BMW xDrive

BMW xDrive is the marketing name for the all-wheel drive system found on the BMW X1, X3, X4, X5, and X6 crossover sport activity vehicles. It is also optional on the 1 Series (2012–present), 2 series (2015-present), 3 Series (2000–present), 4 Series (2014), 5 Series (2005–present), 6 Series (2012–present), and 7 Series (2010–present).

Instead of a permanent torque split (which is featured in earlier systems), xDrive provides variable torque split between the front and rear axles through the use of a multi-plate wet clutch located in the gearbox on the output to the front drive shaft. This setup allows xDrive to modulate the torque split between the front and the rear axles, which is normally split at 40:60 ratio. If wheel slip is detected by the ABS/DSC system, xDrive can react within a tenth of a second to redistribute up to 100% of the engine power to the front or rear axle. The wet clutch is applied through a high speed electric servo motor turning a cam-shaped actuator disc. As the rear drive shaft is hard-coupled to the transmission output, full torque transfer to the front axle can only be achieved if the rear wheels have no traction and are both slipping.

xDrive is connected to the ABS and DSC systems. In the case that wheelspin or directional instability still occurs while xDrive is or has been modulating the torque split, DSC will brake independent wheels to regain traction and improve directional stability without driver intervention.

The front and rear differentials in xDrive vehicles are typically an open differential design, thus relying on brake application by the DSC system to transfer power from the slipping wheel to the wheel with traction.

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