Hybrid city buses, delivery vehicles and taxis could benefit. specially if cost is lower and efficiency is higher than with batteries.

Why not try it in the real world to see how good it really is?

Flywheel, Capacitor, Battery - all 3 are coming to road, Beginning of Electric Age.

The flywheel weighs 5kg and can store 400 kJ.
So, a 45kg flywheel can store 3600 kJ = 1kWh.
While the principle is nice, flywheel technology is not expandable to an equivalent of 'full electric'.
Since full-electric vehicles will have in-wheel motors, it will be more difficult to include it parallel with the electric engine. ultracapacitors will probably be much easier for regenerative breaking.

ke = m v^2

So if you could keep people's top speeds down (in town) you could eliminate the need for regenerative braking.

If you reduce the top speed from 35 to 30 mph in town you reduce the energy by 36% which is about what you can expect from battery powered regenerative braking.

This could be done electronically, with the user opting in for much less cost and disruption than a regenerative braking system ( or in conjunction with one ).

The main thing is to prevent people braking hard at the traffic lights and burning off the energy they have in the vehicle.

"So scratch batteries. High power ultracaps could probably be competitive with the flywheel though, and require far less maintenance."

how would ultracaps work with a CVT? An F1 car is not an electric car, nor does it have in-wheel motors.

"how would ultracaps work with a CVT? An F1 car is not an electric car, nor does it have in-wheel motors."

Just have the torque input into the CVT be an electric motor, not the flywheel.

Roger- I still have concerns about putting this on a road car.

1)Putting this in a road car would require much more maintenance than an electric system, and the basic principle of the idea would be unable to evolve beyond being a mere energy recovery system, as opposed to a primary energy storage system

2) More importantly, the kinetic system is totally dependent on regenerative braking, and cannot be "recharged" while driving at highway speeds like with an electric system (i.e. a Prius acting as a "series-parallel hybrid"). So the article's statement about the flywheel providing continuous benefit is perhaps a bit misleading, as it's a transient benefit. There's also the matter of the flywheel slowing down overnight while parked.

3) TOY's Prius batteries are also fairly wimpy and low-end as far as HEV batteries go, so it's not fair at all to compare those to the top-end F1 flywheel! Cobasys NiMH cells can get up to 55Wh/kg, and the EnerDel cells at least 80. Cobasys also expects improvements in construction to further improve NiMH. Not that I'm a particular fan of this chemistry, but it still has life left in it.

If you want to do a useable energy comparison like you did earlier, and pessimistically assume that only 50% of a battery's energy is actually usable, the batteries still come out on top, and have room to grow.

For F1:
In terms of power generation, a Maxwell ultracap can put out 13, 587W/kg (18 horsepower/kg). To get an output of 80 horsepower, that's 4.44kg - easily comparable to the flywheel at "less than 5kg". The downside is less energy stored per mass.

As already noted, flywheels have a power and energy rating somewhere in the middle between ultracaps and batteries. Once major factor, which has been touched also is the "self-discharge" time. Both ultracaps, and even more so flywheels, have extremely high self-discharge rates. Also, the bearings of a flywheel are one very important part - large scale flywheels (like those powering the magnets in JET and upcoming ITER) also run in a hydrogen filled casing, to reduce atmospheric drag.

Furthermore, I don't think that a pure mechanical system with a flywheel as energy storage has much merit in real-world stop and go driving. In addition to the above mentioned points, the article claims that the CVT has a ratio between 1 and 6; thus you would still need a clutch to provide launch power (accelerating from a standstill), and this clutch would reduce the overall efficiency considerably.

In addition, the article claims that the flywheel could survive a frontal crash unharmed - that rules out all ultra-low friction bearings, as the acceleration forces have to be transmitted to the spinning flywheel. The article indicates, that there is only a single flywheel installed in this setup - which means that during spin-up or spin-down, there will be some unbalanced gyro forces. I guess, that they install the flywheel in such a way, that you have additional downward force on the front car axle during spinup (braking), and additional downward force during spin-down (acceleration) - meaning that the flywheel axle is aligned perpendicular to the vector of primary motion, in the horizontal plane.

However, that would result in interesting forces during cornering.

There is one more interesting story I want to share: according to what I have read once, McLaren and BMW were already doing tests of kinetic energy recovery sytems in their mid-1990 F1 cars. However, due to complains by the other teams (most notable Ferrari), the FIA outlawed all such attempts at the time, stating that this would give an unfair advantage in the F1 racing. I find it very gratifying, that finally, Max Mosley and these guys found their senses again.

In order to push competition further into the "green" aspect of motorsports, it might also be nice to have a long-term rule in place, reducing the allowed fuel per race from year to year. Already there are regulations requiring that a single engine lasts at least two races (qualification and the race) - just compare that to how long a decent internal combustion engine has to operate in the real world...

If someone could find that article about late 1990 FIA :)

You guys saying that "if 5kg = this, then 45kg = that" are funny. You can store 10x as much with the SAME 5kg just by putting it further away from the axis. Same RPM, same weight, but longer moment arm and you increase the energy storage. The only limitation is the strength of the materials holding it all together. Flywheels are very much NOT a matter of weight = energy the way chemical batteries are. The stronger the materials are, the greater the energy storage becomes at the same weight and rpm by simply changing the shape of the flywheel.

Sid:
You are wrong - the amount of energy storable in flywheel is pretty independent of diameter, just depends on tensile strenght of material. Larger diameter - less rpms.
Small diameter flywheels are favourable because they have lower angular momentum for the same energy, thus lower gyroscopic effect.

@realalarms

Presumably the flywheel will slow down quite quickly if the stored energy is not used? The flywheel will slow down due to friction in the bearings and seals but because it runs in a vacuum the losses are low. We estimate that for the flywheel to get from full speed to half speed will take around an hour.

from the Flybrid FAQ:
http://www.flybridsystems.com/FAQ.html

@KS: 3600 sec energy half-live for a zero-load flywheel (even running in a vacuum) energy storage system is indeed a very extreme example of a short-duration energy storage system. I hear that modern ultracaps have an energy half-live in the order of tens of hours (tenfold less energy loss), and a NiMH battery, as used in current production vehicles, the energy half-live is measured in months (about 4000-5000 fold better). Remember that not even the hyped hydrogen economy`s fuel tanks - especially the cryogenic kind - have an energy half-live in the order of months. Hydrogen is quite inventive in finding ways to leak (tunnel) even through the most dense materials...

This just underlines my point that pure mechanical systems won't have any significant real-world applications (when seen in context with the other limitations). Sure, certain niche markets, like Formula-1 or grid power conditioning, do exist, but these are low-volume.

Having that said, I`m still looking forward to the `09 F1 tour, when the races might become more interesting again. With such an short-lived energy storage system, the tactics of the individual driver might finally start to make a real difference again. With the current state of F1 affairs, those races are a rather dull and unthrilling expirience...

Reducing the primary energy allowed for each racecar on a long-term basis would, I believe, start investigation into real energy efficiency measures.

While I agree that using mechanical energy storage is a step back on the road to BEVs, I struggle to see why people on this board are negative on flywheel KER.

Both CVTs and flywheels are already mass produced. Both are relatively cheap (compared to a full HEV) and existing manufacturing infrastructure should adapt to the different specs of a KER relatively easily.

If a flywheel based KER can improve city cycle fuel economy by 25% while only adding $500 to vehicle cost, why complain? Shouldn't we embrace it?

Such a system, imo, could allow for substantial engine downsizing. When a car is initially started the engine could be allowed to temporarily rev to build up energy in the flywheel. That energy could then be released during initial acceleration. The idea would be to provide additional performance while maintaining a small engine (hey, American consumers always want more performance, eh).

In my mind, a 1L turbo 4 putting out ~100hp would be combined with a downgraded F1 system (40,000rpm, same weight, hopefully reduced rpm would increase bearing life, but I'm not a ME) to provide ~140hp for the first 6 seconds of acceleration. The downsized engine would provide substantial fuel economy savings at cruise while the flywheel KER would provide a performance boost and increased fuel economy in city driving.

What's not to love? Where am I off?