Is there a fuel economy gain with a CVT over a conventional automatic or manual transmission (all else being equal)? If so, how much?
I’ve had this up since yesterday hoping someone with knowledge would answer. It is my understanding that the best modern automatics and CVTs give you slightly better mileage than an expert using a manual, usually showing up on the window sticker estimates as about a 1 to 2 mpg increase, but rarely as much as 2.
I think, theoretically yes, because they should be able to maintain their most efficient power band across the speed variations.
Strange thing is, a lot of them are putting in electronic shift points to simulate a conventional gearbox. I assume their marketers have decided people want this, but it makes no sense to me. Case in point: I love a traditional manual, and when I had a chance to finally drive a paddle shifter, I was looking forward to it muchly. Turned out, I hated it. It felt redundant, and despite my manual prefeence, after a few miles, I just flicked this thing over to full automatic and had a much nicer drive from that point onward. So, if I had a CVT, I’d want all the benefits of a true CVT without some weird software messing about with it (sorry, I know this isn’t what you’re asking).
Traditional automatic gearboxes are yesterday’s technology. The losses involved with the torque convertor (or fluid flywheel) are considerable and new systems are much better fuel wise and maintenance wise.
There are several different types of CVT transmissions and the manufacturers will all claim that theirs is the best. Personally I think that a six speed box with electronic shift is the best solution. The Dog above didn’t like the paddle shift and switched to auto - that allowed the computer to take over, and it probably made better decisions than he (or most people) would. These are the gearboxes that European trucks use, although they usually have twelve speeds.
One of the big things is that in addition to just having infinitely close “gears” most CVTs have a maximum possible ratio that’s WAY steeper than what the top gear would normally be on a conventional automatic in the sorts of small cars CVTs usually come in. There’s no reason why they couldn’t, say, cram a 9-speed conventional auto with a super steep overdrive in a Nissan Sentra and get similar performance, but a CVT is cheaper and lighter.
That’s essentially why even conventional autos beat manuals these days. There’s still theoretically a very small efficiency advantage to a manual, but because they think people who buy manuals (in the US anyways) want “sportier” performance they tend to be geared lower than the automatics.
I have a Subaru with a CVT, and there are two obvious benefits, as mentioned. One, the transmission and computer can choose the optimal RPM for speed and economy at any given time, and not have to compromise by choosing a particular gear ratio. Two, the CVT allows the engine revs to drop down at relaxed throttle settings. My car has low engine revs while highway cruising, lower than one would expect from a traditional 5th or even 6th gear. I have no definitive support, but my guess is that a CVT might gain one or two MPG advantage in city driving, but probably several MPG on the highway.
Just an aside, I worked on an early CTV for Borg Warner in the mid-80s. One of the problems was it made test drivers uncomfortable. They wanted that jerk that you get with the changing gears. We actually had to program a slip into the control logic at certain intervals.
And then there is the planetary gear system in the Prius (and other models)
One gas engine to two motor / generators
Brian
Interesting.
Damned humans, always getting in the way of progress.