The Audi A8 flagship sedan now has a new innovation, in the form of predictive active suspension. With predictive active suspension, the A8 can do sports car like handling or extreme ride comfort at a tap of a switch. Available with the A8 TFSIs, the car is meant for the German and European markets.
Part of the A8’s fully active suspension system, the active suspension utilizes electromechanical actuators to adjust the suspension. They can lift up or force down each of the luxury sedan’s wheels individually, to actively manage the body’s ride height in every situation. The active suspension can lift or lower the body by up to 85millimeters from its central position at all four corners within five-tenths of a second.
There are compact electric motors located close to each of the Audi A8’s wheels, running off the car’s 48-volt primary electrical system and governed by power electronics. A belt drive and a compact harmonic drive step up the electric motor’s torque almost 200-fold to 1,100 Nm and apply it to a steel rotary tube. The latter is permanently attached to a preloaded titanium rod located inside it and capable of turning through more than 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 suspension it acts on the spring strut, and at the rear suspension on the transverse link.
Predictive Active Suspension functionality
Predictive active suspension operates highly efficiently. Its average power consumption is in the range of just 10 to 200 watts. Whenever the driving physics try to force the body down on the wheel, for example on poorly surfaced roads, predictive active suspension counteracts this effect. An extremely sharp impulse (on a racetrack) will produce a very short but high energy demand of potentially up to 6 kilowatts. Normally, up to 3 kw pumps into the 48-volt battery.
Drive modes like ‘dynamic’ to ‘comfort plus’ work in tandem with the air suspension, the Audi drive select dynamic handling system (both standard) and predictive active suspension to offer an unprecedented spectrum for driving. In the ‘dynamic’ profile, the A8 acquires the handling of a sports car i.e. corners tighter with 1 g lateral acceleration. However, the car’s body inclination (roll angle) is just 2 degrees, as opposed to more than 5 degrees with standard suspension.
In ‘comfort plus’, the A8 glides with velvety smoothness over any bumps on the road. The predictive active suspension works together with the front camera. Thanks to this camera, the flagship model identifies uneven surfaces before they are reached and predictively regulates the active suspension. Even before the car hits a bump, the predictive function developed in-house at Audi signals the correct positioning travel to the actuators and actively adjusts the suspension. This reduces body movement and compensates almost entirely for long road undulation or similar unevenness. This complex process 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 precisely actuates all suspension components almost in real time.
To further improve ‘comfort plus’, predictive active suspension offers another innovative feature: transverse force reduction. Upon entering a bend, this raises the body on the outer side of the bend while lowering it on the other side. The A8 leans into the bend by up to 3 degrees, rather like a motorcycle. This angle reduces the transverse forces. The effect is especially impressive in the speed range from 80 to 130 km/h and at lateral acceleration of up to 0.4 g. The intensity of transverse force reduction depends on a number of factors: the road speed, the g forces encountered and road conditions. The electronic chassis platform, central suspension control unit, processes the data supplied by the sensors and passes it on to the active suspension’s control unit.
When accelerating hard or braking on straights, the system equalizes the body’s pitching movements, when stopping at lights. The slight overcompensation that it realizes means the occupants are if anything pushed very gently into their seats instead of against their belts. Predictive active suspension even gives the occupants lavish comfort treatment when the car is at a standstill. When the door handle of the A8 is operated, the body is quickly raised by up to 50 mm, for even easier entry and exit. The new “elevated entry” function makes this possible.
Audi A8 pre-sense 360 degree
With pre sense 360°: even greater safety Predictive active suspension also increases passive safety in combination with the “pre sense 360°” safety system, part of the assistance system “City”. It operates in conjunction with the central driver assistance system (zFAS), which uses the merged sensor data to identify hazardous situations around the car. In an impending side impact at more than 25 km/h, the active suspension raises the body by up to 80 mm on the side of the impact. This brings the sill into a better position to absorb the impact energy. Deformation of the cabin and the loads acting on the occupants, above all in the chest and abdominal areas, can thus be reduced by up to 50 percent compared with a lateral collision in which the suspension is not raised.
The predictive active suspension is available for the A8 from August, with an extra 5,450 euros.