Technique - Under the skin of a Formula E car

A Formula E car marks a real revolution in motorsport, as it is a purebred race car that has no traditional internal combustion engine nor fuel tank; just a battery and an electric motor.

Briton Nigel Beresford is vastly experienced. Back in the 80s, he was Jean Alesi’s race engineer at Tyrrell in Formula 1. He then crossed the pound and engineered Paul Tracy’s car at Penske before he was named Head of Engineering.

Later, he was deeply involved in Penske’s effort in ALMS racing with their Porsche LMP2 programme. He is Dragon Racing’s Technical Director and Team manager since Season 1 of the FIA Formula E Championship. Interestingly, Beresford also served as Ayrton Senna’s engineer when the Brazilian tested a Penske PC21-Chevrolet Indy car in December 1992.

Simple, yet efficient

Beresford started by telling us that the organisers of the series made things as simple as possible to start off. “For Season 1, all teams were based in the same compound at Donington Park, near the East Midland airport, which is a major DHL hub, and so transportation was good,” said Beresford. “As far as the car is concerned, the organisers did not want the teams to focus on aerodynamics or the mechanical engineering of the car because Formula 1 and WEC exists for that. They wanted us to focus on the energy saving aspect.”

The Briton continued by explaining that since the paddocks in Formula E are made of giant tents that are moved from one circuit to the next, working conditions are not the best and for the reason, the cars needed to be easy to work on.

“Mechanically, from the rear bulkhead forward, the car is very simple," said Beresford. "The spec tub is produced by Spark and the front suspension is uncomplicated. Braking force is hydraulically produced, and we don’t have the complex brake-by-wire system seen in F1. The carbon material of the discs has two different coefficients of friction, and therefore two distinctly different levels of performance depending on how hot it is. Unfortunately, it is operating in the transition between those two stages, and that’s why you see drivers often locking up their brakes.”

Beresford confirmed that a Formula E car is a handful to drive, even for the former F1 pilots. Weight balance is not perfect with a battery that weighs 330kg (726 lbs).

The novelty is located behind the driver

If the front of the car is very similar to that of any other single seater, the rear end is totally different.

“We just ended Season 3 with this Williams designed and made spec battery, which was looked after by Spark," he added. "Then, it’s our own gearbox – made by Xtrac but designed and commissioned by us, our rear suspension, software and control systems.”

Typically, teams use between one and three-speed gearboxes to suit the different torque characteristic of the motor. Initially, the motors were high speed and low torque, requiring a lot of gears. Now, the trend is towards lower speed, high torque motors, and with a lot of torque, there’s not a need for a high number of gears.

“Our gearbox is very small. Consequently, you don’t have a big casing to mount your suspension on. So, our car and several others feature a carbon structure, like small monocoque, which carries all the suspension loads, and inside that is the gearbox and the transverse mounted motor and the inverter. The inverter is the component, which transforms the DC from the battery to the AC for the motor. We use a motor that is designed and made by Magneti Marelli but that we commissioned.”

A matter of electronics

Beresford insists that a lot of time and efforts are invested in refining the software and control systems, a major factor in the races. “We have 28 kW-h of energy power in the car for each half of the race [because the current battery doesn’t have the capacity to power the car for the entire duration of the race, thus the necessity to change cars around the mid-race point]. The analogy to that is like 28 gallons of fuel in the car. We’re allowed to use it at 170 kW maximum draw from the battery,” he explained.

“Our goal is to reduce friction, so how much oil we have in the gearbox, the type of bearings, number of gears, etc. The software that controls the inverter, and the inverter itself are designed to maintain as much energy as possible, to be as efficient as possible. However, the rule doesn’t allow us to install a lot of sensors on the car. We’re allowed to measure pressures and temperatures, but nothing else. It’s up to the drivers to keep track of the energy consumption. The rear axle powers the car, but also serves to regenerate the battery. We’re allowed to regen up to 150 kW of energy at the rear wheels and that goes back into the battery. We’re getting a braking contribution from the regen. The driver must manage the proportion between how much braking he gets from the hydraulic system and how much he gets from the regen through the race.”

Beresford told us more about the regen mechanism. “At the beginning of the race, the battery is fully charged and will not accept any regen charge. So the driver runs with the standard brake distribution,” he said. “After a few laps, the battery will start to accept regen, so the driver must start to migrate brake balance forward because what he’s moving from the rear is replaced by the braking torque from the motor generative unit [MGU]. By the end of the race, as the battery discharges and gets hotter, it accepts less regen again. Near the end of the race, the driver needs to change the brake balance towards the rear again.”

The engineer also explained that the current, Season 3 Formula E car is aerodynamically quite simple.

“The cars are not really aerodynamically sensitive," he added. "The amount of downforce that the car produces is not huge. We use the aerodynamics more as a balancing aid rather than an overall grip aid. We use rake and front wing angle to achieve that.”

Michelin produces tires that are treaded, and not slicks, so they can be used on dry and wet tarmac. “We had a new Michelin tire for Season 3, the Pilot Sport EV2,” Beresford said. “It was a lot better in terms of lateral grip and traction. The tire is great in term of longevity, but to extract their optimum performance is very tricky. They’re quite temperature sensitive, and they require a lot of temperature management.”

The Formula E will continue to evolve in the next few years and the organisers, and the FIA, predict great things for next season. Soon, the battery will have the capacity to power the car during the entire race. The mid-race car swap will be obsolete, but the drivers will still need to manage the energy consumption of the battery.