Joint clearances with lubricated long bearings in multibody mechanical systems

Proper modeling of joint clearance is of great importance in the analysis a nd design of multibody mechanical systems. The clearance may be due to wear or imperfection in manufacturing. When there is no lubricant in the cleara nce, solid-to-solid contact occurs, The impulse due to contact between the links is transmitted throughout the system. The presence of a lubricant avo ids such contact, as the hydrodynamic forces developed by the lubricant fil m support the loads acting on the bodies and prevent the bodies from coming into contact. In this paper, an analysis of revolute joint clearances in m ultibody mechanical systems with and without lubricant is presented. Squeez e as well as viscous effects are considered utilizing the hydrodynamic theo ry of lubrication in long bearings. Unlike the traditional machine design a pproach, the instantaneous lubricant forces are the unknown and evaluated i n terms of the known geometrical position and velocity of the journal and b earing. In the case of analysis of a joint clearance with no lubricant, a m odified Hertzian relation is used to model the impact or contact between th e journal and bearing, which includes a hysteresis damping term to account for the energy dissipation during impact. The methodology is applied for th e analysis of a slider-crank mechanism having a clearance in the piston pin . The simulations are carried out with and without lubricant and the result s are compared. It is shown that the lubricant results in a steady motion w ith fewer peaks in the required cranking moment far the system.