Recuperation of energy continues to play an increasingly important role in the mobility of the future, including in car suspension. Audi is working on a prototype called eROT in which the hydraulic dampers that are used today are replaced by electromechanical rotary dampers which provide an even more comfortable drive.
Dr.-Ing. Stefan Knirsch, Board Member for Technical Development at AUDI AG, explains the principle behind eROT: "Every pothole, every bump, every curve induces kinetic energy in the car. 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.”
This new eROT system can respond quickly and with minimal intertia. As an actively controlled suspension, it can adapt to the driving style as well as an irregularities in the road surface with a damper characteristic that is almost freely definable through the software to increase functionality. All of this removes the mutual dependence of the rebound and compression strokes that limits conventional hydraulic dampers. The compression stroke has also been configured to be comfortably soft without compromising the taut damping of the rebound stroke while the horizontally arranged electric motors in the rear axle area allows for additional space in the luggage compartment compared to the upright telescopic shock absorbers.
Besides the freely programmable damper characteristic, the eROT system can covert the kinetic energy during compression and rebound in to electricity through the use of a lever arms that absorbs the motion of the wheel carrier. This arm then transmits the force via a series of gears to an electric motor which converts it to electricity. During testing on German roads, he recuperation output was 100 to 150 watts on average – from 3 watts on a freshly paved freeway to 613 watts on a rough secondary road. Under customer driving conditions, this equates to a CO2 savings of up to three grams per kilometer (4.8 g/mi).
The new eROT technology bases itself on a high-output 48 volt electrical system. It's lithium ion battery offers an energy capacity of 0.5 kilowatt hours and peak output of 13 kilowatts while a DC converter connects the electrical system to the 12-volt primary electrical system, which includes a high-efficiency enhanced output generator.
With initial test results for the eROT system showing promise its use in Audi production in the future is definitely plausible. A prerequisite for this is the 48-volt electrical system, a central component of Audi's electrification strategy. The next version is planned for 2017 with a 48-volt system that will serve as the primary electrical system in a new Audi model, feeding a high-performance mild hybrid drive. This system will offer potential fuel savings of 0.7 litres per 100km.