Abstract:
A folding structure of a carrier includes an expansion member connected between a base frame and an extension member. As the expansion member pivotally passes through the point of over-tangency (the turning point of balance of force), the extension member is extended or folded due to a liner bias force provided by the expansion member and also due to the change in length of the expansion member. For example, the expansion member starts to elongate itself when passing through the point of over-tangency, generating a force to extend the extension member in an extended position automatically.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a frame of a baby trailer or a baby stroller, and more particularly, to a folding structure including an extension member assisted with an expansion member. 
   BACKGROUND OF THE INVENTION 
   A trailer adapted at the rear of a bicycle for towing thereby is primarily provided to carry small children and further to interact with them. Since such a trailer has a certain volume and is used outdoors, the frame of the trailer is usually foldable for convenient transportation and storage. A conventional frame is in U.S. patents, such as U.S. Pat. Nos. 5,947,497, 5,474,316 and 5,577,746. In general, the frame includes a lower frame member and an upper frame member having a rear end pivotally connected to a forward end of the lower frame member and extending upward; and a pair of pivot units, each of which has one end pivotally connected to the lower frame member and the opposite end pivotally connected to the upper frame member, defining a cargo compartment. The frame of the trailer is extended by means of the pair of pivot units positioned in a line or in parallel that is fixed by a fastened member, so as to support the upper frame member in an extended position. The frame of the trailer is collapsed by loosening the fastened member to make the pair of the pivot units rotate towards the frame, allowing a pivot point between the upper frame member and the lower frame member to rotate downward and thereby fold the trailer into a compact position. 
   The aforementioned trailer is shifted inwards to the frame and is placed inside thereof after the pair of the pivot members are folded. Hence, it is quiet inconvenient to extend the folded frame. 
   SUMMARY OF THE INVENTION 
   It is one primary object of the present invention to provide an easy and laborsaving way to fold and extend a trailer. 
   According to the aforementioned object of the present invention, on the one hand, an expansion unit is connected between a base frame and an extension support unit. The expansion unit is expanded due to the change in pivoting distance thereof, and thereby assists in extending and collapsing the extension support unit. 
   According to the aforementioned object of the present invention, on the other hand, the extension support unit is extended continuously upward to form a handle, which constitute the same as a baby stroller. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects, as well as many of the attendant advantages and features of this invention will become more apparent by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of the frame of the trailer in accordance with one embodiment of the present invention; 
       FIG. 2  is a side view of the frame of the trailer in an extended position according to one embodiment of the present invention; 
       FIG. 3  is a side view of the frame of the trailer in a compact position according to one embodiment of the present invention; 
       FIG. 4  illustrates an act of folding the frame downward according to one embodiment of the present invention; 
       FIG. 5  illustrates an act of the expansion units passing through the angle of over-tangency according to one embodiment of the present invention; 
       FIG. 6  illustrates an act of folding the frame completely according to one embodiment of the present invention; 
       FIG. 7  is a perspective view of the frame of the baby stroller in accordance with one embodiment of the present invention; 
       FIG. 8  is a side view of the frame of the baby stroller in a compact position according to one embodiment of the present invention; and 
       FIG. 9  illustrates the cross-section of spring stick accessory according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1-3 , which illustrate a folding structure of a carrier according to one preferred embodiment of the present invention, users can make an extension support unit  3  in a fixed position when extending or collapsing a foldable frame  10 . In this embodiment, the foldable frame  10  is in the form of a trailer  100 , which comprises a base frame  2 , a pair of extension support units  3 , a pair of expansion units  4 , and a connecting shaft  5 . 
   The base frame  2  may be a substantially closed rectangular shaft member, a U-shaped shaft member, or a chassis member with substantially closed bottom. The base frame  2  substantially parallels the ground, and is pivotally connected to wheels  20  on both sides thereof. Both forward ends of the base frame  2  are connected to a pair of first pivot members  21  having pivot points  211 , respectively, for connecting the extension support unit  3 . A connecting seat  22  is assembled between two first pivot members  21  for fastening the connecting shaft  5 . An extending section  23  is disposed at the rear of the base frame  2 . A second pivot member  24  is disposed on the extending section  23 . 
   A lower end of the extension support unit  3  is pivotally connected to the pivot point  211  of the first pivot member  21 , and hence the extension support unit  3  is extended or folded by rotating through the pivot point  211 . The extension support units  3  extend upwardly. A crossing shaft  31  is connected to upper ends of the extension support units  3  to ensure the width between the extension support units  3 . A third pivot member  32  is disposed on the upper end of the extension support unit  3 . 
   Two ends of the expansion unit  4  are connected to the second pivot member  24  and the third pivot member  32 , respectively. In one embodiment of the present invention, the expansion unit  4  is an air compressor accessory including a body  41 , an expansion link  42  and a control button for controlling air valves (not shown). Using the control button can adjust the expansion link  42  being fixed or expanded. In another embodiment of the present invention, the expansion unit  4  is a spring stick accessory (as shown in  FIG. 9 ) including a body  41 , an expansion link  42 , a spring  43 , and a fixed component  44 . Using the fixed component  44  can adjust the expansion link  42  being fixed or moved. 
   The connecting shaft  5  has a first end connected to the base frame  2  and a second end adapted to a bicycle for towing the foldable frame  10 . 
   Referring to  FIGS. 4-6 , in accordance with the aforesaid members, the base frame  2 , the extension support units  3  and the expansion units  4  support one another (in the meantime, the expansion links  42  of the expansion units  4  are immovable) to define a cargo compartment  11  (behind a disposed seat cloth) for carrying small children. It is desired to fold the foldable frame  10  by releasing the control button of the expansion units  4 , which in an embodiment of the invention is an air compressor accessory or by loosening the fixed component  44  of the spring stick accessory such that the expansion link  42  is movable. When users collapse the extension support units  3 , the expansion units  4  rotate spontaneously as shown in  FIG. 4 . The distance between the second pivot member  24  and the third pivot member  32  changes while the extension support units  3  move downward, so the expansion link  42  moves towards the inside of the body  41 . As illustrated in  FIG. 5 , when the expansion units  4  pivotally pass through the angle of over-tangency (point of over-tangency) a, the distance between the second pivot member  24  and the third pivot member  32  becomes longer. In the meantime, the expansion link  42  is pushed outward due to force induced by, for example, air pressure or spring strength, that further folds the extension support units  3  in a compact position and locates the same automatically (as shown in  FIG. 6 ). 
   If users would like to extend the foldable frame  10 , the foldable frame  10  will be in an extended position automatically because the expansion link  42  starts to be pushed out after the expansion units  4  pivotally pass through the angle of over-tangency a. The expansion link  42  is then fixed by operating the control button or the fixed component  44 . According to the folding structure of the present invention, the foldable frame  10  is located in an extended position or a compact position automatically by means of the expansion units. 
   In another embodiment, single expansion unit  4  is connected to the base frame  2  and the extension support units  3  to locate the foldable frame automatically. Also referring to  FIG. 7  and  FIG. 8 , the present invention is applied to the frame of a baby stroller  200 , which comprises a front wheel  25  connected to the forward end of the base frame  2  and a handle  33  extended continuously from the extension support units  3 . The frame of the baby stroller  200  is further located in an extended position or a compact position automatically using the folding structure of the present invention. 
   Consequently, the present invention overcomes disadvantages of the prior arts. It becomes easier for users to collapse and expand trailers or strollers. 
   While the invention has been particularly shown and described with reference to the preferred embodiments thereof, these are, of course, merely examples to help clarify the invention and are not intended to limit the invention. It will be understood by those skilled in the art that various changes, modifications, and alterations in form and detail may be made therein without departing from the spirit and scope of the invention, as set forth in the following claims.