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Simple CVT

 Never mind the cones and such
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My idea for a CVT is much simpler than the ones currently made. There are two pnumatic rubber tires in tandem with a belt that connects them together. On each side of the pnumatic wheel, there is a metal disk that is fixed in its place. To vary the ratio, the wheels are either inflated or deflated by a air pump. I'm not exactly sure how this is done, but i know that some cars have systems that can inflate or deflate their tires while the vehicle is in motion (the Hummer H1 has this feature, I'll look for a link). The difference in size depending on inflation is what causes the ratio to change. The fixed metal disks keep the pnumatic wheels expanding up rather than out.

(Sorry if I confused anyone by calling the pnumatic wheels "tires", since this would be an internal transmission and has nothing to do with varying the size of the driving wheels or tires.)

—acurafan07, Apr 15 2007

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       I like it, sorta, as it is at least different. But I think it's going to be like getting traction off a balloon, if it will really change the circumference of the tires.   

       There's going to be wrinkling in the sidewalls, and must be some folding in the tire tread area, or you aren't going to get any difference in circumference at all. I don't think it's going to work. But I'm not fishboning, for some reason.   

       The rotating inflation mechanism is trivial--it's been done.
—baconbrain, Apr 16 2007
   

       There are other ways to make variable diameter wheels. For example a spiral spring. You could probably also do it with a 'Hoberman Sphere' type expanding structure.
—xaviergisz, Apr 16 2007
   

       And a CVT is...?
—DrCurry, Apr 16 2007
   

       DrC, Google is your friend. Also, should be pretty obvious from the category.
—xaviergisz, Apr 16 2007
   

       The implementation of the two main types of CVT that have been mass produced has been quite complicated, but the basic idea isn't complicated in either case. I do rather wonder whether the implementation of this equally simple idea wouldn't turn out to be just as complicated.
—Cosh i Pi, Apr 16 2007
   

       Or maybe to cause it. CVJ for Constant Velocity Joint perhaps?
—Cosh i Pi, Apr 16 2007
   

       CV Joints have always been called CV Joints as far as I have known.
—jhomrighaus, Apr 16 2007
   

       Your tires are not going to change in diameter unless they are actually stretching.
—jhomrighaus, Apr 16 2007
   

       If they stretched would that compromise their durability/ wear them down quickly?
—acurafan07, Apr 16 2007
   

       I'm with baconbrain - I like the idea, though I don't think it will work in practice. I suspect that the flexibility needed to allow expansion will be incompatible with good and durable transmission.   

       I also think the idea would be better without the last edit - unless that part is better thought through and more clearly explained.
—MaxwellBuchanan, Apr 16 2007
   

       I'm pretty certain it could be made to work, but that it wouldn't be a practical solution to any real problem. Either the tyres would wear horribly quickly, or they wouldn't change diameter very much. I don't see it competing realistically with existing mechanisms.
—Cosh i Pi, Apr 16 2007
   

       I don't think it would be able to change diameters quickly enough either.
—BJS, Apr 16 2007
   

       Quickly enough for what application? The sliding pulley cheeks, driven by changes in air pressure, that change how high the belt rides in the pulleys on a DAF/Volvo CVT work quite fast enough.
—Cosh i Pi, Apr 17 2007
   

       Cool. I don't think there's a big change in circumference, though, so your total ratio spread isn't going to be very big. Oh, someone else mentioned it. Okay. You could conceivably compound two or more of these for a wider spread; having them all adjust simultaneously gives a more rapid response, too.   

       Traction of the belt on the tire shouldn't be a problem; my bandsaw blades never slip even in big wet wood. Just run bandsaw blades for your transmission belt.
—elhigh, Apr 17 2007
   

       Looked at them on google, wouldn't they chew through the pnumatic rubber wheels?
—acurafan07, Apr 17 2007
   

       The DAF/Volvo cars seem to do about 40 or 50 thousand miles to a pair of belts (they're big, wide, heavy belts though). The ratio spread is about the same as a typical mechanical four speed box.   

       They've got a pretty substantial steel belt inside them - a bandsaw blade wouldn't be nearly strong enough, and anyway wouldn't fit the conical surfaces of the pulley cheeks. The pulley cheeks are steel, not rubber.   

       The ratio control on the system is very good - they're always in the right "gear". The downside is that there's a lot of frictional loss - the gain in the engine always running in its sweet spot doesn't make up for it, not by a long way. Very nice to drive, though.   

       The inflatable design would need a different grade of rubber, and yes, I think the rubber would wear very quickly unless the whole thing was only transmitting very little power.
—Cosh i Pi, Apr 17 2007
   


 

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