Hybrid Electric Vehicle Basics

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

A variety of hybrid electric vehicles are currently available. Although HEVs are often more expensive than similar conventional vehicles, some cost may be recovered through fuel savings, a light-duty HEV federal tax credit, 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 allows for a smaller engine, resulting in better fuel economy without sacrificing performance.

Regenerative Braking

A hybrid electric vehicle does not require a plug to charge the battery. Instead, it 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 either a series or parallel configuration.

• 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 cost less than full hybrids but provide lower fuel economy than full hybrids.

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

There are different ways to combine the power from the electric motor and the engine. Parallel hybrids—the most common HEV design—have the engine and the electric motor connected to the wheels through mechanical coupling. Both the electric motor and the internal combustion engine drive the wheels directly. Series hybrids, where just the electric motor drives the wheels, are more common in plug-in hybrid electric vehicles.