Gearbox - DCT dual clutch

The usual manual gearbox on the mainstream has helped the driver change the traction and the number of revolutions of the wheel actively to match the road resistance according to the demand. However, in addition to the above function, modern cars also require more smoothness when shifting and leisurely when driving a car. Therefore, 4, 5, 6 or 7-speed automatic transmissions were born.

Using a manual gearbox has the disadvantage of not creating a calming feeling when shifting the gear, while the automatic transmission has a too complicated structure and increases fuel consumption. But, there is a type of gearbox that can eliminate the above disadvantages, it is a dual-clutch gearbox: Dual - Clutch Transmission (DCT), also known as a semi-automatic gearbox.

Brief history

The creator of the dual-clutch system is a young automotive engineer, Adolphe Kégresse is best known for his role as the developer of a half-track vehicle (with front and rear tires). Help the car pass many types of complex terrain. In 1939, Kegresse conceived the idea of ​​a dual-clutch gearbox in the hope of using it in the legendary car, Citroen ' Traction '. Unfortunately, the unfavorable financial situation has prevented the further development plan of this project.

Both Porsche and Audi developed concepts for dual-clutch systems, although it was only used on limited racing versions. The 956 and 962C racing versions were installed with Porsche Dual Klutch - PDK (Porsche dual clutch system). In 1986, the 962 won a 1,000km Monza race for prototype cars (Monza 1,000km World Sports Prototype Championship). This is the first victory for a car equipped with PDK system and semi-automatic gearbox with a gear switch. Audi also made history in 1985 when the Sport Quatro S1 Rally was equipped with a gearbox with dual clutches, won, conquering Pikes Peak in a race to reach the 4,300m high mountain.

Control lever of DCT gearbox

However, the commercial production of gearboxes with dual-clutch was not carried out until VW was a pioneer in mass-gear mass production with dual-clutch with the permission of BorgWarner's DualTronic. Currently, cars equipped with DCT technology are only sold in Europe including: Beatle, Golf, Touran and Volkswagen Jetta; Audi TT and A3; Altea, Toledo, Leon of Seat and Skoda Octavia.

Ford is the second largest dual-clutch technology production application, with the association of Ford Europe and the manufacturer that Ford contributes 50% of the capital in GETRAG-Ford joint venture. This is the system that Ford calls Powershift System, a 6-speed gearbox with a dual-clutch system that first appeared at Frankfurt International Motor Show 2005. With such rapid development, many people set out Question: Will DCT eliminate the Continuously Variable Transmission (CVT) automatic gearbox in the future?

DCT: direct rival of CVT

It can be said that DCT is a direct competitor to CVT gearbox. Both make the car more fuel-efficient and reduce production costs than traditional automatic transmissions. However, when comparing the function and structure, the CVT clearly reveals limitations. In particular, the CVT uses belts to transfer torque and generate numbers, so in the course of operation it is easy to slip and cause significant loss of transmission efficiency, while gearboxes are The dual case still uses the helical gear like a manual transmission to change the gear ratio and torque. With that structure, DCT combines the advantages of both gearboxes that are very popular on many models: automatic transmission and manual transmission.

New construction and improvements

Although called a dual-clutch gearbox, DCT does not have a clutch pedal for the driver to use when shifting the gear. The clutch unit here is a type of wet friction clutch, meaning that the friction plates are soaked in oil and its separation and coupling are controlled by an actuator: hydraulic-electromagnetic. These two clutches operate completely independently of each other, a control of odd-numbered gears (1, 3, 5 and reverse gear), while the remaining clutch is responsible for controlling gear Even numbers (2, 4 and reverse). With such a structure, when the process of increasing the number (1 - 2 - 3 .) or reducing the number (5 - 4), there will be no loss of capacity. At the same time, setting the transmission numbers automatically depends on the engine's operating mode and the road's resistance (if the driver selects the auto mode completely). Therefore, it always ensures the pulling force in accordance with the movement resistance, ensuring the quality of dynamics and fuel economy of cars.

Structure of DCT gearbox

Symbols: 1 : Helical gears fit into the differential; 2 : differential gear; 3 : primary axis number 1; 4 : engine crankshaft; 5 : Primary level 2; 6 : Clutch 2; 7 : Clutch 1; 8 : helical gears fit with the differential; 9 : gears fit with the accelerometer;BR: Pair of digital gears

Structure of wet friction clutch: Like hydraulic torque variable, wet friction clutch uses oil to create pressure to control gears. And the disconnection of the clutch through the piston and the return spring. Control this clutch with electromagnetic and hydraulic structure, like the control of automatic transmission.

The special structure of DCT is the central axis system consisting of two nested coaxial axes. The first axis (red): one end (left) associated with the first clutch (red) with then flowers, on the shaft body consists of 3 different sized gears that match the gears on the shaft First secondary, create number levels: 1, 3, 5. The other axis (green), one head fitted with the second clutch (blue), on the shaft body consists of 2 gears with 2 wheels The teeth on the second secondary shaft create 2 levels 2, 4 and add a reverse number.

The special structure of the central axle system and the clutch duo allows for faster and quieter gear shifting than the traditional manual gearbox. Why so? Let us re-imagine the manual shifting of the manual gearbox: When the operator wants to shift the gear, it is necessary to first reduce the gas then apply the clutch pedal to disconnect the clutch, so the torque The motor does not transmit to the primary axis of the gearbox and the driver performs the gear shift. Next, the driver releases the pedal and the clutch is reconnected simultaneously with the engine power transmitted to the gearbox. Torque is distributed according to the status: ON-OFF-ON during the digital transfer. Thus, the smoothness of the vehicle when gearshift depends very much on the driver's skill. The smaller the time interval, the less vibration and jerky the vehicle will be, and the machine power loss will be minimized.

However, DCT can completely overcome the weakness of the manual gearbox thanks to the independent operation of two clutches. The transfer process is as follows: assuming that at the present time, the vehicle is moving at 1, at this time the clutch 1 is closed (in red), the clutch 2 (in blue) is open, then the power flow is from motor through clutch 1, through shaft and accelerator to primary axis and to differential ( see drawing ). The car continues to increase speed, the computer will search for the next number position, and gear number 2 is selected. When the operator switches the number, immediately clutch 1 will be disconnected, while clutch 2 is closed, and the power line will continue to transmit from the motor to the secondary shaft and drive the differential. Thus, the transfer time from 1 to 2 is very small, so the torque line is almost uninterrupted. According to that principle, when the driver reduces the number of cycles, it will be the opposite.

The whole digital transfer process will be controlled by the computer and instruct the actuator to select gears and rings or disconnect each clutch. If the driver selects fully automatic mode or manual control mode: in automatic mode, the clutch pair acts as a hydraulic torque converter of the traditional automatic transmission, but if the mode is used The number of hands and the driver does not have to take additional action to use the left foot to operate the clutch pedal.

Control unit: Based on information from sensors: digital position sensor, car speed sensor, throttle position sensor, engine speed sensor, etc., the computer will issue a command to control the information. through the actuator structure.

The actuator: In the DCT, the electromagnetic control valve acts as the actuator, carrying out the opening and closing of oil lines. Magnetic control valve includes magnetic steel core, coil.

DCT gearbox cutting image

Compare with manual gearbox and traditional automatic transmission

With manual transmission: two cars have the same engine power, the car using DCT gearbox takes less time than the manual gearbox to achieve the same speed. And at each number shift point, the OFF time is almost equal to)

With automatic transmission: Compared with the traditional automatic transmission (using hydraulic torque and planetary gear structure), DCT has a much simpler and lighter structure. Although the level is still incomparable to it, it will be reasonable to fit in medium-sized vehicles, while reducing the cost of manufacturing cars and creating leisurely for the operator when using automatic mode. and also create excitement for speed enthusiasts in the self-level change mode.

With fuel prices changing with increasing trends, let us wait and see the impulse of fuel savings to bring DCT to where and how popular. However, DCT still reveals a limitation: due to the use of wet friction clutch, it is difficult to transmit a large amount of torque. Therefore, DCT gearbox is only installed on small passenger cars: Volkswagen Beatle, Audi TT . Audi is currently a car manufacturer using the most DCT for the 2006 A3 V6 3.2, TT 3.2 Quatro models, . with called Direct Shift Gears (DSG).