Power transmission device with at least two planetary gear trains

The invention concerns a power transmission device between a heat engine and the wheels of a motor vehicle, said device comprising two independent electric machines (3, 4), at least two planetary gear trains connecting the heat engine and the electric machines with one another and to the vehicle wheels, a mechanical switching device shifting the transmission device from one operating mode to another, each transmission mode corresponding to a different range of transmission ratios, the switching device enabling to connect one of the electric machines directly to the vehicle wheels and a control device monitoring the heat engine, the two electric machines and the mechanical switching device, so that the operating points of the heat engine and of the electric machines correspond to the minimum instantaneous consumption and enable to provide the required power to the wheels.