ATTESA E-TS
The Electronic Torque Split version of this all-wheel drive architecture is a more advanced system developed for Nissan vehicles with a longitudinal drive train layout. It was first used in August 1989 in the R32 Nissan Skyline GT-R and Nissan Skyline GTS4. Although the Skyline GT-R is exclusively AWD with manual transmission, ATTESA E-TS is also used in Nissan models that are available as rear wheel drive (RWD) with automatic transmissions fitted, such as the A31 Nissan Cefiro which was the second Nissan to feature the system exactly a year later in August 1990, and vehicles based on the Nissan FM platform (which are sold in certain markets under the Infiniti luxury brand).
The ATTESA E-TS version uses a mostly conventional RWD transmission. Drive to the rear wheels is constant via a tailshaft and rear differential, but drive to the front wheels is more complex by utilizing a transfer case on the rear of the transmission.
The drive for the front wheels comes from a transfer case bolted on the end of an almost traditional Nissan RWD transmission. A short driveshaft for the front wheels exits the transfer case on the right side. Inside the transfer case a multi-row chain drives a multi-plate wet clutch pack. Drive from the chain is apportioned using this clutch pack in the transfer case "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. This unit is lubricated with its own dedicated NS-ATF fluid supply (Nissan Special Automatic Transmission Fluid) and is not in any way connected to the fluid in the transmission. Some Nissan models have an external cooler with an electric pump to cool this fluid.
Situated on top of the rear differential is a high pressure, low volume electric pump. This pump pressurizes Normal ATF (0-288 psi) into the transfer case to engage the clutch pack. This fluid only engages the clutch pack and does not mix with the NS-ATF lubricating the tranfercase. The higher the fluid pressure the transfer case is supplied with from the pump, the more the clutch pack engages, enabling the torque to the front wheels to be varied. Exiting the transfer case, the front drive shaft runs along the right side of the transmission, into a differential located on the right of the engines sump. This is a cast aluminum unit, with the sump and front differential made as a single unit that cannot be separated. The front right axle is shorter than the left, because 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
To control the ATTESA E-TS system, there is a 16-bit computer that monitors the cars movements 10 times per second to sense traction loss by measuring the speed of each wheel via the ABS sensors. Also a three-axis G-Sensor mounted underneath the center console feeds lateral and longitudinal inputs into a computer, which controls both the ATTESA-ETS 4WD system and the ABS system. The computer can then direct up to 50% of the power to the front wheels. When slip is detected on one of the rear wheels (a rear wheel turn 5% or more than the front wheels), the system directs torque to the front wheels which run a non-limited slip differential. Rather than locking the AWD in all the time or having a system that is "all or nothing", the ATTESA E-TS system can apportion different torque ratios 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 the 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.
Some models fitted with the ATTESA E-TS system (such as the Nissan RS4 Stagea) have a "S" button on the dash. This will bypass the control system of the ATESSA E-TS computer and lock the transfer case into full 4WD. This is to be used at low speeds in snowy/icy conditions only as understeer is greatly increased in this mode.
A reviewer said that the 2009 Infiniti G37's ATTESA E-TS had more sportiness and faster reaction time than competing AWD systems such as Audi's quattro, BMW's xDrive, and Mercedes-Benz's 4MATIC.
Read more about this topic: ATTESA