Driving pulley

A driving pulley for a variable speed transmission, said driving pulley comprising:

• a shaft having two ends;
• two coaxial flanges located on said shaft, each flange having an inner conical wall facing the other for providing therebetween a V-shaped groove for a trapezoidal belt exerting substantially a radial force and a tangential force on the inner conical walls upon application of a torque on said shaft and rotation thereof, one of said flanges, hereinafter called "fixed flange", being rigidly attached at one end of said shaft and transmitting substantially the half of the torque, the other flange, hereinafter called "movable flange" being slidably and rotatably mounted on said shaft, said movable flange transmitting substantially the half of the torque;
• first biasing means for generating a biasing torque opposed to the corresponding half of the torque;
• second biasing means for generating an axial biasing force urging said movable flange away from said fixed flange;
• centrifugal means for generating an axial moving force opposed to the axial biasing force and urging said movable flange towards said fixed flange, the axial moving force being a function of the rotation speed of said driving pulley;
• and
• means for limiting sliding and rotating movements of said movable flange within predetermined limits with respect to said shaft and for imposing a specific mechanical behaviour to said movable flange.