Wear of sprag clutch wedge in overrun state under high temperature condition

Abstract

A formula is proposed based on Archard’s wear model to calculate wedge wear depth in a positive continuous engagement (PCE)-type sprag clutch with double-disc inner cam wedge in the overrun state. Methods to solve for the equation parameters are proposed. Using a sprag clutch with an M50 steel wedge as an example, wedge wear depth variation over time under high temperatures was analyzed. An easy-to-clamp wedge was designed and a high-temperature abrasion testing machine was used to test the wedge. The worn surface profile was observed using a three-dimensional profiler and the wedge wear depth was obtained. The effects of lubrication, temperature and speed on wear were analyzed using mixed-level orthogonal experimental design. Results show that the theoretical values are consistent with test values. Therefore, the model can be used to calculate wear accurately for the overrunning sprag clutch. Lubrication affects wear depth significantly, whereas temperature has a smaller effect and speed has very little influence. Within the experimental scope, when the temperature increased by 1°C, the wear depth increased by approximately 0.0145 μm and when the speed increased by approximately 1 time/minute, the wear depth increased by 0.00854 μm. These results provide theoretical support for optimal sprag clutch design.

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

“…Vernay et al [4] analyzed the mechanical properties of the sprag clutch and the dynamic friction in contacts between the wedge and inner and outer rings under an instantaneous overload. Li et al [5] studied the wear of wedge for sprag clutch during state of overrunning, proposed the calculation equation of wedge wear depth based on Archard wear theory, and discussed the effects of temperature, speed, and lubrication conditions on wedge wear through experimental tests. Huang et al [6] proposed an alternate friction model considering stationary and dynamic friction, and it was applied in the contacts of the outer and inner race.…”