NEWS: KERS flywheel system to power large trucks?

[MetroMPG]

Via GCC:

A company that developed a flywheel energy storage/delivery system for F1 race cars has proposed (at an SAE conference) their use as a less expensive, more efficient option than battery/electric hybridization of trucks & buses.



CVT (left) & flywheel enclosure (right)

There is a surprisingly close match between the energy storage requirements of an urban bus and the current F1 regulations. This also makes the packaging so much easier than an electrical solution; we can even retro-fit a system without impacting on the passenger space.

The system mates the flywheel to a specially developed CVT (that ptero posted about here: http://ecomodder.com/forum/showthrea...sist-8441.html ) to mate the flywheel to the existing drivetrain.

They say the overall efficiency of the system is greater than a battery hybrid primarily because overall losses in their purely mechanical system are less than converting mechanical energy to chemical/electrical energy and back again.

Torotrak claims the system offers more than 30% fuel saving over the London bus test cycle

More info: Green Car Congress: Torotrak to Present Paper Advocating Flywheel Hybrid System for Buses at SAE Commercial Vehicle Conference

Possibly related... http://ecomodder.com/forum/showthrea...r-bus-987.html

[pgfpro]

WOW That is amazing!!!!

[DonR]

Basically the system uses (2) motor/generators. One on the crankshaft (on the Williams F1 car anyway) & one somewhere else attached to a flywheel. When storing energy under braking the generator on the engine spins the motor hooked to the flywheel, making it spin really fast. When the button is pushed, the generator extracts kenetic energy from the flywheel & powers the motor on the crankshaft.

Which is worse, the gyroscopic affect from the flywheel or the drawbacks of batteries?

F1 KERS system using batteries run close to 400V from what they say. Both Ferrarri's & Renault's systems require coolant be run to the batteries. McLaren's does not. I heard somewhere that the batteries liked to be hot, but not too hot was the reason for the coolant.

Don

[MetroMPG]

Originally Posted by DonR

Which is worse, the gyroscopic affect from the flywheel or the drawbacks of batteries?

In a real world bus application, I'd think the gyro effect would be more manageable (slow vehicle = slow transitions changing direction). In racing, maybe less so.

[NiHaoMike]

How does it compare to hydraulics?

[MetroMPG]

That's a good question. I don't know.

[user removed]

Kers is an energy recovery system. The flywheel configuration uses a CVT (continuously variable transmission) which has specific limits to its range of operation.

A Infinitely variable transmission has a lowest "gear" ratio but no highest ratio, there fore the definition of infinite range of operational ratios.

Comparing Kers to a IVT hydraulic hybrid, would be limited to the Launch assist hydraulic hybrid.

Kers works well in specific situations where there are opportunities to recover and reapply energy otherwise lost.

The other hybrid advantage not shared by IC-electric types is the ability to pulse and glide the vehicle with the hybrid components.

This requires very high efficiency in energy conversion and the least possible number of changes in the state of the energy.

My first patent was using the engine as a flywheel and a CVT that would allow the flywheel mode of the engine to apply power to the wheels, even when the flywheel-engine was consuming no fuel.

This is the crucial threshold of the breakthrough in hybrids, not yet realized, to truly be able to pulse and glide the engine to the storage and then to the wheels at exactly the rate of power application that is necessary to maintain a constant speed.

This has always been the crucial component and it must be properly understood.

When I was testing my brother's 90 Honda Civic, I drove 9 miles and averaged 30 MPH. It took 18 minutes per cycle, but the engine was only running 4 minutes 15 seconds.

That's 23.6% of the total time in motion.

In the INNAS link in my "Hydraulic Hybrid revisited" thread they ran the engine 11.9% of the time the vehicle was being driven on the test loop.

Operating the engine only within the range of it's highest BSFC is the key to breaking the "sound barrier" of fuel mileage in vehicles. We hypermilers demonstrate that P&G is the way to get to much higher mileages, especially at lower speeds.

Separating the power application to the wheels from the power generation of the engine is the crucial component.

Think of the storage of energy as a type of shock absorber that allows huge fluctuations of energy application and energy recovery as the shocks on your car absorb irregularities in the road.

Can Kers do that?

Yes if you integrated it into a vehicle and made it so you could pulse the engine and store some of the power in the Kers to be applied after the engine was shut off, while maintaining vehicle speed at a constant rate.
You would be storing the energy in the flywheel that you store in the vehicle when you increase the speed with your pulse.

How does it compare to an IVT hydraulic hybrid.

My best estimate would be they would be comparable.

I am not sure if the Kers system would be as flexible as the IVT HH, and the range of regeneration would not be as broad, since an IVT can regenerate to 0 vehicle speed and the CVT Kers would still require some brakes activity, which could be totally replaced by the IVT HH, at least by my design.

Another factor is cost, which for a Formula 1 car is one thing but for a practical cheap passenger car is another situation totally.

Right now the advocates of HH drives are trying to implement them in vehicles that are large and have a heavy cycle of stop and go operation, like garbage trucks, and other short haul delivery vehicles.

My design could be used on a bicycle. You could charge the bicycle by using it as an exercise machine. Charge the accumulator fully and you would have a reserve of something like 150 horsepower seconds of energy in reserve.

If the system was efficient enough you could sustain a significantly higher speed over a considerable distance with human power alone. If that was not sufficient you could add a small pressure washer engine and pump for even higher sustained speeds.

Imagine this to understand what I am trying to explain. How fast can you push a small light car? Maybe 7 MPH. Now think of how fast you could push it if there was a conveyor belt that moved you at the same speed you had the car moving after the first push. 10 MPH? 15 MPH? 20 MPH?

In other words whatever speed you got it to you could stop pushing and you would be travelling at the same speed as the car.

Thats the key to all machines and efficiency, to make the most out of the energy that you apply. I think a human powered aero bicycle with a hh drive train could average over 45 MPH for 20 miles, using the reserve energy in the accumulator to boost you up to speed but pedalling constantly to keep the pressure levels in the accumulator as high as possible.

it's the reverse of the pulse and glide that runs your overpowered car less than 20% of the time when you P&G.

Like the Gossamer Albatross, the first human powered airplane to travel 45 miles, the pilot could provide enough power to climb to 500 feet and get a short rest while the plane flew on in a glide.

In the bike example you could pack 30 minutes of recharge in the accumulator then 30 minutes of pedalling effort and you would have almost twice the sustained energy you could provide without the reserve.

It will be a game changer, worldwide, when you can transport yourself 40 miles a day without any energy consumption. If you are an old fart like me then carry a battery and electric motor, or the above mentioned pressure washer pump.

Present hybrids can be beat by a launch assist axle and a start stop alternator, for a lot less money than a hybrid system. That will happen within the next few years. The full hydraulic hybrid will follow within a decade and the oil producers will see their monopoly end.

regards
Mech

[user removed]

I have given this some thought.

Kers system with a flywheel and CVT would not be as efficient as a pure hydraulic IVT system.

2 or 4 wheel regeneration down to 0 speed is the key to the difference.

Since the CVT range is limited there is no way that system could totally replace the brake system on a vehicle.

The IVT hydraulic system could replace the brake system. It would need to have an emergency brake like all cars need today, but all the braking done by conventional brakes would be done by the accumulator and IVT.

In the case where the regeneration capacity was reached, braking would be down by restricting the flow of fluid between the high and low pressure sections of the pump without the accumulator involved when it was fully charged. Larger accumulators would be used in regions with significant elevation changes if the total accumulator capacity was found to be insufficient.

Either system Kers or hydraulic would easily exceed the regeneration energy return if done electrically.

Photos are attached showing flow charts from EPA and U of Michigan research comparing electric and hydraulic energy return percentages.
These are a few years old but show the significance of the differences in wheel to wheel energy recovery.

Another thing to consider about the Kers system compared to an in wheel IVT hydraulic drive is Kers still has to apply and recover power through other drive train components which would affect overall efficiency due to additional losses not existing in a pump to accumulator to pump energy pathway.

Every step of energy transfer and conversion has individual losses. The greater number of steps the cumulatively greater losses even when individual losses are small.

Example 4 steps at 90% per step, will produce less than 66% return of the original energy value.

Due to conversion steps and total energy losses it will probably never be possible to build an electric hybrid that can effectively utilize the P&G strategy

regards
Mech

[NiHaoMike]

Some hypermilers have managed to very effectively P&G Prius and Insights. Though they'll probably be able to get even better results with a hydraulic hybrid.

While hydraulic energy storage is extremely good in terms of power density, it has lower energy density than batteries so it would not be as effective going down a high hill.

[user removed]

Absolutely true Mike, I referred to that situation in the post, and to a point you could increase the accumulator size or maximum pressure.

Of course when comparing the electric to hydraulic efficiencies, you also have to understand the downhill distance would have to be 3 times longer to recapture the same amount of usable energy with the electric hybrid.

Batteries take many times longer to accept the same amount of energy as they can apply to the vehicle, while hydraulics do not care whether it is applied or recovered.
A good example is the electric drag racer (Datsun 210) in another thread on this forum that does 10 second 110 MPH 1/4 mile runs. It takes almost 20 minutes to recharge the batteries after a 10 second run.

Now Imagine what an all wheel drive drag racer would do if you had only enough accumulator for a single 1/4 mile run. I guarantee you it would be a whole lot faster than the Datsun, with all 4 wheels pulling at the limit of their traction. The problem would be its weight, which would be considerably lower than the electric drag racer, even if you used a 20-30 gallon accumulator. In fact you might have to add ballast to get better traction.


I hypermile my CVT Insight, using P&G I found that you can accelerate very gradually or climb a very slight hill. Rate of acceleration is measured in 1 MPH per every 3 or 4 seconds. The instant mileage reading changes very little when you are accelerating, but when you get to your target speed and let off the gas just a little more in the deceleration direction you can see mileage jump to between 125 and 150 on the instantaneous bar graph. The speed differences are very small and most other drivers do not realize what you are really doing, compared to P&G in my Echo.

I have managed 70.2 with the CVT Insight for 655 miles on one tank at highway speeds averaging 57 MPH. This week my daily (40 mile trip) average was 75 MPG. Best day was a 19 mile run at 84.1 MPG. Average speed was 36 MPH overall, timed from beginning to end of the run, 19 miles in 32 minutes.

The point is when you hypermile a gas electric hybrid, you are not really using the engine to store the energy to apply it later to the power train, like in traditional P&G as I understand it.

That is because the increased engine efficiency is more than offset by the losses in conversion and reapplication as demonstrated in the comparisons in the photos.

regards
Mech