A continuously variable transmission or CVT is a type of automatic transmission that automatically and seamlessly changes the speed ratio between the engine and the wheels of an automobile vehicle. It is also described as an automatic, single-speed, and gearless transmission. Simpler versions of this transmission have been used in different motorized equipment like power tools and small vehicles like motor scooters and golf carts. Advances in engineering and technology have made CVT a practical alternative to traditional automatic transmission in larger automobile vehicles.
Introduction to CVT: Basics of Continuously Variable Transmission
It is important to understand first how continuously variable transmission works to understand better its advantages and disadvantages. Note that it does not have physical planetary gears or interlocking toothed wheels unlike a traditional automatic transmission or a manual transmission. The most common version of CVT operates on a belt-and-pulley system that allows seamless variability between the highest or lowest gears or speed ratio.
Inside a CVT is a belt that is either made of rubber or linked metals that connects and allows the transmission of mechanical energy between two pulleys. These are the input or driving pulley and the output or driven pulley. Both pulleys are made of two movable plates that can be moved closer or farther apart. This movement increases or decreases the radius of each pulley. The driving pulley is essentially where the energy from the engine enters the transmission while the driven pulley transfers the energy to the driveshaft.
Furthermore, when one pulley increases its radius the other decreases the radius to keep the connecting belt tight. The relative changes between the radii of the two create an almost infinite number of gear ratios. A driving pulley with a small radius and a driven pulley with a larger radius corresponds to a lower gear. A higher gear ratio is produced when the driving pulley has a larger radius while the driven pulley has a smaller radius.
Remember that a continuously variable transmission does not have physical gears. However, for the sake of consensus in language and ease of understanding in discourse among manufacturers and consumers, the term “gear” is commonly used to refer to the ratio of engine shaft speed to driveshaft speed. Other versions of CVT are not made of belts and pulleys. An example is toroidal CVTs which are made of discs and power rollers. These components are analogous to a belt-and-pulley system nonetheless.
Pros of CVT: Advantages of Continuously Variable Transmission
1. Compact Design
One advantage of CVT is that it is lighter and simpler compared to both traditional automatic transmission and manual transmission. Remember that there are no physical gears or a set of planetary gears inside a typical CVT housing. The entire transmission system is based on belts and pulleys. This also requires fewer individual components. The design and components are considerably more straightforward. It relies on a simpler design with fewer moving parts.
This simplified design and smaller footprint make continuously variable transmission ideal for compact vehicles or specific design considerations in which space, engine real estate, and weight are important factors. The entire transmission housing frees up space or requires smaller room compared to bulkier transmission designs. This can even contribute to improved fuel efficiency and reduced weight compared to automatic transmission and manual transmission.
2. Stepless Acceleration
Both traditional automatic transmission and manual transmission use different physical gears to go through different gear ratios in a step-by-step fashion. Shifting between the ratios can create shift shocks or abrupt jerks. CVT varies gear ratio continuously and seamlessly rather than in a stepped manner. This allows for a smoother operation and quicker drive.
Another advantage of CVT is that it allows the engine to rev up almost immediately without any delays associated with gear changes. This allows maximum torque delivery. Remember that torque is a measure of how much force is required to cause an object to rotate.
This type of automatic transmission also eliminates gear hunting as the vehicle decelerates or when it is going up a hill. Take note that a traditional automatic transmission normally struggles while the vehicle is under heavy load. However, under the same scenario, a CVT can almost immediately find the exact gear ratio, thus providing seamless power.
3. Fuel Efficiency
The ratio between engine shaft speed and driveshaft speed is constantly changing in a CVT. In addition, aside from mechanical components, a CVT also has sensors to keep an engine within its optimum power range regardless of how fast or slow the vehicle is traveling. This means that a CVT is more fuel efficient than a traditional automatic transmission or manual transmission during a stop-start traffic situation or when the vehicle is constantly changing speed
It is also worth mentioning that the sensors built inside a CVT allow better fuel efficiency because they balance fuel economy and power requirements. The engine essentially runs at the optimum speed regardless of the wheel speed. Hence, by continuously altering and balancing the gear ratio or the ratio of engine shaft speed to driveshaft speed, a CVT ensures that the most appropriate amount of energy from fuel combustion or other energy input is used.
Cons of CVT: Disadvantages of Continuously Variable Transmission
1. Performance Limitations
A continuously variable transmission can experience more power loss compared to traditional automatic or manual transmissions. This results in a slight reduction in engine efficiency and responsiveness. Furthermore, vehicles equipped with CVTs generally have a lower towing capacity compared to counterparts equipped with other types of transmissions. These make them unsuitable in use cases that require or involve pulling and hauling heavier loads.
It also may not provide the same level of engine performance, overall responsiveness, and driving experience as traditional automatic or manual transmissions. This is noticeable in high-power or high-performance applications. Older CVT designs had some reliability concerns. It is also better to purchase newer vehicles equipped with newer versions of CVTs.
2. Different Experience
Most CVTs under operation can produce noise that is comparable to a failing transmission or slipping clutch. This can be a cause of concern but is normal. However, in a traditional automatic transmission, this can be an indicator of an underlying mechanical problem. CVTs can also sometimes create a feeling of slippage due to the continuous adjustment of the pulleys.
A vehicle equipped with a CVT can provide a different driving experience and a somewhat steeper learning curve. Drivers accustomed to using a traditional automatic transmission or manual transmission will not feel the engine in a CVT vehicle accelerating.
Some drivers might also think that a CVT vehicle is slower although it is not. This is because there is a sudden power burst when pushing the accelerator all the way up in a traditional automatic transmission. The driver can feel this. However, in a CVT on the other hand, the power increase when pushing the accelerator is smooth and rapid.
3. Cost and Maintenance
Another disadvantage of CVT is cost. Note that vehicles equipped with this type of transmission are usually more expensive than their traditional automatic transmission counterparts. This comes from specialized parts, the need to produce and equip electronic control units, and a higher level of manufacturing precision. These drive up the total costs of manufacturing a particular CVT vehicle. Patent royalties also drive up overall costs.
Maintenance and repair costs can also be expensive. Most require more expensive high-quality transmission fluids. A replacement can also cost between USD 3000 to USD 5000. It also does not last nearly as long as a traditional automatic transmission. Furthermore, when it fails, it is usually bound for a complete replacement because individual components can be very expensive or the specific faulty component can be difficult or impossible to procure.
Summary and Takeaways: Pros and Cons of Continuously Variable Transmission
The advantages of continuously variable transmission or CVT are mainly attributed to the fact that it does not have physical gears unlike a traditional automatic transmission or a manual transmission. This translates to other advantages and complements more specific benefits. These include a smaller form factor that is suitable for compact designs, fuel efficiency coupled, and overall mechanical and operational efficiency. All of these advantages translate to comfort and ease of use for drivers of automobiles.
The aforementioned disadvantages of CVT are considerably minimal compared to its advantages. Owners and drivers should still take note of the maintenance and specific repair costs associated with owning CVT vehicles. This also means observing extra care to extend the lifespan of their vehicles or reduce the frequency of repairs. It is also important to underscore the fact that a CVT provides a relatively different driving and user experience than traditional automatic and manual transmissions.
