Auto Channel

Page 1: Introduction
Page 2: Concept
Page 3: Design
Page 4: Power Units
Page 5: Automatic Trans.
Page 6: Suspension
Page 7: All Wheel Drive
Page 8: Body & Safety
Page 9: Light Concept
Page 10: Features/Equipment
Page 11: Production
Page 12: History

All-Wheel Drive

BMW xDrive in the Coupé: A Perfect Match of Driving Dynamics and Safety

• First coupé with BMW’s intelligent xDrive all-wheel-drive system

• Proactive control for enhanced driving dynamics

• Fully variable power distribution for maximum traction

Standard drive with the engine upfront and the drive wheels at the rear guarantees superior performance and maximum driving pleasure also in the new BMW 3 Series Coupé. Fitted lengthwise at the front, the straight-six power units convey their superior output to the rear wheels via either a manual gearbox or an automatic transmission, the superior power provided by the engines being converted particularly effectively and without any loss of dynamism into supreme traction on the road.

To add further benefits in traction to this fascinating driving experience, the new BMW 3 Series Coupé is available not only with standard wheel drive, but also, as a particularly interesting alternative, with BMW’s “intelligentâ€Â' xDrive all-wheel-drive system. Masterminded by an electronic brain, this sophisticated all-wheel drive distributes the power developed by the engine variably between the front and rear axle, enhancing safe and stable transmission of power on slippery surfaces as well as roads with a varying frictional coefficient. And last but certainly not least, xDrive also enhances the agility of the new BMW 3 Series Coupé under dynamic driving conditions.

BMW xDrive is a standard feature on BMW’s Sports Activity Vehicles, and is optional on the Saloon and Touring models of both the BMW 5 and 3 Series. And now xDrive comes for the first time also on a BMW Coupé. Indeed, this combination is particularly attractive and consistent, with xDrive promoting not only traction, but also driving stability, safety, and driving dynamics. So in the BMW 3 Series Coupé all-wheel drive enriches the fascinating driving experience offered by the two-door model by yet another element of pleasure and perfection.

Drive power going to where it is needed.

Featuring an electronically controlled multiple-plate clutch in its power divider, BMW xDrive responds with unusual speed and unique flexibility to changes in driving conditions. Almost instantaneously, drive power is supplied to where it is needed most.

The power divider is flanged in compact arrangement directly on to the manual gearbox or automatic transmission at the rear, feeding drive forces first through a rigid shaft to the rear axle. This main shaft incorporates the electronically controlled multiple-plate clutch diverting a specific share in the engine’s drive power through a by-shaft to the front axle whenever required. This enables xDrive to share out engine power infinitely and variably between the front and rear axles, in an extreme case even connecting the two axles firmly to one another or disconnecting them completely.

Under normal driving conditions the BMW 3 Series Coupé retains its typical driving impression also when fitted with xDrive, thus focusing above all on the rear axle conveying more than 60 per cent of the engine’s power to the road. But at the same time xDrive permanently monitors the stability of the car, intervening whenever necessary by changing the distribution of drive forces in the interest of additional safety and optimum dynamics. And while conventional all-wheel drive only responds once the wheels have started to spin, xDrive anticipates spin in advance, withdrawing drive power from the wheel involved and feeding power instead to the wheels with more grip.

Networked communication for determining wheel slip before it even occurs.

To provide this function, xDrive is directly networked with the car’s DSC Dynamic Stability Control. Hence, the DSC sensors give xDrive all the data required for permanently monitoring driving conditions. Networked in this manner, xDrive serves as a proactive control and safety system determining in advance what is now about to happen.

To anticipate an upcoming situation in advance, the system uses information from both the accelerator pedal and from DSC Dynamic Stability Control. The yaw rate sensor, for example, is able to determine rotational movement of the Coupé while a steering angle sensor monitors the position and lock of the steering wheel. Applying information from the wheel sensors on the speed of the car as well as lateral acceleration, and taking engine data into account, xDrive is able to determine the current driving conditions at all times, even anticipating any upcoming change affecting the car. In the process the system even considers differences in speed between the front and rear wheels, differences in wheel circumference, or clutch wear.

The optimum clutch force in each situation is set via the power divider control unit, the actuator and multiple-plate clutch, then being allocated to each axle in order to provide exactly the right drive forces required for maximum and safe traction at all times. Despite the complex calculations required for this purpose, the distribution of torque is a high-speed, instantaneous process requiring just 100 milliseconds even for the maximum change in power distribution.

Preventing over- or understeer right from the start.

Offering these qualities, all-wheel drive in the BMW 3 Series Coupé improves not only the car’s traction, but also its driving dynamics. In a bend xDrive reduces the usual under- or oversteer by quickly and sensitively distributing drive forces between the front and rear axles. And should the BMW 3 Series Coupé start to oversteer in a bend, with the rear end of the car moving out, xDrive closes the multiple-plate clutch even further and thus feeds extra power to the front wheels. This allows the rear wheels to once again build up higher lateral forces and stabilises the car in the process.

Combined with DSC Dynamic Stability Control, xDrive also recognises any tendency to oversteer at a very early point, intervening even before the driver notices any change in driving conditions and keeping the BMW 3 Series Coupé precisely on track.

BMW xDrive is equally reliable in counteracting understeer: As soon as the Coupé starts to “pushâ€Â' out of a bend on its front wheels, xDrive again recognises what is happening very early on thanks to information provided by DSC. Its immediate action is to reduce torque on the front wheels, in an extreme case feeding up to 100 per cent of the engine’s torque to the rear. DSC Dynamic Stability Control is therefore required to stabilise the BMW 3 Series Coupé by intervening in the brakes only when variable power distribution alone is no longer sufficient to set off over- or understeer.

Using engine power without any losses.

The new BMW 3 Series Coupé with xDrive is particularly dynamic and agile in rapidly climbing mountain passes. When accelerating dynamically out of a bend, for example, the inner rear wheel generally tends to spin. Cars equipped with xDrive are able to counter this tendency by immediately withdrawing some of the engine’s power from the rear axle and feeding that power to the front wheels. So even in such a situation, xDrive turns every horsepower delivered by the engine into superior traction for superior motoring qualities and safety.

Acting instantaneously, xDrive handles even an abrupt change in engine power so effortlessly that the driver will not even notice the change in power distribution. While the time-lag between pressing down the gas pedal and building up engine power is at least 200 milliseconds, xDrive closes or opens the multiple-plate clutch completely within just 100 milliseconds. The result, clearly, is truly homogeneous driving behaviour in every situation.

Optimum comfort when parking the car and when driving in snow.

In everyday traffic xDrive serves furthermore to efficiently eliminate an undesired side-effect of rigid all-wheel-drive systems: Disconnecting the axles completely from one another, xDrive turns into rear-wheel-drive only when parking or manoeuvring the car, without requiring any intervention on the part of the driver. Indeed, all the driver notices is that there is no unpleasant tension or distortion in the drivetrain or any unwanted influence on the steering.

Contrary to conventional all-wheel drive, xDrive handles even extremely difficult road conditions quickly and effectively. In winter, for example, setting off from a snowbound car park into the traffic flowing by is often an unpleasant challenge when the front wheels are running on firm and dry asphalt, the rear wheels on snow or ice. In such a case conventional all-wheel drive always responds with a certain delay and only conveys limited drive forces to the wheels with better grip. By contrast, a BMW Coupé equipped with xDrive is able to accelerate spontaneously even in such a situation, the intelligent all-wheel drive feeding almost 100 per cent of the engine’s power in just 0.1 seconds to where it provides suitable traction. Hence, there is no need for the brakes to intervene in the wheels spinning and there is no loss of drive power.

On gradients with slippery surfaces such as ice or snow, locking action on the front and rear wheels serves furthermore to prevent individual wheels from spinning. Again, therefore, DSC is required to cut back engine power or apply the brakes on the wheels only under far more difficult road conditions. Then, when continuing afterwards, the locking action reduces the risk of losing longitudinal or lateral forces on individual wheels, giving the driver the benefit of safe and agile roadholding and performance. The bottom line, therefore, is that the BMW 3 Series Coupé with xDrive offers all its dynamic benefits equally impressively and consistently also in winter.