Performance of Spherical Bearings for Piston Pumps and Motors

The load, supply pressure and relative sliding velocity of the spherical bearings for piston pumps and motors vary periodically. In designing such bearings, it is important to understand thoroughly not only the steady performance but also the dynamic performance. With this purpose the performance of the spherical bearings are analyzed theoretically and experimentally in this paper. The relative importance, with respect to the load capacity of such bearings, of hydrostatic lubrication, squeeze film and hydrodynamic lubrication, is examined theoretically, and the hydrodynamic lubrication is shown to be negligible. Considering hydrostatic lubrication and squeeze film, the theory of dynamic responses of a spherical bearing system is derived. The calculated values agree fairly well with the experimental data. As a result of the analysis, it is shown that a fluid film lubrication is impossible in the usual spherical bearings for piston pumps and motors, for the radius of a bearing sphere is small to support the load. Then, the two new types of spherical bearings, one with a pocket and the other with a pocket and a check valve, are considered and it is shown that these bearings are able to maintain a fluid film lubrication in a fairly wide operating range of piston pumps and motors without enlargement of the bearing.