Patent ID: 8109166

Claim:
A twin clutch speed-change apparatus, comprising: a transmission having a plurality of gear pairs disposed between a main shaft and a countershaft, and a twin clutch provided on the main shaft, a rotational drive force from a power source being connected/disconnected between the transmission and the power source by the twin clutch, wherein: the main shaft is composed of an inner tube carrying odd speed-change step gears and an outer tube carrying even speed-change step gears; the twin clutch includes a first clutch adapted to connect/disconnect a rotational drive force transmitted to the inner tube and a second clutch adapted to connect/disconnect a rotational drive force to the outer tube; the gear pairs are each composed of an axially slidably attached slidable gear and axially non-slidably attached non-slidable gear to select one gear pair for transmitting the rotational drive force to the countershaft; the slidable gears are each provided on a corresponding one of the inner tube, the outer tube and the countershaft and are each slid by a corresponding one of shift forks each engaging a corresponding one of the slidable gears to connect/disconnect the rotational drive force between the slidable gear and the non-slidable gear coaxially adjacent thereto; the transmission is configured to be able to shift to an adjacent speed-change step by switching the engaging state of the twin clutch when the slidable gear is located at a predetermined position; a dog clutch is provided between the slidable gear and the non-slidable gear coaxially adjacent to the slidable gear so as to transmit the rotational drive force by engaging a dog tooth with a dog hole; and the dog tooth is formed with at least two steps different in axial height from each other between a portion abutted against a lateral wall surface of the dog hole when the rotational drive force of the main shaft is transmitted by the dog clutch and a portion abutted against a lateral wall surface of the dog hole when the rotational drive force of the main shaft is not transmitted by the dog clutch.