In the rotary compressor, the rolling piston and the contacted rotor-journal bearing system are main moving components. They suffer very large periodically varying loads introduced by the inertia force, the contact force and the gas force. These loads change rapidly with speed variation of the compressor. They always lead to serious vibration of the system, and then result in abrasion and performance reduction. In this paper, the dynamic behavior of the rotor-journal bearing system were calculated by solving three-dimensional numerical model using finite element method, and the vibration characteristics of the system were investigated according to the calculation results. The natural frequencies and vibration modes were obtained. The stress, displacement and axis orbit of the rotor center were calculated considering the speed variation of the motor. Via the established numerical model, vibration characteristics of a newly designed compressor can be predicted, and optimization can be done to reduce the vibration.

Dynamic analyses for the rotor-journal bearing system of a variable speed rotary compressor

In conventional rotordynamic modeling, hydrodynamic bearings are often characterized by a set of linear stiffness and damping coefficients obtained from a first-order Taylor series expansion of bearing reactions. Theoretically. these coefficients are only valid for small amplitude motion about an equilibrium position. In this paper, a nonlinear dynamic model that overcomes the small amplitude assumption in the conventional linear analysis is described, By including higher-order terms in the bearing reaction expansion, nonlinearity in the oil film forces for large amplitude motion can be captured and represented by a set of nonlinear stiffness and damping coefficients. These coefficients are functions of static bearing displacement. A finite difference approach is described and is used to solve for these coefficients. The stated model is applied to a conventional slider bearing and a mechanical smart slider bearing that experiences large variations in load. Error assessment is performed numerically on the higher-order solutions to determine an acceptable displacement bound for the higher order coefficients.

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A Nonlinear Dynamic Model With Confidence Bounds for Hydrodynamic Bearings

Refrigeration rotary compressors are widely used in air-conditioners. A rotary compressor has a special rotor-bearing system, since the elastic cantilevered crankshaft is under dynamic transverse forces on different planes. The large deformation of the crankshaft would affect the thickness of the oil film, wear the bearings down or even induce the rotor-to-stator rubs. It is considered as a non-linear fluid–structure interaction problem. To ensure the compressor operating well, the dynamic behaviors of both single-cylinder and twin-cylinder compressors' crankshafts at various speeds are analyzed. The influence of configuration of balancers on the reliability of rotor system is investigated for the further. Calculation results suggest that the vulnerable sections of crankshaft vary with the rotational speed. It is also found that 80% of the dynamic balance is the optimum design condition to reduce the transverse forces on crankshaft and the wear-out of journal bearings.

Dynamic behaviors of the crankshafts in single-cylinder and twin-cylinder rotary compressors

This paper describes the variations in stiffness and damping coefficients in bearing oil films under the influence of large dynamic loads. A rotor-journal bearing system in which large dynamic loads act on the rotor is nonlinear, so it is analyzed as a coupled problem of the equations of motion for the rotor combined with Reynolds equations for all the bearings. By making use of the displacements and velocities of the rotor center obtained through analysis, the stiffness and damping coefficients have been numerically calculated as an unsteady state along the locus of the rotor center. The variations in these coefficients over one rotor revolution are shown for the journal bearings in a rotary compressor. Our results demonstrate that most of the coefficients for all the bearings vary by more than one order of magnitude, and that oil film nonlinearities seriously influence the rotor motion.

Dynamic Analysis of a Rotor-Journal Bearing System with Large Dynamic Loads : Stiffness and Damping Coefficient Variations in Bearing Oil Films

In this study, a practical numerical analysis has been developed in order to investigate the lubrication characteristics between a rolling piston and a crank of rotary compressors. This analysis is treated as a coupled problem of the momentum equations and the Reynolds equation of oil film. Using this analysis, the lubrication characteristics between the rolling piston and the crank for 2-cylinder rotary compressors were evaluated for R22 and R410A. Furthermore, the lubrication characteristics on the journal bearings were also analyzed using the already developed tool [ 1]. Measured pressure and oil viscosity in a inverter driven heat pump system were used as the analysis conditions. The oil film thickness and the motions of the rolling piston and the motor rotor were obtained as the analysis results. It made clear that the lubrication characteristics of the rolling piston and the journal bearings with R41 OA refrigerant is better than those with R22. INTRODUCTION R410A (R32/125, 50/50wt%) is an alternative refrigerant ofR22 for air-conditioners, and its capacities have been evaluated widely. Mineral oil is applicable to R22 system as lubricant, but it cannot be used in R410A system because of poor miscibility with R410A. Therefore, polyolester oil which is miscible with R41 OA is mainly used as alternative oil. The cooling capacity of R41 OA derived from the refrigerant property is about 1.4 times as much as that of R22[2]. So, the discharge volume of compressors for R41 OA is required to redesign to adjust the cooling capacity. It is important to investigate lubrication characteristics of compressors with R410A in order to develop the optimum lubricant and to design compressors for R410A. Therefore, many durability tests and numerical analysis were carried out to evaluate the lubrication characteristics with R 41 OA. In the present study, we developed the practical program for lubrication analysis between the rolling piston and the crank of rotary compressors. The selection of lubricating oil and the optimum design of rotary compressors were done by using this analysis and another analysis for journal bearings in addition to the experimental results of the compressor durability tests and oil lubricity evaluations [3]. In this paper, at first, the governing equations and the procedure of the analysis are described. As an example of the analysis results, the optimum lubrication characteristics between the rolling piston and the crank and on the journal bearings of the 2-cylinder rotary compressor for R 41 OA are shown by relatively comparing with the analysis results for R22. GOVERNING EQUATIONS Fig.l shows the schematic drawing of the compression part in a rotary compressor, and Fig.2 shows the schematic drawing of rolling-piston/crank and its coordinate system for the analysis. The rolling piston is loaded large dynamic forces such as unbalanced forces, gas forces and vane forces. Therefore, the Reynolds equations are used to calculate the reaction force of oil film.

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Lubrication Analysis of Rotary Compressors for HFC Refrigerants

A rotor-journal bearing system for a twin rotary compressor has been nlliDerically analyzed to estimate the reliability and to optimize the bearing design For rotary compressors, large dynamic loads act on the rotor They are unbalanced forces due to eccentric rotation parts and gas forces induced by the difference in pressure between compression and suction gases In such a case, the rotor-journal bearing system becomes nonlinear, because the stiffness and damping coefficients of the lubricating oil film in the bearings vary Such a rotor system is solved as a coupled problem of momentum equations and Reynolds equations for all the bearings The analytical procedure and the results are described in this paper

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H. Hattori

Papers

Dynamic Analysis of a Rotor-Journal Bearing System for Twin Rotary Compressors