| 摘要 |
A bicycle has front and rear wheels, a sprocket coupled to a pedal crank, a sprocket gear, gears on the rear wheel and a gear chain extending around the sprocket gear and an individual one of the rear wheel gears. The chain is adjustably coupled to the individual gears on the rear wheel to respectively increase and decrease the gear ratio relative to the sprocket gear for sprocket speeds above the upper limit and below the lower limit. The upper limit is adjustable as by initially operating up and down switches together within a particular time limit and then operating the up switch for upper limit increments or the down switch for upper limit decrements. The sequence may then be repeated for lower limit adjustments. The movement of a particular number of sprocket ribs past a detector and the time for such movement are measured and processed to determine the sprocket speed. When the sprocket is rotating continuously at a speed below the lower limit, as when coasting downhill, the gear ratio is not changed. The system power is discontinued for no sprocket movement for a continuous time greater than the limited time.
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