Last updated: Feb 2020 by Narasimhan Santhanam
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t is a part of EV Next’s EV Perspectives.
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Introduction
The electric vehicle transmission systems consist of a motor, inverter and battery and these play a major role in the overall working mechanism.
- When a 3 phase input is given to stator it creates a rotating magnetic field and hence induces a current in rotor and it starts rotating. The speed of induction motor depends on the frequency of AC supply, by changing the frequency of power supply, the speed of drive can be changed.
- The IC engine requires speed varying transmission whereas electric vehicle can work on any speed, it does not require a speed varying transmission.
- The power generated in the electric vehicle motor is transferred to a drive wheel via gearbox. The EV uses single-speed transmission because the motor is efficient in wide range of condition.
- The output speed of motor is reduced in two steps that is speed reduction and torque multiplication.
- Open differential can control torque rather than slip differential, the arrangement of differential is another important feature of electric vehicle.
- The traction control of differential can be overcome by two methods that is selective braking and cutting the power supply
- EV can be run by first pedal, it saves huge kinetic energy in the form of electrical as soon as acceleration pedal is applied and hence regenerative braking is introduced in electric vehicle. During regenerative braking, motor acts as generator so wheels drive the motor
- Motor rotor speed less than rmf speed
- Generator rotor speed greater than rmf speed
- The generated electric energy can be stored in battery after conversion.
- Opposing electromagnetic field acts on the rotor, so drive wheel and car will slow down so that vehicle stopped can be controlled using single pedal
- Electric vehicle has planetary gear set and torque converter instead of clutch pack
Hyundai Ioniq Electric Vehicle powertraain displayed at the Auto Expo 2018
As mentioned above, the EVs have only one driving gear (a step-down transmission) because an electric induction motor is efficient from 0 RPM all the way up to around 6,000 RPM (a speed which a car will perhaps never need to run at!). The opposite of ICEs, induction motors generate the vast majority of their torque, which is needed for acceleration, at 0 RPM, and are most efficient at power generation at high RPM, which is needed for cruising. In a frictionless world, it would be helpful – but still not necessary – for an EV to have multiple gears, as fuller advantage could be taken of the motor’s peak efficiency. But for the foreseeable future, adding gears would only complicate a simple, reliable system.
A Hybrid powertrain by Suzuki
In reality, there is no logical reason for a clutch to exist in an electric car. An electric motor can’t stall, which is why a clutch is needed in a traditional internal combustion engine in the first place, so adding a clutch to an electric car doesn’t make rational sense.
Learn more on the key components of the Powertrain: Transmission Systems | EV Motors | AC-DC Motors | Component Suppliers to Major EVs |
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