ATESSA

ATTESA (acronym for Advanced Total Traction Engineering System for All-Terrain) is a four-wheel drive used in some automobiles produced by the Japanese automaker Nissan.

ATTESA
The 'mechanical' ATTESA system was developed for transverse layout vehicles and 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 gearbox 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 centre viscous limited slip differential, into a transfer case splitting drive to a co-located front differential, and tail shaft connected to the vehicles rear differential.

2000+ ATTESA Update
In the new system, as with a normal FWD car, the gearbox contains 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 the driveshaft (i.e. there is no longer a "centre" 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 as there are less losses due to the normal FWD operation, however it is no longer a full-time 4wd system.

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.

ATTESA-ETS Pro
In 1995, with the introduction of the R33 Skyline GT-R, Nissan introduced a new version of their ATTESA system. It was named ATTESA-ETS Pro, as an upgrade from the earlier ATTESA ETS. It was standard equipment in the R33 Skyline GT-R Vspec model, however it was offered as an option on the standard R33 Skyline GT-R, and called the "Active LSD option". It was also standard equipment on all R34 Skyline GT-R models.

ATTESA-E-TS Pro differs from the standard ATTESA-E-TS in a few ways. Where ATTESA-E-TS controls the front to rear torque-split, the Pro is also capable of left-and-right torque split to the rear wheels. This is done via an active rear limited-slip differential. Additionally, the ATTESA-E-TS Pro was marketed as controlling the four-wheel independent ABS braking system. This is not part of the AWD system, but the ECU makes use of the same sensors to determine wheel slip and traction.

On ATTESA-E-TS Pro equipped vehicles, the front differential remains a standard limited slip differential, not being linked to the ATTESA-E-TS Pro system.

ATTESA-ETS (GT-R version)
The 2009 Nissan GT-R uses an updated version of the ATTESA-E-TS, and is designed to work with the car's rear transaxle layout. The system is unique in a way that it utilizes two driveshafts under the vehicle's centerline, with a second driveshaft running slightly to the right of the main driveshaft and engine sending power to the front wheels. It is so far, the only rear transaxle-based AWD system for a front engined car in production.

Unlike the previous ATTESA systems which relied heavily on mechanical feedback, the system in the GT-R uses electronic sensors and hydraulically-actuated clutches. It also has a yaw-rate feedback control system, effectively managing slip angle. Front rear torque split can go from 2:98 during a standing start to a maximum of 50:50

Models and ATTESA type
ATTESA E-TS system is used in the following models:
 * R32 and R33 (1989-1997) GTS4 Skyline
 * GT-R - 1989–2003
 * Nissan Stagea
 * A31 Cefiro
 * Infiniti G35x/Nissan Skyline (V35 & V36)
 * Infiniti M
 * Infiniti FX
 * Infiniti EX35 (with Active Brake Limited Split for side-to-side torque split, as needed)
 * Nissan Fuga (Known as Infiniti M in export markets)

ATTESA E-TS Pro system is used in the following models:
 * R33 (1995-1997) Nissan Skyline GT-R (offered as a factory option)
 * R33 Nissan Skyline GT-R V-spec
 * R34 (1998-2002) Nissan Skyline GT-R (all models)

ATTESA E-TS Pro (GT-R version) is used in the following model(s).
 * 2008/2009 Nissan GT-R