Pulley assembly

1. A pulley assembly for a flexible motor vehicle transmission, comprising a supporting member in the form of a hub that is rotatable about an axis (A), a pulley adapted to cooperate with a belt and connected to said hub to be rotatable about said axis (A), an elastic spiral device interposed between the hub and the pulley and including a sliding portion elastically loaded in a radial direction against a sliding wall carried by one of the hub or pulley thereby forming a radially directed drive force coupling the pulley to the hub, wherein the elastic spiral device further includes a supporting portion having first and second, angularly spaced apart runner devices attached thereto which will apply radial loads to, slide along and be in direct contact with said sliding wall, the elastic spiral device having a leading end with the first runner device being attached to said leading end, the first runner device further including a narrowed leading end, said pulley assembly further including a pair of spaced apart abutting elements fixed to the sliding wall which will receive the narrowed leading end there between be contacted by the first runner device at a stopped position with respect to said sliding wall.

2. The pulley assembly according to claim 1 , wherein said elastic spiral device is rotationally connected to said hub.

3. The pulley assembly according to claim 1 , wherein each of said first and second runner devices are arranged to move with said elastic spiral device and slide along said sliding wall, and include a covering wall radially interposed between said supporting portion and said sliding wall.

4. The pulley assembly according to claim 3 , wherein said supporting portion has a back surface with a concave central segment, and said covering wall defines a convex surface shaped to couple with said concave central segment.

5. The pulley assembly according to claim 4 , wherein said second runner device includes a pair of recesses formed on an inside surface and in a direction parallel to said axis (A) and said convex surface and accommodating side edges of said supporting portion.

6. The pulley assembly according to claim 4 , wherein said elastic spiral device further includes a spiral portion connected to said sliding portion and said covering wall of said second runner device has a radial thickness that increases from said spiral portion towards said supporting portion.

7. The pulley assembly according to claim 3 , wherein said first and second runner devices are co-moulded onto said supporting portion.

8. The pulley assembly according to claim 3 , wherein said first and second runner devices are connected by an adhesive layer to said supporting portion.

9. The pulley assembly according to claim 1 , wherein said first and second runner devices comprise a metallic structure.

10. The pulley assembly according to claim 9 , wherein said first and second runner devices further comprise a layer arranged in contact with said sliding wall and made of a polymeric material, or a fibre-reinforced polymeric matrix composite material, or a friction material.

11. The pulley assembly according to claim 1 , wherein said first and second runner devices comprise a pair of walls covering respective sides of said supporting portion.

12. The pulley assembly according to claim 1 , wherein said pair of abutting elements include a damping device to slow down the rotational movement of said pulley with respect to said hub before impact with said pair of abutting elements.

13. The pulley assembly according to claim 12 , wherein said damping device comprises an inclined surface element fixed onto said sliding wall and cooperating with said elastic spiral device to increase the radial load exerted thereby as said first runner device approaches said stopped position.

14. The pulley assembly according to claim 13 , wherein said pair of abutting elements include a first and a second projection radially protruding from said sliding wall and defining a hollow area there between so that the narrowed leading end will enter into said hollow area to cooperate with said inclined surface element.

15. The pulley assembly according to claim 1 , wherein said first and second runner devices define a first contact zone and a second contact zone, respectively, in which the contact pressure exchanged between said sliding portion and said sliding wall is concentrated.

16. The pulley assembly according to claim 15 , wherein said sliding portion further comprises an intermediate portion radially spaced from said sliding wall and circumferentially interposed between said first and second contact zones.

17. The pulley assembly according to claim 16 , wherein said first and second contact zones are spaced apart by an angle in the range from 150° to 210°.

18. The pulley assembly according to claim 17 , wherein said first and second contact zones are spaced so that the contact pressure resultant is essentially null.

19. The pulley assembly according to claim 17 , wherein said elastic spiral device comprises a plurality of angularly and equally spaced spiral springs.

20. The pulley assembly according to claim 17 , wherein said sliding portion further includes a third contact zone circumferentially and equally spaced from said first and second contact zones.

21. The pulley assembly according to claim 1 , wherein said hub is adapted to be fastened to a rotating member and a seismic mass is connected to said hub to define a dynamic torsional vibration damper.

22. The pulley assembly according to claim 21 , wherein said seismic mass is connected to said hub by an elastomeric band.