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"Continuously variable" electric transmission



 
 
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  #11  
Old December 9th 03, 01:51 AM
meb
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Default "Continuously variable" electric transmission

Richard Schumac wrote:
My searches have not turned up anyone selling a bicycle with a
continuously variable electric transmission. I don't mean an electric
scooter: I mean one in which the crank turns a generator/alternator,
whose output through an electronic controller then drives an electric
motor on the wheel rim(s) or in the hub(s). There would be no chain,
derailleur or gears, except perhaps for some fixed-ratio gearing inside
the generator/alternator or motor assemblies. A control equivalent to a
shift lever sets the ratio between crank torque and RPMs, which can be
varied over some wide range. The rider sets the speed by changing this
ratio and/or the crank RPMs as they find comfortable. Scooter-type
assist would be possible through use of an optional battery. (Earlier
threads on the subject addressed mechanical CVTs and auto-shift
mechanisms, not an all-electric transmission.)
What's the point? Mostly geekiness, I suppose, but the effectively
infinite number of "gears" while reducing the number of moving parts is
appealing. Also appealing is the notion that a battery in the system
would provide load-levelling (hill assist) but with the rider still
ultimately providing all of the energy, unless of course the rider
cheats by re-charging the battery from an external source. For
non-cheaters :_ the battery need only be large enough to help climb one
hill. Efficiency would not be as good as with a conventional drive, but
that's not really a concern for commuters or pleasure riders.
Surely by now someone must make such a thing?




Nobody manufactures such a system. The losses on the conversion and back
would exceed any benefit of the continuous transmission in a commuting
or touring applications.

There might be some off road or winter driving applications in
which multiple wheel drive benefits might overcome the losses and
weight penalty.

The weight of the electric drive would exceed the savings on the
chain/derailleur/internal gear hub of conventional mechanical
drivetrains.

A couple of electric bike systems on the market use regenerative braking
to store energy but still rely on pedal and chain to provide the pedal
propulsion to the wheels. Those that use regenerative braking get power
off the wheel. ZAP’s DX model has regenerative braking on a roller that
engages/disengages the rear tire, twin 200W motors-only regerates at
speeds above 15 mph, its intended to recover energy in hilly areas.
Sanyo has 250/500W brushless front hub motor versions with regenerative
braking charging a very small NiMH battery pack, but it’s not yet
available in the US even though it was supposed to be available last
March. There old website alleged they will have it available as complete
bike (Enacle Gene 27) or kit. Birkestrand’s Rabbit Tool’s EX-Bike (not
yet on the market either) also has regenerative braking on a 500W rear
hub AC motor. Birkestrand will have a kit as well-they’re still working
on getting the reliability of their AC controller up before selling to
the public.

The major electric bike retailers in the US discourage such action
asserting regeneration only extends range about 10% so they don’t think
its worth the weight/expense. I’d like a light weight battery/motor
myself for hills with a recumbent, so I’m watching the Sanyo system
closely and I’m hoping the Sanyo 250W kit falls in the 5-10lb range. I
have a 400W Currie upright (no regeneration), but I wouldn’t put that
extra 25 lb electric system weight on a bent. Those retailers seem
oblivious to the hill issue that is amplified on recumbents.

The continuous ratios have been a high point of the hydraulic drive
systems, but the most optimistic 10% or so losses there take away their
benefit over chain drive. You’re going to get higher losses with the
electric system than the hydraulic in most instances.

If doing so for an engineering exercise or one of those niches I
described, I’d look at a separate high efficiency generator rather than
a motor conversion as the generator.

Among the non-Japanese, Heinzmann is usually the development leader in
hub motors, I’d keep an eye on what they come out with to see if they
have any hub motor systems with regenerative capacity.

Yahoo groups power assist is an electric vehicle group, bicycle
majority, there tends to be very little discussion toward onboard
generation:

http://groups.yahoo.com/group/power-assist/files/

The losses transmitting over the cables from generator to motor should
be trivial compared to the generator and motor losses. The 50-60%
efficiency Dave mentioned sounds low to me based upon my school
experiences with electric motors, but Dave’s figures are higher than
what those previously mentioned retailers allege.



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  #12  
Old December 9th 03, 01:59 AM
Phil Brown
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Default "Continuously variable" electric transmission

What is this fasination with inefficent drivetrains? Until you can get to the
efficentcy of a chain why bother?
Phil Brown
  #13  
Old December 9th 03, 02:27 PM
Raymo853
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Default "Continuously variable" electric transmission

Because it is something different than you are used to using and seeing. It
may not work, may work and not be better, may because a vacuum for yout time
and money but still hopefully richard will learn something from it.

Ray "Rare Positive Morning Mood"


"Phil Brown" wrote in message
...
What is this fasination with inefficent drivetrains? Until you can get to

the
efficentcy of a chain why bother?
Phil Brown



  #14  
Old December 12th 03, 01:54 AM
Jeff Wills
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Default "Continuously variable" electric transmission

meb wrote in message ...

Nobody manufactures such a system. The losses on the conversion and back
would exceed any benefit of the continuous transmission in a commuting
or touring applications.


From the HPV list:

Andreas Fuchs and co have been working at this for the
better part of the last decade, IRRC. They have had several
working bikes, and about 80% efficiency. Where I see the
application being most tasty is AWD trikes and quads.
Instead of a differential you have a logic circuit that
provides proportional power to each hub motor depending upon
the position of the handlebars.

Start he

http://www.autork.com/index-e.html


Jeff
  #15  
Old December 12th 03, 09:43 AM
meb
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Default "Continuously variable" electric transmission

Jeff Wills wrote:
meb wrote in message
...

Nobody manufactures such a system. The losses on the conversion and
back would exceed any benefit of the continuous transmission in a
commuting or touring applications.

From the HPV list:
Andreas Fuchs and co have been working at this for the better part of
the last decade, IRRC. They have had several working bikes, and about
80% efficiency. Where I see the application being most tasty is AWD
trikes and quads. Instead of a differential you have a logic circuit
that provides proportional power to each hub motor depending upon the
position of the handlebars.
Start he
http://www.autork.com/index-e.htmlht...m/index-e.html
Jeff





Jeff,

Looks like they are at least selling to manufacturers. Don’t know if
Jeff or anyone can answer these questions.

I see what appear to be hub motors on all wheels of the semi-recumbent
and quad of Autwork’s customers. The Ecomotion Design link is dead and
the Gilgen site is rather limited. Are those AWD? Are those manufactures
selling to the public yet?

Is Autork implementing and selling a fuel cell storage system or merely
indicating it can interface with such a system?

Any idea if they selling to the general public and if so at what price?

Nice info, thanks.



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  #16  
Old December 17th 03, 09:51 AM
Brett Jaffee
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Default "Continuously variable" electric transmission

Some friends and I were talking about this just the other day, as we were
wondering what bikes might looks like in the far future. As others have
noted, unless you have superconducting motors and wire, the effeciency was
too low.

Actually, we were specifically talking about mountain bikes. Assuming you
could have such a system that was efficient as a mechanical one, why not
put an electric motor in the front wheel too.

Richard Schumacher wrote in
:

My searches have not turned up anyone selling a bicycle with a
continuously variable electric transmission. I don't mean an electric
scooter: I mean one in which the crank turns a generator/alternator,
whose output through an electronic controller then drives an electric
motor on the wheel rim(s) or in the hub(s). There would be no chain,
derailleur or gears, except perhaps for some fixed-ratio gearing inside
the generator/alternator or motor assemblies. A control equivalent to a
shift lever sets the ratio between crank torque and RPMs, which can be
varied over some wide range. The rider sets the speed by changing this
ratio and/or the crank RPMs as they find comfortable. Scooter-type
assist would be possible through use of an optional battery. (Earlier
threads on the subject addressed mechanical CVTs and auto-shift
mechanisms, not an all-electric transmission.)

What's the point? Mostly geekiness, I suppose, but the effectively
infinite number of "gears" while reducing the number of moving parts is
appealing. Also appealing is the notion that a battery in the system
would provide load-levelling (hill assist) but with the rider still
ultimately providing all of the energy, unless of course the rider
cheats by re-charging the battery from an external source. For
non-cheaters :_ the battery need only be large enough to help climb one
hill. Efficiency would not be as good as with a conventional drive, but
that's not really a concern for commuters or pleasure riders.

Surely by now someone must make such a thing?


  #17  
Old December 22nd 03, 06:43 PM
Richard Schumacher
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Default "Continuously variable" electric transmission



"David L. Johnson" wrote:

On Sun, 07 Dec 2003 21:43:10 +0000, Richard Schumacher wrote:

My searches have not turned up anyone selling a bicycle with a
continuously variable electric transmission. I don't mean an electric
scooter: I mean one in which the crank turns a generator/alternator, whose
output through an electronic controller then drives an electric motor on
the wheel rim(s) or in the hub(s).

snippage
Efficiency
would not be as good as with a conventional drive, but that's not really a
concern for commuters or pleasure riders.


Efficiency would indeed be a concern for commuters and pleasure riders if
the efficiency is low enough, as I would presume would be the case. You
have three separate sources of energy loss: the inefficiency of the
generator, the power transmission to the motors, and the motors
themselves. Do you ever notice an electric motor getting hot? That's
wasted energy, and that gets worse as load increases.

The engineers can give reasonable estimates on the energy losses.


Yeah, efficiency in these small machines might be 70% or 80%. Sucky compared to
a chain. But:

Electric drive with regenerative braking and a storage battery allows the rider
to capture for later use energy while going downhill, energy that is otherwise
utterly thrown away as heat in the brake pads. The system would also make use
of low-effort pedalling as in a tailwind, or for that matter while going
downhill. Low-effort pedalling is not tiring even if the efficiency is low.

The net effect of these, at least over sufficiently windy or hilly courses,
would be an increase in overall efficiency. I have not worked out how much wind
or how much hill is enough to tip the balance.


  #18  
Old December 22nd 03, 06:46 PM
Richard Schumacher
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Posts: n/a
Default "Continuously variable" electric transmission



F1 wrote:

Unlike a gas fueled internal combustion motor, an electric motor's peak
torque is 0 rpm, so no transmission is needed. A single gearing is used for
whatever your primary speed will be.


It's still a transmission (it's transmitting power from here to there), it's
just one without any variable mechanical component.


 




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