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The authors investigated analytically, and experimentally the friction torque in a modified 51100 thrust ball bearing. The operating tests and modeling were made at very low axial load in lubricated conditions by using only three balls and a standard steel cage. Two analytical friction moments in the ball–cage contacts based on the friction in the hydrodynamic lubricant film, were developed. An analytical methodology to evaluate the film thickness in the ball – cage contacts was developed, as well. The experiments were conducted by using spin–down method for two viscosities and for rotational speeds between 60 and 240 rpm. Both experiments (with three balls without cage, and three balls mounted in the cage) have been made to validate the proposed models.

Authors propose a theoretical model and an experimental methodology for defining the friction torque in a modified thrust ball bearing, operating in mixed and full film lubrication conditions. The friction torque was measured at low loads and large Λ parameter range using a spin-down method. A comprehensive analytical bearing torque model is described using elastic rolling resistance, curvature effects, inertia forces, disc-air resistance and ball-races hydrodynamic rolling forces, the latter explaining 98% of the final bearing torque. Several sets of hydrodynamic rolling force relationships respecting the transition from IVR to EHL lubrication regime were tested. Final numerical results are shown to be very close to the experimental ones in both full film and mixed lubrication conditions.