Automatic dual-clutch transmission

An automatic dual-clutch transmission for a vehicle, comprising:

• a first input shaft and a second input shaft arranged mutually coaxially;
• a first secondary shaft and a second secondary shaft arranged in parallel to the first and second input shafts;
• a dual clutch having a first clutch for transmitting the rotational drive power from a prime mover to the first input shaft and a second clutch for transmitting the rotational drive power to the second input shaft;
• a first gear change mechanism provided between both of the input shafts and the first secondary shaft and having gear trains of plural stages including a predetermined low speed stage, and a first shift clutch for bringing the gear trains into engagements with both of the input shafts and the first secondary shaft or disengagements therefrom;
• a second gear change mechanism provided between both of the input shafts and the second secondary shaft and having gear trains of plural stages including a reverse stage gear train, and a second shift clutch for bringing the gear trains of the second gear change mechanism into engagements with both of the input shafts and the second secondary shaft or disengagements therefrom;
• an output shaft for receiving the rotation of either of the first and second input shafts and the first and second secondary shafts;
• gears provided on one of the first and second input shafts and constituting a part of the low speed stage gear train and a part of the reverse stage gear train;
• a low speed stage shift clutch included in the first shift clutch for bringing one of the first and second input shafts into engagement with the low speed stage gear train;
• and
• a reverse stage shift clutch included in the second shift clutch for bringing one of the first and second input shafts into engagement with the reverse stage gear train;
• wherein in performing a parking, the low speed stage shift clutch and reverse stage shift clutch are simultaneously engaged to establish a parking lock through connections of one of the first and second input shafts with the low speed stage gear train and the reverse stage gear train;
• wherein each of the first and second shift clutches comprises:
• a clutch hub fixed on one of the first and second secondary shafts and having a gear formed on an external surface thereof;
• an engaging member rotatably provided on said one of the first and second secondary shafts and having a gear formed on an external surface thereof;
• and
• a sleeve being axially movable relative to the clutch hub and the engaging member and formed at an internal surface thereof with a gear which is always in meshing with the gear of the clutch hub and which is able to be brought into engagement with the gear of the engaging member or disengagement therefrom;
• and
• wherein in at least one of the low speed stage shift clutch and the reverse stage shift clutch, the gears of the engaging member and the sleeve are able to mesh with each other at side surfaces thereof which are formed to extend linearly in parallel to an axial direction thereof.