Continuously variable transmission
View Patent ↗A variable speed transmission having a plurality of tilting balls and opposing input and output discs is illustrated and described that provides an infinite number of speed combinations over its transmission ratio range. The use of a planetary gear set allows minimum speeds to be in reverse and the unique geometry of the transmission allows all of the power paths to be coaxial, thereby reducing overall size and complexity of the transmission in comparison to transmissions achieving similar transmission ratio ranges.
1. A power transfer apparatus comprising:
a planetary gearset mounted on a shaft, the shaft defining a longitudinal axis;
a variator comprising: a plurality of balls, each ball having a tiltable axis about which it rotates;
a first disc in contact with the balls; a second disc in contact with the balls; an idler in contact with the balls; and
one or more shift guide sleeves operationally coupled to the idler; wherein the variator is mounted coaxially with the planetary gearset along the longitudinal axis; and wherein the planetary gearset is operationally coupled to the variator.
2. The apparatus of claim 1 , wherein the first or second disc is nonrotatable.
3. The apparatus of claim 1 , wherein the idler is nonrotatable.
4. The apparatus of claim 1 , further comprising a shifting mechanism that shifts the transmission by axially moving the one or more guide sleeves.
5. The apparatus of claim 1 , wherein the planetary gearset comprises:
a ring gear mounted coaxially about the longitudinal axis;
a plurality of planet gears in engagement with the ring gear, each planet gear having a planet shaft about which the planet gear rotates;
a sun gear mounted coaxially about the longitudinal axis and in engagement with the planet gears; and
a planet carrier mounted coaxially about the longitudinal axis and adapted to support and position the planet shafts.
6. The apparatus of claim 5 , wherein the planet carrier is operationally coupled to a drive shaft.
7. The apparatus of claim 6 , wherein the drive shaft receives an input torque from a sprocket, gear, or crank that is operationally coupled to a prime mover.
8. The apparatus claim 5 , further comprising a cage adapted to align the tiltable axes of the balls and to maintain the angular and radial positions of the balls.
9. The apparatus of claim 8 , wherein the cage is nonrotatable.
10. The apparatus of claim 8 , wherein the cage is adapted to rotate about the longitudinal axis.
11. The apparatus of claim 8 , wherein the idler or the cage provides a torque input to the planetary gearset.
12. The apparatus of claim 8 , wherein the planet carrier receives an input torque and is coupled to the first disc, wherein the sun gear is coupled to the cage, wherein the ring gear is fixed and does not rotate, and wherein the apparatus supplies an output torque via the second disc.
13. The apparatus of claim 5 , further comprising a force generator adapted to generate an axial force that increases the traction between the first and second discs, the balls, and the idler.
14. The apparatus of claim 13 , wherein the force generator produces an amount of axial force that is a function of a transmission ratio of the apparatus.
15. The apparatus of claim 1 , further comprising a shaft operationally connected to the idler and adapted to receive a torque from the idler and to transmit the torque out of the apparatus.
16. The apparatus of claim 1 , further comprising a force generator that comprises:
a third disc having a threaded bore;
a first set of ramps operably coupled to the third disc near an outer diameter of the third disc;
a plurality of bearings adapted to engage the first set of ramps; and
a second set of ramps, the second set of ramps operably coupled to the first disc and adapted to engage the bearings.
17. The apparatus of claim 16 , the force generator further comprising:
a rotatable screw adapted to engage the threaded bore;
a third set of ramps, the third set of ramps operably coupled to the screw; and
a fourth set of ramps, the fourth set of ramps operably coupled to the first disc and adapted to engage the third set of ramps.
18. The apparatus of claim 17 , the force generator further comprising:
a thrust bearing contacting the screw; and
a linkage assembly adapted to apply a force to the thrust bearing tending to move the screw away from the first disc in response to a shift in the transmission ratio.
19. The apparatus of claim 18 , wherein in response to a shift in the transmission ratio the linkage assembly varies the axial force applied to the thrust bearing as a function of the transmission ratio.