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Purely mechanical system to give a continuously variable gear ratio 3

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Nemesis4

Nemesis4

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Jul 8, 2009
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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.
 
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I think an ideal variable gear system must be able to operate in both directions through the "gearbox" - with the reverse direction being the inverse ratio as with conventional gear sets. Once again with pushbikes, they usually freewheel on the overrun so ratchet-type arrangements would be OK.
 
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Oh, who made the double-cone tension belt CVT with radially grooved pulleys, and laminar teeth projecting from the belt? That was in production for a long time, I think.

The BYU papers are nicely done. Too bad there wasn't time to actually make something and test it to destruction.

Scrap paper is a less satisfactory measure of intellectual progress than is scrap metal.







Mike Halloran
Pembroke Pines, FL, USA
 
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The distinction "POSITIVE DRIVE" is a bit of a red herring, there are millions of mechanical drives that rely on friction, there are few mechanical ones that would work in the presence of 'cogging' only.

The reason for that is that no slip is a bit of a tough call during engagement.

So, the requirement is BS, hence no answer can be satisfactory.

Cheers

Greg Locock

SIG:please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
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GregLocock - could you further explain what you mean in your last posting? Is the "no slip" you refer to the slight amount of sliding (as opposed to rolling action) that occurs when two gear teeth engage?
 
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so, just for clarity, this post is all about whether making continuously variable "positively engaged" transmissions for on-highway motorized vehicles in the USA and meeting the current set of regulations for such is a theoretical/physical impossibility?

Seems like the simple answer is no, it's not a physical impossibility. Why the ongoing prodding?

...or were we supposed to read through each of the theses and provide some kind of specific feedback about the approaches they propose?
 
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Ivymike - Thank you, that does just about sum up what I was originally asking.
However, my simple answer would be that it is highly likely that it is a theoretical/physical impossibility - so we have slightly different points of view.
Positive engagement continuously variable transmissions ("PECVT's" to those in this specialised field) don't exist now, have never existed and may never exist. This is something of a sweeping statement but I suspect it is true.

Yes, I would very much like somebody to read through the theses and provide specific comment and feedback (they are all on a similar theme and develop the idea from one thesis to the next). I realize they are very heavy going to read but I would like to know what people think - and I suspect that the people at BYU would also like to see some feedback etc.
 
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Are the people at BYU needing feedback the authors of the papers?

Shouldn't the "committee" and the authors' peers be providing such feedback?

Or is the "committee" requesting feedback from this group, so as to offer some insight to the authors of the papers?

or are we fishing for something to "defend" our thesis?
 
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Yes, it does seem to be something of an 'academic exercise'.

How does your theoretical device handle moving off from a standing start while retaining positive engagment? It almost certainly relies on relative motion between a moving part and a stationary part somewhere, otherwise you could call it a Zeno transmission.




Cheers

Greg Locock

SIG:please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
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I have no connection whatsoever with BYU, not being a Mormon and living on a different continent. I was trying to draw out some specialised comment on the variable gear subject from engineers who have worked in the theoretical PECVT field (and there are some). But it doesn't look like it is going to happen - the engineers in question either don't read this forum or are secretive about their work.
It is probably best if I don't reveal whose Nemesis I am - the other three met their demise, I'm afraid.
 
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I don't think there is a non-friction-reliant drivetrain for a motor vehicle in existence, save for a handful of odd circle track parts that either have splines in the clutch, or have the clutch mounted in the transmission so that top gear bypasses it.



 
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GregLocock - On the question of moving away from a standing start - any continuous gear ratio range can be arranged by overall biasing to have an infinitely low (1:0) starting ratio. It can even be arranged so that the ratio range is from negative values (reverse direction that would be), through zero speed and into positive values.
However I don't think any of the commercially available automotive CVTs are arranged like this though - I think DAF used a centrifugal clutch for starting and others have fluid couplings etc. The infinitely low (1:0) ratio can also produce (theoretically) infinitely large amounts of output torque, so if the output was locked for any reason something would self-destruct. In some circles, the 1:0 ratio is referred to (perhaps somewhat cutely) as an "engaged neutral".
 
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... engineers who have worked in the theoretical PECVT field ...
Click to expand...

Perhaps you'd ought to call up the authors of the theses you wrote. I'm sure they've gone on to become engineers. I'm not sure you'll find many "real" engineers working on academic problems. There are always the few that work on researchy stuff in the backwaters of big companies, but the only products that see the light of day are the ones driven by a business case and a list of customer benefits. The EIEIO transmision seems to lack both.
 
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How can infinitely high torque break anything if there is zero motion.

I think a lot of circle track guys stll use a dog clutch and a push start.

All automotive drive systems come down to friction at the road interface unless you are talking about rack and pinion drives or tyres with spikes for use on ice.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
 
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