April 2011

e-Soft board
Theme: Dual clutch transmission
The theme encompasses the following:

Introduction
History
How dual clutch transmission works
Advantages and disadvantages
Examples
Conclusion
References

Introduction:
The 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 "clutch less"
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.
The dual-clutch transmission is an automatic transmission which uses a manual transmission style lay-shaft gear
arrangement. One clutch drives the odd numbered gears and reverse, while the other clutch drives the even
numbered gears. During shifts, the next gear is anticipated and pre-selected. Then one clutch is opened while the
other is closed, allowing shifting without torque interruption. The result is quicker acceleration and refined shift
quality. Further, with the lay-shaft arrangement of gears, there is increased flexibility to optimize gear ratio
selection for performance and fuel economy
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

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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.
History:
This type of transmission was invented by Frenchman Adolphe Kgresse just prior to World War II, but he never
developed a working model. The first actual DCTs arrived from Porsche in-house development, for Porsche
racing cars in the 1980s, when computers to control the transmission became compact enough: the Porsche
Doppelkupplungsgetriebe (English: dual clutch gearbox) (PDK) used in the Porsche 956 and 962 Le Mans race
cars from 1983, and the Audi Sport Quattro S1 rally car.
A dual clutch transmission eliminates the torque converter as used in conventional epicyclic-geared automatic
transmissions. Instead, dual clutch transmissions that are currently on the market primarily use two oil-bathed wet
multi-plate clutches, similar to the clutches used in most motorcycles, though dry clutch versions are also
available.
The first series production road car to be fitted with a DCT was the 2003 Volkswagen Golf Mk4 R32.
As of 2009, the largest number of sales of DCTs in Western Europe is by various marques of the German
Volkswagen Group, though this is anticipated to lessen as other transmission makers and vehicle manufacturers
make DCTs available in series production automobiles. In 2010, on BMW Canada's website for the 3 Series
Coupe, it is described both as a 7-speed double clutch transmission and as a 7-speed automatic transmission. It is
actually a dual clutch semi-automatic.
How dual clutch transmission works:
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

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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.

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Advantages and disadvantages:

Advantages
There are a few both important advantages when it comes to dual-clutch transmission. First of all, as you can see
for yourself, there's the reaction time. The whole assembly works incredibly fast, less than a hundredth of a
second as in the case of DSG designed by Volkswagen.
Secondly, there's the fuel consumption. The dual-clutch clutch gearbox improves the fuel consumption, especially
at cruising speeds because it automatically adjust its settings to maintain the desired speed but keeping the fuel
efficiency at the highest possible level.
Last but not least, there's the comfort it provides. Although it doesn't work as smoothly as a traditional automatic
transmissions and sometimes you may actually feel the shifting process a little bit, a dual-clutch transmissions is
much more appropriate for city driving than a regular manual unit that requires the driver to change gears every
time when needed.
Disadvantages
Although it doesn't look so, the dual-clutch transmission system has a major disadvantage caused by the very
things that make it so worthwhile: the two clutches. While shifting into higher gears can be made surprisingly fast,
there might be a problem when looking to get more power - for overtaking other cars for example. Imagine this:
you're driving outside the city with around 100 km/h, or if you prefer 62 mph and you instantly need more power
to pass the car in front.
Obviously, you press the throttle pedal which immediately transmits information to the gearbox, requiring more
power. The dual-clutch transmission system is indeed ready to give you a boost of power (that's a good thing)
only that it may take a while until you get it. In order to get more power, the system has to shift into a lower gear -
let's say from fifth to second. Because these two gears are handled by different clutches, the whole process
described above takes a bit more than expected.
Examples:
Automakers and their very own dual-clutch transmission systems

2009 Passat CC DSG BMW M3 M-DCT Lancer Evolution X Twin Clutch

SST

Several automakers have already adopted this type of transmission and just as expected, they've marketed them
under different names. Probably the most known system is Volkswagen's DSG one - which stands for Direct-Shift
Gearbox - which is installed on VW, SEAT and Skoda models.
Mitsubishi has also designed its own dual-clutch transmission and installed it on the Lancer Evolution X. The
system is known as the Twin Clutch SST.
Hyundai is quite new in this sector, as the South Korean automaker displayed at the 2009 Geneva Motor Show the
ix-onic concept car equipped with a 6-speed double-clutch transmission. BMW rolled out the first dual-clutch
assemble in January 2008 on the M3 model - it is known as M DCT that stands for M Dual Clutch Transmission.

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BMW
In January 2008, BMW introduced a dual clutch transmission for their M3 model, manufactured by GETRAG,
embedding a DualTronic dual clutch module from BorgWarner, and dubbed M Dual Clutch Transmission (M
DCT). The same transmission is used in the second generation Z4 (the Sdrive35i version), and is an available
option on the 335is and later 135i builds.
Chrysler
Chrysler is scheduled to receive Fiat Powertrain Technologies C635 dual dry-clutch transmission for use on
Chrysler's inline-4 and V6 Pentastar in a C-plus and D-segment car in 2013
Chryslers automatically operated manual transmission
(dual-clutch automatic) was engineered for trucks and cars.
This type of transmission has never successfully been applied
to light-duty vehicles, and never with the degree of
sophistication and cleverness being applied by Chrysler
engineers.
However, it now appears that, as part of Cerberus attempt to
swap Chrysler for GMAC, the transmissions will not be made
for Chrysler; the contract with Getrag to produce them has
been broken.
Fiat Group
Fiat Powertrain Technologies (FPT) started production of "TCT" Dual Dry
Clutch Transmission (DDCT) in early 2010 at the Verrone plant. The C635
DDCT gearbox is used for B (supermini), C (compact car), and D segment
(large family car) cars, and can handle torque up to 350 Nm (258 ftlbf). Fiat's
C635 DDCT gearbox will be introduced in Alfa Romeo MiTo in 2011.
This transmission will eventually show up in the next generation of B, C and D
segment Chrysler products coming to showrooms next year. Just recently, Fiat
announced the Fiat 500 will receive a smaller version of the Dual Dry Clutch
Transmission , this time with seven speeds.

Ford Motor Company

Ford Motor Company has released a wet clutch "Power Shift" transmission on the 2008 Ford Focus (international)
and Ford C-MAX. This wet clutch DCT was designed with gearbox specialist Getrag under the GETRAG FORD
Transmissions joint venture, founded in 2001, and is expected to feature in other Ford and Volvo models. Ford
has announced the US-market version of the Mark VI Ford Fiesta coming in 2011 will feature a dry clutch Power
Shift transmission. Ford also announced the introduction of Power Shift transmission to North American market
by 2010.
General Motors
In the company's restructuring plan, it revealed that dry dual clutch transmission would be available in 2012
calendar year. The GM's dual-clutch gearbox will be introduced on the GMC Granite. The new front-wheel drive
transmission will incorporate the latest innovations for improving fuel economy and performance. The
transmission alone will provide upward of 10 percent improvement in fuel economy over todays conventional
six-speed automatic transmissions.
Honda
In October 2009, Honda launched the VFR1200F, a motorcycle with a 1,200 cc V4 engine and optional DCT
dubbed the Next Generation Transmission. In May 2009, Honda CEO Takeo Fukui mentioned that Honda was
working on a new dual clutch transmission system that could be matched with future hybrids.

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Hyundai
At the 2009 Geneva Motor Show, Hyundai unveiled ix-onic concept car, which was said to feature a six-speed
dual clutch transmission.
On 22 December 2010, Hyundai teased the reveal of its entry-level sports car, the Veloster, a vehicle with a dual-
clutch transmission and an estimated fuel consumption of 40 mpg-US (5.9 L/100 km; 48 mpg-imp). The teaser notes
the date of reveal to be 10 January 2011, when it will be shown at the North American International Auto show.
Lotus
Lotus Cars has submitted a patent application for a lighter, simpler and more compact dual-clutch transmission
system. The gearbox shown in the application is an eight-speed unit, with seven forward gears and reverse.
McLaren Automotive
McLaren Automotive introduced a seven speed dual clutch on MP4-12C. It is made in Italy by Graziano
Mercedes-Benz
The Mercedes SLS AMG use a Getrag AMG 'Speed Shift' seven-speed dual clutch gearbox, mounted at the rear
in a transaxle configuration, and connected to the engine via a carbon fiber driveshaft enclosed in an aluminum
torque tube. According to Mercedes-Benz, it is capable of gear changes in as little as 100 ms. The SLS and the
Ferrari California share the same DCT unit.
Mitsubishi
The Mitsubishi Motors Lancer Evolution X and Lancer Ralliart are supplied with Mitsubishi's Twin Clutch SST
(abbreviated TC-SST, for "Twin Clutch Sport Shift Transmission" or "Twin Clutch Sportronic Shift
Transmission") dual clutch transmission, controllable by steering wheel mounted magnesium paddle shifters. It is
the Getrag-built, Power Shift 6DCT470 transmission in the Mitsubishi Lancer Evolution.
Mitsubishi Fuso Truck and Bus Corporation
The Mitsubishi Fuso Truck and Bus Corporation presented a world first with a double-clutch transmission for
commercial vehicles. The new six-speed M038S6 "Duonic transmission" features wet clutches and incorporates
the ability to creep in traffic for smoother operation. Although Duonic-equipped trucks will probably be driven
mostly in fully-automatic mode, the transmission can also be manually shifted.
Nissan
The Nissan GT-R's rear transaxle six-speed dual clutch transmission also contains the differential for the car's all-
wheel drive (AWD) system. The dual clutch system was built by BorgWarner, partnered with Nissan's gearbox
supplier Aichi Machine Industry, and weighs a total installed mass of 117 kg (258 lb). Nissan reports shift times
of 200 milliseconds.
PSA Peugeot Citron
PSA has dual clutch transmission in Peugeot 4007 and Citroen C-Crosser CUVs, produced by Mitsubishi motors.
Porsche
Porsche AG offers a series production of two new longitudinally-installed, ZF Friedrichshafen AG designed and
built with Porsche '7DT' wet-clutch versions of its previously race-only[5][42] Porsche Doppelkupplungsgetriebe
(PDK) transmission.
Renault
Renault will be introducing a new six-speed dual dry clutch DCT in the early part of 2010. This will initially be
made available on the New Mgane with the dCi 110 DPF engine. The DCT system was built by Getrag. This will
enable these DCT-equipped Meganes to be the marque's first automatic cars to qualify for the Renault eco
signature.

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Volkswagen Group
Volkswagen Group produces DCTs under the Direct-Shift Gearbox (DSG) name, from the German: Direkt-
Schalt-Getriebe. It is used in all of their mainstream marques, including Volkswagen Passenger Cars, Audi,
SEAT, koda, and Volkswagen Commercial Vehicles, and also its top-tier marque Bugatti. Audi originally used
the Direct-Shift Gearbox (DSG) name, it now uses the name "S tronic" for its DCTs.
Railcar use
A different type of dual-clutch transmission has been used in some railcars. The two clutches are placed one on
the gearbox input shaft and the other on the gearbox output shaft. When a gear change is to be made, both
clutches are disengaged simultaneously and a brake is applied inside the gearbox. The gear change is made with
all gears stationary, so no synchronizing mechanism is needed. After the gear change, both clutches are re-
engaged. There would be a significant break in transmission so this system would be unsuitable for shunting
locomotives.
Conclusion:
In a Dual clutch transmission precise and quick shifting is elemental to the function of the transmission, and
transmission efficiency is fundamental to both fuel efficiency and synchronizer function. Although shift quality is
not directly affected by the synchronizers, smooth and quick transition of gears, including up shift, downshift, and
skip shift is logically a significant factor in accomplish the fuel economy objective.
Clutch drag torque, fiction losses, and churning losses must be established in early stages to assist in the design of
the synchronizer parameters Sleeve and synchronizer blocker ring pointing angle (roof angle) must be designed to
maintain index torque above the drag torque in every gear position to preserve gear engagement Synchronizer
cone coefficient of friction must be designed to secure synchronization torque higher than index torque at every
point during synchronization event

To view the Dual Clutch animation please see the below link:
http://www.dctfacts.com/information/dual-clutch-animation.aspx

References:
http://en.wikipedia.org/wiki/Dual_clutch_transmission
http://auto.howstuffworks.com/dual-clutch-transmission2.htm
http://www.autoevolution.com/news/how-dual-clutch-transmissions-work-5458.html
http://www.volkswagen.com/etc/medialib/vwcms/virtualmaster/de/Unternehmen/mobilitaet_und_nachhaltigkeit/d
ownloads/umweltpraedikate.Par.0034.File.pdf/ec_dsg_background.pdf
http://www.fiat500usa.com/2010/05/inside-fiats-dual-dry-clutch.html
http://www.allpar.com/corporate/auto-manual-transmission.html

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