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Old 11-15-2006, 03:38 PM
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BMW X5 #4

New technology to lower emissions and improve fuel economy

The new X5 also utilizes a number of technologies designed to reduce fuel consumption, which in turn lowers CO2 emissions. The approach was to consider all aspects of vehicle operation, with particular attention to reducing friction. The power-steering pump is designed to reduce hydraulic pressure in the system during straight-ahead driving, when no assist is required. In addition, the X5’s new Pentosin power-steering fluid reduces drag in low-temperature operation. Drag-reducing efforts in the differentials include double angular-contact ball bearings, which produce less friction than conventional bearings.

A stronger body structure provides the platform for an all-new suspension

An intensively engineered all-new body structure heightens the X5 capabilities in virtually all respects with only a relatively modest increase in weight. Choice of materials, arrangement and shapes of reinforcing elements, plus distribution of masses front-to-rear and bottom-to-top were all considered in the development of a structure that improves on the original X5’s remarkable capabilities—with respect to handling ability, riding comfort and passive safety. Results include an approximate 15% increase in torsional rigidity.

This structure makes up the foundation for the X5’s new suspension system, which consists of an all-new double wishbone multi-link front suspension. In place of the traditional strut, this new system has an upper lateral A-arm. The double-pivot lower arms are retained, so that on each side there are three links or arms. While the two lower arms preserve the advantages of the double-pivot strut system, the new upper arms increase the engineers’ ability to optimize the system’s handling and riding comfort.

The original system provided a number of benefits, including excellent steering feel and control, outstanding straight-line stability, and excellent steering return coming out of turns. The design also provided generous space for large brakes—a BMW trademark.

The new system accommodates all these requirements while providing a number of benefits of its own. By isolating the shock from lateral forces, the new system reduces friction and improves ride and handling. The anti-roll bars in this new design mount to the wheel carriers instead of the suspension arms, which increases their effectiveness and allows for smaller, lighter weight bars. Finally, the new design allows more flexibility in both shock absorber tuning and suspension geometry.

Enhancing the new front suspension is a new variable-ratio power steering unit, which quickens steering ratio as the wheels are turned farther from their on-center position. This fine-tunes steering response and reduces the amount of turning required at the steering wheel in tight corners or parking maneuvers.

Complementing this front suspension is a revised version of the previous X5 multi-link Integral rear suspension. This already sophisticated system has been adapted to the new X5’s weight, higher performance, run-flat tires and BMW’s own evolving standards of ride and handling. The new X5 now features aluminum upper and lower lateral arms and wheel carriers to reduce weight. More importantly, the reduction is in unsprung weight, which reduces inertia so the wheels can respond more accurately to uneven road surfaces. Finally, a significantly wider front and rear track on both the 3.0si and 4.8i improves agility, while a longer wheelbase improves ride and increases interior space.

Unique in the segment: Active Steering and AdaptiveDrive.

The new BMW X5 is the first vehicle in its class to offer Active Steering as an option. This advanced system developed by BMW offers the right steering ratio at all speeds. Up to a speed of approximately 55 mph (90 km/h), steering behavior is more direct, meeting the requirements of sporting and active driving. Another advantage is that the driver only has to turn the steering wheel twice from lock to lock. At higher speeds, on the other hand, the Active Steering transmission is more indirect, enhancing the directional stability of the vehicle and, accordingly, driving comfort.

Active Steering, when ordered, is combined in the new BMW X5 with Servotronic for optimal power steering boost at all speeds. Active Steering can also help to stabilize the X5 should the driver experience the onset of oversteering or understeering in a bend or in particularly demanding brake maneuvers. When applying the brakes on surfaces with varying frictional coefficients (split-friction braking), for example, Active Steering precisely but discreetly countersteers to help the X5 stop in a sure straight line.

Carefully coordinated interaction of the anti-roll bars and shock absorbers by way of AdaptiveDrive, part of the Sport Package in the U.S., is equally unique in this SAV’s segment. This combination of Active Roll Stabilization and Electronic Damping Control gives the new BMW X5 a standard of handling capability and ride quality never seen before in a vehicle of this kind. Using sensors, AdaptiveDrive constantly monitors and calculates data on the road speed of the vehicle, its steering angle, straight-line and lateral acceleration, body and wheel acceleration, as well as height levels. Then, based on this information, the system controls both the swivel motors on the anti-roll bars and the electromagnetic shock-absorber valves, controlling body roll and damping as required at all times. Simply by pressing a button, the driver can choose either a sporting or a more comfortable basic setting of AdaptiveDrive.
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