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At Mercedes, we’re experts when it comes to motorsports. The Daimler-Motoren-Gesellschaft (DMG) and Benz & Cie companies were among the participants in the first auto race in history, which was held in 1894 on a route between Paris and Rouen. We’ve participated in the Formula 1 races since 1954, and in 2019 we entered the ABB FIA Formula E championship.
Some might suppose that this isn’t much of a challenge for us after 125 years of making motorsports history. But the fact is that Formula E is a completely new challenge even for our experienced colleagues. It’s not just that instead of the hybrid power unit of our F1 car from Mercedes-AMG Petronas Motorsport, our Formula E car has an all-electric drive system — that’s only the beginning. This year and the next three years, all of the teams will be driving cars built on a uniform chassis, known as the “Gen2.” So the motorsports teams won’t be allowed to alter the one component that they especially like to tinker with.
The body, chassis, front suspension, tires, and 52 kWh lithium-ion battery (which is equivalent to around 6,000 smartphone batteries) of the Mercedes-Benz EQ Formula E team’s new Formula E car look exactly the same as those of all the other Formula E cars.
And that makes the technology behind our swift electric race car even more exciting. Franco Chiocchetti is a seasoned veteran in this field. He worked in the DTM racing series for 15 years in all, and he’s worked in the Formula E series for the past five years — first as a race engineer and later on as the head of technical operations. Today he’s the Head of Formula E Track Operations.
The look of the Formula E car: No rear spoiler, a big diffuser, smaller tires
“The Formula E car has a very special look, so our Mercedes-Benz EQ Silver Arrow 01 does too. The car will look like this for the next three years, so we didn’t want its appearance to be boring. Besides, we didn’t want it to look too much like other Formula E cars. In other words, the Mercedes-Benz EQ Formula E team’s car isn’t the typical Formula car with adjustable spoilers at the front and the back,” he explains. In fact, the Formula E car has no rear spoiler at all. Instead, there are two very striking smaller spoilers above the rear wheels. The front wheels are completely covered. Another striking feature is the extra-large diffuser in the rear, which really pulls the car down toward the road surface. The tires also differ from those of a traditional Formula car. They are significantly narrower and only about as big as normal car tires. However, they weigh much less and are all-weather tires that can be used on dry surfaces as well as in the rain.
The heart of the Formula E car: The drivetrain with the battery and the electric motor
Because the chassis is the same in all Formula E cars, aerodynamics don’t play a large role in the development process. But which parts of the car are the engineers still allowed to work on and refine? “The drivetrain of the Formula E car is the area where we are free to continue our development work,” explains Chiocchetti. “But in the final analysis it’s not only the drivetrain. In connection with the drivetrain we can also refine the electronics, the control system, and the automobile software.”
The drivetrain — consisting of the battery and the electric motor — forms the heart of our Formula E car. Located between these two parts is what we call the inverter. It converts the direct current from the battery into alternating current and thus supplies the electric motor with energy. “Season Two was the first season during which we really could do our own development work,” says Chiocchetti. “Back then there were still big differences between the drivetrains of the various automakers. Today we’re about to start Season Six, and all the automakers have installed similar technologies in their drivetrains. Now the only differences between them are fine details such as the axle ratio, motor efficiency, transmission efficiency, and packaging.”
How fast is Formula E?
In the drivetrain, the electric motor is supplied with power by the battery. Depending on how much power a driver wants from the Formula E car, more or less energy will be drawn from the battery. That’s why various performance modes are available on the steering wheel of the Formula E car. The normal racing output is 200 kW (about 270 hp), but 250 kW (about 340 hp) is also available to the drivers for the qualification runs. The Formula E car of the Mercedes-Benz EQ Formula E team accelerates from zero to 100 km/h in 2.8 seconds (incidentally, this is only 0.3 seconds more than a Formula 1 car) and reaches a top speed of 280 km/h.
There’s also the Attack Mode with an output of 235 kW (about 320 hp). However, the drivers are allowed to use this performance mode only to a limited extent. Before every race, the FIA determines how often and for how long the Attack Mode can be used during that particular race. The drivers are then obligated to use this additional power; if they don’t, they will receive time penalties. To activate the Attack Mode, the driver must push the corresponding button on the steering wheel. Within the next five seconds, he must cover a defined section of the track that is outside the racing line.
Before every race, the spectators can decide which drivers should receive the “FANBOOST.” The drivers they choose will be allowed to use 250 kW of power (about 340 hp) for between 2½ and 3 seconds. The five drivers who get the most votes receive the “FANBOOST” and can use their extra burst of speed once during the race, for example for a passing maneuver. The drivers are told that they have received a “FANBOOST” via radio during the race, and they can use this boost whenever they like.
Energy management on the track: Recuperation during the race
As a result of the various “boosts,” the drivers have varying amounts of battery energy available to them during the race. During the race they have to make sure they will have enough energy in the battery to go the full distance. At the same time, they need enough energy to optimize their lap times. That’s why energy management is one of the most important aspects when racing. At the beginning of a race, the team fully charges the battery and cools it significantly below the outside temperature, to approximately between 10 and 20°C. During the race the battery heats up considerably, and heat always means a loss of energy. If you’ve ever left your mobile phone lying in bright sunlight, you’ll know what that means.
A car battery cannot be recharged during the race, because there are no pit stops in Formula E. “Not yet,” says Chiocchetti. “The possibility of having them in the future is under discussion.” Because recharging stops are not yet possible, the driver and the team constantly exchange energy consumption information during the race. The driver is told how much energy he still has available, as well as the team’s recommendation about how to manage it optimally. However, it’s ultimately the driver who decides how much energy he wants to use at which times.
The driver can also improve his car’s energy budget without having recourse to an external charger. He can use the braking procedure to recuperate energy. A Formula E car has both a hydraulic brake and an electric brake. The car recuperates energy during electrical braking using the motor. In this process, the electric motor acts as a generator that transforms the energy of the braking procedure into electrical energy for the battery. This recuperation process makes more energy available to the driver to supplement the energy supplied by the charging process before the race.
Of course recuperation is not possible at the start of the race. “You can compare this to a full bathtub,” Chiocchetti explains. “When the bathtub is full you can’t add any more water to it, because it will overflow. The battery is in exactly this situation at the beginning of a race. When the battery is full, it can’t take on any more energy.” So the driver can’t recover the maximum amount of braking energy during the first five or six rounds, because the battery just can’t take up this energy. That’s why energy management is especially important in the initial rounds of a race, so that not too much energy is lost. Only when the battery’s charge level goes down in the course of the race can all of the energy from the braking procedure be regenerated.
All of these factors are calculated by the Formula E team before the race so that the driver can use optimized energy management to achieve the best lap times. “For example, we could suggest to our driver that he should use a certain amount of energy during the next round,” says Chiocchetti.
Heat means energy loss for the battery
Heat is generated when energy flows into the battery or out of it. When the outside temperature is also high, the teams must take this into account when calculating their energy management strategy in order to prevent a loss of power. This calculation is necessary at temperatures of 72°C and above. That’s why our team always works to keep the temperature of the battery below this level.
As a result, when it’s hot outside, the driver should recuperate less energy through braking, because the flow of energy into the battery generates additional heat. “You develop a sensitivity to the outside temperature and the resulting temperature of the battery,” Chiocchetti explains. “For example, for every additional degree Celsius of the outside temperature we calculate an increase of about 0.3 to 0.5 degrees in the battery temperature. We calculate all of that in advance, and we give the driver the necessary information before the start of the race. Normally you would use x amount of energy from the battery and y amount of additional energy as a result of recuperation. That gives the total amount of energy that is available for the race.”
Depending on the weather conditions, the driver must decide how much energy can be recuperated without ultimately losing more energy due to the additional heating than has been regained from the braking.
Brake balance through brake-by-wire
Brake-by-wire is a system that makes it much easier for drivers to manage their braking energy. This system, which manages the balance between the braking on the front and rear axles, is part of the software of the Formula E car. As mentioned above, the car has a hydraulic braking system as well as an electric one. The electric braking is applied only to the rear axle. The hydraulic system brakes the front and rear axles, but it does not recuperate any energy.
Because energy cannot be recuperated during the first few rounds of the race, the driver cannot use the electric brake at the beginning of the race. He must initially use the hydraulic brake, which then shifts its hydraulic brake balance toward the rear. As the power recuperation increases in the course of the race, the balance of the hydraulic brake shifts more and more to the front, because the electric brake increasingly takes over braking the rear axle. The brake-by-wire system registers this process and controls the brake balance so that it remains well-balanced while simultaneously enabling maximum recuperation. For the most part this happens automatically. As a result, the driver can influence the brake balance by means of changing the speed of the car and the pressure on the gas pedal, while the actual work is done by the system. That means less work for the driver, but the system still maintains an optimal energy recuperation thanks to the right brake balance.
Is the formula for success therefore simply maximum recuperation, minimal energy loss, and fast lap times? Not entirely — these calculations can sometimes go astray. “We’ve also had cases where a Formula E car didn’t reach the finish line because its battery was empty,” says Franco Chiocchetti with a smile. All the same, one thing is certain: Even after 125 years of motorsports, the technology of car racing is far from being exhausted.