What is Variable Transmission


Variable transmission is a type of automatic transmission (AT) that is capable of changing speed flawlessly by means of a continuous range of effective gear ratios. It is adapting and interacting with existing local variables. It is multi-linear and infinite in terms of changing ratio and speed. This is unlike any traditional transmissions that offer a finite number of gear ratios.

Formally, it is referred to as continuously variable transmission or CVT. It is also known as pulley transmission, stepless transmission, and a single-speed transmission.

If you’re wondering if CVT is suitable for modern automobiles, or the way the mechanics work, or even just the simple pros and cons of CVT transmission, this article will attempt to offer you some answers.

History of CVT

We are standing on the shoulder of giants. This is particularly true when talking about continuously variable transmission. In the 1940s, Leonardo DaVinci sketched the very first concept of CVT. However, the technology back then is still not that advanced to realize the whole idea. In 1886, Diamler and Benz first patented this transmission design. Zenit motorcycles integrated the design in their V2 bike model in 1910. Intriguingly, V2 became so successful to the point that it was barred from major hill climbing contests. The fundamental difference in transmission mechanics was cited as the reason of the ban.

It was only in the late 1950s when a Dutch automobile producer named DAF used CVTs in their vehicle.    Still, technological limitations made CVTs incompatible for engines capable of firing more than 100 horsepower.

In the late 1980s, Subaru’s Justy mini-car series offered a CVT option. Honda also used a CVT in their high mileage Civic HX in the late 1990s.  Variable transmissions that are capable of managing more powerful auto-engines were developed during the start of the second millennia.

Currently, big automobile manufacturers like Audi, Honda, Mitsubishi, and Nissan produce car models with CVT option.

How It Works

First, you need to understand that it doesn’t shift like a conventional gearbox. Imagine a bike’s gear system. Same with your usual automatic transmissions, your bike uses a fixed set of gears that offer a fixed number of speeds (ratios). As a rule, the first gear is used for start-up, middle gear is used to accelerate and build-up momentum and the higher gears are used to avoid further mechanical strain and for fuel-efficient cruising.

In the case of CVTs, instead of a linear acceleration as you shift your gear, you actually have a pulley system in place. And instead of gears, CVTs rely on two variable-diameter pulleys. One pulley is linked to the engine and the other is linked to the drive wheel. Every pulley is with a cone. All of which are connected to a chain of belts. These cones move variably closer/further to increase/decrease the diameter of belt’s operation. The internal movement is influenced by several variables such as the position of the gas pedal, the plane where the mobile moves, vehicle speed, engine speed, and so on. To find the perfect combination of speed and efficiency, the ratio always changes based on the mentioned factors. It is distinct from the linear speed build-up of other AT types.

Instead of changing the speed by shifting gears, the CVT continuously varies the ratio using its pulleys. This explains the name continuously variable transmission or pulley transmission. It holds the capacity to adapt different ratios instantaneously. But as a result, this seemingly smooth transmission is perplexing for many due to the excessive sound (some would describe it as “motorboat-y”) and the lack of resistance when changing speed level.

Popular car models that offer a CVT option includes Dodge Caliber, Toyota Corolla, Ford C-MAX hybrid, Chrysler Pacifica hybrid, Mitsubishi Lancer, Scion IQ, Honda Insight, Honda Civic, Honda Accord, Nissan Altima, and many more.

Other Uses of CVTs

Aside from cars, there are also other machines and vehicles that rely on CVTs to perform. Given the wide array of CVT designs available today, there is no wonder why it also holds different functions.

  • Simple CVTs (usually with rubber belt design or variable-pulley design) are commonly used in running small motorized vehicles such as scooters, golf carts, and snowmobiles. Most home mowers and small tractors use simple rubber belt CVT.
  • Medium-sized tractors and other agricultural equipment (e.g. combine harvesters, farm mowers) use hydrostatic CVT design. The stability of this system ensures the needed constant power setting of these machines.
  • Since the 1950s, aircraft power generating instruments have been running with CVTs.
  • Many go-karts also use CVT. Research shows that the incorporation of CVTs increases the performance and lifespan of go-kart’s engine.

Pros of CVT Equipped Cars

  • Efficiency

    The main reason why people choose cars with CVT is that of efficiency. For the past years, efficiency is becoming the name of the game. The Nissan Altima, for example, is considered as the most fuel-efficient sedan with a highway rating of 38 mpg. Other than fuel economy, its efficiency also translates into actual driving. CVTs ability to give power without shifting gear and much engine strain make it very effective during even-speed hilly rides.

  • Easy to Drive

    When it comes to driving controls, cars equipped with CVTs also use the standard AT controls. They have P-R-N-D-L shift pattern and two pedals for brake and acceleration. Well, these gears are not really “gears”. They are more like pre-set points that approximate the distance of pulleys and speed ratios. They are not physically moving gears under the hood but simply software settings.

    For people who are accustomed to driving AT cars, learning the ropes of CVT controls is really not an issue. Despite this similarity, many would argue that the overall feel is different (we will talk about this point later).

  • Quicker Acceleration

    CVTs can provide maximum efficiency and optimum power at the same time. As a result, its acceleration is slightly faster compared to most conventional automatic transmission and manual transmission. This character is attractive to those who enjoy both speed and efficiency.

Cons of CVT Equipped Cars

  • Perception and Public Acceptance

    As mentioned earlier, several drivers find CVT cars perplexing. This is mainly caused by the excessive revving sound when you shift your speed. Despite the similar controls, the feeling that it gives is significantly different. The tremble and noise coming from under the hood are totally discernable. Some would say that it feels like the clutch is slipping in the car when driving.

    This is also true when it comes to the resistance before accelerating. Unlike conventional ATs, CVTs don’t have the sudden burst of speed when you floor the pedal and change gear ratio. What CVT cars give off is the smooth transition from one-speed level to another. Because of this sensation, some drivers get the illusion that CVT cars are slower. In reality, CVTs are on par with ATs in terms of speed. Sometimes even better. To address this concern, manufacturers are starting to develop CVT car models that will give the “kick-down” of a regular AT.

  • Concerns with Regard to Reliability

    Because it took manufacturers some time to develop CVTs that can handle powerful engine, consumers are quite circumspect about the long-term dependability of this transmission. Given the CVT’s history, the public fear did not surface out of a vacuum. In the 1960s, many CVTs are just not suitable when paired with powerful engines that offer more than 100 horsepower. Currently, it is also hard to see standard CVTs under the hood of high-performance race cars or large truck.

    Fortunately, this weakness has become an opportunity for manufacturers. Many modern CVTs are much more durable and compatible with very powerful engines. Nissan, one of the larger producer of CVT cars in the world, sold millions of CVTs that are considered comparable to many conventional AT.

  • Price Tag

    CVT cars are expensive. And because they are expensive, they are also harder to track. In case you encounter some major transmission failures, a typical replacement will easily cost you around $3000 to $5000 dollars. Coupled with the issues of reliability and life-span, many believe that what you’ll get is not worth the price and hassle.

Summary: What is Variable Transmission?

Variable transmission, also called pulley transmission or continuously variable transmission, is an AT-type that can change speed flawlessly by means of a continuous range of effective gear ratios. Unlike most ATs and MTs, CVTs don’t have a fixed number of gears that translate to the car’s speed. Instead, it changes its ratio as internal cones/pulleys move variably closer/further to increase/decrease the diameter of belt’s operation. By interacting with other variables, CVTs achieve the perfect combination of speed and efficiency vis-à-vis its direct environment.

From an engineering standpoint, CVTs offer tremendous potentials. Looking at its recent development, we can say that it is starting to catch-up with other conventional transmission-types (in terms of tech development, at the very least). It also works remarkably as a transmission design. However, marketing the product has been challenging for many manufacturers. It is significantly expensive and the public perception to it is far from excellent.