Automated manual transmissions (hereinafter, referred to simply as “automated MTs”) have been recently developed as systems in which a gear-type transmission for manual shift changes is used to automate the operation of a clutch which is a friction transmission mechanism, and the operation of a synchromesh mechanism which is one type of mesh mechanism. For automated MTs, the start of a shift change first disengages the clutch that transmits and cuts off the torque of an-engine which is a source of driving force, then switches the synchromesh mechanism, and engages the clutch once again.
Also, as described in Japanese Patent No. 2703169, an automated MT is known as a modification of a conventional automated MT. This automated MT has a wet-type multi-disc clutch as one form of friction transmission mechanism, thereby to transmit driving torque via the wet-type multi-disc clutch, even during shift changes. For this automated MT, the start of a shift change transmits input torque to the transmission via the wet-type multi-disc clutch, releasing the torque being transmitted by the gear that was working before the shift change, and disengaging this gear. The selected next change gear will be engaged when rotational control is conducted with the driving torque being transmitted via the wet-type multi-disc clutch and the input-shaft speed of the transmission reaches a speed equivalent to that of the selected next change gear. After that, the wet-type multi-disc clutch will be disengaged. Smooth shift changing that avoids driving torque interruptions can be implemented by, as described above, changing the driving torque in order from the before-shift-change gear ratio equivalent, to the gear ratio equivalent at which the wet-type multi-disc clutch is engaged, and further to the after-shift-change gear ratio equivalent.
In addition, as described in Japanese Patent Laid-Open No. 2000-234654, 2001-295898, and 2003-1200764, a twin-clutch automated MT is known that has two clutches to transmit input torque to the transmission, the two clutches being switched in an alternate fashion to transmit driving torque. In this twin-clutch automated MT, the start of a shift change progressively disengages the clutch that was transmitting the torque before the shift change, and at the same time, progressively engages the clutch of the next gear speed, thereby to change the driving torque in order from the before-shift-change gear ratio equivalent, to the after-shift-change gear ratio equivalent. Thus, driving torque interruptions are avoided and smooth shift changing is achieved.
Unlike the so-called automatic transmissions with a torque converter, the various types of automated MTs described above are free of so-called “creeping” due to the use of the torque converter. During vehicle start, therefore, these automated MTs generate pseudo-creeping by controlling the transmission torque of the particular clutch functioning to transmit and cut off the torque of the engine which is the source of driving force.
During the start of the vehicle with such an automated MT, it is desirable that the time from the release of a brake by a driver to the start of so-called “creeping” should be as short as possible. If the time from the start of clutch engagement to the transmission of torque to the transmission is too long, a feeling of delay in the vehicle start is likely to occur.
Japanese Patent Laid-Open No. Hei 8 (1996)-54031 describes a technique for shortening the time up to the rise of clutch transmission torque by advancing the clutch only through a certain stroke thereof while the vehicle is in a standby condition before being started.