Formula E is as competitive and as close as ever and is getting more so with every passing season. This is great for the sport and fans but makes the engineers’ job hard when all cars on the grid are covered by fractions of a per cent delta in performance.

Winning in Formula E requires keen attention to all the same performance parameters seen across motorsport – car, drivers, team, engineering, infrastructure, equipment and harmony between all the above.

Managing Director and CTO at ‎Envision Virgin Racing Formula E Team, Sylvain Filippi details the engineering challenge of Formula E ahead of the Season 7 opener in Diriyah, Saudi Arabia.

Sylvain Filippi, Managing Director, Envision Virgin Racing during the Diriyah E-prix II at Riyadh Street Circuit on November 23, 2019 in Riyadh Street Circuit, Saudi Arabia. Credit: LAT Images

Power

The Envision Virgin Racing Formula E Team’s season 7 challenger is powered by Audi e-tron MGU05 motor-generator unit. It is a six-phase motor-based, single-speed drivetrain with an internal rotor concept, external magnets and high-efficiency cooling system. 

Audi claims it has managed significant weight savings compared with the previous unit by using lightweight materials and intelligent integration within the Formula E chassis. It achieves an overall efficiency of more than 95% for the powertrain, and the MGU inverter unit has an efficiency of more than 97% in all racing conditions.

Filippi notes ‘The compact size, combined with high performance, is imposing. Suppose you compare the Audi MGU05 with an internal combustion engine delivering a comparable power output of 250kW. In that case, the efficiency is twice as high, and the weight of less than 35kg is much lighter than an IC equivalent – clearly showing what an efficient solution an electric powertrain is.’

Audi e-tron MGU05 motor-generator unit, developed in-house at Audi Sport. Credit: Audi Sport

Control

As power is nothing without control, Envision Virgin Racing’s challenge is to design, develop, and operate software to control the Audi powertrain the way it believes is best to race in Formula E.

Energy management, attack modes, fan boost and other software racing strategies are all done in-house by the team. ‘We develop the software in-house, and it is the team’s IP, and this is the engineering exercise of formula E – there is very little mechanical work done in this series,’ remarks Filippi. 

The software is unique for each track layout and prevailing conditions, and the strategies vary dramatically from one track to the next. Engineers calibrate each sector’s pace and the power strategy for the race and attack modes to operate the car in the best way they see fit. 

Audi e-tron MGU05 motor-generator unit, developed in-house at Audi Sport. Credit: Audi Sport

‘Power strategy depends on the circuit more than anything else. If you go to a low speed, low average power usage per lap track and compare it to a high speed, high average power per lap track, the energy profile and the deployment strategy are vastly different.

‘You must be very flexible and calculate the strategy right to optimise the energy deployment for a given track. Fractions of a per cent efficiency gains or losses over the number of laps all add up here to the delta between P1 and P20. The spec of the cars is so close in race-spec that this is a real challenge.’

Envision Virgin Racing, Audi e-tron FE07 during the Pre-Season Testing at Valencia Circuit Ricardo Tormo on Saturday November 28, 2020 in Valencia, Spain. Credit: LAT Images

The energy deployment and regeneration have a direct effect on the running temperature of the battery and powertrain. ‘When we go to races which are temperature limited, engineers must very accurately anticipate the heat in the powertrain,’ Notes Filippi. ‘This is another factor that will change the power strategy for each race and is another dimension of the technical challenge.

‘Power conversion out of the battery to the driveshaft is very efficient in contemporary Formula E cars, and this technology is very mature. In the early seasons, there was a huge disparity between the drive systems. This no longer exists, despite there being a range of different solutions in terms of hardware and software – the efficiency of each is very similar. You can’t just win a race with a good powertrain anymore; it’s down to that nth degree.’

Envision Virgin Racing, Audi e-tron FE07 during the Pre-Season Testing at Valencia Circuit Ricardo Tormo on Saturday November 28, 2020 in Valencia, Spain. Credit: LAT Images

Looking Ahead

Energy storage is still the central aspect of discussion within Formula E. However, Filippi notes, ‘The discharge rate is so high now that you can deliver a lot of power even if you have low energy storage, but if you want a much longer race, you need a lot more energy stored than what we have now.

‘We doubled the amount of energy stored from generation one to generation two and generation three will be another giant leap forward when we don’t need more energy stored in the battery to achieve what we want to accomplish in formula E. 

Envision Virgin Racing, Audi e-tron FE07 Credit: Envision Virgin Racing

‘If anything, we want a little bit less because we’re going to be using a lot more regeneration and not have to save so much energy. As such, we could reduce the size of the battery and weight of the car, which would make it much faster.

‘If the cars are lighter and smaller, that will be beneficial for racing. The margins will also be amplified given that the cars will have more performance potential, so getting the right strategy will be even more important than it is now.’

Envision Virgin Racing, Audi e-tron FE07 Credit: Envision Virgin Racing