I was riding in a car recently and noticed the engine speed changing fairly erratically - first from the sound, then from the tachometer. The owner of the car, who was driving, told me that this is because it was equipped with a CVT, and it had done this forever - since the test drive and in the years he’s owned it.
Now, it seems to me the point of the CVT is to allow the engine to operate close to its most efficient speed all the time - a discrete transmission has the same job, but coarser resolution in the engine speed to wheel speed mapping. But surely wild, continual fluctuations in engine speed aren’t especially efficient?
Why do cars with CVTs experience these swings in RPM? Is there some ambiguity in the control system?