The DSG dual-clutch gearbox, available in 6-speed and 7-speed versions, is unlike a conventional automatic transmission. Two independent gearboxes are connected under load to the engine in turn, depending on the current gear, via two drive shafts. An output shaft assigned to each gearbox applies the torque to the driven wheels via the differential gear. Clutches and gearboxes are operated hydraulically by the gearbox mechatronics (a combination of mechanics and electronics). The electronic transmission control unit, sensors and hydraulic control unit form one compact unit. The control unit uses information such as engine speed, road speed, accelerator position and driving mode to select the optimum gear and to determine the ideal shift point. The control unit then implements the shift commands in a sequence of precisely co-ordinated actions. Each change takes less than four-hundredths of a second. DSG can be used manually, via the Tiptronic gearlever or the optional paddle shifts.
The EDC is a combination of two parallel half gearboxes, which work together and are both designed like a traditional manual gearbox. The engine torque is transmitted to each half gearbox via a specific clutch:
One clutch looks after the odd-number gears (1st, 3rd and 5th)
The second clutch covers the even-number gears (2nd, 4th and 6th), as well as reverse.
At the perfect moment gears are changed by shifting from one clutch to the other, the first clutch opens whilst the second closes simultaneously which guarantees continuous and smooth traction during gear changes.
The Ford PowerShift is a six-speed dual clutch semi-automatic gearbox produced by the Ford Motor Company.
The Ford PowerShift gearboxes are built by Getrag Ford Transmissions, a joint-venture with Getrag.
PowerShift improves fuel efficiency by as much as 10 percent when compared to a conventional automatic transmission.
The operation of a dual clutch transmission is analogous to two traditional manual transmissions, each with its own clutch, operating in parallel and alternating shifts. The Ford unit is a six-speed with one clutch acting on first, third and fifth gear, and the other used for second, fourth and sixth gear. As first gear is engaged, the 2-4-6 clutch is disengaged and the second gear cogs are engaged. At the appropriate time, the 1-3-5 clutch is disengaged and the 2-4-6 clutch is engaged. While in second gear, the other side shifts from first to third. The process is repeated with quick smooth shifts and none of the efficiency loss normally associated with torque converters.
The PowerShift gearbox is a joint development between Ford, Getrag and Luk and was first introduced in Europe. Both Volvo and Ford use wet clutches and hydraulic actuation. However, the new PowerShift gearbox used in the Ford Fiesta and Ford Focus uses dry clutches and electric motor/solenoid actuation. Some have criticized the PowerShift's rough starts and lack of smooth shifting, but Ford has continually released (but not publicized) upgrades to transmission software and firmware designed to address these concerns
VAG DSG, Renault EDC, Ford Powershift Dual Clutches
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