CAN in all wheel drive

Source: CAN Newsletter June 2006

Volvo has refined their all wheel drive system (AWD) with an active, electronically controlled and electro-hydraulically guided multiple disc clutch. This clutch is networked via CAN to transmit information between the electronic control modules of the clutch and the wheel-, body-, and steering-sensors, which also control the drive and traction dynamics DSTC (dynamic stability and traction control). The clutch distributed the drive power depending on the current level of grip stagelessly. The default power distribution amounts to 95 % to 5 % between front and rear axis, but may be changed depending on the grip state to a maximum 35 % to 65 %. The variable distribution of power to all four wheels Instant Traction is being used in the company’s XC90 V8, as well as in the AWD series of the S60, V70, S80, XC70 and XC90 vehicles. The all wheel drive system avoids understeering on slippery surfaces and distortion of the power steering during parking or maneuvering. The AWD recognizes these situations despite differing revolutions speeds between the axes and does not interfere into the drivers actions. During braking with the help of ABS or the DSTC, the clutch is opened and the back wheels virtually run free. This  decoupling takes less than 100 ms.