Dual Clutch Automatic Transmission (DSG) Advantages and Technical Details

Traffic jams have become commonplace in major cities such as Beijing and Shanghai. Being stuck in a traffic jam while driving a manual transmission car is perhaps the most painful experience for most car owners. Stopping and starting on the road and frequently changing gears are more torturous than the traffic jam itself. Some netizens jokingly said, "I feel sore waist, backache, and leg cramps from pressing the clutch one by one."

Automatic transmission: "I won't change gears even if you kill me"

Automatic transmissions have gradually replaced manual transmissions with convenient operation. On congested roads, car owners can cope with stop-and-go traffic by simply braking. The price of this convenience is higher fuel consumption. Also, when car owners drive on mountain roads and downshift into a corner, the automatic transmission will slowly execute the car owner's downshift command with an attitude of "I won't change gears even if you kill me." The fun of driving disappears in an instant.

Dual-clutch automatic transmission

A dual-clutch transmission, as the name implies, is a transmission that uses two clutches, each operating independently. What are the advantages of a dual-clutch automatic transmission?

Taking Volkswagen's DSG dual-clutch automatic transmission as an example, the manufacturer claims that: DSG's gear shifting action is faster than a manual transmission, bringing more driving pleasure; there is no power interruption during the DSG gear shifting process, and the DSG's extremely fast gear shifting process is imperceptible and there is no sense of frustration. The fuel consumption level of DSG is comparable to that of manual transmission models, or even lower than that of manual transmission models.

How a Dual Clutch Transmission (DSG) works

The manufacturer has introduced many advantages of DSG transmission, but are they exaggerating? Let's take a look at how dual clutch automatic transmission works.

The dual-clutch transmission omits the clutch pedal of the traditional manual transmission and uses an electronically controlled hydraulic system to control the two clutches. The input shaft of the dual-clutch transmission is also divided into two parts. The two clutches are each connected to an input shaft. The hollow outer shaft is used to connect the even-numbered gears in the transmission, and the solid inner shaft embedded in the outer shaft is used to connect the odd-numbered gears. The two clutches cooperate with each other when working, and each is responsible for the power transmission of an input shaft.

Dual-clutch automatic transmission structure diagram

It can be clearly seen from the figure that the red part indicates that clutch 2 controls the odd gears in the transmission through the inner shaft, and the green part indicates that clutch 1 controls the even gears in the transmission through the outer shaft.

When the car is driving normally, a clutch is connected to a certain gear in the transmission, transmitting the engine power to the drive wheels. At the same time, the control unit pre-judges the driver's shifting intention based on the vehicle's driving speed and engine speed, and controls another clutch to be connected to the gear set of the next gear in the transmission. The clutch is still in a disengaged state and no power transmission has yet been performed.

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When shifting gears, the first clutch is disconnected, and the second clutch simultaneously engages the gear set of the next gear in the previously pre-connected transmission with the engine to transmit power to the next gear, so that there is no power interruption. Except for neutral, one clutch in the dual-clutch transmission is always engaged and the other clutch is always disconnected.

Schematic diagram of power transmission of odd-numbered gears of dual-clutch automatic transmission

Schematic diagram of power transmission for even-numbered gears of dual-clutch automatic transmission

Technical advantages of dual-clutch automatic transmission

It is precisely because of this structure that the two clutches cooperate in shifting that the gears are already connected when the gears are switched. The DSG dual-clutch automatic transmission achieves the design goals of smooth shifting, fast shifting, "uninterrupted" power output, and fuel saving. According to Volkswagen's official data, the shifting time of the current popular dual-clutch transmission is only about 0.2 seconds. Even the world's best racers cannot compare with the shifting speed of a dual-clutch transmission. The shifting time of a dual-clutch transmission is also far beyond the limit of human operation.

Dual-clutch transmission R&D and use costs

The dual-clutch transmission is a derivative technology derived from the semi-automatic transmission technology. The DSG-7 dual-clutch automatic transmission that Volkswagen has successfully used on the Golf car is a technical core developed from the manual transmission of mechanical transmission, but its internal structure is similar to that of the traditional manual transmission. Therefore, it inherits the technical advantages of the manual transmission in terms of reliability and easy maintenance. At the same time, the dual-clutch transmission is not much different from the ordinary automatic transmission in terms of use, which is convenient and labor-saving.

Dual Clutch Transmission Product Classification

The most widely used in the market is Volkswagen's DSG series dual clutch transmission, which mainly includes DSG-6-speed dual clutch transmission and DSG-7-speed dual clutch transmission.

The DSG-6-speed dual-clutch transmission uses a "wet" dual clutch. "Wet" means that the dual clutch is installed in a closed oil chamber filled with hydraulic oil. This "wet" structure has better adjustment ability and excellent thermal capacity, so it can transmit relatively large torque. The DSG-7-speed dual-clutch transmission can match engines with a maximum torque of 350 Nm.

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The DSG-7-speed dual-clutch transmission uses a "dry" dual clutch, which consists of three clutch plates of similar size installed coaxially and stacked. Because its "dual clutch" is not installed in a closed oil chamber like the DSG-6-speed dual-clutch transmission, it is called a "dry" dual clutch. The "dry" dual clutch has a simple structure and is therefore more efficient. However, the inherent characteristics of the "dry" clutch's own structure make it able to withstand a lower maximum torque than a "wet" clutch. The DSG-7-speed dual-clutch transmission is used to match small-displacement engines with a maximum torque of no more than 250 Nm.

Development Prospects of Dual Clutch Transmission

Led by Volkswagen DSG, other manufacturers have invested manpower and resources to join the "dual clutch transmission" team. Unlike Volkswagen, other manufacturers are more focused on increasing the maximum torque that the dual clutch transmission can withstand and equipping the dual clutch transmission on sports cars.

M-DCT dual-clutch automatic transmission

BMW M department has developed the latest M-DCT (Dual Clutch Transmission) 7-speed dual clutch transmission based on the 3rd generation SMG (Sequential Manual Gearbox) sequential manual transmission, which is specially designed for V8 engines with a maximum speed of 9000r/min. M-DCT dual clutch transmission has been first equipped on BMW's latest generation M3 coupe and convertible sports car.

Porsche has always used manual transmission and Tiptronic manual/automatic transmission. At present, Porsche has applied its PDK dual-clutch transmission, which has been "hidden" for many years, to the field of civilian sports cars. The structure and operating principle of Porsche's PDK dual-clutch transmission are the same as those of Volkswagen's DSG dual-clutch transmission.

In addition to BMW and Porsche, Nissan has developed a dual-clutch transmission for the GT-R sports car, and Mitsubishi Motors has developed a dual-clutch transmission for the EVO sports car. In the near future, dual-clutch transmissions led by Volkswagen DGS will become the mainstream of transmission technology, and dual-clutch transmissions will be widely used in cars of all levels.