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In this article, you’ll learn what is continuously variable transmission. Its diagram, parts, working, advantages, and applications all are explained with pictures.
Also, you can download the PDF file at the end of this article.
What is CVT Transmission?
With CVT transmissions, you can seamlessly change from one effective gear ratio to another while driving, whereas mechanical transmissions have a fixed number of gear ratios and require hard shifting.
It gets its name from its unique capacity to change the diameter of its pulleys to match different speeds. It acts as a way to move rotational power from one shaft to another.
This transmission system consists of two main components: a driving pulley and a driven pulley, joined by a belt to assist motion transfer. Still, it faces difficulties when managing high torque in automobile applications.
CVTs maintain constant angular velocity regardless of output speed due to their shiftless design. A continuously variable transmission also improves fuel efficiency and smoother acceleration.
CVT transmission systems are also called single-speed, shiftless, or stepless transmissions. These are found in automobiles, tractors, motor scooters, side-by-sides, bicycles, snowmobiles, and earthmoving machinery.
Read Also: Different Types of Internal Combustion Engines
History of CVT Transmission
CVTs have been around for centuries – Leonardo DaVinci designed the first CVT in 1490, but Daimler and Benz didn’t patent it until 1886. Many innovations have made CVTs more efficient, but they date back centuries.
The CVT originally achieved popularity in 1910, when Zenit motorcycles developed a CVT variant that was so efficient that it was prohibited from hill-climbing competitions.
The CVT became widely used by the late 1980s, mostly due to Subaru’s development. A continuously variable transmission is a feature included in practically every model produced by manufacturers nowadays.
Components of CVT Transmission
The following are the main components of CVT transmission:
#1 Pulley and Sleeve
The gears in a typical gearbox are essential for transferring power from the engine to the wheels. The usage of varied gear ratios, such as high torque-low speed or low torque-high speed, is necessary because different vehicles have varying requirements for power and torque.
In a CVT system, this idea is reversed as conical pulleys take the place of the traditional gear arrangement, giving rise to the term “pulley transmission.”
- Drive Pulley or Primary Pulley: The crankshaft of the engine is directly connected to the main pulley.
- Driven Pulley or Secondary Pulley: The drive shaft is connected to the secondary pulley, and this ultimately leads to the wheels of the car.
Both pulleys are made up of moveable and stationary sheaves; a pulley is the result of combining these elements. Each pulley has its axle shaft, which is parallel to the other.
A belt drives the pulleys, whose diameters change in reaction to the movement of the sheaves, allowing for infinite gear ratios. It’s important because the pulleys at both ends have different directions of contraction and expansion. When the driving pulley expands, the driven pulley contracts at the same time, and vice versa.
#2 Push Belt
The CVT system uses the push belt as a means to transfer torque from the driving to the driven pulley. Continuously variable transmissions use two main types of belts:
- V-Shape Rubber Belt: Compared to regular rubber belts, this “V” shape flexible belt offers more flexibility and is often found in scooters.
- Steel Belt: Steel belts are generally used in CVTs because of their sturdy design. These belts have a cluster of small-toothed steel elements and individual thin steel rings. They can move and interact with the pulleys effectively over a broad range of RPMs thanks to their special design, which provides strength and flexibility.
Read Also: 22 Important Car Engine Parts & Their Functions
Working of CVT Transmission
Manual and automatic transmission systems use complex gear-shifting mechanisms, which rely on the engagement of certain gears to create varied gear ratios.
On the other hand, a Continuously Variable Transmission (CVT) has a dual-pulley mechanism that provides an infinite number of gear ratios instead of only one or two.
These pulleys are connected by belt drive; the primary pulley is attached to the engine, while the secondary pulley is attached to the drive shaft. Because of its moving sheaves, each pulley can extend and contract at the same time.
The motion of their sheaves changes the diameter of both pulleys as the engine rotates. The size of one pulley grows while the other lowers, and vice versa. The constant change in pulley size results in a smooth variation in diameters, which generates an endless range of gear ratios.
Let’s examine how this mechanism works:
During Low Speed
The CVT system is activated when the vehicle demands additional torque but not necessarily speed, as is typically the case during beginning acceleration.
As a result of the belt pushing the pulleys, the primary or driving pulley’s movable sheave moves farther from the static sheave, reducing its diameter. At the same time, the driven or secondary pulley gets bigger, which increases torque when the car is first moving.
During High Speed or High Gear
Conversely, during acceleration, when the vehicle requires more speed but less torque, the diameter of the secondary pulley shrinks. The diameter decreases as the moving sheave separates from the static sheave.
The driving or primary pulley grows in diameter simultaneously, creating a certain gear ratio. In this case, one revolution at the driving pulley equals four revolutions at the driven pulley.
What is the Sheave Movement?
There are cylindrical rollers within the conical sheave. Centrifugal force acts upon these rollers, pushing the sheave pocket along the rollers and causing it to move both inside and outside the roller.
These rollers facilitate the dynamic variations in pulley diameters by pushing the pocket inwards or outwards when the engine’s RPM increases or drops.
Types of CVT Transmission
The following are the types of continuously variable transmission:
#1 D-CVT Transmission
The D-CVT features an additional gear and a planetary gear set that is attached to the pulleys’ input and output shafts. A clutch pack is used to engage or disengage the planetary gear set.
Under typical operating conditions, the D-CVT operates similarly to a conventional CVT while accelerating from a stop and moving at low to medium speeds. Engine power is routed via a torque converter and into the input pulley. It is then transferred to the output pulley via a belt, and finally to the wheels.
At higher speeds, the D-CVT enters split mode, utilizing both the belt drive and an extra gear drive. This gear drive transmits power more efficiently, especially at higher speeds when the belt drive may become inefficient.
The D-CVT’s clutch pack activates the gear drive at higher speeds, relieving the belt drive, while the belt drive is fully engaged at low to medium speeds.
#2 Direct-Shift CVT Transmission
Due to the nature of CVT functioning, traditional CVTs may exhibit a delay or sluggishness when accelerating from a stop. To solve this, Toyota has added a launch gear to some of its CVT-equipped vehicles.
Although the D-CVT and Direct Shift-CVT also have extra gears, Toyota takes a whole different approach by including a launch gear that functions similarly to the first gear in a conventional transmission.
When starting from a standstill, the transmission first engages the launch gear before switching to belt drive, much like a CVT. This launch gear aims to increase the vehicle’s responsiveness and transmit power more directly.
When the car is at rest, the launch gear is only engaged to assist in the faster and more efficient acceleration of the vehicle from a stop. When the car gets to a speed where the CVT shifts more smoothly, the launch gear is removed and the transmission shifts like a CVT.
#3 eCVT Transmission
eCVT is a more general term for the hybrid powertrain found in all Toyota hybrid vehicles. Toyota refers to this technology as the “Hybrid Synergy Drive”.
It consists of an internal combustion engine, two electric motors/generators, and a relatively simple planetary gearset known as the “Power Split Device”.
This transmission is known as an “electric CVT” or “eCVT” because it behaves similarly to a typical CVT. Yet, it operates on a completely different concept and avoids almost all of the problems of a traditional CVT.
#4 Toroidal CVT Transmission
The toroidal CVT is a form of the CVT that differs slightly from the pulley-based CVT. Instead of belts and pulleys, the design uses two discs and rollers. Two rollers in the center of two discs. They manage torque distribution, allowing an endless number of gear ratios.
Advantages of CVT Transmission
The following are the advantages of continuously variable transmission:
- It offers a more comfortable ride than a traditional gearing system.
- It provides the best power range possible in every situation, enhancing the vehicle’s fuel efficiency.
- CVT transmission removes the need to look for gear when climbing an elevation.
- It reduces emissions due to improved engine control in all conditions.
- CVTs have improved engine power optimization and are perfect for driving in cities.
Disadvantages of CVT Transmission
The following are the disadvantages of continuously variable transmission:
- The belt’s strength restricts a CVT transmission’s ability to handle torque.
- The CVT has a significantly shorter lifespan than a traditional gearing system.
- Since CVT requires a large central distance, an inline arrangement cannot accommodate it.
- The complexity of the CVT may increase repair expenses.
- During operation, CVT may make a loud noise.
Symptoms of a CVT Transmission Failure
A few symptoms that indicate CVT transmission failure are:
Overheating
Overheating is a common issue that can be caused either by a failing cooling system or by continuously adjusting gear ratios using two pulley systems. It may produce a smell of burning in the vehicle.
Fluid Leakage
The leakage of liquids is another issue. CVT transmissions use transmission fluid, and possible problems are indicated by red, sweet-smelling fluid. Low transmission fluid levels can cause damage to components, which can lead to preset point issues and delayed motion.
Dirty transmission fluid can also have an impact on performance, leading to strange surges, lurches, shaking, and hops in the vehicle.
Noise
Transmission failure can also cause strange noises even when the car is neutral. These sounds can indicate low transmission fluid levels or mechanical wear and tear of the transmission’s parts.
Sudden Loss of Acceleration
A CVT transmission may occasionally suffer an abrupt loss of acceleration, especially if the system overheats.
Difference Between CVT and Automatic Transmission
A comparison of CVT and automatic transmissions is explained in the table below.
| CVT Transmission | Automatic Transmission |
|---|---|
| It employs a belt and pulley system to provide an endless number of gear ratios, hence eliminating fixed gears. | It uses a system of gears with precise ratios that shift automatically in response to speed and load. |
| There are no gears and its ratios are indefinitely flexible. | Its gear ratios (such as first, second, third, etc.) are fixed and distinct. |
| CVT provides a smoother, more seamless driving experience by eliminating sudden gear transitions. | Automatic transmissions may have gear shifts, especially when accelerating. |
| It offers greater fuel efficiency. particularly while driving in urban areas. | It usually has less fuel efficiency because of converter losses and gear changes. |
| This gearbox maintains the ideal RPM while efficiently maximizing engine output. | This may cause a little performance impact and delay in maintaining the ideal engine RPM. |
| Because there are fewer moving parts, it usually requires less maintenance. | The complexity of the gears and clutches might indicate that it needs more maintenance. |
| CVT is commonly seen in tiny cars and provides cost-effective solutions. | These come in a variety of car models and differ in price according to the type and brand. |
Conclusion
That’s it. Thanks for reading. I hope I have covered everything about the “Continuously Variable Transmission” It would be helpful if you could let me know if there was anything I missed or if you have any doubts about anything I wrote.
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Reference and External Links:
- https://en.wikipedia.org/wiki/CVT
- https://auto.howstuffworks.com/cvt.htm
FAQs
In contrast to conventional automatics, the CVT has infinite gear ratio variation capability, which keeps the engine operating at maximum efficiency. Overall, the more gears available in a standard automatic transmission, the more engine power is produced.
If you prefer faster driving, the lack of fixed ratios may make downshifting and upshifting feel less enjoyable. The sound of a vehicle drone during acceleration is another frequent problem associated with a CVT. This is because it frequently requires the engine to run at a high, steady rpm as the car accelerates.
CVTs use a belt-driven mechanism to seamlessly regulate the rotation of the rotor disc or pulley in response to power input and the vehicle’s velocity. As a result, driving is incredibly smooth and free of sudden jolts or jerks, which is especially apparent on lengthy trips.
When the CVT system gets overheated, it may not accelerate smoothly or take longer than usual when the paddle is pressed.