How do hybrid vehicles work?

Hybrid cars are part battery-electric and part conventional cars. The underlying principle of all hybrid vehicles is the use of a temporary energy storage device (usually a battery), which enables the main engine to be operated at close to its maximum efficiency.

Series and parallel hybrids

Two types of hybrid drive have been developed. In 'parallel hybrids', the most common type of hybrid car, the wheels can be either directly powered by the combustion engine or using a battery-powered electric drive-train, or both can be used simultaneously to provide power to the wheels. The Toyota Prius is probably the best known full parallel hybrid.

'Series hybrids', however, use a combustion engine to generate electricity, which then powers an electric motor to provide motive power. In its purest form, the combustion engine is unable to drive the wheel directly. In cases where the engine is relatively small, series hybrids are also known as 'range extended electric vehicles' and the car behaves like an electric vehicle, the battery being charged by the on-board power unit.

In both types of hybrid, when the engine loading is low, the excess energy is stored for later use. When more energy is required, the main engine and the energy storage device work together to deliver the required power. In this way, hybrids provide improved fuel economy and reduced emissions.

Hybrids are also classed either as 'mild' or 'strong' to reflect the degree of battery power incorporated into the design, strong hybrids being able to spend more time in electric-only mode. Most hybrids operate in electric mode at low speeds, which makes them ideal for urban driving. Battery storage enables the use of regenerative braking which tops up the battery during braking, further reducing overall fuel consumption by around 20%.

Driving a hybrid car

The driving performance of hybrids is not unlike that of a conventional car, road handling is very similar and acceleration is broadly comparable or even slightly improved. From the outside, most hybrids look similar to other new conventional models – other than sporting a 'hybrid' badge.

With their additional dashboard information, its from the driving seat you are more likely to be aware of the differences of hybrid car design. Most strong hybrids, for example, will offer three driving modes: 'eco-mode', where the car decides how to most efficiently use conventional and electric power; 'zero-emission-mode', where the car runs purely on electricity; and power-mode, where both engines are used to deliver maximum power on demand.

As all hybrid cars currently on the UK market use conventional petrol or diesel, fuel is dispensed from fuel pumps in exactly the same way as for conventional non-hybrid models. Indeed, the great advantage of petrol- and diesel-fuelled hybrids is that they require no change in fuel and so use the existing fuelling infrastructure.

As the driving range and fuel economy of hybrids is better than their conventional counterparts there are no restrictions on the applications for which they can be used. With no technical barriers to their use, hybrid vehicles therefore possess great potential to become one of the new standard automotive technology of the next decade.

Next: Environmental benefits of hybrid cars >>

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