Patent ID: 7028796

Claim:
A four-wheel drive apparatus for a vehicle in which a first set of wheels are driven by an engine, comprising: 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 a second set of wheels; a battery charged by the electric current supplied from the generator; a first relay switch for switching an electric contact between the generator and the motor; and a second relay switch for switching an electric contact between the battery and the generator, a first voltage detector for detecting output voltage of the battery; and a second voltage detector for detecting output voltage of the generator, wherein the current generated by the generator is alternatively supplied to the motor or the battery, further comprising a controller that controls the first switch to be on and the second switch to be off when the motor is driven, and controls the first switch to be off and the second switch to be on when the battery is charging and, wherein the controller controls a rotor current of the generator based on a difference between the voltage of the battery and that of the generator.