Power train system for hybrid vehicle

Powertrain system (10) for a hybrid vehicle, comprising an internal combustion engine whose operation is capable of producing exhaust gases, a transformation loop (14), via a fluid, of the energy of the exhaust gases into mechanical energy, this loop comprising an auxiliary mechanical energy motorization shaft (20) connected to a hybrid epicyclic gear train (22). The epicyclic gear train (22) comprises a hybridization input (22H) driven by said auxiliary motorization shaft (20), a main input (22N) connected to a main engine shaft (12M) connected to a flywheel of the internal combustion engine and a traction output (22S) which is adapted to be connected to at least one driving wheel of the hybrid vehicle. Hybrid motor vehicle, comprising such a powertrain system.