Hybrid electric vehicles operate by using a combination of two types of motive power, an internal combustion engine and a sizeable electric motor and generator. The main purpose of the electric generator is to recover the kinetic energy otherwise lost through vehicle braking as heat (regenerative braking) and to store it electrically. The electric motor then uses this stored power to help to accelerate and drive the vehicle.
There are two main types of hybrid emerging from the research activities of the car companies.
The first is the complex split-hybrid which uses a large electric motor and a power-split transmission in place of a conventional gearbox. This configuration requires a radical change to the layout of the vehicle. Although vehicles of this type are already in the market, the technology has not been accepted by many car companies due to the high additional investment and unit costs involved. The main benefit of this type of complex hybrid is that in addition to the regenerative mode it allows the engine to run under optimum conditions with consequent improvements in fuel economy and emissions.
The second form of electrical hybrid, known as a parallel hybrid, offers the benefits of regenerative braking but in combination with a conventional fixed ratio transmission. This parallel hybrid arrangement is well suited to existing vehicle layouts and is already on sale in several vehicles in North America. From the number of engineering programmes that have been started across the automotive industry, it is evident that parallel technology is emerging as the preferred hybrid configuration for high volume application.
A useful and more detailed guide to hybrid technology can be found on the US Environmental Protections Agency's website www.fueleconomy.gov
