A method for controlling a power assisted propulsion system in a motor vehicle so as to perform a transition from a lower gear to a higher gear without interrupting a driving torque applied to driving wheels; the propulsion system displays an internal combustion engine provided with a drive shaft and a power assisted transmission comprising in turn: a power assisted mechanical gearbox provided with a primary shaft connectable to the drive shaft and a secondary shaft connected to a transmission shaft which transmits motion to the driving wheels; a power assisted clutch interposed between the drive shaft and the primary shaft of the gearbox to connect and disconnect the drive shaft to the primary shaft of the gearbox; a power assisted brake; and an epicycloidal gear having three rotating elements: a first rotating element connected to the drive shaft, a second rotating element connected to the secondary shaft of the gearbox, and a third rotating element connected to the brake.