Short History of Alfa 4x4's
Shamelessly cribbed from an official Alfa site
Quote:
Short history of Alfa Romeo 4x4 cars
The first four wheel drive system in Alfa Romeo's history made its debut in 1951 on the AR51 - 1900, an off-road car with state-of-the-art engineering features designed for military use. The 'Matta' (or crazy car - as it was affectionately dubbed by those who appreciated its exceptional off-road
properties) is now a real cult item appreciated far beyond the restricted circle of Alfa Romeo collectors.
The Alfa 33 4x4 made its debut in 1983. The layout adopted for this compact saloon meant that the rear wheel drive had to be engaged by means of a lever in the passenger compartment. A central differential prevented any slippage between both axles. Because it offered higher ground clearance than front wheel drive cars, the 33 4x4 acquitted itself well in many critical situations and could pass easily from snowy surfaces to unsurfaced roads. Altogether a multi-facetted car that allowed great flexibility of use.
In 1991, the Alfa 33 was fitted with a sportier interpretation of the four wheel drive concept. The transmission layout of the new Permanent 4 (this was the name of the version) was more complex than its predecessor: a set of sensors managed the action of a viscous coupling that transferred movement to the rear wheels (generally free) when it detected significant differences between wheel rotating speeds across both axles. These features assured the 33 outstanding dynamic performance, an up-to-date blend of high performance, sports handling and top level active safety.
The following year saw the arrival of the 155 Q4. The new Quadrifoglio 4 tag was the emblem of state-of-the art Alfa Romeo sportiness.
One specific feature of the 155 Q4 was the presence of a permanent four wheel drive system with three differentials: a conventional unit at the front; a central epicyclic unit that engaged directly with the gearbox layshaft incorporating an integral Ferguson viscous coupling - and a Torsen unit at the rear.
Under normal conditions, the central distribution distributed drive torque with a slight preference to the rear wheels. If one of the two axles lost grip excessively compared to the other, the Ferguson coupling cut in to transfer drive torque (up to 100%) gradually to the wheels with more grip.
The efficacy of the system was further increased by a Torsen rear differential that acted as a self-locking unit and allowed the wheels to turn at different speeds.
This transmission configuration was combined with a particularly advanced ABS. This technical configuration ensured that the 155 Q4 remained glued to the ground and was easy and entertaining to drive while remaining safe in every situation. These attributes were also displayed by the racetrack versions that fought out the German touring car speed championship. In 1993, the 155 V6 TI saw off the competition to triumph in the DTM with Larini at the wheel.
Alfa Romeo brought the incredible technical experience it had built up over the years to bear when it produced a four wheel drive version of its range leader, the 164. In December 1993, customers were able to buy a 164 Q4 powered by the legendary 231 bhp V6 engine.
In this case, the four wheel drive layout had been further developed to ensure maximum performance and peak driving comfort. The heart of the system was the central Viscomatic viscous coupling developed exclusively by Alfa Romeo in conjunction with Steyr-Puch. The Viscomatic was managed by an on-board electronic system that communicated in real time with the engine control unit and ABS control unit. Moment by moment, the system detected and processed information on four different parameters: total drive torque requested, speed, steering angle and slip difference between front and rear axles. It was able to adjust drive torque distribution between the axles with incredible speed on the basis of vehicle speed, cornering radius, engine rpm, throttle opening and closure and ABS parameters. This guaranteed improved torque distribution at any moment and in any situation.
In this case too, the Q4 drive system was based on a Torsen self-locking rear differential. This rear differential was responsible for the important task of redistributing the torque allocated to the rear end (in real time) between the wheels on the rear axle: this benefited traction and also car handling over mixed routes.
An epicyclic unit was also fitted between the coupling and rear differential to amplify speed differences between coupling input and output. This made it faster and more sensitive while reducing the level of torque managed by the coupling.
