Pros and Cons of a CVT Transmission
An increasing number of vehicles today come equipped with what is known as a continuously variable transmission (CVT) rather than a traditional automatic. What seems like a revolutionary idea has actually been used in passenger vehicles since the late eighties, but the technology is new to a lot of auto owners. But what is a CVT? And what are the pluses and minuses of owning one?
What is a CVT?
A transmission is tasked with delivering the rotational power, or torque, from the engine to the wheels. Most drivers are familiar with one of two types of transmission, a manual (stick shift) transmission, and an automatic. In each case, a collection of gears engage to maximize the engine’s power at a given speed.
To accommodate a wide range of speeds, and to deliver maximum torque when driving on a steep incline or pulling a heavy load, the transmission needs to be able to change the gear sizes, or ratios. With a manual transmission, you select the various gears manually, thus, the name. With an automatic, the transmission does the selecting for you. Either way, low gears offer lots of torque at low speeds and high gears enable your vehicle to attain high speeds. As you accelerate, gears change (or you change them) from low to high, and as you decelerate they shift back downward, assisting your brakes to slow the vehicle.
But a continuously variable transmission is different. There are no gears in a CVT. Rather, this type of transmission relies on two variable-width pulleys, one on the engine side and the other on the drive side, connected by a flexible belt. As the engine speed increases, the width of the pulleys change. One gets larger and the other gets smaller, essentially changing the power ratio between the two of them.
Think of it this way. A conventional automatic (or a manual) transmission with gears is like a bicycle with multiple gears. When you start off on your bike, you begin with low gears. This allows minimum effort from your legs to get the bike going with maximum torque. But the low gears do not allow you to move very quickly. So, you shift to increasingly higher gears as you speed up. That way your legs do not have to pedal so fast. When it is time to slow down, you downshift to lower gears once again. That is what usually happens with a car transmission, automatic or manual.
A CVT is not like a bicycle at all. It is more like a snowmobile or a minibike with one pulley on the engine and the other attached to the track (or rear wheel on the minibike). When you take off, the engine pulley is at its smallest size; the driven pulley is at its largest. As engine speed increases, the pulleys begin to trade sizes, in the way the bike does with its gears, but without actually shifting anything. The transition is smooth and infinite. This allows for seamless acceleration. While other forms of CVT exist, this concept is by far the most common.
Pros of using a CVT
There are several advantages to using this type of transmission. First of all, a CVT can transfer maximum power from a small engine for quicker and more responsive acceleration. That is why automakers include them in vehicles with four-cylinder engines.
A CVT also eliminates that uncomfortable jolt from an abrupt downshift that happens when you mash on the gas pedal when you pass another vehicle. Same thing when you are climbing hills, where a conventional automatic might “search” for the right gear, or a stick shift might get bogged down with a gear that is too high.
In terms of fuel economy, a CVT beats both its automatic cousin and a manual transmission. The transmission is programmed to always be in the right “gear”, with the engine speed matched to the travel speed and in the optimum power band. And highway speeds are possible at low engine rpms. CVTs are also of a simpler construction than other transmissions, with fewer mechanical parts, making them lighter weight.
Because of their relative simplicity, CVTs also cost less to produce, another appealing aspect to both manufacturers and car buyers.
The cons of CVT
Unfortunately, the lower production cost does not boil down to lower repair or maintenance costs. As with your timing belt or serpentine belt, the belt in your CVT can stretch and fail. If a CVT transmission goes bad (depending on the manufacturer, this can be rare or commonplace), it is just as expensive to repair or replace as any other automatic transmission, and can cost more.
A common complaint of drivers new to the experience of a CVT is that it (in some cases) produces a sort of whining sound, almost as if the transmission is slipping. It takes some time to get used to the sound of a CVT. Another grievance is the high, droning sound the transmission makes as it is winding up during acceleration. Because it is maintaining the optimum power band from the engine, rpms can remain higher than if the transmission was repeatedly shifting from gear to gear and the rpms rise and fall.
Some drivers have a tough time adjusting to the lack of shifting. Because they are used to feeling the transmission shift, they miss the sensation. A CVT does remove some of the “performance” feel from the ride. It is not very sporty. Knowing this, some manufacturers even program the powertrain computer to designate set acceleration points in the system to mimic the feeling of shifting gears. Manual “shifting” is also possible with this arrangement.
Seeing as they are becoming more popular, it would seem that the pros outweigh the cons. CVTs seem to be here to stay as more and more cars and SUVs come equipped with the new, not-so-new technology.
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