Abstract:
In a sprocket for a bicycle having a radial bearing acting as a bearing portion, an axial load acting on the bearing can be easily adjusted without having to dismount the components of the bicycle after the bicycle has been assembled. 
     An elastomer is used as a component for an anti-rotation mechanism of an adjusting nut which serves to adjust the axial load of the radial bearing, so that an excessive load is not applied on the radial bearing, which would result in a defective rotation. Further, the axial load acting on the radial bearing can be easily adjusted without having to dismount the components of the bicycle after the bicycle has been assembled.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a sprocket for a bicycle. 
         [0003]    2. Description of the Related Art 
         [0004]    Recently, a sprocket having a radial bearing is widely used for the reason that adopting the radial bearing can enhance the precision of the bearing portion and make it superior in durability. 
         [0005]    However, once the relative position between the inner race and the outer race of the radial bearing in an axial direction has a deviation, it will cause a defective rotation. As a certain amount of load may effect a deviation in the relative position between the inner race and the outer race in an axial direction, and result in a defective rotation, a load like that should be avoided. However, it is necessary to preload a certain amount of load with which swing is not felt in the least, even though a rider pedals a bicycle. 
         [0006]    In a prior example as shown in  FIG. 3 , a left crank is mounted on a shaft with two fixing bolts disposed in the direction perpendicular to the shaft loosely. First, temporarily fixing bolts disposed in the axial direction of the shaft are fastened not to cause the crank to make a defective rotation and an axial swing. Next, the two fixing bolts disposed in the direction perpendicular to the shaft are fastened with equal forces, so that an axial force will not be generated with the left crank locked on the shaft. If the fastening forces of the two bolts are not equal, the two bolts and the left crank may be gradually loosening in use. Therefore, a beginner is required to perform a hard operation, due to the fact that it can be not adjusted after the left crank has been mounted. 
         [0007]    In another prior example as shown in  FIG. 4 , fixing bolts disposed in a direction perpendicular to a shaft are fastened, such that a left crank can not be loosened any more even though a rider pedals a bicycle continuously for a long time. The left crank is secured through a friction to a shaft, or is secured at a locking position to a locking portion provided. At this time, an axial force is not applied to a bearing by the left crank, directly, but indirectly through an elastomer therebetween. As the force is blocked by the elastomer, it can be set without rendering a defective rotation and an axial swing. However, with the elastomer therebetween, when a large force is applied from the left crank side toward a right crank, the shaft will move temporarily toward the right crank to cause an adverse effect on a driving system. Hence, it can be not adjusted after the left crank has been mounted. 
         [0008]    In a still further prior example as shown in  FIG. 5 , a shaft inserted into a left crank and secured therein passes through a sleeve  3 , a left bearing and a right bearing, and then extends into a right crank. An adjusting nut is fastened to a screw thread portion matching with the adjusting nut without causing the shaft to swing. The screw thread portion for the adjusting nut is disposed at a base portion of the shaft for securing the right crank. Next, the portion for securing the right crank which is outside the adjusting nut, is inserted into the right crank, and then, fixing bolts, which are disposed in the direction perpendicular to the shaft are fastened, such that the right crank will not be loosened any more even though a rider pedals a bicycle continuously for a long time. At this time, the right crank abuts the end face of the adjusting nut. An axial force is applied to the adjusting nut by the right crank. Since a sleeve  1  and a sleeve  2  are disposed between the outer races and the inner races of the right and left radial bearings and the relative position of the outer races and the inner races forming the bearings remains unchanged, the force applied to the bearings will not cause the bearings to render a defective rotation. Because the right crank abuts the end face of the adjusting nut, the adjusting nut can not be loosened to change the adjustment. However, this method can not make an adjustment after mounting, either. 
       SUMMARY OF THE INVENTION 
       [0009]    A sprocket for a bicycle is provided in which a radial bearing is used to act as a bearing portion and in which an axial load on the bearing can be easily adjusted without dismounting the components of the bicycle, even after the bicycle has been assembled. 
         [0010]    After a shaft is mounted in a radial bearing, an adjusting nut for adjusting axial load is disposed on the shaft. Next, an anti-rotation mechanism provided with an elastomer is disposed, such that the adjusting nut will not be loosened or tightened up automatically when running a bicycle. Furthermore, when a left crank is combined with the elasmoter, no excessive load is to be applied to the radial bearing. With the anti-rotation mechanism having the elastomer, even though the sprocket is mounted, an axial load on the radial bearing can be easily adjusted without dismounting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a preferred embodiment for the present invention. 
           [0012]      FIG. 2  is an exploded perspective view of the left part of the embodiment of  FIG. 1 . 
           [0013]      FIG. 3  shows a first embodiment of the prior art. 
           [0014]      FIG. 4  shows a second embodiment of the prior art. 
           [0015]      FIG. 5  shows a third embodiment of the prior art. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    A shaft, which has already been put into a right crank and secured therein, is inserted from a radial bearing at the right side of a bicycle and protrudes from another radial bearing at the left side of the bicycle. Further, an adjusting nut is fastened to a thread portion of a screw in a way of not causing a defective rotation and an axial swing. The thread portion of screw is disposed at a base portion of a region for determining the angle of a left crank and press-fitting the left crank. As described later, the rotation of the adjusting nut is restrained by a lock washer, provided with a pawl portion opposite to the adjusting nut. 
         [0017]    Next, the lock washer having a hole slightly larger than a profile of a portion of the shaft for restraining rotation with respect to the left crank and press-fitting the shaft and is secured around the shaft with the pawl portion facing the right crank side. 
         [0018]    The lock washer is restrained from rotating based on the shape of the shaft. When the adjusting nut and the pawl portion of the lock washer face to and are engaged with each other, the adjusting nut is restrained from rotating indirectly due to a friction induced from the pawl portion. Here, the friction can be obtained from the pawl portion, but the way to obtain the friction is not limited to the pawl portion. 
         [0019]    Subsequently, an elastomer is mounted on the shaft. In  FIG. 2 , a wave spring washer is shown, but it is not limited to this. The adjusting nut, the lock washer, and the elastomer are arranged in this order (referring to  FIG. 2 ). 
         [0020]    Next, the left crank is mounted on the shaft and is secured by a fixing bolt. As such, the left crank makes the elastomer compressed and deformed to generate an axial force. With this axial force, the lock washer is pushed toward the adjusting nut to enhance a lock effect of the lock washer. For the embodiment using the radial bearing, the reason why the adjusting nut is sometimes loosened and sometimes tightened up is due to vibration or twist. Basically, a turning force can not be generated to render the adjusting nut sometimes loosened and sometimes tightened up. Therefore, a force for making the elastomer compressed and deformed is previously set in order not to cause the radial bearing a defective rotation. 
         [0021]    When riding the bicycle, the right crank, the shaft, a right dust cover, the inner race of the right bearing, the inner race of the left bearing, a left dust cover, the lock washer, the adjusting nut, the elastomer, the left crank, etc are rotated together, that is to say not only the adjusting nut is naturally rotated. However, the adjusting nut is pressed by the elastomer with the lock washer located therebetween. Therefore, in the case of securing the crank, only the adjusting nut is loosened or tightened up, with an effect that an axial load on the bearing can be adjusted without disassembling of the sprocket, and, with the pawl portion, a fine axial load can be easily adjusted. 
         [0022]    Hereinafter, an embodiment of the present invention will be described with reference to the drawings.  FIG. 1  shows an embodiment of the present invention.  FIG. 2  is an exploded perspective view of the left part of the embodiment as shown in  FIG. 1  of the present invention.  FIGS. 3 and 4  show 3 kinds of prior arts respectively. 
         [0023]    According to the present invention, as shown in  FIG. 1  on a shaft, there are disposed key slots  5   a  for restraining rotation with respect to a right crank and for press-fitting fixation; a thread portion  5   b  of screw, on which an adjusting nut  18  having a pawl portion can be screwed; a portion  5   c  for restraining the rotation with respect to a left crank  2  and for press-fit mounting; and a thread portion  5   d  of screw, on which a fixing bolt  15  can be screwed to secure the left crank. 
         [0024]    Key slots  1   a  for restraining the rotation of the right crank  1  with respect to the shaft  5  and for press-fitting fixation are disposed on the right crank  1 . The key slots  5   a  of the shaft  5  are engaged with the key slots la to make the right crank  1  and the shaft  5  integrated together. Then, large gears  3  and small gears  4  are fixed by using bolts  10 , bolts  12  and nuts  11 . A gear ratio can be selected so that a chain can be derailed onto a selected gear. 
         [0025]    A deformation hole  2   a  and a thread portion  2   b  of screw for restraining rotation of the left crank  2  with respective to the shaft  5  and for press-fitting fixation are disposed on the left crank  2 . A cap bolt  16  can be fastened on the thread portion  2   b  of screw. The cap bolt  16  can be designed to make the sprocket assembled/disassembled by merely using a hex wrench. After a washer  17  and the fixing bolt  15  put inside the thread portion  2   b  of screw, the cap bolt  16  is fastened. When the fixing bolt  15  is loosened to dismount the left crank  2 , the head  15   a  of the fixing bolt touches the inner side  16   a  of the cap bolt, and hence the left crank  2  comes out gradually. On the left crank  2 , there is a side face  2   c  abutting an elastomer  20 . 
         [0026]    On the right side of a bottom bracket shell  14 , there are mounted a right bowl  6  and a spacer  13  in which a bearing  8  and a dust cover  9  are fitted inside the bowl  6 , and the spacer  13  is corresponding to a portion of the bottom bracket shell  14  having a different width. Additionally, the dust cover  9  only abuts the inner race  8   a  of the bearing  8 . 
         [0027]    On the left side of the bottom bracket shell  14 , there are mounted a left bowl  7  and a spacer  13 , in which a bearing  8  and a dust cover  9  are fitted inside the bowl  7 , and the spacer  13  is corresponding to a portion of the bottom bracket shell  14  having a different width. Additionally, the dust cover  9  only abuts the inner race  8   a  of the bearing  8 . 
         [0028]    The shaft  5  is first put into the right crank  1  and secured therein, and then is inserted into the above-assembled bottom bracket. The adjusting nut  18  having a pawing portion facing the left crank side is fastened onto the thread portion  5   b  of screw at the front end of the shaft  5  without causing a defective rotation and an axial swing, thereby the right crank is mounted on the bottom bracket. 
         [0029]    The lock washer  19 , which is outside the adjusting nut  18  and the rotation of which is restrained by the shaft  5 , is secured around the shaft  5  with a pawl portion facing the right crank, the pawl portion of the adjusting nut and the pawing portion of the lock washer being engaged with each other. 
         [0030]    The elastomer  20  is secured outside the lock washer  19 . 
         [0031]    By means of the fixing bolt  15  being screwed with a screw thread  5   d  at the central portion of the shaft  5 , the left crank  2  is mounted outside the elastomer  20  with the rotation of the left crank  2  restrained by the portion  5   c  of the shaft  5 . 
         [0032]    The side face  2 C of the left crank  2  which is opposite to the right crank side is formed to compress the elastomer  20  in the axial direction. Then, the induced compression force is press the lock washer  19  toward the adjusting nut  18 . A friction resistance generated by the engagement of the adjusting nut  18  with the opposite pawl is used in order not to make the adjusting nut sometimes loosened and sometimes tightened up. With the elastomer provided between the left crank  2  and the bearing  8 , an excessive load will not be applied to the bearing, and hence a defective rotation is avoided. 
         [0033]    As shown in the drawings, the lock washer is located between the adjusting nut  18  and the elastomer with the adjusting nut  18  being pressed by the elastomer indirectly. Hence, if the crank is secured, the adjusting nut  18  can be turned to adjust the axial load on the bearing. 
         [0034]    Although, the shaft is secured in the right crank, as shown in the present embodiment, yet the shaft can be secured in the left crank, too. The sprocket has two gears as shown in the present invention, but a sprocket having one gear or three gears is applicable, too. 
         [0035]    With regard to a prior sprocket provided with a radial bearing, for avoiding an excessive load from occurring in an axial direction to cause a defective rotation, a left crank having a cut-out is secured by fastening a bolt in a direction perpendicular to the shaft. However, the cut-out will degrade the strength of the left crank. Therefore, it is necessary to reinforce the wall thickness of the left crank, which resulting in the weight of the left crank becoming too heavy such that the axial load can not be adjusted after an assembly is made. 
         [0036]    Also, in order to minimize the left crank, a bolt-insertion portion is provided in the axial direction of the shaft of the left crank and a bolt is fastened into the shaft for securing the left crank. Moreover, for preventing an excessive load generating in the axial direction from being applied on the radial bearing, an elastomer is provided therebetween. However, when a large force is applied in the axial direction, the elastomer is compressed to cause the shaft to be moved in the axial direction, which renders an adverse effect on a driving system. After continuous use for a long time, the elastomer may be deformed, and causing an axial swing. 
         [0037]    The present invention is to resolve the above problems of the prior arts. In order to minimize a left crank, a bolt insertion portion is provided in the axial direction of a shaft in the left crank and a bolt is fastened into the shaft for securing the left crank. As an elastomer is provided therebetween, an excessive load will not be applied on the radial bearing. Even though a large force is applied in the axial direction, this force is received by the adjusting nut, instead of by the elastomer. Due to the fact that the shaft can not be moved in the axial direction, no adverse effect will be caused on a driving system. For the prior arts, after an assembly is made, an adjustment can not be made. Even though it was not a best adjustment, you can only accept it. However, according to the present invention, after assembly, an adjustment can be made. Therefore, the present invention is very much helpful for users.