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"Continuously variable" electric transmission
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"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? |
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"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. |
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"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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"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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