BMW's new all-wheel-drive system makes Mid East debut at Dubai Motor Show

The xDrive all-wheel-drive system provides not only optimum traction on bad roads, but also ensures an even higher standard of driving safety and performance through its electronically controlled, variable distribution of power front-to-rear.

"The xDrive concept comprises two key ingredients - an electrically activated multiple-plate clutch which changes drive distribution from axle-to-axle, and the familiar Dynamic Stability Control (DSC) system that regulates power to each wheel," said Robert Bailey-McEwan, Managing Director, BMW Group Middle East.

"Responding in just 100 milliseconds, xDrive is quicker than conventional four-wheel-drive systems which rely on the build up of hydraulic pressure to channel drive forces.

"xDrive is the perfect system for maximising the driving enjoyment of BMW's Sports Activity Vehicles, the X3 and X5. Through its variable distribution of drive, front-to-rear, it offers intelligent power as an antidote to loss of control, rather than braking or power reduction via DSC. xDrive keeps the fun in driving," added Bailey-McEwan.

Unlike other all-wheel-drive systems, xDrive is proactive in its effect, taking the driver's commands such as the position of the gas pedal into account to recognise when all-wheel drive will be helpful right from the start, while conventional all-wheel drive systems only respond once the wheels have started to spin. This ensures superior all-wheel-drive performance prior to the commencement of any spinning action.

The "heart" of BMW's xDrive, which cannot be switched off, is housed within the power divider: This is the electronically controlled multiple-plate clutch masterminding the flow of power to the front axle according to current requirements within fractions of a second. In extreme cases the front and rear axle may be totally disconnected or firmly connected to one another, such a firm or rigid connection then acting in the same way as a longitudinal differential on conventional all-wheel drive.

The transverse differential function, that is the distribution of power to both of the front or rear wheels, is provided by the DSC system using the electronic brake intervention function: Whenever a wheel is about to spin without transmitting any power, the brakes are applied and it is slowed down accordingly. This then allows the differential in the axle transmission to automatically feed more power to the wheel on the other end of the axle.

The xDrive uses all the information compiled by the on-demand DSC system, taking, say, any rotating motion of the vehicle into account by way of the yaw rate sensor and determining the lock of the steering wheel by means of the steering angle sensor. Together with information on road speed provided by the wheel sensors, information on lateral acceleration of the vehicle as well as engine data, xDrive is able to determine at an early point in time what current driving conditions are like, thus spreading out drive forces perfectly between the front and rear axle. In practice, this means a considerable improvement in agility, particularly advantageous on winding mountain roads.