Hybrid Electric Vehicles

Hybrid electric vehicles (HEVs) are powered by an internal combustion engine or other propulsion source that can run on conventional or alternative fuel in combination with an electric motor that uses energy stored in a battery. HEVs combine the benefits of high fuel economy and low tail pipe emissions with the power and range of conventional vehicles.

A wide variety of hybrid electric vehicle models is currently available. Although HEVs are often more expensive than similar conventional vehicles, some cost may be recovered through fuel savings or state incentives.

Help from an Electric Motor

Hybrid electric vehicles are powered by an internal combustion engine and an electric motor, which uses energy stored in batteries. The extra power provided by the electric motor may allow for a smaller engine. Additionally, the battery can power auxiliary loads like sound systems and headlights and reduce engine idling when stopped. Together, these features result in better fuel economy without sacrificing performance.

Regenerative Braking

A hybrid electric vehicle cannot plug in to off-board sources of electricity to charge the battery. Instead, the vehicle uses regenerative braking and the internal combustion engine to charge. The vehicle captures energy normally lost during braking by using the electric motor as a generator and storing the captured energy in the battery. The energy from the battery provides extra power during acceleration.

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Fuel-Efficient System Design

HEVs can be either mild or full hybrids, and full hybrids can be designed in series or parallel configurations.

  • Mild hybrids—also called micro hybrids—use a battery and electric motor to help power the vehicle and can allow the engine to shut off when the vehicle stops (such as at traffic lights or in stop-and-go traffic), further improving fuel economy. Mild hybrid systems cannot power the vehicle using electricity alone. These vehicles generally cost less than full hybrids but provide less substantial fuel economy benefits than full hybrids.

  • Full hybrids have larger batteries and more powerful electric motors and larger batteries, which can drive the vehicle on only electric power for short distances and at low speeds. These systems cost more than mild hybrids but provide better fuel economy benefits.

There are different ways to combine the power from the electric motor and the engine. Parallel hybrids—the most common HEV design—connect the engine and the electric motor to the wheels through mechanical coupling. Both the electric motor and the internal combustion engine drive the wheels directly. Series hybrids, which use only the electric motor to drive the wheels, are sometimes found in plug-in hybrid electric vehicles.