Cavitation Erosion Damage in Engine Bearings: Theory and Practice

Abstract

Cavitation erosion damage in engine bearings has assumed increasing importance during the past 5–10 years, probably as a result of the design trends towards higher rotational speeds, and, in some cases, higher rates of change of cylinder pressure rise. In many instances the damage is merely cosmetically undesirable, and of only minor functional significance; this is particularly so when the bearing is overlay plated. In more extreme cases extensive loss of lining material will result, and the consequential adverse effects on oil film conditions will reduce reliability and life of the bearings and associated parts. This paper presents a general background to cavitation erosion damage and examples of specific forms of this type of damage in plain bearings are given. A number of commonly applied palliatives and their effectiveness, based on engine experience, are discussed. A description of computer-based methods for predicting crankshaft journal locus, oil film pressure profile, and film extent is provided. An attempt has been made to rationalize several typical forms of cavitation damage on the basis of the theoretical model. An ultrasonic vibratory test facility used by the authors to determine the relative erosion resistance of the more commonly used bearing materials is described, and results presented.