Dual-clutch transmission

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Part-cutaway view of the Volkswagen Group 6-speed dual-clutch transmission, the Direct-Shift Gearbox (DSG). The concentric multi-plate clutches have been sectioned, along with the mechatronics module. This also shows the additional power take-off unit for distributing torque to the rear axle for four-wheel drive applications. — View this image with annotations
Schematic diagram of a dual-clutch transmission. This shows the layout of two side-by-side single-plate clutches.

A dual-clutch transmission, (DCT) (sometimes referred to as a twin-clutch gearbox or double-clutch transmission), is a type of semi-automatic or automated manual automotive transmission. It uses two separate clutches[1] for odd and even gear sets. It can fundamentally be described as two separate manual transmissions (with their respective clutches) contained within one housing, and working as one unit.[2][3] They are usually operated in a fully automatic mode, and many also have the ability to allow the driver to manually shift gears,[1] albeit still carried out by the transmission's electro-hydraulics.

History[edit]

This type of transmission was invented by Frenchman Adolphe Kégresse just before World War II but he never developed a working model. The first development of the Twin Clutch or Dual-clutch transmission started in the early part of 1980 under the guidance of Harry Webster at Automotive Products (AP), Leamington Spa with prototypes built into the Ford Fiesta Mk1, Ford Ranger & Peugeot 205. Initially, the control systems were based on purely analogue/discrete digital circuitry with patents filed in July 1981.[4] All of these early AP Twin Clutch installations featured a single dry clutch & multi-plate wet clutch. Following discussions with VW/Porsche, DCT work continued from Porsche in-house development, for Audi and Porsche racing cars later in the 1980s,[2] when computers to control the transmission became compact enough: the Porsche Doppelkupplungsgetriebe (English: dual-clutch gearbox) (PDK)[2] used in the Porsche 956[2] and 962[2] Le Mans race cars from 1983,[2] and the Audi Sport Quattro S1 rally car.[5][6]

A dual-clutch transmission eliminates the torque converter as used in conventional epicyclic-geared automatic transmissions.[1] 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.[7]

The first series production road car to be fitted with a DCT was the 2003 Volkswagen Golf Mk4 R32.[2][8][9]

As of 2009, the largest number of sales of DCTs in Western Europe are by various marques of the German Volkswagen Group,[10] though this is anticipated to lessen as other transmission makers and vehicle manufacturers make DCTs available in series production automobiles.[2][11] 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.[12][13]

Overview[edit]

In DCTs where the two clutches are arranged concentrically, the larger outer clutch drives the odd numbered gears,[1][2][8] while the smaller inner clutch drives the even numbered gears.[1][2][8] Shifts can be accomplished without interrupting torque distribution to the driven roadwheels,[1][2][3][5][8] by applying the engine's torque to one clutch at the same time as it is being disconnected from the other clutch.[2][5] Since alternate gear ratios can pre-select[1][2][3][5] an odd gear on one gear shaft while the vehicle is being driven in an even gear,[3] (and vice versa), DCTs are able to shift more quickly than cars equipped with single-clutch automated-manual transmissions (AMTs), a.k.a. single-clutch semi-automatics. Also, with a DCT, shifts can be made more smoothly than with a single-clutch AMT, making a DCT more suitable for conventional road cars.[14][not in citation given]

Clutch types[edit]

There are two fundamental types of clutches used in dual-clutch transmissions: either two wet multi-plate clutches which are bathed in oil (for cooling), or two dry single-plate clutches.[9] The wet clutch design is generally used for higher torque engines which can generate 350 newton metres (258 lbf·ft) and more (the wet multi-plate clutch DCT in the Bugatti Veyron is designed to cope with 1,250 N·m (922 lbf·ft)[2]), whereas the dry clutch design is generally suitable for smaller vehicles with lower torque outputs up to 250 N·m (184 lbf·ft).[2][7] However, while the dry clutch variants may be limited in torque compared to their wet clutch counterparts, the dry clutch variants offer an increase in fuel efficiency,[2] due to the lack of pumping losses of the transmission fluid in the clutch housing.[2]

Clutch installation[edit]

There are now three variations of clutch installation. The original design used a concentric arrangement, where both clutches shared the same plane when viewed perpendicularly from the transmission input shaft, along the same centre line as the engine crankshaft; when viewed head-on along the length of the input shaft, this makes one clutch noticeably larger than the other.

The second implementation utilised two single-plate dry clutches which are side-by-side from the perpendicular view, but again sharing the centre line of the crankshaft.

A latest variation uses two separate but identical sized clutches; these are arranged side-by-side when viewed head-on (along the length of the input shaft and crankshaft centre line), and also share the same plane when viewed perpendicularly. This latter clutch arrangement (unlike the other two variations) is driven via a gear from the engine crankshaft.

Suppliers[edit]

BorgWarner[edit]

BorgWarner Inc. supplies[11] wet dual clutches[2] and electro-hydraulic control modules (mechatronics)[1][11] for these dual-clutch transmissions, along with complete dual-clutch transmission and transaxle assemblies. BorgWarner, who call their technology "DualTronic",[1][11][15] entered series production (excludes Bugatti Veyron) for Volkswagen Group,[5][11] who renamed Direct-Shift Gearbox (DSG) in 2003 in the Volkswagen Golf Mk4 R32.[8][9][15] The company signed further agreements with three other (unnamed) European automotive manufacturers to incorporate their components in DCTs.[16]

On 14 January 2009, BorgWarner announced the establishment of a joint venture with the China Automobile Development United Investment Co., Ltd. (CDUI) which is owned by twelve Chinese automakers. This joint venture is known as the BorgWarner United Transmission Systems Co., Ltd., and is located in Dalian, China. The company has produced various dual-clutch transmission modules beginning in 2011.[17]

The Nissan GT-R uses BorgWarner components which include the dual-clutch module, clutch-control and shift-actuation systems and synchronizer assemblies.[18]

Fiat Powertrain Technologies[edit]

Fiat Powertrain Technologies developed a dual-clutch transmission with Magneti Marelli and BorgWarner called Euro Twin Clutch Transmission. Magneti Marelli produces the control system which integrates BorgWarner's hydraulic actuation module into its own power and transmission control units.[19] It can handle torque inputs of up to 350 N·m (260 lb·ft), making it the highest-torque dry clutch application.[citation needed] Its weight of 81 kg (179 lb), including oil and transmission control unit, its three-shaft architecture, especially axially, allows it to be installed in a several types of B- and C-segment vehicles.[20]

FEV GmbH[edit]

FEV developed a DCT with an integrated Electric Motor, providing hybrid capability. The 7H AMT Transmission provides 7 forward speeds with multiple usage of gears (the electric drive can use unused gears from the combustion engine path): this aims to substantially reduce the complexity of the unit as well as the package size and weight. Another spin-off from this design was the FEV xDCT that provides 10 forward speeds but with the mechanical complexity of a standard 6 speed DCT.[21]

Getrag[edit]

Getrag has developed a range of DCT[22] transaxles, including 7DCL750, a seven-speed transaxle for mid-engine longitudinal applications, capable of taking more than 750 N·m (553 lbf·ft).[23] Getrag will be providing its DCT in its first commercial applications, for the Dodge Journey and Volvo S40 and V50, from mid-2008.[24] Getrag has developed the 6DCT250 dry clutch DCT for use in front wheel drive transverse applications. With use of electro-mechanical actuation, rather than electro-hydraulic, the 6DCT250 transmission surpasses the conventional manual transmission in fuel consumption and CO2 emission.[25]

In the 2nd quarter of 2008, Getrag had signed an agreement with Chrysler to supply its PowerShift DCTs for use in American markets.[5] However, due to the global economic downturn, this was subsequently cancelled.[5][26][27]

In 2006 Getrag was also working with Bosch to develop a DCT for use in hybrid vehicles.[5][28]

Getrag dual-clutch transmissions are used in the BMW M3,[29] BMW 335is, BMW Z4 Sdrive35i,[30] Ferrari California,[31] Ferrari 458 Italia,[32]LaFerrari, Mercedes-Benz SLS AMG,[33] Mitsubishi Lancer Evolution X, Mitsubishi Lancer Ralliart, Ford Fiesta, Ford Focus, Renault Megane, Renault Scenic, Volvo V40, Volvo V60 and Volvo V70 vehicles.[34]

Graziano[edit]

Italian specialist Oerlikon Graziano was in the process of developing a wet clutch DCT for original equipment manufacturer (OEM) fitment into supercars.[35] It aimed to be in production by 2010.[35] Their DCT is aiming to have a torque handling capacity of 750 N·m (553 lbf·ft),[35] and they are also aiming to improve shift quality over their current automated manual transmissions (AMTs).[35] As of 2011, they supplied the 7-speed DCT for McLaren's MP4-12C supercar with a shifting time of 50ms.[36]

LuK[edit]

LuK Clutch Systems, LLC. designed and manufacture the dual dry single plate clutch system for the Volkswagen Group seven-speed DQ200 Direct-Shift Gearbox (DSG) introduced in 2008.[37] This DSG variant is used in smaller cars, with smaller displacement engines with relatively low torque outputs.[37] LuK are naming their technology "XSG" for their overview of automated shift gearbox systems,[38] and "Parallel Shift Gearbox" (PSG) for its own proprietary DCT.[39]

Ricardo[edit]

English specialist consulting engineering company Ricardo plc designed and built the Bugatti Veyron's seven-speed dual wet multi-plate dual-clutch transmission, specifically to cope with the 1,250 N·m (922 lbf·ft) of torque generated by W16 engine.[1][2][5][40]

ZF[edit]

ZF Friedrichshafen AG designed and build with Porsche the two different variants[41] of the Porsche Doppelkupplungsgetriebe (PDK) seven-speed '7DT' dual wet multi-plate clutch transmission.[41][42][43][44][45]

Applications[edit]

BMW[edit]

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 double-clutch transmission" (M DCT ). The same transmission is used in the second generation Z4 (the Sdrive35i and sDrive35is versions), and is an available option on the 335i (coupe, convertible), 335is and later 135i builds.[46]

BYD[edit]

BYD Auto introduces a dual-clutch transimission for its mid-size family sedan BYD G6.[47]

Fiat Chrysler Automobiles[edit]

Chrysler is scheduled to receive Fiat Powertrain Technologies C635 dual dry-clutch transmission for use on Chrysler's inline-4 and V6 Pentastar in the Dodge Dart and a D-segment car in 2013.[48]

Ferrari incorporated a Getrag designed and manufactured seven-speed dual wet clutch transmission in their California and 458 Italia sportscars.[49][50]

Fiat Powertrain Technologies (FPT) started production of "TCT"[51] Dual Dry Clutch Transmission (DDCT) in early 2010 at the Verrone plant.[52] 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 N·m (258 lbf·ft).[52] Fiat's C635 DDCT gearbox was introduced in Alfa Romeo MiTo in 2011.

Ford Motor Company[edit]

Ford Motor Company has released a wet clutch "PowerShift"[2][5] transmission on the 2008 Ford Focus (international)[5][53] and Ford C-MAX. This wet clutch[5] DCT was designed with gearbox specialist Getrag[5] under the GETRAG FORD Transmissions joint venture, founded in 2001,[54][55] and is expected to feature in other Ford and Volvo[53] models. Ford has announced the US-market version of the Mark VI Ford Fiesta coming in 2011 will feature a dry clutch[5] PowerShift transmission. Ford also announced the introduction of PowerShift transmission to North American market by 2010.[2][56]

The Volvo version will be built in Koping, Sweden at Volvo's transmission plant. The PowerShift gearbox will be introduced on the second generation Volvo S60,[56] and then on to the V50[53] and C30[53] models. The XC60 is expected to get this Ford PowerShift gearbox along with other new models to make more sporty cars.

General Motors[edit]

In the company's restructuring plan, it revealed that dry dual-clutch transmission would be available in 2012 calendar year.[57] The GM's dual-clutch gearbox will be introduced on the GMC Granite.[58] 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 today’s conventional six-speed automatic transmissions. The co-developed transmission between GM and SAIC will feature dry, dual-clutch technology. It will provide shift comfort equal to a conventional fully automatic transmission, with superior quality, while reducing CO2 emissions.[59]

Honda[edit]

Motorcycles[edit]

In October 2009, Honda launched the VFR1200F,[60] a motorcycle with a 1,237 cc (75.5 cu in) V4 engine and optional DCT dubbed the Next Generation Transmission.[61] 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.[62]

2012 NC700 series have dual-clutch models available: NC700SD and Honda NC700D Integra. It is the second generation from the six-speed dual-clutch transmission first used on the Honda VFR1200F.

2013 Honda introduced the CTX700DCT, a 670 cc dual clutch motorcycle selling as a 2014 model. [1]

Automobiles[edit]

Honda introduced the Acura RLX Hybrid, Honda Fit Hybrid and Acura TLX with dual clutch transmissions.

Hyundai[edit]

At the 2009 Geneva Motor Show, Hyundai unveiled ix-onic concept car, which was said to feature a six-speed dual-clutch transmission.[63]

Hyundai released the Veloster with the 6-speed EcoShift Dual Clutch Transmission in 2011.

John Deere[edit]

John Deere Tractors introduced DirectDrive in 2012 in agricol tractors.

Lotus[edit]

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[edit]

McLaren Automotive introduced a seven speed dual clutch on MP4-12C made in Italy by Oerlikon Graziano. The design comes with a feature called "Pre-Cog" which allows the driver to preselect the next highest or lowest gear decreasing shift times.[36]

Mercedes-Benz[edit]

The Mercedes SLS AMG use a Getrag[64] AMG 'SpeedShift' seven-speed dual-clutch gearbox, mounted at the rear in a transaxle configuration, and connected to the engine via a carbon fibre driveshaft enclosed in an aluminium torque tube.[64][65] According to Mercedes-Benz, it is capable of gear changes in as little as 100 ms.[65] The SLS and the Ferrari California share the same DCT unit.[66]

Mitsubishi[edit]

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,[67] controllable by steering wheel mounted magnesium paddle shifters.[68] It is the Getrag-built, PowerShift 6DCT470[68][69] transmission in the Mitsubishi Lancer Evolution.[68][69]

Mitsubishi Fuso Truck and Bus Corporation[edit]

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.[70]

Nissan[edit]

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. Much of the dual-clutch system was engineered by BorgWarner,[11] partnered with Nissan's gearbox supplier Aichi Machine Industry, and weighs a total installed mass of 117 kg (258 lb).[71][72] Code named the GR6, the transmission is quite durable in that it is able to hold in excess of 600 lb·ft (810 N·m) of torque. Nissan reports shift times of 150 milliseconds.[73]

PSA Peugeot Citroën[edit]

PSA has dual-clutch transmission in Peugeot 4007 and Citroën C-Crosser SUVs, both of which are based on Mitsubishi Outlander and produced by Getrag. However, dual-clutch transmissions are never offered in other models.

Porsche[edit]

Porsche AG offers a series production[41] of two new longitudinally installed, ZF Friedrichshafen AG designed and built with Porsche[42][45] "7DT" wet-clutch versions[41] of its previously race-only[6][45] Porsche Doppelkupplungsgetriebe[45] (PDK) transmission.

The first variant, the 7DT-45,[41] is used on its 2009 997 Carrera and Carrera S models.[3][42][74][75] This version is also offered on the 2009 Cayman,[3][41] Boxster[3][41] It uses a ZF Sachs ND2015 clutch pack,[41] and has a torque handling capacity of 500 N·m (369 lbf·ft).[41] A higher torque version of the same transmission, the 7DT-70,[41] is also available for the 2010 911 Turbo.[41][76] This is rated at 780 N·m (575 lbf·ft),[41] and uses a different ZF Sachs clutch — the ND2216.[41]

The second PDK variant, the 7DT-75,[41] is available on the 2009 Panamera.[3][41][45][77] This is constructed fundamentally differently from the 7DT-45/7DT-70 versions; in that the internal shafts are mounted above the input shaft, so as to achieve a lower centre of gravity for the Panamera.[41] It also uses just one oil circuit,[41] whereas the 7DT-45/7DT-70 use two separate circuits;[41] with very different specifications of fluids needed.[41]

Both variants use seven forward speeds,[3][43][74] and Porsche claim the Doppelkupplung PDK transmission will replace the outgoing conventional Tiptronic automatic transmissions.[42][74] However, other reliable industry sources state that Porsche still intends to use conventional automatics; with the eight-speed ZF 8HP being cited.[41] Like all DCTs, the Porsche PDK transmission is fundamentally two separate manual transmissions in one.[3] With the 1st, 3rd, 5th, and 7th gears and reverse available on one shaft,[3] and 2nd, 4th, and 6th gears available on the other shaft.[3][78]

Porsche claims noteworthy improvements in CO2 emissions of around 15% when comparing DCT installations against its former automatic transmission,[41] of which half can be directly attributed to the DCT.[41] When compared directly with a manual transmission, 16% improvement can be directly attributed to the DCT.[41]

Renault[edit]

In the early part of 2010 Renault introduced a new six-speed dual dry clutch DCT. This is available on the Mégane with the dCi 110 DPF engine.[79] 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 eco² signature.[79][clarification needed] Since 2012 facelift, Renault Mégane is first French automobile with dual-clutch transmission.

Volkswagen Group[edit]

Volkswagen Group produces DCTs under the Direct-Shift Gearbox (DSG) name,[10] from the German: Direkt-Schalt-Getriebe.[80] It is used in all of their mainstream marques, including Volkswagen Passenger Cars,[11] Audi,[11] SEAT, Škoda, 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.[5]

The first ever worldwide series production DCT was the Volkswagen Group DQ250[10] six-speed dual-clutch transmission,[8] with dual concentric wet multi-plate clutches.[8] It was produced at the Group's Kassel plant[1][2] under exclusive license from Borg-Warner[5][11] for use in transverse powertrain installations, of either front-wheel drive or four-wheel drive (4WD) layouts.[8] The 4WD versions are fundamentally identical to the 2WD versions, but the 4WD versions use an additional bolt-on power take-off unit to direct engine torque to the Haldex Traction rear axle. This DQ250 variant is used in a wide range of models: Volkswagen Passenger Cars (Polo, Golf/Rabbit/Golf Plus, Scirocco, Jetta, Eos, Passat and Touran); Audi cars (A3, and TT); SEAT cars (Ibiza, León, Altea and Toledo); Škoda cars (Octavia and Superb); and Volkswagen Commercial Vehicles (Caddy and T5 Transporter).

A second variant of the Direct-Shift Gearbox went into series production in 2008[9] — the DQ200. This consists of seven forward ratios,[9] but the notable difference over the original DQ250 is the change from wet- to dry-clutches.[2][9] This variant uses two single-plate dry clutches, arranged in a tandem design (instead of concentrically) and are therefore similar in size. The DQ200 is again for use in transverse applications, but is intended for use in smaller cars, with smaller displacement engines that generate relatively low torque outputs.[2][9][10] When used in the latest Golf with the 90 kilowatts (122 PS; 121 hp) engine, this new 7-speed DSG uses roughly 6% (5.9l/100 km for the 7-speed DSG compared to 6.3l/100 km with the 6-speed manual gearbox) less fuel than the same engine with a manual transmission[9] and up to 20% less than a conventional automatic transmission.[9] The original DQ250 also remains available.

Volkswagen Group subsidiary Audi AG have also developed an all-new DCT — the DL501, for use in longitudinal powertrains.[10][81] Like the original transverse DQ250, this DL501 utilises dual wet multi-plate clutches, but unlike the DQ250, this variant uses seven forward ratios.[10] This DL501 variant made its debut in the Q5,[81] and also is used in the latest versions of the A4 (B8)[81] and S4 (B8).[81][82] It is also be considered for use in an all new A6.[81]

The Lamborghini Huracan, uses a double clutch ‘Lamborghini Doppia Frizione' (LDF).While the Aventador uses a robotized manual. After the facelift in 2012 the R8 uses a seven-speed S tronic.

English specialist consulting engineering company Ricardo plc produces the seven-speed DCT for the 736 kilowatts (1,001 PS; 987 bhp) 2005 Bugatti Veyron EB 16.4.[1][5][40]

Railcar use[edit]

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 gearchange 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.

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