A Gen3 Formula E car uses two electric powertrains, one at the front axle and one at the rear axle, to manage acceleration, braking, and energy recovery. The rear motor provides propulsion, while both motors can act as generators during braking. This layout matters because Formula E races are energy limited, so recovering kinetic energy is as important as producing peak power.
The car is designed to turn speed into stored electrical energy instead of wasting most of it as heat in brake discs.
Key Facts
- Rear powertrain maximum drive power is about 350 kW in Gen3 Formula E.
- Front powertrain is used for regeneration only and can recover up to about 250 kW.
- Total regenerative braking power can reach about 600 kW, using 250 kW front plus 350 kW rear.
- Kinetic energy is E_k = 1/2 mv^2, so higher speed gives much more recoverable energy.
- Electrical power during regeneration is P = VI, where V is voltage and I is current.
- Rear friction brakes are not used because rear regenerative braking can provide the required braking torque while recovering energy.
Vocabulary
- Powertrain
- A powertrain is the system that converts stored energy into wheel motion, including the motor, inverter, gearing, and related controls.
- Regenerative braking
- Regenerative braking slows a vehicle by using an electric motor as a generator to convert kinetic energy into electrical energy.
- Inverter
- An inverter is an electronic device that converts direct current from the battery into alternating current for the motor, and also controls power flow during regeneration.
- Friction brake
- A friction brake slows a wheel by pressing pads against a disc, converting kinetic energy mostly into heat.
- Braking torque
- Braking torque is the twisting effect at a wheel that opposes rotation and slows the vehicle.
Common Mistakes to Avoid
- Thinking the front motor drives the car in normal racing is wrong because the Gen3 front powertrain is used for energy recovery, not propulsion.
- Adding front and rear motor powers without checking the mode is wrong because drive power and regenerative braking power are different operating conditions.
- Assuming no rear friction brakes means weak braking is wrong because the rear motor can create strong regenerative braking torque while also recharging the battery.
- Treating recovered energy as perfectly efficient is wrong because the motor, inverter, battery, and tires all cause losses during energy conversion.
Practice Questions
- 1 A Gen3 car recovers 250 kW at the front axle and 350 kW at the rear axle for 4.0 s. How much electrical energy is recovered in joules, assuming no losses?
- 2 A 850 kg Formula E car slows from 60 m/s to 40 m/s. How much kinetic energy is removed from the car? Use E_k = 1/2 mv^2.
- 3 Explain why removing rear friction brakes can make sense in a Gen3 Formula E car, and describe one situation where the control system must carefully balance front and rear regenerative braking.