Double Clutch system is the latest technology in transmission. It combines the pleasure of both worlds: Manual transmission as well as automatic transmission. Before going into details of Double-clutch system, a quick review of the clutch system will be helpful.
It is the mechanical part which lies in between input & output shaft. Output shaft is engaged with input shaft via the clutch assembly.
Input Shaft ------------------Clutch ----------------------Output Shaft
This is the simplest form of transmission & the assembly contains only one clutch. Gears are changed manually with the help of lever. When a driver wants to change from one gear to another, he first presses down the clutch pedal. This operates clutch, which disconnects the engine from the gearbox and disconnects the output & input shaft. With the help of synchronizers, gears are engaged & flow of power continues as soon as clutch pedal is released. It is most common type of transmission in our country with more than 80 % car using this mechanism.
The basic difference between manual & automatic transmission is that in manual transmission gears are engaged manually to get the different gear ratios while in automatic same set of gears are engaged to get different gear ratios. Differentiating factors in automatic transmission are:
a) Omission of clutch pedal in automatic transmission.
b) Selection of driving mode with the rest being handled automatically by the transmission system.
The heart of the Automatic transmission is the “Planetary Gearset”. It has 3 main components:
1) Sun gear at the center.
2) Planet gears surrounding sun gears.
3) Ring gear as outer casing.
These three gears engaged to produce the different gear-ratios automatically which in turn drive the vehicle accordingly.
As the name suggests, Double-clutch transmission uses two clutches, which operates independently of each other. Like automatic transmission, it also has no clutch pedal. Total mechanism of operation is controlled by electronic & hydraulic sensors. One clutch controls the odd gears i.e. 1st, 3rd, 5th & reverse while other clutch takes care of even gears i.e. 2nd, 4th & 6th gear. This facilitates the changing of gears without any interruption in the flow of power from engine to output shaft.
In place of Torque converter, as used by automatic transmission, Double Clutch transmission uses Wet-plate clutches. Lubricating fluid is used to reduce the friction as well as to apply the pressure to the plates. Hydraulic pressure is applied to drive the gears.
Another differentiating factor is the use of dual-clutch transmission shaft as opposed to single shaft in manual transmission. Shaft is divided into outer & inner shaft. Inner shaft is nested into outer shaft which is hollowed from inside. Outer transmission shaft houses even gears while inner shaft supports odd gears in addition to reverse one.
When in operation, one gear is always engaged and another is pre-selected: while the first clutch is transmitting power in one gear, the second clutch has the next gear selected and ready to engage. When the gearshift point is reached, one clutch segment opens in a flash while the other closes. The driver therefore hardly notices the gearshift process.
Advantages of Double-Clutch transmission
The Double-clutch transmission gives the freedom to operate both in automatic mode and with manual shifting:
1) The flexible automatic mode allows the driver to control the whole mechanism automatically by selecting the driving mode only once.
2) If the driver prefers manual gearshift, the gears can be changed with the gearshift. Paddles on the steering wheel or with the selector lever.
3) The gearbox’s high efficiency leads to low fuel consumption and reduced emissions.