As the electrical systems in cars become more complex and emissions rules get tighter, car manufacturers are pursuing every possible avenue in search of energy savings. Audi has taken that search into a new area with its electromechanical rotary (eROT) suspension system that is designed to provide unmatched ride comfort and harvest electricity at the same time.
Although they're more sophisticated than passive dampers, hydraulic suspension systems are still limited in their adjustability. That's because the compression and rebound stroke share a fixed relationship. To achieve compliant compression damping the rebound damping also needs to be soft, which means looser body control. If it's taut body control you're after, the inverse applies.
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By electrically controlling the suspension Audi is able to separate the rebound and compression, meaning soft compression damping and taut rebound damping is possible without using vertical shock absorbers, which also frees up space in the boot.
On top of the potential to improve in-cabin refinement, the eROT system is able to harvest the kinetic energy created when it passes over bumps. The lever arms on the suspension system absorb the movement of the wheel carrier, and then transmit it to an electric motor through a set of gears to create electricity.
At the moment, the whole setup is based on Audi's 48-volt electrical subsystem, which relies on a 0.5-kWh lithium-ion battery and a DC converter to link up with the 12-volt primary electric system.
Under average conditions, Audi says the system recuperates between 100-150 watts, but results differ wildly depending on the road. On billiard-smooth roads it created just 3 watts, and bumpy b-roads returned up to 613 watts. Under average conditions, the energy recuperation could mean CO2 savings of around 3 g/km.
"Every pothole, every bump, every curve induces kinetic energy in the car," says said Dr. Stefan Knirsch, Board Member for Technical Development at AUDI. "Today's dampers absorb this energy, which is lost in the form of heat. With the new electromechanical damper system in the 48-volt electrical system, we put this energy to use. It also presents us and our customers with entirely new possibilities for adjusting the suspension."
Although it has only conducted initial testing of an eROT system prototype, Audi says it's "certainly plausible" to see it in future models. Before that can happen the company needs to perfect its 48-volt electrical system, which will serve as the primary electrical system for a mild hybrid in 2017.