Monitoring of Abnormal Vibration to Prevent Seizure of Crosshead Bearings

The crosshead bearing in large two-stroke diesel engines operates under severe lubrication conditions because hydrodynamic action is limited by low-amplitude, low-velocity oscillation under high specific load. The recent trend toward more compact engines with increased output raises the bearing specific load, thereby significantly increasing the lubrication severity. Therefore it is necessary to find a means to prevent tribological failure such as seizure. In this study, a technique for monitoring abnormal vibration was evaluated using a dynamically loaded bearing seizure test rig that is capable of simulating load patterns and relative oscillations of the crosshead bearing in actual engines. Vibration spikes occur around crank angles of ± 90 deg where the oscillating speed is zero during one cycle. When lubrication is impaired, an abnormal vibration spike caused by severe metal-to-metal contact is generated at a crank angle of approximately +90 deg, where the oil film thickness is a minimum. The frequency of this spike generation increases with the degree of impairment. If running-in is carried out immediately after detecting abnormal vibration, the bearing surface is conformed, thereby avoiding severe metal-to-metal contact damage. The detection of abnormal vibration can be an effective means to prevent seizure of the crosshead bearing.