DSG / TWIN-CLUTCH / Ford PowerShift Focus

[parakitoJDM]

How Dual-clutch Transmissions Work.

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 racecars, 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.

This article will explore how a dual-clutch transmission works, how it compares to other types of transmissions and why some predict that it is the transmission of the future.

1. Hands-On or Hands-Off
A dual-clutch transmission offers the function of two manual gearboxes in one. To understand what this means, it's helpful to review how a conventional manual gearbox works. When a driver wants to change from one gear to another in a standard stick-shift car, he first presses down the clutch pedal. This operates a single clutch, which disconnects the engine from the gearbox and interrupts power flow to the transmission. Then the driver uses the stick shift to select a new gear, a process that involves moving a toothed collar from one gear wheel to another gear wheel of a different size. Devices called synchronizers match the gears before they are engaged to prevent grinding. Once the new gear is engaged, the driver releases the clutch pedal, which re-connects the engine to the gearbox and transmits power to the wheels.

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:

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. We'll learn about these two shafts in the next section.

2.Dual-clutch Transmission Shafts
A two-part transmission shaft is at the heart of a DCT. Unlike a conventional manual gearbox, which houses all of its gears on a single input shaft, the DCT splits up odd and even gears on two input shafts. How is this possible? The outer shaft is hollowed out, making room for an inner shaft, which is nested inside. The outer hollow shaft feeds second and fourth gears, while the inner shaft feeds first, third and fifth.
The diagram below shows this arrangement for a typical five-speed DCT. Notice that one clutch controls second and fourth gears, while another, independent clutch controls first, third and fifth gears. That's the trick that allows lightning-fast gear changes and keeps power delivery constant. A standard manual transmission can't do this because it must use one clutch for all odd and even gears.



Multi-plate Clutches
Because a dual-clutch transmission is similar to an automatic, you might think that it requires a torque converter, which is how an automatic transfers engine torque from the engine to the transmission. DCTs, however, don't require torque converters. Instead, DCTs currently on the market use wet multi-plate clutches. 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.

We'll look at the pros and cons of dual-clutch transmissions next.

3. Pros and Cons of Dual-clutch Transmissions
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. Just one percent of cars produced in Western Europe will be fitted with a CVT by 2012.

Next, we'll look at the history of the DCT and see what the future holds.

4.Dual-clutch Transmissions: Past, Present and FutureThe man who invented the dual-clutch gearbox was a pioneer in automotive engineering. Adolphe Kégresse is best known for developing the half-track, a type of vehicle equipped with endless rubber treads allowing it to drive off-road over various forms of terrain. Both Audi and Porsche picked up on the dual-clutch concept, although its use was limited at first to racecars.
Commercialization of the dual-clutch transmission, however, has not been feasible until recently. Volkswagen has been a pioneer in dual-clutch transmissions, licensing BorgWarner's DualTronic technology.
Ford is the second major manufacturer to commit to dual-clutch transmissions, made by Ford of Europe and its 50/50 joint venture transmission manufacturer, GETRAG-Ford. It demonstrated the Powershift System, a six-speed dual-clutch transmission, at the 2005 Frankfurt International Motor Show. NOW ITS HERE IN FOCUS_TDCi! Kudos to Ford Philippines for marketing this in our shores!

Original article here:
How Dual-clutch Transmissions Work | HowStuffWorks

[parakitoJDM]

Twin Clutch / Direct Shift Gearbox (DSG)

What it is, how it works
The twin-clutch transmission, also known as the Direct Shift Gearbox (DSG), R-Tronic or S-Tronic, is an automated transmissin that can change gears faster than any other geared transmission. Twin-clutch transmissions can be shifted either manually or automatically. They deliver more power and better control than a traditional automatic transmission and faster performance than a manual transmission. Originally markted by Volkswagen and Audi as the DSG and R/S-Tronic transmission, twin-cluch transmissions are now being offered by other automakers.

The twin clutch/DSG is a development of the sequential manual transmission (SMT), which is essentially a fully-automated manual transmission with a computer-controlled clutch. Before we delve into the workings of the DSG, let's start with an explanation of the SMT.

SMT: The control of a manual with the ease of an automatic
Though it has appeared on a few passenger cars, the SMT is widely used in certain forms of racing and is featured on some exotic high-performance cars.

Cars with SMTs have a manual transmission with no clutch pedal; the clutch is automatically engaged. Most SMTs can be shifted automatically or manually, the latter using a shift lever or paddles on the steering wheel. The advantage to an SMT is that it uses a solid coupling, as opposed to a fluid coupling (torque converter) as used in a traditional automatic (including Tiptronic- or manumatic-style transmissions). As with a manual transmission, the SMT provides a direct connection between engine and transmission, allowing 100 percent of the engine's power to be transmitted to the wheels. The SMT provides more immediate response and ensures that the engine RPMs do not drop when the driver lifts off the accelerator (as happens with an automatic), giving her more precise control over power output.

SMTs can also perform matched-rev (or double-clutch) downshifts: When the driver downshifts, the SMT disengages the clutch, shifts to neutral, and re-engages the clutch. The SMT calculates what the engine RPMs will be in the next-lowest gear based on the current road speed, and revs the engine (and, since the clutch is engaged, the transmission) to that speed. It then disengages the clutch, shifts into the lower gear, and re-engages the clutch. The result is a smooth change with no jerk and no sudden deceleration.

SMTs have one major disadvantage, same as a manual: Power must be interrupted while the transmission changes gears.

Twin clutch: An SMT without the lag
The twin-clutch transmission all but eliminates the lag inherent in SMTs. The twin-clutch is essentially two gearboxes with a pair of clutches between them, one for odd gears, one for even gears. When the driver starts out, transmission #1 is in first gear and transmission #2 is in second. The clutch engages and the car starts out in first. When it's time to change gears, the transmission uses the clutches to swap transmissions. The #1 transmission immediately shifts to third gear. At the next change the transmission swaps transmissions again, and #2 shifts to fourth. The twin-clutch transmission's computerized controller calculates the next likely gearchange and shifts the "idle" transmission into that gear. The advantage is the speed of gearchanges: Volkswagen's DSG takes about 8 milliseconds to upshift. Compare that to the SMT in the Ferrari Enzo, which takes 150 ms to upshift. It's also significantly faster than a human: According to Audi, the A3 runs 0-60 in 6.9 seconds with a 6-speed manual and 6.7 seconds with the 6-speed DSG. Like the SMT, the DSG performs double-clutch downshifts and can skip gears (i.e. downshifting from 6th directly to 4th, 3rd, etc).

Driving with a twin-clutch transmission
Most twin-clutch transmissions, incliding Volkswagen's DSG, use a traditional P-R-N-D-S shift pattern. In the case of Volkswagen's DSG, the transmission can shift automatically in either normal (D) or Sport (S) modes. In Normal mode, the DSG shifts to the higher gears early in order to minimize engine noise and maximize fuel economy. In Sport mode the transmission holds the lower gears longer in order to keep the engine in its powerband. This is especially useful for turbocharged cars like Audi A3, Volkswagen GTI and VW Jetta GLI, since the turbocharger is only active at higher RPMs. Sport mode also provides more aggressive downshifts with slight accelerator pedal pressure.
Manual mode is engaged by either sliding the shift lever to the side or pulling one of the paddles on the steering wheel. Once in manual mode, shifts are made by moving the shifter fore and aft or using the paddles (which are marked " " and "-"). If manual mode was engaged with the paddles, pulling and holding the upshift paddle returns the transmission to automatic mode, allowing the driver to quickly downshift to a lower gear for passing and then hand control back over to the transmission.

[REQUEST TO SYSTEM ADMIN ; MODERATOR, can u make this THREAD STICKY? T.I.A]

[knightrider07]

pardon for my ignorance yung twin clutch na sinasabi mo ito ba yung dual padded shift na nakikita ko sa likod ng manibela me plus and minus nakikita ko sa mitsubishi at honda actually naghahanap ako ng topic tungkol dun on how a dual padded shift works.

[ghosthunter]

pardon for my ignorance yung twin clutch na sinasabi mo ito ba yung dual padded shift na nakikita ko sa likod ng manibela me plus and minus nakikita ko sa mitsubishi at honda actually naghahanap ako ng topic tungkol dun on how a dual padded shift works.

no. DSG system has no relation to paddle shifts.

Paddle shifts are basic switches to activate the higher or lower gear from the steering column instead of from the gear selector.

[motocyclist]

any idea if the friction disc will needs replacement overtime?

[niky]

any idea if the friction disc will needs replacement overtime?

Eventually, they'll wear out. All clutches wear out. The question is, when. Properly managed, a standard manual clutch can last around 100,000 - 200,000 kilometers. A dual clutch sees less strain on each clutch, and the computer control ensures that neither will ever see lining-burning slippage or dragging.

In the Focus, the dual-clutch is supplemented by a torque converter, which provides the smoothing action and slips so the clutches don't have to. In the Fiesta, we are getting a true dry system. Durability unknown, but it should be better than the Honda CVT system.

[fireproofjat]

Eventually, they'll wear out. All clutches wear out. The question is, when. Properly managed, a standard manual clutch can last around 100,000 - 200,000 kilometers. A dual clutch sees less strain on each clutch, and the computer control ensures that neither will ever see lining-burning slippage or dragging.

In the Focus, the dual-clutch is supplemented by a torque converter, which provides the smoothing action and slips so the clutches don't have to. In the Fiesta, we are getting a true dry system. Durability unknown, but it should be better than the Honda CVT system.

Hello, good evening! I know this post is from a decade ago.

But going back to the above point, does this mean that Dry clutches are better than Wet type for our country's setting? The recent China cars are using both - Dry for Chery, created by Getrag, I believe also 6DCT250 and Wet for Geely.

[Dr.Kamiya]

AFAIK it depends on the application. Wet clutch is generally used for high-torque/high-power applications. Dry clutch for lighter duty. If you look at the high-end DSG equipped cars (Porsche, Nissan GTRs etc) they're all wet-clutch.

Budget DSG cars almost always use dry clutch.