Dual Clutch transmission-Everything you need to know!
What is Dual Clutch Transmission? First off, there are two kinds of transmission: manual and automatic. In a manual transmission, the driver presses on the clutch pedal while changing the gear lever to choose the required gear. In an automatic transmission, the driver hits the brake pedals and shift the gear lever to the necessary place. When there is a problem in the gearbox, we go for transmission repair as it focuses on the gear. Then, the torque converter, the clutch pack, and the gear set automatically choose the gear. But the best among these is what lies between a manual and automatic transmission, and that is the dual-clutch transmission.
Sports cars and Dual-clutch transmission
In the world of sports cars, the Serial Manual Gearbox (SMG) and Semi-Automatic Manual Gear Box have been the mainstay for a number of years. Likewise, Dual Clutch goes parallel to the technology, and currently, we know it as Dual-clutch transmission – DCT or Direct Shift Gear Box – DSG.
We can also define dual-clutch transmission as the collection of two manual gearboxes. In order to understand the meaning of dual-clutch, we need to review the operation of a standard manual gearbox.
The mechanism behind the dual-clutch transmission
Usually, a driver who drives a manual gearbox has to use the clutch pedal to shift the gear from one to the other. The driver uses the gear lever to disconnect the power steering from the engine to the gearbox. When to change the gear, is the engine’s power goes through the gearbox to its wheels. In this procedure, the engine’s power does not flow to the wheels continuously during standard manual single-clutch transmission. The change of gears causes Shift Shock and Torque Interrupt due to clutch on-off-on rotation. Because of this reason, when an unskilled driver drives a standard manual clutch vehicle, there is a chance of passengers to go back and forth during gear shifting.
In contrast, the dual-clutch transmission uses two clutches but does not have a clutch pedal. Meanwhile, it uses the electronic and hydraulic technology of an automatic transmission using a mechatronic unit. However, in dual-clutch transmission, both the clutches operate independently. From clutch one (K1), the odd gears (one, three, five, seven gears) and from clutch two (K2) the even gears (two, four, six, eight, and reverse gears) activate. This method allows the shifting of gears smoothly without any trouble; with a dual-clutch transmission, the engine’s power travels to the transmission.
The heart of Dual-clutch transmission
The heart of dual-clutch transmission is the Input shaft. While in standard manual gearbox there is one input shaft that holds all the gears, in dual-clutch transmission, there are two input shafts which have odd and even gears. The outer transmission shaft is removed from the inside, and the inner shaft is inserted from within. The outer shaft connects with clutch two (K2) and supplies power to second, third, sixth, and eighth gears. The inner shaft connects with clutch one (K1) and provides power to first, third, fifth, and seventh gears. (Below is a picture of five dual gear clutch in this method). Therefore, K2 controls second and fourth gears while K1 controls first, third, and fifth gears. This is the strategy behind shifting gears and distributing power evenly continuously through the dual-clutch transmission. This is not possible with a standard manual gearbox because it uses only one clutch.
Similarities and differences between transmission systems
The Dual Clutch transmission has a lot of similarities in automatic transmission. Therefore one may think that dual-clutch transmission also requires a torque converter like in automatic transmission to send engine power to the transmission. But dual-clutch transmission does not use a torque converter, and currently, it uses multi-palette wet clutch or dry clutch. Wet clutch limits boiling with an oil bath and is a multi-palette clutch pack. (A lot of motorbikes use this type of single multi-palette clutch pack). Most current dual-clutch productions use a wet clutch, and some manufacturers use the dry clutch that a standard manual gear uses.
Just like in a torque converter, a multi-palette clutch uses hydraulic pressure to operate the gear. (See the diagram below). It is done by the fluid inside the clutch piston. When the clutch engages, the hydraulic pressure in the piston uses steady tension on the springs and works against, creating friction between clutch plates and friction plates. There are tethers inside these friction palettes. They are connected to the tethers on the clutch drum, and on the other hand, it is connected to the gearbox. (For instance, Audi dual-clutch transmission uses small coil springs with a big diaphragm spring. It uses a multi-palette wet clutch.)
When clutches disengage, the fluid pressure in the pistons goes lower. Therefore, the pressure releases from the piston springs. In turn, the pressure releases on the clutch pack and the pressure palette.
Advantages and disadvantages of the dual-clutch transmission
Usually, dual-clutch delivers the fastest upshift of gears in 8 milliseconds, and hence it provides the quickest acceleration compared to any vehicle in the market. The best thing about it is, you have the opportunity to select the shifting of gears like a manual gearbox or let the computerized method handle it.
Another advantage of a dual-clutch is that it contributes to the improvement of fuel economy. That is, the power from the engine to the transmission has no interruptions, thus increasing fuel efficiency. Therefore, if you compare traditional five-speed automatic transmission, there is an increased 10% fuel efficiency in dual-clutch transmission.
A lot of current automobile manufacturers pay keen interest in dual-clutch transmission. But many have a lot of concerns regarding the latest transmission facilities, manufacturing facilities, and their related costs. On the other hand, dual-clutch transmission vehicles can be more costly than other cars, and price-concerned customers will be a big concern in this matter. Another disadvantage of it is the expensive parts in the electronic and hydraulic control unit.
In addition, a lot of manufacturers have heavily invested in alternative transmission technologies, and one of the most prominent ones is CVT (Continuously Variable Transmission). The CVT transmission is a kind of automatic transmission that uses a movable pulley system and belt or chain to change the ratio in gear. CVT reduces shift shock during gear shifting and increases efficiency. But it is not possible for efficient cars to handle high-definition requirements in a vehicle.
But dual-clutch does not have such problems. Therefore, it is suitable for high-definition cars and fuel efficiency. Because of this reason, it acquired more than 25% of the European market in 2012, while CVT has only acquired only 1% of the market.
The history and future of dual-clutch
A Frenchman called Adolphe Kégresse invented a dual-clutch transmission system before World War II. It was intended to be used on Citroën Traction vehicles, and it affected the business situations, thus stopping further developments. Later, Audi and Porsche developed dual-clutch transmission. Porsche introduced PDK (Porsche Dual Klutch) in their 956 and 962C race cars in 1986. Audi introduced its dual-clutch transmission system (Direct shift gearbox – DSG) in their Audi S1 car in 1985.
Presently, the leading dual-clutch transmission pioneer is Volkswagen. But the most significant manufacturer is the Ford automobile company. However, even other automobile companies use dual-clutch transmission technology in their vehicles and continue to develop it.
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