Filtering pulley

1. A filtering pulley comprising;

a hub adapted to be fixed to a rotating shaft, the hub having a first portion and a second portion,

a ring assembled coaxial and rotationally free on a first portion of said hub, wherein the ring carries a closing element that has an annular flange seated inside the ring and an opposing annular flange extending away from the ring;

a disc seated axially interposed between the first portion and second portion of said hub;

an actuator axially interposed between the first portion of said hub and said disc, wherein the actuator extends radially beyond a gap formed between said opposing annular flange of said closing element and said disc;

a dust seal seated in said gap in a sealing engagement with said opposing annular flange of said closing element and with said disc; and

at least one elastic assembly arranged circumferentially with respect to said hub and to said ring and each interposed between a pair of first elements integral with said actuator which rotates with said hub and between a pair of second elements integral with said ring,

characterized in that said at least one elastic assembly comprises a first wire coil spring having a progressive rigidity from a minimum initial end value at both of a first end and a second end thereof according to a parabolic trend with a maximum value between the first and second ends, wherein the progressive rigidity increases from a predetermined threshold value of the angle of relative rotation between said hub and said ring, and, as graphically represented by force (F) versus extension of the spring (X), has a continuously increasing value having a first rectilinear portion and then a second portion where K increases exponentially; and

wherein each at least one elastic assembly forms with said first elements and with said second elements respective angular clearances (σ, α), said ring and said hub-having a free angle (β) of relative rotation equal to the sum of said angular clearances (σ, α).

2. The pulley according to claim 1 , wherein said progressive rigidity of the wire coil spring is a variation of at least one between the pitch and the section of the wire along the length of said spring.

3. The pulley according to claim 1 , wherein said elastic assembly comprises a second spring mutually coaxial with and positioned inside the first wire coil spring.

4. The pulley according to claim 1 , wherein said at least one elastic assembly comprises an anti-warping device.

5. The pulley according to claim 4 , wherein said anti-warping device comprises an element made of polymeric material housed coaxially inside said at least one first wire coil spring.

6. The pulley according to claim 1 , wherein said first elements comprise at least two spokes carried by an actuator integral with the hub.

7. The pulley according to claim 6 , wherein said elastic assembly comprises at least the first wire coil spring sliding circumferentially inside a seat formed between said first elements and/or said second elements.

8. The pulley according to claim 1 , wherein said second elements are protrusions obtained in an element integral with the ring.

9. The pulley according to claim 1 , wherein said disc is part of a dynamic damper.

10. The pulley according to claim 9 , wherein the disc is rotatable with the hub and has a perimeter flange defining an inward axial face facing the ring, and the disc comprises a seismic ring constrained to the inward axial face of the perimeter flange by a ring of elastomeric material that is coaxial therewith about the hub.

11. The pulley according to claim 10 , wherein the seismic ring extends radially outward beyond the perimeter flange of the disc.

12. The pulley according to claim 1 , wherein it comprises stop elements carried integral by one between said hub and said ring.

13. The pulley according to claim 1 , wherein said dust seal is has a V-ring cross-sectional profile.

14. The pulley according to claim 1 , wherein said pair of first elements integral with said actuator are two spokes free to move circumferentially in the chamber.