This study investigated the magnitude and fluctuation characteristics of friction torque in angular contact ball bearings lubricated with lithium-based grease. Leveraging a self-developed friction torque test rig for rolling bearings, a series of controlled experiments were conducted under varying operational parameters, including rotational speed, radial load and thickener content. The reliability of the experimental setup and methodology was validated through comparisons with SKF data, revealing minimal discrepancies and ensuring data accuracy.

Test conditions were carefully selected in accordance with the technical specifications of the bearings and the operational constraints of the test platform, enabling a comprehensive examination of friction torque behavior across a wide range of working scenarios. Real-time torque data were acquired using force sensors and calculated via a torque balance method. Both the magnitude and fluctuation patterns of friction torque were analyzed, with particular attention to their evolution under different speeds, loading conditions, and thickener contents. Friction torque fluctuations were quantitatively assessed through standard deviation analysis, while frequency domain characteristics were extracted using Fourier transform techniques. These analyses provided valuable insights into the underlying mechanisms contributing to friction torque instability. Key findings from the experiments included the observation that, under constant axial load, friction torque increased with rising rotational speed. In contrast, when radial load increased, friction torque initially decreased and then rised. Moreover, friction torque was found to increase significantly with higher thickener content, indicating the complex interaction between lubricant composition and tribological behavior. Rotational speed, radial load, and thickener content were also shown to significantly influence friction torque fluctuation. Higher speeds and heavier loads intensified the fluctuations, whereas the addition of an appropriate amount of thickener effectively suppressed them. This damping effect was attributed to the thickener’s ability to stabilize the lubrication film and limit irregular cage motion. Spectral analysis further confirmed these observations. Friction torque fluctuations were primarily associated with three distinct frequency components. The amplitude of the fundamental frequency corresponding to the rotational speed maintained the same over time while the amplitude of the low-frequency signals arising from cage vortex motion and high-frequency signals linked to rolling element–raceway interactions decreased, indicating the gradual stabilization of friction torque. Overall, this study offered a comprehensive understanding of friction torque dynamics in angular contact ball bearings under grease lubrication. By identifying the key factors influencing both the magnitude and fluctuation of friction torque, it provided meaningful guidance for optimizing bearing design and lubrication strategies. These insights were particularly valuable for high-precision applications where minimizing torque fluctuation was critical to performance and durability. In conclusion, this research advanced the fundamental knowledge of friction behavior in lubricated bearings and offered practical directions for improving reliability and efficiency in demanding mechanical systems. Future work would aim to extend these findings to other bearing types and explore advanced lubrication formulations to further enhance system stability under dynamic operating conditions.