How do Continuously Variable Transmissions Work?
If you’re considering buying a new car — or maybe a used Ford, Saturn, or even a Subaru — you might have heard that the car has what is called CVT or a Continuously Variable Transmission. You get in for a test drive and puzzle over it. You’re driving — and you may be accelerating — but the car doesn’t feel like it is doing any of that. You step on the gas and you don’t get instant power. Instead, it seems to “ramp up.” You’re not sure what to think of it or why it works the way it does.
Why the Continuously Variable Transmission is Perplexing
We’ve all grown up with automatic or manual gear-driven transmissions in our cars, which is why the actions of the continuously variable transmission are so perplexing to some of us. The continuously variable transmission isn’t a new concept. Back in 1490, Leonardo Da Vinci drew what many people believe to be plans of the first continuously variable transmission. Years later in 1886, the first patent for a continuously variable transmission was filed and by 1958, it was introduced in cars.
The continuously variable transmission is perplexing to most drivers who have driven the standard gear transmissions because it has no gears. Instead of gears, it has two variable-sized pulleys connected by a belt. The pulleys are variable-sized as they have been machined in a cone shape, so the belt can move from the smallest end to the largest end seamlessly.
This set up allows the engine to transition to the optimal revs with the most power and the most torque. The downside is that there is more friction which can cause up to 15 percent energy loss (as opposed to just a 5 percent friction energy loss in a gear transmission). Another downside is that if the belts wear out in a CVT they cannot be repaired and the entire transmission has to be replaced.
How Continuously Variable Transmissions Work
One pulley is connected to the crankshaft and is called the “drive pulley.” The other pulley is connected to the rest of the transmission, which is called the “driven pulley.” As one pulley increases its radius, the other must decrease its radius to maintain the tension on the belt. Because the belt can move to the best possible “gear,” the continuously variable transmission has an infinite number of “gears.” When the drive pulley radius is small, you are in low gear. When the drive pulley radius is large, you are in high gear.
Why They’re Better than Gear Transmissions
Continuously variable transmissions are better because they are more fuel-efficient and they’re more effective at selecting the right power for the workload. They’re remarkably simple to operate, which makes them easier to repair. Of course, they take some getting used to. But if you are interested in getting the best possible power, consider a continuously variable transmission.