An idea I had at work

[pimpin4profits]

ok, theres one thing I'm not getting here still. On a cvt is there like and Economy and Performance selector or something, like instead of the standard 1,2,3,D? So would it be like P,R,N,P,E? Thanks for explaining this to me, I haven't read much on these trannys.

[911GT2]

Maranello, think of a CVT as two cone shaped gears connected by a chain or belt. The belt or chain can move infintely up each gear, creating an almost inifinite range of useful gear ratios.

And they can be tuned to either boost performance (staying at max power RPM all the time) or bost economy (staying at max fuel economy RPM all the time). The only disadvantages of a CVT are the inability to adapt to different drive systems (such as AWD) and the inability to handle large amounts of power or torque.

[FenrisOIF]

Well, if you dig REEAAL deep into the patent office website, you'll find that about every major car manufacturer in the world is currently trying to develope a practical CVT. Some of those patents are under the name of that actual company, others by their subsidieries. One I found is patented to Timken, a bearing company that supplies a LOT of stuff to Ford, so do the math.

Truth is, as has already been discussed, they're only any good at really low power applications in the form they are right now. Most of them revolve around two pulleys that, in one way or another, vary their sizes to change the ratio between them. There's at least a dozen different forms of that particular setup, and they all have wear and slip issues. Ford recently publicized an effort to develop one that uses a beefed up chain in between a series of pullies, but I don't think it's working out. It's just too big for practical use, the smallest thing Ford could put it in is the F-250. The smaller ones are practical for transverse mounted engines because the pulley type CVT is very large in diameter, but very short. Again, though, it wont accept large amounts of power because the belt slips and wears out.

Other attempts are based on geometric shapes: discs, bell-shaped devises, and cones. The one I found that seemed the most promising used a pair of cones with a wheel in between them. The cones moved back and forth with the weel in place to change the ratio, but it stated right in the patent that it didn't work due to vibration problems. I know all of this because I'm currently trying to begin the patent process on a completely different setup (or at least as far as I know so far). My buddy and I have been thinking through all the bugs in it for about 2 years now, and have a working model, but patents are expensive and time-consuming. And being stuck out here in the middle of Iraq isn't helping move things along any.

Anyway, the theory is still the same, and the origional post had it right: the idea is that when you want to accelerate that the CVT will downshift untill you reach max-output on the engine, then upshift continuously throughout the acceleration, keeping at that exact RPM. Then, when you've reached the speed you want, it upshifts to the ratio that will render maximum efficiency. If/when it works out, it'll be an absolute breakthrough in both performance and efficiency. We'll just have to wait to see who wins the race to be the first to make it work in a sports car like a Mustang or Corvette.

[foureyedbuzzard]

Similar stuff has existed for industrial applications for years. As others have stated these involve changing the pitch diameters of the drive and driven pulleys. The other method is to use hydraulics with bent axis pumps and motors. Yet another is using power electonics. The problem is is that just because you operate the engine at peak efficiency doesn't mean its economical. There are many times you don't need the power. This is where flywheel, hydraulic, battery, and other storage devices come into play when designing a system built around a power source running at one setting.

[bjdm151]

Dude,

This post is like four years old,

[curtis73]

CVTs have been around for a while. Subaru Justys had them in the 80s. I drove one and it was powerless (but that was the fault of the 1.5L four)

It is just as described. The justy CVT used belts and conical pulleys. Based on the position of your right foot and engine speed, the drive pulley changed the position of the belt - effectively changing the ratios on a sliding rate. The acclerator (in addition to opening the throttle) controlled where the pulleys were. If you put your foot to the floor, the justy would rev to 4000, and the transmission would adjust the cones as you acclerated to keep the same RPM. Then when you back off the acclerator, it "shifts" up to a higher ratio seamlessly. It still transfers power, just that the cones are now adjusted for 1500 rpms.