Step change-speed transmission with centrifugal clutch

A stepless change-speed transmission between the engine and the drive shafts of the driven wheels of a motor vehicle, comprising a main shaft, an expansible driving pulley carried by the main shaft, a driven shaft, an expansible driven pulley carried by the driven shaft, a drive belt which passes around the driving and driven pulleys and hydraulic control means for varying the transmission ratio between the driving and driven pulleys, an epicyclic differential rotatable by the driven shaft to drive the drive shafts, a geared reversing unit for reversing the sense of rotation of the differential to effect forward or reverse drive respectively, hydraulic actuator means for controlling the reversing means, and a hydraulically-operated friction clutch for engaging and disengaging the transmission, the friction clutch being arranged on the drive shaft and including a driving member actuated by the driven pulley and a driven member for actuating the reversing unit, and the reversing unit comprising:

• a driving gear for forward drive rotatably mounted on the drive shaft, transmission means and a driven gear for forward drive engaged with the driving gear for forward drive through said transmission means;
• a toothed clutch sleeve coaxial with the driven shaft and coupled for rotation with the driven member of the friction clutch, the toothed sleeve normally being meshed with the driving gear for forward drive, and being displaceable axially by the hydraulic actuator means to a position of disengagement from the driving gear for the forward drive;
• a driven gear for reverse able to mesh directly with the toothed clutch sleeve when the latter is in its disengaged position, and
• transmission means between said driven gear for forward and reverse drive and the differential;
• wherein the friction clutch comprises an actuating cylinder fixed to the driving member of the clutch and defining a thrust chamber connected to a hydraulic supply circuit and a hydraulic exhaust duct housing a normally-open modulating valve, rotatable with the actuator and with centrifugal closing actuation;
• wherein the modulating valve comprises a centrifugal mass slidable radially in the exhaust duct and carrying an obturator which cooperates with a valve seat formed in the exhaust duct;
• and
• wherein the centrifugal mass is constituted by a substantially cup-shaped slide with a tapering edge acting as an annular obturator and the interior of which defines a pressure chamber communicating with the hydraulic supply circuit with the function of balancing the centrifugal force acting on the centrifugal mass.