Purchasing new hardware? Read our latest product comparisons

Volvo confirms fuel savings of 25 percent with flywheel KERS


April 26, 2013

Volvo's Flywheel KERS

Volvo's Flywheel KERS

Image Gallery (6 images)

After extensive testing of its kinetic flywheel technology, Volvo has announced that the system can boost fuel economy by 25 percent. The company is now looking at integrating the Flywheel KERS system into its production line.

Volvo's Flywheel KERS is fitted to the rear axle. During deceleration, the braking action causes the flywheel to spin at up to 60,000 rpm. Meanwhile, the front-mounted engine shuts off. The energy stored in the spinning flywheel can then be applied via a special transmission toward acceleration or used to power the car once it reaches cruising speed.

Volvo's experimental flywheel is a carbon fiber model that spins in a vacuum to minimize frictional losses. It weighs 13.2 pounds (6 kg) and measures about 8 inches (20 cm) in diameter.

During road testing with a Volvo S60 flywheel test car, Volvo found that when partnered with a four-cylinder engine, the flywheel technology offers up to a 25 percent reduction in fuel consumption versus a comparably performing turbo six-cylinder. It says that the system can also augment the engine with an 80 hp boost, giving it acceleration comparable to a six-cylinder – 0-62 mph (100 km/h) in as quick as 5.5 seconds.

"The flywheel's stored energy is sufficient to power the car for short periods. This has a major impact on fuel consumption," explained Derek Crabb, Vice President Powertrain Engineering at Volvo Car Group. "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."

While the Flywheel KERS system has some clear potential, it's able to store energy only for a finite amount of time while it continues spinning. As such, it's best for driving conditions where there are frequent starts and stops. Like some hybrids and electric vehicles, Volvo's Flywheel-equipped vehicles will get the better fuel economy in the city.

"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," said Crabb.

Source: Volvo

About the Author
C.C. Weiss Upon graduating college with a poli sci degree, Chris toiled in the political world for several years. Realizing he was better off making cynical comments from afar than actually getting involved in all that mess, he turned away from matters of government and news to cover the things that really matter: outdoor recreation, cool cars, technology, wild gadgets and all forms of other toys. He's happily following the wisdom of his father who told him that if you find something you love to do, it won't really be work. All articles by C.C. Weiss

Volvo is becoming interesting again. 4 cylinder from 0 to 100 km/h in 5.5 seconds and at the same time saving fuel? This is nothing but amazing.

I'm also wondering if this would be more logical inside rear drive car? Or this is what they are doing here? In general Volvo produces front drive cars.

Kris Lee

The idea of a flywheel for storing kinetic energy on the rear axel is an interesting new departure from Volvo which they reckon reduces fuel consumption by 25%. Great for urban driving where there's lots of stopping and starting or for undulating terrain making this the ideal car for San Francisco and Monaghan


Congratulations Volvo - re using energy has got to be good'

Gerard Meehan

I suppose that this concept is another function that GPS can be adapted to. Knowing when the vehicle is going to reach its destination, the GPS could ensure that all the stored energy is used up beforehand so that it does not go to waste while the car is parked.

Mel Tisdale

I think it could be used in addition to the regenerative breaks on hybrids and electric cars. The flywheel could be attached to a generator and produce electricity when needed and/or charge the batteries?


No magic here but nice implementation. Since it was tested in a 4-cylinder car how about comparing it to a 4 cylinder car rather than a six i.e., what are the fuel savings then? Is it approximately equivalent to a turbo without the fuel losses associated with higher RPM and fully depressed accelerator? What about the possibility of pairing it with a diesel where RPM are lower by design? Since it is reliant on recovered stopping forces what is the ratio of benefit to weight of vehicle in a standard driving cycle? Is there an optimal braking pressure, such as mashing the brakes and letting the ABS take over, or will feathering the brakes spin the KERS up to full speed? If the vehicle is equipped with handling assistance, will single wheel braking also activate the flywheel?


I agree with BigWarpGuy, that research and development of an all electric car using this flywheel system should be fast tracked. An all electric version might pose quite a challenge to Volvo, the company being accustomed to producing relatively heavy cars these days. Now it will have to get both light and super safe.

Get an electric version out on the street immediately, refine it and offer generation 2.

Dan Lewis

Seems like a metal flywheel would be less expensive as it is the mass that creates the flywheels stored energy. Must be a good reason for CF. I felt the flywheel would also be a good application for the stop start systems in use today as it could be energized in a similar way and then coupled to restart and aid in initial acceleration.


An energy recovery system that can actually pay for itself and wont loose capacity as it ages. Very Good!

Why would anyone think that putting a flywheel energy recovery system on a car that already has an energy recovery system is a good idea? Especially when the the electric car is already too expensive.


Slowburn, I think the issue is more complexity, than cost, as KERS is able to recover a greater percent of braking losses (because of the ability to store more energy in a smaller time frame than chemical battery storage)

The carry on from this is that the range is increased by one of these units, you no longer need some of the chemical batteries capacity, therefore you are able to reduce the cost and weight of the batteries.

Part of the problem with the capital cost of electric cars is the batteries are often an upfront cost, when they probably should be an ongoing cost, like fuel and engine servicing in a conventional car.

The Renault Zoe in the UK is using the strategy of selling you the car, but leasing you the batteries, creating a cost structure that makes much more sense when you try to compare equivalent conventional car costs.

David Khoo

Nothing was said of the probably cost. Basically, it is a good idea but would it be competitive with a hybrid electric car. I would say that the mass of the flywheel should be increased by a factor of about 10 so that it could be used on city buses which presently get only about 6 mpg.

Adrian Akau

re; Adrian Akau

Given the irreducible cost of batteries, and electric motors it can't help but cost less.


Mirmillion for improving the transmission ratio continuous variable transmission (CVT) is used which solves the problem of implying the system in diesel engine

Soham Chowdhury

re; Adrian Akau part 2

An industrial scale flywheel energy recovery system would be good, especially if they used 2 counter rotating wheels on a vertical axis so that they would gyro-stabilize against rollovers without throwing in steering inputs when going over hills. (Particularly useful on double-decker buses.) Garbage collection truck would greatly benefit as well. A 40hp engine powering the hydraulics and feeding the flywheel that moves the truck from house to house. Save the big engine for main roads. ..................................................................

re; David Khoo

The fuel tank is an upfront cost, and on a reasonable estimate of the cars life it will have to be replaced over the life of the car doubling the cost. Renault is just trying to hide this.


re; David Khoo part 2

The KERS highlights another inadequacy of the overly expensive and under-performing EVs.


This is great as a hybrid substitute but EVs essentially store back to batteries for free without additional mechanical complexity. So even if it is twice as efficient as EV regen in city driving, it's probably not worth the added cost. The EV would be happier spending money on a bigger battery or using C-fiber to reduce overall weight.

Doug Liser

This will hopefully soon hit the production lines! It could be designed into a rear axle or present drive assembly for retro fitting to acceptable cars as well. Wiring modifications might be a problem, but not insurmountable. As with present hybrids or EV cars, lifting off the throttle would signal the KERS to engage and start saving up energy supplied by forward motion.

The Skud

A flywheel that is charged and tapped electrically might be cost effective on a already overly expensive and under-performing EV. On a gyrostabilized 2 wheeler storing energy on the gyroscope is unquestionably a good idea.

re; The Skud

Touching the brake would be a better indicator that you want to harvest energy. I coast all the time wanting to maintain speed down gentle hill.


I wonder what factor of safety is applied? 13Lb by 8 inch diameter, at 60K rpm x a 6g colision impact = a bunch of really mad carbon fiber trying to get out of it's cage.

Oh, and to answer protobobby7's question... Steel would simply explode under its own weight. Carbon fiber will stay together...

Please check my math here: So 8 Inch diameter is about 2ft Circumference (Pi * 8 ~ 25 in). At 60,000 Rev/Min = 120,000 Feet/min (div by 5280 feet/mile = 22.7 Mile/min) times 60 mins/hour = HOLY CRAP! 1,363 Miles per hour?

So if you rear end a flywheeled Volvo... look for the doughnut of death to com screaming by at Mach 2.

Tell me more about that containment system please.


Matthew Bailey

re; Matthew Bailey

The rear end accident powerful enough to endanger the flywheel is a high energy event anyway making the additional risk trivial even if it was a steel flywheel. Also unlike a steel when a carbon fiber flywheel comes apart the fiber bits do not individually carry enough energy to harm anyone and there is no way the entire flywheel will come out intact. The first touch of the vacuum container wall will sever a fiber and the flywheel will very rapidly unravel into a soft pile of worthless tangled yarn.


If you increase the speed of the flywheel proportional to it's weight then you will gain the same energy output in proportion to it's mass without the added cost of bringing a heavier flywheel up to speed. That's the problem with heavier flywheels, they lose more energy in the process of bringing them up to speed.

A better understanding of the tradeoffs of a lighter flywheel can be gleaned from studying motor/generator theories and physics. If you have a chance, study lead and lag times from opposing/attracting magnetic fields.

Wireless transmission to an exciter coil in the rotor may prove to yield higher efficiencies if the current research on this alternative to using heavier permanent magnets pan out.

One approach to the safety of a faster spinning flywheel is to utilize a collision detection system. The safety mechanism employed by air bag systems may signal a rapid discharge of the flywheel to protect the occupants and the flywheel itself. Part of the answer to this is to increase the field coil (exciter) output and increase the capacity of the load circuit to handle the higher output and increase safety.

Gary Richardson

In Lean Management theory, it is stated that you can't improve what you can't measure. Therefore, reporting on the device's output/input/losses in terms of Kilowatt hours (KWh) @___MPH, KWh equivalent when comparing to hydraulic, thermal, chemical, etc... storage.

Establishing a baseline metric such as this electrical unit of measure will make it easier for the consumer to see what combination of technologies and in what proportion will benefit them.

Additionally, I'm starting to see the term Energy Return on Investment (EROI) used more often in Renewable energy discussions which also have a stake in utilizing energy storage for intermittent sources such as windmills and solar panels. The use of EROI on future discussions on flywheels, ultracapacitors, batteries, etc is something else to consider.

Gary Richardson

Pity they don't have the drive at the rear and the kers at the front. Try coming to a stop using just your rear brakes. But it'll perform adequately when we all brake gently to a stop...... lol. Would work well for me as I have 3 hills to go over to work everyday :)

Craig Jennings

re; Gary Richardson

Weight density of the flywheel doesn't effect the efficiency of energy storage. The lighter the flywheel the faster it speeds up but it slows under load faster as well. The heavier flywheel resists acceleration more but resists slowing to an equal degree.

re; Craig Jennings

You would have to move the engine, not a difficult problem but they still produce front engine sport cars with a front hood so long that makes them dangerous at intersections.


The choice of CF isn't to reduce the inertia of the flywheel. If you do the maths, it turns out that CF stores more energy for a given size of flywheel, because it allows greater RPM before its own weight tears itself apart. The energy stored is proportional to the rotational moment (which is related to the weight/density of the material), but I believe it goes up with the square of RPM.

Steve Jones
Post a Comment

Login with your Gizmag account:

Related Articles
Looking for something? Search our articles