New internal combustion engines (ICE) are characterised by increasing maximum efficiency, thanks to the adoption of strategies like Atkinson cycle, downsizing, cylinder deactivation, waste heat recovery and so on. However, the best performance is confined to a limited portion of the engine map. Moreover, electric driving in urban areas is an increasingly pressing request, but battery electric vehicles use cannot be easily widespread due to limited vehicle autonomy and recharging issues. Therefore, in order to reduce ICE vehicle fuel consumption, by decoupling the ICE running from road load, as well as permit energy recovery and electric driving, hybrid propulsion systems are under development. This paper analyses a new patent solution for power split hybrid propulsion system with gearbox. The system comprises an auxiliary power unit, adapted to store and/or release energy, and a planetary gear set which is interposed between the ICE and the gearbox. The system is characterized by a further device coupled with the ICE to modulate the resistance torque, in order to use the auxiliary power unit also for regenerative braking. The choice to maintain a gearbox in the propulsion give the possibility to achieve different purposes. It allows to propel the vehicles only with ICE also during the starting of the vehicle maximizing the direct use of mechanical energy and to have only one electric motor/generator, unlike the widespread power split systems which use two electric motors, for managing the vehicle speed and traction torque. Finally, there are also other advantages with the patented system as the possibility of operating only with the ICE in the case of auxiliary power unit, or maintaining the driving style of vehicle with gearbox.