Volvo Testing Flywheel KERS, Claims 20 Percent Fuel Consumption Drop

We’ve seen it Formula 1 over the years, and Porsche has relatively successfully implanted one in its 911 GT3 R Hybrid race cars, but now Volvo is testing one with an aim to bring it to the world of production cars. We’re of course talking about a Kinetic Energy Recovery System (KERS), a lightweight and relatively cheap ‘hybrid’ technology that Volvo claims can make a four-cylinder engine feel like a six while at the same time reduce fuel consumption by as much as 20 percent.

This fall, Volvo will be one of the world's first automakers to test the potential of flywheel technology on public roads thanks, in part, to a grant from the Swedish Energy Agency.

Volvo’s design calls for the flywheel KERS to be fitted to the rear axle of a car. When the driver hits the brakes, the braking energy causes the flywheel to spin at up to 60,000 rpm. When the car starts moving off again, the flywheel's rotation is transferred to the rear wheels via a specially designed transmission.

The engine that drives the front wheels is also switched off as soon as the braking begins. This is because the energy in the flywheel is sufficient enough to accelerate the vehicle when it’s time to move off once again. It can also power the vehicle once it reaches cruising speed.

We’re talking about a significant amount of energy here. If the energy in the flywheel is combined with the full capacity of the car’s engine, it could give an extra boost of 80 horsepower.

Of course, since the flywheel is activated by braking and the duration of the energy storage--i.e. the length of time the flywheel freely spins--is limited, the technology is at its most effective during stop and start driving in the city.

However, Volvo predicts that on a normal drive cycle of mixed city and highway driving, a car’s engine could be turned off about half the time when driving.

A unique element of Volvo’s flywheel KERS is carbon fiber construction, which means the actual flywheel weights just 13.2 pounds and has a diameter of just under eight inches. It also spins in a vacuum to minimize frictional losses.

Compared to more conventional hybrid systems with expensive batteries and electronic control modules, the flywheel KERS is a relatively cheap option and could be fitted to most of Volvo’s lineup. If the tests prove successful we could be seeing some form of the system in production cars within a few years.

Other automakers believed to be focusing on the technology include BMW and Jaguar.


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Joe_Limon - 5/26/2011 12:24:08 PM

+4 Boost

Cool! Finally a mechanical hybrid in a production vehicle without all the energy losses associated with converting mechanical energy to electrical to chemical to electrical to mechanical again. 13.2lbs is fairly light, I wonder if they used a heavy steel center to their flywheel and carbon on the outside in order to maximize the inertial weight of the flywheel without compromising it's top speed.

chewy - 5/26/2011 2:43:19 PM

+1 Boost

Looks like a very mild setup that won't store too much energy, but at least it's also somewhat simple as well.

Joe_Limon - 5/26/2011 3:19:16 PM

+3 Boost

Hmmm... 13.2lbs spinning at 60,000rpm... assuming 12" diameter... could be anywhere from about 1400000-2750000 joules depending on flywheel type... which is equivalent to the kinetic energy in a 3000lb car traveling at 102-142mph. Add in mechanical efficiencies, and I think it is a very good size.

chewy - 5/26/2011 7:47:25 PM

-1 Boost

The flybrid system made for F1 could only store 400kj of usable energy which is good for an 80 hp boost over 6.6 seconds. The flybrid made for production on the Jaguar XF concept also quotes 80 hp for about 7 seconds. Volvo quotes 80 hp over an unspecified amount of time, likely the same 6-7 seconds. That is better than I originally thought but there must be significant drawbacks to this system as no one has really adapted it for production cars. So far it looks like the Jaguar and the Volvo project are extremely similar as both are funded by a relatively small government grants, let's see if this one makes production or just stays a demonstrator.

Joe_Limon - 5/27/2011 10:33:34 AM

+1 Boost

Electric hybrids are more energy dense, meaning they can store and put out more energy overall then mechanical hybrids. However mechanical hybrids are more power dense and more efficient. Meaning they can put higher numbers to the wheel and do so with less waste.

chewy - 5/27/2011 7:23:30 PM

+1 Boost

I understand that, but overall it looks like no one wants to follow this mechanical route, probably because it's not very applicable in actual driving conditions. We'll see if anything ever comes out of this, the fact that neither Jaguar nor Volvo ever put their own money into this system indicates to me that they internally see it as a dead end as 5 million or so from the government isn't enough to make any tech production ready for a manufacturer. I wouldn't mind to be proven wrong but my intuition tells me that flywheel hybrids just don't perform as advertised.

Whelan - 5/26/2011 3:48:41 PM

+4 Boost

This is the first brilliant idea in hybrid tech. As stated above converting all these alternate forms of energy to mechanical takes a lot of power and converting. This is why gas/diesel is still unbeatable in terms of output vs. consumption. Something like this KERS could REALLY make a difference in almost any vehicle without the need for huge weight penalties or special design.

outsider - 5/27/2011 2:38:00 AM

+1 Boost

My simple doubts are:
- Gyroscopic effect influence turning.
- High speed rotating mig mass is not safe.
- The system already being used for AGV-s.
- At the vehicle stop (parking) what is the duration tom stop the rotation?
- Is it safe in case of accident?
- The system mechanical complexity is extrem. Can it be reliable?
- What is the durability of bearings?
- ...