Problem Statement

Bicycles are some of the most popular vehicles in the world due to their low cost and convenience. According to statistical results, over 50 percent of the world population knows how to ride a bicycle. By some estimates, there are already more than two billion bikes in use around the world, and that number could be as high as five billion in 30 years. In spite of the immense size of the bicycle industry, for a relatively long period, the engineering design of bicycles has seen little improvement. Until today, nearly all bicycles has either a single gear ratio or a derailleur design that has a number of discrete gear ratios. Despite these are time-proven designs that are robust and reliable, they are relatively inefficient and outdated. Therefore, by this day, any adjustment to increase the performance or comfort of a bicycle is technically significant and commercially profitable.

Aiming to improve the current bicycle design, Columbia Vector Technologies company has created a Continuous Variable Transmission (CVT) design to remove the intermittent shifting loss that discrete shifting mechanisms face and to simplify the shifting process for the operator. The proposed design utilizes two lever arms with an adjustable applied moment which drives an output shaft. The lever arms moves back and forth, however, only engage with the output shaft in the forward direction due a ratcheting mechanism. It is worth noting that unlike other CVT designs that utilize belts, in this CVT design, there is no slipping at higher torque due to the fact that only chains are used. One interesting effect of the design is the non constant rotational speed of the output crank. This effect has been utilized in order to maximize the use of torque. Although this CVT design is tested on a bicycle, its applications are not limited to bicycles alone, but are useful for applications where there is a high torque and low rotational speed input. Being simple, inexpensive, novel and versatile, our new bicycle non-slip CVT design is promising to have considerable commercial value in the near future.

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