Study on Flow Characteristics of Oil Viscosity Pump for Refrigerant Compressors

 Oil viscosity pumps are typically used for reciprocating compressors in household refrigerators to lubricate the compression mechanism. The oil viscosity pump is a simple structure in which a spiral groove is on the shaft surface. The lubricating oil supplied by this pump has a large influence on the performance and reliability, but the oil viscosity pump is designed based on the experience. We investigated the flow characteristics of the oil viscosity pump from theoretical and experimental study. We performed the study based on the assumption that the oil flow inside spiral groove was steady with two-dimensional viscous flow. As a result, we found that the pressure-flow rate (P-Q) characteristics has a linear relationship when the length of the spiral grooves, the rotational speed of the shaft, and the depth of the spiral grooves are in the limited area

Compressor with Turning-Paired Vane and Piston

With the aim of energy saving of room air conditioners, we are addressing higher efficiency of the rotary compressor that is used most in the world. We focused on a new rotary compressor equipped with a mechanism to restrict the rolling motion of the piston, and performed the dynamics analysis. The new rotary compressor has a small pillar at the tip of the vane and constitutes a turning pair of vane and piston, and it limits the rolling motion of the piston. By means of limiting the piston rotation, the heat transfer to the suction process from the compression chamber will be suppressed, and we can expect higher compression efficiency. Before examining the compression efficiency, we performed the dynamics analysis of this new rotary compressor and examined the forces and dynamic behavior of the components, and the mechanical efficiency of the compressor. Then we have following results. (1)We can clarify the contact point between the vane tip and piston in the turning pair by considering the equilibrium of forces and moments acting on the vane. (2)By reducing the diameter of the pillar at the vane tip, the vane tip friction loss is reduced, and the mechanical efficiency is improved. (3)The new rotary compressor has less vane tip friction loss and on the other hand greater friction loss between the vane side and the cylinder in comparison to the rolling piston rotary compressors. As a result, both compressors have almost the same mechanical efficiency

Lubrication Tests to Support Optimal Performance Design Guidelines for Thrust Slide-Bearings in Scroll Compressors

This study focuses on the role of lubrication in the optimal performance design guidelines for the thrust slide-bearings in scroll compressors. The theoretical analysis of Ishii et al. showed that the minimum friction power loss in the thrust slide-bearing occurs at a certain outer radius of the friction surface. In the theoretical development, the physical thrust slide-bearing was modeled as a cylindrical thrust plate, representing the orbiting scroll, and the flat plate, representing the fixed scroll, with the same friction area as the physical bearing. The outer radius of the friction surface was varied for a fixed inner radius, where the fluid wedge angle between the sliding surfaces, due to axial loading on the thrust plate, was assumed to be constant at a small value. The average Reynolds equation by Patier & Cheng and the solid contact theory by Greenwood & Williamson were applied to calculate the resultant lubrication performance and finally the friction power loss at the sliding surface. The model showed that the friction power loss drastically decreases and then gradually increases, with increasing outer radius of the sliding surface.  The minimum value of friction power loss was about 80% lower than that of the conventional design thrust slide-bering. In order to confirm experimentally this predicted optimal lubrication performance, a thrust slide-bearing cylindrical-model submerged in a refrigerant oil SUNISO-RB68A was operated under pressurized conditions using R410A as the pressurizing gas. The pressure difference across the friction surface of the thrust bearing was fixed at 0.6 MPa, corresponding to the rated operation condition of a small cooling capacity scroll compressor. In the experiments, a special device was fabricated to maintain a constant fluid wedge angle between the friction surfaces due to the net pressure-induced elastic deformation of the thrust plate. The friction power loss at the friction surface was measured over a wide range of orbiting speeds from 1200 rpm up to 6000 rpm for a fixed orbiting radius of 3.0 mm. The resulting measured data exhibited showed the predicted tendency that the lubrication of the thrust slide-bearing is substabtially by increasing the outer radius. The friction power loss decreased with increasing outer-to-inner radii ratio of friction surface. The minimum loss occurred at an outer-to-inner radii ratio of about 2.1 for an operating speed of 3600 rpm, a significant 80% reduction relative to the usual conventional design ratio

Hydrodynamic-Pressure-Induced Elastic Deformation of Thrust Slide-Bearings in Scroll Compressors and Oil Film Pressure Increase Due to Oil Envelopment

This paper presents the concept of the Elasto-Hydrodynamic Lubrication?EHL?of thrust slide-bearings in scroll compressors, resulting in the superior lubrication characteristics of these bearings. The thrust plate undergoes elastic deformation due to axial loading, resulting in the formation of a uniform fluid wedge between the orbiting and fixed thrust plates. This wedge region has very high induced oil film pressure, which explains the remarkably good lubrication characteristics of the thrust slide-bearing. Furthermore, the high oil film pressure induces further local elastic deformation of the thrust plate, forming an EHL oil pocket with the thrust plate and a further increase in the oil film pressure between the sliding surfaces due to this oil envelopment. The formation of the EHL pocket was confirmed using FEM analysis and lubrication tests on the elastic deformation of the thrust plate. Subsequently, the additional increase in oil film pressure, due to the EHL pocket effect, was examined in computer simulations applying the average Reynolds equation for the boundary of elastic deformation of the thrust plate. In these studies, a 6.7% increase in oil film pressure was ascertained for a small cooling capacity scroll compressor driven at 3600 rpm with 0.1 kW motor. The oil envelopment contributes to the superior lubrication performance of the thrust slide bearings scroll compressors

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

Previous studies [Refs. 1, 2] revealed the formation of a uniform oil wedge at the periphery of the thrust plate, caused by the elastic deformation of the orbiting thrust plate due to the pressure difference across the orbiting thrust plate, is a significant factor in the high lubrication performance in thrust slide-bearings. In addition to the uniform wedge formation, the high oil film pressure also induces a local elastic deformation of the fixed thrust plate normal to its surface. The normal thrust plate deformation and the oil wedge effectively form an elasto-hydrodynamic-lubrication (EHL) pocket, even more effectively increasing the oil film pressure between the sliding surfaces, due to the envelopment of the oil, as confirmed in our companion paper [3], and an earlier, less-detailed contribution [4]. 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 and Patier-Chen solid contact theory, 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 frictional force and the frictional coefficient. The calculations considered a variety of pressure differences due to the operation 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 frictional 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 operation pressures to a lower pressure range. Design guidelines for optimizing EHL will be suggested. References: [1] Oku, T., Ishii, N., Anami, K., Knisely, C.W., Sawai, K., Morimoto, T., Hiwata, A. : Theoretical Model of Lubrication Mechanism in the Thrust Slide-Bearing of Scroll Compressors, HVAC&R Research Journal ASHRAE Vol.14, No.2, pp.239-358, 2008-3. [2] Ishii, N., Oku, T., Anami, K., Knisely, C.W., Sawai, K., Morimoto, T., Iida, N. : Experimental Study of the Lubrication Mechanism for Thrust Slide Bearings in Scroll Compressors, HVAC&R Research Journal ASHRAE Vol.14, No.2, 2008-4. [3] Ishii, N., Tsuji, T., Anami, K., Nokiyama, K., Morimoto, T., Sakuda, A., Oku, T., Sawai, K., Knisely, C.W., : “Hydrodynamic-Pressure-Induced Elastic Deformation of Thrust Slide-Bearings in Scroll Compressors and Oil Film Pressure Increase Due to Oil Envelopment,” abstract submitted to 2014 Purdue Herrick Conferences. [4] Ishii, N., Tsuji, T., Oku, T., Anami, K., Knisely, C.W., Nokiyama, K., Morimoto, T., Sakuda, A., Sawai, K. 2012 “Elasto-Hydrodynamic Lubrication Effect in Thrust-Slide Bearings of Scroll Compressors,” 2012 Purdue Conference Paper on (Paper 1438)