What is a hybrid car – part two

Earlier this week we looked at hybrid cars, and at how Toyota’s Hybrid Synergy Drive means the Prius can run on its petrol engine, its electric motor, or both at once. The Prius is the most affordable full hybrid car you can buy in the UK, so how is Hybrid Synergy Drive different from other key fuel saving technologies?

All carmakers are trying to make their cars more efficient. At the end of last year, the EU set a target that by 2015 the average carbon dioxide (CO2) emissions from each new car must be no more than 130 grams per kilometre (130g/km).

Many Toyotas – including the iQ, Aygo and Yaris ranges – are already well under the target thanks to innovations such as the breakthrough Toyota Optimal Drive technology. According to figures from Clean Green Cars, the average CO2 figure for all Toyotas sold in the UK in the first quarter of this year was 136.46g/CO2 – down 6.8% from the year before.

Manufacturers are trying to meet the EU target in different ways:

Stop & Start
Some companies are introducing stop/start systems that switch off the car’s engine when it comes to a standstill – at traffic lights for example – automatically restarting it when the driver’s ready to move off again. Toyota calls this Stop & Start, and has found it can improve combined cycle fuel economy by up to 18%.

Micro hybrid
Some makers use the term micro hybrid to describe a similar system to Stop & Start. But with acceleration only available from a micro hybrid’s engine – rather than the engine and an electric motor – they aren’t strictly hybrids at all. As well as automatically stopping their engine when stationary, micro-hybrids use regenerative braking to store energy in a high-capacity battery as they slow down. This stored power can be used to run car electrics, and pumps for cooling and steering that would normally be powered directly by the engine. With less load on the engine, less fuel is used.

Mild hybrid
A mild hybrid – sometimes called a power-assist hybrid – is more sophisticated than a micro hybrid. There’s generally a bigger battery that can store plenty of charge from regenerative braking, and an electric motor that can use it to assist the car’s engine when needed. Mild hybrids save fuel because energy that would be lost to braking is “re-used” to help accelerate, but they aren’t as sophisticated as a full hybrid like the Prius, and they tend to be less economical. Most importantly, a mild hybrid can’t run on its electric motor alone for zero-emission low speed motoring.

To find out more about the Prius’ Hybrid Synergy Drive, read our earlier post.

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