Patent ID: 8353379

Claim:
An optionally connectable four-wheel drive vehicle comprising : an engine having a drive shaft; two main drive wheels; a main power train permanently connecting the drive shaft of an engine to the main drive wheels, and in turn comprising a transmission and a main differential; two normally driven secondary drive wheels; and an optionally connectable secondary power train for also connecting the drive shaft of the engine to the secondary drive wheels, and in turn comprising a gear drive, and at least one secondary clutch, which is connected on one side to the drive shaft of the engine at a point located upstream from the transmission of the main power train, and on the other side to the secondary drive wheels; wherein the gear drive of the optionally connectable secondary power train has two different, alternatively selectable velocity ratios; the gear drive of the optionally connectable secondary power train comprises two gear pairs, each having a respective velocity ratio; and two secondary clutches, each associated with a respective gear pair and for connecting the gear pair to the drive shaft of the engine upstream from the transmission of the main power train; and each gear pair comprises an input gear connected to the drive shaft of the engine upstream from the transmission of the main power train by the respective secondary clutch; and an output gear which meshes with the input gear and is connected permanently to the secondary drive wheels.