Vibration Analysis of a 2-Pocket Capillary-Control Hydrostatic Journal Bearing

This paper provides additional mathematical models for a 2-pocket capillary-control hydrostatic journal bearing after considering an analytical solution of a conventional 4-pocket configuration. The bearing is designed to carry a constant magnitude of force but varying in direction by +18 degrees about the mean position. It has been used for a testing level hydraulic pump/motor in our laboratory [1]. The need of 2 pockets comes from the fact that the load only changes direction about its mean position, and the necessity of reducing leakage in the pump/motor and utilizing the maximum pressure available. Due to the unsymmetrical pocket and dynamic loading, whirl instability and unbalance response must be considered in designing the bearing.

The instantaneous pressure distribution around the bearing occurs due to the dynamic loading and is obtained by solving the time dependent Reynolds equation. The solution is then used to calculate a flow field on the bearing which can be used to develop stiffness and damping matrices. Both matrices include the effect of squeezing the oil film on the bearing land (which plays an important role in absorbing a suddenly applied load). The effects of the oil in the bearing recesses and the effect of capillary control are also included. Finally, the system configuration parameters are expressed in the equation of motion for vibration analysis.