How does cvt transmission work

Unlike a conventional transmission, which has a fixed number of gears, the CVT can continually change the diameter of the pulleys, giving it the ability to reach any point between its highest and lowest gear ratios.

The primary benefit is fuel economy. A conventional automatic transmission switches between its fixed gears as needed. To reduce this and better keep the engine in its ideal range for power and efficiency, automakers add extra gears, sometimes as many as nine or ten. Because the CVT continually adjusts the ratio between the crankshaft and the wheels, the engine can stay at its ideal rpm for the driving conditions, building power steadily on acceleration without having to rev up and then drop down as with traditional gears.

CVTs do lose more energy to friction than regular transmissions do, but their infinite-ratio performance still makes them more efficient overall. They might originally have been an oddity, but fuel-efficient CVTs are now here to stay. Sign up to receive Driving. A welcome email is on its way. Early CVT-equipped cars, such as those built by Dutch firm DAF, had a familiar whining noise as engine revs soared, but road speed built slowly.

Today the latest CVT-equipped cars have plenty of sound proofing to ensure refinement is improved. Another quirk of the DAF system was that the cars it was fitted to didn't have a reverse gear, instead the CVT box simply worked in reverse, so in theory these cars had a top speed that was achievable going both backwards and forwards.

Technology has progressed so that today the CVT gearbox is a better option than it used to be, both in terms of driving enjoyment and efficiency. Nissan has developed a CVT gearbox called Xtronic which features 'steps' in its power delivery to make it feel more like a conventional gearbox by 'shifting' through the gears.

This has a split power delivery so that the car's engine is either driving the wheels or sending power to the battery. A CVT gearbox doesn't have many moving parts, so it's relatively reliable.

It's also mainly used in low-power applications, so cars running a CVT are usually fairly unstressed. As the two pulleys change their radii relative to one another, they create an infinite number of gear ratios -- from low to high and everything in between.

The simplicity and stepless nature of CVTs make them an ideal transmission for a variety of machines and devices, not just cars. CVTs have been used for years in power tools and drill presses. They've also been used in a variety of vehicles, including tractors, snowmobiles and motor scooters. In all of these applications, the transmissions have relied on high-density rubber belts, which can slip and stretch, thereby reducing their efficiency.

The introduction of new materials makes CVTs even more reliable and efficient. One of the most important advances has been the design and development of metal belts to connect the pulleys. These flexible belts are composed of several typically nine or 12 thin bands of steel that hold together high-strength, bow-tie-shaped pieces of metal.

Metal belts don't slip and are highly durable , enabling CVTs to handle more engine torque. They are also quieter than rubber-belt-driven CVTs. Although such a system seems drastically different, all of the components are analogous to a belt-and-pulley system and lead to the same results -- a continuously variable transmission.

Here's how it works:. The wheels can rotate along two axes. They spin around the horizontal axis and tilt in or out around the vertical axis, which allows the wheels to touch the discs in different areas. When the wheels are in contact with the driving disc near the center, they must contact the driven disc near the rim, resulting in a reduction in speed and an increase in torque i.

When the wheels touch the driving disc near the rim, they must contact the driven disc near the center, resulting in an increase in speed and a decrease in torque i. A simple tilt of the wheels, then, incrementally changes the gear ratio, providing for smooth, nearly instantaneous ratio changes. There is another type of CVT, known as a hydrostatic CVT, that uses variable-displacement pumps to vary the fluid flow into hydrostatic motors.

In this type of transmission, the rotational motion of the engine operates a hydrostatic pump on the driving side. The pump converts rotational motion into fluid flow. Then, with a hydrostatic motor located on the driven side, the fluid flow is converted back into rotational motion.

Often, a hydrostatic transmission is combined with a planetary gearset and clutches to create a hybrid system known as a hydromechanical transmission. Hydromechanical transmissions transfer power from the engine to the wheels in three different modes. At a low speed, power is transmitted hydraulically, and at a high speed, power is transmitted mechanically. Between these extremes, the transmission uses both hydraulic and mechanical means to transfer power.

Hydromechanical transmissions are ideal for heavy-duty applications, which is why they are common in agricultural tractors and all-terrain vehicles. Continuously variable transmissions are becoming more popular for good reason. They boast several advantages that make them appealing both to drivers and to environmentalists. Here are some of the key features and benefits of CVTs:. Cars with CVTs have been common in Europe for years. But it's taken a while for the technology to gain a foothold in the United States.

Sold between and , the Justy never attracted the attention of American drivers. The best way to answer that question is to take one of these cars for a test drive.

When you step on the gas pedal of a car with a continuously variable transmission, you notice the difference immediately. The engine revs up toward the rpms at which it produces the most power, and then it stays there. But the car doesn't react immediately. Even if you don't know much about how a transmission works, you have probably heard of the manual and the automatic.

The CVT is the newest type of transmission. It is sometimes referred to as the shiftless transmission and is a type of automatic.

Autotrader explains the term CVT stands for continuously variable transmission. Depending on the vehicle and the driver, a CVT can provide a smoother driving experience when comparing it to a traditional automatic. According to Carfax , one of the most significant advantages to having a CVT is that they are often more fuel-efficient than a regular automatic.

This is part of the reason that they are becoming a more popular choice for automakers in many vehicles. In order to see how a CVT works, How Stuff Works explains , you need to understand a manual and a traditional automatic. A manual has a set number of gears, and the driver determines what gear ratio they need. An automatic also has a set number of gears, but it uses a hydraulic system that responds to pressure created by the conditions to determine the gear needed without any input from the driver.

A CVT is similar to an automatic in that it doesn't use any input from the driver, but that is where the similarities end.

A CVT doesn't have any gears. Instead, it has two pulleys. One pulley connects to the engine, and the other connects to the wheels. A flexible belt connects the two pulleys.

The width of the pulleys changes depending on how much power the vehicle needs. When one pulley gets larger, the other one gets smaller. Since neither the pulleys or the belt are fixed, they can provide an infinite number of gear ratios, unlike the automatic, which has a set number of gears. Not all CVTs are created the same.