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.
Gone are the days where choices were limited to choosing between manual and automatic, now consumers face an increasing number of acronyms, and not everyone is going to know their CVTs from their DCTs.
Continuously variable transmission (CVT)
Continuously variable transmissions, commonly abbreviated to CVT, are becoming increasingly popular, to the point that they are often mistaken for a ‘standard’ automatic transmission.
A CVT is a transmission that employs two V-shaped pulleys that are 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 a CVT is comprised of fewer elements, cars with CVT transmission are often cheaper to manufacture.
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 then 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 advancements in CVT technology. On top of that, they offer great fuel economy, as torque is retained during gear changes.
Dual-clutch transmission (DCT)
Dual-clutch transmission (DCT) 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 holds the odd numbers, the other the evens – and this makes the process of shifting through them much faster and more accurately than doing it yourself manually. This results in less torque loss when changing. Each gear is used with a clutch to both engage and disengage. This is often a wet clutch like that of a conventional automatic.
Over time, dual clutch transmissions have improved significantly, although they 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 proper ‘driver’s car’.
Automated manual transmission (AMT)
Automated manual transmissions (AMTs) offer manufacturers a cheaper way to utilise an existing manual transmission in a car rather than creating a new automatic transmission.
Cars sporting automatic manual transmissions are less frequently found in New Zealand, but if you drive an Alfa Romeo or a Ford, you might be more familiar with AMT than you first thought.
Normally, AMTs have 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 is no physical connection between the driver and the gearbox, so a computer regulates the gear selection and clutch control. Sometimes, they have a fully automatic mode, but because everything is operated through a computer, there are delays between tasks, which leads to power loss and occasionally harsher operation. Because of this, the AMT can’t really be considered a ‘true’ automatic, especially since it requires calibration.
The operation of AMTs 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.
What about BEVs?
Interestingly, Battery Electric Vehicles (BEVs) with high torque motors do not require a transmission, so many will wonder if this is the end for transmissions as we know them.
Gearbox manufacturer ZF is currently developing a unit that can fit into a range of vehicles and can be mated to a motor with a maximum power rating of 140kW. This is said to improve efficiency by five per cent.