Optimization of EHL Performance in Thrust Slide-Bearings of Scroll Compressors

The present study focuses on aspects of EHL that have both positive and negative effects on the lubrication performance of the thrust slide-bearings in scroll compressors. Theoretical calculations using the average Reynolds equation of Patir-Cheng and the solid contact theory from Greenwood & Williamson, for the boundary of the local elastic deformation of the thrust slide-bearing, were conducted for a small cooling capacity scroll compressor driven at 3600 rpm with 0.1 kW. An approximate method was developed using characteristic curves to determine the oil film axial force, the average oil film thickness, the friction force and the friction coefficient. The calculations considered a variety of pressure differences due to the operating pressure and the thickness of thrust plate. Also, cases with a fixed uniform wedge angle at the periphery were calculated. The calculated results suggest a possible maximum reduction in friction coefficient of about 55% compared to that with a fixed uniform wedge angle. The reduction rate increases with decreasing thrust plate thickness, which, however, restricts the operating pressures to a lower pressure range. Design guidelines for optimizing EHL are suggested.