Continuously Variable Transmission | CVT
|
|
Cutaway of a Ford CVT
|
|
For more information on automotive technology, visit our Auto Encyclopedia Section.
|
|
This continuously variable transmission (CVT) technology is an automatic transmission with the ability to select any drive ratio available in the operating range. In a traditional automatic transmission, a specific gear is selected like third, fourth or fifth gear. However, with the CVT, it will ‘continuously’ choose the best drive ratio available between the engine and the drive wheels under every condition. This is true whether the vehicle is accelerating or cruising. This system is also so smooth, it’s barely perceptible.
- The CVT when speeding up -during acceleration, the CVT adjusts the drive ratio to maximize peak engine horsepower.
- The CVT while cruising -when driving at a constant speed, the drive ratio changes to create a balance between fuel economy and handling.
- The ease of CVT -a CVT is easy to drive with as it’s the same as any automatic transmission. You put your transmission into Drive mode and go. There is no input required from the driver to make things happen correctly.
How it Works
There are several different types of CVT design. However the most common has a metal V-belt that runs between sets of cones, called pulleys, which can be adjusted in diameter as the belt operates. These pulleys are connected by a special steel-link and plate chain. This chain allows the pulleys to infinitely shift the drive ratio between the upper and lower limits.
Essentially the CVT transmission varies the working diameter of the two main pulleys in the transmission. Automatically, these pulley ratios choose the best one. This ‘best ratio’ is determined based on the engine speed and the speed you’re traveling. What does all this mean to the driver? It means a smoother ride, better performance, and a much better fuel economy.
The Elements of a CVT
The parts and pieces of a CVT are simple and minimal. The typical CVT design includes the following components:
- a high density rubber belt
- a microprocessor
- sensors
- a mechanical driving pulley
- a hydraulic driving pulley
History of the CVT
The CVT is not a new concept. Leonardo da Vinci drew a sketch of this system in 1490. Several attempts were made in the early 1900s but it wasn’t until the 1950s that the CVT was built into vehicles. The first models had some issues like jerky movements and were extremely noisey.
The Cars Performance
There is a second generation CVT in the 2007 Dodge Caliber. With it, DaimlerChrysler says that the vehicle achieves a 6-8 percent increase in fuel economy.
Nissan has used CVTs for years in many in their cars destined for overseas market. In the North American market, they have been in the Murano crossover since late 2002. The 2007 and later models of automatic transmission front wheel drive passenger vehicles all come equipped with CVT. Nissan is also saying that the CVT is giving better fuel economy and reducing carbon dioxide emissions.
There are several other automobile manufacturers utilizing the CVT technology. A couple of them are Audi, in their A4/A6 models; BMW in their Mini and Ford in their Freestyle. Honda, Subaru and Saturn are also offering CVT transmissions.
As CVTs hold promise in fuel economy, you’d think they’d be more common on the market. However, the manufacturing costs, torque capacity and the lack of customer acceptance has kept it out of mainstream use. As well, heat is a concern for CVTs. The extreme heat requires special oil that won’t break down at these temperatures.
Technology will improve CVTs over time thus improving gas mileage and functionality even more in the near future.
| 
