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Consortium Showcases Flywheel Hybrid System for Premium Vehicles

A consortium of UK automotive companies is showcasing a prototype flywheel hybrid system for premium vehicles (FHSPV) at the Low Carbon Vehicle event at Millbrook (UK) on 15 September. The system adds up to 82PS (60kW) of recovered energy and is predicted to demonstrate fuel economy gains of 20% relative to the current production model. Testing work is already underway.

Part-funded by the UK’s Technology Strategy Board, FHSPV’s industrial partners include: Jaguar Land Rover, Flybrid Systems, Ford, engineering consultancies Prodrive and Ricardo, and transmission experts Torotrak and Xtrac.

Compared to conventional hybrid systems, flywheel hybrids reduce the number of energy conversions onboard the vehicle, improving the efficiency of the regenerative braking system, according to the partners.

Instead of converting kinetic energy into electricity for storage in a battery, a small continuously variable transmission (CVT) connected to the car’s rear differential transfers the energy directly into a compact, high-speed flywheel. When the driver reapplies the accelerator, the CVT smoothly transfers the energy back to the wheels.

This research project explores the potential for more efficient and cost-competitive hybrid drivetrains that improve fuel economy while enhancing standards of vehicle refinement and performance. We have investigated the base technology, built the prototype and will be testing it in the next few months to see if it lives up to its potential.

—Pete Richings, Chief Engineer at lead partner Jaguar Land Rover

The flywheel-CVT system uses a flywheel developed by Flybrid Systems. Spinning at speeds of up to 60,000 rpm enables the flywheel to achieve a high energy density, making it smaller and easier to package. The CVT, which manages the flywheel’s speed and the flow of kinetic energy, has been built by motorsport firm Xtrac using Torotrak’s traction drive technology.

Automotive consultancy Prodrive is responsible for the system’s configuration and integration into the vehicle. The company is also developing the system’s sophisticated control software and electronics.

Ricardo is providing independent analysis on the potential for alternative technologies within the system. Ford Motor Company is examining the potential for secondary applications for flywheel-CVT systems.



So now we have 3 types of hybrids - electric, hydraulic and flywheel - let the battle commence.

It will probably take 5-10 years for a new mode of hybrids to become popular, it takes a while for the engineers to figure them out, and for the marketing people to build a case for the public.

The flywheel one would be great for stop/start traffic - I am not sure if it could be used for boost acceleration once you were going.

I wonder how long it can store its energy for - maybe only a few minutes.

You could have 2 modes - a regenerative one where it only stores braking energy (which would be most efficient), and a boost mode where it would maintain (say) 80% energy all the time for boost use as well as restart.

Thus, you could set it up for pure economy, or economy+power boost.

It could be good for diesel use in cities - they are already very good for highway driving.

Raymond Bzymek

"The system adds up to 82PS (60kW) of recovered energy".

Well actually kW is a measurement of power not energy. To be technically correct the energy should be stated in kW-Hr. Flywheels, like ultracapacitors are relatively high power but low energy devices. The power number will look more impressive than the (real) energy number. By the way, what is the energy storage capability of the system?

Henry Gibson

Yes it seems that a site that is about energy could make sure that energy and power are correctly stated in their articles. Mostly kilowatts are stated when kWh are meant. ..HG..

Henry Gibson

It is nice to see that flybrid and torotrack are still playing nicely with each other.

Flywheels are very good for power peaks, and mechanical or mostly mechanical systems are very good for energy conservation.

Everybody who reads this site should learn about the flywheel electric locomotives that worked in three rail territory out of London that were able even to start up trains when they were in a short electric gap. The high efficiency controls, before electronics, were very clever. There was not even a pause when the locomotive went through a gap. After WWII, diesel engines became highly developed for the electro diesels that replaced them, but they still could have used flywheels for train start power and gap transits. Each car of the old Long Island EMU should also have had simple flywheels to keep the lights on in the gaps.

Prius automobiles should have been fitted with electric flywheels instead of batteries for lower cost, and then low power but high energy batteries could turn them into plug-in-hybrids. The truth is that electric flywheels could reduce the cost of batteries in any electric car. Switched-reluctance motor-generators can be very efficient and small for very high speed flywheels. There was little reason to not have a super large flywheel directly connected to the Prius engine's crankshaft for super acceleration from stops and the electric motor could easily regulate superhigh power going to the wheels ..HG..


The whole idea is not to use electric conversion. Mechanical transmission is much more efficient. In this system you convert the vehicle's kinetic energy during regenerative braking to kinetic energy in the flywheel and back to kinetic energy in the vehicle again during acceleration. It should be obvious that converting kinetic energy to electricity, then to chemical energy in the battery, then to electricity again and finally, to kinetic energy in the vehicle is notoriously inefficient in this comparison. An electric flywheel is also less efficient.

There are 3 alternatives to HEVs:

HPV: Pneumatic hybrids have about similar efficiency as HEVs, as shown by ETH in Switzerland.

HHV: US EPA has shown that hydraulic hybrids will be more efficient than HEVs.

HKV: Kinetic hybrids have the greatest potential for high efficiency of all options known so far.

It is not necessarily the option with highest efficiency that will win but for sure, more money should be spent on the alternatives so that their merits (and drawbacks) could be investigated in more detail.

Compared to conventional hybrid systems, flywheel hybrids reduce the number of energy conversions onboard the vehicle, improving the efficiency of the regenerative braking system, according to the partners.


I might consider a flywheel range extender for a PHEV. The problem with a 60,000 rpm flywheel in your garage is safety. What happens after 50,000 hours of non-stop spinning and a micro fracture?


The flywheel housing must take care of this. There is no other option. It is not an insurmountable problem. A turbocharger runs at ~200000 rpm but the turbine and compressor housings must tolerate a failure. The power turbine in a turbocompound system on a HD engine runs at ~50000 rpm. The gearbox and fluid coupling with components running at high rpm must be safe.

So, what would happen after 50 000 hours and a micro fracture? Basically nothing... Well, I guess you could hear that the flywheel broke.

Many systems have safety issues. What about high-voltage and batteries in a EV or HEV? Well, experts tell us that they are safe... What about a CNG tank at ~250 bar or the pressure vessel (i.e. the combustion chamber) of a diesel engine running at full speed and ~200 bar? Not to mention the diesel injection system that runs at 2000 bar, i.e. as the weight of the whole car on a finger nail. We are told that those systems are safe, too. If technologies are not safe, they will not be introduced on the market. At least we can hope that this is the case…


The advantage of battery or capacitor storage over mechanical flywheels, taking conversion losses into account is primarily that electricity is fungible.
I'm sure there are many 'more energy efficient means but that must be discounted when.
1; extra systems are employed for the reason that it adds complication.
2; that it is inevitably heavier.
3; In integrating the new system versatility and opportunity is lost.IE the large battery storage can absorb up to the ~ 100klm rage storage limit.
A flywheel cannot do that.Also if the electrical system includes capacitors, then we could expect the electrical efficiencies to near equal that of flywheels, increasing as a factor of time (delay to use) as well as having only a small incremental weight penalty as the capacitor is used in other modes. That weight increase could be in the order of grams rather than kilograms.

I cant really see a future for these systems in ordinary motoring as electrical system (even those not directly required for propulsion ) are increasing in market penetration.

Electrical machines are ubiquitous so mainstream and well understood, well resourced as stock components and - well that's seems to be the only objection, that is the auto makers loose a lot of control over patent and propriety components and services.


Funny - I can't seem to find the discussion about gyro-effect and flywheels here so I am starting it.

Magnetal has performed a calculation of the added gyro-effect from a flywheel. Visit to download it. This says that the added force from the gyro effect is in the region of 10 to 20 N (in a not so pleasant load case).

Answer to mahonj above regarding to self-discharge time... With passive electrodynamic magnetic bearings these can be reduced to about 1-2% per hour.

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