Driven pulley with flyweights effective at low speeds

In a driven pulley of a variable speed transmission, pulley comprising:

• a shaft having two ends;
• two coaxial flanges located on the shaft, each flange having an inner conical wall, the inner walls facing each other and providing therebetween a V-shaped groove for a trapezoidal pulley belt exerting substantially a radial force and a tangential force on the inner walls, one of the flanges, hereinafter called "fixed flange", being rigidly attached at one end of the shaft, the other flange, hereinafter called "movable flange", being slidably and rotatably mounted on the shaft;
• a helicoidal spring, mounted around the shaft, forcing the movable flange to get closer to the fixed flange;
• and
• means for generating an angular displacement of the movable flange with reference to the fixed flange and in function of the distance in-between, said angular displacement being in a direction opposite to the direction of rotation of the pulley;
• the improvement consisting of:
• a substantially annular-conical surface provided on a plate rigidly attached to the shaft, the annular-conical surface having an inner edge and an outer edge, the inner edge being farther from the fixed flange than the outer edge;
• at least two flyweights, symmetrically disposed around the movable flange on a side opposite to said inner conical wall thereon, each flyweight being operatively attached to an arm, the arm being operatively attached to the movable flange and extending therefrom, each of the arm being able to revolve, about a tangential axis disposed at an edge of the plate, between a first position where the corresponding flyweight projects substantially toward and against the annular conical surface and a second position where the corresponding flyweight projects substantially radially with reference to the shaft;
• and
• biasing means for forcing the flyweights to rest against the annular-conical surface, the biasing means generating an axial resultant force for moving the movable flange closer to the fixed flange, the force being maximum at the first position;
• whereby,
• at minimum rotation speed, the flyweights are at the first position;
• and
• as rotation speed increases, the flyweights are subjected to a centrifugal force counterbalancing the biasing means, therefore reducing it and moving the flyweights closer to the second position.