What is a CVT and how does it work?
Continuously variable transmissions (CVTs) are becoming increasingly widespread in the automotive industry. In fact, some automakers now swear by them for several of their models.
Although their use in North America dates back to the late 1980s with the Subaru Justy, the first hybrid models from Toyota and Honda in the mid-1990s followed suit, and Nissan really started the trend a decade later, CVTs are still a little misunderstood - and unloved - by some drivers. Let's try to shed some light on the subject without going into too much technical detail.
How does a CVT work?
Unlike automatic and manual gearboxes, the CVT has no toothed wheels, and therefore no gears that fit together to select the right gear. Instead, two variable pulleys are linked together by a belt, typically metal in the case of automobiles for durability and efficiency.
Each pulley has two cone-shaped moving sides, one of which is variable, i.e. it moves towards or away from the other side to raise or lower the belt. The "V" shape of the belt allows it to fit snugly around the pulley, for maximum adhesion. The pulley connected to the engine drives the second pulley, which is connected to the drive wheels.
Generally speaking, the ratio - or more precisely, the ratio - is selected by a centrifugal device, according to the engine's speed of rotation. In other words, the faster the motor turns, the higher the gear ratio. The two cone-shaped walls of each pulley allow the belt to be positioned almost anywhere, both for the pulley that transmits power and the one that redirects it to the drive wheels. This is why we speak of "continuous variation" and an "infinite" number of ratios (some people mistakenly claim that this type of transmission has only one gear).
What are the pros and cons?
The growing popularity of CVTs today demonstrates that their advantages are considerable, especially in terms of fuel economy and therefore reduced pollutant emissions. Firstly, because there are fewer moving parts, and the engine self-adjusts to the most efficient ratio, it operates continuously within the optimum revolution range, avoiding rapid ups and downs in revs. The result is more efficient, more fuel-efficient vehicle operation.
Secondly, the CVT eliminates the noticeable gear changes of the automatic transmission. Acceleration is smoother and more linear... provided the driver is gentle on the pedal. Under these conditions, the engine's optimized behavior allows you to enjoy a quieter cabin.
On the other hand, many drivers have complained of a sluggishness and lack of sportiness felt in CVT-equipped models, having the impression of driving a vehicle devoid of power and sound. The reality: the acceleration times observed are not very different from those with a manual or conventional automatic. In some cases, there's even an improvement of a few tenths of a second. That said, moderate and more sustained acceleration is accompanied by a buzzing sound that is annoying most of the time.
Another problem with the CVT is that its use is restricted to engines with smaller displacements and not too much torque. Because of the pulleys and belt, it's difficult to channel a lot of power without slipping. There is also a slight loss of engine braking compared to a conventional automatic transmission.
Nissan made a lot of headlines in the 2010s for the unreliability of its Xtronic gearbox in several models (a class action was authorized against the manufacturer), but things have settled down since then. Toyota, Subaru, Hyundai and Kia are brands that generally offer good transmissions of this type.
In short, the CVT is here to stay and even play a bigger role in vehicles. Carmakers are constantly improving it, for example by increasing the belt's durability, finding ways to simulate gear changes and making it compatible with higher-performance applications.
