Spatial Multibody Systems with Lubricated Spherical Joints: Modeling and Simulation

The dynamic modeling and simulation of spatial multibody systems with lubricated spherical joints is the main purpose of the present work. When the spherical clearance joint is modeled as dry contact; i.e., when there is no lubricant between the mechanical elements which constitute the joint, a body-to-body (typically metal-to-metal) occurs. The joint reaction forces in this case are evaluated through a Hertzian-based contact law. The presence of a fluid lubricant avoids the direct metal-to-metal contact. In this situation, the squeeze film action, due to the relative approaching motion between the mechanical joint elements, is considered utilizing the lubrication theory associated with the spherical bearings. In both cases, the intra-joint reaction forces are evaluated as functions of the geometrical, kinematical and physical characteristics of the spherical joint. These forces are then incorporated into a standard formulation of the system's governing equations of motion as generalized external forces. A spatial four bar mechanism that includes a spherical clearance joint is considered here as example.