Abstract:
An eccentrically operated speed-variating device and, more particularly, a differential structure having a high power and high speed with sudden low speed (and zero speed) return function is constructed to include a main transmission shaft, a differential assembly mounted on the main transmission shaft and driven by a speed control arm to move a differential control wheel axially, and an eccentric driving wheel mounted around the main transmission shaft and controlled to change the eccentric radius thereof about the main transmission shaft upon axial movement of the differential control wheel.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1.  1 . Field of the Invention  
           [0002]    The present invention relates to speed-variating device and, more particularly, to a simple structure of eccentrically operated speed-variating device for use in, for example, a bicycle.  
           [0003]    2. Description of the Related Art  
           [0004]    Eccentrically operated speed-variating devices are known. U.S. Pat. No. 5,222,916, entitled “Eccentrically operated speed-variating means with broadened speed variation”, shows an exemplar. This structure of eccentrically operated speed-variating device is functional, however it is complicated and composed of a big number of parts, resulting in high manufacturing cost.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention has been accomplished under the circumstances in view. It is therefore the main object of the present invention to provide an eccentrically operated speed-variating device, which has a simple structure. It is another object of the present invention to provide an eccentrically operated speed-variating device, which is inexpensive to manufacture. To achieve these and other objects of the present invention, the eccentrically operated speed-variating device comprises a main transmission shaft, the main transmission shaft having a longitudinally extended axial center through hole; a sliding shaft axially slidably inserted into the longitudinally extended axial center through hole of the main transmission shaft, the sliding shaft having a first end terminating in an outer thread and extended out of one end of the main transmission shaft and a second end mounted with a linkage pivoted to an inside wall of the main transmission shaft; a differential assembly coupled to the sliding shaft, the differential assembly comprising a synchronous wheel fixedly fastened to the main transmission shaft for synchronous rotation, a differential control wheel arranged in parallel to the synchronous wheel, and a casing provided around the synchronous wheel and the differential control wheel, the differential control wheel having a diameter smaller than the synchronous wheel and a center screw hole threaded onto the outer thread of the sliding shaft; a speed control arm, the speed control arm having a fixed end pivoted to the casing and a free end mounted with two friction wheels of different diameters adapted for friction-contacting the periphery of the synchronous wheel and the periphery of the differential control wheel to force the sliding shaft to move axially in the main transmission shaft when the speed reducing arm turned in one direction relative to the casing; and an eccentric driving wheel mounted around the main transmission shaft and controlled by the linkage of the sliding shaft to change the eccentric radius thereof about the main transmission shaft. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is sectional assembly view of an eccentrically operated speed-variating device according to the present invention.  
         [0007]    [0007]FIG. 2 is similar to FIG. 1 but showing the sliding shaft moved in the main transmission shaft, the eccentric radius of the driving wheel about the main transmission shaft changed.  
         [0008]    [0008]FIG. 3 is an exploded view of a part of the eccentrically operated speed-variating device according to the present invention.  
         [0009]    [0009]FIG. 4 is a schematic drawing showing the friction wheels forced into friction-contact with the synchronous wheel and differential control wheel of the differential assembly according to the present invention.  
         [0010]    [0010]FIG. 5 is a sectional view of a part of the present invention, showing the relative positioning of the main transmission shaft, the sliding shaft, the speed control arm, and the differential assembly according to the present invention.  
         [0011]    [0011]FIG. 6 is an exploded view of a part of the present invention, showing the relative positioning of the sliding blocks between the driving wheel and one clutch control wheel.  
         [0012]    [0012]FIG. 7 is a front view of a part of the present invention showing the sliding blocks positioned in the driving wheel.  
         [0013]    [0013]FIG. 8 is a sectional view of a part of the present invention, showing the sliding blocks positioned in the endless sliding groove of one clutch control wheel.  
         [0014]    [0014]FIG. 9 is a schematic drawing showing the speed control arm provided with two sets of friction wheels. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    Referring to FIGS. from  1  through  5 , an eccentrically operated speed-variating device in accordance with the present invention is shown comprising a main transmission shaft  2 . A sliding shaft  22  is axially slidably inserted into the longitudinally extended axial center through hole  21  of the main transmission shaft  2 . The sliding shaft  22  has an outer thread  23  disposed at one end and connected to a differential assembly  1 . The differential assembly  1  comprises a synchronous wheel  12  and a differential control wheel  11 . The synchronous wheel  12  is fixedly fastened to the main transmission shaft  2  for synchronous rotation. The diameter of the synchronous wheel  12  is greater than the differential control wheel  11 . The outer thread  23  of the sliding shaft  22  is inserted through the center hole of the synchronous wheel  12  and supported on an axle bearing  13  at the synchronous wheel  12  and threaded into the center screw hole  111  of the differential control wheel  11 . The other end of the sliding shaft  22  is mounted with a first link  24  and a second link  25 . The first link  24  has one end pivoted to the sliding shaft  22 , and the other end pivoted to one end of the second link  25 . A pivot  252  pivots the other end of the second link  25  to a part of the main transmission shaft  2  inside the longitudinally extended axial center through hole  21 . A motor  8  is provided and controlled to rotate the main transmission shaft  2 . The sliding shaft  22  is synchronously rotated with the main transmission shaft  2  during operation of the motor  8 . The main transmission shaft  2  has two transverse sliding grooves  211  arranged in the periphery in parallel. A lifting block  31  is coupled to the main transmission shaft  2 , and vertically movable along the transverse grooves  211 . The lifting block  31  has an opening  31  fitting the transverse grooves  211 . An axle bearing  32  is supported on the lifting block  31  around the main transmission shaft  2 . A driving wheel  4  is supported on the axle bearing  32  around the main transmission shaft  2 , having a plurality of equiangularly spaced radial slots  41 . Two clutch control wheels  5  are provided at two sides of the driving wheel  4  around the main transmission shaft  2 , and respectively fastened to a power output wheel hub  6  and a transmission sleeve  7 . The clutch control wheels  5  each have an endless sliding groove  51  disposed at an inner side around the center. The transmission sleeve  7  has one end fixedly mounted with a gear wheel  71  for receiving an external driving force. A plurality of sliding blocks  52  are alternatively mounted in the radial slots  41  of the driving wheel  4  at two sides and respectively coupled to the endless sliding grooves  51  of the clutch control wheels  5 . Each sliding block  52  comprises a roller  53  provided at one side thereof and coupled to one radial slot  41  of the driving wheel  4 , a plurality of springs  523  respectively mounted in a respective beveled receiving space at the other side thereof, and a plurality of needle rollers  522  respectively supported on the springs  523  and facing the endless sliding groove  51  of one clutch control wheel  5 . (see FIGS.  6 ˜ 8 ).  
         [0016]    Two push pins  253  are radially mounted in the main transmission shaft  2  and vertically aligned at two sides, each having an outer end respectively disposed in contact with the inside wall of the lifting block  3  and the inside wall of the axle bearing  32  and an inner end respectively disposed in contact with an endpiece  251  of the second link  25 .  
         [0017]    A casing  61  is provided around the differential assembly  1 . A speed control arm  14  is provided having a fixed end pivoted to the inside wall of the casing  61  and a free end mounted with at least one set of differential transmission wheels, for example, two friction wheels  141  of different diameters. By means of pulling the speed reducing control cable (not shown), the speed control arm  14  is lowered to force the friction wheels  141  into friction-contact with the periphery of the synchronous wheel  12  and the periphery of the differential control wheel  11 . Therefore, when the motor  8  started to rotate the main transmission shaft  2 , the friction wheels  141  are driven by the synchronous wheel  12  to rotate the differential control wheel  11 , thereby causing the differential control wheel  11  to move the sliding shaft  22  axially in the main transmission shaft  2 . At this time, the endpiece  251  of the second link  25  is forced against the push pins  253 , thereby causing the lifting block  3  and the driving wheel  4  to be moved vertically upwards (or downwards). When the lifting block  3  and the driving wheel  4  moved upwards (or downwards), the sliding blocks  52  are moved relative to the radial slots  41  of the driving wheel  4  to change the eccentric radius of the driving wheel  4  about the main transmission shaft  2  (see FIG. 2).  
         [0018]    Further, a fixed friction device  142  is provided at a middle part of the speed control arm  14 . When pulling the speed control arm  14  in the reversed direction, the fixed friction device  142  is forced into friction-contact with the periphery of the differential control wheel  11 , achieving a broader speed variation ratio between the differential control wheel  11  and the main transmission shaft  2 . At this time, the sliding shaft  22  is moved axially toward the right to return the links  24  and  25  to their former positions, and therefore the driving wheel  4  is moved with the axle bearing  32  and the lifting block  3  relative to the main transmission shaft  2  to the zero the eccentric radius of the driving wheel  4  about the main transmission shaft  2 .  
         [0019]    [0019]FIG. 9 is a schematic drawing of an alternate form of the present invention. According to this alternate form, the speed control arm  14  is mounted with two sets of differential transmission wheels (friction wheels)  141  adapted to peripherally engage the wheels  11  and  12 .  
         [0020]    A prototype of eccentrically operated speed-variating device has been constructed with the features of FIGS.  1 ˜ 9 . The eccentrically operated speed-variating device functions smoothly to provide all of the features discussed earlier.  
         [0021]    It is to be understood that the drawings are designed for purposes of illustration only, and are not intended for use as a definition of the limits and scope of the invention disclosed.