Thermohydrodynamic Lubrication Model Applicable to a Slipper of Swashplate Type Axial Piston Pumps and Motors (Effects of Operating Conditions)

A thermohydrodynamic lubrication (THL) model of a hybrid (hydrostatic and hydrodynamic) thrust bearing is developed. It is applicable to a slipper of swashplate-type axial piston pumps and motors. The generalized Reynolds equation, three-dimensional energy equation, and the heat conduction equation are derived. Physical properties such as density, viscosity, specific heat at constant pressure, thermal conductivity, and thermal expansivity of a hydraulic oil are considered as functions of temperature and pressure. The effects of the operating conditions on the temperature rise, clearance shape, and the power loss are shown. The numerical parameters are specified for the fluid-a hydraulic oil with ISO VG 46-supply pressure 7-21 MPa and rotational speed 15-60 rps. The solutions between the slipper model and the circular hydrostatic thrust bearing as well as between the THL and isothermal (ISO) solutions are compared. Increases in the supply pressure, rotational speed, and the revolution-radius increase the maximum temperature and the power loss. Furthermore, the discrepancies between the THL and ISO solutions increase. The rotational speed affects characteristics more than the supply pressure