Contact Analysis And Dynamic Test Of Sprag Overrunning Clutch’s Engaging Process

Sprag overrunning clutch is a key component of the helicopter transmission system,its level of excellence has a crucial impact on the performance and reliability of the aircraft. With the development of aircraft, the speed is getting higher and the load is becoming heavier, so the requriements of the strength and dynamic performance of clutch are getting higher and higher. But the domestic research carried out in these two areas are not enough. This paper selects sprag clutch as the research object, contact analysis and dynamic test of the engaging process as the main research content.First, based on the classic formula of the contact angle of the wedge and the relevant mathematical model of Hertz contact theory to calculate the static contact force and contact stress through Matlab programming for the strength check of clutch; build sprag clutch geometry and Finite Element Method model in ANSYS Workbench, and conduct the finite element simulation of static contact. And compare the iterative calculation results with the finite element simulation results, carry out convergence analysis of the finite element simulation method, explore the influence of the number of arc on simulation results.Then, based on LS-DYNA conduct the sprag clutch dynamic contact analysis.Establish sprag clutch geometric model and finite element model and calculate the output shaft’s speed through the engaging process, the force between the sprag and outside ring, as well as the distribution of the largest contact force between the contact pairs, explore effect of the friction coefficient and the strip spring stiffness on the clutch dynamic contact characteristics.After that, according to the analysis of the results of the contacts, carry out the clutch dynamic test rig principles, design the test stand mechanical systems, data acquisition and control system and complete the test machining, assembly and commissioning, solve the mechanical design and assembly difficulty, oil lubrication and sealing problems, ensure concentricity and levelness of test rig.Finally conduct dynamic performance test to test the clutch drag torque and the speed of the output shaft during the engaging progress in order to verify the results of dynamic contact analysis and get the clutch dynamic performance parameters.