Ferrari have developed a new optional four-wheel drive system, dubbed as "insertable 4x4", which is designed to maximise the performance capability of their sports cars under all conditions.  This latest project follows on from an 'adaptable' four-wheel drive system that was developed in Maranello last year and clearly demonstrates again that Ferrari are looking very closely at this form of traction.

The new insertable four-wheel system seeks to remove the disadvantages of a permanent four-wheel drive arrangement, particularly the loss of engine torque associated with it, by using a system that can be taken out of the equation as required. However Ferrari's engineers have worked hard to remove the obstacles in the way of an optional four-wheel drive system and create a set-up "which is easy and cost effective to implement, free from the drawbacks described above and which at the same time allows for an increase in performance, stability and traction control in all grip conditions."

"Currently, a sporty, high performance car presents rear wheel drive and is provided with a self-locking differential aiming at maximising motive torque transmitted by the rear wheels to the road surface in all conditions," say Ferrari. "Rear wheel drive with self-locking differential is a premium for sporty driving in either optimal grip conditions (dry road) or reasonable grip conditions (wet road); however, such a solution in combination with a high motive torque and large-sized tyres entails very difficult and potentially dangerous driving in poor grip conditions (flooded or icy road).

"The use of permanent or insertable for wheel drive has been proposed in order to improve the driveability of a sports car in poor grip conditions. Whilst permanent four wheel drive considerably improves the behaviour of motor vehicles in poor grip conditions, it presents the drawback of increasing loss of torque in the transmission system and conferring to the car a behaviour in optimal grip conditions which is not always appreciated by drivers.
 

"Insertable four wheel drive allows the driver to decide whether to use rear-wheel drive or four-wheel drive; in this way, the drive may use rear-wheel drive in optimal grip conditions and four-wheel drive in poor grip conditions. However, insertable four-wheel drive is typically complex and costly to manufacture; furthermore, the driver may not realise the presence of sheets of ice on the road and may not therefore engage four-wheel drive in a timely manner.

Ferrari's new insertable four-wheel drive system is based on the traditional RWD layout, where the main driving wheels are constantly connected to the engine via the usual gearbox and clutch arrangement. The second pair of wheels are selectively connected via their new insertable transmission system. "The insertable transmission system presents a second clutch, which on one end is connected with fixed transmission ratios to the crankshaft upstream of the gearbox and on the other is connected with fixed transmission ratios to the secondary driving wheels," say Ferrari. The insertable transmission system also transfers motive torque to the front wheels when a difference between the rotation speed of the front and rear wheels occurs; ie, essentially when the driving wheels slip".

Technically, the secondary clutch, which controls the provision of torque to the front wheels, is controlled by an electronic control unit. Factors such as the vehicle's "longitudinal speed", "longitudinal acceleration", "transversal acceleration",  and accelerator pedal position and movement characteristics, are taken into account as input for the the electronic control unit. The electronic control system has also been engineered to include memory units, called "maps", where parameters describing the vehicle's dynamic characteristics can be stored, each of them optimised for different grip conditions.

Ferrari's new insertable four-wheel-drive system, which has been road-tested, can both be used for their usual mid-engine cars, as well as the front-engine cars with transaxle layout.