AWD: The five types of Subaru systems

Active All-Wheel Drive:

Active AWD is used on all Subaru models powered by the naturally-aspirated four-cylinder boxer engine and equipped with the four-speed automatic transmission, as well as on the turbocharged Forester 2.5L XT equipped with this transmission.

An electronically managed continuously variable transfer clutch actively manages power distribution and ensures that the wheels with the best traction receive more power. Power transfer is governed by slippage in the clutch plates.The Transmission Control Module (TCM) controls the multi-plate transfer clutch.

Active AWD can adjust the power split in an instant, depending on many input factors. If the front wheels begin to slip, the TCM increases hydraulic pressure on the transfer clutch, reducing slippage of the plates and transferring the power to the rear wheels.

As the front wheels regain traction, the TCM reduces pressure on the clutch, increasing slippage of the plates and transferring power to the front. The TCM monitors input from speed sensors on the front and rear drive shafts and also takes input from the throttle position and the transmission. All of these factors cause the TCM to select a software strategy that determines how aggressively it adjusts the power distribution.

Active AWD varies the power distribution according to driving conditions. When throttle input signals acceleration, the system responds by transferring more power to the rear wheels to account for rearward weight transfer. When releasing the throttle indicates deceleration, power transfers to the front wheels to enhance braking performance.

The system enhances cornering performance as well. When the driver lifts off the throttle and applies the brake to enter a turn, power transfers to the front wheels for greater steering control. As the car exits the turn and accelerates, power transfers to the rear wheels for added traction.