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To many drivers, the choice between manual and automatic transmission comes down to geographical location or personal preference. Modern dual-clutch offers the best of both worlds. How does it work? To answer the question, we need a quick history lesson. Most drivers are aware of two transmission types employed when changing gears on the road; manual and automatic.
Those who learned to drive with manual transmission will no doubt remember lessons trying to master the clutch pedal and gear stick. Manual involves the driver pressing on the clutch and manipulating the stick through a set of gears. When not done smoothly, the car can jolt around meaning a not-always comfortable journey for the occupants. Automatic transmission, commonly associated with American car owners, does all the work for the driver using clutches, a torque converter and gears.
Dual-clutch transmission DCT lies in between. The dual clutch transmission operates via several in-built computers.
These computers eliminate the need for the driver to manually change gears and the entire process is automated. In this respect, a DCT can be looked upon as being similar to an automatic transmission. The main difference is that the DCT operates the odd and even gear numbers separately, which prevents the engine from being disengaged from interrupted power flow when the gears are changed.
While a dual clutch transmission looks very similar to an automatic transmission cockpit, this is where the similarities end.
In fact, a DCT has more in common with a manual transmission than it does with an automatic transmission. One of the main advantages of a dual-clutch transmission is its economical fuel saving benefits. As the flow of power from the engine is not disrupted, the rate of fuel efficiency increases. When a driver changes gears using a manual transmission, it take approximately half a second to complete the action.
While this may not sound like much, when compared to the 8 milliseconds some DCT vehicles offer the efficiency becomes apparent. The increased speed when changing gears makes a DCT considerably faster than their manual transmission counterparts. In reality, a dual clutch transmission works in the same way that a standard manual transmission does. It has both auxiliary and input shafts bat house the gears. It also has a clutch and synchronizers.
The main difference is that a DCT does not have a clutch pedal. The need for the clutch pedal is eliminated due to the fact that Hydraulics, solenoids, and computers perform the shifting operation. The driver is still able to instruct the computer system when to perform certain actions through buttons, paddles or gear shifts.
This ultimately improves the overall driver experience and is considered to be one of the most dynamic types of acceleration available. A "wet" clutch is one that bathes the clutch components in lubricating fluid to reduce friction and limit the production of heat.
Several manufacturers are developing DCTs that use dry clutches, like those usually associated with manual transmissions, but all production vehicles equipped with DCTs today use the wet version. Many motorcycles have single multi-plate clutches. Like torque converters, wet multi-plate clutches use hydraulic pressure to drive the gears. The fluid does its work inside the clutch piston, seen in the diagram above.
When the clutch is engaged, hydraulic pressure inside the piston forces a set of coil springs part, which pushes a series of stacked clutch plates and friction discs against a fixed pressure plate. The friction discs have internal teeth that are sized and shaped to mesh with splines on the clutch drum. In turn, the drum is connected to the gearset that will receive the transfer force.
Audi's dual-clutch transmission has both a small coil spring and a large diaphragm spring in its wet multi-plate clutches. To disengage the clutch, fluid pressure inside the piston is reduced. This allows the piston springs to relax, which eases pressure on the clutch pack and pressure plate.
Hopefully it's becoming clear why the DCT is classified as an automated manual transmission. In principle, the DCT behaves just like a standard manual transmission: It's got input and auxiliary shafts to house gears, synchronizers and a clutch.
What it doesn't have is a clutch pedal, because computers, solenoids and hydraulics do the actual shifting. Even without a clutch pedal, the driver can still "tell" the computer when to take action through paddles, buttons or a gearshift. Driver experience, then, is just one of the many advantages of a DCT. With upshifts taking a mere 8 milliseconds, many feel that the DCT offers the most dynamic acceleration of any vehicle on the market.
It certainly offers smooth acceleration by eliminating the shift shock that accompanies gearshifts in manual transmissions and even some automatics.
Best of all, it affords drivers the luxury of choosing whether they prefer to control the shifting or let the computer do all of the work. Perhaps the most compelling advantage of a DCT is improved fuel economy. Because power flow from the engine to the transmission is not interrupted, fuel efficiency increases dramatically. Some experts say that a six-speed DCT can deliver up to a 10 percent increase in relative fuel efficiency when compared to a conventional five-speed automatic.
Many car manufacturers are interested in DCT technology. However, some automakers are wary of the additional costs associated with modifying production lines to accommodate a new type of transmission.
This could initially drive up the costs of cars outfitted with DCTs, which might discourage cost-conscious consumers. In addition, manufacturers are already investing heavily in alternate transmission technologies.
One of the most notable is the continuously variable transmission , or CVT. A CVT is a type of automatic transmission that uses a moving pulley system and a belt or chain to infinitely adjust the gear ratio across a wide range. CVTs also reduce shift shock and increase fuel efficiency significantly. But CVTs can't handle the high torque demands of performance cars. DCTs don't have such issues and are ideal for high-performance vehicles.
In Europe, where manual transmissions are preferred because of their performance and fuel efficiency, some predict that DCTs will capture 25 percent of the market.
The man who invented the dual-clutch gearbox was a pioneer in automotive engineering. Unfortunately, adverse business circumstances prevented further development. Both Audi and Porsche picked up on the dual-clutch concept, although its use was limited at first to racecars. In , a Porsche won the Monza Kilometer World Sports Prototype Championship race -- the first win for a car equipped with the PDK semi-automatic paddle-shifted transmission. Audi also made history in when a Sport quattro S1 rally car equipped with dual-clutch transmission won the Pikes Peak hill climb, a race up the 4,meter-high mountain.
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