BMW X6 M Traction Test on Snow & Ice – Video
BMW xDrive and Dynamic Performance Control: ideal combination for traction and handling in a sports vehicle.
The success of BMW’s xDrive system of all-wheel drive results from the fact that it doesn’t merely improve traction in slippery road conditions, but also helps optimize handling under all road conditions.
With xDrive’s electronically controlled variable torque distribution between the front and rear wheels (via a multi-disc internal clutch), any tendency toward under- or oversteer is kept at bay – before the Dynamic Stability Control system (DSC) detects any need to intervene. Sensors constantly measure any incipient slip at the tires and react lightning-fast to vary the torque distribution appropriately. The programming of this action in the X5 M and X6 M is specific to these models, calibrated for a stronger accent on rear-wheel drive: this is but one of the many ways in which M-typical handling has been imparted to these AWD vehicles.
Dynamic Performance Control (DPC) – heretofore offered only on the X6 and now standard on both M models – augments xDrive by precisely apportioning torque between the left and right rear wheels; steering precision, vehicle stability and agility are thus further optimized. In short, DPC enables BMW to elevate the world standard for handling in AWD vehicles.
The system consists of two multi-disc clutches and two planetary gearsets, one on each side of the rear differential. Each clutch is actuated mechanically by an electric servo motor, which acts on the basis of inputs from the same sensors that feed their information into the DSC system: vehicle speed, throttle position, wheel rotational speed, steering angle and yaw rate.
Each clutch can be partially or fully engaged as dictated by these inputs and the DSC control unit’s complex algorithms, whereby the planetary gearbox increases the wheel speed on its side by up to 10%. In turn, this acceleration of wheel speed achieves the desired influence on handling. A full transfer to the one or other wheel can occur in as little as 100 milliseconds; at a maximum, there can be up to a 1328-lb-ft. torque difference between the two rear wheels.