AWD Transfer System: General

WARNING: This page is about a different car, the 2013 Subaru Forester, 2012 Subaru Forester, 2011 Subaru Forester, and 2010 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.

This all-wheel-drive (AWD) transfer system uses a hydraulic multi-plate type clutch. The clutch is controlled by the TCM through a control valve.

The TCM has in its memory a set of duty ratio data, each defining at what ratio the transfer clutch should transmit the torque for a particular driving condition. Based on the driving condition information it receives from the corresponding sensors (engine torque, vehicle speed, throttle opening, gear range, slip of wheels, etc.), the TCM selects an appropriate duty ratio from the memory and uses it to control the solenoid valve. The solenoid valve then regulates the pilot pressure of the transfer control valve, which creates the pressure to the clutch from the line pressure. The clutch is engaged to a degree determined by the transfer clutch pressure thus created. Through this process, the torque from the engine is distributed to the rear wheels optimally according to driving conditions.