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#11
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"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
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"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
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"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
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"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
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"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. -- |
#16
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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? |
#17
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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. |
#18
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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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