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Old 06-12-2008, 09:07 AM   #1 (permalink)
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Using flywheels to increase FE

Ok, so I saw this mentioned in the thread about the powered trailer and thought I'd start it's own thread because it's a very interesting topic and I haven't seen it covered here as of yet.

Using a large, heavy flywheel on cars to increase FE. First off, are there any manufacturers who actually make these. I know they make lighter ones for racing applications, but I would think that heavier ones would be harder to find because it's more of a niche market per say.

Also, what about making a trailer that simply encloses a very heavy disk that is connected to the wheels of the trailer via a gearing system that would keep the disk spinning long after power from the engine was cut off. I was thinking about this because it would GREATLY improve the ability of a car to do huge gaps of coasting between accelerating while EOCing. The only thing that would be a concern to be would be getting the big lug rolling at first. Since it would be many times heavier then a standard car flywheel, how would you overcome the effort that is needed to get it spinning at first?

I'm sort of thinking of those push cars, the toy cars you push and then when you let go they have a geared flywheel inside that keeps it going for a good time afterward, sort of like a kinetic energy engine almost that would just store up all the energy you created by accelerating and then release it over time.

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Old 06-12-2008, 09:35 AM   #2 (permalink)
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There were experiments with this in the 1970s as far as I know. The flywheel was in a vacuum chamber, otherwise the air drag on the flywheel would rob a lot of energy. I think the use of this was regenerative braking. That would be a good use of the trailer, too. If you have to put useful energy into the flywheel, there is no advantage. If you can store energy that would be wasted, then great.

As far as how to get it spinning: Variable displacement swashplate pump on the trailer wheels, driving a hydraulic motor on the flywheel. The efficiency is not great, but neither is a generator> controller> flywheel-motor combination. With the swashplate flat, no fluid is pumped to the motor. As the swashplate tilts, more fluid goes to the motor. I think an additional pump and motor would be needed to get the energy out of the flywheel again. Electric clutches could disconnect the hydraulics when not in use to reduce parasitic loads of the hydraulic system.

Disadvantages: weight, gyroscopic effect, overspeeding the flywheel causes rupture.
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Old 06-12-2008, 09:47 AM   #3 (permalink)
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Hm, ok, so your saying that the energy needed to be put into spinning it up eat up the advantages of having it spinning.

Why is the gyroscopic effect going to be a problem with a flywheel on a stationary platform? If anything it will make the trailer more stable, wouldn't it?
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Old 06-12-2008, 10:06 AM   #4 (permalink)
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If you can "spin" the flywheel by braking it is a "good" idea, as in it "could" work. But, like ttoyoda said, if you are going to expend the engine more to get it spinning you will in the end use more energy than you will gain.
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Old 06-12-2008, 10:34 AM   #5 (permalink)
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Quote:
Why is the gyroscopic effect going to be a problem with a flywheel on a stationary platform? If anything it will make the trailer more stable, wouldn't it?
Well the trailer is not going to be stationary once the car/trailer is moving. If you suddenly drive onto a section of the road that has a sideways tilt the trailer will want to stay level, i.e. pick a tire up off the ground. Also as you add and remove energy to the flywheel (speed it up or slow it down) you will have the trailer want to move in an equal and opposite direction.
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Old 06-12-2008, 01:58 PM   #6 (permalink)
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Actually you don't want the flywheel to be heavy: you want to make it out of a high-strength material like carbon fiber, so that you can spin it really fast. Getting energy in & out isn't a major problem: embed some magnets, and it becomes the rotor of a motor/generator.

There's quite a bit of research work going on in this area. Just do a search on "high speed flywheel".
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Old 06-12-2008, 05:03 PM   #7 (permalink)
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Getting energy in & out isn't a major problem: embed some magnets, and it becomes the rotor of a motor/generator.
Do you happen to know what the storage efficiency is compared to capacitors or battries?
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Old 06-13-2008, 08:08 AM   #8 (permalink)
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After reading several articles about flywheels it appears that they are best used for providing acceleration rather than constant power. It has to do with how efficiently energy is first transferred to and from the flywheel vs the equivalent amount to/from a battery. The ideal hybrid system would have a flywheel the provide accelerative power and a battery for constant running. This article sums it up pretty nicely:

http://www.hybridcars.com/related-te...l-hybrids.html

This doesn't look like something a backyard mechanic could safely tackle. The forces involved are huge and dangerous if sufficient safety precautions aren't employed. Back in the '90s Chrysler tried, and failed, to build a hybrid flywheel race car. Just google "Chrysler Patriot".
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Old 06-13-2008, 12:46 PM   #9 (permalink)
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Quote:
Originally Posted by ttoyoda View Post
Do you happen to know what the storage efficiency is compared to capacitors or battries?
Well, don't take what I say as gospel: I'm just going by some reading & a physics background. With that caveat:

Flywheels seem to be very, very efficient for short-term energy storage. That is, you can put X amount of energy into one in a very short time, and get out something like 99% of X minutes or hours later.

Batteries are less efficient at input/output: a larger fraction of the energy is wasted as heat, and they are more limited on the rate. On the other hand, they'll store the energy for weeks/months with little loss.

With capacitors, the problem is the exponential nature of the energy output. Without some sort of switching device, the energy all wants to come out in a rush.
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Old 06-13-2008, 01:01 PM   #10 (permalink)
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A Capacitor works almost exactly like rechargeable battery.
Once it's charged up, it will discharge into the load at about the same rate as a battery.
(That's controlled by Ohms Law I=E/R).

The problem with caps is, they don't hold a lot of electrons. The run out of juice a lot faster.
A cap that would do the same job as your standard old car battery would be as big as a house..

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