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"Continuously variable" electric transmission



 
 
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  #11  
Old December 8th 03, 10:59 PM
Chalo
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Default "Continuously variable" electric transmission

(Pbwalther) wrote:

Bicycles lose only a fraction of 1% in friction losses.


Nope. Even surgically clean fixed-gear track bikes have more
mechanical losses than that. Derailleur bikes can easily show 10%
drivetrain losses depending on chainline, wear, etc. That's before
tire losses, which can be much higher yet.

It's hard to imagine any electrical drivetrain not employing
superconductors that would have sub-10% losses, even if it avoided
multiplication and reduction stages. But chain drive isn't
magical-- it's only a little bit more efficient than anything else.

Chalo Colina
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  #12  
Old December 9th 03, 01:05 AM
F1
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Default "Continuously variable" electric transmission

Actually, this might be easier...

http://lancet.mit.edu/motors/motors3.html#tscurve


  #13  
Old December 9th 03, 01:28 AM
David Kerber
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Default "Continuously variable" electric transmission

In article . net,
says...

"Richard Schumacher" wrote in message
...
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?



Unlike a gas fueled internal combustion motor, an electric motor's peak
torque is 0 rpm, so no transmission is needed.


Not necessarily; it depends on the motor design: induction motors tend
to have their peak at low but non-zero speeds unless they have a
capacitor start, while synchronous motors have essentially zero starting
torque, and shaded-pole motors have very low starting torque. DC motors
can have pretty much whatever torque characteristics you want to design
into them.

A single gearing is used for
whatever your primary speed will be.


True; it's easy to design an electric motor to run at a huge range of
speeds, and with sophisticated electronic controls, the efficiency
doesn't decrease a whole lot over that range, either.

--
Dave Kerber
Fight spam: remove the ns_ from the return address before replying!

REAL programmers write self-modifying code.
  #14  
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?


  #15  
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.


  #16  
Old December 22nd 03, 06:46 PM
Richard Schumacher
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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.


  #17  
Old January 6th 04, 02:33 AM
Colin
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Default "Continuously variable" electric transmission

Richard Schumacher wrote in message ...
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.

We all understood what F1 meant, no need to be pedantic.
 




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