Driving pulley for a continuously variable transmission
The driving pulley comprises two centrifugal mechanisms, namely a positive assembly and a negative assembly. Both assemblies comprise a respective set of flyweights subjected to the centrifugal force when the driving pulley rotates. The positive assembly is used as a conventional speed governor that moves one of the two flanges of the driving pulley towards the other in order to increase its winding diameter when the rotation speed increases. The negative assembly is used to apply an opposite force on the positive assembly when the rotation speed is above a threshold value so as to defer the upshift of the CVT to a higher ratio under the action of the positive assembly. This allows to maintain, for instance, a high rotation speed during an intense acceleration and a lower rotation speed when cruising at low vehicle speeds.
1. A driving pulley for a continuously variable transmission, the driving pulley being coaxially mountable around a main shaft and rotatable at a variable rotation speed, the driving pulley comprising:
a first flange having opposite first and second sides, the first side being provided with a conical wall;
a second flange coaxial with the first flange and having a conical wall facing the conical wall of the first flange to form a drivebelt-receiving groove around which a drivebelt is wound, the second flange being axially movable with reference to the first flange;
first means for connecting the first flange to the main shaft in a torque-transmitting engagement;
second means for connecting the second flange to the main shaft in a torque-transmitting engagement;
a positive assembly comprising:
a positive carriage coaxial with the first flange and rigidly connected to the second flange;
third means for connecting the positive carriage to the main shaft in a torque-transmitting engagement;
at least two symmetrically-disposed pairs of radially-converging and mutually-opposite first ramps, each pair having one ramp connected to the positive carriage and another ramp connected to the second side of the first flange; and
radially-movable flyweights, each set between a corresponding pair of first ramps;
fourth means for generating a return force urging the second flange to move away from the first flange;
a negative assembly comprising:
a negative carriage coaxial and axially movable with reference to the first flange, the negative carriage being configured and disposed to be in engagement with the positive carriage;
fifth means for connecting the negative carriage to the main shaft in a torque-transmitting engagement;
at least two symmetrically-disposed pairs of radially-converging and mutually-opposite second ramps, each pair having one ramp connected to the negative carriage and another ramp connected to an end plate fixed with reference to the first flange;
sixth means for connecting the end plate to the main shaft in a torque-transmitting engagement; and
radially-movable flyweights, each set between a corresponding pair of second ramps; and
seventh means for generating a return force urging the negative carriage away from the first flange.
2. A driving pulley according to claim 1 , wherein the first means comprise a hollow drum coaxially disposed around the main shaft, the drum having one end rigidly connectable to the main shaft and a second end rigidly connected to the second side of the first flange.
3. A driving pulley according to claim 2 , wherein the third means comprise a plurality of pairs of radially-projecting cam followers and corresponding axially-extending slots, each pair having one among the cam follower and the slot located on the positive carriage and having the other located on the drum.
4. A driving pulley according to claim 3 , wherein the cam followers are rollers.
5. A driving pulley according to claim 1 , wherein the second means comprise an axially slidable sleeve coaxially mounted around the main shaft, the sleeve rigidly connecting together the second flange and the positive carriage.
6. A driving pulley according to claim 1 , wherein the fourth means comprise a spring mounted between the positive carriage and the negative carriage.
7. A driving pulley according to claim 1 , wherein the fifth means comprise a plurality of pairs of radially-projecting cam followers and corresponding axially-extending slots, each pair having one among the cam follower and the slot located on the negative carriage and having the other located on the drum.
8. A driving pulley according to claim 7 , wherein the cam followers are rollers.
9. A driving pulley according to claim 2 , wherein the end plate is a portion of the drum.
10. A driving pulley according to claim 9 , wherein the seventh means comprise a spring having one end connected to the drum and other end connected to the negative assembly.
11. A driving pulley according to claim 1 , further comprising means for limiting the movement of the negative carriage with reference to the positive carriage.
12. A driving pulley according to claim 11 , wherein the means for limiting the movement of the negative carriage comprise at least one stopper set between an upper part of the negative carriage and a location fixed with reference to the first flange.