How Hybrid Cars Work

July/August 2005
http://www.motherearthnews.com/green-transportation/how-hybrid-cars-work.aspx
The Honda Civic Hybrid achieves is rate dat 46 miles per gallon (mpg) in city driving and 51 mpg highway driving.


COURTESY HONDA

At the heart of every hybrid is the tandem of an internal-combustion engine (powered by gasoline) and an electric motor (powered by batteries). In conventional vehicles, automakers size gas engines to provide enough power for peak acceleration, but that level of power isn't needed most of the time. The addition of an electric motor allows for a smaller gas engine that uses less fuel and can run more often at its peak efficiency.

In most hybrids, when the vehicle idles, the gas engine shuts off and the electric motor is the sole source of power. The electric motor also powers the hybrid at low speeds and supplements the gas engine with extra oomph when the driver accelerates quickly.

To recharge their batteries, hybrids capture kinetic energy as the vehicle slows down, a process called regenerative braking. In conventional vehicles, this energy is lost as heat when brakes apply friction. But in hybrids, the electric motor helps slow the car and transfers some of the kinetic energy to the batteries, which store the power for future use. Hybrids' conventional brakes kick in when needed, such as with sudden stops. Because hybrids recharge themselves, there's no need to plug them into an electrical outlet overnight.