The Alfa 147 on show at the Paris Motor Show this month will represent the world premiere of the self-locking front differential (known as the Q2) that maintains and implements all the attributes of a front wheel drive in terms of active safety and intuitive driving, while increasing driving satisfaction and control. The innovative system also guarantees some benefits typical of four wheel drive but with decidedly lower weight and cost.

The Q2 system is based on the presence of a Torsen mechanical limited slip differential. This differential performs the specific task of distributing torque over the front wheels in a dynamic, continuous manner according to driving and road surface conditions. When combined with the exclusive front double wishbone suspension, the system allows particularly effective tuning of the car. The Alfa Romeo engineers were fortunate because front wheel drive already enjoys an excellent reputation among their customers (it is no mere chance that this alternative is chosen by most car manufacturers). Suffice it to say that over and above the general benefits of this type of structure (weight, passenger room etc.), the understeering behaviour of a front wheel drive engine allows the driver to respond to vehicle stress more intuitively under limit conditions: hence the feeling that front wheel drive is ‘more sincere’ than rear wheel drive.

A significant increase in driving safety, in other words. Opponents argue that front wheel drive can impair full driving satisfaction and control under certain conditions, giving rise to traction problems on corners, performance at the limit of understeer or steering reactions because the steering wheels are also the drive wheels. Alfa Romeo has overcome this disadvantage by developing the Q2 system that offers all the attributes of a front wheel drive system with significantly increased roadholding, traction and stability during over-run. At the same time, it lessens understeer during acceleration, the action of electronic controls and steering wheel vibrations. The following two practical examples highlight the technical potentials of the Q 2 system.
 

Example one: vehicle cornering

When cornering in conditions of poor grip (e.g. wet, snowy or muddy road) or during sporty driving, the inside wheels often lose grip due to the fact that the differential distributes torque to the wheel with the least load and takes torque away from the outside wheel that could be subject to higher friction since it has to bear the additional weight exerted by vehicle roll. This situation may determine two different responses, according to the equipment on the car. On a model without ASR – VDC, the perceived result is slipping of the inside wheel, loss of vehicle control (strong understeer) and lack of acceleration when coming out of the bend. If the vehicle is equipped with ASR – VDC, the steering assistance systems cut in to take power from the engine by adjusting the throttle. This makes it impossible to modulate the accelerator and gives the driver the unpleasant sensation of a loss of power and interaction with the vehicle. The result in both cases is a feeling of being at a standstill on leaving the corner.

What happens if the Q2 system is present: As the inside wheel begins to lose grip, torque is partly transferred to the outside wheel to ensure less understeer, greater stability, higher exit speed from the corner and fewer and less invasive vehicle control system operations. The net result is an increase in driving satisfaction and full control of the vehicle.

Second example: ground with poor grip.

When driving over ground with poor grip, the traction of the drive wheels is often different. For example, when driving after a snowfall or heavy rain, one wheel is on the edge of the carriageway in direct contact with lying snow while the other is in a clean, dry area. In these particular conditions, when the car sets off or accelerates strongly, the wheel subjected to critical friction conditions will slip with strong reactions on the steering wheel, unsatisfactory take-off and the need to make continual corrections to the steering wheel to maintain the trajectory.

What happens if the Q2 system is present: The negative effects are countered due to gradual transfer of torque toward the wheel that is able to exploit the greatest friction coefficient. This makes it easier, for example, to perform a hill start on a mountain road and safer and more comfortable to drive over road sections with poor surfaces.

The sophisticated Q2 system is yet another example of Alfa Romeo excellence in the quest for technical solutions geared for safety and driving satisfaction.