Filtering pulley
A filtering pulley for an accessory transmission of an internal combustion engine that has a hub, a crown, a filtering unit for transmitting the torque interposed between the hub and the crown, a torsion spring, a carrier, and a torque limiting joint. The torque limiting joint has an open-loop strip spring and is configured to slide with respect to said surface when the torque transmitted between the crown and the hub reaches a predetermined level.
1. A filtering pulley for an accessory transmission of an internal combustion engine, comprising;
a hub defining a longitudinal axis (A) and having an outer axially extending annular flange that has a pair of projections extending axially therefrom that are spaced an angular distance apart from one another,
an annular crown provided with a profile configured to cooperate with a transmission belt, externally coaxial around the longitudinal axis (A) and supported in free rotational motion on the hub itself, and
a filtering unit for transmitting the torque interposed between said hub and said crown and comprising a torsion spring, a carrier and a torque limiting joint,
said carrier cooperating by sliding with respect to a portion integral with said hub, said carrier defining a spring holder and a first projection extending along said axis (A) and configured to selectively cooperate through contact with said torque limiting joint,
said torsion spring being operatively interposed between said carrier and said hub and being provided with two ends cooperating in contact with the spring holder of said carrier and said hub, respectively,
said torque limiting joint is mounted in radial interference in contact with an internal surface of said crown, and comprises an open-loop strip spring having a first end, a second end, and a body therebetween, having a second projection extending axially from the first end toward the carrier and configured to cooperate in contact with the first projection of the carrier, having a pair of third projections extending axially from the body and spaced an angular distance apart from one another and apart from the second projection, and being configured to slide with respect to said internal surface of said crown when the torque transmitted between said crown and said hub reaches a predetermined level (T1, T2);
wherein the pair of third projections are positioned to cooperate in contact circumferentially with the pair of projections of the hub;
wherein said crown comprises a machined area in said internal surface comprising a grooved or wavy surface having dimensions to enable a predetermined friction between said strip spring and said crown.
2. The pulley according to claim 1 , wherein said strip spring is radially sized to be spaced by a predetermined distance (H) with respect to said torsion spring, said distance (H) being proportional to a maximum torque that can be transmitted by said torsion spring.
3. The pulley according to claim 1 , in which a free angle between said crown and said hub is defined between said pair of axial projections or said strip spring and said respective axial projections of said hub.
4. The pulley according to claim 1 , wherein said strip spring defines a secondary axial projection extending on an opposite side to said pair of projections, said secondary axial projection being configured to cooperate in contact circumferentially with said first projection of said carrier.
5. The pulley according to claim 1 , wherein said torque limiting joint comprises an actuator element housed in a space circumferentially delimited between two ends of said strip spring, said actuator element being dimensioned axially to cooperate in contact, on one side, with said first projection of said carrier and, on the other, one of said respective axial projections of said hub.
6. The pulley according to claim 5 , wherein said actuator element is a metal lever able to expand said spring under a thrust of said first projection of said carrier.
7. The pulley according to claim 6 , wherein said lever is configured to interact with said ends of said strip spring under torque from said carrier.
8. The pulley according to claim 1 , wherein said portion integral with said hub comprises an annular head on which a bearing is mounted to support said crown.
9. The pulley according to claim 1 , wherein said respective axial projections of said hub are made on a flanged portion integral with said hub, said flanged portion being sized to wrap, in part, externally said torsion spring.
10. The pulley according to claim 9 , wherein said pulley comprises a sliding bearing operatively interposed between said flanged portion and said crown.
11. The pulley according to claim 1 , wherein said carrier defines a radial projection defining a spring holder for one of the ends of said spring.
12. The pulley according to claim 1 , wherein said pulley comprises a damping ring operatively interposed between said carrier and a head element attached to said hub, said damping ring being configured to allow the sliding of said carrier with respect to said head element.
13. The pulley according to claim 12 , wherein said damping ring comprises a first portion radially interposed between said crown and said carrier and a second portion interposed between said carrier and said head element.