Green for go

It's a sign of the times when Formula One motor racing says it wants to become more environmentally friendly.

The Brazilian Grand Prix provided the best finish to a Formula One season for a generation, with Lewis Hamilton overtaking Timo Glock on the penultimate bend to deny Felipe Massa the world championship. The 23-year old is now the youngest champion the sport has ever had.

As the partying ends in Sao Paulo, attention will turn to next season, which starts in Melbourne, Australia in mid March. Next season will see extensive rule changes, including bodywork restrictions, a reintroduction of slick tyres, the banning of tyre warmers, and the arrival of Kinetic Energy Recovery Systems (KERS).

In late 2007, governing body the FIA announced it was freezing the specification of F1 engines for the next 10 years to encourage car makers to develop environmentally friendly technologies such as KERS - a form of regenerative braking - making them the only means for the present by which teams can gain a power advantage.

KERS technology takes a moving vehicle's kinetic energy, which is otherwise wasted during braking, stores it, and then releases it back into the drivetrain as the vehicle accelerates. There are three main types of KERS units - electrical, mechanical and hydraulic - but all are designed to boost acceleration while delivering lower fuel consumption, and therefore CO2 emissions, independently of the vehicle's engine.

One reason behind the FIA's move is to promote the use of eco-friendly technology in road cars by helping manufacturers sell it to the public through its use in F1. Speaking in his keynote address at the Motor Sport Business Forum in Monaco in December 2007, FIA president Max Mosley said: "It is necessary to demonstrate to society that F1 is doing something useful, and it is essential for F1 teams to be able to demonstrate to major companies that they are able to really make a contribution."

Another reason is the thinking behind the freeze on engine design. Mosley told the forum: "The F1 racing engine is fully developed; there is no need to develop it any further. Instead, we will allow manufacturers to spend money on technology that is really useful. The first part of that is the KERS device, which we are introducing in 2009."

There is a third, no less important, reason, and that is to save money by ensuring the sport's engineers do not pursue technologies that are not relevant to road cars. This cuts both ways. Developing new engines and powertrain technologies from scratch to meet growing consumer demand for more economical road vehicles, and to meet stringent CO2 emission regulations being introduced by the EU in 2012, leaves little change from £1bn, so any technology that allows an existing engine design to satisfy these criteria will be welcome.

F1's carbon footprint

Burkhard Goeschel, BMW board member and chairman of the Formula One Manufacturers Advisory Commission, told the Monaco forum: "Formula One should be road-car relevant. The car industry has a big challenge in improving the efficiency of cars and to reduce CO2."

Some may argue this move by the FIA is not before time. With a typical F1 car guzzling nearly a litre of fuel every kilometre and pumping out about 17t of CO2 a year, it's hardly an eco role-model. But it would be unfair to brand the cars themselves planet-killers - 18 or so two-hour races a year, involving about 20 cars, even including attendant testing and qualifications, will not melt the ice caps alone.

So although KERS has the 'green' credentials, the headline aspect of this technology for F1 is its ability to boost performance, particularly when coming out of corners or overtaking. For the 2009 season, the FIA is limiting the amount of energy recovery to 400kJ per lap, giving an extra 80hp for about 6.5 seconds and a likely time benefit of up to 0.3 seconds. From 2011 the FIA plans to double this to 800kJ, and from 2013 double it again to 1,600kJ and allow it to deliver power to all four wheels.

The 2009 limit gives only a modest power gain - one that is offset by the extra 25-35kg a KERS unit adds to a car and its effect on the car's ballast distribution, so drivers will have to be very tactical about when they use the boost. It also takes time to restore the energy, so a driver will not want to use up his lap's worth at some critical point in the track before the others.

So, unsurprisingly, there's a huge amount of debate over the use of KERS in F1. But there is widespread agreement about its value to the commercial sector, and a consensus is emerging that mechanical KERS is the technology that holds the most promise here. The other two approaches - electrical and hydraulic - have applications, and even some advantages, but the mechanical approach seems to trump the others in weight, size and cost at the moment.

The main issue with electrical KERS units is that they are, well, electrical. There are some variations on the essential technology but, broadly, they harness the braking energy by storing it in batteries or capacitors, then releasing it back into the drivetrain through a motor or flywheel.

Although they can be expensive, they offer some flexibility in placing the various components around a vehicle, which in F1 is important for weight distribution. But they also tend to be larger and heavier than a mechanical KERS unit, and in road cars such as the Toyota Prius there is some opinion that the energy storage and hence power output is well under the rated figures during typical vehicle use, the reasoning being that the cars are not usually braked heavily.

KERS' drawbacks

Ironically, there's the green aspect, too. For a technology that's meant to help save the planet, there are some very eco-unfriendly components in electrical KERS units - the batteries for instance. And as recent incidents with the Red Bull and BMW Sauber F1 KERS cars have shown, there can be a risk of battery fires and electric shocks.

That said, in F1 for now at least, this option looks to be the more popular, perhaps partly because F1 teams such as Toyota and Honda already have so much invested in it through their road-car programmes.

The principle behind hydraulic KERS units, by contrast, is to reuse a vehicle's kinetic energy by conducting pressurised hydraulic fluid into an accumulator during deceleration, then conducting it back into the drive system during acceleration.

But there are some fundamental problems here as well. One is the relatively low efficiency of rotary pumps and motors. Another is the weight of incompressible fluids. And a third is the amount of space needed for the hydraulic accumulators, and their awkward form factor. None of this matters too much in, say, heavy commercial vehicles but it makes this option unsuitable for road and racing cars.

Mechanical KERS technology, however, appears to overcome all the drawbacks with the other systems, and the first such commercial product for F1 has been developed by three UK companies - Flybrid Systems, Torotrak and Xtrac.

In essence the system consists of a flywheel connected by a continuously variable transmission (CVT) to the drivetrain. Moving the CVT towards a gear ratio that would speed the flywheel up enables it to store energy, while moving towards a ratio that would slow it down allows it to release energy. A hydraulic clutch separates the drive if the flywheel's revs exceed the system's limits.

The components within each variator include an input disc and an opposing output disc. Each disc is formed so that the gap between the discs creates a toroidal cavity. There are two or three rollers inside each cavity, depending on torque capacity, which are positioned so that the outer edge of each roller is in contact with the toroidal surfaces of the input and output discs. As the input disc rotates, power is transferred via the rollers to the output disc, which rotates in the opposite direction to the input disc.

The angle of the roller determines the ratio of the CVT, so any change in the angle of the roller results in a change in the ratio. So, with the roller at a small radius (near the centre) on the input disc and at a large radius (near the edge) on the output disc the CVT produces a 'low' ratio. Moving the roller across the discs to a large radius at the input disc and corresponding low radius at the output produces the 'high' ratio, and provides the full ratio sweep in a smooth, continuous manner.

Flybrid, the system's integrator, had the idea for it, originally with road cars in mind, while Torotrak provides the underlying CVT gearbox technology and Xtrac designed the CVT under direction from Torotrak and Flybrid, and makes the CVT.

In itself, the system is not an innovative concept and is widely used in other applications, but Flybrid has been able to create enough power storage density in a unit small enough and light enough (25kg) for F1 by making the flywheel spin at about 64,000rpm.

At such speeds, failure of the flywheel would be catastrophic and dangerous, so as well as mounting it in a robust casing - and in a vacuum, to cut windage losses - the main consideration for the unit's control system is safety.

As Flybrid's managing partner Jon Hilton explains: "The control system has multiple levels of redundancy for monitoring the speed of the flywheel, for example in the main control map where the energy figures are stored. There's also a separate strategy for the hydraulic clutch to stop the flywheel's speed getting too high, as well as separate speed sensors in the ECU.

"But there are other issues with the control system," he says. "One is to achieve consistent performance. KERS can vary the brake balance, so if you brake differently each time there is a chance you could lock the wheels." Here though, Hilton adds that the KERS unit can be switched on and off, if the driver needed to use the car's ABS system for example.

"The third issue is onboard diagnostics, to measure parameters such as power output to check for any losses in the system. Even when the technology matures we will still need to keep an eagle eye on the diagnostics - it's a legal requirement in road cars.

"The fourth issue is the vacuum. In F1, there's no vacuum pump; the system is pumped first then fitted and raced. But we will need to maintain the vacuum in road cars over time and monitor it every fortnight or so," he says.

Hilton describes the control unit itself as a "cut-down ECU or grown-up gearbox control unit, depending on which term you prefer", which is based on an existing ECU from a specialist supplier. It drives the hydraulic valves - the main control elements - which in turn operate the hydraulic pistons that operate the CVT. And, while the hydraulic clutch is special to this application, the vacuum, temperature and speed sensors are off-the-shelf, as are the hydraulic valves, although these have had to be re-engineered.

And that's about it. As Hilton says: "The control system is simple because the mechanical system is consistent. In fact it took only a few months to design and develop the control system."

The Flybrid KERS is now being tested with an unnamed F1 team, but the company has always known that the real growth will be in road cars - first in high-end models then later in small, city cars. So it has developed flywheel designs that are less powerful but cheaper to manufacture. As Hilton says: "In road vehicles the crucial factor is the cost of KERS. We calculate our KERS is one-third the cost of electrical systems, because it's a mechanical system.

"But we need a better understanding of how our system will be used in road cars," he says. "So we'll need to tweak it to suit the type of car and how it's likely to be driven - the 'duty cycle' - then feed that into the control system.

"In F1, because the car's going round and round a track, we know in advance what the duty cycle will be, so we can optimise the system. But we can't do that for a road car. The control parameters can be very precise for F1; they have to be more general for road vehicles."

Flybrid, Jaguar and KERS

One of Flybrid's first road-car collaborations is at the premium end of the car industry, with Jaguar Cars, which, according to Hilton, is more interested in the performance aspect of KERS.

Neither Jaguar nor Flybrid are giving out many details about the project at the moment, but it is known that the project is funded partly by the UK government, that the KERS development is taking place on an "existing vehicle platform", and that Jaguar is looking to develop it as a "cost-competitive alternative to other hybrid systems, to prove its effectiveness and viability for production and suitability for modular application", suggesting that the Flybrid KERS is being mated to an existing engine design. A demonstration vehicle is due in the first half of 2010, with the first production road car expected by about 2013.

Also, Hilton says that in general the power output depends on the car and is bespoke to the model, with about 40-60kW (about 54-80hp) being a "sensible figure". And it's been calculated that a 150hp engine with an 80hp KERS unit up could replace a 250hp engine in a current road-going car, with some people suggesting a 50 per cent saving in fuel as well.

But, despite the lack of details, the project has already sparked interest from potential customers. Hilton says a millionaire rang Flybrid after hearing the news to ask to buy the Jaguar demo vehicle; Jaguar said no.

Yet it's city cars that look to be Flybrid's biggest market. The technology is particularly suited its the stop-start nature, when fuel economy and greenhouse gas emissions are at their worst, as the kinetic energy stored in a CVT-flywheel system can help propel a vehicle that has slowed down or stopped. As with other innovations from F1 into road cars, such as traction control and semi-automatics gearboxes, however, we'll see KERS units in high-end models before they cascade down to other ranges.

Buses, trains and KERS

Flybrid is also working on similar applications, such as buses and trains - where Hilton says studies shows fuel savings of 40 per cent and 50 per cent respectively - as well as commercial vehicles and garbage trucks. He even talks of applying the Flybrid KERS to wave power, to store the pulses of energy from successive waves.

For now though, all eyes are on the 2009 F1 season. Again there are few details yet on which teams are using which systems, and how their development is progressing, but it's providing plenty of fodder for the motorsport press at the moment.

What is emerging is that Williams F1, for one, looks set to opt for an electrical flywheel technology, as earlier this year it bought a minority share in UK company Automotive Hybrid Power, now called Williams Hybrid Power, which develops high-energy composite flywheels. Honda and/or Toyota also look set to follow the flywheel route, as could McLaren, while Ferrari, which has criticised the introduction of KERS, is pursuing its own development route.

So, whichever team is the 2009 champion, it could well be down to which KERS technology it uses - which will mean a huge endorsement for the technology and its developer.

Recent articles

Info Message

Our sites use cookies to support some functionality, and to collect anonymous user data.

Learn more about IET cookies and how to control them

Close