Gearing and power transmission apparatus

A gearing and power transmission apparatus comprising:

• a drive shaft of a driving power source;
• an output shaft of a transmission;
• a twin clutch assembly provided between the drive shaft and the output shaft, the twin clutch assembly comprising a first clutch and a second clutch;
• a first input shaft selectively connectable to the drive shaft via the first clutch;
• a second input shaft selectively connectable to the drive shaft via the second clutch;
• a first gear transmission mechanism provided between the first input shaft and the output shaft and comprising plural gear trains by which plural shift stages are respectively established;
• a second gear transmission mechanism provided between the second input shaft and the output shaft and comprising plural gear trains by which plural shift stages, which are different from the plural shift stages of the first gear transmission mechanism, are respectively established;
• plural shift forks movable in parallel with the first and second input shafts to select one of the plural shift stages by switching gear engagement of the plural gear trains in response to movement of the plural shift forks;
• plural fork heads respectively connected to the plural shift forks and positioned so that tip ends of the respective fork heads overlap one another in a direction at right angles to the first and second input shafts, the respective tip ends being formed with reverse C-shaped notches;
• at least one shift and select member having a tip end which is movable inside the notches in the direction at right angles to the first and second input shafts to select one of the plural fork heads, the at least one shift and select member being movable, while the one of the plural fork heads is being selected, in parallel with the first and second input shafts to move the selected one of the plural fork heads to establish a shift stage in the transmission, wherein, while a shift stage is being established by one of the first and second gear transmission mechanisms, a gear engagement of an other one of the first and second gear transmission mechanisms is switched, and
• at least one interlock member comprising at least one restraining portion movable together with the shift and select member in the direction at right angles to the first and second input shafts, the at least one restraining portion extending in the direction at right angles to the first and second input shafts along both inner sides of the notches of the respective tip ends while the respective fork heads are positioned at a neutral position in the direction at right angles to the first and second input shafts to restrain movement of the tip ends of the respective fork heads, the at least one restraining portion comprising a gap into which the tip ends of the respective fork heads extend, the gap being at a position which corresponds to the tip end of the shift and select member, and a dimensional relationship between an outer span H1 of the tip end of each of the fork heads, an inner span H2 of the notch, an outer span P1 of the restraining portion, an inner span P2 of the restraining portion, a width I of the tip end of the shift and select member, and a shift stroke S of each of the fork heads is set to be:
• H2−P1≧0;
• P2−H1+2S≧0;
• and H2−2S−I≧0.