As a key component that transmits the power output of the engine to the wheels, the gearbox will directly determine the driving texture of a car to a certain extent. As we all know, in the current civilian car market, automatic transmissions have become the gearbox with the largest loading volume. But in the automatic transmission, it is divided into three categories: AT automatic transmission, CVT continuously variable transmission and DCT dual clutch transmission, the debate on these three gearboxes has never stopped, so who is the most suitable for home use of these three gearboxes?
AT gearbox in the hearts of many consumers has been known as "the most perfect gearbox", as early as the 60s of the last century, many American cars began to use AT gearbox as a transmission system, but at that time THE transmission often only has a starting gear and a cruise gear. Later, with the development of the automobile industry, there were more and more gears in the AT gearbox, such as the vertical 10AT of the General Motors Group and the horizontal 10AT of Honda.
First of all, from the structural point of view, THE gearbox is the most complex, has more stable characteristics, is the most suitable for intense driving, but the premise must be adjusted in place, otherwise the frustration will be full, and the fuel consumption is not low. The most important component on the AT transmission is the "torque converter", which is used to transmit speed and torque, and the connection between the engine and the automatic transmission is non-rigid to facilitate automatic gearbox shifting. This means that the cost of AT transmissions is often relatively high, and some low-end models are almost unlikely to use AT transmissions.
The CVT stepless gearbox is very different from the AT gearbox, CVT can be said to be one of the simplest structure of the gearbox, it does not have many gear pairs of manual transmission, nor the complex planetary gear set of the AT gearbox, it mainly relies on the main, driven wheel and metal steel to achieve a stepless change in speed ratio, in other words, CVT has no clear gear, its speed does not have the fixed gear ratio of other gearboxes, which can change from 2.455 to 0.658.
And there are many types of CVT gearboxes, which are divided into three categories: electromagnetic, hydraulic and mechanical, but because the cost of electromagnetic CVT gearboxes is relatively high, there is almost no opportunity to contact them in daily life. In addition, the CVT is also divided into steel belt transmission (most Japanese models) and steel chain transmission (general part of the model), and even now there is the Direct Shift CVT transmission (some Toyota models).
Compared to the AT transmission and DCT transmission, the CVT has no shifting action, so the daily driving is quite smooth and there is no power interruption. In addition, the CVT transmission has a wide range of speed ratios, which can be pressed relatively low at high speed cruises, resulting in good fuel economy.
However, compared with the AT gearbox and DCT gearbox, the disadvantages of the CVT gearbox are also very obvious, due to the physical structure, the CVT is doomed to not be able to withstand too much torque (except for the chain CVT), and once the temperature is below 0 degrees Celsius, the cold protection will be turned on, and the gearbox oil temperature must be up before it can accelerate sharply. Speaking of which, the Japanese SUV in my family was "fortunate" to have experienced a CVT gearbox failure in 2018. So for the CVT gearbox, I have always been such a view: ordinary steel belt CVT is only suitable for small displacement family cars, and small displacement family cars are very suitable for CVT gearbox, daily transportation is very comfortable, fuel economy is also very good, can reduce a certain cost of the car.
Compared with THE AT transmission and the CVT transmission, the history of dual clutch is not short, and it has a history of more than 70 years, but its earliest mass production and use was around 1985, when Audi first launched the S‐Tronic gearbox and assembled it into a racing car. After more than thirty years of development, the dual clutch is now very large, and various types of dual clutch transmissions have been derived, the most famous of which are Porsche's PDK and Volkswagen's DSG.
Structurally, the dual clutch transmission is very complex, it has two sets of clutches, and are electronically controlled and propelled by the hydraulic system, and the two sets of clutches correspond to two different sets of planetary gears, so that the transmission shaft is also divided into two parts, the center of the solid drive shaft is responsible for one set of gears, and the hollow drive shaft is responsible for another set of gears.
However, the dual-clutch transmission does not have a torque converter, which also brings different advantages and disadvantages. The advantage is that the use of two sets of clutches work alternately with each other, there is no gap to shift, so the shift speed is relatively fast, and because there is no torque converter, so the power can be the most direct transmission, the natural power loss will be very small, which also improves fuel economy to a certain extent.
The disadvantage is also because there is no torque converter, in the low-speed state, because it will always be 1, 2 gears frequent switching, torque will be relatively large, so there is no hydraulic torque converter "buffer", there will be a significant sense of frustration, especially the dry double clutch transmission, the state of stop-and-go will feel more obvious.
Write at the end:
In fact, these three common gearboxes in general have their own advantages and disadvantages, for family car consumers, combined with their own car purchase needs, it is easy to find the most suitable gearbox for themselves. But take the author's own feelings as an example, if you have requirements for control and want to be relatively smooth, then choose an AT gearbox, and if you want to have good fuel economy on top of the above requirements, then choose DCT gearbox. If you simply want smooth and fuel-efficient, choose the CVT gearbox.