As most of us know by now, the CVT is no longer a rarely-seen Dutch unicorn, like a discarded Vermeer or an Amsterdam sex worker in Nashville. They're becoming the norm on many cars, and in many ways they're much better than the slushboxes they replace. Even so, it's still worth asking: could you have a manual one?
Even asking the question itself is pretty loaded; a poster on a Subaru Impreza owners' forum who asked the question was asked if he was stoned as the first response. But it's really not that terrible a question. I mean, it's a pretty sure thing that the end result wouldn't be very good, at least not compared to the computer-controlled CVTs we have today, but I think the end result could be sort of fun.
There's no real reason a CVT's gear (well, pulley or chain, to be technical) ratios couldn't be changed with a human arm instead of the car itself. The very first CVTs in any real production, DAF's Variomatic, used a combination of engine speed and manifold vacuum to slide those belts on those cones to change ratios. I think we could do it with a lever.
It's important to keep in mind that a manual-controlled CVT is very likely to kill almost every positive quality of CVTs (keeping engine at optimal revs, automatic shifting for those who like that sort of thing), and that this is likely not technically a good idea.
Here's how I'd propose implementing a manual CVT transmission, in the most crudely, simplistic way possible: shift the belts with a lever.
CVTs work, fundamentally, by sliding belts (or nowadays, fancy sleek chains) up and down cones so that they effectively increase (towards base of cone) or decrease (towards top of cone) the diameter of the belt's pulley, which adjusts the ratio of the entire system. So, at the big end of the cone the engine spins faster than the output for very low gearing, and at he small end of the cone the output spins as fast or faster than the engine.
The gear-range-selection lever would be connected to a pair of pulleys that would either push together or separate the drive cones, adjusting the gearing ratio as they do. In my very simplistic setup here, low range would be toward the back of the car, and high toward the front.
A fully realized system would, of course, use a much more sophisticated linkage, and would not need a horseshoe-shaped handle, though I always thought those looked cool. You'd likely want some sort of resistance on the lever or in the system somewhere to keep pressure on the belt to hold its location and keep it from sliding down onto the apex of the cone.
So what would this be like to drive? I've been running little thought-experiments in my head, and while most of the results are inconclusive, I think it's pretty safe to say it would be weird. But likely fun.
You'd start with the lever all the way back in L, and as you gave the car more throttle, you'd smoothly slide the lever up to H. If you wanted to downshift, say, as you enter a turn, you'd slide that lever back a bit and get back on the throttle. Exiting a highway off-ramp, you could get it all the way to H pretty quickly, and you could yank it back a bit if you needed to pass.
Your right arm (left in Japan, UK, Australia, India, etc) would be kept pretty busy. I don't think constant adjustment would be needed, but for maximum efficiency, the more you used the CVT to keep the engine in its sweet spot, rev-wise, the better off you'd be.
You'd have infinite gears to play with, sure, but you'd be free to treat the shifter in the same way Subaru does when they fake gear shifts, and just hit 4 or 6 key locations, treating it like a sort of linear manual shifter.
Oh, and much like an old DAF, a car with a manual CVT should be able to go in reverse as fast as forwards, so that should help getting either parking spots quickly or your car upside down equally quickly.
Is all this a good idea? Probably not. Would I like to try driving a car like this? Hell yes. Plus, think about the wonders it would do for movies like the Fast and Furious series — with an infinite number of gears, all those constant and dramatic gear changes would finally make sense.
What do you guys think? Am I still an idiot, or perhaps ever so slightly less of one?