Audi has added an expensive but high-tech option to its A8 luxury sedan in some markets – predictive active suspension.
Initially the option is restricted to TFSI versions.
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The fully active suspension system uses electromechanical actuators to move wheels individually to actively manage the body’s ride height. The system can lift or lower the body by up to 85mm (3.3 in) from its central position at all four corners within five-tenths of a second.
Compact electric motors located close to each wheel run from the 48-volt primary electrical system and are governed by power electronics. A belt drive and a compact harmonic drive step up the motor’s torque almost 200 times to 1,100Nm (811lb-ft) and apply it to a steel rotary tube attached to a preloaded concentric titanium rod capable of turning through more 20 degrees. From the end of the rotary tube, the force is transmitted to the suspension via a lever and coupling rod – at the front it acts on the spring strut, and at the rear on the transverse link.
Power consumption is 10 to 200 watts – much less than that of comparable hydraulic systems.
Whenever the driving physics try to force the body down on the wheel, the suspension counteracts this effect. An extremely sharp impulse will produce a very short but high energy demand of potentially up to 6 kilowatts. Up to 3 kilowatts can also be fed back to the 48-volt battery.
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By GlobalDataThe system works with the air suspension and drive select dynamic handling system. Using the dynamic profile, the car turns in firmly, and when cornering fast with 1 g lateral acceleration the body inclination (roll angle) is two degrees versus five degrees with standard suspension. Rolling moment is optimally distributed and dive when accelerating or braking is minimised.
The comfort plus profile is much smoother. The predictive suspension works with the front camera which identifies uneven surfaces before they are reached and predictively regulates the suspension by signalling the correct positioning travel to the actuators and adjusting the suspension. This reduces body movement and compensates almost entirely for long road undulation or similar unevenness. This takes just a few milliseconds: the camera generates information about the surface properties 18 times a second. The electronic chassis platform processes the road surface data and actuates all suspension components almost in real time.
Comfort plus adds transverse force reduction. Entering a bend, this raises the body on the outer side of the bend while lowering it on the other side. The car leans into the bend by up to three degrees, rather like a motorcycle. This reduces the transverse forces and is most noticeable from 80 to 130 km/h (50 to 81 mph) and at lateral acceleration of up to 0.4 g.
Ausi even claims a full cup in the holder will not spill.
When accelerating hard or braking the system equalises the body’s pitching movements so occupants are pushed very gently into their seats instead of against their belts.
When the door handle is used, the body is quickly raised by up to 50mm (2in) for easier entry and exit.
In an impending side impact at 25km/h (15.5mph) or more, the active suspension raises the body by up to 80mm (3.1 in) on the side of the impact to bring the sill into a better position to absorb the impact energy. Deformation of the cabin and the loads acting on the occupants can be reduced by up to 50% compared with a lateral collision in which the suspension is not raised, Audi claims.
Option orders open in August 2019 and the price in Germany is EUR5,450.
