This strategy helps our chain maintain a fixed length through eight gear combinations. We’ll set it up so that the biggest front sprocket works only with the smallest rear sprocket, with similar one-to-one private relationships all the way across the gearsets. Now place the same gearset at the pedals, but flip it around. There’s a smallest sprocket and a biggest sprocket, with six in between. Think of a bicycle with numerous gears - let’s say eight of them on the rear wheel. There’s still CVT action going on at a detail level, but such examples can create a more lively and familiar experience - albeit at some cost in fuel economy. This is why many newer CVTs artificially create stepped gear changes - usually in a "Sport" driving mode, but sometimes in normal operation. The car can sound like it's perpetually stuck in a low gear. However, many have found the lack of traditional gear changes to be disagreeably odd, especially aggressive drivers who are more likely to run the engine hard. Many drivers won’t care because that tendency isn’t as noticeable when a vehicle is being driven in a normal, relaxed manner. We’re all used to a steadily rising engine note that’s punctuated by shifts, but that's largely absent with CVT powertrains since they tend to keep the rpm steady and alter the gearing instead. The main drawback that remains is one of perception and emotion, because a CVT changes how an engine sounds and a powertrain responds under acceleration. But control strategies have improved immeasurably in the 10-plus years they’ve been widely used, and further enhancements have come as engines and passenger compartments have been re-optimized with a CVT in mind. And of course the degree to which a CVT lives up to the potential described above is only as good as the software that controls it. The engine can drone if the exhaust system and cabin noise suppression features aren’t designed right. Fuel efficiency and grade drivability are theoretically at their maximum with infinitely variable gears, and there’s no need for a torque converter to guarantee shift smoothness. An infinite gear count means no steps at all, which is why CVTs are sometimes called “stepless” transmissions. The presence of smaller steps also reduces the need for a slushy torque converter, a generally inefficient, power-robbing device that smooths what would otherwise be jarring shift-shock at each gear change.Ī CVT maximizes the potential of this concept. Likewise, more gears reduces the likelihood of back-and-forth dithering on grades because smaller steps keep the engine closer to its sweet spot in terms of power and torque. Fuel economy improves because the engine is more likely to be operating at its most efficient rpm. The obvious endpoint to this trend is infinite speeds, and that’s what a CVT offers.Ī higher gear count reduces the size of the steps between adjacent gears, and that has several benefits. Each successive change improved fuel economy and drivability, and so the trend continued on up through the numbers to the point where most current automatics generally have eight, nine or even 11 speeds. The first automatic transmissions were two-speed automatics, and these were quickly replaced by three-speed and then four-speed automatics. It boils down to fuel economy and having the right "gear" at the right time. Those who expect or prefer a stepped series of gear changes therefore tend to dislike CVT powertrains. However, this makes CVT-equipped powertrains sound fundamentally different because the engine speed tends to remain steady as the transmission continuously and seamlessly alters its gearing to make the car accelerate. Doing so allows the engine to run at its most efficient rpm for the vehicle speed, road grade or load condition that’s present at any given time. What is a CVT? What they do, why they do it, why people don't like them and how they workĬVT stands for Continuously Variable Transmission, a type of automatic transmission that lacks a set number of gears or “speeds.” Instead, this type of automatic can vary the gear ratio infinitely between its lowest starting ratio and highest cruising ratio.
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