ATTESA

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ATTESA (acronym for Advanced Total Traction Engineering System for All-Terrain) is a four-wheel drive system used in some automobiles produced by the Japanese automaker Nissan, including some models under its luxury marque Infiniti.

The 'mechanical' ATTESA system was developed for transverse, or front-wheel-drive vehicles and was first introduced with the RNU12 Bluebird in the Japanese market, entering production in September 1987. The system ran right throughout the U12 series (RNU12/HNU12) and was fitted to numerous U12 models with differing engine and transmission combinations. An almost identical system is fitted to the RNN14 GTi-R Pulsar and the HNU13 Bluebird and the HNP10 Primera, finding usage in numerous other Nissan models.

Quite similar to offerings from other manufacturers, drive passes from the gearbox to a center viscous limited slip differential, into a transfer case splitting drive to a co-located front differential, and tail shaft connected to the vehicle's rear differential.

From 2000 model year onwards, the system received an update where, as with a typical FWD car, the transaxle now contained a differential that drives the front wheels. However, an extra shaft from this differential also drives a bevel gear housed in the transfer case that permanently turns a driveshaft for the rear wheels (i.e. there is no longer a "center" differential). Housed in the rear differential is a viscous coupling that in normal conditions is disengaged. This means that for general driving, the system is FWD only. When the computer detects slippage of the front wheels, the viscous coupling engages and transfers up to 50% of the torque to the rear wheels. This system is superior in some aspects since the standard operation is FWD there is less power lost due to friction. However, it is no longer a full-time 4WD system, and since the coupling is in the rear differential, the driveshaft itself is constantly driven even though it is not connected to anything, which saps some power and efficiency (the analogue being the front driveshaft of a part-time 4x4 truck without locking hubs).