From zero to one hundred in 2.8 seconds, more than 95 percent efficiency within the entire car and preparation for any contingency in every detail, this describes the Audi e-tron FE07 that has been developed by Audi Sport, including its new Audi MGU05 motor-generator unit.
The Formula E regulations are tight and pose a real challenge to the engineers: Besides the software, the electric powertrain is the only area of the Formula E car that the registered manufacturers are largely free to develop. It consists of the MGU, the inverter including the functional software, the transmission and parts of the rear suspension.
“The coming seventh Formula E season will be the first to be held as an official FIA World Championship,” says Stefan Aicher, Head of E-Powertrain Development at Audi Sport. “However, at Audi Sport, we’re celebrating a premiere all of our own: The Audi e-tron FE07 has an all-new electric powertrain that was developed in-house for the first time.” While in recent years a continually optimized version of the powertrain, jointly developed with technology partner Schaeffler, was always used, work on the new MGU inverter unit for the coming world championship started from scratch. “We went to the limits in all areas of this project,” comments Aicher.
The result is a new centerpiece named the Audi MGU05: an electric one-speed drivetrain with an internal rotor concept, external magnets, a highly efficient cooling system and six electrical phases. Moreover, the engineers led by Stefan Aicher managed to clearly save weight once again compared to the previous unit by using lightweight materials and intelligent integration inside the vehicle. “We were able to directly reinvest these savings in the new MGU for the benefit of enhanced efficiency. Even so, the new MGU inverter unit weighs less than 35 kilograms. This was an exceptional achievement by the whole team,” says Aicher.
Efficiency is the key factor of success in Formula E. “That is why we are leaving no stone unturned to reduce the energy loss within the system to an absolute minimum,” says Tristan Summerscale, Formula E Project Leader at Audi Sport. The extensive work done on in-house test benches was a decisive factor in achieving this objective. In numerous tough testing cycles, the entire powertrain was stressed to its limits in order to raise the entire high-voltage system to a maximum performance level. The outcome was successful: “We have achieved an overall efficiency of more than 95 percent for our powertrain. The new MGU inverter unit has an efficiency of even more than 97 percent in all relevant driving conditions.”
The compact size combined with high performance is particularly impressive. “If you compare our MGU with an internal combustion engine delivering a comparable power output of 250 kW, our efficiency is not only twice as high, but our weight of less than 35 kilograms is also much lighter,” says Tristan Summerscale. “This clearly shows what an efficient solution an electric powertrain is.”
In addition to performance and efficiency of the new powertrain, the development of the Audi e-tron FE07 emphasized reliability and safety of the entire car to ensure that the new rear end would be able to handle all of the forces on the race track. Audi Sport puts the car through its paces in numerous tough tests to assure its suitability for racing. One of them involves a lateral load of up to eleven metric tons on the rear structure through the suspension. In other words, roughly the weight of six or seven passenger cars acting on the race car without impairing the structural design of the rear end.
Electric power is supplied to all of the Formula E teams by an identical 385-kilogram McLaren battery. The lithium-ion battery sits between the driver’s seat and the powertrain, has an available capacity of 52 kWh and is recharged within the space of 45 minutes. Since the fifth season, the race cars have been using a brake-by-wire system in which the braking actuator and transfer to the rear wheels are decoupled and electronically controlled. Consequently, brake force distribution is always set for optimal performance and enhanced recuperation efficiency.
Like in Formula One, the driver sits in a carbon fiber monocoque developed according to FIA safety standards. CFRP crash structures at the front, rear and sides ensure maximum safety. In addiiton, there is the Halo system above the cockpit that adds protection for the driver’s head while displaying to the spectators the power mode of the car using a colored LED strip. The minimum weight of a Formula E car is 903 kilograms (including a minimum weight of 80 kilograms for the driver and seat). The electric race car accelerates from 0 to 100 km/h in 2.8 seconds. Top speed on a Formula E track is around 240 km/h.
Preparation for the race days takes place in the ultra-modern simulator at the Neuburg headquarters using a Formula E chassis surrounded by monitors and a screen with a 240-degree curvature for a panoramic view. As a result, the movements of the monocoque and the visual aspects of the track simulation are continuing to get even closer to reality.