Twin Clutch SST

Twin Clutch SST (Sport- or Sportronic Shift Transmission) is the brand name of a six-speed dual clutch transmission developed by Getrag for Mitsubishi Motors. The system was first incorporated in the 2007 Lancer Evolution X, and was designed to be a more performance-oriented system than that developed by rival manufacturers, with shorter gear ratios optimized for acceleration.

TC-SST uses dual clutches to change gears. The TC-SST completes the clutch and gear shifts more quickly than a driver could in a conventional manual transmission, and is also quicker than either an automatic transmission with a torque converter, or a single clutch automated manual transmission. The system's high-efficiency power transmission mechanism is on par with a normal manual gearbox, while allowing quicker gear shifting with no drop-off in engine power, thus offering greater performance and better fuel economy. The system can be operated by both a console-mounted shifter, and magnesium steering wheel paddle shifters; and offers semi-manual and fully automatic modes. TC-SST also works in conjunction with Mitsubishi's S-AWC system.

The operation of TC-SST is smoother than that of a conventional automatic transmission because it uses clutches instead of a torque converter to transmit power. The key to the system's operation is in the electronic and hydraulic controls. TC-SST can select two gears at the same time by putting odd (1st, 3rd, 5th) and even (2nd, 4th and 6th) gears on separate input shafts, each connected to an individual clutch. While one gear is engaged by one of the two electro-hydraulically operated wet multi-plate clutches, the other is pre-selected, awaiting to be engaged by the second wet multi-plate clutch. The TC-SST, in principle, behaves like two three-speed manual transmissions operating on the same output shaft. With both clutches under precise system control, the gear change is made when the clutches are "swapped" simultaneously, allowing fast, smooth gear changes with no interruption in power delivery. Nevertheless, those who prefer the traditional "stick shift" have criticized the level of driver involvement in TC-SST and other dual-clutch transmissions.

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