Filtering pulley

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).