a structure;

an output shaft connectable to a load, the output shaft rotatable about an axis relative the structure;

a thermal engine secured to the structure, the thermal engine having a thermal engine shaft;

an electric motor having a stator and a rotor shaft, the stator secured to the structure, wherein the electric motor is coaxial to the output shaft, and axially overlaps the output shaft;

an epicyclic gearing having a sun gear coaxial to a ring gear, a plurality of planet gears meshed between the sun gear and the ring gear, and a carrier coaxial to the sun gear and to the ring gear, the sun gear, the carrier, and the ring gear being rotatable relative the structure, the output shaft and the rotor shaft both coupled to the carrier, and the thermal engine shaft coupled to the sun gear; and

an overrunning clutch coupling the ring gear to the structure, the overrunning clutch allowing rotation of the ring gear in a first angular direction, and preventing rotation of the ring gear in a second angular direction, the second angular direction opposite the first angular direction.