DUAL CLUTCH TRANSMISSION
A semi-automatic transmission (also known as clutch-less manual transmission, dual-clutch transmission, automated manual transmission, e-gear, shift-tronic, flappy paddle gearbox, or direct shift gearbox) is a system which uses electronic sensors, processors and actuators to do gear shifts on the command of the driver. This removes the need for a clutch pedal which the driver otherwise needs to depress before making a gear change, since the clutch itself is actuated by electronic equipment which can synchronize the timing and torque required to make gear shifts quick and smooth.
Most people know that cars come with two basic transmission types: manuals, which require that the driver change gears by depressing a clutch pedal and using a stick shift, and automatics, which do all of the shifting work for drivers using clutches, a torque converter and sets of planetary gears. But there’s also something in between that offers the best of both worlds — the dual-clutch transmission, also called the semi-automatic transmission, the “clutchless” manual transmission and the automated manual transmission.
In the world of race cars, semi-automatic transmissions, such as the sequential manual gearbox (or SMG), have been a staple for years. But in the world of production vehicles, it’s a relatively new technology — one that is being defined by a very specific design known as the dual-clutch, or direct-shift, gearbox.
So, in a conventional manual transmission, there is not a continuous flow of power from the engine to the wheels. Instead, power delivery changes from on to off
to on during gearshift, causing a phenomenon known as “shift shock” or “torque interrupt.” For an unskilled driver, this can result in passengers being thrown forward and back again as gears are changed.
A dual-clutch gearbox, by contrast, uses two clutches, but has no clutch pedal. Sophisticated electronics and hydraulics control the clutches, just as they do in a standard automatic transmission. In a DCT, however, the clutches operate independently. One clutch controls the odd gears (first, third, fifth and reverse), while the other controls the even gears (second, fourth and sixth). Using this arrangement, gears can be changed without interrupting the power flow from the engine to the transmission.
Sequentially, it works like this:
A car travelling in second gear is controlled by the inner clutch . Power is sent to second gear along the outer transmission shaft
As the car increases speed, the computer detects the next gearshift point and the third gear is pre-selected.
When the driver changes gears, the inner clutch disengages and the outer clutch is activated.
The power is transferred along the inner transmission shafts to the pre-selected gear.
Drivers can also choose a fully automatic mode that relinquishes all gear-changing duties to the computer. In this mode, the driving experience is very similar to that delivered by a conventional automatic. Because a DCT transmission can “phase out” one gear and “phase in” a second gear, shift shock is reduced. More importantly, the gear change takes place under load so that a permanent flow of power is maintained.
An ingenious two-shaft construction separating the odd and even gears makes all of this possible.
Advantages Of Dual Clutch Transmission DCT :
- Better fuel economy up to 15% improvement than conventional transmission.
- No loss of torque transmission from the engine to the driving wheels during gear shifts
- Extremely fast up-shift time of 8 milliseconds.
- Very smooth gear-shift operations.
Disadvantages Of Dual Clutch Transmission DCT :
- Relatively expensive to manufacture and therefore increases new vehicle purchase price .
- Heavier than a conventional manual transmission .
- Expensive transmission fluids/lubricants with dedicated additives are required, which need changing on a regular basis.