Filtering pulley
A filtering pulley for an accessory transmission of an internal combustion engine that has a hub, a crown, a filtering unit or transmitting the torque interposed between the hub and the crown, a torsion spring, a carrier, and a torque limiting joint. The torque limiting joint is coupled to interface with one of the surfaces between the crown and has an open-loop strip spring. The torque limiting joint 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 ( 1 ) for an accessory transmission of an internal combustion engine, comprising a hub ( 2 ), an annular crown ( 3 ) provided with a profile configured to cooperate with a transmission belt ( 5 ), externally coaxial around an axis (A) to said hub ( 2 ) and supported in free rotational motion on the hub itself, and a filtering unit ( 4 ) for transmitting the torque interposed between said hub ( 2 ) and said crown ( 3 ) and comprising a torsion spring ( 11 ), a single carrier ( 12 ) and a torque limiting joint ( 20 ),
said carrier ( 12 ) cooperating by sliding with respect to a portion of said hub ( 2 ), said carrier ( 12 ) defining a first spring holder ( 15 ) and a projection ( 17 ) extending along said axis (A) and configured to cooperate with said torque limiting joint ( 20 ),
said torsion spring ( 11 ) being operatively interposed between said carrier ( 12 ) and said portion of said hub ( 2 ) and being provided with two ends cooperating in contact with respectively said first spring holders ( 15 ) and a second spring holder ( 15 ) integral to said portion of said hub,
said torque limiting joint ( 20 ) being coupled to interference on one surface ( 3 ″) of said crown ( 3 ),
said torque limiting joint ( 20 ) comprising an open-loop strip spring ( 21 ) and being configured to slide with respect to said surface ( 3 ″) when the torque transmitted between said crown ( 3 ) and said hub ( 2 ) reaches a predetermined level (T 1 , T 2 ),
wherein said spring ( 11 ) is operatively interposed between said carrier ( 12 ) and said hub ( 2 ) and wherein said carrier ( 12 ) defines a pair of radial projections ( 14 ) configured to cooperate selectively circumferentially in contact with respective axial projections ( 18 ) integral with said hub ( 2 ).
2. The pulley according to claim 1 , wherein said strip spring ( 21 ) is radially sized to be spaced by a predetermined distance (H) with respect to said torsion spring ( 11 ), said distance (H) being proportional to a maximum torque that can be transmitted by said torsion spring ( 11 ).
3. The pulley according to claim 1 , in which said projections ( 14 ) being angularly opposite each other and in which said projections ( 18 ) of said hub ( 2 ) are angularly opposite to each other.
4. The pulley according to claim 1 , wherein said strip spring ( 21 ) defines an axial projection ( 25 ), said projection ( 25 ) being configured to cooperate in circumferential contact with said projection ( 17 ) of said carrier ( 12 ).
5. The pulley according to claim 1 , wherein said torque limiting joint ( 20 ) comprises an actuator element ( 28 ) housed in a space ( 22 ) circumferentially delimited between two ends ( 21 ′, 21 ″) of said strip spring ( 21 ), said actuator element ( 28 ) being axially dimensioned to cooperate in contact with said projection ( 17 ) of said carrier ( 12 ).
6. The pulley according to claim 5 , characterized in that said actuator element is a metal lever ( 28 ) able to expand said spring ( 21 ) under the thrust of said projection ( 17 ) of said carrier.
7. The pulley according to claim 6 , wherein said lever ( 28 ) is configured to interact with said ends ( 20 ′, 20 ″) of said strip spring ( 21 ) under the thrust of said carrier ( 12 ).
8. The pulley according to claim 6 , wherein said hub defines an axial projection and said lever ( 28 ) is configured to cooperate in contact with said axial projection of said hub.
9. The pulley according to claim 1 , wherein said pulley ( 1 ) comprises a head portion ( 7 ) integral with said hub ( 2 ), a bearing ( 6 ) is mounted on said head portion ( 7 ) of said crown ( 3 ).
10. The pulley according to claim 9 , wherein said portion ( 7 ) defines a spring holder ( 15 ) for one end of said torsion spring ( 11 ).
11. The pulley according to claim 10 , wherein said pulley ( 1 ) comprises a sliding bearing ( 8 ) operatively interposed between said portion ( 2 b ) of said hub and said crown ( 3 ).
12. The pulley according to claim 1 , wherein said first spring holder is defined by radial projections ( 14 ) of said carrier ( 12 ).
13. The pulley according to claim 1 , wherein said pulley ( 1 ) comprises a damping ring ( 13 ) operatively interposed between said carrier ( 12 ) and said portion ( 7 ) integral with said hub ( 2 ), said damping ( 13 ) being configured to allow the sliding of said carrier ( 12 ) with respect to said hub ( 2 ).
14. The pulley according to claim 13 , wherein said damping ring ( 13 ) comprises a portion ( 19 ′) radially interposed between said crown ( 3 ) and said carrier ( 12 ) and a portion ( 19 ″) interposed between said carrier ( 12 ) and said hub ( 2 ).
15. The pulley according to claim 1 , wherein said crown ( 3 ) defines a surface machined portion ( 23 ) on said internal surface ( 3 ″), said strip spring ( 21 ) cooperating in contact with said portion ( 23 ), said surface machined portion ( 23 ) being configured to increase the friction between said strip spring ( 21 ) and said internal surface.