Does anyone know of a bike on the CR bike list spectrum of bikes that had a continuously variable transmission (CVT), even if it were only a failed experiment?
Here's why I'm asking: I'm reading a bit on the history of CVTs and have seen examples of simple, robust CVTs in other kinds of machines dating as far back as the 1920s so far. The CR bike list bikes date that far back, or farther. Bicycle builders seem to have tried almost everything over that time period, so I'm guessing they've at least experimented with a CVT.
Those who understand CVTs can stop here and answer. Those who aren't familiar with them can read on for my best effort description (I'm not an engineer).
A 1920s engineering book by two Fighting Illini professors describes two CVTs: one uses two pullies and a belt; the other uses two pullies and a chain. In both cases, the pully groove is V-shaped and the two V-shaped sides of the pulley (visualize two cones with points facing each other mounted on an axle) are widened and narrowed along the axle (without stopping an engine) to allow the belt or chain to slide up or down the radius of the pulley to vary mechanical advantage continuously, or infinitely, within an upper and lower limit. The CVT belt has a trapezoidal profile; the sides of which ride up and down the smooth, conical faces of the pulley as the cones of the pully widen or narrow. The CVT chain appears to have regular links with teeth on the sides that ride up and down the radially-grooved, conic faces of a pulley, thus allowing chain-bite up and down the pulley face as pulley cones widen and narrow and as radius of chain travel lengthens. Essentially, as the groove of the power pulley cones (imagine the chain wheel on a bike) widens, the radius the belt travels reduces; while the driving pulley cones (imagine the free wheel on a bike) are simultaneously narrowed to increase the radius the belt travels over it. Widening the power pulley groove (that is reducing the radius the belt travels over it) and narrowing the drive pulley groove (that is increasing the radius the belt travels over it) leads to lower "gears" for climbing. Reversing the process leads to higher "gears" for flat or descending surfaces. No change in the distance between power axle and drive axle themselves, which means it could sit fixed in a bike frame just like a chain ring/chain/derailleur/freewheel setup. In principle, no need for a tensioner either, but I wonder if one might be needed?
Regardless, both belt and chain CVTs seem simple enough, robust enough and possibly light enough (depending on materials), to have been tried on a bike by some innovator during the time period of the vintage lightweights on the CR list. No doubt there must have been some mechanical, linkage or materials disadvantage at the time of trial that prevented such a conceptually simple and inexpensive tranny from becoming widely used; otherwise, to paraphrase Chuck S, it would have proliferated. But if, and this is a big if, the problem were largely, oh, say, materials related, and if this problem were remedied, oh, say, recently, with alloys or composites (or by belt synthetics), there could after all these decades just have developed enough path dependent resistance to change based on manufacturers seeking to maintain existing proprietary and strategic market advantages to keep the CVT on the sideline. I apologize for being a bandwidth hog. Thanks in advance.
Don "how fast would Lance be, if he could continuously modulate gearing to topography to optimize O2 usage without a net gain in bike weight" Wilson Los Olivos, CA
D.C. Wilson 805.688.8696 dcwilson3@yahoo.com ----------------------------------------------------------- Note: This message may contain confidential and/or privileged information. If you are not the addressee or authorized to receive this for the addressee, you must not use, copy, disclose or take any action based on this message or any information herein. If you have received this message in error, please advise the sender immediately by reply e-mail and delete this message. Thank you for your cooperation. -------------------------------------------------------------
Take Yahoo! Mail with you! Check email on your mobile phone.
http://mobile.yahoo.com/