The addition of the xDrive system to the facelifted BMW X5 is said to have improved the luxury SUV’s offroad capabilities. XDrive, hill descent control and trailer stability control will be standard on the new X3.

The addition of the xDrive system to the facelifted BMW X5 is said to have improved the luxury SUV’s offroad capabilities. XDrive, hill descent control and trailer stability control will be standard on the new X3.


The new xDrive all-wheel-drive system uses the information gathered by the DSC and yaw rate sensor to determine any rotating movement of the vehicle and the steering angle sensor registering the position of the steering wheel. Together with information on the speed of the vehicle provided by the wheel sensors as a function of lateral acceleration, and on the basis of engine data, xDrive is able to determine the specific driving situation at an earlier point in time, distributing drive power perfectly between the front and rear axles.


Thus xDrive provides any required shift of torque and drive forces between the front and rear axles with maximum efficiency in the shortest possible time, BMW claims. When setting off under everyday motoring conditions, the multiple-plate clutch remains almost completely locked until the X3 has reached a speed of approximately 20 km/h. Then the system distributes engine power fully variably between the rear and front axle, in all cases as a function of driving conditions.


A bearing block is connected to the oil sump of the X3 to allow the use of two drive shafts exactly equal in length. The advantage is that the steering remains free of drive forces, since the drive shaft deflection angle is the same on both sides - at the left and right. A further advantage of this configuration is the maximum steering lock provided in this way, giving the SUV a turning circle of 11,7 m.


The X3 does without an additional reduction gear as required for extreme off-road motoring. BMW claims the absence of a low range gear keeps the X3’s “centre of gravity as low as possible despite ample ground clearance” and saves weight.


Like all other BMWs, DSC can be deactivated on the X3, giving the sporting driver the opportunity to enjoy the dynamic driving qualities of the X3 in a controlled drift. The xDrive all-wheel-drive system, in turn, cannot be deactivated.


Hill Descent Control


HDC is an “intelligent” downhill driving technology for steep gradients. On loose or slippery surfaces, HDC enables the driver to proceed down a hill smoothly without having to intervene. This automatic speed control system, which is integrated with DSC, operates by applying the brakes individually as required on all four wheels.


HDC is activated and deactivated by a button in the cockpit. Available at speeds of less than 35 km/h, HDC automatically reduces the speed of the X3 in a linear deceleration process to approximately 8 km/h, then keeping speed consistently at this level. Now, depending on his requirements, the driver is able to adjust his speed within the HDC control range between 6 and 25 km/h by pressing the “+” and “–” keys on the cruise control in the multifunction steering wheel. And as soon as the driver accelerates above the 35 km/h limit, HDC switches over to the stand-by mode, finally being deactivated at speeds of more than 60 km/h.


Trailer stability control


BMW South Africa is promoting the X3 as being ideally suited for towing a trailer. The trailer stability control system offers additional safety against the risk of vehicle instability building up to cause uncontrolled swerving. The X3 2,5i is configured to tow a trailer of up to 1 800 kg and the 3,0i 2 000 kg.


Trailer stability control recognises such dangerous swaying motion immediately and slows down the vehicle, applying the brakes also on the trailer to reinstate vehicle and trailer stability and once again build up safe driving conditions. The control unit “recognises” that a trailer has been attached as soon as the power supply has been connected to the car, thus being activated and serving to intervene above 65 km/h.


The control function is based on constant supervision of the yaw rate signal informing the DSC control unit of any rotating movement of the vehicle. With this signal being permanently supervised, any pendulum motion is recognised by the typical course of the signal detected by the control unit.


Then, as soon as the signal exceeds a certain limit, brake pressure is built up on all four wheels, providing stopping power without any intervention on the part of the driver. At the same time engine power is briefly reduced to a minimum and the rapid reduction in speed should ensure that the vehicle and the trailer is stabilised in the quickest possible time.

Original article from Car