Once, ‘Nikkei Automotive Technology’ featured a special issue on gearboxes, focusing on the extent to which CVT (Continuously Variable Transmission) could expand its territory in the automatic transmission field. However, the then-unsung third type of automatic transmission, DCT (Dual Clutch Transmission), is now showing a rapid rise in prominence.
DCT is essentially an ‘AMT (Automated Manual Transmission)’ gearbox that automates the shifting work of a manual gearbox, with its uniqueness lying in the integration of two sets of clutches and two sets of gear positions. The two clutches are connected to odd gears such as 1st, 3rd, 5th, etc., and even gears such as 2nd, 4th, 6th, etc., respectively. By alternately switching between the clutches, rapid shifting between even and odd gears is achieved.
In 2003, Volkswagen in Germany was the first to equip this type of automatic transmission in mass-produced vehicles, naming it ‘DSG (Direct Shift Gearbox)’. In the following four years, no other manufacturers followed Volkswagen’s lead. But today, DCT suddenly shows a trend of popularization. In addition to Mitsubishi Motors and Nissan Motor’s new models to be launched this autumn, Ford Group and Chrysler are also increasing their investment in DCT. Many DCT manufacturers predict that by 2015, DCT will occupy 15% to 20% of the global gearbox market.
The reasons why DCT has become a focus today are mainly two-fold. First, compared to conventional AT (Automatic Transmission) equipped with a torque converter and CVT, it does not have slippage, providing a direct acceleration sensation when stepping on the accelerator. Second, the absence of slippage loss in the torque converter and the use of spur gears with higher transmission efficiency than planetary gears result in higher fuel efficiency than ordinary AT. Although there is currently no direct comparison data with CVT, CVT experiences increased fuel efficiency reduction due to metal belt friction loss during high-speed driving. Therefore, for the European market where high-speed driving is more common, DCT is more suitable than CVT.
It is worrisome that Japanese gearbox manufacturers are slightly behind in the development of DCT. DCT is based on the structure of manual gearboxes, yet well-known Japanese gearbox manufacturers have shifted their development focus to AT and CVT. While Japan’s AT has indeed reached the global top level, the DSG, which has only been mass-produced for four years, already possesses a high degree of maturity. Given this situation, it cannot be asserted that the current status of AT is unshakeable. The November issue of ‘Nikkein Automotive Technology’ published on September 28 will feature the latest developments on DCT, which is hoped to serve as a reference for thinking about the future development of automatic transmissions.