KERS explained: how a mechanical Kinetic Energy Recovery System works

Posted on | Author Keith Collantine

A mechanical Formula 1-specification KERS by Flybrid
A mechanical Formula 1-specification KERS by Flybrid

Kinetic Energy Recovery Systems are one of the big talking points off the off-season, as F1 teams weigh up whether to use them on their 2009 F1 cars.

KERS builders Flybrid Systems demonstrated a working Formula 1-spec device at the Autosport International show. I had a chat with managing partner Jon Hilton who talked me through how the system works and what they do to make the devices safe:

This is our demonstrator device for a Formula 1 KERS so the layout of it is correct. The output from middle gear to the car is adapted for every individual car so this is the core bit that would be fitted to any car.

Drive comes into the device’s continuously variable transmission which provides a seamlessly changing ratio between the inputs and the flywheel. Control pistons manage the ratio within the CVT. It contains a clutch, an epicyclic gearbox and a flywheel. The flywheel spins much faster than the input drive – it’s a 5:1 ratio. Controlling the position of the levers manages the torque transfer within the CVT, and therefore how much energy is stored or released.

The energy is stored in the flywheel which spins at 64,000 rpm. We’ve done a huge amount of work on safety, it was our number one concern when we started. We’ve done a lot of testing and the device is completely safe. We’ve applied for patent protections, and some of those are published now, on safety and containment. This device has an outer containment structure made of carbon fibre which is extraordinarily strong. It can contain pressures of up to 1,150 bar, so it’s enormously strong. If something were to break, it would be contained, for definite.

It’s our view that changing the states of the energy – from mechanical at the wheel, to electric, to chemical at the battery, and back again, is a very inefficient route. The energy efficiency in a petrol-electric hybrid is about 37%, where ours is about 60%.

The electric systems is what you would find in a Toyota Prius or Honda Civic Hybrid. Those systems are less powerful – the Prius’s is 23kW, this is 60kW. Performance of the devices in F1 is limited to 60kw, but this one is capable of 100kW, we restrict it to meet the rules, but it is much more powerful than the regulations allow. We are expecting them to increase the limit in the future and we’re ready and waiting for it.

It weighs 25kg in total including all the control hydraulics, the fluid that’s in it, electronics, everything. We looked at two different locations for installing it in an F1 car: one effectively sat on top of the gearbox, the other in fronn of the engine at the bottom of the fuel cell. There’s advantages and disadvantages to either place.

Most F1 teams are expected to use electrical KERS in 2009. But Williams are believed to be considering a mechanical device such as this one. Whether it will perform better than its electrical equivalents we will find out on the track.

Copies of Flybrid’s information leaflet:

Flybrid leaflet 1
Flybrid leaflet 1
Flybrid leaflet 2
Flybrid leaflet 2

More information on Flybrid Systems’ F1 KERS on their website

A mechanical Formula 1-specification KERS by Flybrid (click to enlarge)
A mechanical Formula 1-specification KERS by Flybrid (click to enlarge)

37 comments on “KERS explained: how a mechanical Kinetic Energy Recovery System works”

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  1. No, the large black cylinder on the right is the carbon-fibre flywheel. The two metal discs to the left of it, with bearings in the middle, are the discs of the variator (continuously variable transmission).

  2. When braking the flywheel is attached to the drive system and wound up untill the brake is released. The spinning flywheel is now available for a few seconds to transfer its spinning back to the drive wheels. As soon as braking stops the spinning flywheel will also start slowing down and most probably be useless by the end of the round if no more braking is done. It is possible with a sufficiently large flywheel to stop the car in total because a large flywheel will require all the energy that is released when coming to a standstill etc. Hope this helps.

  3. Robert McKay
    29th March 2009, 14:44

    Just while we’re talking about KERS – is it true to say that the driver chooses where and when it “charges up”? So it’s not that the system automatically charges itself wheneve braking, but the driver has to push a button to charge it when they want?

  4. No, I don’t think so. The charging only happens under braking, so I would imagine that the system recharges as much as it can whenever the brakes are applied. Don’t know how they manage to maintain a consistent brake balance.

    Unfortunately the “batter bar” on the TV only shows the time allowance left for that lap, not the state of charge of the system.

  5. Robert McKay
    29th March 2009, 14:54

    No, I don’t think so. The charging only happens under braking, so I would imagine that the system recharges as much as it can whenever the brakes are applied. Don’t know how they manage to maintain a consistent brake balance.

    Cheers. It sounded like Croft on R5L was alluding to that being the case (the driver selecting when to charge I mean) but I wasn’t sure if this was the case.

    Just another of the many complications of KERS that the fans are somehow meant to know about :-D

  6. It’s interesting how they use the green button. In qualifying 2 we saw Kimi just tap the green button at the start of a straight and the KERS seemed to stay on for a pre-programmed time. In the race we saw others mixing it up a bit more.

  7. I’m no expert but I’m told …
    Don’t really need two rotors, the flywheel is actually very, very light but spins incredibly quickly therefore the gyroscopic effect is minimised and I would imagine on the inverse plan to the engine.

    Someone said “As soon as braking stops the spinning flywheel will also start slowing down” … The flywheel runs in a vacuum with so called frictionless bearings so the loss is absolutely minimal even over many months of storage. I’m told as many as six months, so it can retain the energy for a much greater time than a single lap.

    Someone said “the flywheel operates only operates when the engine is turning”, that is incorrect the flywheel continues to spin for months or until all the energy is drawn from it.


  8. keiththeengineer
    12th October 2009, 19:53

    as a thought could not a kers system be done with harnessing the air compressing ability of the engine to first of all provide braking and then a store of compressed air to provide boost air to replace the now missing ram air due to cornering slowly or even as a pseudo turbo … would be easier to make than the other systems only pipework and valves and a storage volume which is to all intents and purposes empty air at 10 bar which if incorporated into the structure would make it very very stiff when inflated

  9. these flybrids gonna me the race much more interesting… will also decide race outcomes. but i’ve got a question concerning the dynamics of the car. how would adding a 25kg flybrid affect the car while goin ard the corner at low speeds?? would it make it flip… as the flybrids got its own momentem which you’ll have to deal with.

  10. how heat energy dissipated from brakes goes to flywheel
    (without using motor or engine),as it is human powered vehicle….

  11. Alejandro, from what I read, theyre using a magnetic bearing which in theory produces no friction at all, and the flywheel is in a vaccuum, also theoretically, posing no friction

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