Purely mechanical system to give a continuously variable gear ratio 3

[Nemesis4]

I would have thought this subject would be a FAQ - but apparently not. I have always wondered if an "infinitely variable gear" is possible. I am not referring to any of the currently commercially available CVTs etc. but a constantly engaged, positive drive, all teeth and chains (or whatever) system. I far as I can tell this has been an unsolved problem for at least 500 years. I have found personally that most engineers (in the transmission business) are reluctant to speculate at all - I think there is more than a touch of "pseudo science" and "wild-eyed inventors" about the subject. What is the general opinion on the subject?
I notice that currently the Mechanical Engineering department at Brigham Young University is making a major effort in this area. I think you would have to regard BYU as distinctly non "wild-eyed". There have been successive MSc. theses from Brian Andersen, Ryan Dalling and Levi Haupt (all these theses can be read on the internet).
This is all very high-powered academic stuff and they seem to think that they have solved the age-old variable gear problem. Needless to say, none of it makes a lot of sense to me and I remain unconvinced. I would also like opinions on these three theses. Thank you in advance.

 

[MikeHalloran]

If you extend the stepped tooth cone idea to a large number of steps, you basically end up with a conical wire brush. ... which could mate to an identical brush pointed the other way via an internally toothed ring with an arbitrary number of teeth, or a similar brush, moved axially to change the ratio. I wouldn't expect particularly good power density or efficiency or life, but it's theoretically possible.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

I just wonder about the semantics here.

Infinitely variable implies no upper or lower limits.

I think everything being described has a limit on one end so we really mean seamlessly variable within yada yada yada limits.

Regards
Pat
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[evelrod]

I've been lurking around trying to make sense of "most" of this thread...Not doing all that well at it, either.

From the OP I get the need for an purely mechanical IVT with zero slippage...Hmmmmm? If I have it right, you want an automotive application whereby the engine is running and the car is standing still with the drive positively engaged with no slip....That brings up some really serious issues, hey?

Rod

 

[GregLocock]

Nah, you just need a really big flywheel.

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

 

[tbuelna]

evelrod,

Although it is not a "purely mechanical IVT with zero slip", the Torotrak IVT (with its geared neutral architecture) actually can be fully engaged while the vehicle is stopped. It can also creep forward and backward without any shifting.

http://www.torotrak.com/automotive/benauto

Regards,
Terry

 

[YvesLLewelyn]

I have just come across this very long thread. I am a bit surprised that some people are puzzled by (or don't believe at all) the concept of a zero gear speed changing to very low ratios in either direction. This is just standard gear train manipulation.
Also surprising are the people who think that there is no practical application for such things. You could probably argue this point when it comes to cars (I don't like CVTs either or even 4 or more speed automatics) but there would be an enormous market for a zero to 1:1 continuous range transmission in the heavy truck industry. If you have driven (or attempted to drive) a truck with a 15 speed Roadranger non-synchro gearbox you may agree. I think that the RR gearbox is one of the most diabolical and awkward (and dangerous for a novice) devices known to mankind.
This is besides the point that such a mechanical variable box is probably not possible let alone one that would survive in a heavy truck.

 

[ivymike]

well, read the above again, and you'll find that the discussion was (smoewhat secretly) targeted toward cars.