The Audi e-tron prototype combines power and efficiency. With a system output of up to 300 kW, the full-size SUV with a fully electric drive accelerates from 0-62mph in less than six seconds. In the WLTP test cycle, it covers more than 248 miles on one battery charge. One important factor for the long range is its innovative recuperation concept. The electric SUV proved this with an impressive performance at Pikes Peak.
At 4,302 metres (14,115 ft), Pikes Peak looms high in the southern Rocky Mountains. Where Walter Röhrl won the world’s most famous hill climb in the Audi Sport quattro S1 back in 1987, it is the Audi e-tron prototype that is now gaining interest with its recuperation system that is variable. On its 31-kilometre (19-mile) downhill drive, the electric SUV feeds so much energy back to the battery that it can cover approximately the same distance again. The difference in altitude of about 1,900 metres (6,233.6 ft) provides the necessary conditions for this. The Audi e-tron prototype recuperates energy with up to 300 Nm of torque (221.3 lb-ft) and 220 kW of electric power – more than 70% of its operating energy input.
The recuperation concept: from freewheeling to a one-pedal feeling
The recuperation system contributes to up to 30% of the SUV’s range. It involves both the two electric motors and the electrohydraulically integrated brake control system. For the first time, three different recuperation modes are combined: manual coasting recuperation using the shift paddles, automatic coasting recuperation via the predictive efficiency assist, and brake recuperation with smooth transition between electric and hydraulic deceleration. Up to 0.3 g, the e-tron recuperates energy solely via the electric motors, without using the conventional brake – that covers over 90% of all decelerations. As a result, energy is fed back to the battery in practically all normal braking manoeuvres.
The driver can select the degree of coasting recuperation in three stages using the steering wheel paddles. At the lowest stage, the vehicle coasts with no additional drag torque when the driver releases the accelerator pedal. At the highest stage, the electric SUV reduces the speed noticeably – the driver can slow down and accelerate using only the accelerator pedal. There is no need to use the brake pedal in this deceleration scenario.
The wheel brakes are involved only when the driver decelerates by more than 0.3 g using the brake pedal. They respond extremely quickly, thanks to a new electrohydraulic actuation concept.
A hydraulic piston in the compact brake module generates additional pressure and thus additional brake force for the recuperation torque. When automated emergency braking is performed, there are only 150 milliseconds between the initiation of the deceleration and the presence of maximum brake pressure between the pads and disks. Thanks to this rapid pressure buildup, the braking distance is shortened by up to 20% compared with a conventional brake system.
Depending on the driving situation, the electrohydraulically integrated brake control system decides – electrically on each individual axle – whether the e-tron will decelerate using the electric motor, the wheel brake, or a combination of the two. The brake pedal is decoupled from the hydraulic system. The transition from the engine brake to the pure friction brake is so smooth the driver does not notice it.
This system allows the SUV to exploit its maximum recuperation potential in a targeted manner with support from the standard efficiency assist. The system uses radar sensors, camera images, navigation data and Car-to-X information to detect the traffic environment and the route. The driver is shown corresponding information in the Audi virtual cockpit as soon as it would be sensible to take the foot off the accelerator pedal. By interacting with the optional adaptive cruise assist, the efficiency assist can also decelerate and accelerate the electric SUV predictively.
