Volvo Car Group conducts UK testing of Flybrid® KERS technology.

• Volvo Car Group conducts UK testing of Flybrid® KERS technology for passenger cars
• Technology adds 80hp performance boost while cutting fuel consumption by up to 25%
• Part of Volvo Cars’ Drive-E Powertrain research programme, system again shows how drivers needn’t compromise between power and fuel efficiency

Volvo Car Group and engineering company Flybrid Automotive, part of the Torotrak Group, have been conducting UK tests of lightweight Flybrid® flywheel KERS technology that boosts performance while cutting 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 80hp 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.  Just like its recently launched D4 engines, which combine 181hp performance with CO₂emissions as low as 99g/km, the Flybrid® KERS tests deliver similarly impressive results and confirm that it is a lightweight, financially viable and very 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, is pleased to support 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 (Kinetic Energy Recovery System) is fitted to the rear axle of an S60 powered by a 254hp five-cylinder T5 petrol engine. Under braking, kinetic energy which would otherwise be lost as heat is transferred from the wheels to the KERS, and is used to spin a 6kg carbon fibre flywheel at up to 60,000 revs per minute. When the car starts moving off again, energy stored in the spinning flywheel is transferred back to the rear wheels via a specially designed transmission, and can either 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.

Most efficient in city traffic

"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. In other words, the fuel savings will be 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 80 horsepower and, thanks to the swift torque build-up, this translates into rapid acceleration, cutting 0 to 62 mph figures by seconds. The experimental car, a Volvo S60 T5, accelerates from 0 to 62 mph around 1.5 seconds 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.

Carbon fibre for a lightweight and compact solution

Flywheel propulsion assistance was tested in a Volvo 260 back in the 1980s, and flywheels made of steel have been evaluated by various manufacturers in recent times. However, since a unit made of steel is large and heavy and has rather limited rotational capacity, this is not a viable option.

The Flybrid® flywheel that Volvo Cars used in the experimental system is made with the combination of a steel hub and carbon fibre outer. It weighs about six kilograms and has a diameter of 20 centimetres. The carbon fibre wheel spins in a vacuum to minimise frictional losses.

"We are the first manufacturer that has applied 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," concludes Derek Crabb.

ABOUT FLYBRID & TOROTRAK

Torotrak is the global innovator in gearless traction drive technology that increases efficiency and reduces CO₂ emissions in vehicles. The variable-drive technology is being developed for main drive transmissions, superchargers, and engine auxiliary applications, substantially improving fuel economy. Following the acquisition of Flybrid Automotive Ltd in 2014, the company’s flywheel technology portfolio includes a range of highly efficient, lightweight and low cost flywheel Energy Recovery Systems. The company has shown how its technologies can reduce CO₂ emissions, conserve energy, save costs and significantly boost efficiency. Customers include major vehicle manufacturers across road cars, buses, commercial vehicles, off-highway and their tier-one technology suppliers, with several programmes now evaluating production-ready designs.