New flywheel hybrid system, originally developed for use in F1, could be used to power London's buses from late next year
28 April 2015

By the end of next year, 500 buses in London could be using an electromechanical hybrid system originally developed by the Williams Formula 1 team.

Using a composite flywheel to store energy from the brakes and feed it back to an electric motor, it offers a simpler, cheaper and more durable solution than storing the energy in batteries.

The flywheel hybrid system is the first step in a planned revolution in the way buses are designed in a bid to reduce both pollution and noise.

It was first developed by Williams with an F1 application in mind, but the system instead ended up in sports cars competing in the World Endurance Championship.

The advantage of a flywheel system is that it is light, compact and efficient, but the disadvantage is that it can only store energy for short periods. It is suited to racing where cars are continually either accelerating or braking but is of limited use in a road car where there is more long-distance running.

It is, however, ideally suited to an urban bus, which is generally either accelerating or braking and whose substantial mass means a large amount of kinetic energyis produced.

Engineering firm GKN now wants to develop the tech further by mating it to a small diesel engine running continuously as a generator, with most of the energy powering the bus coming from the flywheel itself.

This could cut bus pollution by as much as 50-75%, because diesels are dirtiest when slowing down or speeding up. Running the engine at a constant 1500rpm or so should also make buses quieter.

The flywheel also has significant running cost advantages, as it will mean a smaller engine is needed and no gearbox is required, so the system is tipped to pay for itself within two years.

It would even be possible to fit the powertrain with a small battery pack for short zero-emissions hops - for driving the length of London’s Oxford Street, for example. 

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28 April 2015
Looked at a similar system in Switzerland whilst at uni in the early 90s. That one used a 1 litre Fiat Punto engine as generator.

28 April 2015
Transport for London are taking a risk here; Williams' involvement might slow the buses down.

28 April 2015
Norma Smellons wrote:

Transport for London are taking a risk here; Williams' involvement might slow the buses down.

Based on performances so far this year, it's a good thing they are not going with Mclaren.


I'm a disillusioned former Citroëniste.

29 April 2015
To achieve this, all design work would have to be finalised and bus makers would have to be starting production about now. It seems to me that this is a highly speculative story put out by Williams or GKN, perhaps to generate funding for more development work. In which case we might see flywheel-powered buses some time during the next decade. I don't doubt that there is some merit in the system, but if conventional buses were that inefficient, their brakes would surely be glowing red hot! I suspect that the gains in efficiency are more like the 15-25% norm that we expect from hybrid cars.

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