Posted on: 14 November 2014
In recent years, a couple of significant transmission innovations have reached the automotive market: continuously variable transmissions (CVT) and dual clutch transmissions (DCT). Each of these have transformed the way automatic transmissions function, and that in turn has affected the consumer in positive ways. Here is more information about CVT and DCT transmissions so that you can make informed buying decisions in your next new car purchase:
Continuously variable transmissions
Continuously variable transmissions operate using a simple principle. They consist of a band that is connected between two pulleys; one pulley is powered by the engine, and the other pulley is attached to the car's drivetrain. What makes these pulleys unique is their cone shape. As the vehicle slows or accelerates, the band moves freely along the surface of the cones. When the transmission "senses" that the vehicle needs power for acceleration, one end of the belt or band slides to the narrowest diameter end of the engine-powered pulley and the other end to the widest end of the drivetrain pulley.
When the car is moving at a constant speed and doesn't need as much torque to keep it going along, the reverse applies; the band moves to the wide end of the engine-powered pulley and the narrow end of the drivetrain pulley. This movement back and forth on the surfaces of the cones isn't fixed, as it is with conventional automatic transmissions. Instead, it is a continuous movement, as the name would indicate, and this creates an infinite number of gear ratios.
Dual clutch transmissions
Another automatic transmission innovation that has found its way to market is the dual clutch transmission. The DCT is actually two manual transmissions joined together inside a casing; what separates this from an ordinary car transmission is that it has two clutches. One clutch controls the odd numbered gears (1,3,5) and the second clutch controls the even numbered gears (2,4,6). These clutches automatically trade off gears as the vehicle downshifts and upshifts, resulting in a near instantaneous transition. Repair parts are available at places like Brighton Automotive Inc.
Advantages and disadvantages of continuously variable transmissions
The CVT provides its driver with several advantages, including:
- Superior fuel economy - the transmission is free to find the most fuel-efficient gear ratio at any point during operation
- Faster acceleration - there is no need for a discrete gear change as found in conventional automatics
- Smoother operation - with no shifting, the motion of the car is completely smooth without jolting or lurching
The CVT does have a few disadvantages, such as:
- Noise - the engine will often rev high, and louder, as it seeks to maximize the gear ratio
- Lack of conventional feel - some operators do not like the lack of gear shifts; the emotional discomfort of driving a vehicle that defies their expectations is strong with many drivers
- Unproven reliability - while CVTs appear to be just as reliable as conventional transmissions, there are still unknowns about this technology.
Advantages and disadvantages of dual clutch transmissions
The DCT possesses the following advantages:
- Fast gear changes - the ability of the transmission to keep the next gear available allows for the rapid upshift and downshift capability
- Manual transmission-like construction - many owners prefer the more "rugged" construction of DCT components and the similarity to manual transmissions
- More power than CVT - dual clutch transmissions are more powerful than CVTs, especially for racers and others who need fast shifting and high-powered engines
The DCT has a few disadvantages:
- Potential for overheating - some DCTs have experienced overheating due to lack of lubrication in the clutch
- High repair expense - the newness of the DCT has not allowed many automotive technicians to learn how to repair them; thus, owners are often forced to buy entirely new transmissions or find expensive, specialized shops to conduct repairs
- Lurching at low speed - the DCT is smooth-shifting at higher speeds, but it can be prone to lurching or jolting at low speeds. This makes parking and other slow-speed driving more challenging and frustrating for the driver.