Volvo has invented a new form of hybrid car inspired by Formula 1-style flywheel technology. Lem Bingley, jetted off to Gothenberg to put it through its paces.

A few years ago, when Formula 1 teams were given the chance to add hybrid technology to their screaming cars, engineers worked feverishly to develop the best possible KERS – or kinetic energy recovery system. Every candidate for capturing and storing a car’s momentum was given a grilling, until all the options from compressed air tanks to giant rubber bands had been discarded in favour of two front runners – mechanical KERS that stuffed energy into a fast-spinning flywheel versus electrical KERS that used a battery.

While only electrical KERS has ever raced in a Grand Prix – operating much like a superfast Toyota Prius – a pair of former Renault F1 engineers remained convinced they were onto something with flywheels. So they set up a UK-based company called Flybrid Automotive to try to commercialise their ideas. And not just for racing: KERS could give you that crucial burst of extra overtaking speed on the way to Sainsbury’s, even if you have to buy your own champagne to celebrate when you get there.

Perhaps surprisingly, it is sensible Swedish manufacturer Volvo that seems keenest to use KERS to make you feel like Kimi. We travelled to the company’s secret testing facility – just off Highway 155, about four miles west of Gothenburg in a big building marked 'VOLVO' – to take a precious, one-off KERS prototype for a spin.

Volvo KERS prototype: What is it?

The Volvo KERS prototype may have cost 20 million Swedish kroner to develop – or about two million quid – but it looks distinctly unimpressive. A bog-standard S60 saloon in funereal black, the most covetable thing about it might appear to be the tablet computer docked at the top of the dashboard, for controlling its KERS implant.

In reality, of course, all the value is hiding in the boot. Under a carpeted hatch in the cargo area lurks the KERS kit, a shiny 60kg lump of brushed metal and big sturdy bolts, hooked up to electronic monitoring gear and an extra car battery.

Inside the gleaming case lurks a 6kg flywheel – a finger-thick layer of carbon fibre wrapped around a spoked steel drum. The carbon fibre is needed to hold the wheel together when spun up to its full operating speed of 60,000rpm, at which point the outside edge of the flywheel is travelling at more than 1,400mph in a tight, 20cm circle. That’s about Mach 1.9, well beyond the sound barrier, or it would be if all the air hadn’t been sucked out of the flywheel chamber to reduce friction. Left to its own devices, the wheel takes about half an hour to spin to a stop.

That would be a waste, of course, because the flywheel is connected through a variable-ratio transmission to the S60’s back axle, where it can provide a boost of 80bhp for up to six seconds or so, on command from the car’s computers. The computers, in turn, are commanded by the driver’s right foot.

Volvo KERS prototype: How does it work?

KERS is simply a way to hang onto energy that would otherwise be wasted heating up the brake discs whenever the car slows down, so that it can be turned back into motion again to make the car go faster. In practice, that means the flywheel spins more quickly as the car goes slower and vice versa.

The Volvo KERS prototype has two driving modes, labelled Sport and Hybrid, accessible via the tablet app. In Sport mode, the flywheel spins up to speed at every opportunity – whether you’re slowing down, braking, descending hills or just pootling along, the KERS unit will squirrel away energy from the back axle and stuff it into the flywheel to keep it spinning near its peak. That means the petrol engine works a tiny bit harder to drag the back axle along from time to time, but it means KERS is always ready to pounce when you floor the throttle. At that point, energy is dumped back out of the flywheel and into making you go faster.

KERS supplies up to 80bhp – roughly like having a 1.2-litre engine in the boot – in short bursts. The difference it makes depends on how much power you normally have under the bonnet. Volvo’s test car started life as a fairly pokey five-cylinder T5 car with 254bhp on tap – a Swedish spec not sold in the UK. The addition of KERS makes it quicker than Volvo’s six-cylinder turbo equivalent, with KERS trimming the T5’s 0-62mph time by 1.5 seconds to under 5.5 seconds. Fitted to a more modest four-cylinder car, KERS would be likely to lop about 2.5 seconds off the same sprint. The extra urge would be equally apparent in the crucial 50-70mph caravan-overtaking stakes.

Alternatively, the driver can switch into Hybrid mode, which is designed to improve fuel economy rather than overtaking ability. In this mode, KERS only captures energy when the car would normally be slowing down, feeding it back in gently through the wheels to reduce fuel demand when speeding up again. Volvo’s tests show a very significant 25% fuel saving under the NEDC regime, the test used to produce official consumption figures.

In the real world, KERS should produce worthwhile fuel savings on any road where the driver switches a lot between braking and accelerating, whether taming a twisting B-road on a Sunday afternoon or slogging through the urban sprawl on a Monday morning. It won’t help much on motorways, though.

Volvo KERS prototype: What’s it like to drive?

The strangest sensation behind the wheel of Volvo’s KERS car is the noise. It sounds like a jet engine has been mounted under the bootlid. The volume and pitch of the noise rises and falls according to how much energy is available for boost. Volvo engineers say a production version would be quieter, but we’d be tempted to leave it as it stands. It’s like sitting in the Batmobile.

Actually using KERS power, with a firm prod of the accelerator, sounds like a Batman movie being rewound, however. The whining note falls as the car speeds up, which is not what your ears are expecting. Sounds that gather in pitch along with with rising speed are what we’re all used to hearing behind the wheel.

In Hybrid mode, the car feels entirely normal to drive. Were it not for noises like a washing machine on spin cycle helping you along, you would never guess that £2m had been spent on the car. It’s not slow – it’s still a speedy T5 saloon – but you wouldn’t notice the KERS unless you totted up how much you’d saved in petrol. That’s because Volvo’s software reins back the engine whenever KERS makes a contribution, capping the combined output at 254bhp.

Sport mode is another story, with a peak output of 334bhp. Volvo has set up KERS to step in at 25mph, and hitting that speed with a firmly pressed throttle feels as if half the weight of the car just fell off. It’s reminiscent of a turbo coming on song though it’s even more addictive and relentless, because KERS keeps driving the back wheels even as the engine slugs up through the 6-speed auto gearbox at the front. It feels like you’ve suddenly co-opted the force of gravity, for the few seconds that a full boost lasts.

And because KERS pushes at the back while the engine pulls at the front, you can exploit the extra power even on slippery surfaces and in corners, with four-wheel-drive grip and a traction control system developed for Volvo’s V60 Plug-in Hybrid – a production car that uses a 70bhp electric motor on the rear axle.

Volvo KERS prototype: Will they ever build it?

The initial phase of Volvo’s KERS project is complete – the one-off we drove has already demonstrated the possibilities and given the company a yardstick for the potential economy savings and performance improvements. But that doesn’t mean KERS is ready to appear on a Volvo option sheet any time soon.

Production feasibility is the next part of the problem, and Volvo engineers we spoke to thought that cost and reliability would pose lesser problems than the supply chain. Nobody, as far as they know, is geared up to supply high-precision, carbon-fibre flywheels, ten thousand units at a time.

If that particular nut can be cracked, it seems likely that KERS offers a big enough bang per buck to reach production. We can’t wait.

Volvo KERS prototype: Specifications

Model tested: Volvo S60 T5, KERS prototype
Engine: 2.5-litre, 5-cylinder turbo petrol, plus Flybrid KERS
Power: 254bhp plus 80bhp KERS boost
0-62mph: under 5.5 seconds
CO2 output (Hybrid and Sport modes): 183g/km and 203g/km