Volvo tests S60 with KERS

Volvo has completed testing on a mechanical hybrid drive system that it says delivers similar fuel economy benefits to a conventional hybrid, while offering a hefty performance bonus and being lighter, cheaper to build and easier to maintain.

Petrol and diesel engines are at their thirstiest when they’re getting a vehicle away from standstill. This is why hybrids are at their frugal best around town – they use their electric motor to do that, or at least help out, in conditions where there’s a lot of stop-and-go.

The Chinese-owned Swedish car-maker has finished prototype testing of its flywheel KERS (Kinetic Energy Recovery System), which it says allows a four-cylinder turbo engine to deliver six-cylinder performance with fuel savings of up to 25 per cent.

The company ran the tests in an S60 sedan, in which during deceleration the engine driving the front wheels shuts down while the system directs braking energy to a carbon-fibre flywheel mounted on the rear axle.

Installed in a vacuum casing to help minimise friction resistance, the flywheel is free to spin at up to 60,000rpm and continues to spins until the driver calls on the car to accelerate.

At that point a dedicated transmission unit shifts the flywheel’s kinetic energy to the rear wheels, easing the load on the engine in getting the car moving again. It also helps out when the car reaches cruising speed and gets a top-up every time it decelerates.

This ability to power the car for short periods has a major impact on fuel consumption, said Derek Crabb, the company’s Vice-President of Powertrain Engineering.

“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.”

It helps with performance too, giving the test car a handy 60kW power boost, which Volvo claims is enough to accelerate the experimental S60 to 100km/h in just 5.5 seconds.

That makes it more than half a second faster than even the top-shelf S60 T6, which runs a 224kW/440Nm 3.0-litre turbo petrol six, although it’s not clear what engine is employed in the KERS S60.

Volvo isn’t new to this kind of propulsion assistance. The company experimented with steel flywheels in its six-cylinder 260 model during the 1980s, but they proved too heavy and limited in their spin speeds to be viable.

Today’s carbon-fibre flywheel is 200mm in diameter and weighs just 6kg – sufficient with the forces it achieves at such high rotation speeds to produce the torque required to move a 1500kg car.

Volvo says it will now set to work on evaluating the application of its flywheel hybrid system for use in future Volvo production models.

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