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New Fiat Panda Cross
4x4 drive system

Front-rear torque distribution with the viscous coupling, and locking differential for right-left distribution .

Like other four-wheel-drive (4WD) equipped cars and trucks, the 2006 Panda Cross offers the benefit that twice the torque of a two wheel drive (2WD) can be discharged to the ground, particularly on slippery surfaces.

The configuration chosen for the Panda 4x4 is a four wheel drive transmission with two differentials and a viscous coupling. Four wheel drive is engaged automatically and allows drive torque distribution over the front and rear axle according to the road surface and vehicle application requirements.

In normal driving on asphalt roads, 98% of the drive torque is directed to the front wheels so that the car can behave in a similar way to a front wheel drive vehicle, which is better for fuel economy and lower tyre wear, due to normal small differences in rotating speed between the front and rear wheels.

The Panda 4x4 is also equipped with an antislip system that operates during deceleration by exploiting the potential of the ABS system (i.e. making use of the sensors that record wheel rpm) and the electronic engine control system to prevent the engine braking torque and the viscous coupling from causing the rear end to lock during sudden decelerations on downhill slopes or on bends. Together with the four wheel drive system, this ensures better driving safety over slippery surfaces.

The viscous coupling forms an integral part of the rear differential unit to engage in a relatively immediate, automatic fashion when necessary. It contains a set of perforated or slightly finned discs submerged in a viscous fluid with specific properties: as the temperature rises, fluid viscosity increases. When the two driven wheels slip, they stir up this fluid. As soon as the temperature rises with this friction, the fluid becomes more viscous and tends to drag the discs together and transmit drive torque to the rear axle. The oil acts here as a sensor (it detects abnormal axle speed differences, by its temperature) and as an actuator (it counteracts the slipping effect by increasing its viscosity). 

Locking Differential function - For the first time in the Panda 4x4 range, the Cross SUV version is fitted as standard with the LD (Locking Differential) function which brakes slipping wheel and consequently transfers its torque to the other wheel on the same axis: for example, when starting over snowy, icy or muddy ground. This function can also be activated manually and acts below a threshold of 30 km/h (it disengages automatically over this speed).

The system compares the speeds of the drive wheels on the same axis, between left and right.. The speed is controlled by gradually braking the slipping wheel, increasing the pressure in the corresponding branch of the brake circuit. This allows the differential to transfer torque to the wheel with the best grip to get the vehicle out of trouble.

The Locking Differential function can be engaged only at speeds less than 30 km/h. Above this speed, the function disengages automatically, to safeguard the braking system and viscous coupling against overheating. 


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