Nonlinear TransientRolling-Contact Dynamics of Sprag Overrunning Clutches

This paper presents a unified time-domain framework for the transient rolling-contact dynamics of sprag overrunning clutches with off-center contact kinematics. In these clutches, the sprag rotation center does not coincide with the centers of curvature of its cam surfaces. Consequently, sprag rotation changes the sprag–race contact geometry, producing coupled normal and tangential relative displacements that govern direction-dependent wedging, slip, and separation during one-way torque transmission. To describe transitions among pure rolling, rolling with gross slip, and separation, the formulation couples evolving contact locations and local contact frames with displacement-based normal and tangential force laws. These contact states emerge from the local contact response without switching between separate clutch-state models. The present implementation uses a unilateral normal-contact law and an elastic tangential law bounded by the Coulomb friction limit. Prescribed-motion analysis demonstrates the resulting force–displacement response and its dependence on the direction of sprag rotation. Transient simulations of a simplified torsional powertrain reproduce clutch operating states and their transitions. A comparison of three sprag geometries illustrates competing effects on slip margin, contact loading, and the maximum magnitude of sprag rotation. The framework provides a tool for analyzing transient rolling-contact phenomena in sprag overrunning clutches and supporting design studies.