Influence of dry friction on the irreversibility of cycloidal speed reducer.

Gears with involute profile have been used broadly as power transmission mechanisms. High speed reduction ratios can be obtained with trains of gears, resulting in high power losses due to friction. Compound planetary gears allow obtaining high speed reduction ratios with a lower number of gears involved in the power transmission, hence transmitting it with higher efficiency. Although high efficiency is a main requisite for speed reducers, for some applications it may be desirable to have an irreversible mechanism. A modern trend in power transmission systems is to use cycloidal profile gears. These systems present low backlash, high load capability and higher efficiency due to the rolling motion. Furthermore, their large transmission ratio in single stage allows more compact designs. The present paper deals with the development of a simplified model for the calculation of efficiency of cycloidal speed reducers. The followed approach takes into account the main parameters influencing the efficiency, in particular, the friction and the geometrical properties of the components. The resulting model is used to investigate the relation among efficiency and reduction ratio in order to define the conditions for the irreversibility. A test bench is developed for the validation of the results.