Characterization of Oil Film Control Forces Under Active Lubrication Regime

Journal bearings under active lubrication regime are controlled by servo valves and well-tuned feedback control laws. The servo valves dynamically modify the journal pressure distribution generating active oil film forces. Such forces are dependent on the following parameters: Sommerfeld number, bearing pre-load factor, orifice diameter, excitation frequency, feedback control gain and dynamic parameters of the servo valves, i.e. their natural frequencies, damping factors and pressure-flow coefficients. The theoretical and experimental characterization of such active forces is the main focus and the main contribution of this work. The theoretical analyzes are based on the Modified Reynolds’ equation for active lubrication. The experimental analyzes are carried out by using a special test rig, designed to investigate the behavior of tilting-pad bearings (TPJB) under active lubrication. Relative good agreement between theoretical and experimental behavior of the active oil film forces as a function of the excitation frequency and control gain is achieved. Limitations of the characterization procedure is critically discussed in order to explain some discrepancies between theoretical and experimental results.