Electric Feed Pump
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2009 Volvo S60, 2008 Volvo S60, 2007 Volvo S60, 2006 Volvo S60, and 2005 Volvo S60. However, it is still accessible from the selected car via links, so may be relevant.
The electric feed pump is built into the coupling unit. The pump is supplied with power by the differential electronic module. When the engine is started and exceeds 400 rpm the differential electronic module supplies the feed pump with power.
The feed pump pumps fluid to the annular pistons. This pushes the rollers for the pistons into contact with the cam disc. At the same time hydraulic fluid flows to the operating piston. This eliminates play in the multi-plate clutch pack. The coupling is now able to react and regulate torque distribution rapidly.
All wheel drive is disengaged if there is a fault in the feed pump.