Pulley for a continuously variable transmission
A pulley for a continuously variable transmission is provided with a fixed half-pulley fitted on a supporting shaft and a mobile half-pulley, which is able to slide towards the fixed half-pulley under the thrust of a spring, so as to define a V-shaped race of variable amplitude. The pulley is further provided with a device for compensating the axial thrust, said device being constituted by a cam and a cam follower, which are coupled in contact with one another to impart an additional axial thrust on the mobile half-pulley in response to a torque acting on the pulley. The cam is defined by a tubular body made of plastic material co-moulded on the supporting shaft, whilst the cam follower is made of a single piece with the mobile half-pulley.
1. A pulley for a continuously variable transmission, the pulley comprising:
a supporting shaft;
a fixed half-pulley, wherein the fixed half-pulley is coaxial and fixed to said supporting shaft;
a mobile half-pulley, wherein the mobile half-pulley is coaxial to said supporting shaft and is slidable with respect to said fixed half-pulley, the fixed and mobile half-pulleys defining a race of variable amplitude and the race being engageable by a belt of a drive; and
a device for compensating the axial thrust, the device comprising a first cam and a second cam, wherein said fixed half-pulley and said mobile half-pulley are rigidly connected to the first cam and the second cam respectively, said first and second cam being in contact with one another to impart an additional axial thrust on said mobile half-pulley in a direction of compression of said belt in response, in use, to a torque acting on said pulley; wherein said fixed half-pulley is fixed to said supporting shaft, and wherein said first cam is defined by a single tubular body made of plastic material co-moulded on said supporting shaft, said body being made of plastic material forming a supporting bushing on which said mobile half-pulley is slidably fitted.
2. The pulley according to claim 1 , wherein said second cam comprises a cam-follower portion made of a single piece with said mobile half-pulley.
3. The pulley according to claim 2 , wherein the mobile half-pulley and said cam-follower portion are made of aluminium.
4. The pulley according to claim 1 , wherein said supporting bushing is made of a self-lubricating material.
5. The pulley according to claim 1 , wherein said mobile half-pulley is coupled to said fixed half-pulley with radial play.
6. The pulley according to claim 1 , further comprising:
an elastic element axially pre-loaded for pushing said mobile half-pulley towards said fixed half-pulley; and a positioning device for pre-loading torsionally said elastic element.
7. The pulley according to claim 6 , wherein the positioning device further comprises an adjustment device for varying the torsional pre-loading of said elastic element.
8. The pulley according to claim 7 , wherein the adjustment device is carried by an element of axial pre-loading of said elastic element.
9. The pulley according to claim 8 , wherein the element of axial pre-loading includes a ring of holes and the elastic element comprises a helical spring; the ring of holes being set at an angular distance apart from one another and selectively engageable by one end of said helical spring.
10. The pulley according to claim 1 , wherein the pulley further comprises at least one retention seat made in one of said supporting shaft or said body made of plastic material, and at least one appendage, which is carried by the other one of said supporting shaft or said body made of plastic material and engages said retention seat.
11. The pulley according to claim 1 , further comprising a spacer ring carried by one of said half-pulleys and fitted to a front surface thereof in a position radially internal with respect to said race and facing the other of said half-pulleys.