Variable speed transmission

A variable speed transmission for transmitting a torque produced by an engine to a belt, said transmission comprising:

• a shaft having a first end for connection to said engine, and a second end;
• a pulley having a fixed flange fixedly connected to said second end of said shaft, and a movable flange slidably connected to said shaft and substantially rotatable therewith, said movable flange and said fixed flange having respectively coaxial side cheeks mounted in opposition and defining therebetween a groove for receiving said belt;
• a pressure device rigidly connected to said movable flange, slidably connected to said shaft and substantially rotatable thereon, said pressure device having a pair of pressure units diametrically opposed for pressurizing fluids, each pressure unit comprising:
• a first fluid chamber divided in a first and a second variable compartment, said first and second compartments being connected by a first channel;
• a second fluid chamber divided in a third and a fourth variable compartment, said third and fourth compartments being connected by a second channel;
• a radially movable partition, having a specific weight, for separating said second compartment from said third compartment, said second compartment being closer to said shaft than said third compartment, said movable partition being movable away from said shaft upon subjection of an increasing centrifugal force on the specific weight thereof;
• resilient means for applying a return force toward said shaft for counterbalancing said centrifugal force;
• a fixed partition rigidly connected to said shaft, said fixed partition separating said first compartment from said fourth compartment;
• whereby, in operation, when said shaft rotates, said centrifugal force urges the movable partition away from said shaft, the fluid in said first fluid chamber is urged to circulate from their first compartment into their corresponding second compartment and said fluids in said second fluid chambers are urged to circulate from their third compartment into their corresponding fourth compartment, so that a volume expansion of said fourth compartment and a volume reduction of said first compartment produce a sliding movement of the pressure device and of the movable flange toward the fixed flange, causing a variable transmission of torque from said engine to said belt.