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Volvo KERS system   (Source: Volvo)
KERS system will propel the vehicle from a stop

In the automotive world, a lot of manpower and money is being put into research and development of systems to help boost fuel economy. The most common system today is a hybrid arrangement that uses batteries and electric motors to help propel the vehicle. Another green system is a KERS flywheel like the one used on the Porsche 918 RSR racecar.

The KERS system on the Porsche is activated with a push button to give the car added performance. Volvo is set to start testing its own version of KERS on the public roads of Sweden after receive a grant from the Swedish Energy Agency.

"Our aim is to develop a complete system for kinetic energy recovery. Tests in a Volvo car will get under way in the second half of 2011. This technology has the potential for reducing fuel consumption by up to 20 percent. What is more, it gives the driver an extra horsepower boost, giving a four-cylinder engine acceleration like a six-cylinder unit," relates Derek Crabb, Vice President VCC Powertrain Engineering.

The KERS flywheel that Volvo will use spins at up to 60,000 RPM and gets its energy for the forces created when braking. That rotational inertia is then transferred to the rear wheels via a special transmission. In the Volvo system, the combustion engine will be switched off as soon as braking starts and then the energy in the flywheel will be used to propel the vehicle from a stop and help it accelerate. 

This sort of system will be most effective in stop and go city driving. Volvo estimates that the combustion engine might be able to be turned off as much as half the time. When combined with the combustion engine the energy in the flywheel could add as much as 80hp to the vehicle and increase performance while allowing the car to be more fuel-efficient. 

The Volvo flywheel will be made from carbon fiber instead of steel for maximum efficiency. The flywheel measures a diameter of 20cm and weighs 13 pounds. It also spins in a vacuum to minimize losses. 

"We are not the first manufacturer to test flywheel technology. But nobody else has applied it to the rear axle of a car fitted with a combustion engine driving the front wheels. If the tests and technical development go as planned, we expect cars with flywheel technology to reach the showrooms within a few years," says Derek Crabb. He concludes: "The flywheel technology is relatively cheap. It can be used in a much larger volume of our cars than top-of-the-line technology such as the plug-in hybrid. This means that it has potential to play a major role in our CO2-cutting DRIVe Towards Zero strategy."

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13 Lbs at 60,000 RPM...
By robertisaar on 5/31/2011 12:34:19 PM , Rating: 5
call me scared, but i want one hell of a scattershield between the passenger cabin and the flywheel.

RE: 13 Lbs at 60,000 RPM...
By FITCamaro on 5/31/2011 12:46:02 PM , Rating: 2
Yeah a lot of people don't even think about that. I've seen the pictures of when a clutch gives out and comes through the floorboard. Ain't pretty even if no one is injured.

RE: 13 Lbs at 60,000 RPM...
By Souka on 5/31/2011 2:14:47 PM , Rating: 2
I don't get it

"flywheel will be made from carbon fiber instead of steel for maximum efficiency. The "

How does carbon fiber = maximum efficiency?

RE: 13 Lbs at 60,000 RPM...
By stephenbrooks on 5/31/2011 2:18:02 PM , Rating: 5
Higher tensile strength means it can do more RPM, so more energy stored per unit mass, I'd guess.

What I don't get is how they'll handle this thing while cornering. Remember how gyroscopes or spinning bicycle wheels behave? A large angular momentum is difficult to change in direction!

RE: 13 Lbs at 60,000 RPM...
By Solandri on 5/31/2011 2:20:51 PM , Rating: 5
Kinetic energy of a rotating flywheel goes as mv^2. So doubling the mass doubles the amount of energy it can store. But doubling the max velocity quadruples the amount of energy it can store. So a higher tensile strength material is preferred to a high mass material.

See my comment below on angular momentum. It's possible to cancel it out with two counter-rotating flywheels.

RE: 13 Lbs at 60,000 RPM...
By Solandri on 5/31/2011 2:22:24 PM , Rating: 2
To be more precise, it goes as Iv^2, where I is moment of inertia. For a fixed geometry that's equivalent to mass. But it does mean that you can alter the geometry using the same amount of mass to increase max kinetic energy stored.

RE: 13 Lbs at 60,000 RPM...
By msroadkill612 on 5/31/2011 3:54:30 PM , Rating: 2
Using the existing, much greater mass of the spare as a flywheel at slower revs could work equally well. They seem to spin up well at the tyre shop.

RE: 13 Lbs at 60,000 RPM...
By GulWestfale on 5/31/11, Rating: 0
RE: 13 Lbs at 60,000 RPM...
By Alexvrb on 5/31/2011 7:50:00 PM , Rating: 2
This won't be doing anything bad or dangerous with regards to acceleration. If you don't jam down the accelerator, it isn't going to suddenly dump tons of power to the rear wheels, without the driver asking for it. Volvo generally uses pretty decent quality parts, including the accelerator pedal assembly. No need for a dealer-installed shim here.

is there no way they could simply store the energy in a battery and use it instead of the gas engine when the driver pushes down the accelerator, rather than giving you an extra boost? wouldn't that be both safer and more gas-efficient?
Oh, you mean like the regenerative braking that hybrids have been using for years? Yeah, that would be better, generally speaking.

However, it is much more expensive to build a full hybrid, and it doesn't help acceleration like this does. I mean in theory it could help acceleration, but to increase efficiency they generally use a small Atkinson cycle engine. This really kills off-the-line power. They also add quite a bit of weight with the battery pack.

RE: 13 Lbs at 60,000 RPM...
By erple2 on 6/1/2011 6:00:11 PM , Rating: 2
No, the regenerative flywheel has a better energy conversion rate - there's substantial loss of energy in storing the braking power back into the batteries, loss of energy over time of actually having a charged battery (but I'd place it at more or less similar to friction on a flywheel), and loss of energy in pulling the power out of the battery.

The flywheel tends to be more efficient in all aspects over a battery pack, provided you don't pass some threshold (eventually, you just can't spin a flywheel any faster). It's also substantially lighter, substantially simpler, and substantially cheaper than a hybrid car system.

RE: 13 Lbs at 60,000 RPM...
By titanmiller on 5/31/2011 8:01:47 PM , Rating: 2
The front fan of a large jet airplane can have a mass of hundreds of kilograms and all that mass is spinning at upward of 5,000rpm. Jet engines can produce some of the largest precession forces of anything that I know, but with proper engineering it can be overcome.

RE: 13 Lbs at 60,000 RPM...
By tastyratz on 5/31/2011 4:06:46 PM , Rating: 2
The other thing about carbon fiber is safety. When there is a critical failure of a rotational carbon fiber component it tends to "broom" instead of exploding to chunks of metallic death. While there is a significant mass it will likely just disintegrate behind a decent scattershield. What my concern would be is actually any kind of ring gear... The ring gear on a flywheel when it fails is what turns it into a giant saw blade...

RE: 13 Lbs at 60,000 RPM...
By mtbiker731 on 5/31/2011 12:51:08 PM , Rating: 2
Knowing Volvo and their considerations for safety, I'm sure they won't even think of such a thing... :/

RE: 13 Lbs at 60,000 RPM...
By SunTzu on 5/31/2011 12:57:21 PM , Rating: 2
...what? Volvo is known pretty much all over the world for being the safest cars money can buy. They win the "safest car" competetion practically every year. Or were u joking?

RE: 13 Lbs at 60,000 RPM...
By omnicronx on 5/31/2011 1:15:34 PM , Rating: 3
<sarcasm detector re-enabled>

There you go..

RE: 13 Lbs at 60,000 RPM...
By Pirks on 6/1/2011 4:05:26 PM , Rating: 2
Volvo safety is all marketing while real deal in safety is Saab. Marketing victimized sheeple buy Volvo, while smart people buy Saab.

RE: 13 Lbs at 60,000 RPM...
By cpeter38 on 5/31/2011 2:39:12 PM , Rating: 2
This concept was tried before in the Patriot, a 1990s hybrid Le Mans race car that attached the flywheel to an electric motor/generator. I worked for one of the companies that had attempted (before my time) to supply the power conversion equipment. Fortunately, IGBTs were not very reliable in those days and the company was desourced. All of the senior engineers said that the program was a complete disaster and that they were happy to have lost the contract. There was a rumor that just after we were desourced, a couple of people had died during testing of the mechanical integrity of the flywheel.

There is a nice summary of the Patriot experiment at

There is a longer (and somewhat controversial) account of the Patriot in Common Sense Not Required ( ).

The KERS version avoids many of the pitfalls of the original Patriot race car. However, the fundamental mechanical integrity problem that you point out is still present.

I would be *very* wary of stepping in that first test vehicle!

Bearing Hell
By mars2k on 5/31/2011 1:55:40 PM , Rating: 2
Ok, so this was how many kg spinning at 60K RPM in a sealed chamber on a car chassis that's bouncing all over the place?
Have these guys in Sweden seen our snow pitted roads around Michigan and Illinois?
Tell me again about the bearing.

RE: Bearing Hell
By Solandri on 5/31/2011 2:18:15 PM , Rating: 2
You can translate (move in the x, y, or z axes) a rotating mass just the same as if it weren't rotating. So a bumpy road doesn't present any difficulties. Any suspension system capable of supporting 13 pounds steady relative to its bearings would suffice.

The problem with a 60k RPM mass would be that the huge angular momentum resists rotation. I had thought any flywheel would be mounted horizontally (like most CD players) because of this. Cars mostly turn around the z-axis, so if you mount the flywheel with its angular momentum vector along the z-axis, it doesn't change the car's turning characteristics.

However, from the diagram, it looks like they're mounting it vertically. At high RPM, this will make it easier for the car to turn in one direction, harder to turn in the other. The Sopwith Camel (WWI biplane) exploited this for improved maneuverability in one direction. But it's something I would consider to be a distinct disadvantage in a car.

A possible solution is to have two counter-rotating flywheels mounted next to each other. They rotate at the same RPM, but in opposite directions. That cancels out the angular momentum, resulting in no change to turning characteristics. (OTOH, the containing structure must be twice as strong since the two flywheels will try to turn in opposite directions every time you rotate them.)

RE: Bearing Hell
By BZDTemp on 6/1/2011 5:32:41 PM , Rating: 2
I have been wondering about this as well but they do run similar systems on F1 cars and they are able to change direction like nothing else.

RE: Bearing Hell
By AngelOfTheAbyss on 5/31/2011 2:41:49 PM , Rating: 2
I'm quite certain the Swedes have their own snow pitted roads to test on. The country extends above the arctic circle:-)

RE: Bearing Hell
By SunTzu on 5/31/2011 2:49:03 PM , Rating: 2
You do realize we get a shitload more snow, and colder temperatures, then anywhere in the US except possibly Alaska, right?

RE: Bearing Hell
By msroadkill612 on 5/31/2011 5:03:50 PM , Rating: 2
maybe i miss something, but why cant flywheels work because of snow?

on topic
By msroadkill612 on 5/31/2011 3:46:49 PM , Rating: 2
not new. But maybe better than minimal boost batteries (like prius
which i reckon is the way to go). use existing mass as flywheels. -
spare wheel (tried lifting one lately), heavy battery or passenger :)

Batteries dont regenerate from brakes. They cannot absorb braking
energy - only slow charge.

RE: on topic
By Alexvrb on 5/31/2011 7:59:44 PM , Rating: 3
A good full hybrid is capable of recovering a good chunk of energy from the brakes. The battery packs can take in energy faster than you're giving them credit for, at least when they're not near a full charge. Plus if they felt it was necessary, they could use supercaps to recover as much as possible, and feed it back to the electric motor(s) and/or battery pack as needed. Kind of like a cache hierarchy.

RE: on topic
By shiftypy on 6/6/2011 6:11:05 AM , Rating: 2
Speaking of brakes
If KERS is only active on rear axle it can only absorb a smaller portion of braking energy. If I recall correctly brake balance is split like 65-35 between front and rear. Else you just lock up rear wheels.
So on mild braking you can get the power, but in real world slowing doen before a traffic light it can't possible get all the kinetic energy

By Souka on 5/31/2011 2:33:53 PM , Rating: 3
Bring back the spinner wheel/hubs that were so "cool" a few years back...except make them heavier...there ya go... 4-wheel KERS! :)

RE: idea...
By msroadkill612 on 5/31/2011 3:59:51 PM , Rating: 2
On the right track - is a huge amount of momentum in the wheels - just has to be transferred to something which spins at idle.

By BZDTemp on 6/1/2011 6:42:28 AM , Rating: 2
And a system with blue flags should also be implemented.

A on a more serious note I see KERS as another band aid just like other hybrid systems. In principle using brake energy for something more useful than heating brake discs is great, except the more kit we put in cars the more energy is needed to move them (plus more can go wrong).

By redraider89 on 6/2/2011 2:04:30 PM , Rating: 1
Electric engines just transfer the burning of fuel to the electric company who have to burn the fuel to produce the electricity that electric car scam-ees buy thinking they are "saving the planet". Which, if you just changed a word, but it would still mean the same thing, they are believing they are "saving the world". That reminds me of The Matrix where Cypher asks Neo, "What a mind job. So you're here to save the world?" This electric car business is just that, a mind job.

By FITCamaro on 5/31/11, Rating: -1
RE: Prepare
By mephit13 on 5/31/2011 1:09:35 PM , Rating: 5
You probably thought that about the Prius as well. So far, I haven't heard a single Prius owner complain about needing a new starter every 6 months, or at all for that matter. Do you need to find fault with every new technology that claims to make cars more environmentally friendly? Do you hate fuel injectors as well?

RE: Prepare
By YashBudini on 5/31/2011 1:12:09 PM , Rating: 3
Do you hate fuel injectors as well?

He lives in a 4 barrel world.

RE: Prepare
By Samus on 6/1/2011 12:45:50 AM , Rating: 3
Every starter I've ever replaced has likely failed from elemental damage, not overheating. The only people who cook their starters are the morons with 4BBLs that continue crankin' with a flooded engine.

Bosch and Denso have been making brushless starters for stop-start technology since its advent a decade ago. I've never heard of one failure, and truthfully, your alternator, steering pump or A/C compressor are far more likely to fail, which is why modern alternators cut off at high RPM, most vehicles manufactured now have electrohydrolic steering (not a mechanical pump, but an electric one) and all electric and most hybrids now have electric A/C compressors, which are super reliable as they're single speed and have no clutch (mostnA/C compressor failures are in fact clutch-related.)

RE: Prepare
By FITCamaro on 5/31/2011 2:21:19 PM , Rating: 1
Even a Prius doesn't shut off the motor every time you brake. Only when you come to a complete stop.

RE: Prepare
By FITCamaro on 5/31/2011 2:22:36 PM , Rating: 1
And to quote.

In the Volvo system, the combustion engine will be switched off as soon as braking starts and then the energy in the flywheel will be used to propel the vehicle from a stop and help it accelerate.

Well what if you're just slowing down for traffic? Then the engine will shut off and has to turn back on when you get back on the gas a few seconds later.

RE: Prepare
By FaaR on 5/31/2011 3:34:52 PM , Rating: 5
What they mean is that fuel supply will be shut off... The crankshaft doesn't neccessarily have to stop. Even if it does, the engine's probably going to be equipped with a start-stop system, integrating a brushless generator/motor on the crank.

I don't see why you think the starter would wear out all the time, if it's not for your general assmule stubbornness when it comes to anything beyond 1968ish technology for ICEs... You know, the rest of the world has moved beyond pushrod hemi engines and those kind of cast iron stove clunkers that you Americans are so irrationally fond of. You're going to have to as well, just get used to the idea now and it'll be easier.

RE: Prepare
By shiftypy on 6/6/2011 6:05:00 AM , Rating: 2
KERS will provide the acceleration when you get back on the gas, so you won't feel delay.

If this idea works, it will provide 80% of hybrid advantages without any disadvantage.

RE: Prepare
By FITCamaro on 5/31/2011 2:24:13 PM , Rating: 1
One more caveat, so what happens if you have a car with a manual transmission? If you do, you probably use your brakes far less than with an automatic. Typically when stopping, I take the car out of gear and just coast to a stop, only using the brakes when necessary.

I doubt you'd generate much energy from a very leisurely braking stop.

RE: Prepare
By sorry dog on 5/31/2011 3:06:39 PM , Rating: 2
take a stroll down to your local Volvo dealer and tell me how many manuals you see...

I bet it's probably 1 or 2 max for the showroom C30 that you'd have to special order to get in an manual.

I was at Toyota dealer last month for parts and just for a grins I told the sales guy I needed to buy a car in the next day or two, but told him I'd only buy a manual. Out a 600 cars on the lot he only had a 4 banger pickup to show me.

Manuals are fast becoming extinct.

RE: Prepare
By DWwolf on 5/31/2011 3:15:53 PM , Rating: 3
In the USA maybe.

RE: Prepare
By jabber on 5/31/2011 6:52:35 PM , Rating: 2
Yeah automatics are considered rather effeminate where I come from. For bank managers wives only.

Manuals rule!

There is a social stigma if you've only passed the automatic driving test. :)

RE: Prepare
By FITCamaro on 5/31/2011 3:17:25 PM , Rating: 2
I don't really care how rare they are. I care about what I want to drive. I want to drive manuals. So any new/used vehicles I buy in the future will be dependent on them having manual transmissions. If one brand doesn't make them, I won't buy that brand.

I wouldn't buy a Toyota anyway considering they are the most boring car brand out there.

RE: Prepare
By YashBudini on 5/31/2011 6:14:50 PM , Rating: 2
I wouldn't buy a Toyota anyway considering they are the most boring car brand out there.

And rummaging through junk yards looking for rare parts makes your heart go pitty pat?

Colossal waste of time, just like waiting for the WS-6 option was, as opposed to the more obtainable & far less expensive WS-7.

RE: Prepare
By FITCamaro on 6/1/2011 7:57:20 AM , Rating: 2
My GTO is a 2006 you dumbass.

And the WS6 option relates to the Firebird. Not the Camaro.

There's also no such thing as a WS7. It was just a badge cooked up by a company for people who bought 4th gen Formulas, wanted the WS6 hood, but didn't buy the WS6 package. There might have been a couple other companies that cooked up that badge for various performance packages they sold. But it was not an official GM RPO.

To answer your question, hell yes I'd rather own a classic car that required some parts search than a boring ass Toyota that has all the excitement of a turtle running a marathon.

RE: Prepare
By YashBudini on 6/2/2011 8:31:07 PM , Rating: 2
My GTO is a 2006 you dumbass.

I was like you in my teens, but I grew out of it. I have huge doubts about you however. And I never had a need to be "in your face" about it like you.

You really should consider increasing your vocabulary, its just the SOS, like your rah-rah-ing GM products.

Speaking of dumbass have you figured out how Medicaid works yet or are you sticking to your prior misinformation?

RE: Prepare
By YashBudini on 6/2/2011 8:34:00 PM , Rating: 2
My GTO is a 2006 you dumbass

Oh and a new one no less? Oh God, you just can't get enough of irony can you? The first part of this sentence and the last part.

RE: Prepare
By Kiffberet on 6/2/2011 9:03:58 AM , Rating: 2
In the UK and Europe, automatics are for taxi drivers, or old woman.

I'd say at least 90% of cars on the road are manual, and those with automatics have to deduct 20% off the resale price, because no one wants them.

RE: Prepare
By stryfe on 5/31/2011 3:28:11 PM , Rating: 3
You probably thought that about the Prius as well. So far, I haven't heard a single Prius owner complain about needing a new starter every 6 months, or at all for that matter
The Prius actually doesn't have a starter per se. A starter is just a small electric motor which cranks the engine. Because the Prius is a parallel hybrid where the electric motor resides between the engine and transmission that electric motor can be used to start the engine making a dedicated starter redundant.

RE: Prepare
By GTVic on 5/31/2011 1:18:53 PM , Rating: 2
Maybe they should use a flywheel to start the engine also? Dibs on the patent.

RE: Prepare
By cpeter38 on 5/31/2011 1:55:13 PM , Rating: 2
Every stop/start hybrid sold in the US has a significantly upgraded starting system. Starter wear is an obvious and easy failure mode to avoid.

RE: Prepare
By tastyratz on 5/31/2011 3:58:48 PM , Rating: 2
Upgraded starters, batteries, alternators... still wear items (especially the batteries) but marginal in comparison to savings.

My concern personally with new technologies involving more stopping and less starting of the gas engine? Operational temperature. These engines are going to cool off and find themselves far more likely to operate out of their efficiency range be it both fuel economy and emissions, especially in colder climates. I am sure engineers considered that, but starters were an easy fix, you cant warm an engine without using energy...

RE: Prepare
By Philippine Mango on 5/31/2011 7:23:31 PM , Rating: 2
You don't think engineers of these cars have this sort of stuff figured out by now? All the "faults" with the features that hybrids employ are all conjecture and are based on incorrect assumptions. Just think of any issue a hybrid vehicle could have with a given technology and then just realize that the automakers have already devised a solution to it. To touch on your point about the engine cooling down, in cold climates, at least with the Prius, the engine will come on periodically to keep the catalytic converter and engine warm. These cars when operating are constantly monitoring various sensors and will compensate accordingly. On the original Honda Insight (2000-2006), in very cold weather, the start stop system either will not operate at all or will shut off only very briefly, especially if the user is running the heat.

RE: Prepare
By Solandri on 5/31/2011 2:25:24 PM , Rating: 2
Starters for an engine are only needed for electro-mechanical systems, like a hybrid, or regular starter battery.

This is a purely mechanical-mechanical system. You could directly dump rotational energy from the flywheel into the engine to get it started. No starter motor needed (instead you'd need some sort of mini-transmission). Think of it as a fancy version of the pull-cord needed to start a lawn mower.

"I modded down, down, down, and the flames went higher." -- Sven Olsen
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