In the Delta HF 4X4, Lancia opted for a four-wheel drive system with an in-built torque-splitting action to ensure that the available power was going to the wheels with the most traction at any given time, thus ensuring the most efficient use of the available power and torque.
Three differentials are at the heart of the system. Drive to the front wheels is linked through a free-floating differential; drive to the rear wheels is transmitted via a 56/44 front/rear torque-splitting Ferguson viscous-coupling-controlled epicyclic central differential. At the rear wheels is a Torsen (torque sensing) rear differential. The Torsen differential is a true 'intelligent' differential in the way it distributes torque. It divides the torque between the wheels according to the available grip, and does so without ever locking fully: maximum lockup is 70%.
The HF Integrale transmission systems incorporates permanent 4-wheel drive, a front transversely mounted engine and five-speed gearbox. An epicyclic centre differential normally splits the torque 56 per cent to the front axle, 44 per cent to the rear. However a noiseless, fully automatic Ferguson viscous coupling balances the torque split to give the optimal division between front and rear axles depending on road conditions and tyre grip. The Torsen rear differential further divides the torque delivered to each rear wheel according to grip available. By using the interaction between a worm screw and helical gear (movement is transmitted from screw to gear only) the Torsen system ensures that the wheel with less weight or grip receives less torque and therefore maintains traction. A free floating front differential completes the system to ensure maximum traction even at speed on adverse road surfaces.
