Volvo's Plug-and-play AWD

"Volvo and all-wheel drive just go together," says Anne Bélec, the new president of Volvo Cars North America.

"Volvo and all-wheel drive just go together," says Anne Bélec, the new president of Volvo Cars North America. It may seem that way now since nearly half of all Volvos sold in the U.S. in 2004 came equipped with AWD, but the automaker didn't actually begin offering the feature until the late 1990s when it debuted on the 850 wagon. But with the proliferation of models of varying size and weight—from the compact S40 sedan to the sizable XC90 SUV—Volvo engineers had to come up with a cost-effective way to provide unique tuning. So they developed what is essentially a plug-and-play AWD module.

The mechanical portion of the AWD system is largely the same for every model. Designed by the Swedish supplier Haldex (www.haldex.com; Stockholm, Sweden), it uses a mechanical pump, control valve and wet multi-plate clutch to deliver up to 95% of power to the rear wheels in instances when front wheel traction is lost. (In normal driving, 95% of power is directed to the front wheels.) It also has an auxiliary electric pump that pre-pressurizes the system to ensure near-instantaneous power transfer. The difference comes in with the computer module mounted on the rear differential that controls the electric pump and control valve. Each module is programmed with six different software parameters based on the characteristics of the various vehicles. When it is installed on the assembly line the module communicates via the car's multiplex network with other ECUs to determine which model it's in, and then adjusts to the correct parameter automatically.—KEW