Patent Publication Number: US-2019195321-A1

Title: Continuously variable transmission

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/584,132, filed Dec. 29, 2014 and scheduled to issue on Jul. 31, 2018 as U.S. Pat. No. 10,036,453, which is a continuation of U.S. application Ser. No. 13/710,304, filed Dec. 10, 2012 and issued as U.S. Pat. No. 8,920,285 on Dec. 30, 2014, which is a continuation of U.S. application Ser. No. 11/842,081, filed Aug. 20, 2007, which is a continuation of U.S. application Ser. No. 11/243,484, filed Oct. 4, 2005 and issued as U.S. Pat. No. 7,762,919 on Jul. 27, 2010, which claims the benefit of U.S. Provisional Application No. 60/616,399, filed on Oct. 5, 2004. Each of the above-identified applications is incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The field of the invention relates generally to transmissions, and more particularly to continuously variable transmissions (CVTs). 
     Description of the Related Art 
     There are well-known ways to achieve continuously variable ratios of input speed to output speed. The mechanism for adjusting an input speed from an output speed in a CVT is known as a variator. In a belt-type CVT, the variator consists of two adjustable pulleys having a belt between them. The variator in a single cavity toroidal-type CVT has two partially toroidal transmission discs rotating about a shaft and two or more disc-shaped power rollers rotating on respective axes that are perpendicular to the shaft and clamped between the input and output transmission discs. 
     Embodiments of the invention disclosed here are of the spherical-type variator utilizing spherical speed adjusters (also known as power adjusters, balls, sphere gears or rollers) that each has a tiltable axis of rotation; the adjusters are distributed in a plane about a longitudinal axis of a CVT. The rollers are contacted on one side by an input disc and on the other side by an output disc, one or both of which apply a clamping contact force to the rollers for transmission of torque. The input disc applies input torque at an input rotational speed to the rollers. As the rollers rotate about their own axes, the rollers transmit the torque to the output disc. The input speed to output speed ratio is a function of the radii of the contact points of the input and output discs to the axes of the rollers. Tilting the axes of the rollers with respect to the axis of the variator adjusts the speed ratio. 
     SUMMARY OF INVENTION 
     One embodiment is a CVT. The CVT includes a central shaft and a variator. The variator includes an input disc, an output disc, a plurality of tiltable ball-leg assemblies, and an idler assembly. The input disc is rotatably mounted about the central shaft. Each of the plurality of tiltable ball-leg assemblies includes a ball, an axle, and at least two legs. The ball is rotatably mounted to the axle and contacts the input disk and the output disk. The legs are configured to control the tilt of the ball. The idler assembly is configured to control the radial position of the legs so as to thereby control the tilt of the ball. In one embodiment, the CVT is adapted for use in a bicycle. 
     In one embodiment, the variator includes a disk having a splined bore and a driver with splines. The splines of the driver couple to the splined bore of the disk. 
     In one embodiment, a shift rod extends through the central shaft and connects to the idler assembly. The shift rod actuates the idler assembly. 
     In one embodiment, a cam loader is positioned adjacent to the input disc and is configured to at least partly generate axial force and transfer torque. In one embodiment, a cam loader is positioned adjacent to the output disc and is configured to at least partly generate axial force and transmit torque. In yet other embodiments, cam loaders are positioned adjacent to both the input disc and the output disc; the cam loaders are configured to at least partly generate axial force and transmit torque. 
     Another embodiment is a spacer for supporting and separating a cage of a CVT having a hub shell that at least partially encloses a variator. The spacer includes a scraper configured to scrape lubricant from a surface of the hub shell and direct the lubricant toward the inside of the variator. In one embodiment, the spacer includes passages configured to direct the flow of lubricant. 
     Another aspect of the invention relates to a torsion disc for a CVT. The torsion disc includes a spline bore about its central axis, an annular recess formed in the disc for receiving the race of a bearing, and a raised surface for supporting a torsion spring. 
     Yet another feature of the invention concerns a shaft for supporting certain components of a CVT. In some embodiments, the shaft has a splined flange, a central bore spanning from one end of the shaft to a point beyond the middle of the shaft, and one or more flanges for attaching to various components of the CVT. In one embodiment, flanges on the shaft are adapted to couple to stators of the CVT. 
     A different aspect of the inventive CVTs relates to an axial force generating system having a torsion spring coupled to a torsion disc and an input disc of the CVT. The axial force generating system may also include one or more load cam discs having ramps for energizing rollers, which are preferably located between the load cam disc and the input disc and/or output disc of the CVT. 
     Another feature of the invention is directed to an axle and axle-ball combination for a CVT. In some embodiments, the axle includes shoulder portions and a waist portion. The axle is configured to fit in a central bore of a traction roller of the CVT. In some embodiments, the bearing surface between the axle and the ball may be a journal bearing, a bushing, a Babbitt lining, or the axle itself. In other embodiments, the axle and ball utilize retained bearings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of one embodiment of a CVT. 
         FIG. 2  is a partially exploded cross-sectional view of the CVT of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a second embodiment of a CVT. 
         FIG. 4  is a partially exploded cross-sectional view of the CVT of  FIG. 3 . 
         FIG. 5 a    is a side view of a splined input disc driver that can be used in a CVT. 
         FIG. 5 b    is a front view of the disc driver of  FIG. 5   a.    
         FIG. 6 a    is a side view of a splined input disc that can be used in a CVT. 
         FIG. 6 b    is a front view of the splined input disc of  FIG. 6   a.    
         FIG. 7  is a cam roller disc that can be used with a CVT. 
         FIG. 8  is a stator that can be used with a CVT. 
         FIG. 9  is a perspective view of a scraping spacer that can be used with a CVT. 
         FIG. 10  is a cross-sectional view of a shifter assembly that can be used in a CVT. 
         FIG. 11  is a perspective view of a ball-leg assembly for use in a CVT. 
         FIG. 12  is a perspective view of a cage that can be used in a ball-type CVT. 
         FIG. 13  is a cross-sectional view of another embodiment of a CVT. 
         FIG. 14  is a perspective view of a bicycle hub incorporating an embodiment of a CVT. 
         FIG. 15  is a top elevational view of various assemblies of an embodiment of a CVT incorporated in the bicycle hub of  FIG. 14 . 
         FIG. 16  is a partially exploded, perspective view of certain assemblies of the CVT of  FIG. 15 . 
         FIG. 17  is a top elevational view of certain assemblies of the CVT of  FIG. 15 . 
         FIG. 18  is a cross-sectional view along section A-A of the assemblies of  FIG. 17 . 
         FIG. 19  is a perspective view of one embodiment of a shift cam assembly that can be used with the CVT of  FIG. 15 . 
         FIG. 20  is a top elevational view of the shift cam assembly of  FIG. 19 . 
         FIG. 21  is a cross-sectional view along section B-B of the shift cam assembly of  FIG. 20 . 
         FIG. 22  is perspective view of a cage assembly that can be used with the CVT of  FIG. 15 . 
         FIG. 23  is a front elevational view of the cage assembly of  FIG. 22 . 
         FIG. 24  is a right side elevational view of the cage assembly of  FIG. 22 . 
         FIG. 25  is a partially exploded, front elevational view of certain axial force generation components for the CVT of  FIG. 15 . 
         FIG. 26  is a cross-sectional view along section C-C of the CVT components shown in  FIG. 25 . 
         FIG. 27  is an exploded perspective view of a mating input shaft and torsion disc that can be used with the CVT of  FIG. 15 . 
         FIG. 28  is a perspective view of the torsion disc of  FIG. 27 . 
         FIG. 29  is a left side elevational view of the torsion disc of  FIG. 28 . 
         FIG. 30  is a front elevation view of the torsion disc of  FIG. 28 . 
         FIG. 31  is a right side elevational view of the torsion disc of  FIG. 28 . 
         FIG. 32  is a cross-sectional view along section D-D of the torsion disc of  FIG. 31 . 
         FIG. 33  is a perspective view of the input shaft of  FIG. 27 . 
         FIG. 34  is a left side elevational view of the input shaft of  FIG. 33 . 
         FIG. 35  is a top side elevational view of the input shaft of  FIG. 33 . 
         FIG. 36  is a perspective view of a load cam disc that can be used with the CVT of  FIG. 15 . 
         FIG. 37  is a top side elevational view of a ball and axle assembly that can be used with the CVT of  FIG. 15 . 
         FIG. 38  is a cross-sectional view along section E-E of the ball and axle assembly of  FIG. 37 . 
         FIG. 39  is a top elevational view of the bicycle hub of  FIG. 14 . 
         FIG. 40  is a cross-sectional view along section F-F of the hub of  FIG. 39  showing certain components of the bicycle hub of  FIG. 14  and the CVT of  FIG. 15 . 
         FIG. 41  is a perspective view of a main shaft that can be used with the CVT of  FIG. 15 . 
         FIG. 42  is a top side elevational view of the main shaft of  FIG. 41 . 
         FIG. 43  is a cross-section view along section G-G of the main shaft of  FIG. 42 . 
         FIG. 44  is a top elevational view of an alternative embodiment of a CVT that can be used with the bicycle hub of  FIG. 14 . 
         FIG. 45  is a cross-sectional view along section H-H of the CVT of  FIG. 44 . 
         FIG. 46  is a cross-sectional view of a CVT that can be used with the bicycle hub of  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The CVT embodiments described here are generally of the type disclosed in U.S. Pat. Nos. 6,241,636, 6,419,608 and 6,689,012. The entire disclosure of each of these patents is hereby incorporated herein by reference. 
       FIG. 1  illustrates a spherical-type CVT  100  that can change input to output speed ratios. The CVT  100  has a central shaft  105  extending through the center of the CVT  100  and beyond two rear dropouts  10  of the frame of a bicycle. A first cap nut  106  and second cap nut  107 , each located at a corresponding end of the central shaft  105 , attach the central shaft  105  to the dropouts. Although this embodiment illustrates the CVT  100  for use on a bicycle, the CVT  100  can be implemented on any equipment that makes use of a transmission. For purposes of description, the central shaft  105  defines a longitudinal axis of the CVT that will serve as a reference point for describing the location and or motion of other components of the CVT. As used here, the terms “axial,” “axially,” “lateral,” “laterally,” refer to a position or direction that is coaxial or parallel with the longitudinal axis defined by the central shaft  105 . The terms “radial” and “radially” refer to locations or directions that extend perpendicularly from the longitudinal axis. 
     Referring to  FIGS. 1 and 2 , the central shaft  105  provides radial and lateral support for a cage assembly  180 , an input assembly  155  and an output assembly  160 . In this embodiment the central shaft  105  includes a bore  199  that houses a shift rod  112 . As will be described later, the shift rod  112  actuates a speed ratio shift in the CVT  100 . 
     The CVT  100  includes a variator  140 . The variator  140  can be any mechanism adapted to change the ratio of input speed to output speed. In one embodiment, the variator  140  includes an input disc  110 , an output disc  134 , tiltable ball-leg assemblies  150  and an idler assembly  125 . The input disc  110  may be a disc mounted rotatably and coaxially about the central shaft  105 . At the radial outer edge of the input disc  110 , the disc extends at an angle to a point where it terminates at a contact surface  111 . In some embodiments, the contact surface  111  can be a separate structure, for example a ring that attaches to the input disc  110 , which would provide support for the contact surface  111 . The contact surface  111  may be threaded, or press fit, into the input disc  110  or it can be attached with any suitable fasteners or adhesives. 
     The output disc  134  can be a ring that attaches, by press fit or otherwise, to an output hub shell  138 . In some embodiments, the input disc  110  and the output disc  134  have support structures  113  that extend radially outward from contact surfaces  111  and that provide structural support to increase radial rigidity, to resist compliance of those parts under the axial force of the CVT  100 , and to allow axial force mechanisms to move radially outward, thereby reducing the length of the CVT  100 . The input disc  110  and the output disc  134  can have oil ports  136 ,  135  to allow lubricant in the variator  140  to circulate through the CVT  100 . 
     The hub shell  138  in some embodiments is a cylindrical tube rotatable about the central shaft  105 . The hub shell  138  has an inside that houses most of the components of the CVT  100  and an outside adapted to connect to whatever component, equipment or vehicle uses the CVT. Here the outside of the hub shell  138  is configured to be implemented on a bicycle. However, the CVT  100  can be used in any machine where it is desirable to adjust rotational input and output speeds. 
     Referring to  FIGS. 1, 2, 10 and 11  a CVT may include a ball-leg assembly  150  for transmitting torque from the input disc  110  to the output disc  134  and varying the ratio of input speed to output speed. In some embodiments, the ball-leg assembly  150  includes a ball  101 , a ball axle  102 , and legs  103 . The axle  102  can be a generally cylindrical shaft that extends through a bore formed through the center of the ball  101 . In some embodiments, the axle  102  interfaces with the surface of the bore in the ball  101  via needle or radial bearings that align the ball  101  on the axle  102 . The axle  102  extends beyond the sides of the ball  101  where the bore ends so that the legs  103  can actuate a shift in the position of the ball  101 . Where the axle  102  extends beyond the edge of the ball  101 , it couples to the radial outward end of the legs  103 . The legs  103  are radial extensions that tilt the ball axle  102 . 
     The axle  102  passes through a bore formed in the radially outward end of a leg  103 . In some embodiments, the leg  103  has chamfers where the bore for the axle  102  passes through the legs  103 , which provides for reduced stress concentration at the contact between the side of the leg  103  and the axle  102 . This reduced stress increases the capacity of the ball-leg assembly  150  to absorb shifting forces and torque reaction. The leg  103  can be positioned on the axle  102  by clip rings, such as e-rings, or can be press fit onto the axle  102 ; however, any other type of fixation between the axle  102  and the leg  103  can be utilized. The ball-leg assembly  150  can also include leg rollers  151 , which are rolling elements attached to each end of a ball axle  102  and provide for rolling contact of the axle  102  as it is aligned by other parts of the CVT  100 . In some embodiments, the leg  103  has a cam wheel  152  at a radially inward end to help control the radial position of the leg  103 , which controls the tilt angle of the axle  102 . In yet other embodiments, the leg  103  couples to a stator wheel  1105  (see  FIG. 11 ) that allows the leg  103  to be guided and supported in the stators  800  (see  FIG. 8 ). As shown in  FIG. 11 , the stator wheel  1105  may be angled relative to the longitudinal axis of the leg  103 . In some embodiments, the stator wheel  1105  is configured such that its central axis intersects with the center of the ball  101 . 
     Still referring to  FIGS. 1, 2, 10 and 11 , in various embodiments the interface between the balls  101  and the axles  102  can be any of the bearings described in other embodiments below. However, the balls  101  are fixed to the axles in other embodiments and rotate with the balls  101 . In some such embodiments, bearings (not shown) are positioned between the axles  102  and the legs  103  such that the transverse forces acting on the axles  102  are reacted by the legs  103  as well as, or alternatively, the cage (described in various embodiments below). In some such embodiments, the bearing positioned between the axles  102  and the legs  103  are radial bearings (balls or needles), journal bearings or any other type of bearings or suitable mechanism or means. 
     With reference to  FIGS. 1, 2, 3, 4 and 10 , the idler assembly  125  will now be described. In some embodiments, the idler assembly  125  includes an idler  126 , cam discs  127 , and idler bearings  129 . The idler  126  is a generally cylindrical tube. The idler  126  has a generally constant outer diameter; however, in other embodiments the outer diameter is not constant. The outer diameter may be smaller at the center portion than at the ends, or may be larger at the center and smaller at the ends. In other embodiments, the outer diameter is larger at one end than at the other and the change between the two ends may be linear or non-linear depending on shift speed and torque requirements. 
     The cam discs  127  are positioned on either or both ends of the idler  126  and interact with the cam wheels  152  to actuate the legs  103 . The cam discs  127  are convex in the illustrated embodiment, but can be of any shape that produces a desired motion of the legs  103 . In some embodiments, the cam discs  127  are configured such that their axial position controls the radial position of the legs  103 , which governs the angle of tilt of the axles  102 . 
     In some embodiments, the radial inner diameter of the cam discs  127  extends axially toward one another to attach one cam disc  127  to the other cam disc  127 . Here, a cam extension  128  forms a cylinder about the central shaft  105 . The cam extension  128  extends from one cam disc  127  to the other cam disc  127  and is held in place there by a clip ring, a nut, or some other suitable fastener. In some embodiments, one or both of the cam discs  127  are threaded onto the cam disc extension  128  to fix them in place. In the illustrated embodiment, the convex curve of the cam disc  127  extends axially away from the axial center of the idler assembly  125  to a local maximum, then radially outward, and back axially inward toward the axial center of the idler assembly  125 . This cam profile reduces binding that can occur during shifting of the idler assembly  125  at the axial extremes. Other cam shapes can be used as well. 
     In the embodiment of  FIG. 1 , a shift rod  112  actuates a transmission ratio shift of the CVT  100 . The shift rod  112 , coaxially located inside the bore  199  of the central shaft  105 , is an elongated rod having a threaded end  109  that extends out one side of the central shaft  105  and beyond the cap nut  107 . The other end of the shift rod  112  extends into the idler assembly  125  where it contains a shift pin  114 , which mounts generally transversely in the shift rod  112 . The shift pin  114  engages the idler assembly  125  so that the shift rod  112  can control the axial position of the idler assembly  125 . A lead screw assembly  115  controls the axial position of the shift rod  112  within the central shaft  105 . In some embodiments, the lead screw assembly  125  includes a shift actuator  117 , which may be a pulley having a set of tether threads  118  on its outer diameter with threads on a portion of its inner diameter to engage the shift rod  112 . The lead screw assembly  115  may be held in its axial position on the central shaft  105  by any means, and here is held in place by a pulley snap ring  116 . The tether threads  118  engage a shift tether (not shown). In some embodiments, the shift tether is a standard shift cable, while in other embodiments the shift tether can be any tether capable of supporting tension and thereby rotating the shift pulley  117 . 
     Referring to  FIGS. 1 and 2 , the input assembly  155  allows torque transfer into the variator  140 . The input assembly  155  has a sprocket  156  that converts linear motion from a chain (not shown) into rotational motion. Although a sprocket is used here, other embodiments of the CVT  100  may use a pulley that accepts motion from a belt, for example. The sprocket  156  transmits torque to an axial force generating mechanism, which in the illustrated embodiment is a cam loader  154  that transmits the torque to the input disc  110 . The cam loader  154  includes a cam disc  157 , a load disc  158  and a set of cam rollers  159 . The cam loader  154  transmits torque from the sprocket  156  to the input disc  110  and also generates an axial force that resolves into the contact force for the input disc  110 , the balls  101 , the idler  126  and the output disc  134 . The axial force is generally proportional to the amount of torque applied to the cam loader  154 . In some embodiments, the sprocket  156  applies torque to the cam disc  157  via a one-way clutch (detail not shown) that acts as a coasting mechanism when the hub  138  spins but the sprocket  156  is not supplying torque. In some embodiments, the load disc  158  may be integral as a single piece with the input disc  157 . In other embodiments, the cam loader  154  may be integral with the output disc  134 . 
     In  FIGS. 1 and 2 , the internal components of the CVT  100  are contained within the hub shell  138  by an end cap  160 . The end cap  160  is a generally flat disc that attaches to the open end of the hub shell  138  and has a bore through the center to allow passage of the cam disc  157 , the central shaft  105  and the shift rod  112 . The end cap  160  attaches to the hub shell  138  and serves to react the axial force created by the cam loader  154 . The end cap  160  can be made of any material capable of reacting the axial force such as for example, aluminum, titanium, steel, or high strength thermoplastics or thermoset plastics. The end cap  160  fastens to the hub shell  138  by fasteners (not shown); however, the end cap  160  can also thread into, or can otherwise be attached to, the hub shell  138 . The end cap  160  has a groove formed about a radius on its side facing the cam loader  154  that houses a preloader  161 . The preloader  161  can be a spring that provides and an initial clamp force at very low torque levels. The preloader  161  can be any device capable of supplying an initial force to the cam loader  154 , and thereby to the input disc  134 , such as a spring, or a resilient material like an o-ring. The preloader  161  can be a wave-spring as such springs can have high spring constants and maintain a high level of resiliency over their lifetimes. Here the preloader  161  is loaded by a thrust washer  162  and a thrust bearing  163  directly to the end cap  160 . In this embodiment, the thrust washer  162  is a typical ring washer that covers the groove of the preloader  161  and provides a thrust race for the thrust bearing  163 . The thrust bearing  163  may be a needle thrust bearing that has a high level of thrust capacity, improves structural rigidity, and reduces tolerance requirements and cost when compared to combination thrust radial bearings; however, any other type of thrust bearing or combination bearing can be used. In certain embodiments, the thrust bearing  163  is a ball thrust bearing. The axial force developed by the cam loader  154  is reacted through the thrust bearing  163  and the thrust washer  162  to the end cap  160 . The end cap  160  attaches to the hub shell  138  to complete the structure of the CVT  100 . 
     In  FIGS. 1 and 2 , a cam disc bearing  172  holds the cam disc  157  in radial position with respect to the central shaft  105 , while an end cap bearing  173  maintains the radial alignment between the cam disc  157  and the inner diameter of the end cap  160 . Here the cam disc bearing  172  and the end cap bearing  173  are needle roller bearings; however, other types of radial bearings can be used as well. The use of needle roller bearings allow increased axial float and accommodates binding moments developed by the rider and the sprocket  156 . In other embodiments of the CVT  100  or any other embodiment described herein, each of or either of the can disc bearing  172  and the end cap bearing  173  can also be replaced by a complimentary pair of combination radial-thrust bearings. In such embodiments, the radial thrust bearings provide not only the radial support but also are capable of absorbing thrust, which can aid and at least partially unload the thrust bearing  163 . 
     Still referring to  FIGS. 1 and 2 , an axle  142 , being a support member mounted coaxially about the central shaft  105  and held between the central shaft  105  and the inner diameter of the closed end of the hub shell  138 , holds the hub shell  138  in radial alignment with respect to the central shaft  105 . The axle  142  is fixed in its angular alignment with the central shaft  105 . Here a key  144  fixes the axle  142  in its angular alignment, but the fixation can be by any means known to those of skill in the relevant technology. A radial hub bearing  145  fits between the axle  142  and the inner diameter of the hub shell  138  to maintain the radial position and axial alignment of the hub shell  138 . The hub bearing  145  is held in place by an encapsulating axle cap  143 . The axle cap  143  is a disc having a central bore that fits around central shaft  105  and here attaches to the hub shell  138  with fasteners  147 . A hub thrust bearing  146  fits between the hub shell  138  and the cage  189  to maintain the axial positioning of the cage  189  and the hub shell  138 . 
       FIGS. 3, 4 and 10  illustrate a CVT  300 , which is an alternative embodiment of the CVT  100  described above. Many of the components are similar between the CVT  100  embodiments described above and that of the present figures. Here, the angles of the input and output discs  310 ,  334  respectively are decreased to allow for greater strength to withstand axial forces and to reduce the overall radial diameter of the CVT  300 . This embodiment shows an alternate shifting mechanism, where the lead screw mechanism to actuate axial movement of the idler assembly  325  is formed on the shift rod  312 . The lead screw assembly is a set of lead threads  313  formed on the end of the shift rod  312  that is within or near the idler assembly  325 . One or more idler assembly pins  314  extend radially from the cam disc extensions  328  into the lead threads  313  and move axially as the shift rod  312  rotates. 
     In the illustrated embodiment, the idler  326  does not have a constant outer diameter, but rather has an outer diameter that increases at the ends of the idler  326 . This allows the idler  326  to resist forces of the idler  326  that are developed through the dynamic contact forces and spinning contact that tend to drive the idler  326  axially away from a center position. However, this is merely an example and the outer diameter of the idler  326  can be varied in any manner a designer desires in order to react the spin forces felt by the idler  326  and to aid in shifting of the CVT  300 . 
     Referring now to  FIGS. 5 a , 5 b , 6 a , and 6 b   , a two part disc is made up of a splined disc  600  and a disc driver  500 . The disc driver  500  and the splined disc  600  fit together through splines  510  formed on the disc driver  500  and a splined bore  610  formed in the splined disc  600 . The splines  510  fit within the splined bore  610  so that the disc driver  500  and the splined disc  600  form a disc for use in the CVT  100 , CVT  300 , or any other spherical CVT. The splined disc  600  provides for compliance in the system to allow the variator  140 ,  340  to find a radial equilibrium position so as to reduce sensitivity to manufacturing tolerances of the components of a variator  140 ,  340 . 
       FIG. 7  illustrates a cam disc  700  that can be used in the CVT  100 , CVT  300 , other spherical CVTs or any other type of CVT. The cam disc  700  has cam channels  710  formed in its radial outer edge. The cam channels  710  house a set of cam rollers (not shown) which in this embodiment are spheres (such as bearing balls) but can be any other shape that combines with the shape of the cam channel  710  to convert torque into torque and axial force components to moderate the axial force applied to the variator  140 ,  340  in an amount proportional to the torque applied to the CVT. Other such shapes include cylindrical rollers, barreled rollers, asymmetrical rollers or any other shape. The material used for the cam disc channels  710  in many embodiments is preferably strong enough to resist excessive or permanent deformation at the loads that the cam disc  700  will experience. Special hardening may be needed in high torque applications. In some embodiments, the cam disc channels  710  are made of carbon steel hardened to Rockwell hardness values above 40 HRC. The efficiency of the operation of the cam loader ( 154  of  FIG. 1 , or any other type of cam loader) can be affected by the hardness value, typically by increasing the hardness to increase the efficiency; however, high hardening can lead to brittleness in the cam loading components and can incur higher cost as well. In some embodiments, the hardness is above 50 HRC, while in other embodiments the hardness is above 55 HRC, above 60 HRC and above 65 HRC. 
       FIG. 7  shows an embodiment of a conformal cam. That is, the shape of the cam channel  710  conforms to the shape of the cam rollers. Since the channel  710  conforms to the roller, the channel  710  functions as a bearing roller retainer and the requirement of a cage element is removed. The embodiment of  FIG. 7  is a single direction cam disc  700 ; however, the cam disc can be a bidirectional cam as in the CVT  1300  (see  FIG. 13 ). Eliminating the need for a bearing roller retainer simplifies the design of the CVT. A conformal cam channel  710  also allows the contact stress between the bearing roller and the channel  710  to be reduced, allowing for reduced bearing roller size and/or count, or for greater material choice flexibility. 
       FIG. 8  illustrates a cage disc  800  used to form the rigid support structure of the cage  189  of the variators  140 ,  340  in spherical CVTs  100 ,  300  (and other types). The cage disc  800  is shaped to guide the legs  103  as they move radially inward and outward during shifting. The cage disc  800  also provides the angular alignment of the axles  102 . In some embodiments the corresponding grooves of two cage discs  800  for a respective axle  102  are offset slightly in the angular direction to reduce shift forces in the variators  140  and  340 . 
     Legs  103  are guided by slots in the stators. Leg rollers  151  on the legs  103  follow a circular profile in the stators. The leg rollers  151  generally provide a translational reaction point to counteract translational forces imposed by shift forces or traction contact spin forces. The legs  103  as well as its respective leg rollers  151  move in planar motion when the CVT ratio is changed and thus trace out a circular envelope which is centered about the ball  101 . Since the leg rollers  151  are offset from the center of the leg  103 , the leg rollers  151  trace out an envelope that is similarly offset. To create a compatible profile on each stator to match the planar motion of the leg rollers  151 , a circular cut is required that is offset from the groove center by the same amount that the roller is offset in each leg  103 . This circular cut can be done with a rotary saw cutter; however, it requires an individual cut at each groove. Since the cuts are independent, there is a probability of tolerance variation from one groove to the next in a single stator, in addition to variation between stators. A method to eliminate this extra machining step is to provide a single profile that can be generated by a lath turning operation. A toroidal-shaped lathe cut can produce this single profile in one turning operation. The center of the toroidal cut is adjusted away from the center of the ball  101  position in a radial direction to compensate for offset of the leg rollers  103 . 
     Referring now to  FIGS. 1, 9 and 12 , an alternative embodiment of a cage assembly  1200  is illustrated implementing a lubrication enhancing lubricating spacer  900  for use with some CVTs where spacers  1210  support and space apart two cage discs  1220 . In the illustrated embodiment, the support structure for the power transmission elements, in this case the cage  389 , is formed by attaching input and output side cage discs  1220  to a plurality of spacers  1210 , including one or more lubricating spacers  900  with cage fasteners  1230 . In this embodiment, the cage fasteners  1230  are screws but they can be any type of fastener or fastening method. The lubricating spacer  900  has a scraper  910  for scraping lubricant from the surface of the hub shell  138  and directing that lubricant back toward the center elements of the variator  140  or  340 . The lubricating spacer  900  of some embodiments also has passages  920  to help direct the flow of lubricant to the areas that most utilize it. In some embodiments, a portion of the spacer  900  between the passages  920  forms a raised wedge  925  that directs the flow of lubricant towards the passages  920 . The scraper  910  may be integral with the spacer  900  or may be separate and made of a material different from the material of the scraper  910 , including but not limited to rubber to enhance scraping of lubricant from the hub shell  138 . The ends of the spacers  1210  and the lubricating spacers  900  terminate in flange-like bases  1240  that extend perpendicularly to form a surface for mating with the cage discs  1220 . The bases  1240  of the illustrated embodiment are generally flat on the side facing the cage discs  1240  but are rounded on the side facing the balls  101  so as to form the curved surface described above that the leg rollers  151  ride on. The bases  1240  also form the channel in which the legs  103  ride throughout their travel. 
     An embodiment of a lubrication system and method will now be described with reference to  FIGS. 3, 9, and 10 . As the balls  101  spin, lubricant tends to flow toward the equators of the balls  101 , and the lubricant is then sprayed out against the hub shell  138 . Some lubricant does not fall on the internal wall of the hub shell  138  having the largest diameter; however, centrifugal force makes this lubricant flow toward the largest inside diameter of the hub shell  138 . The scraper  910  is positioned vertically so that it removes lubricant that accumulates on the inside of the hub shell  138 . Gravity pulls the lubricant down each side of V-shaped wedge  925  and into the passages  920 . The spacer  900  is placed such that the inner radial end of the passages  920  end in the vicinity of the cam discs  127  and the idler  126 . In this manner the idler  126  and the cam discs  127  receive lubrication circulating in the hub shell  138 . In one embodiment, the scraper  910  is sized to clear the hub shell  138  by about  30  thousandths of an inch. Of course, depending on different applications, the clearance could be greater or smaller. 
     As shown in  FIGS. 3 and 10 , a cam disc  127  can be configured so that its side facing the idler  226  is angled in order to receive lubricant falling from the passages  920  and direct the lubricant toward the space between the cam disc  127  and the idler  226 . After lubricant flows onto the idler  226 , the lubricant flows toward the largest diameter of the idler  226 , where some of the lubricant is sprayed at the axles  102 . Some of the lubricant falls from the passages  920  onto the idler  226 . This lubricant lubricates the idler  226  as well as the contact patch between the balls  101  and the idler  226 . Due to the inclines on each side of the idler  226 , some of the lubricant flows centrifugally out toward the edges of the idler  226 , where it then sprays out radially. 
     Referring to  FIGS. 1, 3 and 10 , in some embodiments, lubricant sprayed from the idler  126 ,  226  towards the axle  102  falls on grooves  345 , which receive the lubricant and pump it inside the ball  101 . Some of the lubricant also falls on the contact surface  111  where the input disc  110  and output disc  134  contact the balls  101 . As the lubricant exits on one side of the ball  101 , the lubricant flows toward the equator of the balls  101  under centrifugal force. Some of this lubricant contacts the input disc  110  and ball  101  contact surface  111  and then flows toward the equator of the ball  101 . Some of the lubricant flows out radially along a side of the output disc  134  facing away from the balls  101 . In some embodiments, the input disc  110  and/or output disc  134  are provided with lubrication ports  136  and  135 , respectively. The lubrication ports  135 ,  136  direct the lubrication toward the largest inside diameter of the hub shell  138 . 
       FIG. 13  illustrates an embodiment of a CVT  1300  having two cam-loaders  1354  that share the generation and distribution of axial force in the CVT  1300 . Here, the cam loaders  1354  are positioned adjacent to the input disc  1310  and the output disc  1334 . The CVT  1300  illustrates how torque can be supplied either via the input disc  1310  and out through the output disc  1334  or reversed so that torque is input through the output disc  1334  and output through the input disc  1310 . 
       FIG. 14  depicts a bicycle hub  1400  configured to incorporate inventive features of embodiments of the CVTs described here. Several components of the hub  1400  are the same as components described above; hence, further description of such components will be limited. The hub  1400  includes a hub shell  138  that couples to a hub cap  1460 . In some embodiments, the hub  1400  also includes an end cap  1410  that seals the end of the hub shell  138  opposite the hub cap  1460 . The hub shell  138 , the hub cap  1460 , and the end cap  1410  are preferably made of materials that provide structural strength and rigidity. Such materials include, for example, steel, aluminum, magnesium, high-strength plastics, etc. In some embodiments, depending on the specific requirements of a given application of the technology, other materials might be appropriate. For example, the hub shell  138  may be made from composites, thermo plastics, thermoset plastics, etc. 
     Referring now to  FIG. 14 , the illustrated hub  1400  houses in its interior embodiments of the CVTs presented herein. A main shaft  105  supports the hub  1400  and provides for attachment to the dropouts  10  of a bicycle or other vehicle or equipment. The main shaft  105  of this embodiment is described in further detail with reference to  FIGS. 41-43 . In some embodiments, as illustrated in  FIGS. 15-18 , a CVT  1500  includes a shifting mechanism that incorporates a rod  112  with a threaded end  109 . Nuts  106  and  107  lock the dropouts  10  to the main shaft  105 . In the embodiment of  FIG. 14 , the hub  1400  includes a freewheel  1420  that is operationally coupled to an input shaft (see  FIG. 33  and  FIG. 40 ) for transferring a torque input into the CVT  1500 . It should be noted that although various embodiments and features of the CVTs described here are discussed with reference to a bicycle application, through readily recognizable modifications the CVTs and features thereof can be used in any vehicle, machine or device that uses a transmission. 
     With reference to  FIGS. 15 and 16 , in one embodiment the CVT  1500  has an input disc  1545  for transferring torque to a set of spherical traction rollers (here shown as balls  101 ).  FIG. 16  is a partially exploded view of the CVT  1500 . The balls  101  transfer the torque to an output disc  1560 . One ball  101  is illustrated in this embodiment to provide clarity in illustrating the various features of the CVT  1500 , however, various embodiments of the CVT employ anywhere from 2 to 16 balls  101  or more depending on the torque, weight and size requirements of each particular application. Different embodiments use either 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 or more balls  101 . An idler  1526 , mounted coaxially about the main shaft  105 , contacts and provides support for the balls  101  and maintains their radial position about the main shaft  105 . The input disc  1545  of some embodiments, has lubrication ports  1590  to facilitate circulation of lubricant in the CVT  1500 . 
     Referring additionally to  FIGS. 37-38 , the ball  101  spins on an axle  3702 . Legs  103  and shift cams  1527  cooperate to function as levers that actuate a shift in the position of the axle  3702 , which shift results in a tilting of the ball  101  and, thereby, a shift in the transmission ratio as already explained above. A cage  1589  (see  FIGS. 22-24 ) provides for support and alignment of the legs  103  as the shift cams  1527  actuate a radial motion of the legs  103 . In one embodiment, the cage includes stators  1586  and  1587  that are coupled by stator spacers  1555 . In other embodiments, other cages  180 ,  389 ,  1200  are employed. 
     Referring additionally to  FIGS. 41-43 , in the illustrated embodiment, the cage  1589  mounts coaxially and nonrotatably about the main shaft  105 . The stator  1586  rigidly attaches to a flange  4206  of the main shaft  105  in this embodiment. An additional flange  1610  holds the stator  1587  in place. A key  1606  couples the flange  1610  to the main shaft  105 , which has a key seat  1608  for receiving the key  1606 . Of course, the person of ordinary skill in the relevant technology will readily recognize that there are many equivalent and alternative methods for coupling the main shaft  105  to the flange  1610 , or coupling the stators  1586 ,  1587  to the flanges  1620 ,  4206 . In certain embodiments, the main shaft  105  includes a shoulder  4310  that serves to axially position and constrain the flange  1610 . 
     The end cap  1410  mounts on a radial bearing  1575 , which itself mounts over the flange  1610 . In one embodiment, the radial bearing  1575  is an angular contact bearing that supports loads from ground reaction and radially aligns the hub shell  138  to the main shaft  105 . In some embodiments, the hub  1400  includes seals at one or both ends of the main shaft  105 . For example, here the hub  1400  has a seal  1580  at the end where the hub shell  138  and end cap  1410  couple together. Additionally, in order to provide an axial force preload on the output side and to maintain axial position of the hub shell  138 , the hub  1400  may include spacers  1570  and a needle thrust bearing (not shown) between the stator  1587  and the radial bearing  1575 . The spacers  1570  mount coaxially about the flange  1610 . In some embodiments, the needle thrust bearing may not used, and in such cases the radial bearing  1575  may be an angular contact bearing adapted to handle thrust loads. The person of ordinary skill in the relevant technology will readily recognize alternative means to provide the function of carrying radial and thrust loads that the spacers  1570 , needle thrust bearing, and radial bearing provide. 
     Still referring to  FIGS. 14, 15 and 16 , in the embodiment illustrated, a variator  1500  for the hub  1400  includes an input shaft  1505  that operationally couples at one end to a torsion disc  1525 . The other end of the input shaft  1505  operationally couples to the freewheel  1420  via a freewheel carrier  1510 . The torsion disc  1525  is configured to transfer torque to a load cam disc  1530  having ramps  3610  (see  FIG. 36 ). The load cam disc  1530  transfers torque and axial force to a set of rollers  2504  (see  FIG. 25 ), which act upon a second load cam disc  1540 . The input disc  1545  couples to the second load cam disc  1540  to receive torque and axial force inputs. In some embodiments, the rollers  2504  are held in place by a roller cage  1535 . 
     As is well known, many traction- type CVTs utilize a clamping mechanism to prevent slippage between the balls  101  and the input disc  1545  and/or output disc  1560  when transmitting certain levels of torque. Provision of a clamping mechanism is sometimes referred to here as generating an axial force, or providing an axial force generator. The configuration described above of the load cam disc  1530  acting in concert with the load cam  1540  through the rollers  2504  is one such axial force generating mechanism. However, as the axial force generating device or sub-assembly generates axial force in a CVT, reaction forces are also produced that are reacted in the CVT itself in some embodiments. Referring additionally to  FIGS. 25 and 26 , in the embodiment illustrated of the CVT  1500 , the reaction forces are reacted at least in part by a thrust bearing having first and second races  1602  and  1603 , respectively. In the illustrated embodiment, the bearing elements are not shown but may be balls, rollers, barreled rollers, asymmetrical rollers or any other type of rollers. Additionally, in some embodiments, one or both of the races  1602  are made of various bearing race materials such as steel, bearing steel, ceramic or any other material used for bearing races. The first race  1602  butts up against the torsion disc  1525 , and the second race  1603  butts up against the hub cap  1460 . The hub cap  1460  of the illustrated embodiment helps to absorb the reaction forces that the axial force mechanism generates. In some embodiments, axial force generation involves additionally providing preloaders, such as one or more of an axial spring such as a wave spring  1515  or a torsion spring  2502  (see description below for  FIG. 25 ). 
     Referring to  FIGS. 15-18, 22-24 and 43 , certain subassemblies of the CVT  1500  are illustrated. The stator  1586  mounts on a shoulder  4208  of the main shaft  105  and butts up against the flange  4206  of the main shaft  105 . The stator  1587  mounts on a shoulder  1810  of the flange  1610 . Here, screws (not shown) attach the flange  4206  to the stator  1586  and attach the flange  1610  to the stator  1587 , however, in other embodiments the stator  1587  threads onto the shoulder  1810 , although the stator  1587  can be attached by any method or means to the shoulder  1810 . Because the flanges  1610  and  4206  are nonrotatably fixed to main shaft  105 , the cage  1589  made of the stators  1586  and  1587 , among other things, attaches nonrotatably in this embodiment to the main shaft  105 . The stator spacers  1555  provide additional structural strength and rigidity to the cage  1589 . Additionally, the stator spacers  1555  aid in implementing the accurate axial spacing between stators  1586  and  1587 . The stators  1586  and  1587  guide and support the legs  103  and axles  3702  through guide grooves  2202 . 
     Referring now to  FIGS. 15-21, 37, 38 , the ball  101  spins about the axle  3702  and is in contact with an idler  1526 . Bearings  1829 , mounted coaxially about the main shaft  105 , support the idler  1526  in its radial position, which bearings  1829  may be separate from or integral with the idler  1526 . A shift pin  114 , controlled by the shift rod  112 , actuates an axial movement of the shift cams  1527 . The shift cams  1527  in turn actuate legs  103 , functionally resulting in the application of a lever or pivoting action upon the axle  3702  of the ball  101 . In some embodiments, the CVT  1500  includes a retainer  1804  that keeps the shift pin  114  from interfering with the idler  1526 . The retainer  1804  can be a ring made of plastic, metal, or other suitable material. The retainer  1804  fits between the bearings  1829  and mounts coaxially about a shift cam extension  1528 . 
       FIGS. 19-21  show one embodiment of the shift cams  1527  for the illustrated CVT  1500 . Each shift cam disc  1572  has a profile  2110  along which the legs  103  ride. Here the profile  2110  has a generally convex shape. Usually the shape of the profile  2110  is determined by the desired motion of the legs  103 , which ultimately affects the shift performance of the CVT  1500 . Further discussion of shift cam profiles is provided below. As shown, one of the shift cam discs  1527  has an extension  1528  that mounts about the main shaft  105 . The extension  1528  of the illustrated embodiment is sufficiently long to extend beyond the idler  1526  and couple to the other shift cam disc  1527 . Coupling here is provided by a slip-fit and a clip. However, in other embodiments, the shift cams  1527  can be fastened to each other by threads, screws, interference fit, or any other connection method. In some embodiments, the extension  1528  is provided as an extension from each shift cam  1527 . The shift pin  114  fits in a hole  1910  that goes through the extension  1528 . In some embodiments, the shift cams  1527  have orifices  1920  to improve lubrication flow through the idler bearings  1829 . In some embodiments the idler bearings  1829  are press fit onto the extension  1528 . In such embodiments, the orifices  1920  aid in removing the idler bearings  1829  from the extension  1528  by allowing a tool to pass through the shift cams  1527  and push the idler bearings  1829  off the extension  1528 . In certain embodiments, the idler bearings  1829  are angle contact bearings, while in other embodiments they are radial bearings or thrust bearings or any other type of bearing. Many materials are suitable for making the shift cams  1527 . For example, some embodiments utilize metals such as steel, aluminum, and magnesium, while other embodiments utilize other materials, such as composites, plastics, and ceramics, which depend on the conditions of each specific application. 
     The illustrated shift cams  1527  are one embodiment of a shift cam profile  2110  having a generally convex shape. Shift cam profiles usually vary according to the location of the contact point between the idler  1526  and the ball-leg assembly  1670  (see  FIG. 16 ) as well as the amount of relative axial motion between the ball  101  and the idler  1526 . 
     Referring now to the embodiment illustrated in  FIGS. 16, and 18-21 , the profile of shift cams  1527  is such that axial translation of the idler  1526  relative to the ball  101  is proportional to the change of the angle of the axis of the ball  101 . The angle of the axis of the ball  101  is referred to herein as “gamma.” The applicant has discovered that controlling the axial translation of the idler  1526  relative to the change in gamma influences CVT ratio control forces. For example, in the illustrated CVT  1500 , if the axial translation of the idler  1526  is linearly proportional to a change in gamma, the normal force at the shift cams  1527  and ball-leg interface is generally parallel to the axle  3702 . This enables an efficient transfer of horizontal shift forces to a shift moment about the ball-leg assembly  1670 . 
     A linear relation between idler translation and gamma is given as idler translation is the mathematical product of the radius of the balls  101 , the gamma angle and RSF (i.e., idler translation=ball radius*gamma angle*RSF), where RSF is a roll-slide factor. RSF describes the transverse creep rate between the ball  101  and the idler  126 . As used here, “creep” is the discrete local motion of a body relative to another. In traction drives, the transfer of power from a driving element to a driven element via a traction interface requires creep. Usually, creep in the direction of power transfer is referred to as “creep in the rolling direction.” Sometimes the driving and driven elements experience creep in a direction orthogonal to the power transfer direction, in such a case this component of creep is referred to as “transverse creep.” During CVT operation, the ball  101  and idler  1526  roll on each other. When the idler is shifted axially (i.e., orthogonal to the rolling direction), transverse creep is imposed between the idler  1526  and the ball  101 . An RSF equal to 1.0 indicates pure rolling. At RSF values less than 1.0, the idler  1526  translates slower than the ball  101  rotates. At RSF values greater than 1.0, the idler  1526  translates faster than the ball  101  rotates. 
     Still referring to the embodiments illustrated in  FIGS. 16, and 18-21 , the applicant has devised a process for layout of the cam profile for any variation of transverse creep and/or location of the interface between the idler  1526  and the ball-leg assembly  1570 . This process generates different cam profiles and aids in determining the effects on shift forces and shifter displacement. In one embodiment, the process involves the use of parametric equations to define a two-dimensional datum curve that has the desired cam profile. The curve is then used to generate models of the shift cams  127 . In one embodiment of the process, the parametric equations of the datum curve are as follows: 
       theta=2*GAMMA_MAX* t -GAMMA_MAX 
         x =LEG*sin(theta)−0.5*BALL_ DIA *RSF*theta* pi/ 180 0.5*ARM*cos(theta)
 
         y =LEG*cos(theta)−0.5*ARM*sin(theta)
 
       z=0 
     The angle theta varies from minimum gamma (which in some embodiments is −20 degrees) to maximum gamma (which in some embodiments is +20 degrees). GAMMA_MAX is the maximum gamma. The parametric range variable “t” varies from 0 to 1. Here “x” and “y” are the center point of the cam wheel  152  (see  FIG. 1 ). The equations for x and y are parametric. “LEG” and “ARM” define the position of the interface between the ball-leg assembly  1670  and the idler  1526  and shift cams  1527 . More specifically, LEG is the perpendicular distance between the axis of the ball axle  3702  of a ball-leg assembly  1670  to a line that passes through the centers of the two corresponding cam wheels  152  of that ball-leg assembly  1570 , which is parallel to the ball axle  3702 . ARM is the distance between centers of the cam wheels  152  of a ball-leg-assembly  1670 . 
     RSF values above zero are preferred. The CVT  100  demonstrates an application of RSF equal to about 1.4. Applicant discovered that an RSF of zero dramatically increases the force required to shift the CVT. Usually, RSF values above 1.0 and less than 2.5 are preferred. 
     Still referring to the embodiments illustrated in  FIGS. 16, and 18-21 , in the illustrated embodiment of a CVT  100 , there is a maximum RSF for a maximum gamma angle. For example, for gamma equals to +20 degrees an RSF of about 1.6 is the maximum. RSF further depends on the size of the ball  101  and the size of the idler  1526 , as well as the location of the cam wheel  152 . 
     In terms of energy input to shift the CVT, the energy can be input as a large displacement and a small force (giving a large RSF) or a small displacement and a large force (giving a small RSF). For a given CVT there is a maximum allowable shift force and there is also a maximum allowable displacement. Hence, a trade off offers designers various design options to be made for any particular application. An RSF greater than zero reduces the required shift force by increasing the axial displacement necessary to achieve a desired shift ratio. A maximum displacement is determined by limits of the particular shifting mechanism, such as a grip or trigger shift in some embodiments, which in some embodiments can also be affected or alternatively affected by the package limits for the CVT  100 . 
     Energy per time is another factor. Shift rates for a given application may require a certain level of force or displacement to achieve a shift rate depending on the power source utilized to actuate the shift mechanism. For example, in certain applications using an electric motor to shift the CVT, a motor having a high speed at low torque would be preferred in some instances. Since the power source is biased toward speed, the RSF bias would be toward displacement. In other applications using hydraulic shifting, high pressure at low flow may be more suitable than low pressure at high flow. Hence, one would choose a lower RSF to suit the power source depending on the application. 
     Idler translation being linearly related to gamma is not the only desired relation. Hence, for example, if it is desired that the idler translation be linearly proportional to CVT ratio, then the RSF factor is made a function of gamma angle or CVT ratio so that the relation between idler position and CVT ratio is linearly proportional. This is a desirable feature for some types of control schemes. 
       FIGS. 22-24  show one example of a cage  1589  that can be used in the CVT  1500 . The illustrated cage  1589  has two stators  1586  and  1587  coupled to each other by a set of stator spacers  1555  (only one is shown for clarity). The stator spacers  1555  in this embodiment fasten to the outer periphery of the stators  1586  and  1587 . Here screws attach the spacers  1555  to the stators  1586  and  1587 . However, the stators  1586  and  1587  and the spacers  1555  can be configured for other means of attachment, such as press fittting, threading, or any other method or means. In some embodiments, one end of the spacers  1555  is permanently affixed to one of the stators  1586  or  1587 . In some embodiments, the spacers  1555  are made of a material that provides structural rigidity. The stators  1586  and  1587  have grooves  2202  that guide and support the legs  103  and/or the axles  3702 . In certain embodiments, the legs  103  and/or axles  3702  have wheels (item  151  of  FIG. 11  or equivalent of other embodiments) that ride on the grooves  2202 . 
       FIG. 24  shows a side of the stator  1586  opposite to the grooves  2202  of the stator  1586 . In this embodiment, holes  2204  receive the screws that attach the stator spacers  1555  to the stator  1586 . Inner holes  2210  receive the screws that attach the stator  1586  to the flange  4206  of the main shaft  105 . To make some embodiments of the stator  1586  lighter, material is removed from it as shown as cutouts  2206  in this embodiment. For weight considerations as well as clearance of elements of the ball-leg assembly  1670 , the stator  1586  may also include additional cutouts  2208  as in this embodiment. 
     The embodiments of  FIGS. 25, 26 and 36  will now be referenced to describe one embodiment of an axial force generation mechanism that can be used with the CVT  1500  of  FIG. 15 .  FIGS. 25 and 26  are partially exploded views. The input shaft  1505  imparts a torque input to the torsion disc  1525 . The torsion disc  1525  couples to a load cam disc  1530  that has ramps  3610 . As the load cam disc  1530  rotates, the ramps  3610  activate the rollers  2504 , which ride up the ramps  3610  of the second load cam disc  1540 . The rollers  2504  then wedge in place, pressed between the ramps of the load cam discs  1530  and  1540 , and transmit both torque and axial force from the load cam disc  1530  to the load cam disc  1540 . In some embodiments, the CVT  1500  includes a roller retainer  1535  to ensure proper alignment of the rollers  2504 . The rollers  2504  may be spherical, cylindrical, barreled, asymmetrical or other shape suitable for a given application. In some embodiments, the rollers  2504  each have individual springs (not shown) attached to the roller retainer  1535  or other structure that bias the rollers  2504  up or down the ramps  3610  as may be desired in some applications. The input disc  1545  in the illustrated embodiment is configured to couple to the load cam disc  1540  and receive both the input torque and the axial force. The axial force then clamps the balls  101  between the input disc  1545 , the output disc  1560 , and the idler  1526 . 
     In the illustrated embodiment, the load cam disc  1530  is fastened to the torsion disc  1525  with dowel pins. However, other methods of fastening the load cam disc  1530  to the torsion disc  1525  can be used. Moreover, in some embodiments, the load cam disc  1530  is integral with the torsion disc  1525 . In other embodiments, the torsion disc  1525  has the ramps  3610  machined into it to make a single unit for transferring torque and axial force. In the embodiment illustrated, the load cam disc  1540  couples to the input disc  1545  with dowel pins. Again, any other suitable fastening method can be used to couple the input disc  1545  to the load cam disc  1540 . In some embodiments, the input disc  1545  and the load cam disc  1540  are an integral unit, effectively as if the ramps  3610  were built into the input disc  1545 . In yet other embodiments, the axial force generating mechanism may include only one set of ramps  3610 . That is, one of the load cam discs  1530  or  1540  does not have the ramps  3610 , but rather provides a flat surface for contacting the rollers  2504 . Similarly, where the ramps are built into the torsion disc  1525  or the input disc  1545 , one of them may not include the ramps  3610 . In load cam discs  1530 ,  1540  in both embodiments having ramps on both or on only one disc, the ramps  3610  and the flat surface on discs without ramps can be formed with a conformal shape conforming to the rollers  2504  surface shape to partially capture the rollers  2504  and to reduce the surface stress levels. 
     In some embodiments, under certain conditions of operation, a preload axial force to the CVT  1500  is desired. By way of example, at low torque input it is possible for the input disc  1545  to slip on the balls  101 , rather than to achieve frictional traction. In the embodiment illustrated in  FIGS. 25 and 26 , axial preload is accomplished in part by coupling a torsion spring  2502  to the torsion disc  1525  and the input disc  1545 . One end of the torsion spring  2502  fits into a hole  2930  (see  FIG. 29 ) of the torsion disc  1545 , while the other end of the torsion spring  2502  fits into a hole of the input disc  1545 . Of course, the person of ordinary skill in the relevant technology will readily appreciate numerous alternative ways to couple the torsion spring  2502  to the input disc  1545  and the torsion disc  1525 . In other embodiments, the torsion spring  2502  may couple to the roller retainer  1535  and the torsion disc  1525  or the input disc  1545 . In some embodiments where only one of the torsion disc  1525  or input disc  1545  has ramps  3610 , the torsion spring  2502  couples the roller retainer  1535  to the disc with the ramps. 
     Still referring to the embodiments illustrated in  FIGS. 15   25  and  26 , as mentioned before, in some embodiments the application of axial forces generates reaction forces that are reacted in the CVT  1500 . In this embodiment of the CVT  1500 , a ball thrust bearing aids in managing the reaction forces by transmitting thrust between the hub cap  1460  and the torsion disc  1525 . The thrust bearing has a race  1602  that butts against the hub cap  1460 , which in this embodiment has a recess near its inner bore for receiving the race  1602 . The second race  1603  of the thrust bearing nests in a recess of the torsion disc  1525 . In some embodiments, a wave spring  1515  is incorporated between the race  1602  and the hub  1460  to provide axial preload. In the illustrated embodiment, a bearing  2610  radially supports the hub cap  1460 . 
     The applicant has discovered that certain configurations of the CVT  1500  are better suited than others to handle a reduction in efficiency of the CVT  1500  due to a phenomenon referred to herein as bearing drag recirculation. This phenomenon arises when a bearing is placed between the torsion disc  1525  and the hub cap  1460  to handle the reaction forces from axial force generation. 
     In some embodiments as illustrated in  FIG. 1 , a needle roller bearing having a diameter about equal to the diameter of the load cam disc  1530  is used to minimize the deflection of the end cap  160 . In underdrive the speed of the torsion disc  157  (input speed) is greater than the speed of the end cap  160  (output speed). In underdrive the needle roller bearing (thrust bearing  163  in that embodiment) generates a drag torque opposite the direction of rotation of the torsion disc  1525 . This drag torque acts on the torsion disc  1525  in the direction counter to the axial loading by the load cam disc  1530 , and acts on the end cap  160  and thus the hub shell  138  and output disc  134  in the direction of the output tending to speed up the rotation of those components, these effects combining to unload the cam loader  154  thereby reduce the amount of axial force in the CVT  1500 . This situation could lead to slip between or among the input disc  110 , balls  101 , and/or output disc  134 . 
     In overdrive the speed of the torsion disc  1525  is greater than the speed of the end cap cap  160  and the needle bearing generates a drag torque acting on the torsion disc  1525  in the direction of the rotation of the torsion disc  1525  and acting on the end cap  160  against the output rotation of the end cap  160 . This results in an increase in the axial force being generated in the CVT  1500 . The increase in axial force then causes the system to generate even more drag torque. This feedback phenomenon between axial force and drag torque is what is referred to here as bearing drag recirculation, which ultimately results in reducing the efficiency of the CVT  100 . Additionally, the drag torque acting against the end cap  160  acts as an additional drag on the output of the CVT  100  thereby further reducing its efficiency. 
     The applicant has discovered various systems and methods for minimizing efficiency losses due to bearing drag recirculation. As shown in  FIGS. 25, 26, and 40 , instead of using a needle roller bearing configured as described above, some embodiments the CVT  1500  employ a roller thrust bearing having races  1602  and  1603 . Because the amount of drag torque increases with the diameter of the bearing used, the diameter of the races  1602  and  1603  is less than the diameter of the axial force generating load cam disc  1530  and in some embodiments is as small as possible. The diameter of the races  1602  and  1603  could be 10, 20, 30, 40, 50, 60, 70, 80, or 90 percent of the diameter of the load cam disc  1530 . In some embodiments, the diameter of the races  1602  and  1603  is between 30 and 70 percent of the diameter of the load cam disc  1530 . In still other embodiments, the diameter of the races  1602  and  1603  is between 40 and 60 percent of the diameter of the load cam disc  1530 . 
     When a ball thrust bearing is used, in some embodiments the rollers and/or races are made of ceramic, the races are lubricated and/or superfinished, and/or the number of rollers is minimized while maintaining the desired load capacity. In some embodiments, deep groove radial ball bearings or angular contact bearings may be used. For certain applications, the CVT  1500  may employ magnetic or air bearings as means to minimize bearing drag recirculation. Other approaches to reducing the effects of bearing drag recirculation are discussed below, referencing  FIG. 46 , in connection with alternative embodiments of the input shaft  1505  and the main shaft  105 . 
       FIGS. 27-35  depict examples of certain embodiments of a torque input shaft  1505  and a torsion disc  1525  that can be used with the CVT  1500  of  FIG. 15 . The input shaft  1505  and the torsion disc  1525  couple via a splined bore  2710  on the torsion disc  1525  and a splined flange  2720  on the input shaft  1525 . In some embodiments, the input shaft  1505  and the torsion plate  1525  are one piece, made either as a single unit (as illustrated in  FIG. 1 ) or wherein the input shaft  1505  and the torsion disc  1525  are coupled together by permanent attachment means, such as welding or any other suitable adhesion process. In yet other embodiments, the input shaft  1505  and the torsion disc  1525  are operationally coupled through fasteners such as screws, dowel pins, clips or any other means or method. The particular configuration shown here is preferable in circumstances where it is desired that the input shaft  1505  and the torsion disc  1525  be separate parts, which can handle misalignments and axial displacement due to load cam disc  1530  growth under load, as well as uncouple twisting moments via the splined bore  2710  and the splined shaft  2720 . This configuration is also preferable in certain embodiments because it allows for lower manufacturing tolerances and, consequently, reduced manufacturing costs for a CVT. 
     Referencing  FIGS. 16, 28-32 , in the illustrated embodiment, the torsion disc  1525  is generally a circular disc having an outer periphery  3110  and a splined inner bore  2710 . One side of the torsion disc  1525  has a recess  3205  that receives the race  1603  of a thrust bearing. The other side of the torsion disc  1525  includes a seat  3210  and a shoulder  3220  for receiving and coupling to the load cam disc  1530 . The torsion disc  1525  includes a raised surface  3230  that rises from the shoulder  3220 , reaches a maximum height in a convex shape, and then falls toward the inner bore  2710 . In one embodiment of the CVT  1500 , the raised surface  3230  partially supports and constrains the torsion spring  2502 , while a set of dowel pins (not shown) helps to retain the torsion spring  2502  in place. In such embodiments, the dowel pins are placed in holes  2920 . The torsion disc  1525  shown here has three splines on its splined bore  2710 . However, in other embodiments the splines can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more. In some embodiments, the number of splines is 2 to 7, and in others the number of splines is 3, 4, or 5. 
     In some embodiments, the torsion disc  1525  includes orifices  2910  for receiving dowels that couple the torsion disc  1525  to the load cam disc  1530 . The torsion disc  1525  may also have orifices  2930  for receiving one end of the torsion spring  2502 . In the illustrated embodiment, several orifices  2930  are present in order to accommodate different possible configurations of the torsion spring  2502  as well as to provide for adjustment of preload levels. 
     The torsion disc  1525  can be of any material of sufficient rigidity and strength to transmit the torques and axial loads expected in a given application. In some embodiments, the material choice is designed to aid in reacting the reaction forces that are generated. For example, hardened steels, steel, aluminum, magnesium, or other metals can be suitable depending on the application while in other applications plastics are suitable. 
       FIGS. 33-35  show an embodiment of an input torque shaft  1505  for use with the CVT  1500 . The torque input shaft  1505  consists of a hollow, cylindrical body having a splined flange  2720  at one end and a key seat  3310  at the other end. In this embodiment, the key seat  3310  receives a key (not shown) that operationally couples the input shaft  1505  to a freewheel carrier  1510  (see  FIG. 14, 15 ), which itself couples to the freewheel  1420 . The surfaces  2720  and  3410  are shaped to mate with the splined bore  2710  of the torsion disc  1525 . Thus, concave surfaces  2720  of some embodiments will preferably be equal in number to the splines in the splined bore  2710 . In some embodiments, the concave surfaces  2720  may number 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more. In some embodiments, the concave surfaces  2720  number 2 to 7, and in others there are 3, 4, or 5 concave surfaces  2720 . 
     As shown, the input shaft  1505  has several clip grooves that help in retaining various components, such as bearings, spacers, etc., in place axially. The input shaft  1505  is made of a material that can transfer the torques expected in a given application. In some instances, the input shaft  1505  is made of hardened steel, steel, or alloys of other metals while in other embodiments it is made of aluminum, magnesium or any plastic or composite or other suitable material. 
       FIG. 36  shows an embodiment of a load cam disc  1540  (alternately  1530 ) that can be used with the CVT  1500 . The disc  1540  is generally a circular ring having a band at its outer periphery. The band is made of ramps  3610 . Some of the ramps  3610  have holes  3620  that receive dowel pins (not shown) for coupling the load cam disc  1530  to the torsion disc  1525  or the load cam disc  1540  to the input disc  1545 . In some embodiments, the ramps  3610  are machined as a single unit with the load cam discs  1530 ,  1540 . In other embodiments, the ramps  3610  may be separate from a ring substrate (not shown) and are coupled to it via any known fixation method. In the latter instance, the ramps  3610  and the ring substrate can be made of different materials and by different machining or forging methods. The load cam disc  1540  can be made, for example, of metals or composites. 
     Referencing  FIG. 37  and  FIG. 38 , an embodiment of an axle  3702  consists of an elongated cylindrical body having two shoulders  3704  and a waist  3806 . The shoulders  3704  begin at a point beyond the midpoint of the cylindrical body and extend beyond the bore of the ball  101 . The shoulders  3704  of the illustrated embodiment are chamfered, which helps in preventing excessive wear of the bushing  3802  and reduces stress concentration. The ends of the axle  3702  are configured to couple to bearings or other means for interfacing with the legs  103 . In some embodiments, the shoulders  3704  improve assembly of the ball-leg assembly  1670  by providing a support, stop, and/or tolerance reference point for the leg  103 . The waist  3806  in certain embodiments serves as an oil reservoir. In this embodiment, a bushing  3802  envelops the axle  3702  inside the bore of the ball  101 . In other embodiments, bearings are used instead of the bushing  3802 . In those embodiments, the waist  3806  ends where the bearings fit inside the ball  101 . The bearings can be roller bearings, drawn cup needle rollers, caged needle rollers, journal bearings, or bushings. In some embodiments, it is preferred that the bearings are caged needle bearings or other retained bearings. In attempting to utilize general friction bearings, the CVT  100 ,  1500  often fails or seizes due to a migration of the bearings or rolling elements of the bearings along the axles  3702 ,  102  out of the balls  101  to a point where they interfere with the legs  103  and seize the balls  101 . It is believed that this migration is caused by force or strain waves distributed through the balls  101  during operation. Extensive testing and design has lead to this understanding and the Applicant&#39;s believe that the use of caged needle rollers or other retained bearings significantly and unexpectedly lead to longer life and improved durability of certain embodiments of the CVT  100 ,  1500 . Embodiments utilizing bushings and journal material also aid in the reduction of failures due to this phenomenon. The bushing  3802  can be replaced by, for example, a babbitt lining that coats either or both of the ball  101  or axle  3702 . In yet other embodiments, the axle  3702  is made of bronze and provides a bearing surface for the ball  101  without the need for bearings, bushing, or other linings. In some embodiments, the ball  101  is supported by caged needle bearings separated by a spacer (not shown) located in the middle portion of the bore of the ball  101 . Additionally, in other embodiments, spacers mount on the shoulders  3704  and separate the caged needle bearings from components of the leg  103 . The axle  3702  can be made of steel, aluminum, magnesium, bronze, or any other metal or alloy. In certain embodiments, the axle  3702  is made of plastic or ceramic materials. 
     One embodiment of the main shaft  105  is depicted in  FIGS. 41-43 . The main shaft  105  is an elongated body having an inner bore  4305  for receiving a shift rod  112  (see  FIGS. 16 and 40 ). As implemented in the CVT  1500 , the main shaft  105  is a single piece axle that provides support for many of the components of the CVT  1500 . In embodiments where a single piece axle is utilized for the main shaft  105 , the main shaft  105  reduces or eliminates tolerance stacks in certain embodiments of the CVT  1500 . Furthermore, as compared with multiple piece axles, the single piece main shaft  105  provides greater rigidity and stability to the CVT  1500 . 
     The main shaft  105  also includes a through slot  4204  that receives and allows the shift pin  114  to move axially, that is, along the longitudinal axis of the main shaft  105 . The size of the slots  4204  can be chosen to provide shift stops for selectively determining a ratio range for a given application of the CVT  1500 . For example, a CVT  1500  can be configured to have a greater underdrive range than overdrive range, or vice-versa, by choosing the appropriate dimension and/or location of the slots  4204 . By way of example, if the slot  4204  shown in  FIG. 42  is assumed to provide for the full shift range that the CVT  1500  is capable of, a slot shorter than the slot  4204  would reduce the ratio range. If the slot  4204  were to be shortened on the right side of  FIG. 42 , the underdrive range would be reduced. Conversely, if the slot  4204  were to be shortened on the left side of  FIG. 42 , the overdrive range would be reduced. 
     In this embodiment, a flange  4206  and a shoulder  4208  extend from the main shaft  105  in the radial direction. As already described, the flange  4206  and the shoulder  4208  facilitate the fixation of the stator  1586  to the main shaft  105 . In some embodiments, the bore of the stator  1586  is sized to mount to the main shaft  105  such that the shoulder  4208  can be dispensed with. In other embodiments, the shoulder  4208  and/or the flange  4206  can be a separate part from the main shaft  105 . In those instances, the shoulder  4208  and/or flange  4206  mount coaxially about the main shaft  105  and affix to it by any well known means in the relevant technology. In the embodiment depicted, the main shaft  105  includes a key seat  4202  for receiving a key  1606  that rotationally fixes the flange  1610  (see  FIG. 16 ). The key  1606  may be a woodruff key. The main shaft  105  of some embodiments is made of a metal suitable in terms of manufacturability, cost, strength, and rigidity. For example, the main shaft can be made of steel, magnesium, aluminum or other metals or alloys. 
     The operation of the hub  1400  having one embodiment of the CVT  1500  described above will now be described with particular reference to  FIGS. 39 and 40 . The freewheel  1420  receives torque from a bicycle chain (not shown). Since the freewheel  1420  is fixed to the freewheel carrier  1510 , the freewheel  1420  imparts the torque to the freewheel carrier  1510 , which in turns transmits the torque to the input shaft  1505  via a key coupling (not shown). The input shaft  1505 , riding on needle bearings  4010  and  4020  mounted on the main shaft  105 , inputs the torque to the torsion disc  1525  via the splined bore  2710  and splined surfaces  2720  and  3410  of the input shaft  1505 . Needle bearing  4010  is preferably placed near or underneath the freewheel carrier  1510  and/or freewheel  1420 . This placement provides appropriate support to the input shaft  1505  to prevent transmission of radial loading from the freewheel carrier  1510  as a bending load through the CVT  1400 . Additionally, in some embodiments a spacer  4030  is provided between the needle bearings  4010  and  4020 . The spacer  4030  may be made of, for example, Teflon. 
     As the torsion disc  1525  rotates, the load cam disc  1530  coupled to the torsion disc  1525  follows the rotation and, consequently, the ramps  3610  energize the rollers  2504 . The rollers  2504  ride up the ramps  3610  of the load cam disc  1540  and become wedged between the load cam disc  1530  and the load cam disc  1540 . The wedging of the rollers  2504  results in a transfer of both torque and axial force from the load cam disc  1530  to the load cam disc  1540 . The roller cage  1535  serves to retain the rollers  2504  in proper alignment. 
     Because the load cam disc  1540  is rigidly coupled to the input disc  1545 , the load cam disc  1540  transfers both axial force and torque to the input disc  1545 , which then imparts the axial force and torque to the balls  101  via frictional contact. As the input disc  1545  rotates under the torque it receives from the load cam disc  1540 , the frictional contact between the input disc  1545  and the balls  101  forces the balls  101  to spin about the axles  3702 . In this embodiment, the axles  3702  are constrained from rotating with the balls  101  about their own longitudinal axis; however, the axles  3702  can pivot or tilt about the center of the balls  101 , as in during shifting. 
     The input disc  1545 , output disc  1560 , and idler  1526  are in frictional contact with the balls  101 . As the balls  101  spin on the axles  3702 , the balls  101  impart a torque to the output disc  1560 , forcing the output disc  1560  to rotate about the shaft  105 . Because the output disc  1560  is coupled rigidly to the hub shell  138 , the output disc  1560  imparts the output torque to the hub shell  138 . The hub shell  138  is mounted coaxially and rotatably about the main shaft  105 . The hub shell  138  then transmits the output torque to the wheel of the bicycle via well known methods such as spokes. 
     Still referring to  FIGS. 39 and 40 , shifting of the ratio of input speed to output speed, and consequently a shift in the ratio of input torque to output torque, is accomplished by tilting the rotational axis of the balls  101 , which requires actuating a shift in the angle of the axles  3702 . A shift in the transmission ratio involves actuating an axial movement of the shift rod  112  in the main shaft  105 , or in rotation of the shift rod  312  of  FIG. 3 . The shift rod  112  translates axially the pin  114 , which is in contact with the shift cams  1527  via the bore  1910  in the extension  1528 . The axial movement of the shift pin  114  causes a corresponding axial movement of the shift cams  1527 . Because the shift cams  1527  engage the legs  103  (via cam wheels  152 , for example), the legs  103  move radially as the legs  103  move along the shift cam profile  2110 . Since the legs  103  are connected to the axles  3702 , the legs  103  act as levers that pivot the axles  3702  about the center of the balls  101 . The pivoting of the axles  3702  causes the balls  101  to change axis of rotation and, consequently, produce a ratio shift in the transmission. 
       FIG. 44  and  FIG. 45  show an embodiment of a CVT  4400  having an axial force generating mechanism that includes one load cam disc  4440  acting on the input disc  1545  and another load cam disc  4420  acting on the output disc  1560 . In this embodiment, the load cam discs  4440  and  4420  incorporate ramps such as ramps  3610  of the load cam discs  1530  and  1540 . In this embodiment, neither of the input disc  1545  or the output disc  1560  has ramps or is coupled to discs with ramps. However, in other embodiments, it may be desirable to provide one or both of the input disc  1545  or output disc  1560  with discs having ramps, or building the ramps into the input disc  1545  and/or output disc  1560  to cooperate with the load cam discs  4420 ,  4440 . The CVT  4400  of some embodiments further includes a roller retainer  4430  to house and align a set of rollers (not shown) that is between the load cam disc  4420  and the output disc  1560 . In the embodiment shown, the roller retainer  4430  radially pilots on the output disc  1560 . Similarly, there is a roller retainer  4410  between the load cam disc  4440  and the input disc  1545 . The rollers and discs described with reference to these embodiments can be of any type or shape as described above for previous axial force generating devices. In some embodiments the angles of the ramps incline from the surface of the disc at an angle that is (or is between) 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 degrees or more or any portion between any of these. 
       FIG. 46  illustrates an embodiment of a CVT  1600  having an input shaft  4605  and a main shaft  4625  adapted to decrease bearing drag recirculation effects. The CVT  100  includes an axial force generator  165  which generates an axial force that is reacted in part by a needle roller bearing  4620 . A hub cap  4660  reacts drag torque and axial forces from the needle roller bearing  4620 . In other embodiments, the needle roller bearing  4620  is replaced by a ball thrust bearing and in other embodiments the ball thrust bearing has a diameter smaller than the diameter of the needle roller bearing  4620 . 
     In this embodiment, the main shaft  4625  has a shoulder  4650  that provides a reaction surface for a washer  4615 , which can also be a clip, for example (all of which are integral in some embodiments). The input shaft  4605  is fitted with an extension  1410  that reacts against a bearing  4645 . The bearing  4645  can be a thrust bearing. As shown, the input shaft  4605  and driver disc (similar to the torsion disc  1525 ) are a single piece. However, in other embodiments the input shaft  4605  may be coupled to a torsion disc  1525 , for example, by threading, keying, or other fastening means. In the illustrated embodiment, some of the reaction force arising from the generation of axial force is reacted to the main shaft  4625 , thereby reducing bearing drag recirculation. In yet another embodiment (not shown), the extension  1410  is reacted against angular thrust bearings that also support the input shaft  4605  on the main shaft  4625 . In this latter embodiment, the shoulder  4650  and washer  4615  are not required. Rather, the main shaft  4625  would be adapted to support and retain the angular thrust bearings. 
     In many embodiments described herein, lubricating fluids are utilized to reduce friction of the bearings supporting many of the elements described. Furthermore, some embodiments benefit from fluids that provide a higher coefficient of traction to the traction components transmitting torque through the transmissions. Such fluids, referred to as “traction fluids” suitable for use in certain embodiments include commercially available Santotrac 50, 5CST AF from Ashland oil, OS #155378 from Lubrizol, IVT Fluid #SL-2003B21-A from Exxon Mobile as well as any other suitable lubricant. In some embodiments the traction fluid for the torque transmitting components is separate from the lubricant that lubricates the bearings. 
     The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention can be practiced in many ways. As is also stated above, it should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to including any specific characteristics of the features or aspects of the invention with which that terminology is associated. The scope of the invention should therefore be construed in accordance with the appended claims and any equivalents thereof.