Analytical Modeling and Optimization of Logarithmic Sprag Clutch Considering Profile Modification

Abstract

A new analytical model of a logarithmic sprag clutch considering profile modification is proposed to reflect the effect of profile parameters on the dynamic contact pressure distribution during the engagement, especially the edge stress of a sprag roller. In the model, a nonlinear iteration method of normal force including the logarithmic profile model with three parameters and structural deformations of races is given. The alternate friction model considering stationary and rate-dependency friction is formulated and applied in the contacts between the sprag rollers and races. Then, the kriging model describing the relationship between the maximum contact stress throughout the engagement and the profile parameters is established and validated, and the kriging-based optimization of the design parameters is proposed using genetic algorithms. In subsequent analysis, based on the presented analytical model and optimization process, the maximum contact stress throughout the engagement can decrease greatly through optimizing the profile parameters. Therefore, the results of the present paper could aid in the design of the logarithmic sprag clutch and help avoid end crush failure and low cycle fatigue of the sprag roller.