Abstract:
A bottom bracket assembly for a bicycle is comprised of a spindle and at least two cartridge bearings. The inner races of the cartridge bearings are axially fixed on the spindle by abutting stop elements. Crank arms attached to the ends of the spindle axially abut the outer stop elements, thus ensuring the precise and consistent axial location of the crank arms. Since the inner bearing races are fixed axially, the outer race of at least one cartridge bearing may be allowed to float in an axial direction to ensure proper alignment of the inner and outer races and the greatest possible bearing life for the bottom bracket.

Description:
This application claims the benefit of Provisional Application No. 60/262,731, filed Jan. 19, 2001. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the field of bicycles, more particularly to a bottom bracket assembly for a bicycle. 
     BACKGROUND OF THE INVENTION 
     Typical human powered bicycles are propelled by pedals mounted on cranks at opposite ends of an axle. The cranks drive the axle, on which usually one or more sprockets are mounted that engage a chain to transfer the rotary motion to a rear wheel. The part of the bicycle frame where the axle is mounted is called the bottom bracket. Here, the axle is rotatably held in a bearing, so that it can rotate with very low friction. 
     For mounting the axle with low friction, ball bearings are employed, consisting of inner and outer races with interposed bearing balls. In many known bottom bracket assemblies, the inner race is formed as a part of the axle or spindle. However, this has proven to create a number of problems. Bearing races must be very hard, and hence brittle, due to high contact stresses present in rolling element ball bearings. Brittleness, however, is highly undesired for the spindle because it reduces the ability of the spindle to absorb high impact energies occurring in some situations. 
     One example of a bottom bracket bearing assembly where the inner races of ball bearings are formed by the spindle itself is described in French patent 270,698 to Bazille. 
     Other known bottom bracket bearings of the prior art make use of sealed cartridge bearings, which integrate the two races with the bearing and are available as readily assembled units. Cartridge bearings can easily be replaced when worn or damaged. The successful use of cartridge bearings in bicycle bottom brackets, however, requires the designer to ensure that the inner and outer bearing races are correctly aligned. If axial loads lead to misalignment of the bearing races during assembly or use of the bottom bracket, damage is likely to occur. 
     If the both the inner and outer bearing races of a cartridge bearing are fixed axially in the bottom bracket assembly, correct alignment can only be ensured by very tight control of manufacturing dimensions and tolerances. The distance between the fixed positions of the two outer bearing races must be nearly identical to the distance between the inner bearing races. This has proven to raise manufacturing cost and make the overall bottom bracket design intolerant to manufacturing and assembly variations. 
     A number of known bottom bracket assemblies of the prior art solve the problem of correct alignment of the inner and outer bearing races by allowing the inner races to float on the spindle while the outer races are fixed in an outer bracket portion, typically being clamped between a shell and adapters inserted at both ends. However, this design makes it difficult to efficiently incorporate crank stops into the bottom bracket. Crank stops are a desirable addition to a bottom bracket because they ensure correct and consistent axial alignment of the installed crank arms. 
     U.S. Pat. No. 3,903,754 to Morroni and U.S. Pat. No. 4,093,325 to Troccaz both show bottom bracket assemblies where a spindle is rotatably mounted in the bottom bracket by cartridge bearings. The inner races of the cartridge bearings are spaced apart by shoulders on the spindle while the outer races are spaced apart by a tubular spacer or shell. Axial alignment of the inner and outer bearing races in this case can only be accomplished by matching the width of the shoulders and the tubular spacer, using very tight dimensional tolerances. 
     U.S. Pat. No. 4,545,691 to Kastan shows a bottom bracket assembly for a bicycle where the inner races of the cartridge bearings are fit on the axle and are clamped between a shell and an adapter to fix their axial position. The outer races are butted against shoulders located in the bearing adapters. During initial assembly, the bearing adapters are allowed to float. The adapters are then tightened into axial alignment with the inner bearing races by a tapered split ring. 
     The present invention aims to provide a bottom bracket assembly for a bicycle, where in a simple construction cartridge bearings can be used advantageously. 
     SUMMARY OF THE INVENTION 
     According to the invention, there is provided a bottom bracket assembly for a bicycle that uses cartridge bearings. Inner races of the cartridge bearings are fit on the spindle and are fixed in both axial directions by abutting stop elements. 
     According to a first aspect of the invention, the outer races of the cartridge bearings are mounted such that they are free to move in both axial directions. This eliminates the need for very tight control of manufacturing dimensions and tolerances. 
     Providing the outer bearing races with adjacent gaps in both axial directions allows for these races to be shifted small distances during installation or under high load during use. The inventor has recognized that the inner bearing races are less likely to be damaged by high axial loads since the spindle provides good support for these races, especially if they are press-fit thereon. The outer bearing races, however, even if they are press-fit into the outer bracket portion, known as the adapters, are more likely to be damaged. The adapters are usually thin-walled and are often manufactured from lightweight materials. Consequently they do not provide as much support as the stiffer spindle. Allowing the outer races to float by a small amount axially when subjected to high loads, such as encountered in a crash situation, effectively helps to protect these bearing races from damage. 
     According to a second aspect of the invention, the inner races of the cartridge bearings are fit on the spindle and are clamped between abutting inner and outer stop elements. The ends of the spindle comprise adapting portions to receive crank arms. The stop elements fixing the inner races of the cartridge bearings on the spindle also serve as stop elements for the axial location of the crank arms. 
     Crank arm stop elements, henceforth known as crank stops, are useful because they provide consistent axial location of the crank arms when they are installed on the spindle. In prior art bottom brackets that allow the inner bearing races to float on the spindle to achieve correctly aligned races, crank stops could only be provided by steps included in the spindle. These steps increase machining complexity and lead to a reduction in bearing strength because the bearing must fit over the step. Consequently the inner bearing races must be a larger diameter than otherwise would be necessary. For a fixed outer bearing race diameter, using larger inner bearing races results in smaller bearing balls, thus reducing the overall load carrying capability and life of the bearing. Thus, according to the second aspect of the invention, there is provided a very simple construction to effectively utilize cartridge bearings of sufficient strength and provide crank stops without increased machining complexity. 
     Numerous other benefits and advantages will become apparent from the following detailed description of a preferred embodiment of the invention with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a bicycle. 
         FIG. 2  shows a partial longitudinal cross-sectional view of a first embodiment of a bottom bracket of the bicycle from  FIG. 1 . 
         FIG. 2A  is an enlarged fragmentary detail of the area labeled  2 A in  FIG. 2 . 
         FIG. 2B  is an enlarged fragmentary detail of the area labeled  2 B in  FIG. 2 . 
         FIG. 2C  is an enlarged fragmentary detail of the area labeled  2 C in  FIG. 2A . 
         FIG. 3  is a partial longitudinal cross-sectional view of the bottom bracket assembly of  FIG. 2  with installed crank arms. 
         FIG. 3A  is an enlarged fragmentary detail of the area labeled  3 A in  FIG. 3 . 
         FIG. 4  is a partial longitudinal cross-sectional view of a second embodiment of a bottom bracket assembly. 
         FIG. 4A  is an enlarged fragmentary detail of the area labeled  4 A in  FIG. 4 . 
         FIG. 4B  is an enlarged fragmentary detail of the area labeled  4 B in  FIG. 4 . 
         FIG. 5  is a partial longitudinal cross-sectional view of third embodiment of a bottom bracket assembly. 
         FIG. 5A  is an enlarged fragmentary detail of the area labeled  5 A in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  generally shows a bicycle  10  with a bicycle frame  12 , on which are mounted crank arms  14 ,  16  with pedals  18 . Crank arms  14 ,  16  are connected to an axle  20 , which is rotatably held in frame  12 . 
       FIG. 2  shows an axial or longitudinal cross section of the area where the axle, or spindle  20 , is received in the bicycle frame  12 . 
     On top of  FIG. 2  there is shown a tube forming part of the bicycle frame  12 , attached to a tubular sleeve  22  containing a first embodiment of a bottom bracket assembly generally indicated as  24 . 
     This first embodiment of a bottom bracket assembly according to the present invention includes the spindle  20 , preferably of steel, which has adapting portions  26  on both axial ends to receive crank arms. The adapting portions  26  comprise an outer portion adapted to be received in the hub portion  54  of the cranks  14 ,  16  and an inner thread  28  for fixing the cranks to the spindle. 
     The spindle  20  is mounted in the bottom bracket by means of two cartridge bearings  30 ,  32  arranged near the ends of the bottom bracket assembly  24 . Cartridge bearings  30 ,  32  are sealed cartridge bearings, available as readily assembled units. As can be seen in  FIG. 2A , which is an enlarged view of the area  2 A of  FIG. 2 , each cartridge bearing  30 ,  32  comprises inner and outer bearing races  34 ,  36  with bearing balls  38  there between. 
     The bottom bracket assembly  24  arranged in sleeve  22  comprises an outer bracket portion  40 , consisting of a cartridge shell  42  and two adapter cups  44 . 
     The inner bearing races  34  of cartridge bearings  30 ,  32  are press-fit over the spindle  20 . Adapter cups  44  are fit onto the outer races  36  of cartridge bearing  30 ,  32 , such that the outer races  36  are held in the outer bracket portion  40 . 
     Spindle  20  has enlarged annular steps  46  arranged at a distance from its opposite ends. The inner bearing races  34  of cartridge bearings  30 ,  32  are fit on the spindle  20  and axially abut against steps  46 . 
     Further fit on the spindle are stop rings  48  acting as crank stop elements. The crank stops  48  are press-fit over the spindle  20  and clamp the inner bearing races  34  between the crank stops  48  and the spindle steps  46 . The inner bearing races  34  are thus axially fixed. 
     On the other hand, the outer bearing races  36 , which are received in the adapter cups  44 , are free to float a small amount axially between a shoulder acting as bearing stop  50  of the adapter cups  44  and the axial ends  52  of the shell  42 . As can be seen in  FIGS. 2A ,  2 B and  2 C, gaps  54  are provided to both axial sides of the floating outer bearing races  36 . Gaps  54  may be of unequal size for each bearing. In the embodiment shown the outer race  36  of cartridge bearing  30  to the left in  FIG. 2  has only very small gaps of 0.05 mm length, which are only visible in the enlarged view of  FIG. 2C . The outer race  36  of cartridge bearing  32  to the right in  FIG. 2  has gaps of roughly 0.5 mm, which allow the outer race  36 , to axially move by the corresponding distance. 
     This bottom bracket assembly with axially fixed inner races  34  and floating outer races  36  eliminates the need for very tight dimensional tolerances. In prior constructions of this type, the length of sleeve  42  would have to match exactly the distance between spindle steps  46 . According to the present invention, sleeve  42  is deliberately made shorter than that distance. 
     During installation, the outer bearing race  36  will axially move to a position where the inner and outer races of bearings  30 ,  32  are aligned. Also, if during use high axial loads occur, outer bearing races  36  can axially shift by a small amount to counter said loads, such as encountered in a crash situation. In case of excessive axial forces, one of the outer bearing races  36  will butt against either the bearing-stop  50  in the adapter  44  or the respective end  52  of the shell  42 . Sufficiently close tolerances can be easily held in manufacturing to keep this axial movement under an amount noticeable by the bicycle rider. The present invention thus produces a bottom bracket assembly with correctly aligned inner and outer bearing races that is highly tolerant of variations in both the manufacturing process of the bottom bracket assembly itself and installation of the bottom bracket assembly into a bicycle frame  12 . 
     As shown in  FIG. 2 , the bottom bracket assembly is installed in tube  22  of a typical bicycle frame  12  by outer threads provided on the adapter cups  44 . 
       FIG. 3  shows the bottom bracket assembly  24  with installed cranks  14 ,  16 . Cranks  14 ,  16  each include a hub portion  54  with a central hole, which receives the adapting portions  26  at the ends of spindle  20 . Adapting portions  26  in this first embodiment comprise a star-like outer cross-sectional shape with longitudinal splines at the ends of spindle  20 . These splines are received in a correspondingly shaped hole of hubs  54 , such that cranks  14 ,  16  are rotatably fixed onto spindle  20 . 
     As can be seen in  FIG. 3  and the enlarged view of  FIG. 3A , hub portion  54  axially abuts against crank stop  48 , thus ensuring consistent axial location of the crank arms when they are installed on the spindle  20 . This is especially important with regard to crank arm  14  to the right in  FIG. 3 , which is shown to carry a number of sprockets  56 . The defined axial location of these sprockets is important for optimum chain shifting operation. 
     As can be seen again in the enlarged view of  FIG. 3A , the elements are provided on spindle  20 , in the following order, from the inside to the outside: spindle step  46 , inner race  34  of cartridge bearing  32 , crank stop  48 , crank hub  54 . 
       FIG. 4  shows a second embodiment of a bottom bracket assembly  60 . This second embodiment of a bottom bracket assembly closely resembles the first embodiment of  FIGS. 2 ,  2 A,  2 B,  2 C,  3 , and  3 A. The same reference numerals are used for corresponding elements. Bottom bracket assembly  60  will consequently not be described in detail, but reference will only be made to elements different from the first embodiment. 
     In the second embodiment, spindle  20  is solid and not hollow as the spindle of first embodiment. Also, adapting portions  26  for mounting crank arms are shaped differently. Instead of spline shaped adapting portions in the first embodiment, here adapting portions  26  of the spindle have a square cross-section. These adapting portions  26  can be received in correspondingly shaped hub portions of crank arms (not shown) in the same way as the spline shaped adapting portions shown in  FIG. 3 . 
     As in the first embodiment, cartridge bearings  30 ,  32  are provided. The inner races  34  of cartridge bearings  30 ,  32  are clamped between steps  46  on the spindle  20  and crank stops  48 , such that they are axially fixed. Of the outer bearing races  36 , the outer bearing race of cartridge bearing  30  to the left in  FIG. 4 , shown in detail in  FIG. 4A  is also axially fixed. As shown in the enlarged view of  FIG. 4A  the end of shell  42  and bearing stop  50  of adapter cup  44  axially abut against the interposed outer race  36  of cartridge bearing  30 . 
     On the other hand, outer race  36  of cartridge bearing  32  to the right in  FIG. 4  has gaps  54  provided at both axial ends thereof, such that it can move axially by a small amount. 
     It has been found that the above construction with only one outer race being allowed to float is enough to correctly align the bearing races and eliminate the need for tight dimensional tolerances. 
       FIG. 5  shows a third embodiment of a bottom bracket assembly  70 . Again, the construction resembles first and second embodiments. The same reference numerals are used for corresponding elements. The third embodiment will not be explained in detail, but reference will be made only to the differences to the first and second embodiments. 
     As can be seen in  FIG. 5 , spindle  20  is mounted with cartridge bearings  30 ,  32  in outer bracket portion  40 . In the third embodiment the outer bracket portion  40  only comprises one adapter cup  44 . The other adapter cup is integrated with the cartridge shell to form a single component  72 . As can be seen in the enlarged view of  FIG. 5A , this configuration produces a bottom bracket assembly in which the outer race  36  of the right end bearing  32  can float axially. Combination element  72  has a bearing stop  50  to limit axial movement of the inner bearing race  36  to one side. On the other axial side of the outer bearing race  36 , the outer bracket portion is open. 
     Although the invention has been explained in relation to its preferred embodiments, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.