| 摘要 |
PURPOSE: A pedal driving system for a bicycle is provided to prevent the bicycle from overturned by rapid lowering of inertia by optimizing relative load according to propulsive force. CONSTITUTION: A pedal driving system for a bicycle is composed of a driving sprocket(23) coupled rotatably to a rotary shaft(14) of a frame(10), pedals(21) coupled to the rotary shaft and rotating the driving sprocket, a driven sprocket(30) installed at the frame, a chain shifting unit, and a tension unit compensating the relative displacement of the chain and keeping the tension of the chain. The driven sprocket is connected to the driving sprocket by a chain(100), receives driving force from the driving sprocket, and rotates a rear wheel(110). The chain shifting unit shifts the speed of the chain relatively to the driven sprocket according to the rotary angle of the pedals, and includes an elliptical shift rail(41) and a shift assembly(50) connected to the shift rail and pulling/pushing the chain. The shift rail is formed at one surface of the driving sprocket and, has a pair of points(42a,42b,43a,43b) on the major axis and minor axis. The tension unit includes a base bracket(71) fixed to a rotary shaft(15) coupled to the driven sprocket, a tension arm(72) coupled rotatably to the end of the base bracket, an elastic member(73) biasing the tension arm, a connecting gear(62) coupled rotatably to the end of the base bracket, and a tension gear(63) coupled rotatably to the end of the tension arm.
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