planetary ECVT for Bicycles

[autodoctor911]

I was wondering if anyone has seen any bicycle drive systems, either production or prototype that use an electric motor connected to the chain drive in a way as such that the motor drives one element of a planetary, while the pedal force runs another, and the third element drives the bike. It seems like a natural way to eliminate the need for gears altogether, since the flat torque curve of the electric motor could be used to vary the amount of rpms the pedals turn at any given speed, while helping to assist at the same time. since you could vary the rpms of the motor with the speed of the bike to maintain a good cadence without any gears. this would also seem to get around having to have a torque sensor for certain markets where only pedal assisted motor operation is allowed. Depending on the torque output of the motor, you could set up the fixed gear ratio between the bicycle cranks and the motor to run just about any power level you wish, or you could add a second motor that would iether act on another planetary tied into the first to vary the torque of the output without changing the required input torque from the cranks, or just use the second motor to drive the wheel directly for more speed, while the first is just a low power motor to act as a continuously variable gearbox for the rider input.

 

[autodoctor911]

I would think you could design a very low power system that would have great range with very little weight, that wouldn't really be much faster than a normal bike, but actually lighter than a nuvinci cvt or even an internal gear hub.

 

[shock]

Wait.. What ??

 

[Miles]

Not exactly what you're proposing but:

http://www.endless-sphere.com/forums/viewtopic.php?f=4&t=7931
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=10998
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=7358

 

[Toorbough ULL-Zeveigh]

:more: Not exactly what you're proposing but:


http://endless-sphere.com/forums/viewtopic.php?f=41&t=45365&start=15#p662850
http://endless-sphere.com/forums/viewtopic.php?f=7&t=38025&p=554421
http://www.bikeforums.net/showthread.php/812121-KERS-bicycle

 

[amberwolf]

I was wondering if anyone has seen any bicycle drive systems, either production or prototype that use an electric motor connected to the chain drive in a way as such that the motor drives one element of a planetary, while the pedal force runs another, and the third element drives the bike.

So what happens when you can't pedal hard enough to provide reaction torque for the motor to push against? Would you have a one-way clutch in there to prevent forcing the person's feet to pedal backwards?

 

[Dauntless]

Sounds a lot like what you have on 3 wheelers, either 3 speed hub or derailleur, with a powerplant on it. Think of phrases such as "Jackshaft, " "CVT" and "Freewheel" intergrated into it. You pedal up to the speed of the bike by shifting gears, it meets up at the jackshaft where you may or may not be fast enough but the freewheel lets the rest of the drive go, the CVT maintains the motor speed. I've thought about this one a lot, but the right drivetrain for it has to be refined.

 

[crossbreak]

Sounds a lot like what you have on 3 wheelers,

WTF? Where exactly did you extract this from his post?

So what happens when you can't pedal hard enough to provide reaction torque for the motor to push against? Would you have a one-way clutch in there to prevent forcing the person's feet to pedal backwards?

The reaction torque can be set by electronics. There is same drag of course, but if the drag is greater than the reaction force done by the rider, somethings engineered completely wrong here.

The efficiency might no be very good. A part of the power is split here, going through electronics, loosing almost 50% here in average. If you wanna go further into details here, then you should read some papers about the prius. I would suppose some but the ones I know are almost all german. You might search for "power split drive" to get some info about the various eCVT known yet.

 

[Dauntless]

Maybe reading the whole thing helps.

Sounds a lot like what you have on 3 wheelers, either 3 speed hub or derailleur, with a powerplant on it.

WTF? Where exactly did you extract this from his post?

that use an electric motor connected to the chain drive in a way as such that the motor drives one element of a planetary, while the pedal force runs another, and the third element drives the bike.

 

[JennyB]

So what happens when you can't pedal hard enough to provide reaction torque for the motor to push against? Would you have a one-way clutch in there to prevent forcing the person's feet to pedal backwards?

If your feet are forced backwards then what you have is a Chinese windlass. Take the case where the torque split is 50:50, as if pedal and motor inputs were on the two halfshafts of a car differential and the output is the propshaft. If the inputs are equal the the output revs equal motor revs. Normal pedal cadence matches most efficient motor revs. Now load is applied until the pedals stall. Output revs are now half the motor revs. As load increases and the pedals are forced into reverse, the effective gear ratio falls even faster, approaching zero as the reverse pedal revs rise to match the motor revs.

I think. :?

 

[crossbreak]

....I think. :?

Hey Jenny, I think your thoughts are right, the differential is a good point of view to learn how this stuff works since it has equal reduction ratios on both sides. It's better than a normal planetary, it just shows things more clearly. You can visualize the prius drive using the prius driving simulator http://www.wind.sannet.ne.jp/m_matsu/prius/ThsSimu/index_i18n.html

 

[bobc]

also
http://endless-sphere.com/forums/viewtopic.php?f=28&t=27132
which I've still not gotten round to assembling...... :^(

 

[autodoctor911]

I found this link on another topic here:
http://www.bike-eu.com/Home/General/2010/3/NexxtDrive-Claims-Most-Advanced-e-Bike-Transmission-BIK003881W/

this is the kind of system I am thinking of. Is anyone making it.
to me the mechanical, and electric motor portion are fairly simple, and I don't really see much new technology to patent there, but the software and electronics to control it are where the work needs to be done. Not my area of expertise for sure, but the main challenges/goals will be to figure out how to efficiently apply torque in each of the two motors to make it work like a seamless CVT to the rider pedaling. Ideally, you could get on the bike, start pedaling, and your torque and cadence could be adjusted to preference with a throttle like device(the more throttle, the harder it is to pedal, and the faster you will go). but with 2 motors, you could go faster and still not have to pedal hard. Maybe if the second motor is just a direct drive to the wheel, you could use one twist throttle for controlling it as on a normal ebike, and another twist throttle to adjust the desired torque feedback to the crank, where the controller would have to do a little calculating based on the different rpms of the various components to find the desired current supplied to the assist motor that is acting like a transmission.