Wear Analysis of Support Spring of Sprag Clutch during State of Overrunning

Abstract

This paper analyzes the wear of the support spring of sprag clutches for different structural parameters during overrunning state. Specifically, the stiffness model of the support spring is established based on the characteristics of the variable helix angle, and also the supporting force model is established according to the energy conservation law during the working process of the sprag clutch. Meanwhile, the relative rotation speed between the support spring and the wedge is analyzed by dynamic simulation method. Furthermore, the wear model of the support spring in process of overrunning is established based on Archard wear theory. The results show that there is a linear relationship between supporting force and spring radial displacement compression. In addition, increasing free length and wire diameter of springs will aggravate the wear of springs, whereas enlarging pitch diameter of springs will reduce it. When free length is increased from 270 to 290 mm, the wear time is reduced by 20.88%; when wire diameter is increased from 0.5 to 0.7 mm, the wear time is reduced by 42.75%; when pitch diameter is increased from 2 to 2.4 mm, the wear time is increased by 3.35%. The degree of influence of the structural parameters on the spring wear from large to small is free length, wire diameter, and pitch diameter. Exactly speaking, when wear time is 100 hr, the relative sensitivity of structural parameters affecting the wear of the support spring is in order of free length (2.2), wire diameter (0.97), and pitch diameter (0.08). The research provides a reference for the design and optimization of the support spring for highly reliable sprag clutches.