What are Hybrid Electric Vehicles (HEVs) and how do they work?


A hybrid electric vehicle uses a gasoline/diesel engine along with a battery to power an electric motor. Both of these power sources are configured through different settings to attain specific objectives: enhancing driving range, increasing fuel efficiency, or increasing the power of the vehicle.

Key Components of a Hybrid Electric Car

  • Battery (auxiliary): In an electric drive vehicle, the low-voltage auxiliary battery provides electricity to start the car before the traction battery is engaged; it also powers vehicle accessories.
  • DC/DC converter: This device converts higher-voltage DC power from the traction battery pack to the lower-voltage DC power needed to run vehicle accessories and recharge the auxiliary battery.
  • Electric generator: Generates electricity from the rotating wheels while braking, transferring that energy back to the traction battery pack. Some vehicles use motor generators that perform both the drive and regeneration functions.
  • Electric traction motor: Using power from the traction battery pack, this motor drives the vehicle’s wheels. Some vehicles use motor generators that perform both the drive and regeneration functions.
  • Exhaust system: The exhaust system channels the exhaust gases from the engine out through the tailpipe. A three-way catalyst is designed to reduce engine-out emissions within the exhaust system.
  • Fuel filler: A nozzle from a fuel dispenser attaches to the receptacle on the vehicle to fill the tank.
  • Fuel tank (gasoline): This tank stores gasoline on board the vehicle until it’s needed by the engine.
  • Internal combustion engine (spark-ignited): In this configuration, fuel is injected into either the intake manifold or the combustion chamber, where it is combined with air, and the air/fuel mixture is ignited by the spark from a spark plug.
  • Power electronics controller: This unit manages the flow of electrical energy delivered by the traction battery, controlling the speed of the electric traction motor and the torque it produces.
  • Thermal system (cooling): This system maintains a proper operating temperature range of the engine, electric motor, power electronics, and other components.
  • Traction battery pack: Stores electricity for use by the electric traction motor.
  • Transmission: The transmission transfers mechanical power from the engine and/or electric traction motor to drive the wheels.


HEVs use fuel as a primary source of power and do not require an external electrical source to recharge their batteries. A true HEV has both an internal combustion engine (ICE) and an electric motor. Both the ICE and electric motor work together to propel the vehicle. This combination helps increase the efficiency of the engine. The power distribution allows vehicles to achieve optimum power under most driving conditions.


Please enter your comment!
Please enter your name here