Basic Continuously Variable Transmission explained with Legos

Tony Markovich

In recent years, the search for better fuel efficiency and smoother shifting has produced automatic transmissions with double-digit gears. Alternatively, the same quest has boosted the popularity and usage of a different type of automatic transmission without any fixed gears, the continuously variable transmission, or CVT. YouTuber Sariel's Lego Workshop recently took the time to build a CVT demonstration model out of Legos to help explain how they work.

Sariel begins by showing the model's input and output shafts that are parallel to each other. Each shaft has a cone attached to it, and they are inversely placed so that the large part of one cone is next to the small part of the other cone. The two cones are connected using a rounded rubber band. 

By shifting the rubber band up and down the cones, the machine changes the effective ratio between the cones. So, a 1:4 ratio can be smoothly transitioned to 4:1. No clutch is required to operate the mechanism, and it eliminates hitches or pauses between gear changes. CVTs are also advantageous over 9- or 10-speed automatics in that they are far less complex and weigh less. 

To demonstrate how the CVT operates in a vehicle, Sariel used a joke about Top Gear. The original Top Gear is represented by a faster-moving car that has the rubber band around the large part of the cone on the input shaft. Top Gear without former hosts Richard Hammond, Jeremy Clarkson, and James May is represented by a slow-moving car with the rubber band around the large part of the cone on the output shaft. 

For an even more detailed explanation of how CVTs work — albeit one that doesn't involve toys — you can click here.

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