Revisiting Mobility-Based Predictions of Cyclic Minimum Film Thickness in Big-End Connecting Rod Bearings

This article compares elastohydrodynamic lubrication (EHL) and mobility-based solution methods for the determination of cyclic minimum film thickness h_min * encountered in four-stroke, big-end connecting rod bearings. Mobility-based solution methods are substantially faster than the EHL method for such bearings, so quantifying the accuracy of mobility-based methods is an obvious benefit to the engine designer. Production-level connecting rods are modeled and analyzed using an established mass-conserving mode-based EHL formulation, accounting for realistic oil feed arrangements and realistic housing deformation associated with structural inertia and surface pressures. From a large set of dimensional studies, it is observed that h_min * calculated using mass-conserving EHL can be bounded by results obtained from finite-bearing mobility formulations, provided that a non-dimensional bearing number Λ falls below a critical value Λ _crit ≈ 4. A set of five independent validation dimensional studies supports this observation.