A CVT is a continuously variable transmission, a type of automatic transmission that trades fixed-gear ratios for infinitely variable ratios courtesy of two pulleys and an intervening belt or chain. Dating back in the U.S. to the late 1980s, CVTs can offer benefits to fuel efficiency and, with the engine more often at optimal rpm (or revs), performance.
But it comes at a cost. With engine revs taking longer to catch up and often lingering at high rpm longer than they would with a traditional automatic, CVTs can make for noisy engine droning or the sensation of pulling a heavy object with a rubber band — you pull a while, then it catches up — as revs take too long to rise after you apply the gas.
In response to that, most automakers have adapted CVTs to behave more like traditional automatics under certain conditions. Most modern examples will hold a fixed ratio under hard acceleration to mimic the rise, momentary drop and rise again in revs that you’d expect from an automatic transmission upshifting gears. To mimic a downshift, many CVTs will expedite the rise in revs when driver input calls for passing power. And some, like the 2.0-liter Toyota Corolla’s Dynamic-Shift CVT, go so far as to employ a fixed-ratio 1st gear for more linearity between engine revs and acceleration as you start off.
It’s worth noting that such actions trade incremental fuel efficiency for consumer acceptance — CVTs are inherently efficient because they don’t have to adopt fixed ratios and can thus move more gradually between low rpm and high rpm — but overall fuel economy in any given car is the product of myriad systems. EPA fuel economy on the 2.0-liter Corolla’s CVT, for example, is terrific.
One final note: Automakers often market the transmissions for hybrids or plug-in hybrids as CVTs or electronic CVTs. In almost all modern cases, they’re technically not — such drivetrains employ electronic power-split devices, not belts and pulleys — but the outcome is similar. Such transmissions have infinitely variable ratios to behave much like a CVT. As such, we often call them CVT-style transmissions.
Of course, you shouldn’t confuse them with the fixed-gear automatics employed among some hybrids and plug-in hybrids; examples range from the Hyundai Sonata Hybrid (six-speed automatic) to the plug-in BMW X3 xDrive30e (eight-speed auto). There’s nothing CVT, in mechanics or style, about those.