Dynamic analysis of a flexible shaft in a scroll compressor considering solid contact and oil film pressure in journal bearings

Abstract

Solid contact between the shaft and sleeve is a frequent failure mode in scroll compressors because of the large gas forces and high operating speeds required to meet the demands of compact size and high efficiency. In this paper, the dynamic behavior of a shaft with four degrees of freedom is analyzed considering gas, centrifugal, bearing, and contact forces. Oil film pressure of the journal bearing is determined by applying the finite element method to the Reynolds equation. When contact between the shaft and sleeve arises from flexible and rigid motion of the shaft, the contact force is calculated by applying asperity contact theory. Equations of motion of the shaft are developed using a finite element model of a Timoshenko beam and solved with a central difference method. To verify our analysis, we compared our results with those of previous studies and the results of commercial program analysis for each step involved in validating journal bearing, contact force, and dynamic behavior of a rigid shaft. The flexibility of a shaft and the contact between the sleeve and shaft should be taken into account when predicting the dynamic behavior of the shaft in a scroll compressor.