DIRECT-SHIFT GEARBOX

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

Introduction

Operation

Advantages & disadvantages

Applications

Notes

External links

Introduction

The engine drives two 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]. In comparison, the SMT in the Enzo Ferrari takes 150 ms to upshift^[1][2]. The quoted time for upshifts is the time the wheels are completely non-powered.

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 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.

Advantages & disadvantages

'Advantages'

★ Extremely fast shift time of 8 milliseconds when shifting to the gear the transmission is expecting

★ Practically no power loss, due to the use of clutches instead of a torque converter

★ Better fuel economy than the planetary geared automatic transmission and manual transmission

★ Both clutches can disengage when travelling downhill, allowing the car to coast
'Disadvantages'

★ When shifting to a gear that the transmission did not anticipate, shift time is lengthy (around 400ms, depending on the situation)

★ Can be expensive to manufacture, this discourages many automakers

★ They are heavy: 75kg vs. 47.5 for comparable Getrag DSG and Manual models

★ Being complex mechanisms there is more to potentially break

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, Golf GTI/R32, Touran, Eos, Golf, and Jetta/Bora.
Other companies rumored to soon use the DSG gearbox:

★ BMW M3 (7 Speed DSG available starting in 2008) NOTE: BMW is not part of VW Group and VW Group has denied interest in selling the product to other companies, though rumors of a DSG gearbox in a BMW persist.

Notes

1. How the Direct Shift Gearbox works - from About.com Cars
2. Transmission | Twin-Clutch Gearbox - from AutoZine Technical School
3. How the Direct Shift Gearbox works - from About.com Cars
4. Transmission | Twin-Clutch Gearbox - from AutoZine Technical School

External links

★ Technical explanation of manual transmissions

★ Audi TT 3.2 DSG review

★ Informative article from Just-Auto.com

★ Video comparing a Golf GTI with a manual transmission and a Golf GTI with DSG

★ Audi DSG video