Patent ID: 8684881

Claim:
A transmission gear box for bikes comprising: a main shaft that is connected to pedals and crank arms of each bike; a transmission gear unit having a plurality of transmission mode gearshifts provided in parallel and interlocked with the main shaft and receives a driving force transmitted from the main shaft to thus shift a transmission mode; a lever manipulation unit that selects one of the transmission mode gearshifts of the transmission gear unit according to manipulation of a transmission mode shift lever, to thus manipulate one of cables connected to the respective transmission mode gearshifts; and a clutching unit that is operated by one cable selected by the lever manipulation unit to thus make one of ring gears of the transmission gear unit fixed in a gear tooth engagement coupling manner and to thereby manipulate a transmission mode shifting process of the transmission gear unit, wherein the transmission gear unit comprises: a planet gear carrier that is spline-combined and interlocked with the main shaft; a plurality of planet gears that are pin-coupled and interlocked with the planet gear carrier and are disposed in parallel with each other; a plurality of the ring gears that are disposed in parallel with each other in correspondence to the planet gears, in which gear teeth are formed on inner circumferential surfaces of the ring gears so as to be respectively engaged with those of the planet gears; and sun gears and a sun gear shaft that output a transmission mode shifted driving force with respect to the driving force of the rotating main shaft to the outside when one of the ring gears is fixed by the clutching unit.