Power transmission apparatus using planetary gear having a plurality of gear trains and methods of use thereof

A power transmission apparatus using a planetary gear having a plurality of gear trains, the power transmission apparatus comprising:

• a cover (110) which is open or closed;
• a housing (100) provided with a speed changing locking unit (120) therein;
• a carrier (10) installed inside the housing (100);
• a planet gear set (20) including three or more different sized planet gears (20a, 20b and 20c), in which at least three of the planet gear sets are installed on one side of the carrier (10) to rotate freely;
• a ring gear set (30) including different sized ring gears (30a, 30b and 30c) rotating independently of each other, in which the planet gears (20a, 20b and 20c) mesh with internal teeth of the ring gears (30a,30b, and 30c), respectively;
• a sun gear set (40) including different sized sun gears (40a, 40b and 40c) formed in one body to be meshed with external teeth of the planet gears (20a, 20b and 20c) and having an output shaft (41) which outputs power to an outside of the housing (100);
• and
• an input shaft (50) which is aligned coaxially to the output shaft (41) and rotates the carrier (10) by external force transmitted from the outside of the housing (100),
• wherein the speed change locking unit (120) locks and releases selectively one of the ring gears (30a, 30b and 30c);
• and
• wherein the input shaft (50) extends out of the housing (100) by passing through a shaft extension (12).