| 摘要 |
A two directional multi-speed shifting gear of middle axle is made of outer ring, bearing ring, starwheel, freewheel screw cup, freewheel plate, core teeth, inner and outer pawls, and chainwheel etc. The chainwheel is fixed on the outer ring through thread or hole. The starwheel is geared with inner teeth of the outer ring and the core teeth. The outer pawl is mounted on pawl hub, the later is fixed on the bottom bracket case of the cycle frame. The middle axle is passed through and fixed with the freewheel plate, the core teeth and the right crank, and then inserted into the bottom bracket case. With such a shifting gear, a pedal cycle may be given a unique function that when the cycle is moving forward, the changing of it's moving speed in the very moving direction may be in-situ realized by variating the shifting gear through pedalling to enable the crank to be rotating in either positive or inversive directions.
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