Variable speed transmission for motor vehicles

Claim 1

Device for transmitting motion from the driving shaft to the axle shafts of the two driven wheels of a motor vehicle through a stepless speed variator with expandable pulleys, comprising: - a drive shaft (3) driven by the driving shaft (1); - a hollow main shaft (18) rotatably mounted on the drive shaft and carrying an expandable driving pulley (19); - an epicyclic reversing unit (4) for selectively transmitting motion from the drive shaft (3) to the main shaft (18) in the conditions of forward movement, idling, and rearward movement; - a driven shaft (22) carrying an expandable driven pulley (21) which is driven by the driving pulley (19) through a V-belt (20); - hydraulic actuating means (7,11) for controlling the expansion of the expansible driving and driven pulleys (19, 21); - a gear reduction unit (23, 24, 25, 26) driven by the driven shaft (22); - a differential gear (27) driven by the gear reduction unit and driving the two axle shafts (28, 29) of the vehicle, characterised in that the epicyclic reversing unit comprises: - a fixed support structure (12); - an input sun wheel (5) carried by the drive shaft (3); - an output sun wheel (17) carried by the main shaft (18); - a planet carrier (9); - a plurality of pairs of meshed planet wheels (13,14) rotatable on pins (15, 16) carried by the planet carrier (9), one wheel (13) of each pair meshing with the input sun wheel (5) and the other wheel (14) of each pair meshing with the output sun wheel (17); - - a first hydraulically-operated friction clutch (8) operable to render the planet carrier (9) rigid with the drive shaft (3), and - a second hydraulically-operated friction clutch (10) operable to render the planet carrier (9) rigid with the fixed support structure (12).