AA Motoring answers queries about different transmissions
We often receive queries from AA members on our online forum about the reliability of vehicle transmissions — particularly when customers are in the market for a new vehicle. Considering the wealth of models in today’s market, it’s no surprise.
Gone are the days where choices were limited to conventional manual and automatic. Consumers now face an increasing number of acronyms, and not everyone is going to know their CVT from their DCT.
Continuously variable transmission (CVT)
Continuously variable transmission, abbreviated to CVT, is becoming increasingly popular — to the point that it’s often mistaken for standard automatic transmission.
It’s a transmission that employs two V-shaped pulleys driven by a flexible metallic belt to continually change through the range of gear ratios. As the car accelerates, the belt drives up the surfaces of the pulley, shifting it seamlessly through its gears. This takes away the need for a clutch and, as CVT is comprised of fewer elements, cars with CVT transmission are often cheaper to manufacture meaning they have gained a strong position in the market.
To the regular driver, cars with CVT transmissions may feel slow to react under sudden acceleration, or when carrying a lot of weight. Its characteristics are well suited to light passenger cars as they provide a smooth, comfortable ride and continuous power, but more manufacturers now include this type of transmission on larger vehicles due to CVT advancements. On top of that, they offer great fuel economy, as torque is never lost during gear changes.
Dual-clutch transmission (DCT)
This transmission combines the benefits of a conventional manual transmission, with the use of a dual clutch and a physical gear selection.
DCT uses two sets of gears, one with the odds and one with the evens, making the process of shifting through them much faster and more accurate than doing it manually. Each gear is used with a clutch to engage and disengage the gear. This is often a wet clutch like that of a conventional automatic.
Dual clutch transmissions have improved significantly but must stay calibrated or their performance can deteriorate. A good DCT can feel a lot like a regular manual transmission, but it also boasts strong performance benefits, making this a good option for someone after a “driver’s car”. Automated Manual Transmission (AMT)
AMT offers manufacturers a cheaper way to utilise an existing manual transmission in a car, rather than creating a new automatic transmission. Cars sporting automatic manual transmission are less frequently found in New Zealand, but if you have an Alfa Romeo or a Ford, you may be more familiar with AMT than you first think.
Normally, AMT has a manual transmission setup that consists of controlled actuators and sensors. The actuators typically control the clutch and gear selection using electric or electro hydraulics. The sensors monitor gear selection, engine speed and clutch control. Unlike a conventional manual transmission, there’s no physical connection between the driver and the gear box, so a computer regulates the gear selection and clutch control. Sometimes they often have a fully automatic mode, but because everything is completed through a computer, there are delays between tasks, leading to power loss and harsh operation. Because of this AMT can’t really be considered a true automatic, especially since it requires calibration as well.
The operation of AMT isn’t the fastest, but it may appeal to drivers who enjoy the excitement of a gear stick without having the hassle of controlling the clutch.