SCIENCE AND ENGINEERING OF FORMULA E CARS

WHAT IS FORMULA E?

Formula E is quite new and also quite alien to many car and motorsport fans, so it’s useful to explain a little more about the series. It’s often assumed that Formula E is merely an electrified version of a conventional motorsport, and also that it’s a rival to F1. It uses a one-day format to minimize disruption in the city and many of its operational and logistical ideas are with sustainability in mind; for example everything is sea-freighted between races to sidestep the emissions of air-freight.

WORKING

For season 8 there is an updated car, named the Gen2EVO, with revised bodywork. Then the third-generation car comes in, with more power and energy recovery systems that will prove to be yet another milestone in the series.

  • Powertrain

  • Battery

  • Motor

  • Inverter

POWERTRAIN

With an electric vehicle, the basic layout can be compared, but there is little the same between the two types. The Battery is analogous to the fuel tank, storing the energy for the motor. Albeit the battery is much heavier for the same energy storage as petrol, but also the battery does not get lighter as with a fuel tank during a race.


An electric motor is a swap for the combustion engine, in contrast to the battery, an electric motor is smaller and lighter than an equivalent engine. Plus it only has one moving part, therefore less bearings, friction and things to go wrong. A genuine advantage is that the motor can also act as a generator, creating electrical energy under braking that can be stored in the battery. This is the equivalent to a combustion engine creating petrol to go back into the tank, something that is simply can’t do! As the one device can operate in both modes, the motor is often called a Motor Generator Unit or MGU for short.

Under acceleration the battery provides energy through the inverter the power the motor, driving the rear wheels through a reduction gearbox and differential. Under braking, the Inverter switches and the motor generates electric, creating a drag on the drivetrain to help ‘brake’ the rear wheels. The electricity created goes to the battery and increases the remaining charge available to the driver through the race.


BATTERY

Central to the Formula E race car is the battery, as it’s at the core of the powertrain and is mounted in the middle of the car. Its commonly called the Battery, the Formula E nomenclature is RESS (Rechargeable Energy Storage System), while it’s also sometimes termed the ‘Traction’ battery, because it drives the car as opposed to the 12v auxiliary battery.


This is twice the performance of the older Gen1 battery, the increase in energy storage allows the cars to race for the full +45 minute race without recharging or car swaps. The downside being the unit’s weight, there are 250kg of cells alone, plus the associated internal structure, connections, cooling and casing bring the battery up to over 400kg.


MOTOR

The technically inclined motoring fan will probably view an electric motor or generator, as the type of thing used as an alternator or starter motor on a road car. These are Brushed motors, where the magnetic stator is on the outside and the coiled armature spins inside. Carbon blocks (brushes) transfer the current between the stator and wiring, by literally rubbing against the contacts on the spinning armature, not a very efficient set up.

Modern motors reverse this design, permanent magnetic rotor now spins inside, while the coiled windings are formed in the body around it. Thus, the coils are stationary and no longer need the carbon brushes. Thus, these types of motor care called ‘brushless’.


Next the electric set up uses AC and not a DC supply, by running multiple pairs of magnets/coils (poles), to further enhance the efficiency of the set up. Given a DC power supply in the form of the battery, an inverter is required to create the requisite 3-phase AC output. In this this layout the motor generates torque twice from each pole as the AC


To make a motor more powerful, it becomes restrictive to make it larger in diameter as the tip speed of the magnets will increase, so the motor needs to be longer. For season 6 the motors are allowed to produce a maximum 250kw (in Qualifying) which is 335hp. Currently in Formula E most teams run a single motor, these are still tiny, 20-30cm in diameter and 30-40cm long, while weighing near to 20kg.


INVERTER

At its core the inverter has a power circuit-board, the two DC (battery) cables come in one side and the three AC (motor) cables the other. They pass via bus bars to these switches, which are controlled by a separate logic circuit-board, in order to translate the current from one form to another. The quicker the switches can switch, the more power they can handle and fewer electrical losses along the way the better the inverter’s performance will be.

While an inverter not requiring anything more than air cooling is a possibility, currently the switches and internal bus bars still require cooling, this is done with a cold-plate set up. The power circuit board is mounted against an aluminium plate with internal water-cooling passages, to conduct the heat away into the same cooling circuit as used for the motor.


THE FUTURE

Going further into the future, there will be an increase in power, while still understanding that the series races on tight street circuits so there is a ceiling on the maximum output for obvious safety reasons. There will also be undoubtedly an increase in regenerative braking means there may not be front disc brakes.

The sky is the limit, but all of these technologies will be reflected in the road car EV industry and will continue to make Formula E the tech great technology incubator it was set up to be.


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