Study on Bearing Characteristics of Reciprocating Compressor for Refrigerator

In recent years, in order to reduce the energy consumption of refrigerators through reduction of input power and improved refrigeration capacity, reciprocating compressors are gradually converted to inverter type. Correspondingly, we have studied the sliding bearing characteristics of the crankshaft journal at variable speed which is the key to improving the efficiency of reciprocating compressor. Generally, the characteristics of a sliding bearing are explained with a Stribeck curve. In the fluid lubrication regime, there is sufficient lubricant between metal surfaces. As the rotational speed decreases, the viscous resistance is reduced and it will result in the reduction of friction coefficient. Conversely, it is widely known that further reduction of rotational speed will shift to boundary lubrication regime where the friction coefficient increases due to metal to metal contact. In the inverter reciprocating compressor, it is presumed that the sliding of crankshaft on bearing at high rotational speed is in fluid lubrication regime. The input power can be reduced with gradual decrease of friction coefficient by lowering rotational speed, but then the sliding characteristic of the crankshaft at each rotational speed was unclear such that when the speed is too low it will progress into the boundary lubrication regime. This paper explains our experimental study to obtain a Stribeck curve at low load, low speed, and low viscosity oil in inverter operation using a bearing tester that estimate sliding crankshaft on bearing. The results obtained enable the prediction of sliding characteristic of crankshaft and optimization of the bearing property in reciprocating compressor