What is a Continuously Variable Transmission? – Pros & Cons

A continuously variable transmission (CVT) is a type of automatic transmission that can provide smooth, stepless gear ratio changes using two pulleys that are connected by a steel band.

Instead of using 6 to 9 fixed gears like a traditional automatic transmission, the diameter of the pulleys adjusts constantly depending on the driving situation to provide the optimal gear ratio and power to the wheels.

It may also be referred to as a stepless, single-speed or pulley transmission.

In This Guide

Why CVTs?

One way to improve a vehicle’s fuel efficiency is to manage engine speed (RPMs). The higher they go, the more gas an engine will consume.

Maintaining the optimum engine speed with the limited number of gear ratios available in a traditional automatic transmission can be a bit difficult, which is one of the reasons why manufacturers are exploring the use of CVTs.

Automatic vs. CVT Transmissions

Traditional automatic transmissions use a set of gears that reduce RPMs at certain fixed intervals (typically 6 to 9 gear ratios or “speeds”) as the vehicle speeds up. The gears change in relation to throttle input and vehicle speed.

A CVT on the other hand, uses a single steel band that can be adjusted to an infinite number of gear ratios by a set of pulleys. This allows the vehicle’s computer to instantly change the position of the band so that the engine consumes as little fuel as possible.

How Does a CVT Work?

cvt_eplanationNo matter how many forward gears it has, a conventional automatic transmission won’t be able to shift to a higher gear and reduce the engine speed, until the predetermined RPM and/or vehicle speed are reached.

This shift logic/programming is designed to respond to a driver’s throttle input. That way the transmission can maintain lower gears during acceleration, then upshift to save fuel once the driver reduces pressure on the gas pedal (low gears = rapid acceleration / high gears = low RPM cruising).

These constant up/down RPM changes allow the vehicle to gain momentum, but running at a consistent engine speed would be far more efficient.

Cvt_list01The beauty of CVT is that its computer can instantly calculate the ideal engine speed for any situation, then adjust the transmission gear ratio to hold that RPM until it needs to change.

So for example, if you stab the throttle when the light turns green, the engine in your Nissan Altima or Toyota Corolla (for example), will immediately jump to 5000 rpm and stay there until you let off the gas. Then it’ll drop back to a cruising speed of around 1800 rpm, because the CVT has adjusted itself to an Overdrive ratio.

This saves fuel by instantly switching from the engine’s high-RPM power band to a low-RPM cruising ratio, with no gas-burning stops in between.

To make all of this possible, it uses a flexible steel band/belt that’s suspended between two pulleys. One of these adjustable cone pulleys is connected to an input shaft from the engine, and the other one lives on the output shaft which sends power out to the wheels.

The two cone-shaped sides of each pulley can be pushed in-and-out by the computer, using highly pressurized CVT transmission fluid. As the two ends spread apart, the V-shaped CVT band slides down into the pulley to create a higher gear ratio and reduce engine speed. Conversely, as the two ends draw together, you’ll get a lower gear ratio and be able to attain more speed.

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Pros & Cons of a CVT Transmission

Thanks to its innovative design, a CVT can achieve a near-infinite number of gear ratios, which allows the computer to keep the engine running efficiently in all situations. This makes it the ideal transmission for hybrids like the Toyota Prius.

However, recent design and software advancements have allowed CVTs to be adapted to conventional gas-powered economy cars like the Toyota Corolla and Honda Civic, full size crossovers like the Nissan Pathfinder, powerful luxury cars like the Audi A4 V6, and even sports cars like the Subaru WRX.

Like all choices in life, the CVT has definite advantages and drawbacks. Let’s take a look at few:

Advantages of a CVT Transmission

Exceptional fuel economy
Because of its infinite, instantaneous adjustability, the CVT can increase fuel economy by keeping the engine RPMs low and constant, whenever possible. The vehicle’s computer can lower the gear ratio to suit changing road conditions, then return to a fuel-sipping OD ratio as soon as conditions allow.

Smooth operation
Since there’s no gears to change, you won’t get that constant ‘bumping’ through the gears, or those endless up/down engine RPM surges. It is designed to keep the engine turning at a consistent speed. So you’ll have a smoother ride, and no more of that ‘jerking’ as you accelerate.

Lower initial cost
Unlike a conventional automatic transmission, it takes fewer moving parts to build a CVT. This helps manufacturers to keep their production costs low, which is one reason they’re becoming the go-to transmission for fuel-sipping economy cars.

Disadvantages of a CVT Transmission

They can be hard to get used to
For the uninitiated, a Continuously Variable Transmission is going to take a bit of getting used to. First of all, they are designed to keep the motor humming at a constant RPM, so you’ll have to ‘tune out’ the appliance-like engine sound (or you could just turn the radio up).

There’s also no perceivable gear changes. And when you combine that audible/tactile disconnect, with the constant thrumming of the engine, it can feel a bit like a transmission that’s either slipping or stuck in a low gear.

Hesitant power delivery
When you stomp on the gas, and essentially ask your CVT to downshift, the power delivery may not feel quite right. On a conventional automatic, clutch packs will clank together as the transmission shifts down, the RPMs spike, and you’re suddenly hurled forward.

On a CVT transmission, those pulleys have to squeeze together in order to create a lower ratio, and there may be a brief pause in acceleration as the CVT belt or band adjusts itself. Many automakers offer software updates to lessen this “rubber band” effect. But most CVT owners just learn to plan their moves in advance.

Repairs can be costly
Even though a CVT has fewer components than a traditional automatic transmission, those parts can be rather costly to replace. The most common CVT transmission problems have to do with fluid pressure control, software glitches, and CVT Band replacement / CVT Belt replacement (these can last 60,000 to 150,000 miles, depending on the manufacturer).

It takes special training to be able to perform CVT transmission repairs, so parts and labor may be rather expensive. So if you’re planning to buy a vehicle that has a Continuously Variable Transmission, you may want to find a transmission shop that’s qualified to do CVT transmission repair.

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Over to You

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1 thought on “What is a Continuously Variable Transmission? – Pros & Cons

  1. My Nissan Rogue 2011 recently had its Valve body ass’y replaced along with the transmission cooler at a cost to me, although Nissan allegedly paid for a portion of that overall cost. The problem I have before the above took place and now as before will not shift to a higher ratio from a stand still. RPMs reach nearly 5,000 RPMs and still not change UNLESS I remove foot from gas pedal for a second or two at which time the RPMs drop and gear ration changes into what feels like normal operation. Could it be the Transmission Computer Module or TCM, as it may be called.

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