• Oct 31st 2007 at 4:07PM
  • 11
Do your remember the hybrid system that stores braking energy not as electricity but in a rotating flywheel as kinetic energy? Well, the system is going to be mated to a special CVT transmission able to change 6-to-1 ratio within one revolution. That is, in 50 ms, the transmission can go to almost zero to full power.

The Kinetic Energy Recovery System (KERS), which is soon going to be tested with a Chevy V8 engine, becomes part of the transmission system of the car and it is light: for F1 applications, the variator and flywheel each weigh less than 5kg in a system with a total mass that does not exceed 25kg. This is both good for the upcoming Formula 1 hybrid racers and for regular car use, where it has a huge potential to help reduce CO2 emissions and pollutants.

The developers say that the device is twice as efficient as electric hybrids. And it's got an additional benefit: since the flywheel is vacuum sealed, the system is silent, except for the links to the transmission and bearings, which is something they're working on.

The flywheel is made from high-strength steel and composite material in which the maximum stresses are less than in the con-rod of a conventional internal combustion engine.

Flybrid, Torotrak and Xtrac promise to keep us updated on the evolution of this system, which you can check by clicking the Read link. Full press release after the jump.

[Source: Flybrid]

Xtrac and Flybrid to reveal technical details of flywheel 'kinetic energy recovery system' at global conference

* Motorsport experts to discuss mechanical alternative to hybrid electric vehicle technology for future road cars
* Fast-acting flywheel system offers up to twice the efficiency, half the mass and more rapid transfer of energy compared with current battery systems

Martin Halley, chief engineer with transmission technology specialist Xtrac and Jon Hilton, managing partner of Flybrid Systems, a new company taking a fresh look at hybrid vehicle technology, will describe the technical innovations behind their groundbreaking mechanical flywheel 'kinetic energy recovery system' (KERS) - which also incorporates advanced traction drive technology from Torotrak - at a forthcoming high-level motorsport industry conference.

"The Federation Internationale de l'Automobile (FIA) regulatory body, which governs motorsport, has recognised that motor racing provides a unique opportunity to demonstrate new technologies which could be relevant to the automotive mainstream," said Halley, whose presentation will provide an overview of new F1 regulations and the technology and materials required to develop the sophisticated transmission system required for a mechanical based KERS system.

"The new rules being drawn up for F1 will stimulate the development of new and exciting technologies, within a competitive environment, which may otherwise not have occurred. This means rapid product development is required right here and right now," commented Hilton, whose technical paper will discuss the recovery and storage of braking energy in a mechanical-based flywheel system.

Flybrid has already secured one unnamed F1 team as a customer and is confident others will follow given the benefits of a fast-acting flywheel system, which offers up to twice the efficiency, half the mass and more rapid transfer of energy compared with hybrid battery electrical systems. The company is also well on its way to bench testing a flywheel KERS system adapted for road car applications using a Chevrolet V8 engine.

Flybrid's brake regenerative system uses advanced gearbox technology provided by transmission specialists Torotrak and Xtrac. The system employs a small and sophisticated ancillary gearbox manufactured by Xtrac incorporating a continuously variable transmission (CVT) design licensed from Torotrak. Torotrak's patented traction drive technology is being developed for motorsport applications by Xtrac under an exclusive licensing agreement. Xtrac can sub-license the CVT 'variator' technology to Flybrid and other motorsport teams who may wish to design and build their own flywheel.

The role played by Flybrid, Torotrak and Xtrac in designing a mechanical KERS solution for F1 could be instrumental in developing this pioneering vehicle technology for more fuel efficient road cars without resorting to the expense and complexity of battery systems. Compared with hybrid electric vehicles, which use batteries for energy storage, a mechanical KERS system utilises flywheel technology as a highly efficient alternative to recover and store a moving vehicle's kinetic energy.

The combination of gearbox-variator and flywheel would form part of the driveline assembly. The kinetic energy is stored during a braking manoeuvre and is then released back into the driveline as the vehicle accelerates. Flybrid, Torotrak and Xtrac claim that compared to the alternative of battery systems, a mechanical KERS system can provide a more compact, lighter and environmentally-friendly solution.

Torotrak's patented technology is a vital element in a mechanical system as it provides a continuously variable connection between the flywheel and the vehicle driveline. Xtrac's exclusive licence and development of the system for motorsport applications allows it to design, manufacture, assemble and distribute complete variator systems and discrete components to F1 and other motorsport customers.

For F1 applications, the variator and flywheel each weigh less than 5kg in a system with a total mass not exceeding 25kg. This relatively low mass is a major advantage both for race and road cars. The high level of mechanical efficiency combined with the variator's ability to change ratio very rapidly helps to optimise flywheel performance. The transmission system selects the appropriate ratio depending on the torque demand and can change its 6-to-1 ratio within one revolution.

"Performance calculations show we can go from zero to full power in 50ms," says Hilton. "This is faster than the driver can apply the brake pedal."

Flybrid, Torotrak and Xtrac all see the potential for wider application beyond motorsport – initially on high-performance road cars – both as an aid to performance and as a means of developing vehicles with reduced fuel consumption and CO2 levels. Applied to road cars the system supports the current motor industry trend for smaller powertrains; a lightweight kinetic energy recovery system providing a means of boosting acceleration and overall performance and economy independently of the vehicle's internal combustion engine.

An ancillary flywheel is particularly suited to stop-start driving situations when real-world fuel economy is often at its worst. In these conditions, the variator can assist the launch of a vehicle which has slowed down or come to a standstill. In heavily congested traffic, where a car is frequently stopped and restarted, the system can help alleviate the heavy fuel consumption and emissions of greenhouse gasses normally associated with these conditions. However, unlike hybrid electric vehicles, a mechanical KERS system continues to provide the benefits of kinetic energy recovery throughout the speed range, and its benefits are maintained on the open road.

"This is a major plus point for a mechanically-based kinetic energy recovery system," says Halley, "in which the variator can also handle energy flows a lot faster than an electric vehicle."

"On a directly comparable basis, a flywheel system offers up to twice the efficiency of a kinetic energy recovery system that stores its energy in a battery," adds Hilton. "The overall in-out efficiency of a mechanical drivetrain feeding energy into a flywheel and back out to the vehicle again via an ancillary transmission system is approximately 65-70 per cent compared with 35-45 per cent for a hybrid battery-electric system. Fundamentally, this is because a purely mechanical system doesn't have to convert the kinetic energy into electrical and chemical energy as with a battery system."

"What this means is that with a flywheel each time the brakes are applied at least 65 per cent of the energy is available to re-accelerate the vehicle," explains Hilton, "whereas the best that can be achieved with existing battery technology is 45 per cent."

Flybrid has filed various technical patents to tackle the key engineering issues of safety and noise. The flywheel is made from high-strength steel and composite material and has been designed with a high factor of safety in which the maximum stresses are significantly less than in the con-rod of a conventional internal combustion engine.

"The flywheel also runs in a vacuum which is a natural barrier to noise," says Hilton. "For optimum refinement in a road car the engineering effort would be focussed on the transmission system and bearings - which provides the only noise path - it's exactly the same test and development process in other words as for a normal powertrain."

Halley and Hilton will join other influential figures from the automotive and motorsport industries attending the Global Motorsports Congress being held in Cologne on 5-6 November 2007 - where the hot topic of conversation is expected to be the future eco-friendliness of motorsport and the 'green revolution' in F1 envisaged by FIA president Max Mosley. This leading global industry event takes place the same week and in the same location as the Professional MotorSport World Expo, where Xtrac will be exhibiting a wide range of transmission systems alongside other leading motorsport manufacturers.

Later this year Chris Brockbank business development manager Torotrak will present a paper describing the sophisticated variator traction drive technology, which is a key part of the mechanical KERS system, at the CTi Transmission Symposium on 4/5 Dec 2007 in Berlin.

Adrian Moore, technical director, Xtrac, will similarly present a technical paper describing the technology behind the KERS system at the World Motorsport Symposium, which takes place on 29/30 November at Oxford Brooks University's brand new engineering centre. He joins other senior engineers who will be bringing their particular expertise to bear on subjects that are of special relevance to the growing demand that motorsport technologies should be of more relevance to the road car of tomorrow.

Moore will also discuss the mechanical KERS system with mainstream automotive engineers and technical experts attending the Global Powertrain Congress being held in Vaals in the Netherlands in June 2008.


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    • 1 Second Ago
  • 11 Comments
      • 7 Years Ago
      Anyone have any ideas as to why this was not considered as a strictly non-mechanically-but electically-linked storage via flywheel with the flywheel configured for input and output as an electrical generator/motor? I am not conversant with electronics and electrical mechanics so this is really out there for me. But, if it were possible, it would seem that you would still have the storage advantages and not have to figure conversion losses? I can see that you might have to have some type of variable controller to match input and output to the variable flywheel speeds-is that a practical possibility?
      • 7 Years Ago
      There are 3 big problems this design faces, due to using a mechanical drive:

      1. it requires a rotating shaft seal to a vacuum chamber that runs at a high RPMs. That adds friction and wear, and could leak air, increasing drag on the flywheel.

      2. The continuously variable speed drive would be frequently shifting, and would be subject to a considerable amount of wear and energy loss due to slippage and friction.

      3. There would be gyroscopic effects that could cause problems whenever the vehicle turned or tilted. This problem could be solved by using a fully gimbaled support, allowing the flywheel to tilt in any direction, but that would greatly complicate the drive mechnism.

      All of these problems could be easily solved by going to an electrical drive system. This mechanical drive is more complicated, more expensive, less reliable, heavier, and may even be less efficient. I really don't understand why they are stubbornly trying to make a fully mechanical version work.
        • 6 Years Ago
        The idea behind KERS is to use the energy lost due to braking to resume movement a short while later. Cars are not fuel efficient at pull-away. Using recovered energy in city traffic will do wonders for your millage.

        Firstly, electrical KERS is far easier and simpler to implement with current technology. It is not necessarily safer and cheaper than mechanical systems. And definitely not more efficient.

        Secondly, it is ideal for running the electrical systems of your car, leaving your engine to only turn the wheels. That alone will increase your millage.

        Thirdly, it is also ideal if you want to stop you car today and re-use the energy next month.

        Now to your points
        #1 Even if the chamber was filled with a low viscosity oil, the energy loss over 5 minutes will be a lot less than with generating electric current, charging a battery, discharging the battery and driving an electric motor with energy loss due to heat generated in all 4 stages. If you make the flywheel heavier, you can reduce the RPM (less drag). A 10kg flywheel at 5000RPM has the same energy as a 5kg flywheel at 10000RPM with almost half the drag.

        #2 Read up a bit about toriodal CVT transmissions. You'll find that the wear is a lot less than with other forms of transmissions. That makes them cheaper than manual transmissions with clutches.

        #3 The gyroscopic inertia problem can be overcome by using 2 flywheels on the same axis rotating in opposite directions, negating gymbals and special transmissions.

        Problems with using Electrical systems
        a Conventional electrical generators generate heat as a byproduct. Increasing the temperature of a metal conductor increases the resistance which generates more heat.

        b You either need a high-speed generator which will increase the drag due to air-friction or a low speed generator which requires a transmission, increasing the complexity and weight.

        c Read points a and b for motors as well. The points hold true even if the motor and generator is the same device.

        d To reduce the temperature in the conductors you'll either need thick wires (increasing weight) or use high temperature super conductors which will increase the cost.

        e Batteries. Let us ignore the fact that they are filled with corrosive and/or noxious chemicals and heavy metals, and cause a lot of damage to the environment in production. Batteries are heavy (the equivalent weight of flywheel can store a lot more energy for a short time). They also generate heat when charging AND discharging. I do not want to be in an accident, but I definitely do not want to be in an accident with a battery powered car. The cost of replacing the batteries alone might not even cover the savings in gas.

        An alternative to batteries (the biggest drawback for me), is so-called super capacitors. Unfortunately the technology is still pretty young and not considered economically viable.

        f Due to all the heat generated, you need a cooling system which use (you guessed it) more energy.

        All the technological advances in materials, bearings and transmissions give mechanical systems the edge for KERS use on cars.
        All points above leave me to conclude that mechanical (flywheel-driven) KERS is more practical than electrical methods.

        A final note. Transferring power in the same form is almost always more efficient than converting to another form as there is always an energy loss in the conversion process.
      • 7 Years Ago
      If this is cheaper and safer than batteries, then let the best technology for the intended purpose win. But what about the existing fleet? It will take YEARS to replace them all. What if you could DOUBLE or even TRIPLE the fuel mileage of ANY standard existing car by simply modifying the automatic transmission so that it would capture and reuse 97+% of the breaking energy and could accelerate from 0-60 in 4 seconds?

      What if this modification only cost around $3,000.00 without using batteries or electric motors and also doubled the life of the car?

      http://peswiki.com/index.php/Directory:Hydristor_Corporation
      • 6 Years Ago
      Can't we live together? Without the gas? Use this flywheel as part and parcel of the power system where a flywheel motor /generator set is powering the car the fast acting transmission is mediating the RPM needs. The main mass flywheel runs an electric mo/gen and the transmission could do what it usually does only better. It would be able to spin up the main flywheel with any excess energy during braking and store enough to start the car from a dead stop.
      • 7 Years Ago
      normanchodrick -

      If you're looking for near instantaneous storage and release of electrical energy, it's probably best to skip the whole mechanical flywheel system and head straight for capacitors. Today's supercapacitor technology has the capacity to fill this need; controls and efficiency are the challenges.
      • 7 Years Ago
      Awesome. I'd love to drive a car with flywheels instead of batteries. Or even for home power storage.
      • 7 Years Ago
      It appears to have an advantage over electric hybrids, in that it is simpler and more powerful, lighter.

      However, The hybrids have an advantage of more flexibilty, advancement to near no oil use. Batteries you can line the floor of the vehicle, lowering center of gravity. Also allows in-wheel hub motors allowing more control of the wheels. Also, with plug in models, you can go on pure electric potentially for months (provided you drive short enough distance, plug in every night).

      In the long term, I think electric hybrids are a better bet. We'll get over the costs and complexity.
      • 7 Years Ago
      There are 3 big problems this design faces, due to using a mechanical drive:

      1. it requires a rotating shaft seal to a vacuum chamber that runs at a high RPMs. That adds friction and wear, and could leak air, increasing drag on the flywheel.

      2. The continuously variable speed drive would be frequently shifting, and would be subject to a considerable amount of wear and energy loss due to slippage and friction.

      3. There would be gyroscopic effects that could cause problems whenever the vehicle turned or tilted. This problem could be solved by using a fully gimbaled support, allowing the flywheel to tilt in any direction, but that would greatly complicate the drive mechnism.

      All of these problems could be easily solved by going to an electrical drive system. This mechanical drive is more complicated, more expensive, less reliable, heavier, and may even be less efficient. I really don't understand why they are stubbornly trying to make a fully mechanical version work.
      • 7 Years Ago
      To #7: Although the company seems to be backed up by Formula 1, you're completely right to take this with a pinch of salt.
      • 7 Years Ago
      I followed the links, and it seems that while a demonstration was performed ten years ago, there is nothing actually available. It sounds very good, but is it another 100mpg carburator type device.
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