BMW under wraps
CAMOUFLAGE: NEXT GENERATION OF 3 SERIES GOES THROUGH ‘GREEN HELL’
Baptism of fire for drive and suspension technology at Nürburgring.
The next generation of the BMW 3 Series Sedan is just completing the crucial stages on the way to serial production maturity. There was only one possible setting when it came to driving dynamics testing and set-up runs: the legendary Nordschleife at Nürburgring.
Test runs at the “Green Hell” traditionally serve as a baptism of fire for the drive and suspension technology of newly developed BMW models. A particularly extensive testing programme was developed for the camouflaged prototypes of the new BMW 3 Sedan.
After all, the comprehensive renewal of the wheel suspension, steering, damping/suspension and brakes provided the developers with a broad range of opportunities to optimise ride comfort and dynamic performance, enabling the ultimate sports sedan for the mid-range premium segment to mature lap by lap.
The underlying concept of the four-door model shows just how much the development process for the new series is geared towards enhanced sporty flair. The centre of gravity is 10mm lower than in the predecessor model, axle load distribution is balanced at a harmonious 50:50 and the total weight adjusted for fittings is as much as 55kg less.
The rigidity levels of the body structure and suspension attachment have been significantly enhanced. The car’s agility and steering precision benefit from expanded track widths, while increased wheel camber levels offer additional potential for maximum transverse dynamics.
In terms of the engine portfolio, one particularly striking feature is a thoroughly revised 4-cylinder petrol engine.
It is the most powerful ever to be fitted in a BMW series production model, yet its fuel consumption figures are still 5% below those of the predecessor engine: one contributing factor here is the further developed 8-speed Steptronic transmission.
A particulate filter optimises the emissions response of the new engine, enabling it to meet the Euro 6d-TEMP exhaust standard.
Not only is the body lighter and more rigid, the same is also true of the front and rear axle in the new BMW 3 Series Sedan. The result is a specific orientation of the axle kinematics and elastokinematics towards supreme yet sporty drive properties.
The key feature in terms of suspension development in the new BMW 3 Series Sedan is its innovative damping system, with lift-related dampers. As such, the vibrations that occur when compensating for bumps on the road and during dynamic cornering can be neutralised precisely – the perfect basis for striking a unique balance between sporty flair and ride comfort.
Long known for its diversity, the track layout of the Nürburgring Nordschleife quickly transpired as the perfect setting for selective refinement of the interaction between the new damping technology and the other suspension components. “We’re using the lift-related dampers as an active set-up element so as to create supreme driving properties in all conditions,” says Peter Langen, head of Driving Dynamics.
“With short spring travel, a sensitive damping response ensures comfortable vibration compensation. When the car passes over large bumps, the body movements are controlled by increased damping forces.”
The lift-related dampers are a standard feature of the suspension technology in the new series. In a specific set-up they also form part of the M sports suspension, which additionally includes a lowering of 10mm, 18-inch light alloy wheels and mixed tyres. This provides a boost to driving dynamics.
The increased damping forces can be felt on the Nordschleife in particular: in the M sports suspension these are 20% higher than in the standard suspension.
“This means the difference from the standard suspension is much more perceptible than before,” says Langen.
“We’ve also made the M sports suspension much sportier, with more rigid bearings and stabilisers, harder springs and additional body struts.”
To further reinforce the car’s dynamic characteristics, the new M sports suspension is offered solely in combination with the Variable Sports Steering. In addition to the speed-related steering assistance Servotronic, this also provides a variable steering ratio. It responds with much greater precision to slight steering movements.
The harmonious set-up of the steering system can be felt on long bends as well as when changing direction in rapid succession. A linear build-up of steering forces and optimised feedback increase precision when cornering.
The M sports differential is able to perfectly demonstrate its qualities on both the Nordschleife and the Grand Prix circuit. The electronically controlled locking function in the rear axle differential is linked to Dynamic Stability Control DSC, ensuring needs-oriented limitation of rotation speed compensation between the rear wheels on the inside and on the outside of the bend.
It is possible to pre-emptively influence both understeering and oversteering without brake intervention.
The active differential lock distributes drive torque selectively between the rear wheels. In this way, it prevents slip on a wheel with reduced surface grip while ensuring that the engine power can be used unrestrictedly.
“Unlike conventional mechanical locks, the regulated M sports differential can optimise so much more than just traction,” says Langen.
“There is a particularly tangible increase in drive stability in the event of load changes, for example.”
For sporty driving, the active differential lock provides much higher levels of transverse acceleration as well as a perceptible boost in dynamic performance when accelerating out of bends.
It also supports optimised stability, precision and cornering predictability in the new BMW 3 Series Sedan – without brake intervention.