A dual-clutch transmission is an automated manual transmission that allows by means of two sub-transmission fully automatic gear changes without interruption of traction. The transmission control unit selects the gear automatically or by operator request ( shift paddles / selector ) within the framework of approved speed ranges. In contrast to the automatic transmission with a hydraulic torque converter transmission of the torque over one of two couplings which connect the two sub-transmission to the drive is carried out. As with the automatic transmission with hydraulic torque converter also this principle allows gear changes without interruption of traction. Here, by simultaneously includes a clutch, while the other opens. In large series, a dual-clutch gearbox for the first time under the name Direct Shift Gearbox (DSG ) by VW in 2003, has been introduced. Manufacturers of wet-running double clutch is the supplier BorgWarner. Since 2008, dry-running 7-speed direct shift gearbox for small volume engine to 125 kW and torque to 250 Nm arrive at VW used. Followed in 2009 with the DQ500 another model that is offered up to 500 Nm in larger vehicles.
As the principle image to the right, there is a dual-clutch transmission from two automated transmission structures, each with a clutch. One transmission unit transmits the even gears ( shown in gray), the other the even gears ( shown in blue ). The reverse ( not shown here) can be assigned to the even or odd depending on the gear transmission concept. From Radsatzprinzip the partial transmission correspond to a manual transmission vehicle, these are not described in detail here. A special feature is the transmission output. Both transmission work on a common transmission output.
The end of the switching
An electronic transmission control decides according to the switching programs ( especially) the speed or speed and the driver's request ( accelerator lever ) on the gear selector and controls the switching operations. The integrated actuator actuates the sub-transmission and the clutches electromechanically or hydraulically.
Before shifting to the switching transition is first -load branch inserted (prefix). Then the coupling of the selected gear is closed, and that of the previously polluted Ganges opened simultaneously (torque transfer ). By electronically matched " loops " of the two clutches is done in this stage adaptation of the engine speed to the new gear ratio. It is thus connected without interruption of traction. The duration of this phase is to avoid a sharp jerk, made from the difference in speed, and amounts to a few hundredths to tenths of a second. The car looks much more agile and accelerates faster.
Can, however, be connected in reverse only from a straight in an odd transition and no interruption. The controller selects this reason, depending on the situation of a temporary support gear from the other part transmission. For example, mechanically engaged and the second gear when driving in third gear at a relatively low speed and relatively high load, only the dual clutch has to be actuated in order to actually transmit the torque about the preselected support gear (in this case the second ) and its translation will allow effective. If in the example situation but manually or requested by kick-down ( depressing the accelerator pedal) the first gear, the transmission shifts nevertheless briefly in the second, and only then in the first.
The dual clutch transmission is an automatic transmission. The operation of the transmission corresponds largely to the handling of other fully automatic transmission. The driver's actions are only in the form of operations of the selector lever before the trip starts, for reversing and parking required or in special situations, such as too high a gear at steep gradients recommended. If the driver wants the manual gear selection, it can trigger this example, via shift paddles on the steering wheel or by tapping ( forward or back ) of the selector lever a second lane.
In dual-clutch transmissions are usually two wet plate clutches or dry-running friction disc clutches are used.
Dry running couplings in dual clutch transmissions are fitted as standard only in the compact class with motors up to about 250 Nm of torque, as the removal of the larger heat loss is difficult to achieve at higher powers.
Wet clutches allow for the same size higher torque and vehicle masses. The occurring during switching and starting heat loss is dissipated via a cooling oil flow. As oil sump usually the transmission itself will be used. The oil thus serves both to cool the clutch and to lubricate the gear set. A wet double clutch has always been a certain amount of drag torque in the open state, thereby leads to higher no-load losses, resulting in an efficiency reduction result. In addition, the operation of the oil pump makes it (power 500 watts) for a reduction in the overall efficiency by a total of 3-4%.
Moreover, the double clutch transmission are different in the arrangement of the couplings. Are usual in addition to the arrangement of two couplings of the same diameter in a row ( see schematic diagram) and constructions in which a different wheel diameter interleaving of the two clutches allows ( see Figure VW DSG). The advantage of this arrangement is a shorter overall length of the transmission.
Variants of the actuators
As with the automated manual transmission are different concepts with the use of different actuators to perform the switching operation and for actuating the clutch: hydraulic actuators and electromechanical actuators. Both principles have both advantages and disadvantages. Thus, the hydraulic actuator which operates with a built-in hydraulic cylinders, for example faster as the electro-mechanical actuator which operates with a built-in electric motors, consumes less power.
History and brand names
In 1939, the French inventor Adolphe Kégresse and 1940 the Darmstadt Professor Rudolf Franke reported on the first patents for a kind of dual-clutch transmission. But it was only in the 1980s, it (Porsche double-clutch gearbox) was presented by Porsche under the name PDK. The first studies on the PDK went back to the year 1969, when working for Porsche engineer Imre Szodfridt PDK encouraged. This resulted in the Porsche transmission type 919, the development of which was supported by former Porsche chief technology officer Ferdinand Piëch, but which did not reach the series production due to rougher shifting. As part of the development of the Porsche 956/962, PDK has been reinstated to date and multiply by Porsche in racing.
At Volkswagen, has been around since 2003, the dual-clutch transmission (DSG ) in series.
Names or brands at car manufacturers and suppliers:
- Audi Quattro S1 ( Rally Sport touring car ) The Audi Quattro S1 has won the DK gear much more important
- Nissan GT -R ( in transaxle design )
- BMW - M DCT Drive logic (since March 2008 in the M3, since September 2008 335i coupe / convertible and the Z4 sDrive35i, available since March 2010 at the 135i coupe / convertible, since September 2011 in the BMW M5 and BMW M6 in the beginning of 2012 )
- Chrysler - Power Shift ( presentation at the IAA 2007 Dodge Journey in combination with 2.0 -liter Turbo Diesel)
- Ferrari - ( January 2009, 7 -speed dual clutch transmission in the California, 458 Italia and F12berlinetta; Ferrari FF 4RM four-wheel drive )
- Ford - Powershift (launched in spring 2008 )
- Mercedes -Benz - Speed Shift DCT ( 7 -speed dual clutch transmission in the SLS AMG)
- Mitsubishi - Twin Clutch SST ( Sport Shift Transmission, presentation November, 2007 Lancer Evolution X )
- Peugeot 4007
- Renault - EDC (Efficient Dual Clutch)
- Volvo - Power Shift ( May 2008 to May 2010 in the C 30, S 40 and V 50, and later in C 70 in combination with the 2.0 - liter turbo diesel; further applications: XC60 in combination with the 2.0T petrol engine, V70, S80, S60 in combination with the T4 and T5 petrol engines)
- Kia Ceed
- Bugatti - DSG ( in the Veyron, 7 -speed DSG since 2005)
- Artega - DSG (presentation in the Artega GT, 6 -speed DSG from VW)
- Audi - S tronic ( until mid-2005 under the name of DSG; , next to the DSG for transverse engine now 7 -speed DSG ( DL501, the first and only DSG for differential - controlled all-wheel drive ) and 550 Nm for longitudinal engines in the A4, A5, A6 A7 and Q5)
- Seat - DSG (6- speed DSG in Altea since 2004, in Leon and Ibiza ( since 2006), 7 -speed DSG in Leon, Altea, Altea XL since 2009)
- Škoda - DSG (6- speed DSG since 2004, 7 -speed DSG in February 2009, available in the model series Octavia II, Superb II, Fabia II, Rapid, Roomster and Yeti )
- Volkswagen - DSG (6- speed DSG ( wet clutch ) since 2003, available for motors up to 380 Nm (DQ 250), 7 -speed DSG ( wet clutch ) since 2009-600 Nm (DQ 500), available in T5; 7 - speed DSG ( dry clutch ) since 2007 up to 250 Nm (DQ 200), available in various models)
- Volkswagen Commercial Vehicles - DSG (7- speed DSG ( wet-running double clutch ) was launched in September 2009 at the T5GP with 2.0 -liter TDI)
- Porsche - PDK (since July 2008 at the Porsche 911, from February 2009 in the Cayman and Boxster, as of October 2009, the Panamera and 911 Turbo and Turbo Cabrio )
- McLaren MP4 -12C
- First dual-clutch gearbox for motorcycles in 2010 in the new Honda VFR 1200 F
Recalls, and known issues in production use
Dual clutch transmission of the Volkswagen Group were the subject of recalls due to technical problems in some countries of the world. So 13,500 vehicles with DSG were recalled because of problems in the workshops in 2009 in the United States.
2013 Volkswagen in China had to recall about 384,000 vehicles because there had been problems with dual clutch transmissions. After Volkswagen information these problems associated with extreme weather conditions (heat and cold) and high traffic (lots of stop and go traffic).
In Japan, 2013, some 91,000 vehicles were recalled.
In November 2013, the Volkswagen group called 257,000 worldwide 1.6 million vehicles with dry running 7- speed dual- clutch transmission back them in Germany. Affected are the trademarks of Volkswagen, Audi, Seat and Skoda.
In Sweden, the sale of taxes was in 2012 set the type VW Passat with DSG, as it had come repeatedly to problems in the taxi business.
Hybrid drive via gear train
A starter-generator is mounted on the input shaft of one of the two partial transmissions, a hybrid drive can be realized which allows in addition to the operating modes of the parallel hybrid additional modes, otherwise require an additional coupling, which is already integrated in the dual clutch transmission. However, as arranged starter generator can not replace the flywheel as parallel hybrids and crankshaft start generators allow. If the starter generator separated by the open clutch from standstill, so sluggish lossless combustion engine, this will allow an electric vehicle drive, brake energy recovery and electrical operation of the air conditioning. If the starter generator on the closed clutch subtransmission connected to the current internal combustion engine, it can support an electric motor or charged for battery charging and its operating be affected. Here, if the other sub-transmission also connected due to the gear selector to the motor, so the first part transmission in neutral needs to be. Requirements are in addition to the two already present couplings, the two pre-existing partial transmissions and the ability to operate the sub-transmission in neutral, for each function sufficient characteristics of the battery and the starter generator.