Patent ID: 8235859

Claim:
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 ( 20 a , 20 b and 20 c ), 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 ( 30 a , 30 b and 30 c ) rotating independently of each other, in which the planet gears ( 20 a , 20 b and 20 c ) mesh with internal teeth of the ring gears ( 30 a , 30 b , and 30 c ), respectively; a sun gear set ( 40 ) including different sized sun gears ( 40 a , 40 b and 40 c ) formed in one body to be meshed with external teeth of the planet gears ( 20 a , 20 b and 20 c ) 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 ( 30 a , 30 b and 30 c ); and wherein the input shaft ( 50 ) extends out of the housing ( 100 ) by passing through a shaft extension ( 12 ).