Audi is fitting its largest crossover models with a new, active anti-roll system that the company said enhances cornering capability and reduces body roll without sacrificing ride comfort. Unlike other active anti-roll systems, Audi’s electromechanical roll stabilization (eAWS) doesn’t rely on hydraulics and is claimed to be “virtually maintenance-free.”
Large crossovers and SUVs can be challenging to engineer with assertive vehicle dynamics because their weight and higher center of gravity typically mitigate against sporty cornering unless the suspension is uncomfortably stiff. But the powered anti-roll bars at each axle in the eAWS system permit a comparatively soft tune for the base suspension, firming cornering dynamics only when required.
In conventional suspension designs, Audi said in a release, “Torsionally flexible anti-roll bars between the left- and the right-hand side of the axle are proven means of compensating [for vehicle body roll in hard cornering]. They help reduce the body’s tendency to roll by applying reverse torsion torque to the suspension on the outside and inside of the corner, thus counteracting the body’s tendency to roll. However, an effect that is desirable in cornering may impair ride comfort in straight-line driving on roads with bumps or potholes.”
Audi’s said its eAWS solves the compromise between a comfortable suspension tune and assertive handling for heavy, high-riding vehicles, saying, “using sensors to capture and detect the situation, the system is designed to intervene with pinpoint precision only when less body roll is desired. Thus, the spring rate of the stabilizers on uneven and straight roads is lowered to a basic level and the spring and damper forces act by and large independently on the left- and right-hand wheels.”
Quick response, no hydraulics
At each axle, the eAWS system “splits” the concept of a single anti-roll bar into two stabilizer “halves.” An electric motor, operating through a “three-stage planetary gearbox,” generates the torque that acts on either half of the anti-roll bar. The company said up to 1,200 Nm (885 lb-ft) can be applied at each axle. Power for the system comes from the vehicle’s onboard 48-volt electrical system, which is governed by a control unit for each axle that is part of Audi’s Electronic Chassis Platform (ECP) central processor.
The company said the system can react in milliseconds, based on data from sensors monitoring vehicle speed and ride height, plus dynamic aspects such as roll and pitch, road friction coefficient and even under- or oversteer conditions. And “uUnlike hydraulic [active anti-roll systems], the eco-friendly electromechanical system does not require oil circuits and is maintenance-free,” Audi said, adding that the eAWS system also can recuperate the energy from the vehicle’s suspension movement and return that energy to the lithium-ion battery pack.
“The electromechanical solution uses energy more efficiently as well,” Audi concluded, saying, “In contrast to hydraulic circuits, it does not have to store and provide pressure.” The eAWS system currently is available for the Q7, SQ7, Q8 and SQ8 crossovers. “In sporty driving and at high cornering speeds, the car feels more stable and at ease,” the company claims, adding that eAWS is engineered to not completely neutralize body roll, but to create an “authentic feel” appropriate to the driving situation.Continue reading »