Filtering pulley
A filtering pulley for an accessory transmission of an internal combustion engine has a hub, a crown, a filtering unit for transmitting the torque that is 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 a surface of the crown when the torque transmitted between the crown and the hub reaches a predetermined level.
1. Filtering pulley for an accessory transmission of an internal combustion engine, comprising a hub, an annular crown provided with a profile configured to cooperate with a transmission belt, externally coaxial around an axis to said hub 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 one of said hub and said crown, said carrier defining a spring holder and a projection extending along said axis and configured to cooperate with said torque limiting joint,
said torsion spring being operatively interposed between said carrier and said one between said hub and said crown and being provided with two ends cooperating in contact with respective spring holders integral with said carrier and said one between said hub and said crown,
said torque limiting joint being coupled by interference on one surface of the other between said crown and said hub
said torque limiting joint comprising an open loop strip spring and being configured to slide with respect to said surface when the torque transmitted between said crown and said hub reaches a predetermined level,
wherein said strip spring defines a pair of axial projections configured to cooperate selectively circumferentially in contact with, respectively, at least one axial projection integral with said hub and at least one projection axial integral with said carrier.
2. The pulley according to claim 1 , wherein said axial projection carried by said hub defines a seat within which said axial projection can move circumferentially, said seat extending angularly by an angle included between 130° and 150°.
3. The pulley according to claim 1 , wherein said axial projection carried by said carrier defines a seat within which said axial projection can move circumferentially, said seat extending angularly by an angle included between 35° and 45°.
4. The pulley according to one of 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 axially dimensioned to cooperate in contact, on the one hand, with said projection of said carrier and, on the other, said projection of said hub.
5. The pulley according to claim 4 , wherein said actuator element is a metal lever able to expand said spring under the thrust of said projection of said carrier.
6. The pulley according to claim 4 , wherein one of said two ends of said strip spring defines a circumferential protuberance extending into said space and configured to cooperate in contact with said actuator element, said protuberance extending in proximity of said axial projection cooperating with said projection integral with said hub.
7. The pulley according to claim 4 , wherein said actuator element has a trapezoidal section, where the plan of said section is circumferential and the thickness of said actuator element is radial.
8. The pulley according to claim 7 , wherein said trapezoidal section defines a pair of equal inclined lateral portions.
9. The pulley according to claim 8 , wherein the inclination of said inclined side portions is between 20° and 40°.
10. 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.
11. The pulley according to claim 1 , wherein said projections are made on a flanged portion integral with said hub, said flanged portion being sized to wrap, in part, externally said torsion spring.
12. The pulley according to claim 11 , wherein said pulley comprises a sliding bearing operatively interposed between said flanged portion and said crown.
13. The pulley according to claim 1 , wherein said carrier defines a radial projection defining a spring holder for one of the two ends of said torsion spring.
14. The pulley according to claim 1 , wherein said pulley comprises a damping ring operatively interposed between said carrier and said portion integral with said hub, said damping being configured to allow the sliding of said carrier with respect to said portion.
15. The pulley according to claim 14 , wherein said damping ring comprises a portion radially interposed between said crown and said carrier and a portion interposed between said carrier and said portion integral with said hub.