Abstract:
The length adjustment of an expandable rod is attained by a drive gear and a driven gear which is engaged with the drive gear and gear slots of an inner tube of the expandable rod. The inner tube is located inside an outer tube of the expandable rod by a locating member which is provided with a locating projection capable of locating in one of the gear slots of the inner tube.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to an expandable rod, and more particularly to a mechanism for adjusting length of the expandable rod. 
   2. Description of Related Art 
   The conventional expandable rod is widely used in the truck for locating loads and is provided with a gear mechanism for adjusting length of the expandable rod. The gear mechanism comprises a gear, a gear-locating device, a spring, and a control lever. The gear mechanism is defective in design in that the length adjustment of the expandable rod can not be attained with ease and speed, and that the components of the gear mechanism are not shielded to prevent them from being damaged by impact. 
   SUMMARY OF THE INVENTION 
   The primary objective of the present invention is to provide an expandable rod with a length adjustment mechanism free of the deficiencies of the conventional expandable rod described above. 
   In keeping with the principle of the present invention, the foregoing objective of the present invention is attained by an adjustment mechanism comprising a support frame for fastening pivotally a first gear and a second gear such that the first gear is engaged with the gear slots of an inner tube of the expandable rod, and that the second gear is engaged with the first gear. The second gear is provided with a single bevel edge, which is engaged with the actuating piece of an actuating shaft at the time when the actuating shaft is turned counterclockwise, thereby causing the second gear to turn so as to drive the first gear. As the first gear is driven to turn by the second gear, the inner tube is actuated by the first gear in motion to expand. 
   The features and the advantages of the present invention will be more readily understood upon a thoughtful deliberation of the following detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a perspective view of a first preferred embodiment of the present invention. 
       FIG. 2  shows a partial exploded view of the first preferred embodiment of the present invention. 
       FIG. 3  shows a complete exploded view of the first preferred embodiment of the present invention. 
       FIG. 4  shows a longitudinal sectional view of the first preferred embodiment of the present invention in combination. 
       FIG. 5  is a longitudinal sectional view to show the disengagement of the second gear with the actuating shaft of the first preferred embodiment of the present invention. 
       FIG. 6  is a top plan view to show the engagement of the first gear with the second gear of the first preferred embodiment of the present invention. 
       FIG. 7  shows a cross-sectional view of the first preferred embodiment of the present invention in combination. 
       FIG. 8  shows a longitudinal sectional view of the first preferred embodiment of the present invention in action. 
       FIG. 9  is a top plan view to show the disengagement of the first gear with the second gear of the first preferred embodiment of the present invention. 
       FIG. 10  shows a cross-sectional view of the first preferred embodiment of the present invention as shown in FIG.  9 . 
       FIG. 11  shows a perspective view of a second preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As shown in  FIGS. 1-10 , an expandable rod of the present invention comprises an inner tube  10 , an outer tube  20 , a support frame  30 , a first gear  41 , a second gear  42 , a locating member  70 , and a frame cover  80 . 
   The inner tube  10  is provided in an outer wall with a series of gear slots  11 , which are arranged at an interval along a longitudinal direction of the inner tube  10 . The inner tube  10  is slidably fitted into the outer tube  20 . The outer tube  20  is provided at one end with a through hole  21  corresponding in location to the gear slots  11  of the inner tube  10 . 
   The support frame  30  is mounted on the one end of the outer tube  20  and is provided with two lugs  31 , each having a first shaft hole  01 , a second shaft hole  02 , and a third shaft hole  03 . 
   The first gear  41  is mounted on a first shaft  51  in conjunction with two shaft sleeves  53 . The first fhaft  51  is mounted in the support frame  30  such that the first shaft  51  is fastened at both ends thereof with the first shaft holes  01  of the two lugs  31  of the support frame  30 . The first gear  41  is engaged with the gear slots  11  of the inner tube  10 . 
   The second gear  42  is mounted on an actuating shaft  60  which is fastened at both ends with the second shaft holes  02  of the two lugs  31  of the support frame  30 . The second gear  42  is engaged with the first gear  41  and is urged by a spring  54  which is fitted over one end of the actuating shaft  60 . The second gear  42  has one end  47  which is provided with a single bevel edge  43 . The actuating shaft  60  is provided in an outer wall with a retaining slot  62  for accommodating an actuating piece  44  in conjunction with a spring  45 . The actuating piece  44  has a single bevel edge  46  which is jutted out of the retaining slot  62  and is capable of engaging the single bevel edge  43  of the one end  47  of the second gear  42  at the time when the actuating shaft  60  is turned counterclockwise, thereby driving the second gear  42  to turn, as illustrated in FIG.  8 . As the actuating shaft  60  is turned clockwise, the single bevel edge  46  of the actuating piece  44  of the actuating shaft  60  is disengaged with the single bevel edge  43  of the second gear  42 . As a result, the second gear  42  is no longer driven by the actuating shaft  60  to turn. 
   The locating member  70  is pivoted to the support frame  30  by a pivot  52  which is fastened to the third shaft holes  03  of the two lugs  31  of the support frame  30 . The locating member  70  is formed of a press portion  71  and a locating portion  71  which is provided with a locating projection  73  capable of locating in one of the gear slots  11  of the inner tube  10  via the through hole  21  of the outer tube  20 . The locating portion  72  is provided with a protuberance  75  having a pivoting hole  76  by which the protuberance  75  is pivoted to the actuating shaft  60 . The pivoting hole  76  is provided in the inner wall with a guide edge  77 , which rests against the one end  47  of the second gear  42  at the time when the press portion  71  is pressed, thereby causing the second gear  42  to displace so as to disengage the first gear  41 , as shown in  FIGS. 9 and 10 . 
   The first gear  41  and the second gear  42  are shielded by a frame cover  80  which is fastened to the two lugs  31  of the support frame  30 . 
   The actuating shaft  60  is fastened at one end with a handle  61  to facilitate the turning of the actuating shaft  60 . When the handle  61  is turned counterclockwise as shown in  FIG. 8 , the second gear  42  is actuated to drive the first gear  41  to turn, thereby causing the inner tube  10  to move in relation to the outer tube  20 . 
   As illustrated in  FIGS. 9 and 10 , when the locating member  70  is pressed, the protuberane  75  of the locating member  70  moves upward to cause the second gear (drive gear)  42  to displace so as to become disengaged with the first gear  41  (drive gear). As a result, the inner tube  10  can be easily slid into or out of the outer tube  20 . 
   As shown in  FIG. 11 , the support frame  30  is provided with an arresting piece  32  for confining the handle  61  in such a way that the handle  61  can not be turned in a full circle. Without the arresting piece  32 , the handle  61  can be turned freely at 360 degrees. 
   The embodiments described above are to be regarded in all respects as being illustrative and nonrestrictive. Accordingly, the present invention may be embodied in other specific forms without deviating from the spirit thereof. The present invention is therefore to be limited only by the scopes of the following claims.