US Patent 7028796 Four-wheel drive apparatus using motor, and method thereof

A four-wheel drive apparatus for a vehicle with front wheels driven by an engine comprises a generator connected to the engine for generating an electric current; a motor driven by the electric current supplied from the generator and supplying power for driving rear wheels; a battery charged by the electric current supplied from the generator; a first relay switch for switching electric contact between the generator and the motor; a second relay switch for switching electric contact between the battery and the generator, wherein, the current generated by the generator is alternatively supplied to the motor or the battery.