What is continuously variable transmission (CVT)?
23 August 2016
In the past, automobile manufacturers only offered drivers two types of transmissions:
manual transmission, which requires the driver to manually shift between the different gears of the transmission using the clutch pedal;
and automatic transmission, designed to carry out these shifts automatically.
Today, in addition to these two options, there’s also semi-automatic transmission, dual clutch transmission, and continuously variable transmission (CVT), which is becoming increasingly popular with automobile manufacturers.
The origins of continuously variable transmission
The first patent relating to CVT (or Continuously Variable Transmission) dates back to 1886 in Europe and 1935 in the United States. However, it wasn’t until the late 1980s that Subaru made the first attempts at integration. But it was finally on models from Honda and Toyota that its use became known to the general public at the end of the ‘90s.
Then, in 2003, Nissan became the first automobile manufacturer to produce it on a large scale.
CVT: how does it work?
Continuously variable transmission (CVT) has very little to do with its manual and automatic predecessors. In effect, it possesses two variable rotating pulleys connected by a belt. There’s therefore no gear or serrated wheel, as is the case in manual and automatic transmissions.
One of the pulleys is connected to the engine, and the other to the drive wheels. It’s therefore the belt (rubber or metal) connecting these two pulleys that’s used to perform the power transfer. This is where the principle of speed variation, which refers to the ability to continuously vary the engine’s gear ratio, comes from.
To return to the CVT operating mechanism, it should be mentioned that each of the pulleys consists of two mobile conical elements, one of which is variable. Depending on whether this variable element approaches or moves away from the other side, the belt also rises and descends. Based on the distance between the sides of the pulleys, the belt descends more or less near the centre and changes the engine’s ratio.
Generally speaking, a centrifugal device chooses the ratio based on the engine’s rotational speed. In other words, the faster the engine rotates, the more the gear ratio will tend to increase. And since the belt tends to position itself virtually anywhere depending on the movements of the cone, we’re therefore talking about “continuous variation” related to an “infinite” number of ratios.
The advantages of continuously variable transmission
The two main advantages of CVT will undoubtedly delight environmentalists: fuel economy and low CO2 emissions.
The proof of this is simple: since the engine automatically shifts to the most efficient ratio, it therefore continually operates in the optimal range. More efficient and economical, CVT makes gear shifting imperceptible. You can therefore enjoy a quiet, soundproof cabin when you’re driving, and some passengers will even be surprised by the gentleness of the engine.
It should be noted, however, that this peaceful condition is only possible if the driver doesn’t press too forcefully on the accelerator. This isn’t necessary, though, since you can accelerate smoothly and totally reliably thanks to the mechanism of this transmission.
Subaru models with continuously variable transmission
Continuously variable transmission (CVT) was introduced in most Subaru vehicles starting in 2010 under the name “Lineartronic.” In particular, you can find it in models such as the Subaru Crosstrek, Outback, Impreza, and Forester.