CVT gearbox: how it works and how the hybrid e-CVT differs

• A CVT gearbox has no fixed gears. The ratio changes continuously: a steel belt or chain runs between two conical pulleys whose effective diameter varies.
• Steady high revs when accelerating are normal for a CVT and aren't a sign of slipping. Simulated gears, such as those of the Nissan Qashqai III with the Xtronic gearbox, add a sense of shifting.
• Toyota's hybrid e-CVT isn't a belt CVT. It consists of a planetary gearset and two motor-generators, with no belt or pulleys.
• A CVT suits relaxed driving and town traffic and helps keep fuel consumption low. It's less suited to sporty driving and frequent towing of heavy trailers.
• In a used car, the condition of the gearbox is revealed by diagnostics and a test drive. Both are part of the CarAudit™ inspection that Carvago carries out on every car it sells.

The CVT gearbox is one of those automatics that often catch drivers off guard on their first drive. The car accelerates, but the engine stays at the same revs and there's no gear change to be heard. On top of that, alongside the abbreviation CVT, ads also feature the similar-looking label e-CVT, which hides entirely different technology. If you can tell these designs apart, you'll know what behaviour is normal for the car and which gearbox parts wear in use. For a comparison with the other designs, see the overview of types of automatic transmission; the right fluid and service intervals are covered in the article automatic transmission fluid change.

CVT stands for continuously variable transmission, a gearbox with a continuously variable ratio. In the common mechanical version, the power is transmitted by a steel belt or chain running between two pulleys.

Each pulley consists of two cones facing each other. When they move closer together or further apart, the radius on which the belt runs changes:

• When pulling away, the belt runs close to the centre of the input pulley and far from the centre of the output pulley. This creates a short ratio for an easy start.
• As speed rises, the ratio gradually shifts the other way. The gearing gets taller and the engine doesn't have to rev unnecessarily.

The principle is reminiscent of a bicycle derailleur. But a CVT doesn't move a chain between several sprockets. It changes the radius continuously, so there are no fixed intermediate steps anywhere in its range.

The electronics select the ratio according to how much power the driver wants. At the same speed, the engine therefore runs at different revs when cruising gently on the flat and when climbing a hill or overtaking.

In a gearbox with fixed gears, engine revs rise with road speed and drop again when the gearbox shifts up. A CVT doesn't need this cycle. When you floor the accelerator, the engine quickly revs up to the speed of maximum power and stays there. Meanwhile, the gearbox continuously lengthens the ratio and the car accelerates.

So the driver hears a constant engine note while the speed keeps rising. This mismatch between sound and acceleration is known as the ‘rubber-band’ effect. In a healthy gearbox, the belt isn't slipping; the speed changes because the ratio changes.

With a light throttle, the same thing works in reverse. The gearbox keeps the engine at low revs and adjusts the ratio so that the car travels at the desired pace without revving the engine unnecessarily.

What are simulated gears?

The electronics can control a CVT so that it behaves like a stepped automatic when accelerating. Instead of changing the ratio continuously, it uses several preset ratios and moves between them. The revs then drop noticeably during acceleration, just as they do with a gear change.

This is how the Xtronic gearbox in the Nissan Qashqai III (from 2021) works under hard acceleration, for example. Simulated gears don't turn a CVT into a stepped gearbox. They only change the way the electronics control it, bringing its behaviour closer to what drivers are used to.

In Toyota hybrids, e-CVT refers to the continuously variable relationship between the combustion engine's revs and the car's speed. Mechanically, it's an entirely different solution from a belt CVT.

The Toyota C-HR I 2.0 Hybrid (2020 model year) uses a planetary gearset, two motor-generators and a reduction gear. A motor-generator is an electric machine that either drives the wheels or generates electricity, as required.

The planetary gearset connects the combustion engine with both electric machines. The electronics control their speeds and so change how fast the combustion engine turns relative to the wheels. No belt moves and no gear is shifted.

The combustion engine's power flows to the wheels partly mechanically through the gearset and partly electrically through the motor-generators. Depending on the situation, the battery either supplies energy or stores it, for example during regenerative braking.

What the e-CVT mainly has in common with a belt CVT is the sound. Under hard acceleration, a hybrid also holds the engine at high, almost constant revs; the same effect is simply produced by a different design. Being a hybrid doesn't automatically mean a car has an e-CVT: hybrids from other manufacturers often use dual-clutch or conventional automatic gearboxes.

Smoothness and fuel consumption

A CVT changes ratio without jolts and without jumps in revs. That makes it well suited to town driving, queues and relaxed touring. The cabin stays calm and starts are smooth.

A CVT keeps the engine at the revs where it works most efficiently, which helps fuel consumption. The actual consumption, however, depends mainly on the engine, the car's weight and its aerodynamics. With an e-CVT, electric assistance, regenerative braking and driving with the combustion engine switched off come into play as well, which is why Toyota's full hybrids tend to be most economical in town.

Sporty driving

When driving briskly, the usual link between revs, sound and acceleration is missing. Under load, the engine stays at high revs for a long time and is clearly audible. Simulated gears soften this impression, but the principle of the gearbox stays the same. If you want to feel the shifts and get an instant response, you'll be happier with a dual-clutch gearbox or a torque converter automatic.

Towing a trailer

A CVT gearbox doesn't rule out towing, but sustained heavy loads heat the fluid and put strain on the belt and pulleys. That's why manufacturers set the trailer weight separately for each version of a car and restrict it considerably for some. You'll find the valid figure in the registration certificate of the specific car. You can't take the figure from another version of the same model or from a different hybrid.

CVTs are most common in small and compact cars and crossovers with petrol engines, typically from Japanese brands. Toyota's full hybrids rely on the e-CVT. A pair of crossovers of the same size illustrates both designs:

These models serve as examples of the designs, not as buying recommendations. Within a single model range, gearboxes differ by engine and version, so the type of gearbox depends on the specific version, not just on the model name.

Don't transfer experience from one design to the other. In a belt or chain CVT, the belt, the pulleys and the starting element wear through friction. Toyota's e-CVT doesn't have these parts, but it's an integral part of the hybrid drivetrain, and its condition is tied to the condition of the whole system.

Don't judge the gearbox by the rev counter. High, steady revs at full throttle are normal. Shuddering when pulling away, jolts, jerking or a whining noise from the gearbox are not.

Factor in fluid maintenance. A CVT needs fluid that exactly matches the manufacturer's specification, because both power transmission and gearbox control depend on it. There's no single interval for all CVTs, and the e-CVT has its own maintenance schedule.

Diagnostics and a test drive reliably tell the normal characteristics of the design apart from an emerging fault. Both are part of the CarAudit™ inspection.

You can recognise a CVT gearbox in an ad from the abbreviation, but not its condition. That's why Carvago inspects every car before it's sold.

• CarAudit™ with diagnostics and a test drive: a technician goes through up to 270 checkpoints, including the technical components, diagnostics and a drive. The customer knows the result before deciding to buy.
• Assurance and warranty: Carvago stands behind the condition of the car stated in the CarAudit™ certificate and gives every car a free extended warranty.
• A wide choice: Carvago has the widest selection of used cars: roughly a million cars from sellers in several European countries. If you're looking for a specific model with a CVT or a hybrid with an e-CVT, you're choosing from an order of magnitude more cars than on your home market alone.

How can I tell a belt CVT from an e-CVT in an ad?

The label CVT or the trade name Xtronic means a mechanical CVT with a belt or chain. The abbreviation e-CVT on a Toyota full hybrid means a planetary gearset with motor-generators.

Can a CVT gearbox have a torque converter?

Yes. The CVT changes the ratio and the torque converter provides a smooth start, so the two complement each other in one gearbox. Other CVTs use a clutch to pull away.

Does e-CVT mean the hybrid can be charged from a socket?

No. The gearbox label says nothing about charging. A full hybrid generates its own electricity while driving; only a plug-in hybrid is charged from a socket.

1. https://www.nissan-global.com/EN/INNOVATION/TECHNOLOGY/ARCHIVE/XTRONIC_CVT/
2. https://europe.nissannews.com/en-GB/releases/new-nissan-qashqai-electrified-powertrains-accelerate-europes-best-selling-crossover-into-the-future
3. https://mag.toyota.co.uk/2020-toyota-c-hr/
4. https://carvago.com/car-delivery
5. https://carvago.com/caraudit
6. https://carvago.com/how-carvago-works