Kiyoshi Sawai

Theoretical Model of Lubrication Mechanism in the Thrust Slide-Bearing of Scroll Compressors

This study presents a theoretical model of the remarkably good lubrication characteristics of the thrust slide-bearings found in scroll compressors experimentally by Ishii et al. (2007). It has been suggested that the thrust plate undergoes elastic deformation due to axial loading. As a result of this deformation, a fluid wedge is believed to form at the periphery of the thrust plate. The fluid wedge angle between the sliding surfaces was calculated with a finite element method analysis and then used in the average Reynolds equation from Patir and Cheng (1978, 1979) to analyze the fluid lubrication on rough sliding surfaces. The plastic and elastic contacts between the orbiting and fixed thrust plates were analyzed using the solid contact theory from Greenwood and Williamson (1966). The derived theoretical model permitted the calculation of the oil film pressure, the solid contact force, the fluid frictional force, and the solid shearing drag force. These results were used, in turn, to determine the resultant friction coefficient at the thrust slide-bearing. Finally, it is shown that the predicted theoretical results agree well with the experimental lubrication test results of Ishii et al. (2007). The proposed theoretical development appears to model accurately the essential mechanism for the remarkably good mixed fluid-and-solid lubrication in a thrust slide-bearing.

Experimental Study of the Lubrication Mechanism for Thrust Slide Bearings in Scroll Compressors

This study focuses on the effect that a pressure difference across the orbiting thrust plate of a thrust-slide bearing has on the improved lubrication of the bearing in scroll compressor applications. A thrust slide bearing model submerged in a refrigerant oil, VG-56, was operated under pressurized conditions using R-22 as the pressurizing gas, where the pressure difference across the friction surface of the thrust bearing was adjusted from 0 to 1.0 MPa and the friction force and friction coefficient at the thrust slide bearing were measured over a range of orbital speeds. As a result, significant improvement in lubrication at the thrust slide bearing due to the pressure difference was identified. Furthermore, careful observation of the wear state of the thrust slide bearing revealed the formation of a fluid wedge between the sliding surfaces due to axial loadings. This fluid wedge appears responsible for the observed improvement in lubrication. In addition, the wedge formation was quantitatively investigated using finite element method (FEM) analysis of the elastic deformation of the thrust plate. The FEM analysis was subsequently validated through strain measurement on the thrust plate.