Continuously variable transmission
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.
1. A shifter for facilitating the adjustment of a transmission ratio of a continuously variable transmission (CVT) having a plurality of shift pins, the shifter comprising:
a shift screw having a first set of threads and a surface for engaging a shifter actuator;
a shift pin hub having a second set of threads and a plurality of fingers, the fingers configured to engage the plurality of shift pins, wherein the first and second set of threads are configured such that a rotation of the shift screw causes an axial translation of the shift pin hub; and
a pivot arm assembly coupled to the shift pin hub, wherein the pivot arm assembly comprises
a substantially u-shaped body having one or more pivot arms, wherein distal ends of the pivot arms are configured to receive ends of a traction planet axle,
a slot configured to receive at least one of the plurality of fingers of the shift pin hub to form a slotted joint, and
a through hole in the u-shaped body receiving one of the plurality of shift pins.
2. The shifter of claim 1 , wherein the pivot arm assembly comprises a planet axle.
3. The shifter of claim 2 , wherein the axial translation of the shift pin hub causes a tilting of the planet axle.
4. The shifter of claim 1 , further comprising a cage coupled to the pivot arm assembly.
5. The shifter of claim 4 , wherein the cage comprises a plurality of skew surfaces.
6. The shifter of claim 1 , wherein the pivot arm assembly comprises a cam surface formed into the one or more pivot arms.
7. The shifter of claim 6 , wherein the cam surface is operably coupled to a traction sun of the CVT.
8. The shifter of claim 1 , wherein
the shift pin hub comprises a substantially hollow cylindrical body having a first end and a second end, the plurality of fingers formed on the first end, the second set of threads formed on the second end and adapted to couple to the shift screw.
9. The shifter of claim 8 , wherein at least one of the plurality of fingers of the shift pin hub comprises a slot extending radially from the cylindrical body.
10. The shifter of claim 8 , wherein the cylindrical body of the shift pin hub is adapted to axially translate.
11. The shifter of claim 1 , wherein
the slot is formed on the u-shaped body between the one or more pivot arms, and wherein
the through hole is perpendicular to the slot.
12. The shifter of claim 1 , wherein the u-shaped body comprises an inner periphery having a cam surface.
13. The shifter of claim 12 , wherein the cam surface is operably coupled to a traction sun to produce an axial translation of the traction sun.
14. The shifter of claim 13 , wherein the cam surface is adapted to transfer an axial force to a cam roller support ring of the CVT.
15. The shifter of claim 12 , wherein the cam surface comprises a profile defined at least in part by a radius of a traction planet of the CVT.
16. The shifter of claim 12 , wherein the profile is defined at least in part by a roll-slide factor (RSF).
17. The shifter of claim 16 , wherein the RSF is in the range of 1 to 2.5.