Tribo-dynamics of coupled multi-clearance diesel engine bearings under dynamic misalignment

Crankshaft tilt misalignment alters the load-transfer path in the diesel engine crank–connecting-rod mechanism, whereas the tribo-dynamics of coupled multi-clearance bearings with dynamically varying local misalignment remain less understood. This study investigates the connecting-rod big-end bearing (CRBEB), connecting-rod small-end bearing (CRSEB), and bilateral piston-pin boss bearings (PPBBs) as coupled multi-clearance bearings under crankshaft tilt. A multi-clearance tribo-dynamic model is developed by coupling Lagrange-equation-based multibody dynamics, transient mixed lubrication, and an asperity contact model. The formulation retains the rocking degrees of freedom of the connecting rod and piston pin, and further captures the dynamic journal–bearing misalignment within the bearing clearances induced by their posture evolution. On this basis, the propagation of dynamic misalignment and the mechanism of load redistribution in multi-clearance bearings under crankshaft tilt are elucidated. The results show that crankshaft tilt causes synchronous rod-pin rocking and asymmetric load redistribution toward the tilted-side PPBB, leading to higher oil-film pressure and asperity contact in the tilted-side end-face region. Compared with the single-clearance model, the additional compliant load-transfer paths provided by the CRSEB and PPBBs alleviate local load concentration in the CRBEB. However, increasing crankshaft tilt angle or CRBEB radial clearance still aggravates asymmetric lubrication and rocking response within the multi-clearance model. Wear analysis and engine tests show consistent upper-shell end-face damage tendency and enhanced high-frequency vibration impacts under worn conditions. This study provides mechanistic support for interpreting tribo-dynamic responses and bearing shell fault signatures in coupled multi-clearance bearings in diesel engines.