Patent Publication Number: US-2009232436-A1

Title: Bicycle bearings

Description:
TECHNICAL FIELD 
     One aspect of the present invention relates to a bicycle that has a frame with a bottom bracket shell, with the bottom bracket shell holding a bottom bracket for bearing a crank shaft having crank arms carrying pedals. 
     BACKGROUND OF THE INVENTION 
     It is conventional for the bottom bracket of a bicycle to comprise ball bearings for bearing the crank shaft. Thus, the crank shaft can rotate substantially without friction, i.e. pedaling is not rendered difficult by friction. Because the bottom bracket shell has a inner diameter that is larger than the outer diameter of the crank shaft plus the size of the ball bearings, a cap or another adapter made of steel may be screwed into the bottom bracket shell to reduce the inner diameter. 
     BRIEF SUMMARY OF SOME ASPECTS OF THE INVENTION 
     One aspect of the present invention is the provision of improvements to a bicycle of the type described above. In accordance with one aspect of the present invention, a bicycle has a frame with a bottom bracket shell, with the bottom bracket shell holding a bottom bracket for bearing a crank shaft having crank arms carrying pedals, wherein the bottom bracket comprises at least one bush bearing (e.g., a bushing that is used as a bearing). Thus, friction between the bottom bracket and the crank shaft occurs, which makes it easier to perform tricks on a BMX freestyle bicycle. 
     Other aspects and advantages of the present invention will become apparent from the following. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail with reference to an exemplary embodiment depicted in the drawings, in which: 
         FIG. 1  is a partially sectional bottom view of a portion of the exemplary embodiment, 
         FIG. 2  includes a side view and a cross-sectional sectional view of the bottom bracket of  FIG. 1 , 
         FIG. 3  a partially sectional view like  FIG. 1 , with another (e.g., an alternative) bottom bracket for use in place of the bottom bracket of  FIG. 1 , 
         FIG. 4  a left side view of the exemplary embodiment, and 
         FIG. 5  is a partially sectional side view of a portion of the exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT 
     A bicycle  1  has a frame  3  that supports a rear wheel  5  at the rear of bicycle  1  and, by way of a fork  8  at the front of bicycle  1 , the frame  3  supports a front wheel  10  of bicycle  1 . The frame  3  is of a diamond-like form comprising or consisting of a main “triangle” having a top tube  12 , a seat tube  14 , a down tube  16  and a short head tube  18 , and two rear “triangles”, each having a seat stay  20  (e.g., tube), a chain stay  22  (e.g., tube), and the seat tube  14  as a common part of all rear “triangles”. 
     A bottom bracket shell  24  is provided where the down tube  16 , the seat tube  14 , and the two chain stays  22  are connected (e.g., the down tube  16 , seat tube  14 , and chain stays  22  are mounted (e.g., welded) to the bottom bracket shell  24 ). The bottom bracket shell  24  is a short tube running side to side, a direction which is called “axial” hereinafter. With respect to the axial direction of the bottom bracket shell  24 , the seat tube  14 , the down tube  16 , and the chain stays  22  are projecting from the bottom bracket shell  24  in a direction which is called “radial” hereinafter. 
     The bottom bracket shell  24  holds a bottom bracket  26 , and the bottom bracket  26  bears a crank shaft  30 , which is arranged in the axial direction. A crank arm  32  is mounted on each of the two ends of the crank shaft  30 , and each crank arm  32  bears a pedal  34  in a conventional manner. On one side of the bottom bracket shell  24 , a front gear  36  is mounted on the crank shaft  30 . The front gear  36  is typically mounted for rotating with the crank shaft  30  in a conventional manner, with the front gear  36  typically being linked, in a conventional manner, to the rear wheel  5  via a chain and rear gear. 
     According to the exemplary embodiment of the invention, the bottom bracket  26  comprises two bush bearings  26   a  (e.g., bushings that are used as bearings), with the bush bearings  26   a  being arranged in the axial direction and fixed to the bottom bracket shell  24 . According to the exemplary embodiment of the invention, the bush bearings  26   a  are not antifriction bearings (e.g., the bush bearings  26   a  are not ball bearings). More specifically according to the exemplary embodiment of the invention, the inner diameter of the bush bearings  26   a  corresponds to (e.g., is substantially the same as, such as by being slightly larger than) the outer diameter of the crank shaft  30 , so that the bush bearings  26   a  are configured as “friction bearings” (e.g., there is typically direct, sliding contact between the inwardly facing inner surfaces of the bush bearings  26   a  and the corresponding outwardly facing outer surfaces of the crank shaft  30 , and any provision of fluid lubricant (for reducing the friction associated with the direct, sliding contact) typically does not result in a film of lubricant that is thick enough to avoid direct, sliding contact between the inwardly facing inner surfaces of the bush bearings  26   a  and the corresponding outwardly facing outer surfaces of the crank shaft  30  (e.g., the bush bearings  26   a  are not fluid bearings)). 
     The radial size of the bottom bracket shell  24  offers different realizations of (e.g., designs of) the bottom bracket  26 . As mentioned above for the exemplary embodiment of the present invention, the inner diameter of the bush bearings  26   a  corresponds to the outer diameter of the crank shaft  30 . Depending on the inner diameter of the bottom bracket shell  24  (compared to the outer diameter of the bush bearings  26   a ), the bush bearings  26   a  may be fixed to the bottom bracket shell  24  directly or via an adapter, called cap  26   b.  Such a cap  26   b  is preferably made of an aluminum alloy and has preferably an annular shape. Throughout this disclosure, “preferably” should be understood to at least mean “optionally”. 
     The cap  26   b  is preferably provided with a step  38  (e.g., an annular shoulder), defining a part which is covering (e.g., at least partially covering) the front side (e.g., end face) of the bottom bracket shell  24 , and a projecting part (e.g., an annular projection) which is pressed in (e.g., press-fit in) the bottom bracket shell  24 . Alternatively, the bush bearings  26   a  may be fixed directly to the bottom bracket shell  24 , in which case the bottom bracket shell  24  is preferably provided with a step  38  (e.g., shoulder) on each side, defining a receptacle for the bush bearing  26   a,  with the bush bearing  26   a  being pressed into (e.g., press-fit in) the bottom bracket shell  24 . 
     In accordance with an alternative embodiment of the present invention, the bush bearings  26   a  are pressed on (e.g., fixedly connected to) the crank shaft  30 , with the bush bearings  26   a  being borne (e.g., pivotably borne) within the receptacle of the bottom bracket shell  24 . In accordance with this alternative embodiment, the bush bearings  26   a  are configured as “friction bearings”, for operating by way of direct, sliding contact. 
     The upper part of the fork  8  may be referred to as a fork shaft  8   a.  On top of the fork shaft  8   a,  a stem  40  is mounted. The stem  40  may be mounted to the fork shaft  8   a  in any suitable manner. For example, the stem  40  may be conventionally mounted to the fork shaft  8   a  by press-fitting. As another example, the stem  40  may be mounted to the fork shaft  8   a  by way of clamping ring, as described in U.S. patent application Ser. No. 12/069,291, which was filed Feb. 8, 2008. The entire disclosure of U.S. patent application Ser. No. 12/069,291 is incorporated herein by reference. 
     The handlebar  42  is mounted (e.g., in a conventional manner) on the stem  40  for steering the front wheel  10 . The head tube  18  is bearing the fork shaft  8   a  by way of at least one, preferably two bush bearings  44 , one at the upper end of the head tube  18 , and one on the lower end of the head tube  18 . In accordance with the exemplary embodiment, the bush bearings  44  are the same as the bush bearings  26   a  (e.g., the bush bearings  44  are “friction bearings”), except that they may be different sizes. The inner diameter of the bush bearings  44  corresponds to (e.g., is substantially the same as, such as by being slightly larger than) the outer diameter of the fork shaft  8   a.  The outer diameter of the bush bearing  44  is the same as or larger than the inner diameter of the head tube  18 , so that the bush bearings  44  are fixed to the head tube  18 . 
     In the exemplary embodiment of the present invention, the bush bearings  44  are fixed to the head tube  18  directly. The head tube  18  is preferably provided with a step  38  (e.g., shoulder) at each end, for defining a receptacle for the bush bearing  44 , with the bush bearing  44  being pressed into (e.g., press-fit in) the head tube  18 . 
     In accordance with an alternative embodiment of the present invention, the bush bearings  44  are pressed on (e.g., fixedly connected to) the fork shaft  8   a,  with the bush bearings  44  being borne (e.g., pivotably borne) respectively within the receptacles of the head tube  18 . In accordance with this alternative embodiment, the bush bearings  26   a  are configured as “friction bearings”, for operating by way of direct, sliding contact. 
     It is also possible for a conventional ball bearing to be used at the lower end of the head tube  18  instead of the lower bush bearing  44 . It is further possible for a conventional ball bearing to be used at the upper end of the head tube  18  instead of the upper bush bearing  44 . 
     It will be understood by those skilled in the art that while the present invention has been discussed above with reference to exemplary embodiment(s), various additions, modifications and changes can be made thereto without departing from the spirit and scope of the invention as set forth in the claims.