GreenPlease wrote:
Basically, we're talking about something like this for both the front and rear:
http://www.wavetransmission.com As the front expanded the rear would contract and vice versa. The chain line would be perfectly straight and chain tension would be constant. This is not fundamentally different than the CVT arrangement you suggest. The only real difference is that chains are way more efficient than belts!
Just estimating from information gleaned from various patents (expandable chainrings are a surprisingly old idea!) a 400% gear range should be possible.
My experience with CVT's is with mechanical plant in air conditioning applications. Static pulleys need to be swapped out to change fan speed (for example). And pulleys only come in specific sizes so the possible fan speeds are stepped, much like the cassettes we have on our bikes. Before the common usage of VSD's (variable speed drives) that change the driving motor speed, to affect a speed change in the fan, there were adjustable pulleys. You could either adjust a manual set of pulleys to provide the one constant speed you needed, or alternatively, have adjustable in motion pulleys that could open and close the pulleys, resulting in changing the effective diameter of the DriveR and DriveN pulleys, to change the speed of the fan, with a constant motor speed. With the advent of VSD's adjustable in motion pulleys have gone out of favour. Given the cost of air conditioning energy consumption and the near universal use of V-Belts in the past, I'd assumed the efficiency was at least reasonable. I'd have to go back to my notes (which I can't be bothered doing) to confirm the actual losses.
While the changing chainring diameter you have, with a chain, has efficiency benefits (I think) it still has a stepped approach and off the top of my head, I'm thinking that might be somewhat limiting. It is intriguing however. I need to think more about this.
Thanks for the link. It's certainly cool
TriDork
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