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Williams' flywheel formula is finding uses in motor sport, motoring and beyond
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The Kinetic Energy Recovery System – KERS – was introduced to Formula One for the 2009 season. It recovers energy otherwise wasted under braking and feeds it back into the driveline. And for Formula One it represented, in more ways than one, real change.
KERS was – and is – a conscious attempt to nudge F1 towards a more environmentally sustainable future. The cars themselves have become more efficient, but of greater importance is the intention to orientate the sport towards research areas that are valued in the world beyond the paddock gates.
As the automotive industry migrates towards plug-in hybrid electric vehicles (PHEV) and full electric vehicles (EV), so the science and technology behind building lighter battery packs, better power management software and stronger composite structures has become a growth industry. KERS places the cutting-edge engineering talents of F1 in the vanguard of that research, to re-establish a tradition of technology transfer between track and road.
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This transfer never truly went away, but the perception that it had arose in the 1990s as F1 became more specialised. Instead of high-profile items such as the anti-lock brakes and paddle-shift gearboxes developed by previous generations, F1 in the 21st century improved the science of thin-wall casting, aerodynamics software and new fuel additives. What it didn't do was deliver the eye-catching fully packaged new technologies that had previously been part of the relationship. The architects of KERS hoped to restore that link.
The regulations were deliberately left open. Rather than encouraging a repetitious design war focused on a single technology, the FIA hoped engineers would pursue a variety of KERS solutions, kick-starting a technical diaspora. So far, the best example in action is the Williams flywheel.
With the reintroduction of KERS – in 2011 – F1 has become a racing series for mild hybrids, and, just like mild hybrids on the road, most F1 teams have adopted batteries as their energy storage medium. Indeed, most KERS use off-the-shelf battery packs bought from the same few manufacturers that supply the motor industry. |
But Williams went their own way. Believing in the potential of the flywheel as a superior energy storage device, they invested heavily in Williams Hybrid Power (WHP) – a business looking way beyond Formula One. WHP has already enjoyed racing success with its magnetically loaded composite (MLC) flywheel, but a far bigger prize will be theirs if they successfully break out of the motor sports arena. The next generation of PHEV and EV cars and buses are being firmly targeted by the flywheel, but Williams is also evolving the basic concept as an environmentally responsible energy storage technology for everything from light rail systems to wind farms.
HOW IT WORKS
Flywheels are not new. Using a rotating mechanical device to store then release kinetic energy is familiar to anyone who has seen a potter at work on a wheel. More recently, flywheels have been used in laboratories to generate short, high-power bursts of energy that would cause disruption if pulled directly from the grid. Where WHP is breaking new ground is in its use of composite materials – specifically carbon-fibre that until its recent commercialisation would have been too expensive for mass-market use – to create a high-speed compact device suitable for installation in a mobile application. A car, bus, or commercial vehicle, for example.
The WHP flywheel unit is made from easily recyclable materials, and uses largely established production techniques. It also has a relatively small number of parts.
"We have a filament-wound carbon-fibre rotor, an integral part of which is a magnetically loaded composite (MLC) portion at the inner diameter," says Operations Director Gordon Day. "That part of the rotor contains – interspersed within the composite – discrete magnetised particles that act as the rotating magnetic element of an electro-magnetic motor/generator. The other part, a traditional iron-core-and-copper-winding stator, sits stationary inside that spinning rotor, and the entire device is encased in an aluminium housing."
WHP's prototype rotors weigh about 12kg. When fully charged (for example, by regenerative braking energy) the flywheels are designed to reach speeds of about 40,000rpm. Within the vacuum of the housing, that speed dissipates only very slowly, during which time the kinetic energy is available for conversion into electrical current.
"In simple terms one can think of our flywheel as a mechanical battery," says Day. "It has a positive and negative terminal and only an electrical connection to the drivetrain. There is no mechanical link: it can be thought of as a drop-in replacement for a battery – and as a very efficient solution where high-power response is demanded."
RACING APPLICATIONS
While the flywheel was tested extensively on Williams' FW31 F1 car, it made its racing debut in a Porsche GT3R in the 2010 Nürburgring 24 hours. It came agonisingly close to victory, leading at the 22-hour mark before suffering (non-flywheel related) mechanical problems and retiring soon after.
As part of the Porsche Intelligent Performance hybrid development programme, the race car had been designed around the flywheel energy storage technology. To deliver the continuous 120kW (160bhp) performance specified by Porsche, WHP produced a 59kg flywheel system. A lithium-ion battery design with equivalent performance would have weighed significantly more.
"It was an engineering challenge to run at the Nürburgring," says Day. "Porsche had aggressive performance targets and the time scales were tight, but this is part of the beauty of using motor sports to advance a technology – the white heat of development is fed by competitive forces. The deadline of an upcoming race isn't going to move."
ON THE ROAD
Using the flywheel in endurance racing is something WHP view as a natural stepping-stone to the eventual goal of putting the flywheel on the road, and it couldn't have come at a better time: 2011 is an interesting year for road cars with a varied range of PHEVs and EVs appear in dealerships. Very much a proof-of-concept exercise, EVs such as the Nissan Leaf and Citroën C-Zero are not only more than twice the price of similarly sized conventional cars, but their range is limited to less than 150km. They are, however, the forerunners of what consensus within the automotive industry predicts is the future of the car. It is an area in which WHP expects the flywheel to play a significant part.
"My interest was always to apply the technology outside motor sport," says managing director Ian Foley. "As an engineer with Lotus in the early 1990s, working on active suspension both for Team Lotus in Formula One and the road car side of the business, I saw how a technology developed for racing could be adopted by major car companies. When KERS was announced I saw it as an opportunity to do something similar. From day one my vision was to develop the flywheel for F1 and use that as a route to proving the technology and marketing it to automotive companies."
Interestingly, once the flywheel gets away from the track and onto the road, Foley believes it has potential to complement – rather than compete with – battery technology. Using the F1-derived flywheel, the next generation of EVs will potentially be lighter and cheaper than those currently on offer.
He says: "The best estimate of the medium future is that the car we'll be driving is a PHEV range-extended vehicle – basically something with a small internal combustion engine supplemented by a big slab of batteries. The typical short commute or shopping run will just use the batteries, with the range-extending IC engine coming in for longer journeys. Currently the battery pack for a 2011 PHEV/EV weighs around 250kg. While the most efficient manufacturers are getting the cost of that pack down to around $10,000, essentially it's still too heavy and too expensive."
A significant consideration is that, much like rechargeable batteries in the home, those used by the automotive industry work best if they're being charged or allowed to discharge at a slow and steady rate. Sudden spikes of incoming current from brake regeneration, or outgoing under heavy acceleration, rapidly reduce their lifespan. The flywheel, on the other hand, is the ideal device for rapid charging and discharging. It can trickle-charge the batteries, or be trickle charged by them, while acting as a buffer between the storage cells and the driveline.
"The life of a battery is a function of peak current," says Foley. "Drawing out excess current decreases the life of a battery, which for an automotive application will have to last at least 10 years, which means battery slabs have to be over-sized to meet the requirements of that lifespan.
"A flywheel would smooth out the interactions, allowing the batteries to function closer to their ideal state, which would encourage smaller, lighter battery packs. Or, another possibility, the energy stored in the flywheel will allow car-makers to fit lead-acid batteries rather than expensive lithium-ion cells currently used. Lead-acid batteries are not so high-powered, but they are cheap, and in combination with the power provided by the flywheel, may provide a better, lower-cost solution."
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HOW IT WORKS
 Engine – a conventional flat-six 350kW (470hp) driving the rear wheels. It has no physical connection to the flywheel.
 Power electronics.
 Front axle portal shaft containing two 60kW (80bhp) electric motors powering the front wheels under acceleration. Under braking the process is reversed and the unit becomes a generator.
 High-voltage cable.
 Flywheel is located in the cockpit and connected via positive and negative terminals just like a battery system would be. It stores rotational energy, spinning at up to 40,000rpm and is charged during braking. By pressing a button the driver can reverse the process: the flywheel is electromagnetically braked and its stored kinetic energy is converted back into electrical current.. |
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For a system designed to harvest regenerative braking energy, there's no better setting for a debut than the 100-plus corners of the Nordschleife. While short on the outright pace of its rivals (including its non-hybrid GT3R sister car), the Porsche 911 GT3R Hybrid still led the 2010 Nürburgring 24 Hours after 22 hours of racing.
The GT3R Hybrid is treated more as a 'racing laboratory' than a purely competitive motorsport project. It is a testament to the hybrid system's superior economy (longer stints and fewer pitstops) that it did so well.
Given the nature of endurance racing, the GT3R has a larger flywheel unit than a single-seater racer, delivering twice the 60kW (80bhp) specified in the 2009 F1 KERS regulations. A departure, however, from the F1 application is the addition of two dedicated axle motors as part of a motor-generator unit. They drive the front wheels and complement a petrol engine delivering 350kW (470bhp) to the rear wheels.
Under braking, the motor-generator converts energy into an electric current that charges up the Williams Hybrid Power flywheel. Stored as rotational energy, the flywheel in turn becomes a generator when required, delivering current to the axle motors. Unlike a battery system, it suffers no calculable deterioration in performance from the constant deep charge/discharge cycles.
The hybrid GT3R delivers a 6-8 second power burst automatically to the axle motors under acceleration. A 'boost-paddle' on the steering wheel also allows a discretionary extra kick
of power for overtaking.
Hybridisation adds around 130kg overall: a flywheel weighing some 45kg and the 68kg 'portal shaft' containing the motor-generator. The rest comprises cooling systems and electronics controllers.
Porsche later confirmed that its development programme would look at shedding weight, but focus primarily on refining the power-electronics software, so adding greater flexibility to the KERS management while increasing its level of integration with the overall powertrain management system.
Since its debut with Porsche Intelligent Performance, the hybrid has raced problem-free in China and the USA. It won no trophies, but picked up a string of awards at the Professional Motorsport World Expo.
The project won the Vehicle Development of the Year award; team leader Dr Daniel Armbruster was named Design Engineer
of the Year, and the WHP flywheel won Powertrain Innovation of the Year. The judges said it "changed perceptions about hybrids by introducing fresh technology to a new area of motorsport and showing how it could be incorporated into a race vehicle that has much in common with a road car." |
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BEYOND THE ROAD
While WHP works from laboratories inside the Williams HQ at Grove, Oxfordshire, other applications for the flywheel are being developed at the Williams Technology Centre in the Gulf state of Qatar. WTC is taking the base technology and applying it to static applications: essentially building scaled-up devices intended for use with renewable power generation or in mass transit systems.
Whereas WHP is working on flywheels weighing tens of kilograms, with power ratings of around 100-150kW and capable of storing between 0.25kWh and 0.5kWh, the devices being developed by Williams in Qatar will have a power rating of 500-750kW, capable of storing 7-8kWh. They will weigh about three-quarters of a tonne.
Damien Scott, general manager at the WTC, says that, while on a larger scale, the technology is the same and will play similar if grander roles.
"For example, in support of mass transportation systems – primarily metros and light rail – the MLC flywheel acts as a high-power buffer; it will absorb regenerative braking energy when trains slow or stop and then introduce it back into the line when others accelerate. This improves overall efficiency of the operation while stabilising the interface with the local electricity grid."
CONNECTING WITH RENEWALS
The idea of the giant flywheel acting as a buffer between a generating device and the grid is equally relevant, says Scott, when using the flywheel in conjunction with renewable power generators, such as wind turbines or solar arrays.
"So-called 'strong' grid applications is a term broadly covering the field of improving the efficiency, stability and reliability of electricity grids," he says. "That is becoming increasingly important as more intermittent renewable generation sources, like wind or wave power, are connected to a grid. These generation sources produce electrical output that isn't constant, smooth or predictable, unlike the output from nuclear or coal/gas-fired generators. As the proportion of these generation sources grows they will unbalance the localised grid – but if you can introduce very high-power energy storage to act as a buffer, it's possible to fill in supply troughs and shave demand peaks. This smoothing makes the grid more efficient, reliable and, importantly, allows the introduction of renewable energy generation sites onto that grid to be accelerated."
Renewables are expected to have a democratising effect on power generation. Alongside mainstream generators, local communities and large industrial concerns are beginning to generate their own power and are, of course, selling the surplus onto the grid.
One stumbling block to greater uptake is the issue of 'noisy' power; the jagged and unpredictable nature of home-grown generation makes it poorly suited to grids accustomed to the smooth, conditioned output of power stations. Coupling renewable sources to flywheels, or placing flywheels between a host of renewable generation sources and the grid can, potentially, alleviate the problem and create conditions suitable for much greater take-up.
"This is going to be seen more and more in countries where increasing distributed on-site generation is being adopted," says Scott. "Because of the instabilities many small intermittent sources would introduce if directly connected to the grid, there will be incentives – financial or otherwise – for large industrial or residential developments to become more self-reliant on wind or solar, but without putting all that noise back onto the grid. That's when high-power energy storage potential – such as the flywheel – is a big advantage."
BEYOND PROTOTYPING
As Williams grow ever more confident in their technology, efforts are turning to developing real world applications and productionising the concept. Closer to the Formula One design, WHP is the more advanced of the two groups. Aside from Porsche's motor sport applications WHP is participating in an ongoing development project with Jaguar-LandRover. Joint projects with other European car manufacturers and commercial vehicle builders are also progressing. The firm intention is to introduce the low-volume manufacture of production flywheels within the next two years; mass volumes will follow.
At WTC the project is less advanced, though the centre is already working with Siemens' mass transit division to assess the potential of the larger flywheel for light rail use. It also has an ongoing project with the giant UK-based grocery chain, Sainsbury's, to identify potential flywheel uses ranging from integration with renewable on-site electricity generation at retail stores, to supporting energy recovery at depots.
While at one level the flywheel's F1 origins may seem irrelevant to potential customers of such industrial size and scope, everyone involved in the project acknowledges the race team's vital role as a catalyst to successful development of the application.
"With Williams behind it, the project gained a lot of credibility in the marketplace," says Foley. "Being part of Williams really helps us to market ourselves, and to effectively punch above our weight."
"WHP is a separate company, but we're in partial incubation at the moment," adds Day, "living on the F1 premises and enjoying usage of the technology and structure of the racing team, plus the capabilities of various departments at Grove. The team has a wealth of technical expertise, it has a laboratory in which we can do analysis and experimentation on our composite chemistry; we're able to make use of the manufacturing capability of the factory and it's of great help at this early stage to be able to rely on the quality assurance systems, as well as to quickly get product that we need. Basically, we can use the infrastructure around us."
Williams hasn't used its flywheel technology in F1 this season under the revamped KERS regulations. The ban on refuelling with knock-on packaging constraints has made it a less effective proposition than it was under the original 2009 KERS regulations. However, that isn't particularly important any more. The project is up and running and its future beyond motor sports is bright. KERS has done its job perfectly.
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