Why, after publication of last article, foreign AT and domestic double clutches, public has a different attitude towards domestic consumers? At that time, I discovered that a lot of people didn't understand gearboxes. Some people even said that design of dual clutch gearboxes is more complex and advanced than automatic transmissions. This classmate said following:
The dual clutch is an improvement based on AT. The AT has a simple design, so cost is low and failure rate is low. It's not high production cost of an AT as you said. The double clutch structure is complex, so cost is high and failure rate is also higher.
I have to admire success of brainwashing public. Today we will talk about design and characteristics of CVTs, automatics and dual clutch transmissions, and how to choose them.
Gearbox
AT transmissions are commonly referred to as automatic transmissions, but automatic transmissions are general term. The scientific name of AT is hydraulic automatic transmission, which consists of a hydraulic torque converter, a planetary gear and a hydraulic control system. The principle of operation is variable speed. and torque are achieved through a combination of hydraulic transmission and gear train. , where word "hydraulic" refers to hydraulic torque converter, which is most important component of AT gearbox and soul of AT gearbox. The hydraulic torque converter consists of pump wheel, turbine wheel and guide wheel components, and performs functions of torque transmission and clutch.
Thanks to buffering and speed control function of hydraulic torque converter, AT gearbox starts relatively smoothly, to a certain extent, avoiding disappointment when engaging feedback lock-up clutch. In addition, due to effect of torque converter, shifting is not as direct, shifting speed is slower than a dual-clutch transmission, and power delivery lacks a sense of immediacy. And maximum torque that an AT gearbox can handle is relatively high, so high power models usually use AT gearboxes (except PDK). In general, if you want to save yourself from anxiety and want to get a certain amount of driving pleasure, then choose an AT gearbox.
Advantages: wide torque range, smooth shifting, driving pleasure, low failure rate, small size
Disadvantages: complex structure, high cost, difficult research and development, relatively low transmission efficiency
Dual clutch transmission
Dual clutch transmission is a general term for transmissions in which shifting operations are carried out using two sets of clutches, including a dry double clutch and a wet double clutch. Some people think that dual clutch transmission is an improvement on AT transmission, but it is not. The dual clutch transmission is actually an improvement on manual transmission. The dual clutch transmission is a combination of two sets of manual transmissions. The two clutches respectively control connection and disconnection of two sets of gears and engine, so that when "1st gear" is engaged, "2nd gear" is ready. "3rd gear" is also ready in advance when "2nd gear", etc. in order to save shift time interval and realize fast shifting.In general, two clutches are connected with two input shafts, and shift and clutch operations are realized by a mechatronic module integrating electronic and hydraulic components, which is simpler in structure, than an automatic gearbox.
The outstanding feature of Dual Clutch Transmission is that gearshift is direct and crisp, but Dual Clutch Transmission does not work at low speeds due to shifting fluctuations at low speed of this transmission. will be confused whether to upshift or downshift, and at that time frustration will arise. In view of this situation, adding a hydraulic torque converter kit can make it easier, such as dual clutch kit found in Honda Spinner. In addition, frequent engagement of clutch caused by slippage at low speeds can cause gearbox to overheat, to mitigate this phenomenon, it is recommended to purchase a wet dual clutch. In addition, because of frequent contact of clutch, it is easy to cause wear and tear, and maximum torque that dual clutch gearbox can handle is limited, so many high-end Volkswagen models use AT gearboxes. Overall, ride and life of dual clutch gearboxes have improved significantly, but there is still a lag compared to AT gearboxes.
Advantages: fast shifting speed, lower cost, simpler structure, direct power transmission, high transmission efficiency and driving pleasure.
Disadvantages: relatively poor smoothness at low speed, large volume, relatively poor quality stability
Stepless transmission
Continuous Variable Transmission in English is called Continuous Variable Transmission, and in direct translation it is a continuously variable transmission, which we often call a continuously variable transmission. At beginning it was continuously variable through rubber belts, then gear drives, and then to modern steel belt continuously variable drives, but in any case, change in speed is carried out by changing diameter of two conical disks.
The outstanding advantage of CVT is smooth shifting, no idling problem, but no driving pleasure. As for economical CVT gearbox that many talk about, it's actually only theoretical because CVT gearbox requires a more powerful hydraulic pump. At same time, due to steel belt transmission, maximum torque that variator can transmit is also small.
Advantages: smooth power, simple structure, small size, low cost
Weaknesses: low torque capability, no driving pleasure, insufficient gear ratio, theoretical fuel economy
The differences and characteristics of CVT, AT and Dual Clutch transmissions are shown above. It is recommended to choose gearbox according to your situation. If there are many busy roads, it is not recommended to choose a dual clutch box. gearboxes. If you're looking for a driving feel, chasing a CVT is not recommended, and AT gearbox is safest bet.