Filtering pulley for a belt drive
A filtering pulley for an accessory drive of an internal combustion engine, having a hub suitable for connection to an engine accessory, an annular crown provided with a profile configured to cooperate with a drive belt, a coil spring able to transmit torque between the crown and the hub, a first carrier constrained to a first end of the spring and a second carrier constrained to a second end of the spring. The annular crown is externally coaxial to the hub and supported in a rotationally free manner on the hub, and each of the carriers is rotationally coupled to both the hub and the crown with a limited possibility of relative rotation with respect to each of them.
1. A filtering pulley for an accessory drive of an internal combustion engine, comprising:
a hub,
an annular crown provided with a profile configured to cooperate with a drive belt, externally coaxial to the hub and supported in a rotationally free manner on the hub, and
a filtering unit interposed between the hub and the crown and comprising;
a coil spring able to transmit torque between the crown and the hub,
a first carrier constrained to a first end of the spring; and
a second carrier constrained to a second end of the spring,
wherein each of said first and second carriers are fitted in a freely rotational manner to both the hub and the crown with an angular play with respect to the hub and the crown.
2. A pulley according to claim 1 , characterized in that the ends of the spring are constrained to the respective carriers to prevent slipping off by way of relative rotation.
3. A pulley according to claim 1 , characterized in that said carriers are supported on said hub and are housed within said crown.
4. A pulley according to claim 1 , characterized in that rotational coupling between each of the carriers, the hub and the crown is obtained by at least one projection carried by each carrier and respective stops carried by the hub and by the crown.
5. A pulley according to claim 1 , characterized in that rotational coupling between each of the carriers, the hub and the crown is obtained by at least respective projections carried by the hub and by the crown and at least a stop carried by each carrier.
6. A pulley according to claim 1 , characterized in that rotational coupling between each of the carriers, the hub and the crown is obtained by at least one projection carried by the carrier and at least corresponding projections carried by the crown and by the hub.
7. A pulley according to claim 6 , characterized in that said projections carried by the hub and by the crown are configured so as not to directly interact with each other during the relative rotation between the hub and the crown.
8. A pulley according to claim 6 , characterized in that the projections of said carriers extend in the axial direction, and that the projections carried by the hub and by the crown are radial, the projections of said carriers being configured so as to cooperate with both a corresponding projection of the crown and a corresponding projection carried by the hub.
9. A pulley according to claim 8 , characterized in that each carrier comprises a pair of projections arranged at 180°, corresponding pairs of projections being carried by the hub and by the crown.
10. A pulley according to claim 9 , characterized in that said projections carried by the crown are integral with the crown, and that at least one of the projections carried by the hub is integral with a drive ring fitted on the hub.
11. A pulley according to claim 9 , characterized in that said projections carried by the crown are integral with the crown, and that at least one of the projections carried by the hub is integral with a drive ring fitted on the hub, wherein said filtering unit comprises a damping assembly that comprises an element integral with the hub, an element integral with the crown and elastic means acting on one of said elements to keep said elements in axial contact with one another so as to slide following a relative rotation between said hub and said crown, and said element integral with the hub is said drive ring.
12. A pulley according to claim 1 , characterized in that said filtering unit comprises a damping assembly interposed between said crown and said hub.
13. A pulley according to claim 12 , characterized in that said damping assembly comprises an element integral with the hub, an element integral with the crown and elastic means acting on one of said elements to keep said elements in axial contact with one another so as to slide following a relative rotation between said hub and said crown.
14. A pulley according to claim 1 , characterized in that said coil spring has a winding direction such that the wire is always stressed in compression, both when the crown tends to overtake the hub and when the hub tends to overtake the crown.