Charging down hill

Pikes Peak in Colorado is a familiar place for Audi. This iconic mountain – home to the famed Pikes Peak International hill climb has been conquered three times by the brand, with legendary names like Walter Röhrl and Michele Mouton having taken on the treacherous climb – and won.

Audi also used the testing road into the clouds to demonstrate the prowess of its autonomous driving technology, piloting an unmanned TTS up the 4300m mountain in 2010.

In 2018, another Audi is making its mark on the mountain, but rather than up, it is demonstrating its prowess on the way down. 

The Audi e-tron prototype has shown its class-leading recuperation powers, using each of the 31 kilometre downhill drive to recover a further kilometre of travel.

The electric of the e-tron prototype feeds so much energy back to the battery that it can cover approximately the same distance again, and the difference in altitude at Pikes Peak of about 1900 metres provides the perfect conditions to demonstrate. 

Indeed, the Audi e-tron prototype recuperates energy with up to 300Nm of torque and 220kW of electric power which is more than 70 percent of its operating energy input – no series production model has achieved these sorts of figures, making this a milestone event.

The recuperation system contributes to up to 30 percent of the electric SUV’s range using the two electric motors and the electro-hydraulically 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 Audi e-tron prototype recuperates energy solely via the electric motors, without using the conventional brake – that covers over 90 percent of all decelerations. As a result, energy is fed back to the battery in practically all normal braking maneouvres.

In addition, the e-tron prototype’s recovery system is fully adjustable, allowing the driver to 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 and the driver can slow down and accelerate using only the accelerator pedal. This creates the one-pedal feeling and 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 electro-hydraulic actuation concept. Audi is the first manufacturer worldwide to use this concept in a series production vehicle with electric drive. 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 percent compared with a conventional brake system. 

The performance of the e-tron prototype is extraordinary. Its two electric motors have an output of 265kW and develop 561Nm (of torque – delivering this peak performance for up to 60 seconds. This allows acceleration from a standstill to the electronically limited top speed of 200 km/h several times consecutively without output losses and by shifting from drive range D to S and fully depressing the accelerator, the driver can activate boost mode. This is available for eight seconds and produces 300kW of system output and 664Nm of torque allowing the e-tron prototype to sprint from 0 to 100km/h in less than six seconds.