Continuously Variable Transmission (CVT) : Definition, Parts, Working, Types Pros & Cons [PDF]

In this article, you’ll learn about continuously variable transmission (CVT) with diagrams, how it works, its parts, benefits, and uses. You can also download a PDF at the end.

What is a Continuously Variable Transmission or CVT Transmission?

You can smoothly switch between gear ratios while driving in a CVT transmission. Mechanical transmissions have a set number of gears. They also need hard shifting. It’s called a CVT because it can change the size of its pulleys. This is done to match different speeds. This will help to transfer rotational power between the shafts.

The system has two main parts: a driving pulley and a driven pulley, connected by a belt to transfer motion. However, it struggles to handle high torque in cars. CVTs keep a constant angular speed no matter the output speed because of their shiftless design. They also improve fuel efficiency and provide smoother acceleration.

CVT systems are also known as single-speed or shiftless, or stepless transmissions. They’re used in cars, tractors, scooters, ATVs, bicycles, snowmobiles, and heavy machinery.

CVT Transmission

CVT Transmission History

CVTs have been used for a long time. Leonardo DaVinci designed the first one in 1490. It wasn’t patented until 1886 by Daimler and Benz. They’ve become more efficient over time. Their history goes back centuries.

The CVT became popular in 1910 when Zenit motorcycles created a version so efficient that it was banned from hill-climbing competitions. By the late 1980s, CVTs became widely used thanks to Subaru’s development. Today, nearly every car model includes a continuously variable transmission.

Parts Of A Continuously Variable Transmission

Following are the main components of CVT transmission:

Parts of CVT Transmission

#1 Push Belt

The CVT system uses a push belt. It is used to transfer torque between the driving and driven pulleys. There are two main types of belts used in CVTs:

  • V-Shape Rubber Belt: More flexible than regular belts, often found in scooters.
  • Steel Belt: Commonly used in CVTs for its strong and flexible design. Made of small steel elements with thin steel rings, these belts handle a wide range of RPMs and work well with the pulleys.

#2 Pulley and Sleeve

In a regular gearbox, gears transfer power from the engine to the wheels, using different gear ratios for varying power and speed needs.

In a CVT system, traditional gears are replaced by conical pulleys, which is why it’s called a “pulley transmission.”

  • Drive Pulley (Primary Pulley): Connected directly to the engine’s crankshaft.
  • Driven Pulley (Secondary Pulley): Connected to the drive shaft, which powers the wheels.

Both pulleys have movable and stationary parts. The belt drives these pulleys, and their diameters adjust based on the sheaves’ movement, providing infinite gear ratios. When one pulley expands, the other contracts, allowing for smooth and seamless changes in gear ratios.

Working Of A Continuously Variable Transmission

Manual and automatic transmissions use complex gear-shifting systems. They engage specific gears to create different gear ratios. A Continuously Variable Transmission (CVT) uses a dual-pulley system. This offers an infinite number of gear ratios.

The pulleys are connected by a belt. The primary pulley is linked to the engine. The secondary pulley is connected to the drive shaft. Each pulley can expand and contract at the same time due to its moving parts.

As the engine rotates, the sheaves adjust the diameter of both pulleys. When one pulley increases in size, the other decreases, and this continuous change creates a smooth variation in gear ratios. This allows for an infinite range of gear ratios.

Let’s take a closer look at how this mechanism works:

During Low Speed

The CVT system kicks in when the vehicle needs more torque without increasing speed, like during initial acceleration. As the belt pushes the pulleys, the movable sheave of the primary (driving) pulley moves away from the static sheave, reducing its diameter. Meanwhile, the secondary (driven) pulley expands, increasing torque when the car starts moving.

During High Gear or High Speed

During acceleration, when the vehicle needs more speed but less torque, the diameter of the secondary pulley decreases as its moving sheave moves away from the static sheave. The main pulley gets bigger as it turns, which makes a certain gear ratio. In this case, one turn of the driving pulley makes the driven pulley turn four times.

What is Sheave Movement?

The rollers in the variable transmission are designed to facilitate the dynamic variations in pulley diameters. This is accomplished by pushing the pocket of the roller inwards or outwards when the engine’s RPM increases or drops.

what is CVT Transmission?

CVT Transmission Types

Following are the main types of continuously variable transmission:

#1 D-CVT Transmission

The D-CVT has an extra gear and a planetary gear set. They are connected to the input and output shafts of the pulleys. A clutch pack is used to engage or disengage the planetary gear set.

Under normal conditions, the D-CVT works like a standard CVT. It happens when accelerating from a stop and at low to medium speeds. Engine power goes through a torque converter to the input pulley. It’s then transferred to the output pulley via a belt. Then finally to the wheels.

D CVT Transmission

At higher speeds, the D-CVT switches to split mode, using both the belt drive and an additional gear drive. This gear drive transmits power more efficiently, especially when the belt drive becomes less effective at high speeds.

At higher speeds, the D-CVT’s clutch pack activates the gear drive, reducing the load on the belt drive. At low to medium speeds, the belt drive remains fully engaged.

#2 Direct-Shift CVT Transmission

Traditional CVTs can be sluggish. This generally happens when accelerating from a stop due to their design. To fix this, Toyota has added a launch gear. This is added to some of its CVT-equipped vehicles. This helps for quicker acceleration.

Both D-CVT and Direct Shift-CVT have extra gears. Toyota takes a different approach by adding a launch gear. This works like first gear in a traditional transmission.

Direct-Shift CVT Transmission

When starting from a stop, the transmission engages the launch gear first, then switches to the belt drive like a regular CVT. This launch gear is designed to make the vehicle more responsive and deliver power more directly.

When the car is at rest, the launch gear engages. This engagement help with faster and more efficient acceleration from a stop. Once the car reaches a speed where the CVT can operate smoothly, the launch gear disengages. The transmission shifts like a regular CVT.

#3 eCVT Transmission

eCVT is a term used for the hybrid powertrain. This is for all Toyota hybrid vehicles. Toyota calls this technology “Hybrid Synergy Drive.”

The eCVT system includes an internal combustion engine, two electric motors/generators, and a simple planetary gearset called the “Power Split Device.”

e CVT Transmission

This transmission is called an “electric CVT” or “eCVT”. This is because it functions like a typical CVT. However, it uses a completely different concept. Also it avoids most of the issues found in traditional CVTs.

#4 Toroidal CVT Transmission

The toroidal CVT is a variation of the CVT. It uses discs and rollers instead of belts and pulleys. It features two rollers positioned between two discs. It manages torque distribution and allow for an infinite number of gear ratios.

Toroidal CVT Transmission

Advantages of CVT Transmission

Here are the advantages of a continuously variable transmission (CVT):

  • It provides a smoother, more comfortable ride than traditional gear systems.
  • It ensures the best power range for any situation, boosting fuel efficiency.
  • It eliminates the need to shift gears when climbing hills.
  • It reduces emissions by improving engine control in various conditions.
  • CVTs optimize engine power and are ideal for city driving.

Disadvantages of CVT Transmission

Here are the disadvantages of a continuously variable transmission (CVT):

  • The belt’s strength limits the CVT’s ability to handle high torque.
  • CVTs generally have a shorter lifespan compared to traditional gear systems.
  • The CVT’s design requires a large central space, making it unsuitable for inline arrangements.
  • The complexity of CVTs can lead to higher repair costs.
  • CVTs may produce more noise during operation.

Symptoms of a CVT Transmission Failure

Following are few symptoms of CVT transmission failure :

#1 Overheating

Overheating is a common issue in CVTs, often caused by a failing cooling system or the constant adjustment of gear ratios with the pulley systems. It may result in a burning smell in the vehicle.

#2 Fluid Leakage

Leakage of transmission fluid is another issue with CVTs. Problems are often indicated by red, sweet-smelling fluid. Low fluid levels can damage components, leading to preset point issues and delayed movement.

Dirty transmission fluid can affect performance, causing the vehicle to experience strange surges, lurches, shaking, and hops.

#3 Noise

Transmission failure can produce unusual noises even when the car is in neutral. These sounds might signal low transmission fluid levels or mechanical wear and tear on the transmission components.

#4 Sudden Loss of Acceleration

A CVT may occasionally experience sudden loss of acceleration, especially if the system overheats.

Difference Between CVT and Automatic Transmission

CVT TransmissionAutomatic Transmission
Belt and pulley system with infinite gear ratios, no fixed gearsSystem of gears with set ratios that shift automatically
Continuously flexible, no distinct gearsFixed and distinct ratios (e.g., first, second, third, etc.)
Smoother, with no sudden gear shiftsGear shifts may be noticeable, especially during acceleration
More fuel-efficient, especially in city drivingLess efficient due to converter losses and gear changes
Maintains ideal RPM, maximizing engine outputMay experience slight delays in maintaining optimal RPM
Fewer moving parts, typically requires less maintenanceMore complex, with gears and clutches needing more maintenance
Found in smaller cars, cost-effective optionUsed in a wide range of cars, with varying prices depending on brand and type

Conclusion

That’s it! Thanks for reading. I hope I’ve covered everything about the “Continuously Variable Transmission.” If you think I missed something or have any questions, feel free to let me know.

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