Half a croissant, on a plate, with a sign in front of it saying '50c'
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Regenerative Constant Rev Flywheel Driven Petrol Electric Engine

Venturing deep into the territory of an idea that probably exists in someone's back yard.
  [vote for,

Completely ignoring one of the best bits of halfbakery advice: write about things you know, stay silent about those you don't, I'm going to talk about car engines. Without a safety net. None of the concepts here are new but hopefully there is something original in the way they have been brought together.

Start with a petrol driven engine.

This drives a shaft upon which is a flywheel. The engine could itself spin saving weight, but adding complexity.

Also on this shaft is an electric motor that can act as a dynamo.

Somewhere there must also be a clutch so that the engine can turn over without tearing its guts out on a stationary flywheel.

Now, working on the assumption that engines are most efficient at a constant RPM (rather than revving up and down), the engine spins up to speed and stays at that RPM. You should be able to adjust the RPM by some control in the car. Let's call this the rev lever. High for sport. Lower for economy.

Now that we've got the engine started (probably with the aid of the electric motor) it is driven at your chosen RPM and the same motor/dynamo charges a power storage device (battery/fuel cell etc).

The car has had a few moments to warm up (engine's warm, power storage device has some charge in it) and it's time to pull out into traffic. You press gently on the accelerator pedal and the shaft starts driving the wheels through a continuously variable transmission gearbox. (You need a CVT because the revs of the engine aren't changing so to change speed you need to change gear).

Now, pulling out into traffic firstly involves getting the car moving. This puts load on the shaft and slows the flywheel. To compensate the electric motor and/or the petrol engine are brought into play to increase the revs back to the amount set by the rev lever.

The amount the electric motor and petrol engine are used depend on several factors:
The speed demanded by the driver (how hard they push the accelerator).
The amount of charge left on the charge storage device.
The current revs of the engine.
The desired setting of the revs lever.

Now, you want to slow down. You lift your foot off the accelerator pedal a bit. The CVT shifts to a lower gear. The engine is given less fuel and the dynamo used to increase the load on the shaft, generating power to be stored, while bleeding off your speed. The maximum braking the engine can provide is the combined braking of the petrol engine (lost energy) and the dynamo (partially recycled energy). Need more braking? Use the brakes. Hopefully the dynamo and energy storage device together are capable of sapping energy at a rate to stop the car in all but emergency circumstances. Throughout all this, the shaft continues to spin at, or close to, your chosen RPM.

And that's about it. The petrol engine works as efficiently as it can for your chosen level of performance. The dynamo recycles what it can when you decelerate, using that power to help you accelerate, and the flywheel just smooths things over.

If you want to get really complex, you can add additional clutches so that you can disengage different parts of the drive at will, but whether that's a good idea is too much for my tiny little brain to handle at this point.

st3f, Oct 28 2003

Gnome Rotary Engine http://www.benncomm...bck/gnome/gnome.htm
Spinning radial engine with stationary crank [toiyabe, Oct 04 2004, last modified Oct 21 2004]

EMD http://www.gmemd.com/en/locomotive/
congratulations, you've reinvented the Diesel Electric Locomotive. [Marked-For -Deletion] Widely known to exist. [ato_de, Oct 04 2004, last modified Oct 21 2004]

How Stuff Works - Diesel locomotives (including diesel-electrics) http://travel.howst...esel-locomotive.htm
Wheels driven directly by electric motors, no regenerative braking mentioned, variable rpm, no flywheel. [st3f, Oct 04 2004, last modified Oct 21 2004]


       Um, what was the idea again?
DrCurry, Oct 28 2003

       I'm not an engine expert either, but isn't this how most diesel train engines operate, maybe minus the flywheel? I was given to understand they ran the diesel motors at constant RPM to run a generator. The wheels are actually pushed by electric motors.   

       Apologies if I missed some detail in your design.
krelnik, Oct 28 2003

       new title?
dickity, Oct 28 2003

       UB: The flywheel provides fast response. It only has to drive the wheels until the electric motor takes up the slack. The electric motor's there to smooth the power delivery of the petrol engine. Hopefully by driving the petrol engine at constant revs and slowly changing the fuel injection rate there are some economies to be gained.   

       DrC: Humans have fast-twitch and slow-twitch muscles. This has a fast (flywheel) and medium (electric) 'twitch' drives. Both are eventually driven by the petrol engine. Any questions: see if they are answered in the text.   

       krelnik: I thought about diesel-electrics, but in my experience they always rev the engine when they start moving. [edit: thinks again. now I'm not so sure]   

       dickety: Any suggestions? [edit: sorry dickity]
st3f, Oct 28 2003

       Early airplane engines did spin around a stationary crankshaft, essentially using the engine block as a flywheel. Can you say "torque-steer"?
toiyabe, Oct 28 2003

       first of all, it's dickity, dick*i*ty   

       what about "st3f's engine-related idea"   

       I can follow that better than what you got now
dickity, Oct 28 2003

       This seems similar, but worse, than the 'conventional' hybrid design (having an i.c.engine+e.motor, economies are gained via regen braking and reduced size of engine (closer to 1L than 2L)).   

       One part of the problem is that the optimum (in terms of efficiency) engine rpm vary to some extent with load/car speed - the most extreme and obvious example of this is the comparison of cruising down the road (maybe 2000 rpm optimal) vs waiting at traffic lights (0 rpm optimal). This lends itself to stopping and starting the engine, which indeed some hybrids do.   

       Part of the problem is defining how you expect the vehicle to perform. A conventional non-hybrid may be at its most efficient around 2000 rpm in many situations - but will produce peak power output at say 5500 rpm and thus allow demanding manoeuvres (eg overtaking) albeit at reduced efficiency, but with little effect on overall efficiency. The constant-rpm idea may result in a design that's heavier and does less.
benjamin, Oct 28 2003

       OK, we've got batteries (or some other suitable energy storage device), an IC engine to replenish the energy in said device, and electric motors at the wheels. All the big flywheel adds is a way to store quickly recoverable energy, essentially a mechanical capacitor. This was often done in lab work that required high-amperage power for a short duration. (ever hear that loud engine spool-down sound that seems to occur before any major power-consuming event (I.E. firing the "doomsday laser") in old sci-fi movies? that's the flywheel-dynamo releasing it's stored energy.) This would be unneccesarily heavy in a car, and "supercapacitors", currently in development, should fill this need quite nicely.
Freefall, Oct 28 2003

       Too bad this idea didn't do so well. I was hoping to use one of my favorite engineering terms: "brake specific fuel consumption".
Worldgineer, Oct 31 2003

       ...and now you just have.
st3f, Oct 31 2003

       Continuously Variable Transmissions keep the engine spinning at the most efficient RPM for the throttle, eliminating the need for clunky shifting and your left foot.
Condiment, Oct 31 2003

       If the engine drives a variable output hydraulic pump then this pump drives a variable speed hydraulic motor then the system would work. Imagine the output of the pump is controlled by the system pressure & the motor is also controlled by the system pressure. By using a vane type pump & motor the offset of the central spindles will give varying outputs & requirements respectively. For example, if the engine is running at a constant speed & the car meets an incline then the load increases consequently the pressure in the system rises. This in turn will move the motor spindle towards being almost concentric, reducing the flow but increasing torque. At the same time the increase in pressure will force the motor spindle further offset now it requires more flow per revolution. This system now gives a direct relationship between load & speed ie. with the same engine rpm the speed increases & decreases depending on the incline. To control the travelling speed the throttle will control a pressure valve, the higher the pressure is set the faster you will go. This is achieved by the valve not letting the spindles displace so easily.
liam2, Jun 05 2004

       I am sure I have seen a documentary on this idea.   

       First versions were available in thirties USA. Giant gyroscope within large sedan running bicycle configuration car wheels. The car had outrigger caster wheels for when the gyroscope was off, but otherwise it travelled upright like a motorbike. As I remember it had problems with fighting the inertia of the gyroscope in a turn.   

       More modern developments followed with flywheels running at 150,000 rpm on magnetic bearings, similar to linear tracks, which caused fatal explosions. The electrics failed and the bearings collapsed sending the 5kg flywheel out of perfect balance. The finely machined flywheel became just so much shrapnel.
active8, Jul 05 2004


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