Abstract:
The present invention is a two-piece bicycle crank set comprising of two monolithic, thin-wall continuous tubular members. Each tubular member includes a crank arm and a one-half portion of a crank axle, where the crank arm and the portion of the crank axle form a continuous thin-wall tubular shape. The two tubular members are coupled precisely midway between two bearing sets within a bracket shell of a bicycle. The coupling connecting the two tubular members can include an outer sleeve, an inner sleeve, two exteriorly tapered and internally threaded bushings and a threaded stud. Turning the threaded stud positions the bushings to expand the inner sleeve, whereby the crank axle portions of the two tubular members are secured within the inner sleeve and the outer sleeve by the expanding inner sleeve. Alternatively, an interference fit coupling connects the two tubular members, and includes a mortise member and a tenon member. The tenon member fits into and interlocks within the mortise member to secure the first tubular member to the second tubular member. The interference fit coupling can further include an attachment bolt and a separation bolt to facilitate assembly and disassembly of the coupling.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part (CIP) of applicant&#39;s U.S. patent application Ser. No. 09/580,336, filed May 26, 2000 now abandoned, entitled “Two-Piece Bicycle Crank Set,” which application claims priority to U.S. Provisional Patent Application No. 60/136,669, filed May 28, 1999, entitled “Two-Piece Bicycle Crank Set.” The above referenced patent applications are incorporated in their entirety herein by this reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a bicycle crank set assembly, and more particularly to a two-piece, tubular, continuous and tapered crank set combining high strength with light weight. 
     BACKGROUND OF THE INVENTION 
     In bicycle racing, the weight, strength, and rigidity of bicycle components are of ultimate importance to bicycle enthusiasts. Lighter components (especially the rotating parts) having superior strength and rigidity are much sought after. 
     Information relevant to attempts to address these component characteristics can be found in the following U.S. Pat. No. 5,493,937 to Edwards; U.S. Pat. No. 4,704,919 to Durham; and U.S. Pat. No. 5,924,336 to Richardson. However, each of these references suffers from one or more of the disadvantages described below. Therefore, these references do not effectively combine maximum load bearing capability with minimum weight. 
     Many existing bicycle crank sets include a two-piece crank axle having intricately joined crank arms. The crank arms are often separate members mechanically attached to the crank axle portions and sometimes reinforced with gussets. The mechanical attachments and reinforcing gussets undesirably result in a build up of weight at the attachment locations. 
     The present invention solves this problem by providing a continuous tubular member of monolithic design, combining a one-half crank axle portion with a crank arm. This design avoids weighty joint and joint reinforcements, efficiently providing superior strength and rigidity while minimizing weight. 
     Many existing crank sets include crank arms having a constant cross-section along the crank arm length. Since bearing loads addressed by crank arms are not constant over the crank arm length, a crank arm having a constant cross-section does not offer superior load carrying capabilities in relation to weight, thus being detrimental to achieving a maximum strength and rigidity to weight relationship. 
     The present invention provides tapered crank arms, analyzed for load bearing capacity at each point along the crank arm length. This design efficiently provides the minimal cross-section necessary, at each point along the crank arm length, to accommodate the loads faced at each point along the crank arm length. The monolithic and continuous design distributes all stresses uniformly and equally over each piece of the crank set. 
     Some existing crank sets join two crank axle portions within a bracket shell with a spline joint. Due to the nature of cyclical loads bearing on the crank axle, the weakest portion of the crank axle occurs at its smallest diameter, or at a stress concentration point. Since a spline joint joins one smaller diameter crank axle portion within another larger diameter crank axle portion, the overall crank axle bearing capacity is limited to its smaller diameter portion. Considering the limited dimensions of the bracket shell, the spline joint does not offer maximum load bearing capacity relative to overall crank axle diameter. 
     The present invention provides a uniform crank axle diameter of tubular design, efficiently maximizing load bearing capacity relative to crank axle diameter. 
     Existing crank sets having larger diameter crank axles with excessively reinforced and weighty couplings further require larger and heavier bearing sets or bearing set placement outside the bracket shell (as in Richardson). Since the boundary conditions of the bracket shell are fixed, larger bearing sets result in less space to accommodate large diameter crank axles. Therefore, there exists a need for bearing sets made of higher strength materials, so that smaller bearing sets could accommodate the crank axle loads. These smaller bearing sets would offer more space within a typical bracket shell for larger diameter crank axles, thus increasing crank axle bearing capacity without resorting to bearing set placement outside the bracket shell, which has the disadvantage of widening the crank set assembly. 
     The present invention solves this problem by providing high strength bearing sets of a diameter substantially smaller than that in existing crank sets, thus accommodating crank axles of larger diameter within the fixed diameter of the bracket shell and providing a crank set of superior load bearing capacity. 
     SUMMARY OF THE INVENTION 
     The present invention is a directed to a two-piece bicycle crank set combining superior strength and rigidity with light weight. The crank set comprises two thin-wall tubular members. The tubular members include crank axle portions of relatively large diameter and light weight, tapered crank arms where torsional, bending and shear loads determine the tubular cross sectional size at each location along the crank arm length and a reinforcing insert at the distal end of the crank arm to accommodate a variety of pedal axles, or a tubular pedal axle incorporated within the continuous, monolithic crank axle and crank arm tubular member. 
     In one aspect of the present invention, the crank set is significantly lighter than existing crank set assemblies and has superior load bearing capability. The crank set is designed with torsional, bending and shear loads determining the dimensions of the tubular crank axle and the tapered crank arm cross-section. The tubular members are designed and shaped to distribute all stresses uniformly and equally over the continuous tubular member. 
     In one aspect of the present invention, the crank set includes bearing sets having ultra high strength ball bearings allowing for smaller bearing sets than those found in existing crank set assemblies, therefore providing additional space within the bracket shell for a larger diameter crank axle. 
     In another aspect of the present invention, the crank set is split midway along its crank axle, with each crank set piece containing precisely one-half of the total crank axle length. The two, one-half crank axle portions are coupled within the bracket shell precisely midway between the two bearing sets. Connecting the crank axle portions precisely midway between the two bearing sets effectively eliminates all shear loads. 
     In another aspect of the present invention, the bicycle crank set comprises a first tubular member, a second tubular member, a spider connected to the second tubular member, and a coupling securing the first tubular member to the second tubular member within a bracket shell. The first and the second tubular members include a crank arm and a portion of a crank axle forming a continuous and monolithic thin-wall tubular shape. 
     In another aspect of the present invention, the first and the second tubular members further include a pedal axle, where the crank arm, the portion of the crank axle and the pedal axle all form a continuous and monolithic thin-wall tubular shape. In another of its aspects, a spider is further incorporated into the continuous, thin-wall tubular shape of the second tubular member. 
     In another aspect of the present invention, the first and the second tubular members are injection molded and made of aramid fiber composite material. Alternatively, the first and the second tubular members could be injection molded and made of carbon and glass fiber composite material. Further, the first and the second tubular member could be steel stamped parts of clamshell design and electron beam or laser welded together to form the continuous and monolithic thin-wall tubular shape. 
     In another aspect of the present invention, the coupling includes an outer sleeve, an inner sleeve, two exteriorly tapered and internally threaded bushings, and a threaded stud. Turning the stud threadably positions the bushings to expand the inner sleeve, securing the crank axle portions of the first and the second tubular members between the inner and the outer sleeves of the coupling. 
     In another aspect of the present invention, the coupling includes a mortise member and a tenon member. The tenon member fits into the mortise member to secure the crank axle portion of the first tubular member to that of the second tubular member. This coupling can further include an attachment bolt that passes through a clearance hole in one of the tubular members and threadably engages an attachment hole in the other tubular member. Threading the attachment bolt into the attachment hole securely interlocks the tenon member into the mortise member. The mortise and the tenon members can be either tapered or non-tapered. This coupling can further include separation bolt, where removing the attachment bolt and threading the separation bolt into and through the clearance hole forces the tenon member apart and away from the mortise member. 
     In another aspect of the present invention, the clearance hole has a diameter of 10 mm and the attachment hole has a diameter of 8 mm. The diameter of the attachment bolt can be 8 mm and the diameter of the separation bolt can be 10 mm. 
     In another aspect of the present invention, the tenon and the mortise members are made of boron composites. Alternatively, the tenon and the mortise members can be made from high strength metal materials. 
     In another aspect of the present invention, the crank set further includes two bearing sets and the coupling within the bracket shell is located precisely midway between the two bearing sets. The bearing sets can include an outer cup, an inner cup, seals and ceramic balls. The ceramic balls can housed within the outer cup, the inner cup and the seals and can be separated from one another by retainers. The outer cup is in communication with the bracket shell and the inner cup is in communication with the crank axle portion of one of the tubular members. The ceramic balls can be made of silicon nitride. The outer and the inner cups can be made of 52100 steel and can be hardened and sputer coated with titanium aluminum nitride to provide an overall hardness exceeding Rockwell 90. The seals can be spring loaded Teflon garter. The retainers can be made of mylar, nylon, Delrin or an adequate engineering plastic. 
     In another aspect of the present invention, the crank arm further includes an internally threaded titanium insert capable of housing a variety of pedals. The crank arm can include a compression molded solid carbon fiber and glass composite portion, in the vicinity of the titanium insert, to house the titanium insert. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown. 
     FIG. 1 illustrates a top, cross-sectional view of a two-piece crank set coupled within a bracket shell, in accordance with the present invention; 
     FIG. 2 illustrates a top, cross-sectional exploded view detailing the crank set housing shown in FIG. 1; 
     FIG. 3 illustrates a right side elevation view of the crank set housing shown in FIG. 1, showing a tubular crank arm; 
     FIG. 4 illustrates a left side view of the crank set housing shown in FIG. 1, showing a tubular crank arm with connected spider; 
     FIG. 5 illustrates a top, cross-sectional exploded view of a coupling portion of the crank set shown in FIG. 1, with bushings in an non-operational position; 
     FIG. 6 illustrates a top, cross-sectional exploded view of the coupling shown in FIG. 5, with the bushings in an operational position; 
     FIG. 7 illustrates a side, cross-sectional view of a reinforcing insert used to support a pedal axle, in accordance with the present invention; 
     FIG. 8 illustrates a side elevation view of the coupling shown in FIG. 5, without including the bushings; 
     FIG. 9 illustrates a top plan view of another embodiment of the tubular member shown in FIG. 3, including a crank arm, a portion of a crank axle and a reinforcing insert aperture, in accordance with the present invention; 
     FIG. 10 illustrates a side plan view of another embodiment of the tubular member with connected spider shown in FIG. 4, in accordance with the present invention; 
     FIG. 11 illustrates a top plan view of an alternative embodiment of the tubular member with connected spider shown in FIG. 4, including a crank arm, a portion of a crank axle, a spider and a pedal axle, in accordance with the present invention; 
     FIG. 12 illustrates an exploded and perspective view of an interference fit coupling, including a mortise member and a tenon member, in accordance with the present invention; 
     FIG. 13 illustrates an exploded and perspective view of a tapered four coupling, including a male member and a female member, in accordance with the present invention; 
     FIG. 14 illustrates a top, cross-sectional detailed view of an interference fit coupling centered between two bearing sets within a bracket shell, in accordance with the present invention; 
     FIG. 15 illustrates a perspective view of a retaining ring with ball bearings of a bearing set, in accordance with the present invention; 
     FIG. 16 illustrates a perspective view of an outer cup with integral inner seal of a bearing set, in accordance with the present invention; 
     FIG. 17 illustrates a perspective view of an attachment bolt for an interference fit coupling or tapered four coupling, in accordance with the present invention; 
     FIG. 18 illustrates a perspective view of the tubular member shown in FIG. 9, with a tenon member of an interference coupling attached to the tubular member (also having an inner cup with integral outer seal press fit onto the tenon member), in accordance with the present invention; 
     FIG. 19 illustrates a side plan view of the tubular member with connected spider shown in FIG. 10, further showing a tab covering an access hole for coupling assembly and disassembly, in accordance with the present invention; and 
     FIG. 20 illustrates a perspective, exploded view of a crank set assembly with an interference fit coupling, in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein like numerals indicate like elements, there is shown in the drawings in general, and in FIG. 1 in particular, a two-piece bicycle crank set  8 , comprising two, continuous thin-wall tubular members  10 , each tubular member  10  including a continuous crank arm  40 , a one-half crank axle  50 , and a reinforcing pedal axle insert  80 . The crank arms  40  are tapered. The reinforcing inserts  80  (detailed in FIG.  7 ), inserted in the distal end of the crank arm  40 , are solid core and include a standard interior thread within pedal axle aperture  30 , allowing for attachment of a variety of pedals (not shown). The drive side continuous tubular member  10  further includes a spider  60 , on which chain gears are mounted (not shown). 
     The two continuous tubular members  10  each contain a crank axle  50  portion precisely equaling one-half of the total crank axle length of the crank set  8 . Therefore, the connection between the tubular members  10  is centrally located between two bearing sets  16  within a bracket shell  14 . Other embodiments may have the tubular members  10  containing other than precisely one-half of the crank axle, meaning the connection between the tubular members  10  is not centrally located between the two bearing sets  16  within the bracket shell  14 . 
     Referring to FIG. 2, each continuous tubular member  10  of this embodiment has a convoluted split  12 . When the continuous tubular members  10  are brought together in a mating position, the crank arms  40  are located 180° from each other. Thus, the torque from one crank arm  40  is transmitted to the other crank arm  40 . 
     A sleeved coupling  100  secures the two continuous tubular members  10  together. The convoluted split  12  attachment of the two, one-half crank axles  50  are sandwiched between an inner sleeve  110  and an outer sleeve  120  of the sleeved coupling  100 , as shown in FIGS. 2 and 5. The inside diameter  130  of the inner sleeve  110  is conically tapered from its mid-section to its outer edges. 
     Two matching bushings  140 , having outside diameters  160  exteriorly tapered to accommodate the conically tapered inside diameter  130  of the inner sleeve  110 , are placed in each end of the inner sleeve  110 . When the bushings  140  are drawn together, as shown in FIG. 6, they expand the inner sleeve  110 , squeezing the one-half crank axles  50  against the outer sleeve  120 . The bushings  140  are threaded on their inside diameter  170 , and are drawn together on a threaded stud  150 . One bushing  140  is threaded right-handed and the other bushing  140  is threaded left-handed. The threaded stud  150  is reversed threaded at each end to match the bushings  140  and to allow both bushings  140  to come together on the stud  150  by turning the stud  150 . Turning the stud  150  one way forces the bushings  140  together, securing the one-half crank axles  50  to the outer sleeve  120 . Turning the stud  150  the opposite way releases separates bushings  140 , releasing the one-half crank axles  50  from secure attachment to the outer sleeve  120 . 
     The stud  150  has a hexagonal hole  180  extending through its length, as shown in FIG.  8 . The stud  150  is turned with a matching hex key wrench inserted into the hole  180  (not shown). 
     This design provides several advantages for bicycle crank set assemblies. Referring to FIG. 1, the continuous tubular member  10  is shaped to distribute the stresses in the crank set uniformly and equally throughout. This design distributes structural stresses uniformly along the thin-wall  20  of the continuous tubular member  10 , from the pedal axle insert  80 , down the crank arm  40 , across the crank axle, to the spider  60  holding the chain gears (not shown). The spider  60  reinforces the drive side continuous tubular member  10 , since it is an integral part of it. Fabricating the spider  60  out of tubular sections also minimizes the weight. 
     As a further advantage, the use of standard-thread, solid core reinforcing inserts  80  allows the mounting of a variety of sophisticated pedals with little additional weight. The two continuous tubular members  10  are further designed for practical and easy installation on a bicycle. By splitting the crank set midway along the crank axle in a precise manner, easy installation is achieved while maintaining structural integrity. The convoluted split  12  of the continuous tubular members  10  allows transmission of the torque from one side of the crank set to the other side of the crank set without stress concentration at the central joint. 
     Although the crank set can be fabricated from a host of materials, the crank set is preferably fabricated of materials oriented to make full use of their ultimate strength. In one embodiment, the material is an aramid fiber composite. In another embodiment, the material is a carbon and glass fiber composite. In yet another embodiment, the continuous tubular members  10  are steel stamped parts, made into clamshells and electron beam or laser welded together. 
     The tapered design of the continuous crank arm  40  of the present invention requires approximately two-thirds of the material of a non-tapered crank arm (i.e. a straight crank arm requires nearly twice as much material as the crank arm of the present invention). Further, the tapered crank arm can carry the same load as a straight crank arm. Therefore, structural performance is maintained while weight is significantly decreased. 
     Another embodiment of a one piece, monolithic and continuous tubular member  10  begins with FIG.  9 . FIG. 9 illustrates a monolithic and continuous thin-wall tubular member  10  (alternative to that in FIG. 3) including a crank axle  54 , a crank arm  40  and a pedal axle reinforcing insert aperture  82 . The tubular member  10  can be made of a composite material having thin-wall  20  construction, such as aramid fiber composites or carbon and glass fiber composites. Alternatively, the tubular member  10  can be steel stamped parts of clamshell design, electron beam or laser welded to together. The composite embodiment is injection molded and is literally a one-piece, continuous and monolithic tubular member. The steel embodiment, although steel stamped and welded together, is continuous and monolithic nonetheless, as the tubular member  10  has no discontinuities in form, no mechanical junction (connection) points, and no reinforcing gussets. The continuous and monolithic design of either the composite or steel embodiment minimizes weight without sacrificing strength and rigidity. 
     FIG. 10 illustrates a side elevation of another embodiment of a drive-side continuous tubular member  10  (alternative to that in FIG.  4 ), showing a spider  60 , a crank arm  40  and a pedal axle reinforcing insert aperture  82 . FIG. 11 illustrates a plan view of another embodiment of the drive-side continuous tubular member  10  shown in FIG. 10, showing a crank axle  54 , a spider  60 , a crank arm  40  and a pedal axle  32 . The drive-side tubular member  10  can also be made of a composite material having thin-wall  20  construction, or steel stamped welded parts, and incorporates the pedal axle  32  into the continuous one-piece monolithic construction. 
     The spider  60  includes sprocket tangs  61  to connect the chain gear (not shown). In the composite embodiment of the drive-side tubular member  10 , the area of the spider  60  in the vicinity of each sprocket tang  61  is solid and capably withstands the loads imposed by the chain gear. In the steel stamped embodiment of the drive-side tubular member  10 , the sprocket tang  61  is hollow and is formed as an integral part of the clamshells. 
     FIG. 12 illustrates an interference fit coupling  200  having a mortise member  202  and a tenon member  204 . The mortise and the tenon members  202 ,  204  are made of steel and each include cylindrical, tubular walls  207  terminating with a flared tip  216  arrangement (the flared tip arrangement is better illustrated in FIG.  14 ). The mortise and the tenon members  202 ,  204  are cylindrically sleeved over the crank axle  54  portions of the tubular members  10  to form a crank axle extending from each tubular member  10  of the crank set  8  equal to exactly one-half of the total crank axle length of the crank set  8 . A line  52 , shown in each of FIGS. 9 and 11, illustrates the extent that the flared tip  216  arrangement of the mortise or the tenon members  202 ,  204  extends over (is sleeved over) the crank axle  54  portions of each tubular member  10 . A 0.009 inch to 0.011 inch thick layer of high strength epoxy structural adhesive, such as 3M DP-420, can be used to attach the mortise or the tenon member  202 ,  204  to the crank axle portion  54  of the tubular member. 
     The one-half crank axle  50  portions of the tubular members  10  (as shown in FIGS.  18  and  20 ), which include the mortise  202  or the tenon  204  member sleeved over the crank axle  50  portion of the tubular member  10 , are non-tapered and align opposing crank arms  40  180° from each other. FIGS. 18 and 20 also illustrate an outer cup  220  and an inner seal  229  press fit onto the one-half crank axle portion  50 . The interference fit coupling  200  effectively transmits all torque and bending moments across the coupling  200 , as the central location of the coupling  200  (between the two bearing sets  16 , as shown in FIG. 14) within the bracket shell  14  eliminates all shear loads. The interference fit coupling  200 , therefore, avoids any undesirable backlash or play in the crank set  8  due to high loads or wear. 
     FIG. 13 illustrates a tapered four coupling  210  having a male tapered four member  212  and a female tapered four member  214 . The male and female members  212 ,  214  each have four tapered sides, each having equal surface area. The tapered four coupling  210  is made of steel and each member  212 ,  214  includes a cylindrical, tubular wall  207  terminating with a flared tip  216  arrangement. Similar to the interference fit coupling  200 , the male and the female members  212 ,  214  are cylindrically sleeved over and adhered to the crank axle  54  portions of the tubular members  10  to form a crank axle extending from each tubular member  10  of the crank set  8  equal to exactly one-half of the total crank axle length of the crank set  8 . The line  52 , shown in each of FIGS. 9 and 11, also illustrates the extent that the flared tip  216  arrangement of the male and the female tapered four members  212 ,  214  extend over (are sleeved over) the crank axle  54  portions of each tubular member  10 . 
     The tapered four coupling  210  also aligns opposing crank arms  40  180° from each other and effectively transmits all torque and bending moments across the coupling  210 , as the central location of the coupling  210  (between the two bearing sets  16 ) eliminates all shear loads. 
     The interference fit coupling  200  and the tapered four coupling  210  distributes all loads across the point of attachment of the one-half crank axle portions  50  in a uniform and seamless fashion. The flared tip arrangement  216  minimizes any uneven stress distribution. The sleeved coupling  200 ,  210  design also facilitates the distribution of bearing loads over a greater area, minimizing concentrated loads on the tubular member  10 . Concentrated loads on the tubular members  10  must be minimized if the tubular members  10  are to be made of composite materials. 
     The interference fit coupling  200  is superior to splined, or even the tapered four coupling  210 , due to a more economical and simpler fabrication process. The tapered four coupling  210  is cast, forged or stamped and then requires significant machining before use. The interference fit coupling  200  can be machined from a standard milling machine and used immediately. Other couplings also require refinement, or a higher level of machining, after initial fabrication. The interference fit coupling  200  is extremely rugged; overtightening during assembly will cause no damage. 
     For assembly and disassembly purposes, the interference fit coupling  200  and the tapered four coupling  210  include a clearance hole  206  within one crank axle  50  portion, and an attachment hole  208  within an opposite crank axle  50  portion. The clearance hole  206  has a larger diameter than the attachment hole  208 . The clearance hole and the attachment holes are interiorly threaded. 
     To assemble the interference fit coupling  200  or the tapered four coupling  210 , a threaded attachment bolt having a diameter equal to that of the attachment hole  208  can be placed through the clearance hole  206  and into the attachment hole  208 . Threading the attachment bolt  209  (shown in FIG. 17) into the attachment hole  208  draws the mortise  202  and the tenon  204  members (or the male and the female members  212 ,  214  of the tapered four coupling  210 ) into interlocking engagement, due to a head of the attachment bolt  209  being larger than the diameter of the clearance hole  206 . The attachment bolt  209  can be a 4.9 gram titanium Allen head bolt. 
     It is to be understood, however, that the attachment bolt  209  can be used to facilitate coupling assembly (the pulling together of either the mortise and the tenon members  202 ,  204  of the interference fit coupling  200  or the male and the female tapered four members  212 ,  214  of the tapered four coupling  210 ). The attachment bolt  209  is not necessary to hold the respective members of the interference fit coupling  200  or the tapered four coupling  210  together during crank set  8  use. The attachment bolt  209  can be removed after coupling  200 ,  210  assembly. 
     Removal of a tab  42  (shown in FIGS. 1,  2 ,  3 ,  4 ,  18  and  19 ) provides access to the coupling (whether the sleeved coupling  100 , the interference fit coupling  200 , or the tapered four coupling  210  is being used) within the bracket shell  14  for coupling assembly and disassembly (for operation of the threaded stud  150  or for installation/removal of the attachment bolt  209  or separation bolt). The tab  42  is titanium, is press fit within a recess in the crank arm  40 , and contains a double O-ring to seal out contaminants. 
     To disassemble the interference fit coupling  200  or the tapered four coupling  210 , the attachment bolt  209  is removed and a threaded separation bolt (not shown) having a diameter equal to that of the clearance hole  206  is threaded into and through the clearance hole  206  until an end of the separation bolt forces the tenon member  204  out of engagement with the mortise member  202 , or the male tapered four member  212  out of engagement with the female tapered four member  214 . Alternatively, the attachment bolt  209  can be threaded through the attachment hole  208  while the separation bolt is threaded through the clearance hole  206  so that an end of each bolt meet within the coupling  200 ,  210 . Turning one, or both bolts against the end of the other bolt will also separate the mortise member  202  from the tenon member  204 , or the male tapered four member  212  from the female tapered four member  214 . Using both the attachment bolt  209  and the separation bolt for disassembly insures that no marring or crushing occurs to the interlocking members of the interference fit coupling  200  or the tapered four coupling  210 . 
     The interference fit coupling  200  and the tapered four coupling  210  are preferably fabricated from ultra-high strength, corrosion resistant metal having outstanding fatigue properties and high toughness. In one embodiment of the invention, 17-4 PH is used, an age hardened stainless steel. 17-4 PH steel can be hardened to yield strengths over 200,000 psi (standard steels have a strength of 60,000 psi). 17-4 PH steel has incredible toughness, corrosion resistance and fatigue strength. 
     FIG. 14 illustrates a top, cross-sectional detail view of an interference fit coupling  200  centered between two bearing sets  16  within a bracket shell  14 . Each bearing set  16  includes an outer cup  220 , an inner cup  222 , ceramic balls  224 , a retaining ring  226 , an outer seal  228  and an inner seal  229 . 
     In one embodiment of the present invention, the ceramic balls  224  are 3.2 mm silicon nitride. The outer and the inner cups  220 ,  222  (the outer cup  220  is shown in FIG. 16) are 52100 steel and are hardened to approximately Rockwell 60. The cups  220 ,  222  are then sputer coated with titanium aluminum nitride, giving the cups  220 ,  222  a hardness of over Rockwell 90. In addition to extreme hardness, the sputer coating enhancing the lubricity of a surface of the cups  220 ,  222  and provides corrosion resistance. The retaining ring (shown in FIG. 15) can be mylar, nylon, Delrin, or any engineering plastic capable of separating the ceramic balls  224  and preventing ball on ball grinding. The seals  228 ,  229  (the inner seal  229  is shown in FIG. 16 as an integral part of the outer cup  220 ) are spring loaded Teflon garter seals, offering 25 to 50 times more pressure on the crank axle than rubber lip seals while having less retarding torque. Similarly, the outer seal  228  is formed as an integral part of the inner cup  222 . 
     Referring to FIG. 20, assembling the crank set  8  within the bracket shell  14  is accomplished as follows: the outer cups  220  with integral inner seals  229 , housing the retaining ring  226  and ceramic balls  224 , are threaded into the bracket shell  14 ; the one-half crank axle  50  portions of the tubular members  10  (with the inner cups  222  and integral outer seals  228 ) are inserted into each end of the bracket shell  14  (within the outer cups  220  and the retaining rings  226 ); the interference fit coupling  200  is mated (using the attachment bolt  209  if desired); and, the outer and the inner cups  220 ,  222  of the bearing sets  16  are slightly separated to pre-load the bearing sets  16  (taking any play out of the crank set  8 ). Either the outer or the inner cup  220 ,  222  can be screwed out, providing lateral movement of approximately two to three millimeters in the crank set  8  for adjustment within the bracket shell  14 . The assembly process requires no shims or spacers. The outer cups  220  are secured in place with Locktite. 
     To accommodate standard pedals, the reinforcing insert  80  of the composite embodiment of the crank set  8  is interiorly threaded and made of titanium. The reinforcing pedal axle insert  80  is either molded or epoxied in place within the reinforcing insert aperture  82  of the crank arms  40 . An area of the composite crank arm  40  (in the vicinity of the aperture  82 ) is made of solid carbon fiber and glass composite and is compression molded. The hollow sections of the crank arm  40  can either be compression molded around a Styrofoam plug or bladder molded with a custom shaped nylon bladder, or a straight latex bladder. In the steel version of the crank set  8 , the reinforcing insert  80  is machined separately and welded in place either at the end of the crank arm  40  or through the crank arm  40 . No additional material, such as gussets, surrounds the reinforcing insert  80 . 
     These and other advantages of the present invention will be apparent to those skilled in the art from the foregoing specification. Accordingly, it will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention.