'Flybus' prototype may be hybrid bus of future

September 8, 2011 by Nancy Owano, Phys.org weblog

(PhysOrg.com) -- The "Flybus" prototype bus aims to showcase how hybrid electric buses can be inexpensive, cost efficient and easy on the environment. Reports out this week say that the Flybus is being readied for testing. The consortium of companies that created the prototype wlll stage a presentation at this year’s Low Carbon Vehicle event in the UK, at Rockingham Motor Speedway in Corby, Northamptonshire.

Treansportation engineers will want to see how the Flybus rates in a focus on what is next in the evolution of the hybrid bus and solutions that can ease fuel consumption and CO2 emissions. Cost has been a challenge with standard hybrids.

The new Flybus hybrid has taken on cost considerations with a unique energy-saving approach. The bus makes use of the "flywheel" technique demonstrated earlier this year by Porsche in Detroit. The flywheel can feed back into the wheels on the vehicle's acceleration. The technique is praised as a way to generate emissions-free energy. The system takes the kinetic energy that is generated from the braking stops-and starts of a city bus run and sends it back to the vehicle. The team's goal has been to come up with an energy-efficient redistribution process, supported by a continuously variable transmission system.

Key features of the Flybus prototype are a Ricardo Kinergy flywheel as the medium for energy storage and a Torotrak continuously variable transmission (CVT) which transfers energy to the flywheel. The Ricardo Kinergy flywheel uses low-cost magnetic coupling.

As interesting as the construct is the structure of the group, the Flybus consortium, that came up with the bus hybrid. The consortium is an example of what happens when there is a synergy between government and technologists at different companies who can put pieces of a product engineering puzzle together, drawing on varied areas of expertise, in an innovative way. The collaborative is partly funded by the UK’s Technology Strategy Board as part of its Low Carbon Vehicles initiative.

Flybus flywheel-based mechanical hybrid system. Torotrack presentation.

The Flybus consortium would like to see its prototype through the next stages so that bus operators can look forward to less fuel costs and brake wear. The group unites bus maker Optare, engineering consultancy Ricardo, technology specialist Torotrak, and Allison Transmission.

London plans to introduce 90 hybrid buses to service this year. The city has been looking toward hybrid buses for some time. In the 2004 Energy Strategy plan, the Mayor adopted for London the government’s national targets to reduce carbon emissions by 60 per cent by 2050 from the 1990 level. Hybrid buses are taken seriously as a next step toward that goal.

Explore further: Hybrid Bus in the City: A Prototype with a Future

More information: Press release

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not rated yet Sep 08, 2011
Are the original brakes removed or disconnected?
5 / 5 (5) Sep 08, 2011
Neither. Think of it as a system that works much like when you shift gears down instead of braking (only that in thsi case yo're not using the resistance of the motor to slow you down but store the energy in a flywheel). It's just a separate 'braking' system which can also feed back the energy during acceleration.
There have been separate braking systems utilized in trucks / buses before. Retarder systems (electomagnetic eddy current brakes)are an example of this. But the 'real' brakes are kept on board because these systems work best when the bus is at some speed (i.e. they usually don't work well for the last few meters of braking)
1.4 / 5 (10) Sep 08, 2011
Just drill more oil, and if that isn't sufficient; coal gasification and liquefaction are technologies that Germany used in 1943 to run its war machine. I suspect we can do so as well in 2011.
4.3 / 5 (6) Sep 08, 2011
Shootist, regardless of whether is CO2 as a cause of climate change, it's still not a good idea to pollute the only atmosphere we have...
5 / 5 (3) Sep 08, 2011

It seems to me that there would be considerable torque on the flywheel while the bus turns. It may be better to mount it so that the axis of rotation is vertical.
not rated yet Sep 08, 2011
I wonder what the net gain in efficiency is? The flywheel and transmission system must be heavy, making it take that much more energy to get the bus moving when the flywheel isn't charged up. This kind of system wouldn't be benneficial in a vehicle that goes for long periods between stops and starts either. Imagine a 10 year old car with 500 extra lbs of flywheel in it. It's on its third owner, a 18 year old kid with not money. The flywheel system hasn't worked in a while, but the owner doesn't want to put any money into such an old car, so you just have 500 lbs of dead weight. Same goes for your Prius. Once the batteries reach the end of thier expected lifetime, the car is essentially scrap. Nobody is going to replace the batteries when the rest of the car is so old.
5 / 5 (4) Sep 08, 2011
This kind of system wouldn't be benneficial in a vehicle that goes for long periods between stops and starts either

You just have figured out why they put it in a bus.

As the flywheel has to be bolted in line with the crankshaft of the engine

Not necessarily. You could put it at any location if you included some abgled gear.

A large rotating mass will create a considerable gyroscopic force when cornering, so the optimal alignment (from a stability point of view) would be to have a vertical axis of rotation.

However with something as massive as a bus that may not be necessary (as these types of flywheels have been tried decades ago in trucks without too much problems).
not rated yet Sep 08, 2011
How can the flywheel be affected by the bus turning?
A large rotating mass will create a considerable gyroscopic force when cornering, so the optimal alignment (from a stability point of view) would be to have a vertical axis of rotation.

Exactly! You beat me to it.
not rated yet Sep 08, 2011
you have just figured out why they put it on a bus

Exactly what i wanted to say
This kind of system wouldn't be beneficial in a vehicle that goes for long periods between stops and starts either

but it would be immensely beneficial for a vehicle that stops and starts every quarter mile, and drives every day, like...a city bus...what a great idea!

I would like to point out another benefit that has been completely overlooked. Considering that a bus may stop and start every quarter mile or less (including stop lights), you waste a lot of TIME with slow acceleration. If you speed up the bus's initial acceleration by 50%, you could purchase fewer busses and run faster service, saving money, and increasing incentive to ride the bus. This would be true in any city where there are dedicated bus lanes, or the traffic runs faster than the bus.
not rated yet Sep 08, 2011
"If you speed up the bus's initial acceleration by 50%, you could purchase fewer busses and run faster service, saving money, and increasing incentive to ride the bus." The added ridership you talk about would be mostly due to the thrill seakers wanting to try standing up while these new Super busses lept into action after each stop. But in all seriousness,with added torque would come added structural stresses which would need to be addressed, possibly making the vehicule even heavier. Maybe 50% would be a tad extreme.
not rated yet Sep 08, 2011
admittedly 50% was just a number I threw out.

I would like to point out though, that bus acceleration is primarily limited by the weight of the bus and the output of the the motor.

A 50% increase in acceleration would not actually seem like that much if you were in the bus, because the acceleration is so paltry to begin with. It would add stress to the drivetrain, which is heavy duty to begin with.

A bus can handle much harder breaking than the increased acceleration I'm proposing, so I really doubt that it would be a problem.

Also, the 0-60 time of a bus is generally 40-50 seconds.
You could double it, and it would still be smoked by a prius, and just about every other vehicle on the road.
5 / 5 (1) Sep 08, 2011
From the artcile:
"The technique is praised as a way to generate emissions-free energy."

I won't explain what is wrong with this scentence, we all know, but really the author should know better than this.
5 / 5 (1) Sep 09, 2011
Time will tell if the mechanical KERS (flywheel) will be superior to simply using an electric variant (as in formula 1 cars, where most teams now use a KERS which stores the braking energy as electrical energy in an accumulator).

For city buses the latter could be accomplished using supercapacitors. Although these can't hold the charge for long they mostly don't need to given the frequncy of start/stop maneuvers (and an electric systm is way less maintenance intensive than a mechanicl one. Also it's a bit safer during a crash...but the latter problem doesn't really concern busses because if you crash a bus so hard that you rip out the flywheel and open it up then you're in the range of worst-case-crashes where such effects are the least of your problems)

Personaly I find an electric system much more 'elegant'.
not rated yet Sep 09, 2011

I believe that for larger vehicles that make frequent stops, they have found that mechanical hybrid systems are more cost effective and/or efficient.

The battery and motor system is a lot more expensive, and does not capture the energy as quickly. However a flywheel system tends to lose energy more quickly than the battery system, and is not as ideal for long distances.

And I completely disagree with the idea that the battery system as more 'elegant'. it requires so much more engineering. Adding a flywheel is a much simpler, more elegant solution, whether or not it is more effective.
not rated yet Sep 12, 2011
And I completely disagree with the idea that the battery system as more 'elegant'.

Elegant in terms of: Do you ever need to look after it (service, replacement)?

And I'm not sure it requires more engineering. Adding additional gears seems a lot more complex (and prone to failure) than adding a system that basically has no moving and/or touching parts.Plus you can put the capacitors anywhere you want (whereas the flywhee has to be somewhere close to the crank shaft)

It's a bit like solid state memory devices are more elegant than rotating discs mit mechanical read/write heads.

Formula one cars use the braking energy frequently (probably more frequently than a bus would) - and basically all teams have switched over to electrical KERS because it just doesn't break down as much.
not rated yet Sep 12, 2011
The flywheel only needs a few gears to engage/disengage from the system. It doesn't need a whole transmission.

On the semantic idea of elegance, I will continue to disagree with you :). I don't agree with your analagy, as the electric hybrid system still needs an electric motor, so you need more equipment in the equation.

The placement of the flywheel doesn't necessarily need to be on the crankshaft, as evidenced by porche's concept car, where it was under the passenger seat.

Although, I'm not sure what advantage they were seeking by doing that way.

Admittedly, I don't know the specifics of the formula one situation, but you have to admit that the situation would put far different strains at high speed than stop and go - and they would probably use the flywheel at extremely high velocities to save weight.

But time will tell in the end.

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