Abstract:
An expander nut is for being assembled to an upper end of a steering tube of a bicycle. The expander nut includes a base nut, two wedge halves having interlocking tapered surfaces and assembled to the base nut, a top cap mounted on the wedge halves, and a bolt screwed to the base nut for controlling the wedge halves to slide relatively along the tapered surfaces so that the wedge halves move outward to wedge an inner surface of the steering tube.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates to bicycle parts, and more particularly, to an expander nut for being assembled atop a stem of a bicycle so as to pull the stem downward to preload a set of head parts of the bicycle. 
   2. Description of Related Art 
   Various assembling parts for assembling a stem, a set of head parts, a head tube and a steering tube of a bicycle have been developed to date. One instance is U.S. Pat. No. 7,204,502, titled “Steering Bearing Assembly for Vehicle”. In the following description related to this prior patent, all recited elements are referred to the numerals indicating the corresponding elements shown in the drawing sheet of the published Patent as can be obtained from the USPTO Web Patent Databases. This prior patent disclosed a head tube  30  accommodating a steering tube  23  and having a top bearing  40  and a bottom bearing  45  assembled to the top and bottom ends thereof. A handlebar stem tube  62  of a handlebar assembly is mounted atop the steering tube and preloads the top bearing  40  at the top end the head tube  30 . A bolt  65  is installed in the top of the steering tube  23  to exert a downward force to the handlebar stem tube  62  so that the handlebar stem tube  62  presses downward and thus position the top bearing  40 . Finally the handlebar stem tube  62  is tightened onto the steering tube  23  of the bicycle so that the stem, the head parts, the head tube and the steering tube are well assembled. 
   Referring to  FIG. 1  provided in the present application, the bolt  65  recited in the aforementioned prior patent is composed of a start nut  651 , a screw  652  and a top cap  653 . The screw  652  centrally passing through the top cap  653  and getting engaged with a threaded hole  654  of the start nut  651 . The star nut has two discs of hardened steel each with a plurality of sharp tabs  655 . The start nut  651  is placed into the steering tube so that the sharp tabs  655  engage on the internal bore of the steering tube. Due to the configuration of the discs, the start nut  651  is allowed to move inward the steering tube and retained from leaving the steering tube. The top cap  653  presses on the top of the stem so that when the screw  652  is tightened, the top cap  653  is pushed downward and in turn preloads the top bearing  40 . 
   In the past when steering tubes were made from steel the star nut  651  was acceptable. Now steering tubes are made from aluminum alloy or even from carbon composite materials and so the damage that a star nut can cause when it is hammered in position is unacceptable and potentially dangerous. Besides, once the star nut  651  is assembled it cannot be removed without causing further damage and destructive deformation. Thus, the traditional device is unfavorable to stem replacement or head-parts preload adjustment. 
   Another instance is U.S. Pat. No. 5,737,974, titled “Fastening Assembly of Bicycle stem”. In the following description related to this prior patent, all recited elements are referred to the numerals indicating the corresponding elements shown in the drawing sheet of the published Patent as can be obtained from the USPTO Web Patent Databases. In the prior patent, an assembly composed of a bolt  2 , a stop cover  12 , a spring torsion  6 , an arresting tube  4 , and a tightening head  3 , gives a upright tube  1  a downward force. The spring torsion  6  is settled between the stop cover  12  and the arresting tube  4 . The bolt  2  passes through the stop cover  12  and the arresting tube  4  to engage with a threaded hole of the tightening head  3 . The arresting tube  4  is configured to have outward expandability. The tightening head  3  is settled in the arresting tube  4  and has a tapered outer periphery. When the bolt  2  is tightened, the tapered outer periphery of the tightening head  3  expands the arresting tube  4  to abut against the inner surface of the steering tube  7 . The stop cover  12  pressed by the bolt  2  exerts the downward force to the upright tube  1 , so as to fasten the head parts  9 . 
   Though the spring torsion  6  is configured to compress when the arresting tube  4  is expanded, it can sometimes resile before the arresting tube  4  wedges the steering tube and thus causes the whole assembly to fail in preloading the upright tube  1 . Besides, as the arresting tube  4  is substantially a tube with slots formed thereon and the tightening head  3  uses the tapered outer periphery to expand the arresting tube  4  from inside and support the expanded arresting tube  4  to tightly wedge the inner surface of the steering tube  7 , gaps and concentrated point load between the arresting tube  4  and the steering tube  7  out of uneven expansion tend to happen and damage the steering tube. 
   SUMMARY OF THE INVENTION 
   Hence, one objective of the present invention is to provide an expander nut for assembling a stem, a set of head parts, a head tube, and a steering tube of a bicycle. The disclosed expander nut exerts an axial load to the stem by a non-destructive means so as to assemble and position the previously recited components. 
   Another objective of the present invention is to provide an expander nut that causes no gaps and gives a very uniform hoop stress within a steering tube, thereby eliminating concentrated point load to the steering tube and prolonging service life of the steering tube. 
   Another objective of the present invention is to provide an expander nut that can easily be removed and reassembled without damage and requires only standard hand tools for assembly and disassembly thereof. 
   Another objective of the present invention is to provide an expander nut that can be economically made of aluminum or engineering plastics. 
   Another objective of the present invention is to provide an expander nut that eliminates use of a compression spring that is usually heavy, and thus is light in weight. 
   The expander nut of the present invention comprises a cylindrical base nut mounted thereon a first wedge half and a second wedge half. The two wedge halves having a first tapered surface and a second tapered surface, respectively, when combined, jointly form a close circular ring. A top cap is placed atop the circular ring and is such fastened to the base through a bolt that the first wedge half and the second wedge half are allowed to move relatively along the flat tapered surfaces thereof, thereby making the circular ring diametrically expanded. The wedge halves are placed atop a steering tube of a bicycle so that the resulting circular ring can be diametrically expanded under control of the top cap to wedge and exert an even hoop pressure upon an inner wall of the steering tube. Meantime, the top cap provides a preload to an upper end of a stem that is mounted around the steering tube and so as to make the stem press a set of head parts located therebelow. Finally the assembly of the stem, the head parts, the head tube, and the steering tube is accomplished by tightening the stem onto the steering tube. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention as well as a preferred mode of use, further objectives and advantages thereof will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is an exploded view of a bolt with a star nut according to a prior art; 
       FIG. 2  is an exploded view of an expander nut of the present invention; 
       FIG. 3  is a perspective view of the expander nut in a first position; 
       FIG. 4  is a perspective view of the expander nut in a second position; 
       FIG. 5  is a schematic drawing showing the expander nut is used to assemble a stem, a set of head parts, a head tube and a steering tube of a bicycle, wherein a first wedge half and a second wedge half of the expander nut cooperatively wedge an inner surface of the steering tube; 
       FIG. 6  is a schematic drawing showing that after the wedge halves wedge the inner surface of the steering tube, a bolt is loosened and a top cap is adjusted; 
       FIG. 7  is a schematic drawing showing the bolt tightened to press the top cap downward; and 
       FIGS. 8 and 9  are schematic drawings showing the expander nut disassembled from the steering tube. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   While a preferred embodiment is provided hereinafter for illustrating the concept of the present invention as described above, it is to be understood that the components of the embodiment shown in the accompanying drawings are depicted for the sake of easy explanation and need not to be made in scale. 
   As can be seen clearly from  FIG. 2 , an expander nut of the present invention a base nut  10 , a first wedge half  20 , a second wedge half  31 , a top cap  41 , and a bolt  50 . 
   The base nut  10  has centrally a threaded hole  11  and peripherally an annular accommodating groove  13 . 
   The first wedge half  20  has a flange  21  extended inward from a bottom thereof to be received in the accommodating groove  13 . An anti-rotation device  14  is provided at the base nut  10  for preventing the first wedge half  20  from sliding along the accommodating groove  13 . According to the present embodiment, the anti-rotation device  14  is a grub screw  141  extended radially in the base nut  10 . The grub screw  141  serves to engage one end of the flange  21  so as to prevent the first wedge half  20  from sliding along the accommodating groove  13 . 
   The second wedge half  31  and the first wedge half  20  jointly form a close circular ring. The circular ring has an outer diameter L 1  slightly greater than a diameter L 2  of a bottom of the base nut  10  (shown in  FIG. 5 ). The two wedge halves  20 ,  31  are interlocked with a first tapered surface  22  and a second tapered surface  32  so as to closely jointly form the close circular ring. The first tapered surface  22  and the second tapered surface  32  each has a taper angle ranging between 10 and 20 degrees. A plurality of protruding castellations  34  spaced at a certain distance from one another are formed at a top  33  of the second wedge half  31 . Therein, tops of the protruding castellations  34  are preload surfaces  35 . 
   The top cap  41  centrally has a through hole  42  and radially has a plurality of through slots  43 . At a bottom of the top cap  41 , between each two adjacent said through slots  43 , a pocket-shaped preload portion  44  is provided. 
   The bolt  50  passing through the through hole  42  of the top cap  41  gets engaged with the threaded hole  11  of the base nut  10 . The second wedge half  31  is tethered to bolt  50  by a spring clip  5  so as to remain the second wedge half  31  and the first wedge half  20  connected. 
   Referring to  FIGS. 3 and 4 , the top cap  41  and the second wedge half  31  can engage in two alternative positions as be described in detail below. 
   The first position is shown in  FIG. 3 . Therein, the preload portions  44  (shown in  FIG. 1 ) of the top cap  41  align with the preload surfaces  35  of the protruding castellations  34  formed on the second wedge half  31 . When the bolt  50  is tightened, the top cap  41  pushes the second wedge half  31  downward. Due to the interlocked first tapered surface  22  and the second tapered surface  32 , when the second wedge half  31  slides downward, the expander nut diametrically expands outward. 
   In the second position, as shown in  FIG. 4 , the protruding castellations  34  of the second wedge half  31  are received in the through slots  43  of the top cap  41 . In virtue of the anti-rotation device  14  provided at the base nut  10 , the first wedge half  20 , the second wedge half  31  and the top cap  41  are retained from rotation. 
   The above-discussed first and second positions are for the expander nut to wedge a steering tube and press a stem of a bicycle. According to  FIGS. 5 ,  6  and  7 , a stem  81 , head parts  82 , a head tube  83  and a steering tube  84  are assembled in a conventional manner. 
   In  FIG. 5 , the base nut  10 , the first wedge half  20  and the second wedge half  31  of the expander nut are placed into the steering tube  84  at an upper end thereof. At this time, the top cap  41  and the second wedge half  31  are combined in the first position, meaning that the preload portions  44  of the top cap  41  contact the preload surfaces  35  of the second wedge half  31 . When the bolt  50  is tightened, the expander nut is diametrically expanded as indicated by Arrow A, so that outer surfaces of the first wedge half  20  and the second wedge half  31  tightly wedge the inner surface of the steering tube  84 . Consequently, the steering tube  84  receives an even annular pressure without concentrated point load, thereby having prolonged service life. 
   In  FIG. 6 , after the bolt  50  is loosened, the top cap  41  is allowed to rotate and then has its through slots  43  aligned with the protruding castellations  34  of the second wedge half  31 . At this time, since the first tapered surface  22  and the second tapered surface  32  remains self-locking between the wedge halves  20  and  31 , it is ensured that the wedge halves  20  and  31  still tightly wedge the steering tube  84  without loosening. 
   Referring to  FIG. 7 , the bolt  50  is tightened again to pull the top cap  41  downward so that the protruding castellations  34  get retained in the through slots  43 . Thus, the top cap  41  and the second wedge half  31  are combined in the second position. Thereby, the expander nut of the present invention is retained from rotation and tightly wedges the steering tube  84 . The downward pulled top cap  41  preloads the stem  81  and makes the same press and in turn position the head parts  82  located below the stem  81 . Finally the stem  81  is tightened onto the steering tube  84  and the assembly is accomplished. The top cap  41  provides an axial load to the stem  81  by a non-destructive means and facilitates assembling the stem  81 , the head parts  82 , the head tube  83  and the steering tube  84 . 
     FIGS. 8 and 9  further illustrate how the expander nut is disassembled form the steering tube  84 . The expander nut can easily be disassembled from the steering tube  84  of the bicycle by loosening the bolt  50  and then tapping the bolt  50  down, as indicated by Arrow F. Thereby, the bolt  50 , the base nut  10  and the first wedge half  20  move downward to release the self-locking between the two wedge halves  20 ,  31 . The expander nut can now be withdrawn by lifting the top cap  41 . The expander nut can easily be removed and reassembled without damage by using standard hand tools. 
   The present invention has been described with reference to the preferred embodiment and it is understood that the embodiment is not intended to limit the scope of the present invention. Moreover, as the contents disclosed herein should be readily understood and can be implemented by a person skilled in the art, all equivalent changes or modifications which do not depart from the concept of the present invention should be encompassed by the appended claims.