KERS explained: how a mechanical Kinetic Energy Recovery System works

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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 2

More information on Flybrid Systems’ F1 KERS on their website

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

Author information

Keith Collantine
Lifelong motor sport fan Keith set up RaceFans in 2005 - when it was originally called F1 Fanatic. Having previously worked as a motoring...

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

  1. Kieth, thanks so much for getting this info out!! So many of us have just been sitting here waiting to see a decent bit of info on KERS for quite some time, (though we’d still love a cross section drawing or three).

    Also, 1000Kw in 25Kg at 60% efficiency,, wow!! That’s a darn nice setup!

    Are you going to interview the electric KERS groups as well?

    1. Needed too know!! Thanks. not even that into f1. just the tech/mech.

  2. HounslowBusGarage
    11th January 2009, 17:56

    So the mechanical is getting on for twice the efficiency of the electical systems. And yet only Williams are considering it. I wonder why that is – is it more difficult to house in the most weight-beneficial place? Please note it’s 100Kw not 1,000 Fred. 1,000 kw would be incredible!
    I wonder how the additional power comes in – like a small explosion I suspect. Might be quite difficult to drive with under some circumstances.
    Thanks for the insight Keith.

    1. CVT, hence quite smoothly. F1 drivers absolutely do not need more unpredictability or lack of control, I’m sure we all agree.

  3. Very interesting ! Maybe they could contact some of the American car companies – right now they are all coming up with plans for greener cars. Still I do not fully understand how it works, perhaps some simple drawings in their website would be helpful for us non – technical folks.
    Congratulations to Flybrid, and best wishes for the future
    Very impressive !

  4. doh! carried the 1 a bit far didn’t I (I understood the true power,, just a keyboard mistake, thanks)
    You’ve got a pointHounslowbusgarage, on the whole power return feel, slam it on mid corner and that could self punt you into the armco by breaking traction pretty much instantaneously (well if you’re already completely on the edge that is).

  5. whatever it is it is good and it is better that everyone is uncertain which way they should go. technology that makes anything go faster or longer is good for F1 and it was a great idea to standardise boring bits and make a few real go fast bits.

  6. Keith, one question I’m dying to knwo the answer to and can’t really judge from the pics…

    How big is it?

    1. Judging by the size of reflection of some momento in the glass; It seems about 1 foot long; and diameter of that black cylinder could be about half-foot.

  7. Max wants everyone to go the flywheel route to save weight, and although it may be more efficient at transfering the stored energy back, it is still a flywheel turning at 64,000 rpm. If it breaks thats very dangerous (although I am happy with Flybrid’s idea of surrounding it in carbon fibre).
    The advantage that storing the energy in batteries has is that you can then use the energy to produce a zero-emmission car for running in the pits or through towns(which is what Citroen are using for their C4 WRC car). whereas the flywheel only operates when the engine is turning.

  8. The other factor that I question is, That is one big giro?! Get it up to 64,000 rpm and you may not be able to go round any corners !!!

  9. Williams is not using the flybrid system. They are part owners of their own company Williams Hybrid Systems. Their’s is a unique system that uses a mechanical/electrical flywheel. The electrical energy is stored in the carbon fibre flywheel through a patented technology.

  10. A fabulous piece of technology and the kind of thing F1 should embrace, even if just for the sheer ingenuity.
    I understand peoples concerns at the thought of a 64,000rpm paperweight flying through the air – or possibly even razor sharp shards of one exploding all over the place.
    However how do the kinetec energies of this compare to those of a piston moving up and down at an engine speed of 19,000rpm. Or the vanes of a low intertia ceramic turbine spinning at 250,000rpm? OK, low inertia for sure but what if the casing fractured etc.
    Anyway, it’s worth the potential risks!

  11. Sounds silly but will the weather affect kers? F1 cars are known to be temperamental and dependent on optimum weather conditions (as well as track of course), to get the most out of the car. I wish I could say I’m wiser for reading this although I’m always fascinated with man’s ingenuity and inventiveness. I just want the battery in my mobile or MP3 player to last a whole lot longer than they currently do… maybe they can help lol (smile)…

  12. Excellent article, but damn, wish i could say i fully get it :) . For one thing i don’t get the need behind the epicyclic gearbox, one would think the CVT would take care of all gearing?
    Also, would i be correct in thinking the energy stored would decrease over time? ie, after braking the flywheel speeds up, but then starts spinning down due to friction?
    If significant power is lost to friction, then the best moment to use it would be shortly after heavy braking.

  13. Lots of questions! So, I’ll only add a little one.

    Luke S: his question about gyroscopic effect…will it be a problem? (Do we have a mechanical engineer in the crowd?) I can’t believe they would go to all the trouble of building this if GE was, in any way, a significant problem.

    1. Mahmoud Samir
      28th March 2009, 8:55

      hi, for sure gyroscopic effect is taken into consideration
      so they should use 2 counter rotating flywheels or they should choose the best orientation position for the flywheel & the least severe orientation is to have the flywheel’s rotational axis perpendicular to the road or track

  14. Hey Keith, in another post (which I can’t find) you said that the KERS boost may only be used once per lap, but says it “may be used for up to 6.6 seconds per lap”. Is that one 6.6 second boost or six 1.1 second boosts?

    1. As I understand they have a set quantity of use per lap, which translates to 6.6s if the KERS operates at maximum power. They can use that in multiple bursts per lap, not just one long shot. Perhaps at some circuits it would be more beneficial to have a lot of little bursts of power than one big blast.

      1. Keith,
        Don’t forget that (as far as I am aware) while it must be driver activated the duration of each usage is pre-programmed.


  15. The reason for the epicyclic gearbox, in additon to CVT, is to get the revs down from the 64000 of the flywheel to something that the CVT can survive at. It would be extremely difficult to built a CVT to operate at 64000.

  16. Note that the maximum output of current KERS devices is limited to around 80 bhp – so only around 10% extra power. And the driver is in control of it and will know what to expect. Rather less dramatic, and more predictable, than a turbo coming in.

    Would be nice if they had something on the TV so that we could see when the drivers were using it.

  17. @ Max

    Thank you. Now, the reason behind using said epicyclic gearbox as opposed to a simpler reduction mechanism, is it robustness? performance?

  18. Generally the advantage of an epicyclic gearbox over a simple pair of spur gears is that you get multiple contact with the input pinion. The load is shared between the three or four contacts with the planetary gears, so the gears can be much smaller. As well as resulting in a compact gearbox, it enables you to use a smaller diameter pinion gear, so reducing the tooth speed – possibly a major consideration when it’s doing 64000 rpm.

  19. That makes a lot of sense, many thanks Max!!!

  20. Perhaps there are two flywheels working in opposite directions?

  21. 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).

  22. 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.

  23. 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?

  24. 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.

  25. 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

  26. 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.

  27. 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.


  28. 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

  29. 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.

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

  31. 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

  32. My question is about KERS flywheel , how can we determine the time required to store energy in flywheel or angular velocity if flywheel before manufacturing it.

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