A planetary-drive two-gear automatic transmission comprises a sun gear (21), a duplex planet gear (24), a planet carrier (22), a gear ring (23), a belt brake ring (3), and a locking ring (4). The planet carrier (22) is provided with an annular boss (221). The locking ring (4) is disposed between the outer surface of the gear ring (23) and the inner surface of the annular boss (221). The inner surface of the locking ring (4) is fixedly connected to the outer surface of the gear ring (23). One part of the outer surface of the locking ring (4) is in contact with the inner surface of the annular boss (221), and the other part of the outer surface of the locking ring (4) is sleeved with the belt brake ring (3). One end of the belt brake ring (3) is fixedly connected to a transmission casing, and the other end of the belt brake ring (3) is connected to a gearshift actuator. The gear ring (23) and the planet carrier (22) are engaged or disengaged by means of the locking ring (4) and the brake ring (3), so as to achieve the effect of gear shifting; the response speed is high, the motion is stable and free of impact; a clutch, a synchronizer and a gearshift mechanism are not required, few parts are used, and the structure is simple. The variation range of a drive ratio can be increased by changing a tooth ratio of a planetary system. The planetary-drive two-gear automatic transmission is suitable for industrial use.
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