Direct-Shift Gearbox
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| Transmission types |
|---|
| Manual Continuously-variable |
The Direct-Shift Gearbox (Direktschaltgetriebe) is a dual-clutch gearbox designed by BorgWarner and initially licensed to Volkswagen Group (which owns the Volkswagen, Audi, SEAT, Bentley, Bugatti, Lamborghini, and Škoda brands). By using two clutches, fast shifts can be achieved, and the torque converter of a regular automatic transmission is eliminated.
Contents |
[edit] Introduction
Essentially, the engine drives both clutch packs. The outer clutch pack drives gears 1, 3, and 5 (and reverse). The inner clutch pack drives gears 2, 4, and 6. Instead of a standard large dry clutch, each clutch pack is a collection of four small wet interleaved clutch plates. Due to space constraints, the two clutch assemblies are concentric. Because the alternate clutch pack's gearing can be pre-selected (predictive shifts taking place while the other section is in use), un-powered time while shifting is avoided because power is simply switched from one gearbox to the other. The DSG takes about 8 milliseconds to upshift[1][2]. Compare that to the SMT in the Enzo Ferrari, which takes 150 ms to upshift[1][2]. The quoted time for upshifts is the time the wheels are completely non-powered.
[edit] Operation
Once the driver has selected D for drive, the transmission's first clutch is engaged and the first gear is selected on the first shaft. The driver instructs the car to accelerate, as the car accelerates the transmission's computer lines up second gear on the second shaft (which coincidentally is connected to the second clutch). Depending on the amount of power being requested by the driver (full throttle or normal driving) the car then upshifts. During this sequence, the DSG disengages the first clutch while engaging the second clutch (all power from the engine is now going through the second shaft), thus completing the shift sequence. This sequence happens in 8 ms, and there is practically no power loss.
Once the vehicle has shifted up to second gear, third gear is lined up and is pending. Once the time comes to shift, the second clutch disengages and the first clutch re-engages. Downshifting is similar to upshifting but in reverse order. The cars computer senses the car slowing down or more power required, and thus lines up a lower gear on one of the shafts not in use, and then completes the downshift.
[edit] Advantages & disadvantages
Advantages
- Extreme fast up shift and downshift time of 8 milliseconds
- Practically no power loss whatsoever, because of the short shift time
- Better fuel economy than the planetary geared automatic transmission and manual transmission
- When the car is going downhill the clutch disengages, allowing the car to coast
Disadvantages
- Response time from letting off the throttle and then reapplying is lengthy, around 400ms, depending on the situation
- Can be expensive to manufacture, this discourages many automakers
[edit] Applications
VW group vehicles available in Europe with the DSG gearbox include:
- Audi TT and A3. Audi have named the DSG "S-Tronic" in newer models.
- Bugatti Veyron 16.4 (* not a Borg Warner DSG, but marketed as one due to parent company)
- SEAT Altea, Toledo, and León
- Škoda Octavia
- Volkswagen Passat, New Beetle, Golf/Rabbit/GTI/R32, Touran, Eos, and Jetta/Bora.
[edit] Notes
- ^ a b How the Direct Shift Gearbox works - from About.com Cars
- ^ a b Transmission | Twin-Clutch Gearbox - from AutoZine Technical School
