Investigation of the four-bar linkage in a rear derailleur system with experimental verification

Abstract

The derailleur system on a bicycle can be time-saving or labour-saving for riders by changing the suitable reduction ratio. In this study, a mathematical model of the four-bar linkage mechanism in a spatial rear derailleur is developed to simulate the cable force in shifting. The relation between the cable force and cable displacement is obtained and verified. It is found that friction between the cable and adjusting screw unit is a key factor. Then, the mathematical model is used to optimize the cable force. By changing the position of coupler point, we can reduce not only the maximum cable force by 9.26% but also the force difference between the maximum and minimum by 65.5%. Finally, a roller design to replace sliding contact between the cable and the adjusting screw unit is proposed to reduce the friction force.