Driving pulley of a continuously variable transmission
The driving pulley has a fully clutched mode of operation where a drivebelt and a driveshaft are coupled together in a torque transmitting engagement and also has an unclutched mode of operation where there is substantially no torque transmitting engagement between the drive belt and the driveshaft. The driving pulley comprises at least one transitional clutch spring that is in a first position when the driving pulley is in the unclutched mode of operation and that is in a second position when the driving pulley is in the fully clutched mode of operation. The at least one transitional clutch spring remains substantially in its second position regardless of the relative axial distance between the sheaves when the driving pulley is in the fully clutched mode of operation. A method of operating a driving pulley is also disclosed. The proposed concept provides a smoother engagement during the transition from the unclutched mode to the fully clutched mode.
1. A driving pulley for a continuously variable transmission, the driving pulley having a fully clutched mode of operation where a drivebelt and a driveshaft are coupled together in a torque transmitting engagement and having an unclutched mode of operation where there is substantially no torque transmitting engagement between the drivebelt and the driveshaft, the driving pulley being rotatable about a rotation axis and comprising:
a first and a second sheave coaxially disposed with reference to the rotation axis, the sheaves having mutually-facing conical walls defining a drivebelt-receiving groove, the drivebelt-receiving groove having a variable width depending on a relative axial distance between the first and the second sheave;
an actuation mechanism having one side axially movable within a range of axial positions, the relative axial distance between the two sheaves being selected by moving the side of the actuation mechanism within at least a portion of its axial position range and the driving pulley being set in one among the fully clutched mode of operation and the unclutched mode of operation depending on the axial position of the side of the actuation mechanism; and
at least one transitional clutch spring being in a first position when the driving pulley is in the unclutched mode of operation and being in a second position when the driving pulley is in the fully clutched mode of operation, the at least one transitional clutch spring remaining in its second position and substantially in a same compression state regardless of the relative axial distance between the sheaves when the driving pulley is in the fully clutched mode of operation; and wherein when the at least one transitional clutch spring is in the same compression state, the distance between the side of the actuation mechanism and the second sheave remains substantially the same and the actuation mechanism is what moves the second sheave relative to the first sheave.
2. The driving pulley as defined in claim 1 , characterized in that the at least one transitional clutch spring generates a greater axial return force at its second position than that at its first position.
3. The driving pulley as defined in claim 1 , characterized in that a selection between the fully clutched mode of operation and the unclutched mode of operation of the driving pulley is provided by a friction engagement between at least two components, at least one of these components being a component of the driving pulley.
4. The driving pulley as defined in claim 3 , characterized in that the components providing the friction engagement include the conical walls of the sheaves, the distance between the sheaves being wider than a drivebelt width when the driving pulley is in the unclutched mode of operation.
5. The driving pulley as defined in claim 3 , characterized in that the components providing the friction engagement include at least two selectively-engagable contact surfaces, at least one of these surfaces being on a back side of one of the sheaves and at least another one of the contact surfaces being rigidly connected to the driveshaft, the contact surfaces being axially movable relative to another one of the contact surfaces.
6. The driving pulley as defined in claim 5 , characterized in that the first and the second sheaves are mounted on a hub, the hub having an inner portion configured and disposed to receive the driveshaft therein.
7. The driving pulley as defined in claim 6 , characterized in that the components providing the friction engagement include four contact surfaces, one being provided on the back side of the first sheave and forming a first pair of contact surfaces with a corresponding one of the other contact surfaces, another one of the contact surfaces being provided on the back side of the second sheave and forming a second pair of contact surfaces with a corresponding one of the other contact surfaces.
8. The driving pulley as defined in claim 7 , characterized in that at least one of the contact surfaces of each pair comprises a friction pad.
9. The driving pulley as defined in claim 8 , characterized in that the at least one transitional clutch spring has one side connected to the friction pad.
10. The driving pulley as defined in claim 1 , characterized in that the at least one transitional clutch spring includes at least one annular spring.
11. The driving pulley as defined in claim 10 , characterized in that the at least one annular spring is fully compressed when the driving pulley is in a fully clutched mode of operation.
12. A method of operating a driving pulley in a continuously variable transmission, the driving pulley being operatively mounted to a driveshaft and receiving a drivebelt between opposite first and second sheaves that are coaxially disposed with reference to a rotation axis, the sheaves having mutually-facing conical walls defining a drivebelt-receiving groove, the drivebelt-receiving groove having a variable width depending on a relative axial distance between the first and the second sheave, the method comprising: bringing the driving pulley from an unclutched mode of operation towards a fully clutched mode of operation using an actuation mechanism having one side axially movable within a range of axial positions, the relative axial distance between the two sheaves being selected by moving the side of the actuation mechanism within at least a portion of its axial position range and the driving pulley being set in one among the fully clutched mode of operation and the unclutched mode of operation depending on the axial position of the side of the actuation mechanism, the drivebelt being substantially out of a torque transmitting engagement with the driveshaft in the unclutched mode of operation and being in a torque transmitting engagement with the driveshaft in the fully clutched mode of operation; mitigating an axial impact during a transition from the unclutched mode of operation to the fully clutched mode of operation by compressing at least one clutch spring in the driving pulley; and operating the driving pulley in the fully clutched mode of operation while the at least one clutch spring remains substantially in a same compression state; wherein when the at least one transitional clutch spring is in the same compression state, the distance between the side of the actuation mechanism and the second sheave remains substantially the same and the actuation mechanism is what moves the second sheave relative to the first sheave.
13. The method as defined in claim 12 , characterized in that bringing the driving pulley from the unclutched mode of operation towards the fully clutched mode of operation includes decreasing an axial distance between the sheaves and increasing the friction engagement between the sheaves and the drivebelt.
14. The method as defined in claim 12 , characterized in that bringing the driving pulley from the unclutched mode of operation towards the fully clutched mode of operation includes decreasing an axial distance between a plurality of contact surfaces, the decrease of the axial distance increasing the friction engagement between the contact surfaces.
15. The method as defined in claim 14 , characterized in that the method includes keeping the sheaves and the drivebelt in a friction engagement during the unclutched mode of operation.
16. The method as defined in claim 12 , characterized in that the at least one clutch spring includes an annular spring.