What is a hybrid car?
A hybrid car is a car with two engines - a petrol or diesel engine and a supplementary electric motor that gives an extra boost to the main engine when pulling away and accelerating.
The result is a fuel-efficient alternative to a large engine car: hybrid engines mean you can buy a large, Hybrid family sized car with the fuel efficiency of a much smaller model. Indeed, Honda believe their current 1.3 litre hybrid petrol-electric engine in their Honda Civic IMA saloon gives similar performance to a 1.8 litre engine with the fuel economy of a 1.0 litre.
The Toyota Prius is probably the best known hybrid vehicle available today. The Prius is a spacious family hatchback with good performance and all the features you would expect from an executive car, yet because of its hybrid technology the Prius provides better economy and lower emissions than most small city cars.
How does a hybrid car work?
Petrol and diesel engines are extremely inefficient: even with modern engines, only about 20% of the energy released by burning fuel is used to provide forward momentum.
A 150bhp engine typically only uses 15bhp when cruising at 60mph. So with a little help on accelerating, a 20-25bhp engine is all that is needed to power a car - the rest is just waste.
Electric motors are exceptionally efficient: they're about 90% efficient. Even better, they provide maximum power from standstill, when a petrol engine is least efficient.
So in a hybrid car, the petrol engine is scaled down and an electric motor is added to help the car accelerate.
Because an electric motor provides maximum power when pulling away, this means a hybrid system can use the efficiency of an electric motor to reduce the heavy acceleration strain from the petrol engine, thereby saving fuel.
When running at high speed the petrol engine trickle charges the batteries to ensure the electric motor has sufficient charge to take over when the car gets to lower speeds. Hybrids also use a technique called regenerative braking when the car is slowing down; using the electric motor as a brake and generating electricity to recharge the batteries using the momentum of the car.
When the petrol engine is not needed to charge batteries or power the car, it switches off. So when slowing down or stopped, the petrol engine is switched off.
Are all hybrid cars the same?
No they're not. Some hybrid cars, like the Toyota Prius, allow the electric motor and the petrol engine to work independently of each other so the car can be powered by petrol or the electric motor or both together.
This means that at low speeds the electric motor can power the car completely. This has a big advantage in stop-start traffic and slow moving city driving where the petrol engine need not be switched on at all.
Other hybrids, like the Honda Civic IMA, use the petrol engine and the electric motor in tandem. This is a much more efficient method for higher speed driving, but means the petrol engine needs to be running to power the car.
Hybrid technology isn't purely in use for economy, however. Lexus use hybrid technology to provide high performance vehicles. The emphasis is on performance rather than economy. Fuel economy is little different to a non-hybrid vehicle, but performance, especially acceleration from low speeds is significantly better.
What are the advantages and disadvantages of a hybrid car?
For many journeys, hybrids can provide significantly improved fuel efficiency and environmental benefits compared to their non-hybrid counterparts.
Hybrids aren't the answer for everyone, however. By their nature, they provide their best performance on short and medium journeys involving stop-starts and non motorway motoring commuting too and from work, for example. However, on high speed motorway driving, where the electric motor is not used, hybrids offer very little benefit over a fuel-efficient diesel car.
Hybrids also cost significantly more than the equivalent petrol or diesel only models. The company car tax and road tax are significantly less, as are the running costs, but only high mileage users can expect to save money on a hybrid car compared to buying the equivalent petrol model.
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