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Volvo adds spin to fuel savings

Full circle: Volvo’s rear axle-mounted kinetic energy recovery system can give a big performance boost as well as savings at the pump.

A lightweight flywheel can make big cuts to fuel bills, says Volvo

Volvo logo29 Apr 2013

By BARRY PARK

VOLVO has tested a fuel-saving flywheel for a car that spins as fast as a centrifuge used for enriching the uranium needed to power nuclear reactors.

The Swedish car-maker says the rear axle-mounted flywheel, which spins 60,000 times every minute once it reaches its top speed, can cut up to a quarter off a turbocharged four-cylinder car’s fuel bill when compared with a turbocharged six-cylinder car with a similar performance level.

Volvo said the Formula One style flywheel kinetic energy recovery system (KERS), which converts energy lost during braking into mechanical energy that is then transferred to the rear wheels using a specially designed transmission, adds an extra 60kW of power.

According to the car-maker, the engine switches off as soon as the vehicle starts braking. The energy stored by the flywheel is fed back to the rear wheels when it starts moving again, or to power the vehicle when it is at highway speeds.

Volvo vice-president of powertrain engineering Derek Crabb claimed the flywheel stores enough energy to power the car for short periods.

“This has a major impact on fuel consumption,” he said. “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.

“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 stops and starts.

“In other words, the fuel savings will be greatest when driving in busy urban traffic and during active driving.”

The technology is also said to give the car a more sporty feel, and in Volvo’s S60 mid-size sedan prototype the flywheel cuts its 0-100km/h sprint from 8.3 seconds down to 5.5 seconds.

Volvo says it has also designed the flywheel to be lightweight compared with steel-based designs trialled as far back as the 1980s.

The car-maker’s modern-day interpretation is a 20cm ring made of carbon-fibre that weighs about six kilograms. It also spins in a vacuum to minimise friction losses.

Volvo is now looking at how the technology can be used in its future cars.

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