Direct-Shift Gearbox - Advantages and Disadvantages

Advantages and Disadvantages

Advantages

• Better fuel economy (up to 15% improvement) than conventional planetary geared automatic transmission (due to lower parasitic losses from oil churning) and for some models with manual transmissions;
• No loss of torque transmission from the engine to the driving wheels during gear shifts;
• Short up-shift time of 8 milliseconds when shifting to a gear the alternate gear shaft has preselected;
• Smooth gear-shift operations;
• Consistent shift time of 600 milliseconds, regardless of throttle or operational mode;

Disadvantages

• Achieving maximum acceleration or hill climbing, while avoiding engine speeds higher than a certain limit (e.g. 3000 or 4000 RPM), is difficult since it requires avoiding triggering the kick-down-switch. Avoiding triggering the kick-down-switch requires a good feel of the throttle pedal, but use of full throttle can still be achieved with a little sensitivity as the kick-down button is only activated beyond the normal full opening of the accelerator pedal.
• Marginally worse overall mechanical efficiency compared to a conventional manual transmission, especially on wet-clutch variants (due to electronics and hydraulic systems);
• Expensive specialist transmission fluids/lubricants with dedicated additives are required, which need regular changes;
• Relatively expensive to manufacture, and therefore increases new vehicle purchase price;
• Relatively lengthy shift time when shifting to a gear ratio which the transmission ECU did not anticipate (around 1100 ms, depending on the situation);
• Torque handling capability constraints perceive a limit on after-market engine tuning modifications (though many tuners and users have now greatly exceeded the official torque limits.); Later variants have been fitted to more powerful cars, such as the 300 bhp/350Nm VW R36 and the 272 bp/350 Nm Audi TTS.
• Heavier than a comparable Getrag conventional manual transmission (75 kg (170 lb) vs. 47.5 kg (105 lb));
• Mechatronic units in earlier models are prone to problems and requires replacement units