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New Audi A8’s robot suspension explained

Published: 17 June 2017

► Next A8’s fiendishly clever suspension
► Enables ‘agility you wouldn’t expect’
► Carving into corners could be next

Thanks to its 48-volt architecture the new Audi A8 is shaping up to be the company’s most technically advanced car to date.

The latest tit-bit to be drip-fed from Ingolstadt ahead of the car’s official reveal this summer is a detailed look at its new active suspension system. However, unlike the massively expensive and, relatively, heavy hydraulic systems pioneered by Lotus back in the 1980s and perfected by Williams in its all-conquering FW15C F1 car, Audi is employing advanced 2kW electric motors at each corner to alter the damper settings every 15 milliseconds to iron out the ride, according to the head of the A8’s suspension development, Thomas Muller.

Audi A8 active suspension

Rear-steer, active diff, air suspension: tech galore on 2017 Audi A8

Speaking exclusively to CAR, Muller explained that the active suspension is just one element in the car’s chassis dynamics that also embraces the air suspension, steering, rear-wheel steering, ESP, quattro all-wheel drive and active rear differential managed by a single powerful chassis electronic control unit (ECU).

With ±5° rear-wheel steering the A8’s turning circle is reduced to 11.4 mtrs, 90 cms less than the outgoing model and 20cms less than an A4; this not only makes manoeuvring in tight, urban spaces easier, says Muller, but enables quicker and more stable lane-change especially at speed.

The all-wheel steering shifts the point of rotation towards the rear wheels resulting in less lateral head movement for back seat passengers.

Audi A8 rear-wheel steering

Active suspension ‘three times more efficient than a hydraulic system’

But it is the active suspension that really enthuses Muller. In its normal state the car sits on the air suspension, the dampers powering up only when required. As such, energy consumption is minimal: ‘At highway speeds it’s about 20W, on rough roads 250W and lapping the Nürburgring consumes 400W, about two to three times more efficient than a hydraulic system.’

Key to this is a novel belt drive linking the ‘strain wave gear’ and the motor; the former allows a very high 1:80 ratio thanks to its unique design. Incidentally this technology was first used in the 2007 A4’s steering set-up.

Audi A8 active suspension

The active suspension is controlled via inputs from the forward-facing ADAS camera that ‘reads’ the road surface, transmitting signals to the control to raise or lower the suspension accordingly to cope with sleeping policemen or shallow pot holes, as well as a myriad of electronic sensors. The system has the capability of generating 16kN per second and, when combined with a bandwidth between zero and 6Hz, means the damper is being altered every 15 milliseconds.

As well as smoothing out longitudinal movements, body roll under hard cornering is halved as higher g-forces are encountered, giving the new luxury saloon a sense of agility ‘you wouldn’t expect’, claims Muller.

Active suspension could help lift occupants out of harm’s way in a side impact

It’s not all about comfort, though, there’s also a safety element. By linking in the pre-sense side sensors the suspension will jack up the ride height so that any side impact is taken by the sill structure and cross car beams rather than the door(s).

This is just the beginning of the development, says Muller, revealing that Audi is studying vehicle behaviour like ‘carving’ where the car leans into the corner to see what effect that has on the driver, passengers and vehicle safety. 

Audi A8 2017 body

By Ian Adcock

CAR's engineering whizz, making sense of oily bits and megabytes

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