US20070155567A1 - Continuously variable transmission - Google Patents

Abstract

Traction planets and traction rings can be operationally coupled to a planetary gearset to provide a continuously variable transmission (CVT). The CVT can be used in a bicycle. In one embodiment, the CVT is mounted on the frame of the bicycle at a location forward of the rear wheel hub of the bicycle. In one embodiment, the CVT is mounted on and supported by members of the bicycle frame such that the CVT is coaxial with the crankshaft of the bicycle. The crankshaft is configured to drive elements of the planetary gearset, which are configured to operationally drive the traction rings and the traction planets. Inventive component and subassemblies for such a CVT are disclosed. A shifting mechanism includes a plurality of pivot arms arranged to pivot about the centers of the traction planets as a shift pin hub moves axially.

Description

RELATED APPLICATIONS
• This application claims priority to U.S. provisional patent application No. 60/738,865, which was filed on Nov. 22, 2005 and is hereby incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The field of the invention relates generally to transmissions, and more particularly to continuously variable transmissions (CVTs).
• 2. Description of the Related Art
• Embodiments of the CVTs disclosed here can be used in any machine, device, vehicle, etc., where it is desired to adjust the ratio of input speed to output speed. A bicycle is one such application. The drivetrain of a bicycle typically consists of pedals coupled to cranks for driving a crankshaft, which is received in, and supported by, frame members of the bicycle. The crankshaft is coupled to a sprocket that transfers power to the rear wheel of the bicycle by a chain. A cog at the rear wheel receives power from the chain and is adapted to interface with the rear wheel hub for driving the rear wheel of the bicycle. Some bicycles are provided with internally geared rear hubs, where a set of gears is arranged to receive power from the cog and drive the rear wheel. In some applications, a bicycle is provided with a CVT at the rear hub to drive the rear wheel.
• However, there remains an unfulfilled need for a CVT that is received and supported by the frame members of the bicycle at a location forward of the rear wheel or rear wheel hub. The embodiments of the CVTs disclosed here address this and other needs in the field of continuously variable transmissions.
SUMMARY OF THE INVENTION
• The systems and methods described herein have several features, no single one of which is solely responsible for the overall desirable attributes. Without limiting the scope as expressed by the claims that follow, the more prominent features of certain embodiments of the invention will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description of Certain Inventive Embodiments,” one will understand how the features of the systems and methods provide several advantages over related traditional systems and methods.
• One aspect of the invention relates to a bicycle having a plurality of bicycle frame members, a crankshaft operationally coupled to one or more cranks of the bicycle, and a continuously variable transmission (CVT) coaxially coupled with, and coaxially mounted about, the crankshaft.
• Another aspect of the invention is addressed to a bicycle having a crankshaft coupled to a rotatable planetary gear set carrier coupled, and a plurality of planet gears coupled to said carrier. A ring gear, rotationally constrained, can be coupled to the planet gears, which can be coupled to a sun gear coupled. A first traction ring is operationally coupled to the sun gear, and a plurality of traction planets are coupled to the traction ring. A second traction ring is coupled to the traction planets. Power is transferred sequentially from the crankshaft to the planetary gear set carrier, to the planetary gears, to the sun gear, to the first traction ring, to the traction planets, and to the second traction ring. In another embodiment, the crankshaft is additionally coupled to a cage that is adapted to support the traction planets axially and radially and to transfer power to the traction planets.
• Yet another aspect of the invention concerns a bicycle transmission having a planetary gear set configured for coupling to a crankshaft of a bicycle and to be mounted coaxially about the crankshaft. The bicycle transmission can further have a continuously variable variator coupled to the planetary gearset configured to be mounted coaxially about the crankshaft.
• Still another aspect of the invention is directed to a shift screw and a shift pin hub for facilitating the adjustment of a transmission ratio. In another regard, the invention relates to a device for actuating an axial translation of an idler or traction sun as the transmission ratio is adjusted. In one embodiment, the traction sun actuation device includes a plurality of cam rollers configured to interface with a cam surface of a pivot arm. Another aspect of the invention covers the pivot arms having an integral cam surface for facilitating the axial translation of the traction sun.
• In one aspect the invention is directed to a cage for a transmission. The cage has a plurality of splines for engaging corresponding splines of a transmission housing. The cage can further can a plurality of slots with skew roller reaction surfaces.
BRIEF DESCRIPTION OF THE FIGURES
• FIGS.1 is schematic cross-section of continuously variable transmission (CVT) implemented on the frame of a bicycle.
• FIG. 2 is a schematic cross-section of yet another embodiment of a CVT implemented on the frame of a bicycle.
• FIG. 3 is a perspective view of still another embodiment of a CVT that can be implemented, among other things, on the frame (such as the bottom bracket) of a bicycle.
• FIG. 4A is a perspective, cross-sectional view of the transmission ofFIG. 3.
• FIG. 4B is a cross-sectional view of the transmission ofFIG. 3.
• FIG. 4C is a partial, exploded view of certain assemblies and components of the transmission ofFIG. 3.
• FIG. 4D is a partial, exploded view of certain assemblies and components of the transmission ofFIG. 3.
• FIG. 5 is a perspective, partially exploded view of certain components of a housing for the transmission ofFIG. 3.
• FIG. 6A is a perspective view of a planetary gear set carrier that can be used with the transmission ofFIG. 3.
• FIG. 6B is an elevational side view of the planetary gear set carrier ofFIG. 6A.
• FIG. 7A is a perspective view of a cage that can be used with the transmission ofFIG. 3.
• FIG. 7B is a perspective view of a cage component of the cage ofFIG. 7A.
• FIG. 7C is a second perspective view of the cage component ofFIG. 7B.
• FIG. 8A is a perspective view of a planet-pivot-arm assembly that can be used with the transmission ofFIG. 3.
• FIG. 8B is a cross-sectional view of the planet-pivot-arm assembly of Figure A.
• FIG. 9 is a perspective view of a traction ring and clamping force generation assembly that can be used with the transmission ofFIG. 3.
• FIG. 10A is a perspective view of an input driver that can be used with the transmission ofFIG. 3.
• FIG. 10B is another perspective view of the input driver ofFIG. 10A.
• FIG. 10C is a cross-sectional view of the input driver ofFIG. 10A.
• FIG. 10D is a perspective view of an output driver that can be used with the transmission ofFIG. 3.
• FIG. 10E is another perspective view of an output driver that can be used with the transmission ofFIG. 3.
• FIG. 10F is a cross-sectional view the output driver ofFIG. 10D.
• FIG. 11A is a perspective view of a shift screw that can be used with a shifting actuator of the transmission ofFIG. 3.
• FIG. 11B is a cross-sectional view of the shift screw ofFIG. 11A.
• FIG. 12A is a perspective view of a shift pin hub that can be used with a shifting actuator of the transmission ofFIG. 3.
• FIG. 12B is a cross-sectional view of the shift pin hub ofFIG. 12A.
• FIG. 13A is a detail view A ofFIG. 4B showing a traction sun actuation device that can be used with the transmission ofFIG. 3.
• FIG. 13B is a perspective view of the traction sun actuation device ofFIG. 13A.
• FIG. 13C is a side elevational view of traction sun actuation device ofFIG. 13B.
• FIG. 13D is an exploded view of the traction sun actuation device ofFIG. 13B.
• FIG. 14A is a perspective view of certain components of the CVT ofFIG. 3 showing a shifting actuator for the CVT.
• FIG. 14B is second perspective view of certain components shown inFIG. 14A.
• FIG. 14C is a cross-sectional view of the components shown inFIG. 14A.
DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS
• Reference will now be made in detail to the present embodiments(s) (exemplary embodiments) of the invention, an example(s) of which is (are) illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts (elements).
• The CVT embodiments described here are generally related to those of the type disclosed in U.S. Pat. Nos. 6,241,636; 6,419,608; 6,689,012; and 7,011,600. The entire disclosure of each of these patents is hereby incorporated herein by reference. Additionally, U.S. patent application Ser. No. 10/788,736 (now U.S. Pat. No. 7,011,600) was included as Appendix A of the provisional application from which this application claims priority. The disclosure of U.S. patent application Ser. No. 11/543,311, filed Oct. 3, 2006, is hereby incorporated by reference herein in its entirety.
• The preferred embodiments will now be described with reference to the accompanying figures, wherein like numerals refer to like elements throughout. The terminology used in the description presented herein is not intended to be interpreted in any limited or restrictive manner simply because it is being utilized in conjunction with a detailed description of certain specific embodiments of the invention. Furthermore, embodiments of the invention may include several novel features, no single one of which is solely responsible for its desirable attributes or which is essential to practicing the inventions herein described.
• As used here, the terms “operationally connected,” “operationally coupled”, “operationally linked”, “operably connected”, “operably coupled”, “operably linked,” and like terms, refer to a relationship (mechanical, linkage, coupling, etc.) between elements whereby operation of one element results in a corresponding, following, or simultaneous operation or actuation of a second element. It is noted that in using said terms to describe inventive embodiments, specific structures or mechanisms that link or couple the elements are typically described. However, unless otherwise specifically stated, when one of said terms is used, the term indicates that the actual linkage or coupling may take a variety of forms, which in certain instances will be obvious to a person of ordinary skill in the relevant technology.
• For description purposes, the term “radial” is used here to indicate a direction or position that is perpendicular relative to a longitudinal axis of a transmission or variator. The term “axial” as used here refers to a direction or position along an axis that is parallel to a main or longitudinal axis of a transmission or variator. For clarity and conciseness, at times similar components labeled.
• FIG. 1 illustrates one embodiment of abicycle transmission100 mounted in abicycle frame102 rather than the rear hub of the bicycle (not shown). The illustrated embodiment integrates asupport structure104 of the transmission into theframe102 of the bicycle. The major components of thetransmission100 include avariator106, a planetary gear set110 and asupport structure104. The planetary gear set110 of the illustrated embodiment includes acentral sun gear112, a set of planet gears114 that orbit and surround thesun gear112, a set of planet gears114 that orbit and surround thesun gear112, and aring gear116 that surrounds the set of planer gears114. InFIG. 1, a dashed circle is used to better illustrate the location of thering gear116 that, in the illustrated embodiment, is integrated with thesupport structure104. Each of the planet gears114 rotates about arespective planet shaft118, and aplanet carrier120 supports theplanet shafts118. In the exemplary embodiment ofFIG. 1, the planet gears114 are compound planetary gears.
• As described in the embodiments described in U.S. Pat. No. 7,011,600, thevariator106 of the illustrated embodiment includes aninput ring124, anoutput ring126, and a set ofplanet balls130 in contact with, and between, theinput ring124 and theoutput ring126. An idler132 is placed between, and in contact with, theplanet balls130, and is analogous to thesun gear112 of the planetary gear set110. Thevariator106 operates as illustrated and described in U.S. Pat. No. 7,011,600.
• Cranks140 of a bicycle provide torque input into theplanet carrier120. Theplanet carrier120 rotates the planet gears114 about thesun gear112. Thering gear116 is fixed and the planet gears114 drive thesun gear112. Thering gear116 is fixed, and the planet gears114 drive thesun gear112. Theplanet carrier120 is connected to thecage142 of thevariator106. Thesun gear112 is connected to theinput ring124 via acam loader144, a set ofbearings146 andramps148 that generates axial force that is proportional to the amount of torque applied, although any axial force generating mechanism described in U.S. Pat. No. 7,011,600 or known or described in previous publications can be used. Therefore, in the illustrated embodiment, torque is supplied to the variator106 from both thesun gear112, via theinput ring124, and thecarrier120, via thecage142. Thevariator106 takes and sums the two torque inputs and varies the output speed to theoutput ring126 and out via anoutput sprocket150. The illustrated embodiment includes anoptional reaction sleeve152 to react the axial force generated as well as athrust bearing154 for reacting the axial thrust generated to clamp theinput ring124 and theoutput ring126 to theplanet balls130.
• In the embodiment illustrated inFIG. 2, a second embodiment is illustrated that also utilizes the planetary gear set110 as an input to thevariator106. In this embodiment, torque again is applied from thecranks140 to thecarrier120 and output through thesun gear112. In this embodiment, however, thecarrier120 is not attached to thecage142 and, therefore, torque is only input to thevariator106 through theinput ring124 while thecage142 is fixed to theframe102.
• Analternative transmission300 will now be described with reference toFIGS. 3-13D. Thetransmission300 can use components similar to those described above with reference to the embodiments of thetransmission100. However, the use of a similar or identical reference name for a component does not necessarily introduce into an embodiment (or aspect of the embodiment) any characterizations associated with a previously described embodiment.
• FIG. 3 is a perspective view of thetransmission300. In one embodiment (in a bicycle application, for example), power can be provided to thetransmission300 viacranks350, and power can be delivered out of thetransmission300 via asprocket348. Thetransmission300 can include acentral hub shell390 that, along withend caps302 and346, forms ahousing345 for most of the components of thetransmission300. In one embodiment, thehousing345 can be configured to be implemented on a bicycle frame, such as in the bottom bracket of the bicycle, for example. However, thetransmission300 can be used in any machine or vehicle where it is desired to adjust the ratio of input speed to output speed, or vice versa. That is, although various embodiments and features of the transmissions described herein are discussed with reference to a bicycle application, a person of ordinary skill in the relevant art will readily recognize modifications of and to thetransmission300, and features thereof, that can be used in any vehicle, machine, or device that uses a transmission to adjust the ratio of input to output speeds.
• ReferencingFIGS. 4A-4D now, an exemplary embodiment of certain assemblies and components of thetransmission300 will now be described. In one embodiment, thetransmission300 can include a set of planet-pivot-arm assemblies410 positioned between aninput traction ring330 and anoutput traction ring336. The planet-pivot-arm assemblies410 can include an array oftraction planets332 in contact with theinput traction ring330, theoutput traction ring336, and atraction sun333. Thetransmission300 can include aninput driver326 for operationally driving theinput traction ring330. Theoutput traction ring336 is configured to operationally driver theoutput driver340. Preferably, thetransmission300 includes aninput load cam328 positioned between theinput driver326 and thetraction ring330. The transmission preferably also includes anoutput load cam338 located between theoutput traction ring336 and theoutput driver340. In the embodiment illustrated, acage356 is provided to support and guide the planet-pivot-arm assemblies410, as well as to provide stiffness and/or rigidity to thetransmission300. It should be noted that the previous recitation of components of thetransmission300 can be expanded or reduced, and that enumerated members can be combined together and continue to perform their intended functions, without departing from the scope of present invention.
• Thecranks350 are coupled to provide torque to a crank shaft orcentral shaft360, which is generally positioned and supported in thehousing345 bybearings395. Thecentral shaft360 can also be configured to provide radial and axial support for certain assemblies of thetransmission300. For purposes of description, thecentral shaft360 defines a longitudinal axis of thetransmission300 that will serve as a reference point for describing the location and or motion of other components of thetransmission300. 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 thecentral shaft360. The terms “radial” and “radially” refer to locations or directions that extend perpendicularly from the longitudinal axis.
• In one embodiment, thecranks350 couple to a first stage planetary gear set via thecentral shaft360. The first stage planetary gear set includessun gear312, compoundplanetary gears310,carrier320, andring gear316. Thecentral shaft360 couples to thering gear316. Thecarrier320 is configured to receive and support, onplanetary gear axles318, the compound planetary gears310. In one embodiment, thecarrier320 is rotationally and axially fixed, and can be part of (or attached to) thehousing345.
• Thering gear316 drives the compoundplanetary gears310, which orbit around and drive thesun gear312. Theinput driver326 is coupled to and receives torque from thesun gear312. Theinput driver326 delivers torque via theinput load cam328 to theinput traction ring330, which transfers torque to the planet-pivot-arm assemblies410. Theoutput driver340 receives torque from the planet-pivot-arm assemblies410 via theoutput traction ring340 andoutput load cam338. Theoutput driver340 is coupled to and delivers torque to thesprocket348. Although a sprocket is used in this example, other embodiments of thetransmission300 can use a pulley, a freewheel, a cog, etc.
• In some embodiments, theinput traction ring330 and theoutput traction ring340 are substantially similar. Atraction ring330,340 preferably includes a traction surface for transmitting torque through frictional or hydroelastodynamic contact with thetraction planets332. In some embodiments, atraction ring330,340 can include ramps that form part of a load cam assembly (seeFIG. 10). The traction surface of thetraction ring330,340 can be inclined at about 45 degrees from vertical, which in this case refers to a plane surface extending radially.
• Acage356 includes aninput cage352 and an output cage354 (seeFIGS. 7A-7C), and circumscribes and supports the planet-pivot-arm assemblies410, as depicted inFIGS. 4A-4D. A planet-pivot-arm assembly410 can include atraction planet332. Thetraction planets332 are in contact with and are radially supported by thetraction sun333. An exemplary planet-pivot-arm assembly410 is depicted inFIG. 9. Thetraction sun333 can be a generally cylindrical tube. In some embodiments, thetraction sun333 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.
• A planet-pivot-arm assembly410 can havepivot arms380, which can be operationally coupled to a traction sun actuation device382 (see FIGS.4B and13A-13D). As will be discussed further below, the tractionsun actuation device382 can be used to translate axially thetraction sun333 when the speed ratio of thetransmission300 is adjusted. Thepivot arms380 can be coupled to ashift pin hub374 via hub pin fingers376 (seeFIG. 13A) and shift pins (not shown). Theshift pin hub374 can be used to actuate the planet-pivot-arm assembly410 in response to a shifting input. Shifting, or adjustment of the speed ratio, of the transmission will be further described below with reference toFIGS. 11A-12B.
• To handle axial reaction forces and provide a rolling contact between moving and stationary members of theCVT300, thrust bearings can be provide on either or both of the input and output ends of theCVT300. At the input side, generally referring to the area where thecentral shaft360 couples to thering gear316, an input thrust bearing is located between the stationary, first stageplanetary carrier320 and theinput driver326. The input thrust bearing, in the embodiment illustrated inFIG. 4, includes aninput bearing race322 that is received and supported in a recess of thecarrier320. The input thrust bearing also has a set ofrollers324 that can be positioned and supported by a roller retainer. Therollers324 can be balls, barreled rollers, asymmetrical rollers or any other type of rollers. In one embodiment, theinput driver326 is provided with an integral bearing race that cooperates with therollers324 and theinput bearing race322 to complete the input thrust bearing.
• On the output side, generally referring to the area where theoutput driver340 is located, an output thrust bearing can be positioned between theoutput driver340 and theend cap346, which can have a recess for receiving and support anoutput bearing race344. Thus, in this embodiment, theend cap346 helps to react the axial forces that arise in thetransmission300. The bearing races322,344 can be made of various bearing race materials such as steel, bearing steel, ceramic or any other material suitable for bearing races. The output thrust bearing includes a set ofrollers342 positioned and supported in roller retainer. In one embodiment, theoutput driver340 can have an integral bearing race that cooperates with theoutput bearing race344 and therollers342 to complete the output thrust bearing.
• ReferencingFIG. 5 now, in one embodiment, thehousing345 includes acentral hub shell390, aninput end cap302, and anoutput end cap346. In one embodiment, the end caps302,346 fasten to thecentral hub shell390 with fasteners (not shown); however, the ends cap302,346 can also thread into, or can otherwise be attached to thecentral hub shell390. Thecentral hub shell390 can be provided withinternal splines392 formed integral with the inside of thehub shell390 to engage withcomplimentary splines925 of thecage356. The end caps302,346 are generally flat discs, although either or both can have a curved shape or other configuration. As shown inFIG. 5, theend cap346 can be provided with arecess1405 adapted to receive and support theoutput bearing race344. The central bores of the end caps302,346 can be adapted to receive thebearings395 for providing positioning and rolling contact with respect to other components of thetransmission300. The end caps302 and346 can be made of, for example, aluminum, titanium, steel, high strength thermoplastics, or thermoset plastics. Depending on the embodiment, the end caps302 and346 are preferably made of a material suitable to provide rigidity and stiffness to thetransmission300, as well as to react the axial forces that arise in thetransmission300 during operation.
• Turning toFIGS. 6A-6B now, the first stageplanetary carrier320 can be adapted by machining, or formed as an integral piece, to be capable of axially and radially supporting the compoundplanetary gears310. Thecarrier320 includesbore holes605 adapted to secure and receive theplanetary shafts318. Thecarrier320 can includecavities610 and615 formed integral with thecarrier320 to receive the compoundplanetary gears310. Acentral bore620 of thecarrier320 can be configured to receive a bearing396, which serves to locate, and provide a rolling interface for, the input driver326 (seeFIG. 4B, for example). As previously mentioned, in some embodiments thatcarrier320 can be configured to form part of thehousing345 and/or to receive and support thebearing race322.
• Passing toFIGS. 7A-7C, acage356 can have two halves,input cage half352 andinput cage half354. In one embodiment, the cage halves352,354 can be substantially similar. Hence, the cage halves352,354 can be interchangeable. Is some embodiments, thecage356 is shaped to provide a stationary, reaction support structure for thepivot arms380; that is, thecage356 is configured to provide the angular alignment (about the longitudinal axis of the central shaft360) for the pivot arms380 (and consequently, the traction planet axles334) as thepivot arms380 pivot radially inward and outward about thetraction planets332 during shifting of the transmission ratio.
• In one embodiment, theslots915 of thecage356 guide the planet-pivot-arm assemblies410 along skew surfaces910 through contact with theskew rollers1220. The skew surfaces910 provide reaction surfaces for theskew rollers1220 as the planet-pivot-arm assemblies410 pivot or tilt inslot915 when the transmission ratio of theCVT300 is adjusted. In some embodiments, the corresponding slots ofcage halves352,354 are offset slightly in the angular direction, relative to one another, to reduce potential deleterious effects on shifting, for example, that can be caused by skewing (relative to a lateral axis) of the traction planet axles334 (seeFIG. 9A).
• Turning toFIGS. 8A and 8B now, in one embodiment, the planet-pivot-arm assembly410 can include atraction planet332, atraction planet axle334, and pivotarms380 having a slotted joint1210. The planet-pivot-arm assembly410 can also includeskew rollers1220, which are rolling elements attached to each end of apivot arm axle334 and provide for rolling contact of thetraction planet axle334 along skew surfaces910 of theinput cage352 andoutput cage354. The planet-pivot-arm assembly410 can includebearings374. Theskew rollers1220 and thebearings374 can be supported by thetraction planet axle334. Thetraction planet axle334 passes through a bore formed in the radially outward end of apivot arm380.
• In one embodiment, thepivot arms380 are machined with a curvature suitable to axially translate thetraction sun333 in reaction to a shift mechanism input. Thepivot arms380 can be provide with acam surface1230. As will be further described below with reference toFIGS. 13A-13D, the curvature of thecam surface1230 can be configured to produce a desired axial translation of thetraction sun333 during shifting of the transmission ratio.
• Thetraction planet axle334 can be a generally cylindrical shaft that extends through a bore formed through the center of thetraction planet332. In some embodiments, thetraction planet axle334 interfaces with the surface of the bore in thetraction planet332 via needle or radial bearings that align thetraction planet332 on thetraction planet axle334. Thetraction planet axle334 extends beyond the sides of thetraction planet332 where the bore ends so that thepivot arms380 can actuate a shift in the position of thetraction planet332. Where thetraction planet axle334 extends beyond the edge of thetraction planet332, it couples to the radial outward end of thepivot arms380. Thetraction planet axle334 passes through a bore formed in the radially outward end of thepivot arms380.
• In various embodiments, the interface between thetraction planets332 and thetraction planet axles334 can be any of the bearings described in other patents or publications. In some embodiments, thetraction planets332 are fixed to, and rotate with, theplanet axles334. In the embodiment ofFIG. 8A, thebearings374 are positioned between thetraction planet axles332 and thepivot arms380 such that the transverse forces acting on thetraction planet axles332 are reacted by thepivot arms380 as well as, or alternatively, thecage356. In some such embodiments, thebearings374 can be radial bearings (balls or needles), journal bearings, or any other type of bearings or suitable mechanism.
• Typically, traction- type transmissions use a clamping mechanism to prevent slippage between thetraction planets332 and the traction rings330,336 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. With reference toFIGS. 4A-4D and9, clamping force generation mechanisms that can be used with thetransmission300 will now be described.
• As mentioned above with reference toFIGS. 4A-4D, some embodiments of thetransmission300 preferably include aninput load cam328 and/or anoutput load cam338. The following discussion of aload cam700 applies equally to bothload cams328,338. In one embodiment, aload cam700 includesload cam rollers705 andramps710, which can be formed integral with a traction ring, such as input or output traction rings330 and336. Therollers705 can be supported and positioned in a suitable roller retainer, forexample roller retainer720. In some embodiments, atraction ring330,340 can includes about16ramps710, with eachramp710 having about a10 degree incline. In certain embodiments, theramps710 are helical and have a lead equivalent to about 55-66 mm over a 160-degree span. Theinput load cam328 includesrollers327 and ramps integral with theinput traction ring330, and the outputload cam assembly338 includesrollers337 and ramps integral with theoutput traction ring336. Therollers705,327,337 can be spherical, cylindrical, barreled, asymmetrical or other shape suitable for a given application.
• In some embodiments, theramps710 are provided on a ring that is fastened to theinput driver326 or to theinput traction ring330; alternatively, each of theinput driver326 and the input traction ring can be fitted with rings having theramps710. In some embodiments, theinput traction ring330 and theload cam assembly328 are an integral unit, effectively as when the ramps1610 are built into theinput traction ring330, and therollers705 androller retainer720 form a distinct assembly.
• During operation of thetransmission300, the first stageplanetary sun gear312 imparts torque to theinput driver326. Theinput driver326 transfers torque to theinput traction ring330 via theramps710, which can be integral with theinput traction ring330. As theinput driver326 rotates, theramps710 activate therollers705, which ride up theramps710. Therollers705 wedge in place, pressed between theramps705 and a surface of theinput driver326, and transmit both torque and axial force through theramps705 from theinput driver326 to theinput traction ring330. The axial force then clamps thetraction planets332 between theinput traction ring330, theoutput traction ring336, and thetraction sun333.
• Turning toFIGS. 10A-10C now, aninput driver326 can be a generallycircular plate552 with acentral bore554, which is adapted with a spline or other fastening device to engage thesun gear312. Theinput driver326 includes asurface556 that engages theload cam rollers327. Thesurface556 can be flat or can have load cam ramps, such as the ramps shown on the input traction ring330 (seeFIGS. 4B and 9, for example). In one embodiment, theinput driver326 includes abearing race558 that cooperates with theinput bearing race322 and therollers324 to provide the functionality of a thrust bearing for supporting axial loads and rolling contact between stationary and rotating components.
• ReferencingFIGS. 10D-10F now, anoutput driver340 can be a generallycircular plate560 having a central bore with aflange562, which is adapted to receivebearings395 and to engage with, for example, asprocket348. In another embodiment, theflange562 can be adapted to receive abearing391 that locates and supports theoutput end cap346. Theoutput driver340 includes asurface564 that is configured to engage theload cam rollers337. The surface546 can be flat or can have load ramps, such as the ramps shown (but not referenced) on theoutput traction ring336. In one embodiment, theoutput driver340 includes abearing race566 that cooperates with theoutput bearing race344 and therollers342 to provide the functionality of a thrust bearing, as discussed above with reference to theinput driver326. Thebearing race566 is located on a side of theoutput driver326 that is opposite to the side having thesurface564.
• ReferencingFIGS. 11A-12B now, the speed ratio of thetransmission300 can be adjusted using theshift screw370 and theshift pin hub374. In one embodiment, ashift wheel375 can be used to drive theshift screw370. Theshift wheel375 can be, for example, a pulley or a compound gear adapted to be actuated by a linear actuator such as a cable or a chain (not shown). Thehousing345 can be suitably adapted to allow the linear actuator to access theshift wheel375.
• Theshift pin hub374 is coupled to thepivot arms380 by shift pins (not shown) that fit in thefingers376 and in theshift pin hole1212 of the pivot arms380 (seeFIGS. 8A-8B). Thefingers376 are configured to fit in the slot1280 of thepivot arms380. Theshift pin hub374 is provided with a threadedend580, in one embodiment, to allow theshift screw370 to actuate theshift pin hub374 via correspondingshift screw threads1005 of theshift screw370.
• Theshift screw370 can mount coaxially with and is rotatable about thecentral shaft360. In one embodiment, theshift screw370 can be axially constrained by thesun gear312 and thering gear316. Suitable thrust bearings can be positioned between theshift screw370 and, respectively, thesun gear312 and the ring gear316 (seeFIG. 4B, for example). In one embodiment, theshift screw370 includes ashift screw flange1010 adapted to couple to theshift wheel375.
• To adjust the speed ratio of thetransmission300, a shift input is provided by the linear actuator (chain, cable, etc.) to theshift wheel375, which rotates theshift screw370. Theshift screw threads1005 engage the shiftpin hub threads580, and since theshift screw370 is constrained axially at the same time that theshift pin hub374 is constrained rotationally, theshift screw370 causes theshift pin hub374 to move axially. The axial translation of theshift pin hub374 causes thepivot arms380 to pivot on the pivot pins (not shown) coupling the shiftpin hub fingers376 and thepivot arms380. Thepivot arms380 pivot about the centers of theplanets332. Because thepivot arms380 are coupled to thetraction planet axles334, the pivoting of thepivot arms380 causes thetraction planet axles334 to tilt radially inward or outward, which results in a change in the relative point of contact between thetraction planets332 and, respectively, theinput traction ring330 and theoutput traction ring336. This change the relative point of contact between thetraction planets332 and the traction rings330,336 results in a change in the speed ratio of thetransmission300.
• In some embodiments, it is preferable that thetraction sun333 translate axially as thepivot arms380 tilt thetraction planet axles334. Translation of thetraction sun333 can be accomplished by a tractionsun actuation device382, which in one embodiment is positioned between thetraction sun333 and thepivot arms380. In one embodiment, the tractionsun actuation device382 includescam rollers1805 adapted to engage thecam surface1230 of thepivot arms380. Thecam rollers1805 can be supported and positioned on camroller support ring1810 havingsupport extensions1812. To react and transfer axial forces, an angular contact thrust bearing is positioned between thesupport ring1810 and thetraction sun333. In the embodiment illustrated inFIGS. 13A-13D, abearing race1811 is integral with thesupport ring1810, abearing race1825 is suitably coupled or affixed to thetraction sun333, and a set of bearingrollers1820 is supported and positioned by a bearingroller retainer1815. In some embodiments, a tractionsun actuation device382 can be provided for each of end of thetraction sun333, as illustrated inFIGS. 4A-4D.
• As thepivot arms380 pivot about theplanets332, thecam surface1230 of thepivot arms380 acts on thecam rollers1805, which transfer an axial force to the camroller support ring1810. Thecam rollers1805 are provided withflanges1807 to engage thepivot arms380, and thereby thesupport ring1810 is constrained from rotation about thecentral shaft360. Thesupport ring1810 then transfers the axial force to thetraction sun333 via thebearing race1810, bearing rollersl820, andbearing race1825. As will be discussed further below, the curvature or profile of thecam surface1230 determines the relative speed between the speed of axial translation of thetraction sun333 vis-à-vis the speed of change of the tilt of thetraction planet axles334.
• The profile of theshift cam surface1230 usually varies according to the location of the contact point between thetraction sun333 and thetraction planets332, as well as the desired amount of relative axial motion between thetraction planets332 and thetraction sun333. The profile of thecam surface1230 can be such that axial translation of thetraction sun333 relative to thetraction planets332 is proportional to the change of the tilt of the traction planets axles334. The angle of tilt of thetraction planet axles334 is referred to herein as “gamma.” The applicant has discovered that controlling the axial translation of thetraction sun333 relative to the change in gamma influences CVT ratio control forces. For example, if the axial translation of thetraction sun333 is linearly proportional to a change in gamma, the normal force at thecam surface1230 and thecam roller1805 is generally parallel to thetraction planet axles334. This enables an efficient transfer of a shift moment about thetraction planets332 to horizontal shift forces that translate thetraction sun333.
• A linear relation between translation of thetraction sun333 and gamma change is given as translation of thetraction sun333 is the mathematical product of the radius of theplanets332, the gamma angle and RSF (that is, translation oftraction sun333=ball radius*gamma angle*RSF), where RSF is a roll-slide factor. RSF describes the transverse creep rate between thetraction planets332 and thetraction sun333. 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 operation, thetraction planet332 and thetraction sun333 on each other. When thetraction sun333 is translated axially (that is, orthogonal to the rolling direction), transverse creep is imposed between thetraction sun333 and thetraction planets332. An RSF equal to 1.0 indicates pure rolling. At RSF values less than 1.0, thetraction sun333 translates slower than thetraction planet332 rotates. At RSF values greater than 1.0, thetraction sun333 translates faster than thetraction planet332 rotates.
• A process for defining a profile for thecam surface1230 for any variation of transverse creep and/or location of the interface between thetraction sun333 and thepivot arm380 andcam roller1805. 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 profile for thecam surface1230. The curve is then used to generate models of thecam surface1230. 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 thecam rollers1805 on each side of thetraction sun333. The equations for x and y are parametric. “LEG” and “ARM” define the position of the interface between thepivot arm380,cam roller1805, andtraction sun333. More specifically, LEG is the perpendicular distance between the longitudinal axis of thetraction planet axle334 to a line that passes through the centers of the twocorresponding cam rollers1805. ARM is the distance between centers of thecam rollers1805 on either side of thetraction sun333.
• RSF values above zero are preferred. 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. 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 thetraction planet332 and the size of thetraction sun333, as well as the location of thecam roller1805.
• Linear axial translation of thetraction sun333 relative to gamma is not the only desired relation. Hence, for example, if it is desired that the translation of thetraction sun333 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 the position of thetraction sun333 and CVT ratio is linearly proportional. This is a desirable feature for some types of control schemes.
• It should be noted that while several embodiments have been described above that implement a continuously variable variator in conjunction with a planetary gear set for a bicycle transmission, in other embodiments the planetary gear set is not used. Rather, the crankshaft can be directly, or through a load cam assembly, coupled to theinput driver326 or theinput traction ring330 of the variator.
• Turning toFIGS. 14A-14C now, ashift actuator1 can be provided to actuate theshift wheel375. As shown, theend cap302 and/or theplanetary gearset carrier320 can be adapted to allow theshift actuator1 to engage theshift wheel375. Theend cap302 can have, for example, holes2 that allow theshift actuator1 to enter and exit thehousing345. In one embodiment, thecarrier320 supports the shift wheel375 (on an axle or pin that is not shown) and, hence, thecarrier320 can be provided withholes3 that allow theshift actuator1 to pass into and out of thecarrier320 to access theshift wheel375. Theshift actuator1 can be, for example, a shift cable, wire, belt, etc. If theshift wheel375 is a gear with teeth, theshift actuator1 can be a chain, for example. It will be obvious to a person of ordinary skill in the relevant technology that other shift actuators can be used to control theshift wheel375.
• 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.

Claims (24)

1.-14. (canceled)

15. A bicycle comprising:

a crankshaft;

a rotatable planetary gear set carrier coupled to the crankshaft;

a plurality of planet gears coupled to said carrier;

a ring gear, rotationally constrained, coupled to the planet gears;

a sun gear coupled to the planet gears;

a first traction ring operationally coupled to the sun gear;

a plurality of traction planets coupled to the traction ring; and

a second traction ring coupled to the traction planets.

16. The bicycle ofclaim 15, further comprising a cage coupled to the crankshaft and adapted to transfer power to the traction planets.

17. The bicycle ofclaim 16, wherein the traction planets are spherical rollers.

18. The bicycle ofclaim 15, further comprising an axial force reaction sleeve.

19. The bicycle ofclaim 15, further comprising an axial thrust bearing.

20. The bicycle ofclaim 15, further comprising a traction sun.

21. The bicycle ofclaim 15, further comprising at least one load cam assembly.

22. The bicycle ofclaim 21, wherein the load cam assembly comprises load cam rollers and ramps.

23. A bicycle comprising:

a crankshaft;

a rotatable planetary gear set carrier coupled to the crankshaft;

a plurality of planet gears coupled to said carrier;

a ring gear, rotationally constrained, coupled to the planet gears;

a sun gear coupled to the planet gears;

a first traction ring operationally coupled to the sun gear and coaxially mounted about the crankshaft;

a plurality of traction planets coupled to the traction ring; and

a second traction ring coupled to the traction planets and coaxially mounted about the crankshaft.

24. The bicycle ofclaim 23, further comprising a cage rigidly coupled to members of the frame of the bicycle, the cage configured to support the plurality of traction planets axially and radially.

25. The bicycle ofclaim 23, further comprising a housing that is integral with the frame members of the bicycle.

26. A bicycle transmission comprising:

a planetary gear set configured for coupling to a crankshaft of a bicycle and to be mounted coaxially about said crankshaft; and

a continuously variable variator coupled to said planetary gearset configured to be mounted coaxially about said crankshaft.

27. The bicycle transmission ofclaim 26, wherein the transmission is configured to be mounted on frame members of the bicycle.

28. The bicycle transmission ofclaim 27, wherein the transmission is mounted forward of the rear wheel.

29. The bicycle transmission ofclaim 28, wherein the transmission is mounted on the bottom bracket of the bicycle.

30. The bicycle transmission ofclaim 26, wherein the crankshaft is coupled to a carrier of the planetary gearset.

31. The bicycle transmission ofclaim 26, wherein the crankshaft is coupled to a ring gear of the planetary gearset.

32. The bicycle transmission ofclaim 26, wherein the ring gear of the planetary gearset is constrained rotationally.

33. The bicycle transmission ofclaim 26, wherein the crankshaft is coupled to a cage of the variator.

34. The bicycle transmission ofclaim 26, wherein a sun gear of the planetary gearset is coupled to an input driver of the variator.

35. The bicycle transmission ofclaim 26, wherein a carrier of the planetary gearset is constrained rotationally.

36. The bicycle transmission ofclaim 26, wherein a cage of the variator is rigidly coupled to the frame members of the bicycle.

37-50. (canceled)

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