Experimental Study on Journal Bearing Characteristics in Reciprocating Compressors for HFC-134a

This paper describes the experimental characteristics of cantilever type journal bearings in reciprocating compressors for HFC-134a. The purpose of this study is to compare the effects of bearing material, chemically treated shafts, bearing stiffness and refrigerant solubility in the oil to the characteristics of journal bearings lubricated with a mixture ofHFC-134a and lubricating oil As a result, when using a cast iron bearing, it is possible to improve the journal bearing characteristics by using a manganous phosphate shaft and a bearing having lower stiffness. The aluminum bearing has better bearing characteristics than the cast :iron bearing both in the fluid lubrication and the boundary lubrication conditions. Alkylbenzene oil has better bearing characteristics than ester oil only in the boundary lubrication condition. lNTRODUCI'ION With increasing concern about protecting the global environment, even after switching refrigerant from CFC-12 to HFC-134a for refrigerator compressors, further improvement toward higher efficiency has been fervently demanded In reciprocating refrigerator compressors, the rate of friction loss in the main bearing, which is generally structured in a cantilever design, is particularly high within the mechanical. loss. But there are few studies about bearing characteristics on cantilevere type bearings(ll, chemically treated shaft and refrigerant solubility in refrigeration oil This study evaluates the effect of a variety of factors mentioned above by measuring bearing characteristics on a bearing test maclrine by using the bearings and shafts whlch are used in a reciprocating compressor for a refrigerator. :METHOD OF EXPERIMENTS (I) Bearing Structure in a Reciprocating Compressor The schematic view of a reciprocating compressor for a household refrigeraror is shown in Fig. 1. This compressor has two journal bearings, one at the main bearing and the other at the connecting rod bearing. The main journal bearing, wlrich has a cantilever structure and is located on the motor side, supports the entire compression load which acts on the eccentric of the shaft. The refrigeration oil dissolved wlth refrigerant HFC134a is taken into the oil pipe located at the bottom of the shaft and is supplied to the eccentric of the shaft and the main bearing. (2) The Structure of the Bearing Test Maclrine The schematic view of the bearing test machine used for this study is shovm in Fig. 2. In this test machine, the shaft tD be tested is driven by a inverter motor and a dynamic load is applied by a hydraulic vibrator. The shaft torque is measured by a torque converter: The dynamic load is applied once every rotation in synchronized with the shaft rotation and the fluctuating load is measured by a load converter.