ATTESA-ETS
The Electronic Torque Split version of this all-wheel drive architecture was developed for usage in Nissan's vehicles with a longitudinal drive train layout, and was first used in August 1989 in the R32 Nissan Skyline GT-R and Nissan Skyline GTS4. It utilizes what is mostly a conventional RWD gearbox. Although the Skyline GT-R is exclusively AWD, ATTESA-ETS is also used in Nissan models that are also available as RWD such as the A31 Nissan Cefiro which was the second Nissan to feature the system exactly a year later in August 1990. Drive to the rear wheels is constant via a tailshaft and rear differential, however drive to the front wheels is more complex by utilizing a transfer case at the rear of the gearbox. The drive for the front wheels comes from a transfer case bolted on the end of an almost traditional RWD transmission (although the bell housing is slightly different to allow the driveshaft for the front wheels to pass it, the main body is exactly the same as the RWD transmission, the tail-shaft is different to couple to the transfer case). A short driveshaft for the front wheels exits the transfer case on the right side. Inside the transfer case a chain drives a multi-plate wet clutch pack, torque is apportioned using a clutch pack center "differential" (the system thus does not involve a regular gear differential as in a full-time 4WD layout, but rather a center clutch), similar to the type employed in the Steyr-Daimler-Puch system in the Porsche 959. On the rear differential is a high pressure electric oil pump, this pump pressurises Normal ATF oil (0-288psi) into the transfercase to engage the clutchpack. The higher the oil pressure the transfer case is supplied with, the more the clutch pack engages, this is how the torque to the front wheels is varied. The transfer case has its own dedicated ATF (Nissan special ATF) oil to lubricate the chain/clutch pack. The front driveshaft runs along the right side of the transmission, into a differential located on the right of the engine's oilpan. The front right axle is shorter than the left, as the differential is closer to the right wheel. The front left axle runs through the engine's sump to the left wheel. Video of ATTESA system components The ATTESA-ETS layout is more advanced than the ATTESA system, and uses a 16bit microprocessor that monitors the cars movements at 100 times per second to sense traction loss by measuring the speed of each wheel via the ABS sensors. A three axis G-Sensor mounted underneath the center console feed lateral and longitudinal inputs into an ECU, which controls both the ATTESA-ETS 4WD system and the ABS system. The ECU can then direct up to and including 50% of the power to the front wheels. When slip is detected on one of the rear wheels (rear wheels turn 5% or more than the front wheels), the system directs torque to the front wheels which run a viscous LSD. Rather than locking the AWD in all the time or having a system that is "all or nothing", the ATTESA-ETS system can apportion different ratios of torque to the front wheels as it sees fit. This provides the driver with an AWD vehicle that performs like a rear wheel drive vehicle in perfect conditions and can recover control when conditions aren't as perfect. From factory, the system is set up to provide slight oversteer in handling, and in fact the harder the car is cornered the LESS the 4wd system engages the front wheels. This promotes the oversteer rather than understeer which is apparent in most AWD/4WD vehicles. The advantage to a more traditional ATTESA (Viscous LSD) system is response in hundredths of a second.
