Electric and Hybrid vehicle Powertrains.


In a vehicle, Powertrain comprises the main components that generate power and deliver that power to the road or any medium they travel. In EVs, the vehicle is powered at-least in part by electricity and electric motor. For fully electric vehicles, they eliminate engine altogether and solely depends on electric motor.

EV configuration not only include 100% electric vehicles. Various hybrid, mild hybrid, plug-in hybrid vehicles are there. Some differences are there in configuration of Powertrains in these vehicles.

Different Powertrain configurations of EVs are:-

BEVs are entirely powered by electric energy. Powertrain of BEVs is less complicated and designed according to that. It consist of a large motor, a battery pack and a transmission system. Type of transmission used varies the clutch, gearbox, differential and fixed gearing. There are many variations depending on all the factors mentioned above. However, a basic BEV system is shown below.

Unlike BEVs, Mild hybrid vehicles depends on two energy sources.

  • Internal combustion engine'
  • Electric motor
Mild hybrid vehicle has a conventional internal combustion engine with an oversized starter motor that can be also used as a generator. Basically called as integrated starter generator(ISG). Also a large sized battery pack powered and recharged by motor. In mild hybrid vehicle, engine must be on while moving and motor can be used to idle stop, in which engine is stop when vehicle is at idle. Motor can be used at high loads to assist the engine and increase vehicle performance. At low loads, it recharges the battery. Mild hybrid vehicle powertrain is shown below.

In series hybrid vehicles, there is a single path to power the wheels of vehicle, with two energy sources. There is a fuel tank which feeds an engine, which is coupled to a generator to charge the battery. Battery will provide electrical energy to motor or generator to power the wheels through a transmission. Motor/generator is also used to recharge the battery during deceleration or braking.
Schematics of series hybrid electric vehicle powertrain is shown below.

Mode of operations of series hybrid powertrain are:-

  • Hybrid traction
  • Electric only traction
  • Engine only traction
  • Engine traction and battery charging
  • Battery charging and no traction
  • Regenerative braking
  • Hybrid battery charging

In parallel hybrid electric vehicles, there are two paths to power the wheels of the vehicle.
  • Engine path  
  • Motor path. 
Transmission couples motor and engine, allowing either one or both to power the wheels. Its control is more complex than series hybrid as of the need to efficiently couple the motor and engine in order to achieve the driveability and performance. Schematics of parallel hybrid powertrain is shown below.

Different mode of operation are:-

  • Hybrid traction
  • Engine only traction
  • Electric only traction
  • Regenerative braking
  • Battery charging from engine
This mode of operation has both series and parallel energy paths. Motor/generators sometimes include a gearing or power split couples allows the engine to recharge the battery. This configuration can be complex or simple depending on the number of motor/ generator and how they used.
This is also called Complex hybrid, Split parallel hybrid or Power split hybrid.
Schematics are shown below.

Credits:- Publish by MIT Electric vehicle team 2008.

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