Love them or hate them, most of us still don’t quite comprehend how a continuously variable transmission actually (CVT) converts the engine’s rotation into drive. Witchcraft or the dark arts have been floated but as it remains, the only consistent aspect was the floaty feeling of those transmissions.
Petrolheads despise it but performance was never its primary objective. Efficiency was its birthright. You’ll always hear how CVTs have a near-infinite number of gear ratios that allow the engine to operate at a low RPM to make the most of every drop of fuel.
Driving hard with it can be a pain often described as equal to being kicked between the legs. Slow throttle response and that droning exhaust note that’s become synonymous with it are among the reasons for its persecution.
However, CVTs are pure engineering genius and if you’re going to hate on it, at least have the decency to understand its workings. Don’t hate what you don’t get.
Granted, our understanding of it was a little clouted as well but this simple explanation by Sariel’s Lego Workshop channel on YouTube perfectly illustrates how it rolls; pun intended.
CVTs work by running a metal or rubber band between to two cones serving as pulleys. One cone pulley is rotated by the engine and the other drives the wheels. As both diameters can be adjusted on the fly, the CVT can create an infinite number of ratios to maximise efficiency.
Sariel created a CVT based on its simplest mechanics from Lego bits and proceeds to demonstrate how the cone pulleys moving to change the ratio affects speed between 1:4 (speed x 4, torque / 4) to 4:1 (speed / 4, torque x 4).
In layman’s terms, that’s the engine output cone pulley spinning four times to turn the drive cone pully once. On the other end, the drive cone pulley four times with a single revolution. Everything in between is game.
Every single piece used in the build is from Lego, including that special rounded rubber band that makes it easier to slide between among the cone pulleys. Sariel also goes on to demonstrate an inherent weakness of a CVT; its inability to handle a tonne of torque. The video mentions that a toothed band would help for his Lego CVT but even in real life, torque is the arch nemesis of this transmission.
This very torque limitation has kept CVTs out of heavy-duty applications such as commercial trucks. Nonetheless, the Williams F1 team did test a CVT in its Renault-powered FW15 Formula 1 car but it never raced because the FIA banned CVTs.
Maybe even the FIA knew how despised CVTs would be.