Oil Film Thickness measurements in a Dynamically Loaded Journal Bearing—A Comparison of Measured and Calculated Minimum Oil Film Thickness with Newtonian Lubricating Oils

As previously reported an experimental apparatus has been built that allows direct measurement of the oil film thickness in a bearing that is subjected to dynamic toads and shaft speeds representative of those occurring in automobile engine connecting-rod, big-end bearings. The measurement system allows the locus of journal centers to be plotted within the bearing clearance circle while the bearing is subjected to dynamic loads. In comparison with making similar measurements in an engine, this apparatus allows accurate measurements while the oil film is subjected to carefully controlled conditions representative of those in an engine.

Measurements have been made for two test bearings with several single grade Newtonian oils while the journal bearing was subjected to a wide range of constant and dynamic loads while the shaft was rotating at 2000 rpm, and to sinusoidal loads while the shaft was not rotating. These measurements are compared with transient analyses calculated using a computer program that models the test bearing and uses measured loads. The program, based on the Booker mobility method, uses Ocvirk's short bearing approximation, Moes' finite-length-bearing approximation, and Goenka's finite element analysis of the Reynolds equation.

For all three types of loads the measured minimum oil film thicknesses show good agreement with values calculated using the Booker program.