notch  62  is aligned with the lubrication fitting  34  (see  FIG. 3A ), thereby providing access of lubricant to the thrust bearing assembly  41  (see  FIG. 3B ). A preferred thrust bearing  40  is shown in  FIG. 6 , and a cross-sectional view of the thrust bearing  40  taken along line  6 A— 6 A of  FIG. 6  is shown in  FIG. 6A . The thrust bearing  40  comprises ball bearings  66  held by a bearing race  68 . The race  68  preferably has an outside diameter of approximately 34.75 millimeters, and an inside diameter of approximately 20.3 millimeters. The ball bearings  66  preferably comprise thirteen ball bearings of approximately 5.55 millimeter diameter. 
   While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.