Page 1: Overview
Page 2: Safety, Agility, Traction, and Driving Pleasure All in One
Page 3: BMW xDrive
Page 4: The Arjeplog Testing Base
Safe, Superior and Pre-Emptive - BMW xDrive.
Never before was BMW able to offer its customers such a wide range of all-wheel-drive cars as in the 2006 model year. Indeed, comprising no less than four model series and almost 30 different models, the choice of all-wheel-drive options offered by BMW is truly outstanding. Precisely this is why BMW is in the lead also in this growing market segment, with BMW xDrive proving its merits in vehicles of all kinds. So it is no surprise that one out of every four BMWs delivered to customers today comes with all-wheel drive.
More traction and greater precision for enhanced driving pleasure.
Supreme driving characteristics and optimum traction on all roads and surfaces – these are “onlyâ€Â' two of the benefits offered by BMW’s intelligent xDrive permanent all-wheel-drive system combining the dynamic performance of rear-wheel drive with the traction benefits of drive power going to all four wheels.
The electronically controlled all-wheel-drive system distributes drive forces within fractions of a second, feeding engine power precisely to the right axle where this power can be translated directly into traction and forward thrust on the road. This variable distribution between the front and rear axle means a significant improvement of driving dynamics, agility, driving stability, and motoring comfort in practice. And these substantial benefits of BMW xDrive come out clearly in all of BMW’s all-wheel-drive models.
A further point is that BMW xDrive offers its positive effects not only when traction problems have already become evident. Instead, the system is able to determine in advance whether a loss of traction is developing and is therefore able to take appropriate counteraction in good time. Precisely this explains why xDrive sets the standard in all-wheel-drive technology.
For while conventional all-wheel drive only responds to the wheels once they have started spinning, xDrive acts in advance, actively withdrawing drive power from the axle with less grip and re-distributing this power to the wheels benefiting from greater traction on the road beneath. The central “brainâ€Â': the electronically controlled clutch.
Starting at the power divider behind the gearbox or automatic transmission, drive power is initially transmitted to the rear axle via the main shaft. The main shaft incorporates an electronically controlled multiple-plate clutch serving in turn to convey some of the torque via a layshaft to the front axle.
When driving in a straight line under normal conditions, 40 per cent of the drive power goes to the front, 60 per cent to the rear axle. As a result, a BMW featuring xDrive is virtually just as agile and dynamic in everyday motoring as a BMW with rear-wheel drive. Whenever necessary, however, drive forces may be transmitted variably and with infinite control to the front and rear axles by way of the multiple-plate clutch.
The multiple-plate clutch within the power divider takes only 100 milliseconds to completely open or close, performing this operation so smoothly and gently that the occupants will not notice anything.
What the driver will notice, however, is the even more harmonious behaviour of the car in a bend, the reduction of steering forces required and the higher standard of driving comfort, with DSC Dynamic Stability Control cutting in far more rarely than otherwise in controlling the brakes.
BMW all-wheel-drive cars do not suffer the disadvantages of permanent all-wheel-drive systems with a rigid, pre-determined distribution of drive forces such as undue tension in the drivetrain and steering under high frictional forces. This, quite simply, is because the axles are completely disengaged from one another in extremely tight bend radii, e.g. when manoeuvring, with the traction potential of all-wheel-drive being used again only when the wheels are subject to excessive slip.
Networked system for even greater safety.
Establishing a network with DSC Dynamic Stability Control permanently measuring and determining important parameters such as the steering angle, lateral acceleration and the yaw rate of the car, xDrive is able within fractions of a second to respond to any inadmissible deviation from ideal driving behaviour before the driver even notices what is happening. Drive forces are distributed between the front and rear axle in such a way that the car builds up a yaw force counteracting any inclination to under- or oversteer. In most cases, therefore, the car will stabilise without requiring any intervention in the brakes by DSC. To distribute drive forces quickly and precisely, the xDrive all-wheel-drive system, DSC and engine management are all connected to one another by ICM Integrated Chassis Management. The system is therefore able to intervene in the brakes as required parallel to the distribution of drive forces in order to enhance both traction and driving dynamics. And if necessary, engine management may also adjust and vary the drive forces.
Through this intelligent network, the xDrive all-wheel-drive system is able to respond quickly and precisely to any change in driving conditions, in the process increasing both safety and driving dynamics by a significant margin.
In the new BMW X5 even the optionally available Active Steering is integrated in this all-round network. Whenever the car oversteers, when countersteering forces are required, or in braking manoeuvres on surfaces with a varying frictional coefficient (modal split), appropriate but discreet countersteering is able to prevent the vehicle from serving out of control, ensuring that the car regains its driving stability.
Distributing drive forces as required.
Under normal conditions, drive power is distributed 40 per cent to the front and 60 per cent to the rear. But under very dynamic conditions or on road surfaces changing substantially, the distribution of drive forces may be varied infinitely as required.
The system is designed to completely disengage the front axle in an extreme case or, going to the other extreme, to connect the front axle rigidly to the axle at the rear. The rigid connection of the two axles established when required is the same as a 100 per cent longitudinal lock with conventional all-wheel drive on some models.
Superior handling under all driving conditions.
BMW xDrive compensates even an abrupt change in gas and engine load so smoothly and gently that the driver will not even notice any change in the distribution of drive forces.
In bends xDrive reduces both under- and oversteer by distributing drive power quickly and sensitively between the front and rear axles. Whenever the rear end of the car starts to swerve round (oversteer), the multiple-plate clutch will transmit more drive power to the front wheels, allowing the rear wheels to build up more side support and stabilise the car. And being combined with DSC, BMW xDrive recognises the risk of oversteering at a very early point in time, intervening before the driver even notices what is happening.
When understeering the car “pushesâ€Â' out of a bend over its front axle.
In this case the drive power conveyed to the front axle is consistently reduced, with up to 100 per cent of the drive power being conveyed to the rear wheels in an extreme case. So only if over- or understeer cannot be compensated by variable power distribution alone will DSC be activated in addition, intervening in the brakes and, if necessary, reducing engine power.
BMW cars featuring xDrive are particularly agile and nimble on fast but winding mountain roads. Because with the rear wheels easily tending to spin when accelerating dynamically out of a bend or hairpin, BMW xDrive instantaneously diverts some of the drive power from the rear axle to the front axle.
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