Evaluating rotational torque of tapered roller bearings with various oils using the KRL shear stability tester

This study investigates lubricant-induced power losses of tapered roller bearings. Rotational torque was measured with a KRL shear stability tester using five lubricants, including base oils and gear oils. Two conditions were examined: one without temperature control and one under controlled temperature. In the test without temperature control, the initial torque matched the predicted kinematic viscosity at the start. After a certain period, torque values converged across all oils. The relationship between torque and kinematic viscosity, calculated from oil temperature, shows that the torque depends primarily on kinematic viscosity, with no significant effects from other factors. In the test under controlled temperature, torque values correlated with the predicted kinematic viscosity and showed consistency with the calculated viscosity at each rotational speed. Thus, in this test as well, torque appears primarily dependent on kinematic viscosity. Comparison with torque values calculated using the SKF model of bearing friction suggests that the rotational torque observed in these tests primarily reflects changes in the viscosity-dependent rolling friction behavior. However, torque tended to be lower than the rolling frictional moment (M_rr) under conditions where the oil film was thin. As a result, the rotational test using the KRL shear stability tester may estimate energy loss due to the kinematic viscosity. However, it remains difficult to assess the influence of other factors, such as oil type and additives, with this test.