Transfer Case- Service Techniques: xDrive: Introduction

xDrive is an all-wheel drive system that links Dynamic Stability Control (DSC) system to an electronically controlled multi-plate clutch in the transfer box.

The electronically controlled multi-plate clutch smoothly distributes the drive torque as required to the front axle. The rear axle is always powered.

All of the drive torque is applied to the rear axle when the multi-plate clutch is separated.

• > E53, E83
• > E70

xDrive constantly communicates with the DSC. The drive-dynamic input information is computed in the DSC control unit.

Important information is:

• Accelerator pedal position
• Engine torque
• Drive-dynamic state

The DSC calculates the necessary locking torque. The locking torque is communicated to xDrive. This allows xDrive to register whether the vehicle is able to follow the driver's commands. xDrive intervenes to counter the threat of any tendency for wheel spin, oversteer or understeer. xDrive regulates drive torque distribution between the two axles to meet driving demands.

Only if xDrive cannot maintain the vehicle's course on its own will DSC also intervene. Engine output is reduced and individual wheels are specifically braked.

The drive torque is delivered to the axle that has better traction when road conditions change, such as on snow, ice or a loose road surface.

The transfer cases are matched to vehicles as follows:

• E53: ATC 500 transfer case

  (ATC = Active Torque Control)

• E70: ATC 700 transfer case
• E83: ATC 400 transfer case

The transfer cases differ in the following points:

• Different number of plates in the multi-plate clutches
• Different clearance between the input and output shafts to the front axle
• Propeller shaft inserted into the front axle differential on the E53, E70, and flange-mounted on the E83

The transfer case is designed to be stronger on the E53, E70 in order to match the higher engine torques.

The advantages: 

xDrive delivers the following advantages through demand-oriented drive torque distribution:

• Outstanding driving stability fully up to the limit range
• Optimal forward momentum
• Excellent traction in all road situations

xDrive is standard equipment on the E70, E83 and on the E53 from October 2003 with the new model version.