"Continuously variable" electric transmission
Richard Schumacher
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?
David L. Johnson
> 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.
--
David L. Johnson
__o | Deserves death! I daresay he does. Many that live deserve
_`\(,_ | death. And some that die deserve life. Can you give it to
(_)/ (_) | them? Then do not be too eager to deal out death in judgement.
-- J. R. R. Tolkien
David Kerber
says...
I doubt it. The loss in efficiency over a mechanical
transmission would make most any ride a real chore.
--
Dave Kerber
Fight spam: remove the ns_ from the return address before replying!
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David Kerber
david....@lehigh.edu says...
> 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.
In those small sizes, you would be very lucky to beat 50% to 60%
efficiency.
Mike Farnes
> 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
>
>...
>
> Surely by now someone must make such a thing?
I don't think you'll find anything in production but there's an
article about such a thing here:
http://petrix.dreifels.ch/fb/images/1_wsj_shorter_1.pdf
Regards,
Mike
Bill Hennessy
thing. Yes, I've looked.
F1
"Richard Schumacher" <no-...@thank-you.com> wrote in message
news:3FD3F34E...@thank-you.com...
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.
F1
http://lancet.mit.edu/motors/motors3.html#tscurve
David Kerber
formu...@removethisearthlink.net says...
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.
Brett Jaffee
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 <no-...@thank-you.com> wrote in
news:3FD3F34E...@thank-you.com:
Richard Schumacher
"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.
Richard Schumacher
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.