Description & Operation: xDRIVE

xDrive is a new four-wheel-drive system that delivers continuously variable input torques to the front and rear axles. xDrive comprises Dynamic Stability Control (DSC) and an electronically controlled multi-plate clutch in the transfer case. The DSC triggers the electronically controlled multi-plate clutch to supply continuously variable and power-oriented input torques to the front and rear axles. The rear axle is always powered. All of the input torque is applied to the rear axle when the multi-plate clutch is separated. xDrive communicates permanently with the DSC and receives from it, for instance, the following information:

• Whether the accelerator is pressed or released.
• Whether the engine torque is increasing or decreasing.
• Whether the car is driving straight ahead or in a curve.

xDrive continuously evaluates this information to detect whether the car can respond to the driver's requirements. xDrive intervenes to counter the threat of any tendency for wheelspin, oversteer or understeer. xDrive regulates input torque distribution between the two axles to meet driving demands. DSC only ever engages (by reducing engine power output and selective braking of individual wheels) should xDrive need assistance to keep the car on course. The input torque is delivered to the axle that has better traction when road conditions change, such as on snow, ice or a loose road surface.