Gearing up for its seventh season competing in the all-electric Formula E racing championship, German automaker Audi has revealed its new spec race car, the appropriately named Audi E-Tron FE07, which will compete under the flag of Audi Sport ABT Shaeffler.
Many parts of the FE07's design are dictated by the International Automobile Federation and Formula E rules. The spec carbon-fiber chassis with spec carbon-fiber bodywork, the bespoke 18-inch Michelin road tires, even the 52 kWh McLaren Applied Technologies lithium-ion battery are all shared by every car on the Formula E grid. But there's more than brightly colored livery separating these cars. Teams are allowed to develop their own electric powertrain tech (within spec, of course), power management and regenerative braking software to give their drivers an edge.
Power from the battery flows through a custom inverter to the new MGU05 six-phase AC motor-generator, which Audi Sport developed completely in-house. Output is regulated to 250 kW (about 335 horsepower) but can be boosted to 285 kW (around 382 horsepower) for a limited "Attack Mode." The carbon-fiber-housed motor spins at around 20,000 peak RPM, but a single-speed reduction gearbox mated to carbon-fiber driveshafts on the rear axle brings that down to more manageable road speeds.
The MGU05 and its inverter together weigh a scant 35 kilograms (about 77 pounds), but provide enough thrust to launch the 903 kilograms (about 1,991 pounds including the driver) FE07 from zero-to-100 km/h (62 mph) in just 2.8 seconds with a top speed around 149 mph. Audi claims above 97-percent energy efficiency from MGU05 -- more than double that of the best internal combustion engines -- or around 95-percent powertrain efficiency, including the gearbox. Built around the limitations of current battery technology, however, Formula E's main event E-Prix races only last a furious 45 minutes.
Tucked into its 18-inch aluminum wheels are hydraulic brakes with carbon-fiber discs, but perhaps a more important bit of braking hardware is the MGU05 motor-generator itself. Working in concert with friction brakes, the FE07's brake-by-wire system is able to make use of strong rear-axle regenerative braking to recapture as much energy as possible during coasting and deceleration to boost range.
Allan McNish, former Formula 1 driver and current Team Principal of Audi Sport ABT Schaeffler, explained how regenerative braking and power management play a huge role in helping the driver get the absolute most performance out of the battery's capacity and can make the difference between a decisive victory and running out of juice just short of the checkered flag.
"You've got a maximum, by regulation, 52 kilowatt-hours of energy at the start -- that's what everybody has -- and you want to make that zero at the end," said McNish. "You want to go as fast as possible in between, but if you just go flat out and don't recuperate energy, you won't make it; there's no way, the car will stop. Therefore, we need to try to recuperate energy exactly as when we're driving the E-Tron with its paddles, brakes or lift-off -- exactly as we do on the road. However [with the E-Tron FE07], we're trying to do it in extreme ways."
Simulation and software tuning further hone the basic regen technology, allowing the team to fine-tune the car's power management software to a specific course, determining when to accelerate and when to brake with regen or friction. There's also a surprising amount of attention paid to lifting and coasting. Of course, it comes down to the human driver to execute on the plan, but McNish explained how this simulation allows the FE07 to dramatically improve its efficiency at the Formula E Mexico City circuit.
"I would say in Mexico, for example, we have about 40% of energy coming back into the battery," said McNish. "We've got a 52 kWh battery and we'll be putting about 21 kilowatts back in there. Historically, that would have been lost energy, but now we're able to harness it and use it for our range. So, we effectively have a range extender by what we are recuperating back into the battery."
The stakes are higher than ever with the 2021 Formula E season being held as an official FIA World Championship for the first time ever. Audi Sport also sees the series as a chance to showcase its technologies, many of which have already made their way into the roadgoing E-Tron line of electric vehicles -- including theand , as well as the upcoming and .
Will its technology and software know-how lead the Audi Sport ABT Schaeffler Formula E Team and Audi Formula E factory driver Lucas di Grassi to victory? We'll be keeping an eye on the finish line during its debut race this weekend in Valencia, Spain on Nov. 28.