Crank variable-speed gear device for increasing rotational power

A crank variable-speed gear device (100) for bicycles, which comprises a crank shaft (112) rotatably supported by a shaft housing (110) in a shell (S) provided on a frame structure (F) of a bicycle, and a pair of crank arms (114, 116) provided at both ends of the crank shaft (112) symmetrically to each other such that phases thereof are opposite each other and disc-type inner end parts (114a, 116a) thereof are fixedly mounted at the crank shaft (112), the crank variable-speed gear device comprising:

• (a) a housing (120) mounted on the crank shaft (112), and having a central opening (121) formed therein, a recess (122) formed in a radial inner surface of a first side of the housing (120), and a chain ring mounting part (123) provided at a second side of the housing (120) so as to protrude from the other side of the housing (120) by a designated length;
• (b) a gear assembly disposed in the housing (120) and in the recess (122), and comprising a sun gear (140) mounted on a radial outer surface of the shaft housing (110) in the housing (120), planetary gears (150) disposed so as to revolve about the sun gear (140) while being engaged with the sun gear (140) through one side of a radial outer surface of each thereof, and a ring gear (160) disposed outside the planetary gears (150) so as to be engaged with a remaining side of the radial outer surface of each of the planetary gears (150) and provided with a second gear toothed part (162) formed on a radial inner surface of the ring gear (160);
• and
• (c) a latch assembly disposed in the housing (120) and on the second side of the housing (120) so as to be coupled thereto, and comprising a latch body (170) having a plurality of latch sites (175) formed on a radial inner surface thereof, a plurality of first latches (118) respectively disposed on the latch sites (175), a latch ring (180) disposed so as to be inserted into the latch body (170) and having a second latch engaging portion (182) formed on a radial inner surface thereof, second latches (176) disposed in the second latch insertion recesses (147) formed on a radial outer surface of the sun gear (140) such that upper end parts of the second latches (176) are engaged with the second latch engaging portion (182), a latch guide (190) disposed in the latch body (170), a lock ring (200) mounted on a radial outer surface of the latch body (170), and a ring-shaped fastening bracket (220) fixedly mounted on one side surface of the latch body (170).