PURPOSE: To provide a compact and inconspicuous motive power device which does not exert influence on a bicycle body and maneuverability in a bicycle having a prime mover by using a combination of efficient bevel gears and spur gears.
CONSTITUTION: In a motive power device for a bicycle having a prime mover, the device has an engine where a crank shaft 72 is arranged between a front wheel and a pedal crank shaft 104 toward the rear of the bicycle, and has a flywheel magnet 82 installed on the rear end of the crank shaft 72, a speed reduction gear part 90 having a single stage of bevel gear pairs 92 and 94 and two stages of spur gear pairs 95, 97, 99 and 101 which are connected to an engine part 70 through a centrifugal automatic clutch 83 and are arranged in a spiral shape and can change according to a car body structure and a crank shaft 104 joined to a driving sprocket 103 through a free wheel 105 by passing penetratingly through the axis of an output shaft of the speed reduction gear part 90.
KOBAYASHI YOSHIO
UENOYAMA KAZUYUKI
YAMAZAKI KENJI
YAMAZAKI SEISAKUSHO KK