Transient tribo-dynamic performance and stability of tilting-pad journal bearings under step load and misalignment

Abstract

Although tilting-pad journal bearings (TPJBs) have been extensively implemented in powertrains, research on their transient performance and stability remains insufficient, particularly under impact load and misalignment conditions. In this study, a novel transient tribo-dynamic model is proposed, coupling thermo-elasto-hydrodynamic (TEHD) effects and journal misalignment. The finite difference method (FDM) and Euler method are employed to solve the governing equations. The effect of step load on the nonlinear dynamic response of TPJBs is investigated, and journal bi-directional misalignment is further classified into two distinct cases (same sign and opposite sign). Moreover, an extended TPJBs stability analysis approach is developed by introducing critical oil-film thickness and temperature to supplement classical stability metrics. The results indicate that the same sign bi-directional misalignment most significantly reduced the oil-film thickness and increased the oil-film temperature. In contrast, the influence of the opposite sign bi-directional misalignment on TPJBs performance is weaker than that of the y-direction misalignment. Meanwhile, through the extended stability metrics, the failure modes of TPJBs under different lubricants are defined. For VG-46, instability occurs when the oil temperature exceeds its threshold. In contrast, for HP-8A, instability occurs when the oil-film thickness falls below its threshold. This study provides theoretical support for the optimization design of bearings.