Volvo Car Group and Flybrid Automotive, part of Torotrak Group, have been conducting UK tests of lightweight Flybrid flywheel KERS technology to boost performance and cut fuel consumption and emissions.
The four-year partnership, using real-world driving data from tests on public roads and test tracks in both Sweden and the UK, has shown that the flywheel-based hybrid technology can deliver an 80bhp performance boost, together with fuel savings of up to 25 per cent.
The research forms part of Volvo’s continued Drive-E Powertrain research and development programme, which demands no compromise between performance and efficiency.
Like its recently launched D4 engines, which combine 181bhp performance with CO2emissions as low as 99g/km, the Flybrid KERS (kinetic energy recovery system) tests deliver similarly impressive results and confirm that it is a lightweight, financially-viable and efficient solution.
The system is the first full-scale trial of a rear-axle mounted flywheel system in a front-wheel-drive passenger car and is the result of a partnership between Flybrid, Volvo and the Swedish government.
Flybrid Automotive founder Jon Hilton, now commercial director of Torotrak plc following Flybrid’s acquisition by the Group in 2014, said of Volvo’s UK testing: “This car is a great demonstration of how close to market this technology could be, and how class-leading fuel efficiency can be combined with real performance and driver enjoyment.”
The Flybrid KERS is fitted to the rear axle of an S60 powered by a 254bhp five-cylinder T5 petrol engine. Under braking, kinetic energy which would otherwise be wasted as heat is transferred from the wheels to the KERS, and is used to spin a 6kg carbon fibre flywheel at speeds up to 60,000 revs/min.
As the car begins to move off again, energy stored in the rotating flywheel is transferred back to the rear wheels through a specially designed transmission. This energy can be used either to boost power or reduce load on the engine.
The combustion engine that drives the front wheels is switched off as soon as braking begins. The energy in the flywheel can then be used to accelerate the vehicle when it is time to move off again or to power the vehicle once it reaches cruising speed.
"The flywheel's stored energy is sufficient to power the car for short periods. This has a major impact on fuel consumption. Our calculations indicate that it will be possible to turn off the combustion engine about half the time when driving according to the official New European Driving Cycle," explains Derek Crabb, vice president powertrain engineering at Volvo Car Group.
Since the flywheel is activated by braking, and the duration of the energy storage - that is to say the length of time the flywheel spins - is limited, the technology is at its most effective during driving featuring repeated deceleration and acceleration cycles. Fuel savings are thus greatest when driving in busy urban traffic and during active driving.
If the energy in the flywheel is combined with the combustion engine's full capacity, it will give the car an extra 80bhp and, thanks to the swift torque build-up, this translates into rapid acceleration, cutting zero to 62mile/h figure by seconds.
The experimental car, a Volvo S60 T5, accelerates from zero to 62mile/h some 1.5s quicker than the standard vehicle. The KERS drive to the rear wheels also offers the experimental car part-time four wheel drive to add extra traction and stability under acceleration.
Flywheel propulsion assistance was tested in a Volvo 260 in the 1980s, and flywheels made of steel have been evaluated by various manufacturers in recent times. A flywheel made of steel is large and heavy and has limited rotational capacity.
The Flybrid flywheel used by Volvo Cars in the experimental system uses a combination of steel hub and carbon fibre outer. It weighs 6kg and is 20cm in diameter. The carbon fibre wheel spins in vacuum to reduce frictional losses.
"We are the first manufacturer to apply flywheel technology to the rear axle of a car fitted with a combustion engine driving the front wheels. The next step after completing these successful tests is to evaluate how the technology can be implemented in our upcoming car models," claims Crabb.
Flybrid automotive has worked with JaguarLandRover but in that application in a Jaguar saloon the front-engined car is rear-wheel drive.
Meanwhile, Geely Automotive-owned Volvo Car’s plan is working, according to president and chief executive officer Håkan Samuelsson, when recently he reported net profit for 2013 of US$301.9 million compared with US$66m a year ago.
The automaker sold 427,840 new vehicles last year – up one per cent from 421,951 in 2012.
Samuelsson said: "This strong turnaround from the first half of 2013 is further tangible proof of Volvo Car Group’s progress in implementing its transformation plan. This full-year profit represents a significant turnaround compared to the result for the first six months of 2013."
The carmaker recently reported February sales up 4.6 per cent year on year – the eighth consecutive month of growth.
China’s Zhejiang Geely Holding Group acquired Volvo Car Group in 2010 from Ford Motor Company after paying US$1.8 billion in a largely all-cash deal.
Retail sales are forecast to grow five per cent this year, according to Samuelsson.
"We are delivering on the plan we set out four years ago: focus on profitability, revitalise the brand, reinforce our product strengths and leverage our potential and position in China. 2013 was a year of groundwork, successfully preparing the way for the future. This year our total sales are forecast to increase and we will – with the XC90 – reveal the first product of a portfolio that will delight our customers, paving the way for the company’s future growth."
Sales in 2014 will continue to grow, driven by steady growth in key markets using improved products. Samuelsson said Volvo in China would build on a strong sales performance in 2013, when sales rose 45 per cent to 61,146 cars.
New models like the S60L and the sales start of the V40 Cross Country as well as a further expansion of the dealer network would support growth.
In the US, Volvo now has a line of refreshed S60, XC60, XC70 and S80 models, the sales of the V60 sports wagon and the roll-out of the Drive-E powertrains are expected to start soon. ∎
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