Gearboxes with an external power split comprise a mechanical summation gearbox (planetary gearbox) in the direct flow of power and an adjustable gearbox (hydrostatic transmission) in the parallel circuit. The rotation speed of the drive shaft can be varied depending on the transmission ratio produced by the adjustment of the hydrostatic transmission, part of the power to be applied is transmitted by the hydraulics (Figure A 12).
Alternative: internal power split.