A motor-driven hinge device may include a hypocycloid hinge mechanism driven by a drive shaft, two metal side plates intended for connection to the seating portion and to the backrest, a brushless motor, and a planetary gear train positioned between the brushless motor and the drive shaft. The planetary gear train may include a sun gear connected to the motor rotor, and a plurality of planet gears, each planet gear having a first set of teeth engaging with the sun gear and with a first stationary ring gear, and a second set of teeth engaging with a second ring gear rigid with the drive shaft.