Acceleration tests are fun, unless your brakes don’t respond. Audi tests every system to failure, and that includes the new regenerative brakes on the e-tron ptototype. Starting from the summit of the famous mountain, four prototypes were loaded with journalists and engineers. The e-tron will arrive with 3 distinct modes for recharging the battery when the brake pedal is pressed.
Trains have been using this technology for decades. To slow down, the electric motors are reversed which makes them generators. While locomotives waste the recovered energy as heat, Audi sends it back to the batteries. After averaging the data from several downhill runs, each kilometer coming down added another km to the range. The Park Service won’t let you down the mountain if your brakes are overheated, and the nominal temperature of passenger cars is 100 degrees. The e-tron rotors were only 48 degrees, which was 3 degrees above ambient temperature.
This presents a problem, as traditional disc brakes don’t work well at comfortable temperatures. If you never get your calipers hot enough to boil away the night’s condensation, the pistons will become rusty in their bores. Audi has addressed this by developing low-temperature pads and rotors that will only be used for 10% of braking in normal driving. With 90% of the braking energy going back into the batteries, it makes the e-tron one of the most efficient electric cars ever built.