Twin-Clutch transmission system

A transmission system is comprised of a twin-clutch transmission (3) which comprises a first clutch (C1) for selecting a first gear-ratio group and a second clutch (C2) for selecting a second gear-ratio group. A control unit (7) for controlling the twin-clutch transmission is arranged to calculate an estimated engine revolution speed produced in the event that one of two gear ratios adjacent to the present gear ratio is selected by executing one of upshift and downshift, and to disengage one of the first and second clutches which is engaged to select the gear-ratio group including the other of the two gear ratios adjacent to the present gear ratio when the estimated engine revolution speed is out of a normal operation speed range.