A compact four-wheel drive system for motor vehicles

Described herein is a transmission system for motor vehicles in which the engine and the gear shift are set in a transverse direction with respect to the direction of travel of the vehicle, the system comprising: a front differential (3) having a gear-train carrier (10) driven by the pinion (4) of the secondary shaft of the gear shift for transferring motion to the axle shafts (6a, 6b) of the front wheels of the vehicle; a rear differential (7); and a central differential (5a) constituted by a limited-slip differential. The central differential has, among other things: one crown wheel (19), which is connected to the support (19b) of the ring bevel gear (8a) for transmission to the rear, and another crown wheel (20), which is connected to the gear-train carrier (10) of the front differential (3); and means for connecting one crown wheel (19) to the ring bevel gear (8a) and for connecting the other crown wheel (20) to the front differential (3), said means consisting of two co-axial hollow shafts (19a and 10a), which are grooved at their ends.