25 Years of All-Wheel Drive BMWs

via BimmerFile

For 25 Years BMW has been a leader in all-wheel drive technology. From the first 325iX to the latest X3 all-wheel drive has been a important and continually growing part of BMW’s business. We at BF have often derided the need for all-wheel drive as being born out of marketing. And while it’s true that many people driving xDrive equipped cars may not need the system, there are those that not only need it but require it. It’s because of this that, 25 after it’s introduction, BMW has expanded the all-wheel drive option to almost every car they make. BMW currently offers 45 models in which xDrive provides variable distribution of drive between the front and rear wheels. These models extend all the way from the BMW X models via the BMW 3 Series and BMW 5 Series ranges to the BMW 7 Series family of luxury Saloons.

1985 saw all-wheel drive offered for the first time for the BMW 3 Series – both as an extension of the model range and as an alternative to the customary BMW rear-wheel drive. By now BMW was using the transfer of power to both axles not only to optimise traction on loose surfaces and in adverse weather conditions, but also to enhance dynamic performance though corners. The latest version of the BMW xDrive all-wheel-drive system rises to this challenge more effectively than ever. Linking the all-wheel-drive system up with Integrated Chassis Management (ICM) means that all situations on the road can be recognised and evaluated to allow the necessary control interventions to be made at an early stage. These can be carried out by xDrive either on its own or in combination with Dynamic Stability Control (DSC) or Performance Control. The power is distributed quickly and with great precision to where it is needed, ensuring that the driver enjoys the handling characteristics he would expect from a BMW – even under extremely dynamic cornering.

In contrast to other manufacturers, who use all-wheel drive principally to make up for the shortfall in traction suffered by front-wheel-drive vehicles, BMW tunes its xDrive system to provide handling typical of rear-wheel drive. Even in normal situations on the road, all-wheel-drive BMW models send the lion’s share of drive to the rear wheels, the same place where the brand’s cars with only one driven axle turn power into optimum dynamic performance. This ensures that the hallmark BMW steering precision is virtually free from drive forces in all-wheel-drive models as well. Indeed, all-wheel drive actually enhances the driving experience through corners. In order to enable particularly precise turn-in and a high level of directional stability, the latest-generation xDrive sends more drive to the rear axle on the way into corners. And that takes the brand’s characteristic driving pleasure to a new level once again.

All-wheel-drive technology from BMW: rigorous further development, dynamic growth.

Over the last 25 years at BMW, all-wheel drive has developed from an option initially limited to selected models to a growth driver for the ongoing expansion of the model range. At the time it was launched in the second-generation BMW 3 Series, all-wheel drive was offered exclusively in conjunction with a 2.5-litre six-cylinder in-line petrol engine producing 126 kW/171 hp. Today, xDrive can be specified for the BMW 3 Series in tandem with any of three six-cylinder petrol engines, a four-cylinder petrol unit and a six-cylinder diesel powerplant.

The permanent all-wheel drive of the BMW 325iX unveiled in 1985 channelled power to the front and rear wheels at a constant 37 : 63 percent split. Visco locks in the transfer case and final drive took their cues from the difference in rotation speed between the front and rear wheels to provide virtually fixed connections if required, and in this way optimise traction and driving stability. From 1988 customers could also order a Touring variant of the BMW 325iX.

Three years later came the arrival of all-wheel drive in the BMW 5 Series, accompanied by the debut of electric control systems governing the distribution of power. The newly developed system had multi-plate clutches which could be controlled automatically and continuously to vary the usual distribution of drive in normal conditions – 36 : 64 percent between the front and rear wheels – as required. Initially, a hydraulically controlled multi-plate clutch was used at the rear axle, but this was later replaced by electronically controlled brake inputs. The control unit of the all-wheel-drive system took into account wheel speed signals from the anti-lock braking system, the rotational speed and position of the engine’s throttle valves and the status of the brakes when analysing the driving situation.

From the outset the all-wheel-drive system of the BMW 525ix – fitted with a six-cylinder petrol engine developing 141 kW/192 hp – proved to be

a superior concept to that of its competitors. The electronic control system allowed extremely rapid and precise reactions, which also led to neutral and safe handling characteristics in tricky conditions on wet or snow-covered roads. The first all-wheel-drive BMW 5 Series was available in both Saloon and Touring guise.

The creation of the Sports Activity Vehicle (SAV) segment opened up totally new dimensions for all-wheel drive. BMW caused a sensation with the introduction of this innovative new vehicle concept in 1999. The BMW X5 captured the imagination of its customers with a level of dynamic performance unmatched among its off-road peers. The characteristics of the BMW all-wheel-drive system also served this set of priorities. In normal driving conditions, engine power was distributed at a ratio of 38 : 62 between the front and rear wheels via a planetary gear set, while the standard-fitted Dynamic Stability Control (DSC), Automatic Differential Brake (ADB-X) and Hill Descent Control (HDC) equipped the BMW X5 equally as well for sporty driving as for challenges off the beaten track.

Innovative vehicle concepts and xDrive give BMW the edge.

Since the SAV concept successfully established itself in the shape of the BMW X5, BMW has been constantly building on its stand-out position in the all-wheel-drive vehicle market through the introduction of new models and the further development of its drive transfer system. All-wheel drive was made available for the BMW 3 Series once again as early as 2000 – this time in conjunction with two petrol engines and one diesel unit.

In 2004 BMW picked up the pioneering baton once more when it introduced the SAV concept into another vehicle segment. With more compact dimensions than the BMW X5 and even more agile handling, the BMW X3 was likewise very much one of a kind and indeed remained the only premium model in its class for a number of years.

BMW also stole a march on its competitors in the development of all-wheel-drive technology. The newly developed xDrive all-wheel-drive system, introduced for the BMW X5 alongside the launch of the BMW X3, boasted an extremely fast-working, electronically controlled multi-plate clutch in the transfer case and linked up with the DSC driving control system. This allowed it to provide an unrivalled platform for power distribution that could be adjusted as necessary at all times. For the first time, the driving situation could be analysed not only on the basis of wheel speed, but also using data supplied by the DSC system on steering angle, accelerator position and lateral acceleration, including the driving status deduced from these parameters. This laid the foundations for xDrive to become the world’s only intelligent all-wheel-drive system, a status it retains to this day. In contrast to conventional all-wheel-drive systems, which merely react to wheels that are already spinning, xDrive can identify any tendency to oversteer or understeer at an early stage and counteract it pre-emptively by adjusting the distribution of drive.

Over the years that followed it was not only the two X models that benefited from the exceptionally rapid and precisely calculated distribution of power, but also the BMW 5 Series Saloon and Touring models and the BMW 3 Series. In 2005, all-wheel-drive variants were introduced both for the fifth generation of the BMW 3 Series and for the fifth-generation BMW 5 Series launched a short time earlier. More than 600,000 units of the first-generation BMW X3 were sold worldwide before it handed over to the new model in 2010. A little earlier the BMW X5, the second generation of which had been in production since 2006, had passed the million-unit mark.

Assured traction, superior dynamics: BMW xDrive with new calibration and Dynamic Performance Control.

The extraordinary potential of both the BMW X model concept and xDrive technology has since spawned another wave of innovations. For example, the BMW X6 – still the world’s only Sports Activity Coupé – was launched in 2008, and the BMW ActiveHybrid X6 is also fitted with xDrive.
Since 2009 the BMW X1 has been the only vehicle of its kind in the premium compact segment.

As in the new BMW X3, xDrive can also be combined with Performance Control in the BMW X1 to make its handling even more agile. Carefully calculated brake impulses applied to the inside rear wheel around a corner combine with a simultaneous increase in engine power to ensure that the vehicle turns in extremely quickly and precisely. The BMW X6 is fitted as standard with Dynamic Performance Control, giving it even greater scope for adjusting the distribution of power. This system teams up with xDrive to provide the most captivating expression yet of BMW’s hallmark driving pleasure through corners. Dynamic Performance Control uses variable distribution of drive between the inside and outside rear wheel to enable exceptional agility and stability around corners, even under sudden load changes or in overrun.

The interplay of xDrive and Dynamic Performance Control can be experienced at its most intense in the BMW X5 M and BMW X6 M. The first high-performance sports cars with all-wheel drive to come out of BMW M GmbH are powered by an eight-cylinder engine with M TwinPower Turbo technology developing 408 kW/555 hp.

Alongside the impressive progress of the BMW X models, the range of all-wheel-drive variants of other model series has also been consistently expanding. xDrive is now available not only for the Saloon and Touring versions of the BMW 3 Series but also for the Coupé; a total of 15 model variants from the 3 Series range now have all-wheel drive. Four engine variants of the BMW 5 Series Gran Turismo are also available with xDrive. With its new set-up designed to enhance agility and precision through corners, xDrive offers a better platform than ever when it comes to providing an intensive driving experience and an ideal combination of dynamic capability and comfort. It was therefore no surprise to see all-wheel drive also being welcomed into the BMW 7 Series range. Customers can choose from three all-wheel-drive variants of the luxury Saloon – the BMW 750i xDrive, BMW 750Li xDrive and BMW 740d xDrive.

In addition, xDrive intelligent all-wheel drive is set for launch in the new sixth generation of the BMW 5 Series Saloon. The system will be available initially in the BMW 550i xDrive powered by a 300 kW/407 hp eight-cylinder engine, with two six-cylinder models and the first xDrive variants of the new BMW 5 Series Touring following in due course.