Twin Clutch SST

Twin Clutch SST (Sport Shift Transmission or Sportronic Shift Transmission) is the brand name of a 6 speed twin-clutch transmission developed by Mitsubishi Motors. The system was first incorporated in the 2007 Lancer Evolution X.

TC-SST, Mitsubishi's first-ever automated manual transmission, uses dual clutches to change gears. The TC-SST shifts more quickly than a driver could in a pure manual transmission. It is also much 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 manual and fully automatic modes.

TC-SST also works in conjunction with Mitsubishi's S-AWC system.

Operation

The structure of TC-SST is less complex 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 advanced and precise 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 extremely fast, smooth and lag-free gear changes with no interruption in power delivery.

The odd and even gear shafts are linked via a transfer gear, resulting in a shorter overall transmission length. The transmission ECU, sensors and solenoids are all housed within the transmission valve body. The TC-SST is equipped with a transmission oil cooler and uses automatic transmission fluid (ATF).

Drive modes

TC-SST allows switching between three shifting programs: Normal, Sport and S-Sport.

• Normal mode

For use around town and other normal driving situations, Normal mode uses relatively low-speed shift points to deliver unobtrusive shifting together with optimum fuel economy.

• Sport mode

For use when driving in the mountains or when engine braking is required, Sport mode uses higher shift points and quicker shifting to deliver instant throttle response.

• S-Sport mode

Compared with Sport mode, S-Sport mode keeps the engine turning at higher revs, allowing even faster shifting.

External links

• "Twin Clutch-SST (Sport Shift Transmission) systematic", TC-SST schematic, .pdf file, Mitsubishi Motors North America press release