We've all seen them, on the expressway, at the stoplight idling next to us and even safely parked in the garage. Hybrid Electric Vehicles (HEV) are increasingly common for a number of reasons including increased fuel economy, lower emissions and improved performance. Combining conventional internal combustion engine (ICE) technology with electric propulsion assistance, HEV's are outperforming the gas guzzlers of yesteryear.

The first gasoline-electric hybrid automobile in the world was developed in 1900 by Ferdinand Porsche. [1] Over the next 97 years, readily available fossil fuels made alternative fueling methods a non-issue to automakers and consumers. With the release of the Prius in 1997, Toyota was the first automaker to roll out a widely available HEV. With a then estimated fuel economy of 45 miles per gallon (mpg) (4.5L/100km) in the city and 52mpg (5.2L/100km) on the highway paired with rising gas prices worldwide, the first mass produced HEV was well received by the auto buying public. Most, if not all major automakers quickly followed suit and worldwide sales of HEV's skyrocketed.

With most major automakers now producing HEV's, there are multiple drive trains to choose from, each with distinct benefits for consumers to choose from. Included in the choices are parallel hybrids, series hybrids, power-split hybrids, full hybrids and mild hybrids. In parallel hybrids the ICE and electric motor are each connected to the mechanical transmission and are able to simultaneously transmit power to drive the wheels. Series hybrids use only the electric motor to power the drive train, using the ICE to generate reserve power and recharge the batteries. Power-split hybrids share many characteristics with series and parallel HEV's allowing for overall higher fuel efficiency. Full hybrids are able to utilize only the engine, only the batteries or a combination of both. The ability to switch back and forth between power sources as well as sharing them adds complexity in the design of full hybrids. A mild hybrid cannot be driven solely on its electric motor, lacking the power necessary to propel the vehicle. An oversized starter makes for quick restarts of the engine after coasting, braking or stopping. Mild hybrids also incorporate regenerative breaking to recapture energy normally released in the form of heat to replenish the car battery's electric power.

There are also plug-in HEV's that use rechargeable batteries for power. Taking advantage of the electricity in your home you are able to charge your battery while parked in the garage. Plug-in HEV's eliminate fears associated with running out of energy on long trips by having a backup ICE available for additional power creation.

References:

[1] http://en.wikipedia.org/wiki/Hybrid_electric_vehicle

[2] http://www.afdc.energy.gov/afdc/vehicles/electric_basics_hev.html