There are two most common types of transmissions used in cars: manual and automatic. However, there is a third type of transmission called Continuously Variable transmission or CVT. CVTs were introduced late 1980s and are at the center of attention now since they typically provide better fuel economy compared to other types of transmissions.
In this article, we provide a comprehensive guide on how CVTs operate and discuss their benefits over other common transmissions. We will also compare CVTs with regular transmissions.
How does a CVT work?
Technically, a CVT is classified as an automatic transmission as the driver is not required to shift between the forward gears or push a clutch pedal while driving. However, CVTs are fundamentally different from regular automatic transmissions in both form and function.
CVTs offer a unique ability to change seamlessly through an infinite number of effective gear ratios from maximum and minimum speeds. This ability provides drivers with a smoother riding experience with no typical shift shocks seen in traditional transmissions.
To provide smooth movement, a CVT employs belts and pulleys in its mechanism to adjust vehicle moves at various speeds so that the transmission changes the engine’s output speed without any interruptions from changing gears. Thus, unlike other traditional automatic transmissions, a CVT is not limited to a fixed number of preset gears and, instead makes use of unlimited great ratios to adjust the conditions and speed of a vehicle at any given moment. As a CVT allows smooth changes without any hard shift points, it is often known as a Single-speed or Shiftless transmission.
But how does a CVT achieve an unlimited gear ratio? CVTs are equipped with two opposing cone-shaped pulleys, input and output pulleys, with a chain or belt which offers to run between them, very similar to a chain in a bicycle. While one cone is connected to the engine output shaft, the other directs power to the driveshaft and drive wheels. Gear ratios change due to the movement of the pulleys. As the pulleys move closer or apart, the chain or belt moves up and down around the two cones’ sides and, as a result, the diameter of the chain or belt increases or decreases, causing a change to the gear shift ratio based on the power required. As the car is moving, these changes happen continuously and make the engine operate at the most efficient RPM at various ranges of vehicle speeds, providing a smoother ride without noticeable gear shifts.
Types of CVTs
There are several types of CVTs and each one is designed for specific applications and performances. Let’s have a look at the main types and discuss their typical uses:
Pulley-Based CVT
- Overview: This is the most common type of CVT and is primarily used in small to medium-sized cars.
- Mechanism: It uses a system of variable-diameter pulleys connected by a belt or chain, which allows making seamless changes in gear ratios.
- Applications: It has been widely used in passenger vehicles by manufacturers like Toyota, Honda, and Nissan. It is known for its fuel efficiency and smooth driving experience.
Toroidal CVT
- Overview: It makes use of discs and rollers instead of pulleys and belts.
- Mechanism: The system employs input and output discs with rollers that tilt to change the contact points and provide variable gear ratios.
- Applications: This CVT is suitable for performance vehicles due to its higher torque capacity. The transmission is applied in some luxury and high-performance cars to offer both power and smooth acceleration.
Hydrostatic CVT
- Overview: This CVT transmission is distinguished since it uses hydraulic fluid to transfer power.
- Mechanism: It employs a hydraulic pump and motor to convert mechanical energy to hydraulic pressure and back, which allows continuous variation in gear ratios.
- Applications: It is definitely ideal for heavy-duty applications like agricultural and industrial machinery. Providing stronger moves and precise control, Hydrostatic CVTs are most suitable for equipment that requires reliable power and durability.
CVTs vs. traditional automatic transmissions
As you may already know, automatic transmissions involve a complex number of gears, clutches, brakes and principal devices. Thus, the regular automatic transmissions provide a finite number of gears, referred to as speeds. The terms such as 6-speed automatics, as an example, refer to six gears provided in a transmission. These gears are activated once the vehicle reaches a certain speed.
However, it is different in Continuously Variable Transmissions. A CVT does not include individual gears but has a variable gear that shifts according to driving conditions. Thus, drivers do not feel the shift from one gear to the next but notice a change in engine speed or RPM when pressing the gas or brake pedal, which improves the driving experience.
Pros and cons of CVTs
CVTs offer several advantages over regular automatic transmissions that make them an attractive alternative for various vehicles and applications. Here are the most important ones:
Fuel Efficiency
- Optimal engine speed: CVTs are designed to adjust the most efficient RPM of an engine, which reduces fuel consumption compared to traditional automatic transmissions. Thus, CVT-equipped vehicles often achieve better fuel economy, particularly in city driving and stop-and-go traffic.
Durability
- Fewer moving parts: Based on their design, CVTs include fewer moving parts compared to conventional transmissions, which reduces damage and repair requirements.
- Absence of gear shifts: Once there are no gear shifts, there is less stress on transmission components, which results in a longer lifespan and potentially reduces maintenance costs.
Control
- Better power and speed control: CVTs offer precise control over power delivery and speed combinations, which leads to smoother acceleration and a better driving experience.
- Improved driving experience: Since the driver has no manual role in the continuous adjustment of the gear ratio and there is an automatic seamless transition between speeds, driving a vehicle with a CVT vehicle can be more comfortable as well as enjoyable.
Lighter Weight
- Since there are no gears to maintain the proper driving ratio, CVT transmissions are lighter and smaller than standard transmissions. Thus, the gear system takes up less space under the hood and reduces car weight, which makes it a practical option for compact vehicles.
However, CVTs may come with some disadvantages, too.
Reliability Concerns
- Durability and capability: CVTs usually offer better everyday driving experience, but they may suffer from durability problems under high-stress conditions or heavy loads. Also, they may not be ideal for high-speed applications, like driving a sports car.
- Component Failure: Some parts of a pulley-based CVT, such as a belt or chain, could wear out or fail regularly, leading to costly repairs.
Maintenance Costs
- Higher costs: Compared to a regular automatic transmission, it could be more expensive to maintain and repair a CVT due to its specialized parts and the technology involved.
- Frequent Fluid Changes: Hydrostatic CVTs require regular fluid changes due to their function. This can also add to the maintenance expenses.
Noisiness
- Noises: Some drivers find CVTs to be noisier than regular automatic transmissions. They mainly report higher noises at high speeds, for example driving on a highway.
Considering all the advantages and disadvantages of CVTs, they are getting more and more popular among automakers and car owners. Experts are doing their best to improve CVTs and overcome their shortcomings. Therefore, future CVTs could gain better acceptance in the automobile market.
