Design Guidelines for Offset Journal Bearings in Two-Stroke Engines

Abstract

Offset journal bearings are an attractive design option for cross-head and piston bearings for two-stroke engines. Two-stroke engine design has seen a resurgence in the last few years due to potential gains in engine efficiency over their four-stroke counterparts. The cross-head and piston bearings comprising such engines, however, are characterized by non-reversing loads with limited oscillating journal motion, the combination of which provides poor bearing performance for conventional cylindrical bearings. The division of bearing journal and sleeve into offset segments allows for periodic load relaxation in the segments and development of squeeze-film action which substantially improves bearing performance. Offset bearings have been in production for the past 60 years, but there are no general design guidelines available to the engine analyst. This thesis provides predictions of the primary bearing performance factors, cyclic-minimum film thickness and cyclic-maximum film pressure, over a wide range of design parameters found in production-level, two-stroke engines

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